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1. 0c cceceeeeeeeeceeeeeeeeeeeeeaeeeeeeeseeeesaeeetaeeeeneeee 69 5 10 DSP Parameter Descriptions 0 ccccceeeeeeeeeeeeeeeeeeeeeeeeeeseaeeeeaeeeeeeeees 69 5 10 1 Specifying fixed run lONnQths ceeceeeeeceee cesses ceeeeeseeeeseaeeseneeeeaes 71 5 10 2 Setting the slow filter parameters cccceeeeeeeseeceeeeeseteeeeneeeeenees 71 5 10 3 Setting the fast filter parameterS cccccceeeeeseeceeeeetteeeeeeeeeeeees 72 5 10 4 Setting ThreSholds cceccecceceeeseeceeeeeeeeeeeeeaeeeeaeeseeeeeseaeeeeaeeeeeees 72 5 10 5 Setting the Pile up inspection parameters cccccccseeeeseeeeeeees 74 5 10 6 Setting the Analog Gain GAINDAC ccccceseeeeereeeeeeeeeteeeeeees 74 5 11 Standard Program Variants ccccccceeeeeseeceeeeeceeeeeneeseeeeeseaeeesaeeeeneeees 75 5 11 1 MCA acquisition with reset type preamplifiers ceeeeeees 75 5 11 2 MCA acquisition with RC type preamplifiers ceeeeeeeees 75 APPeNdICes ancre oie ea elo an E EE 77 Appendix A GLOBSET Specification s seseeeeeeeeeeeeeneeeneeensstnssenssrnssrnssrensressrnn 77 Appendix B GENSET Version 1 Specification ccccccceeeeceeeeeeeseteeeeneeeeeeeeees 78 Appendix C PARSET Version 1 Specification c cccceceeseeeeeeeeeeeeeeeeaeeeeeeees 79 Appendix D MicroDXP Hardware Specification c cccccceseeeeeeeeeeeeeeeseeeeneeees 80 Board Dimensions and MOunting c ccc
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3. Maximum Typical X ray pulse height 250uV 625mV 100mV Input voltage range 5V 3V Decay time t 100ns infinity 50us Table 1 5 Analog input signal constraints for resistive feedback preamplifiers Note that the maximum input range is less than for pulsed reset preamplifiers 1 2 3 Power Requirements The microDXP requires several DC voltage supplies to operate In cases where the user will provide their own power supply to generate these voltages such power supplies should conform to the specifications described in section Appendix D The onboard digital circuitry draws from a 3 3V supply input with on board regulators employed to produce 2 5V for the DSP and 3 0V for the ADC The analog circuitry runs on 5 0V either supplied directly or indirectly through on board LDO regulators Customers not wishing to worry about power supply requirements are advised to purchase MicroComU companion boards The MicroComU boards will take care of generating all required voltages at the required currents and noise performance The MicroComU microDXP board set may be powered from a USB port or from a single external DC supply such as the AC wall adapter included with the USB Rapid Development Kit Clock Speed Voltage Current Power Comment MHz Supply mA mW 8 VCC 89 7 296 0 3 3V digital includes ADC 8 V 20 3 101 5 5V analog includes VGA 8 V 23 3 116 5 5V analog 514mW Total po
4. Reserved set to 0 1 Update SlopeDAC or OffsetDAC value to match SlopeDAC or OffsetDAC adjustments disabled current rate DEFAULT 2 Use Finite Impulse Response FIR filter to Use Infinite Impulse Response IIR filter to calculate baseline average calculate baseline average DEFAULT 3 Acquire baseline values for histogramming and Disable baseline acquisition averaging DEFAULT 4 Adjust fast filter threshold to compensate for Disable fast filter threshold adjustment rate shifts 5 Correct for baseline shift either in FiPPI pulse Disable baseline correction reset or DSP RC feedback DEFAULT 6 Apply residual baseline correction DEFAULT No residual baseline correction 7 Disable writing baseline values to baseline Continuously write baseline values to baseline history circular buffer history circular buffer DEFAULT 8 Indicates special task or calibration run specified Indicates normal acquisition run by WHICHTEST 8 6 2009 68 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 9 Histogram DeltaBaseline Histogram raw baseline DEFAULT baseline lt baseline gt 10 Enable baseline cut Disable baseline cut DEFAULT 11 15 Reserved set to 0 Reserved set to 0 Table 5 2 Data acquisition tasks controlled by the DSP parameter RUNTASKS 5 9 Special Tasks WHICHTEST Special tasks are selected by starting a run with bit 8 of the RUNTASKS parameter set The following tasks are currently
5. The most important are digital settings of the spectrometer unit i e the values of the DSP parameters such as the decimation filter length etc 15 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 The values of these parameters can be captured into an ASCII file in microManager Please attach a copy of this file if possible Capturing an oscilloscope image of the preamp output will be extremely helpful This can done with the diagnostic tool included in microManager For general questions and DXP hardware issues please email microDXP xia com 1 4 4 Feedback XIA strives to keep up with the needs of our users Please send us your feedback regarding the functionality and usability of the microDXP and microManager software In particular we are considering the following development issues 1 4 4 1 Export File Formats We would like to directly support as many spectrum file formats as possible If we do not yet support it please send your specification to software_support xia com 1 4 4 2 Fast Communications Currently the hardware supports three communications interfaces an RS 232 serial port a synchronous DSP serial port and IDMA parallel DSP access Only the RS 232 interface and recently the IDMA parallel DSP interface have been implemented thus far in software and firmware We are interested in feedback about the support of the DSP serial port interface 1 4 4 3 Hardware
6. parameter storage on a per peaking time basis For each Peaking Time the DSP stores a complete set of all related spectrometer parameters into non volatile memory as outlined in 1 1 1 2 Five Peaking Times are available for each FiPPI decimation each decimation provides a range of peaking times included in the purchase yielding a maximum of fifteen 15 independently optimized Peaking Times Re selecting an optimized Peaking Time conveniently retrieves all relevant digital filtering and peak inspection parameters e g gap time thresholds pileup inspection interval etc from non volatile flash memory This functionality is particularly beneficial in embedded systems The configuration and optimization procedures can be delegated to the development kit platform i e the MicroComU companion board and MicroManager software leaving a very tight data acquisition command set for the embedded system itself The configuration process need only be performed once though of course the parameter sets be modified at any time Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 Under NRE terms XIA develops customized firmware to support specialized data acquisition modes and to support auxiliary hardware functions see 1 1 1 3 Custom OEM Features The C bus can be used to control various devices e g x ray tubes and DACs and the four auxiliary lines can be individually configured as inputs e g
7. sososanoeaenenenennnenenennnenenrnrnesesrsnsesrsrsrsenrnenne 14 1 4 3 Email and Phone Support ssssssesseesseessssnesiesisssnnsrensnnsrnnnennnrennnt 15 TAA Feedback rriteni ar N EONA EN TENEKE EN ES 16 1 4 5 The Accelerated DevelOPmenT ADOPT Program s s s 16 2 Using the microDXP wicic cc cesccs cecteceecceecece cescectetececeee cuscceeereencececustectere aapa iaa 18 2 1 Board State and Configuration cccccccseceeneceeeeeeeeeeeeeeeeeeeeeseeeeseaeeeeneeees 18 2 1 1 Board Information and Status ccccceesceceeeeeeeeeeeeeeeeeeeeeseaeeseneeesaes 18 Z2 Serial Numba reesei eaoaai a a aa a aE a aa a iene 19 2 1 3 Firmware Version sa iesse sinais a ES OROS 19 2 1 4 Idle and Sleep Modes cecccceseeeeeeeceeeeeeeaeeeseaeeeeeeeseeeeseaeeseeeesaes 19 2 1 5 On Board Temperature ceccccccsceeesceceeeeeceeeeeeeeeeeeeeseeeeseaeeseeeenaes 19 2 2 Global Settings and the GLOBSET ceccceeeeeeeeeeeeeeeeeeeeeeeeeeeeseaeeeeneeees 19 2 2 1 Preamplifier Settings ccccccceeeeeeeceeeeeceeeeeeeaeeeeeeeseeeesaeeseaeeeeaes 20 2 2 2 Advanced Processor SettingS ccccccceceeeeeseeeeeeeeseeeeeeeeeseneeeeaes 21 2 3 MCA Settings and GENSETS ecccececeeeeeeeeeeeee cece eeeeaeeeeaeeseneeeseaeeesaeeneneeee 21 2 3 1 Selecting the GENSET ccceeceeeseeceeeeeeeeeeeeeeeeeeeeeeeeeeesaeeeeaeeesaes 22 232 MOAS ZE a a a Gee cater etvacech a a Oeecat tees 22 2 3 3 MCA Granularity Bin Width
8. 232 auxiliary and power connections Still this interface does not involve many active components i e the I C and auxiliary digital I O are simply routed to additional connectors The pushbutton interface might include an additional microcontroller but could be implemented simply in logic 2 As drawn the power supply is integrated on the interface board with the same requirements as in the previous example As stated there optional voltage regulators for the analog circuitry are included on the microDXP for systems in which high quality power supplies are not available Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 3 Again some additional mechanical design i e enclosure design may be necessary Simple User internal Interface WBA l microDXP 12C Peripheral e g smart detector Power Supplies bias HV supply x ray tube etc l Advanced Interface VA Electromechanical or pneumatic result based on x ray data Figure 1 3 A system with a fully embedded host and user interface with real time controls via the Auxiliary digital I O Although the figure above shows a flex cable used to interface the microDXP board to the Advanced Interface board it is also possible to use the board to board connector on the microDXP as was done with the recently introduced MicroComU companion board Designing the system described above using conventional spectroscopy components wo
9. 5 fail the MAXWIDTH test Thus in Figure 4 11 only pulse 1 passes both pileup inspection tests and indeed it is the only pulse to have a well defined flattop region at time PEAKSAMP in the slow filter output Digitized MultiPile kfig 960921 Passes Fails PEAKINT PEAKINT Test Test Passes MAXWIDTH Fails MAXWIDTH Fast Filter PEAKSAMP gt Slow Filter 5 10 15 20 25 30 Time us Figure 4 11 A sequence of 5 x ray pulses separated by various intervals to show the origin of both slow channel and fast channel pileup and demonstrate how the two cases are detected by the DXP 8 6 2009 55 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 Note that PEAKINT and MAXWIDTH are both DSP parameters and are normally set automatically In particular there is almost never any benefit to a longer value of PEAKINT than the standard value as it does not improve energy resolution and only decreases throughput for a given input rate Please see 5 10 5 for details on how to adjust MAXWIDTH 4 9 Input Count Rate ICR and Output Count Rate OCR During data acquisition x rays will be absorbed in the detector at some rate This is the true input count rate which we will refer to as ICRy Because of fast channel pileup not all of these will be detected by the DXP s x ray pulse detection circuitry which will thus report a measured input count rate ICRm which will be less than I
10. ANY INDIRECT SPECIAL INCIDENTAL OR CONSEQUENTIAL DAMAGES IRRESPECTIVE OF WHETHER XIA LLC OR THE VENDOR HAS ADVANCE NOTICE OF THE POSSIBILITY OF SUCH DAMAGES Contact Information XIA LLC 31057 Genstar Rd Hayward CA 94544 USA microDXP xia com for microDXP microCOM or MicroComU hardware support software_support xia com for microManager software support 510 401 5760 Micro Digital X ray Processor Technical ReferenceManual Manual Conventions 8 6 2009 mdo microDXP MAN 1 1 2 Through out this manual we will use the following conventions Convention Description Example The symbol leads you The sequence through nested menu File Page Setup Options items DAQExplorer directs you to pull down the items and dialog box File menu select the Page options Setup item and choose Options from the sub menu Bold Bold text denotes items expand the Run Control that you must select or section of the DAQExplorer click on in the software to access the run presets such as menu items and dialog box options Bold Bold text within Start Run indicates the denotes a command command button labeled button Start Run monospace Items in this font Setup exe refers to a file denote sections of code called setup exe on the host file contents and syntax computer examples window Text in quotation refers Options indicates the to window titles and wind
11. BASETHRESH with larger BASETHRADJ values resulting in more conservative BASETHRESH values In the rare case the baseline threshold is set incorrectly by the DSP algorithm we recommend adjusting BASETHRADJ rather than BASETHRESH itself The use of a slow threshold introduces significant errors in the counting Statistics Specifically the dead time per event is markedly different for x rays above and below the threshold SLOWTHRESH should only be used if v Your detector has a very thin window and operates in a vacuum v You understand that it is not possible to compute input count rates for x ray peaks below the threshold relative to x ray peaks above the threshold Setting a threshold to zero disables that threshold Individual thresholds can also be enabled and disabled via the lowest 3 bits of the parameter FIPCONTROL 8 6 2009 73 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 FIPCONTROL Meaning if 0 Meaning if 1 BIT 0 THRESHOLD event THRESHOLD event discrimination enabled discrimination disabled 1 BASETHRESH event BASETHRESH event discrimination enabled discrimination disabled baseline discrimination baseline discrimination enabled enabled 2 SLOWTHRESH event SLOWTHRESH event discrimination enabled discrimination disabled Table 5 5 Threshold control via FIPCONTROL The two methods of disabling thresholds are equivalent except in the case of
12. ICR levels The theoretical form from Poisson statistics for a channel that suffers from paralyzable extending dead time is given by OCR ICR exp ICR ta Equation 4 12 where qtq is the dead time Both the DXP and analog systems OCRs are so describable with the slow channel dead times tq shown in Table 4 3 The measured ICRm values for both the DXP and analog systems are similarly describable with the fast channel dead times taf as shown The maximum value of OCR can be found by differentiating Equation 4 12 and setting the result to zero This occurs when the value of the exponent is 1 i e when ICR equals 1 tq At this point the maximum OCRmmax is 1 e the ICR or 57 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 OCR max Ie tg 0 37 tg Equation 4 13 These are general results and are very useful for estimating experimental data rates Table 4 3 illustrates a very important result for using the DXP the slow channel deadtime is nearly the minimum value that is theoretically possible namely the pulse basewidth For the shown example the basewidth is 4 6 us 2L Gg while the deadtime is 4 73 us The slight increase is because as noted above PEAKINT is always set slightly longer than Lg Gg 2 to assure that pileup does not distort collected values of Vx The deadtime for the analog system on the other hand is much larger In fact as shown the throughput for
13. Version of the GENSET used internally 2 POLARITY 1 0 Preamplifier signal polarity 0 negative 1 positive 3 RUNTASKS Bitwise flag Each bit controls a separate task register Will be in manual 4 FIPCONTROL Controls various FiPPI operations Used for debugging primarily 5 PRESETLENLO Low word of preset run length 6 PRESETLENHI High word of preset run length 7 PRESET Preset type 0 no preset 1 realtime 2 livetime 3 output events 4 input events 8 RESETINT Reset time in microseconds 9 TAURC Preamplifier RC decay time in microseconds unused for reset preamplifier 10 IDLEMODE Idle mode as defined in command 0x46 11 IDLEDELAY Delay before entering idle after end run in seconds 12 SLEEPMODE Sleep mode see command 0x47 13 TRACEWAIT Number of clock ticks between successive samples when taking ADC trace see command 0x11 14 STATSMODE Sets the response to the 0x06 Read Run Statistics command STATSMODE 0 default yields the short response 21 bytes STATSMODE 1 yields the long response is 29 bytes including UNDERFLOWS and OVERFLOWS 8 6 2009 77 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 Appendix B GENSET Version 1 Specification Five MCA related GENSETs i e five MCA formats are available ID Parameter Format Description NUMGENSET 16 0 Number of GENSET parameters NOT including N
14. When starting with a new detector it is important first to set SLOWGAP to a minimum of 3 and at least one unit greater than the smallest value in decimated clock cycles see Table 4 2 that encloses the entire preamplifier risetime per 5 10 2 8 6 2009 49 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 Decimation ADC Decimated Decimated Peaking Time Samples Clock Clock cycle Range averaged frequency interval in ps 0 1 8 MHz 125 ns 0 75 3 1 2 4 MHz 250 1 5 6 2 4 2 MHz 500 ns 3 12 3 8 1 MHz 1 0 us 6 24 4 16 500 kHz 2 0 us 12 48 Table 4 2 For decimation 0 the slow filter output is sampled a fixed time after the x ray is detected PEAKSAM must be set properly to achieve optimum performance For example consider a preamplifier with a pulse risetime of 460ns For decimations 1 2 3 and 4 SLOWGAP would be set to 3 or greater For decimation 0 SLOWGAP would be set to 5 or greater 4 6 2 Peak Sampling vs Peak Finding The figures below demonstrate the two approaches For decimations 2 and 4 the slow filter output is monitored over a finite interval of time and the maximum value within that interval is selected This method is referred to as peak finding The interval is set automatically solely based on the values of the DXP parameters SLOWLEN and PEAKINT SLOWLEN and PEAKINT are both automatically derived from the peaking time value s
15. a baseline value that wanders at low frequencies The goal is to achieve a baseline average that has a sufficient number of samples to average out the high frequency noise but which still reflects the local instantaneous baseline Generally speaking Number of Baselines to Average is set to achieve the best energy resolution performance over the desired range of input count rate There are two considerations worth emphasizing 1 Excess detector preamplifier noise and pickup all decimations The values in the table above implicitly assume a flat noise spectrum from the preamplifier A high frequency noise peak can result in poor relative performance at the corresponding resonant peaking time Often this problem can be mediated though not eliminated by increasing the number of baseline samples in the average for the affected peaking times On the other hand excess low frequency noise i e wandering can be remedied by reducing the number baseline samples in the average 2 High rate performance decimation 0 At higher rates i e gt 50 deadtime the slow filter returns less and less often to baseline thus the time between baseline samples grows longer This is the primary cause of degraded energy resolution at high rates Firmware of decimation 2 and above now employs a proprietary circuit that virtually eliminates this problem resulting in industry leading count rate stability This improvement cannot however be implemented
16. aiies anenai n eee oe ia a iaei a 27 2 6 2 Stopping a RUN oon eee cece ceeeceecceceeeceeeeeeeaaeeaaaeeseeeeseaeeeeaaeeseaaeeaes 27 2 6 3 Reading a Spectrum eeececeeeecceeeeeeneeceeeeeseaeeeeaaeseeeeeseeesseaeeseaeeenaes 27 2 6 4 Reading and Calculating the Run Statistics ec eeeeeeeeeees 28 2 6 5 Specifying fixed run INQths ceeececeeeeeceeeeeeeeeceeeeeseeeeeseaeeseneeeeaes 28 2 7 DiaQnOstiC TOOIS oasa aa aa a ra a A 29 2 7 1 ADC Trace REadout ececccecceceeeeeeneeceeeeeseaeeeeeaeeeeeeeseeesseaeeseeeeeaes 29 2 7 2 Baseline Diagnostics 0 00 cece eeececeeeeeeeeeeeeneeeeeeenaeeeeeeaeeeesenaeeeeneaaes 29 2 7 3 DSP Parameters Readout cccecsceceeeeeceeeeeeeeeeeeeeeseeeeeseaeeneeeeeaes 29 3 MicroDXP Functional Description ccceceeeeeeeeeeeeeeeeneeseeeseeeseeeseeeeeeeneeeeeeenes 30 3 1 Organizational OVerView ccccceccceceeeeeeeeeceeeeeceeeeeaaeeeeaeeeeeeeeseaeeseaaeeeeneeees 30 3 2 The Analog Signal Conditioner ASC eccceeeeeceeeeeeeeeeeteeeeeseeeeseaeeeeeeeees 30 3 2 1 Dynamic Range Reduction 0 cc ceeeceeeeeeeteeeeeneeeeeenaeeeeeenaeeeeeeaaes 31 3 22 NyquistiCritenOniinctesitinei oe iaia ait ania iia Sentai 33 3 3 The Analog to Digital Converter ADC ecccceeceeeceeeeeeneeseeeeeceeeeseaeeeeneeees 33 3 4 The Filter Pulse Detector amp Pile up Inspector FIPPI ee eeeeeeeeeeees 33 341 FIPP DeCimation ossaa ia Ni e 34 3 4 2 FIPPI Co
17. data bitwise XOR excludes escape character Response if successful Ox1B 0x00 0x03 0x00 0x00 0x0B 0x10 0x18 8 6 2009 the escape character the command is always returned the low byte that sets the number of data bytes the high byte that sets the number of data bytes status is ok the low byte of the new RUNID 0x1B 27 the high byte of the new RUNID 0x1B 27 bitwise XOR excludes escape character 86 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 Response if unsuccessful 0x1B the escape character 0x00 the command is always returned 0x01 the low byte that sets the number of data bytes 0x00 the high byte that sets the number of data bytes 0x01 status indicates an error 0x18 bitwise XOR excludes escape character 8 6 2009 87
18. gain option provides 32dB of 16 bit precision digitally controlled gain This allows the microDXP to be optimized for a wide range of x ray energies and allows for a real hardware calibration 1 1 3 Application Examples The microDXP miniaturized circuit board can easily be incorporated into a variety of benchtop portable networked and embedded x ray and y ray spectroscopy data acquisition systems In the first example below the microDXP MicroComU board set runs on a laboratory benchtop under the control of an x86 Personal Computer No user hardware design is required no power supplies are needed and no microDXP hardware or firmware modifications are necessary In the second example below the microDXP runs either on the laboratory benchtop as a peripheral device under the control of an x86 Personal Computer or similarly in portable systems under the control of a PDA Minimal user hardware design and no microDXP hardware or firmware modifications are required In the third example a more complex dedicated system is considered The I C serial bus is used to control a smart x ray tube and detector HV bias supply and the auxiliary digital I O drives electromechanical or pneumatic components in real time based upon user defined metrics of acquired data Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 1 1 3 1 Example 1 General Purpose Spectrometer Using USB 2 0 and MicroComU Companion Board I
19. given set of requirements The specification sheet provided with your microDXP lists the options that have been implemented Note The firmware options and clock speed can be upgraded in the field whereas the power supply and gain options require physical modifications to the hardware Please contact XIA at microDXP xia com for more information about hardware options and upgrades 1 1 2 1 Communications and Power Interface The microDXP hardware offers three communications options via two high density connectors a flat flex cable for low and medium speed serial communications and a board to board connector that offers both serial protocols plus high speed parallel access In all cases the power communications and auxiliary digital I O is carried on a single connector and the analog input signal enters via a Separate connection to ensure immunity from electro magnetic interference The standard assembly offers RS 232 communications and auxiliary I O via the flex cable interconnect RS 232 runs at 115kbaud with burst rates up to 10 Kbytes sec The flex interconnect also supports Analog Devices DSP serial port SPORT communications for faster data transfers up to 2 Mbytes sec This option is targeted for multi channel systems and will require some user hardware and DSP code development A third communications option offers parallel IDMA access to DSP memory for transfer rates up to 10 Mbytes sec This interface is used as the basis for
20. microDXP acquires data until a stop command is received from the host A fixed run length can be specified using the parameters PRESET and PRESETLENO 1 as follows PRESET specifies the type of run 0 indefinite default 1 fixed realtime 2 fixed energy filter livetime 3 fixed output events 4 fixed input counts PRESETLENO PRESETLEN 1 specifies the length of preset fixed length run as a 32 bit quantity For fixed real time or live time the units are 500 nanosecond intervals 5 10 2 Setting the slow filter parameters SLOWLEN SLOWGAP 8 6 2009 71 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 The DXP uses a trapezoidal filter characterized by the peaking time Tp and gap time Ty The peaking time is determined by the SLOWLEN and DECIMATION values SLOWLEN is the interval of time in units of decimated clock cycles during which the decimated ADC signal is integrated referred to as the peaking time DECIMATION is automatically sensed by the DSP and should not be modified For Tp and Tg in usec and the pipeline clock Fe in MHz the following gives the value of SLOWLEN and SLOWGAP SLOWLEN Fox Tp 2 DECIMATION e g At DECIMATION 4 Tp 16 usec yields SLOWLEN 8 for an 8MHz clock or SLOWLEN 16 for a 16MHz clock The user will want to be able to choose the peaking time based on resolution and throughput requirements as described earlier in this document SLOWG
21. panel Select the desired setting and press the Apply button to test Note that the Bin Size changes as a result Press the 22 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 Save button to store the setting to the currently selected GLOBSET in nonvolatile memory The RS 232 command to set BINGRANULAR is 0x84 Note that this command does not save the setting to nonvolatile memory Please refer to the RS 232 Command Specification for details 2 3 4 Base Gain To maintain perfect energy calibration a unique analog gain setting can be stored for every combination of peaking time and MCA format The Base Gain is the approximate gain value appropriate for a given MCA size and dynamic range The scale is 0 to 100 the value 100 applies maximum gain to the input signal In microManager we recommend using the ROI calibration routine described in the Rapid Development Kit User Manual to set the Base Gain Base Gain can also be edited directly in the Acquisition tab of the Settings panel Select the desired setting and press the Apply button to test Press the Save button to store the setting to the currently selected GLOBSET in nonvolatile memory The RS 232 command to set the base GAINDAC value is 0x88 Note that this command does not save the setting to nonvolatile memory Please refer to the RS 232 Command Specification for details 2 3 5 Reading the Current GENSET The RS 232 command to read the
22. rates In microManager RESETINT is set via the Reset Interval field in the Detector tab of the Settings panel Simply enter the desired value in microsecond units and press the Apply And Save button The RS 232 command to set and save RESETINT to nonvolatile memory is Ox8A Please refer to the RS 232 Command Specification for details 2 2 1 4 Pre Amplifier Signal Polarity Preamplifier signal polarity denotes the polarity of the preamplifier output signal Please read through 4 1 for a description and figures relating to the preamplifier signal polarity Briefly a positive polarity preamplifier produces a voltage step with a rising edge The DSP parameter POLARITY must be set correctly POLARITY 0 for negative polarity POLARITY 1 for positive polarity In microManager POLARITY is set via the Polarity field in the Detector tab of the Settings panel Select the desired polarity and press the Apply And Save button The RS 232 command to set and save POLARITY to nonvolatile memory is 0x87 Please refer to the RS 232 Command Specification for details 2 2 2 Advanced Processor Settings The advanced processor settings enable and disable various Digital X ray Processor functions and correspond to bits of the DSP parameter RUNTASKS Typically these settings should only be modified as directed by XIA LLC engineers In microManager the advanced processor settings are accessed in the Advanced tab of the Settings panel Please
23. refer to Chapter 5 and specifically section 5 8 for further details 2 3 MCA Settings and GENSETs 8 6 2009 The GENSET specified in Appendix B is a table of MCA related parameters e g the number of bins and bin granularity preset length of run etc Parameters within the GENSET can be modified and stored such that a standardized MCA format can be implemented with a single command Five 5 GENSETs and thus five MCA formats can be stored and retrieved 21 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 2 3 1 Selecting the GENSET In microManager GENSET settings are accessed via the Acquisition tab of the Settings panel GENSETs 0 4 can be selected via the GENSET drop down list Modifications to MCA settings can be tested by pressing the Apply button and saved to nonvolatile memory via the Save button The RS 232 command to select a GENSET is 0x83 Note that this command simply retrieves one of five tables of MCA settings from nonvolatile memory Please refer to the RS 232 Command Specification for details 2 3 2 MCA Size This command is used to change the number of bins in the multi channel analyzer MCA via the DSP parameter MCALEN In microManager MCALEN is set via the Number of MCA Bins field in the Acquisition tab of the Settings panel Select the desired number and press the Apply button to test the setting Press the Save button to store the setting to the c
24. supported Number Test Segment 0 Set ASC DAC values to current value of GAINDAC SLOPEDAC or OFFSETDAC 1 Acquire ADC trace in history buffer 2 Gain calibration 3 Slope calibration measure SLOPEMULT 4 Measure ADC non linearity 5 Not currently used 6 Put DSP to sleep while FPGA logic is downloaded 7 Not currently used 8 OffsetDAC calibration measure OFFDACV AL 9 10 Not currently used 11 Program FiPPI 12 Set internal polarity to current value of POLARITY parameter 13 Not currently used 14 Not currently used 15 RC feedback calibration trace of baseline filter and decimator values 16 RC feedback calibration trace of event filter and decimator values Table 5 3 Special tasks and test segments that can be selected with the DSP parameter WHICHTEST 5 10 DSP Parameter Descriptions As noted above DSP operation is based on a number of parameters Some are control parameters required to operate the DXP some are calibration values determined by the DSP and others are run statistics NOTE in general you will not want to modify these parameters directly but only through a host control program like microManager or if you are a programmer through a software library like XIA s Handel library Variable Type Description Reference PROGNUM Constant Program variant number CODEREV Constant Current DSP program revision HDWRVAR Constant Hardware variant DSP reads
25. the slope gets rather large in order to balance the high energy deposition rate in the detector under these conditions the baseline due to the slope is by far the dominant factor in the baseline By default the DSP continually adjusts the slope to match the current rate these slope adjustments result in an instantaneous change in the baseline If the baseline due to the slope generator is included in the baseline mean the change in the calculated mean would be delayed relative to the change in the slope due to the effect of all the baseline samples prior to the slope change For this reason the baseline due to the slope is subtracted out of the overall baseline prior to calculating the mean value and added back in prior to loading the FiPPI baseline subtraction register The residual baseline included in the mean reflects the detector leakage current and should be fairly constant with rate to the extent that the leakage current does not depend on rate The calibration procedure used to determine the baseline due to the slope generator is performed during the initial startup procedure By default the baseline due to the slope generator is taken out of the baseline average You can choose to include the slope baseline in the mean e g for diagnostic purposes you can do so by clearing the residual baseline bit 6 in RUNTASKS 5 5 5 Baseline Cut As specified above a baseline cut is available to exclude baseline samples that include re
26. this from interface FPGA FIPPIREV Constant FiPPI design revision DSP reads this from FiPPI FPGA FIPPIVAR Constant FiPPI design variant DSP reads this from FiPPI FPGA DECIMATION Constant Slow filter decimation factor DSP reads this from FiPPI FPGA RUNIDENT Returned Run identifier RUNERROR Returned Error code if run is aborted 0 for success BUSY Returned DSPs current acquisition status Values listed below Acquisition Statistics LIVETIMEO 1 2 Statistic Intermediate filter live time in 500 nsec units 8 6 2009 69 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 ELIVETIMEO 1 2 Statistic REALTIMEO 1 2 Statistic EVTSINRUNO 1 Statistic UNDRFLOWSO 1 Statistic OVERFLOWSO 1 Statistic FASTPEAKSO 1 Statistic NUMASCINTO 1 Statistic NUMRESETSO 1 Statistic NUMUPSETSO 1 Statistic NUMDRUPS0O 1 Statistic NUMDRDOSO 1 Statistic NUMZIGZAGO 1 Statistic BASEEVTSO 1 Statistic BASEMEANQO 1 Statistic Control parameters WHICHTEST Parameter RUNTASKS Parameter BINFACT1 Parameter MCALIMLO Parameter MCALIMHI Parameter TRACEW AIT Parameter ASCTIMOUT Parameter YELLOWTHR Parameter REDTHR Parameter PRESET Parameter PRESETLENO 1 Parameter Energy filter live time in 500 nsec units Elapsed acquisition time in 500 nsec units Number of events in MCA spectrum Number of MCA underflow events Number of MCA overflow events Number of input events detected by FiPPI Number of ASC interrupts Number of rese
27. though excessive radiated noise is to be avoided If a switching supply is used it should be well shielded from the microDXP Supply voltages of 5 5V are regulated on board by default to generate 5 0V to power the analog components The microDXP is thus intended to tolerate some conducted EMI lt 100mV pk pk from switching supplies The 5V analog regulators can be bypassed and thus a slight reduction in power achieved if low noise ie linear or carefully designed switching supplies are used If the regulators are bypassed only minimal LC filtering will be applied at the board entry point Current draw on the analog supplies is dominated by the optional variable gain amplifier which alone draws 12 5mA The remaining analog circuitry draws roughly 10mA The total required current is conservatively 15mA without variable gain 30mA with variable gain XIA has recently introduced the MicroComU companion board to complement the microDXP The MicroComU will generate all voltages required by the microDXP at the required currents and noise performance The MicroComU microDXP board set may be powered off the USB bus or off a single external AC power adapter Customers wishing not to have to worry about power supply design are advised to purchase MicroComU companion boards 84 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 Regulated Supply Option lt 20mV pk pk noise Voltag
28. to subsequently save the current PARSET as described below Please refer to the RS 232 Command Specification for details 2 4 4 Baseline Average Length A running average of baseline measurements is computed which is then subtracted from sampled peak values to compute the energy of corresponding incident x rays The number of baseline samples averaged is set in microManager as Baseline Average Length In the DSP this is converted into the parameter BLFILTER according to the equation Baseline Average Length 32768 BLFILTER Please refer to section 4 4 for a thorough discussion of baseline averaging In microManager BLFILTER is accessed via the Acquisition tab of the Settings panel Select the desired Baseline Average Length from the drop down list Modifications for the selected PARSET can be tested by pressing the Apply button and saved to nonvolatile memory via the Save button The RS 232 command to modify BLFILTER is 0x92 Note that this command does not save the change to nonvolatile memory To do so it is necessary to subsequently save the current PARSET as described below Please refer to the RS 232 Command Specification for details 2 4 5 Thresholds Proper triggering on input events depends on good threshold settings particularly for the so called Trigger fast filter and Baseline intermediate filter thresholds The DSP parameters THRESHOLD BASETHRESH and SLOWTHRESH correspond to thresholds applied to the Trigger fas
29. us N 2 3 00 12 0 us N 3 6 00 24 0 us N 4_ 12 0 48 0 us 8 6 2009 Kcps Even time invariant systems with cusp like filters are still expensive due to the computational power required to rapidly execute strings of multiply and adds One commercial system exists which can process over 100 Kcps but it too costs over 12K per channel The DXP processing system developed by XIA takes a different approach because it was optimized for very high speed operation and low cost per channel It implements a fixed length filter with all w values equal to unity and in fact computes this sum afresh for each new signal value k Thus the equation implemented is i k 2L G 1 i k L 1 Equation 4 3 where the filter length is L and the gap is G The factor L multiplying Vx k arises because the sum of the weights here is not normalized Accommodating this factor is trivial for the DXP s host software The operations are carried out using hardwired logic in a field programmable gate array FPGA that is called the FiPPI because is implements Filtering Peak capture and Pileup Inspection In the FiPPI Equation 4 3 is actually implemented by noting the recursion relationship between Vx k and Vx k 1 which is LVx k L Vxkit Vk VeL ViL G Vk 2L G Equation 4 4 While this relationship is very simple it is still very effective In the first place this is the digital equivalent of triangular or trapezoidal if G 0 filtering which is the analog indus
30. will be necessary for applications utilizing the I C bus Please contact XIA to discuss this development 36 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 3 7 Interface to Host Computer PDA NOTE As of August 2009 the IDMA parallel communications interface is now implemented in order to communicate with the new MicroComU companion board The RS 232 communications port has always been supported The SPORT interface is still not implemented at this time 8 6 2009 The microDXP interfaces to a computer or PDA via one of two connectors the standard flex cable port or the high speed DMA port Currently only the flex cable port is supported 3 7 1 Flex Cable Interface A 0 5mm pitch flex cable provides the connection to power serial communications and auxiliary digital lines The flex cable provides for two dimensions of freedom but does require alignment along the axis that bisects all of the contacts Please refer to Appendix D for connector locations and pinouts Flex Cable Interface Resources Resource Function Description RS 232 low rate serial Default communications interface communications rc low rate serial Peripheral device interface e g communications indicators DACs etc SPORT mid rate serial Alternate serial communications communications interface e g for multi channel systems that require moderate readout bandwidth AUX0
31. 0 x B Pin Name Description 1 AVDD Positive DC supply voltage for analog signal conditioner Regulated 5 0V or unregulated 5 5V if on board regulator present 2 AVSS Negative DC supply voltage for analog signal conditioner Regulated 5 0V or unregulated 5 5V if on board regulator present 3 GND Internal ground connection 4 3 3VCC 3 3V DC supply for on board digital components 5 3 3VCC 3 3V DC supply for on board digital components 6 GND Internal ground connection 7_ SDA TC data line 8 SCL IC clock 9 ExtInt External interrupt line active low 10 Gate Inhibits data acquisition active low 11 GND Internal ground connection 12 RX RS 232 microDXP receive host microDXP 13 TX RS 232 microDXP transmit microDXP host 14 GND Internal ground connection 15 Vprog PIC programming voltage 16 ProgData PIC programming data line 17 ProgClk PIC programming clock 18 AuxO Auxiliary configurable digital I O line connects to FiPPI 19 Auxl Auxiliary configurable digital I O line connects to FiPPI 20 GND Internal ground connection 21 Aux2 Auxiliary configurable digital I O line connects to FiPPI 22 Aux3 Auxiliary configurable digital I O line connects to FiPPI 23 3 3VCC 3 3V DC supply for on board digital components 24 SPORT_CLK DSP serial port clock line ADSP218x SPORT 25 GND Internal ground connection 26 SPORT_TDATA DSP serial port transmit data line ADSP218x SPORT 27 SPORT_
32. 2009 used to handle such housekeeping chores as updating statistics These routines are described in more detail below 5 6 1 ASC Monitoring There are four main tasks performed by the ASC interrupt routine 1 Detects Resets reset type detectors only 2 Adjusts the slope generator to match the event rate reset type detectors only 3 Adjusts the offset value to keep the signal in range RC feedback detectors only 4 Moves the signal back to the center of the ADC range whenever it drifts out of range high or low The ASC interrupt routine is triggered whenever the FiPPI detects the ADC going out of range The DSP first triggers a short reset If the signal merely drifted out of range to begin with the short reset will bring the signal back to the center of the ADC range and data taking resumes If instead the signal was driven out of range by a preamplifier reset the short reset will not bring the signal back into range In this case the DSP triggers a long reset and then holds the signal at the center of the ADC range for a time determined by the parameter RESETINT which specifies the dead time after a reset in microsecond units After the reset interval the signal is released and data taking resumes The DSP keeps track of how many times the signal drifts out of range in both directions and adjusts the slope such that the number of drifts high NUMDRUPS roughly matches the number of drifts low NUMDRDOS If the DSP determ
33. 3 Reserved Auxiliary digital I O lines Connect to FiPPI GATE DAQ control Inhibits data acquisition when low EXTINT DSP interrupt Extra interrupt line active low 3 7 2 High Speed Interface A high density board to board connection is also included on the microDXP The so called high speed interface includes all resources carried on the flex cable interface plus Direct Memory Access DMA to the DSP It was included for applications requiring very fast data transfer rates High Speed board to board Interface Resources Resource Function Description DMA High rate parallel Direct Memory Access to DSP communications memory for the highest bandwidth data transfers RS 232 Low rate serial Default communications interface communications rc Low rate serial Peripheral device interface e g communications indicators DACs etc SPORT Mid rate serial Alternate serial communications communications interface e g for multi channel systems that require moderate readout bandwidth 37 Micro Digital X ray Processor Technical Reference Manual 8 6 2009 mdo microDXP MAN 1 1 2 AUX0 3 Reserved Auxiliary digital I O lines Connect to FiPPI GATE DAQ control Inhibits data acquisition when low EXTINT DSP interrupt Extra interrupt line active low 38 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 4 Digital Filtering Theory of Oper
34. 5 us 1 2 250 ns 1 5 ps 500 ns 3 0 us 2 4 500 ns 3 0 us 1 0 us 6 0 ps 3 8 1 0 us 6 0 us 2 0 us 12 0 us 4 16 2 0 us 12 0 us 4 0 us 24 0 us 5 32 4 0 us 24 0 us 8 0 us 48 0 us 6 64 8 0 us 48 0 us 16 0 us 96 0 us Table 3 1 Available peaking time ranges by FiPPI decimation and pipeline clock speed 3 4 2 FiPPl Code Variants The FiPPI pipeline topology for RC type preamplifiers is different than for reset type preamplifiers thus two standard code variants are offered for each decimation Additionally any use of the auxiliary digital I O will require per instance FiPPI configuration variant Please contact XIA to discuss this development 3 5 The Digital Signal Processor DSP 8 6 2009 The Digital Signal Processor acquires and processes event data from the FiPPI and controls the ASC through DACs The processor is an Analog Devices ADSP 2183 16 bit Fixed Point DSP optimized for fixed point arithmetic and high I O rates Different DSP program variants are used for different types of data acquisition and different preamplifier types Chapter 5 describes in detail the DSP operation its tasks and parameters which control them The ADSP 2183 has 16K words of 16 bit wide data memory and 16K words of 24 bit wide program memory part of which is used as data memory to hold the MCA spectrum If more memory is required for special purposes up to 4 Mbytes of extended memory can be added by speci
35. AP is the gap time visible as the flat top region of the trapezoid SLOWGAP Pegg 2 DECIMATION Subject to the restriction that it must exceed 3 SLOWGAP is set such that the flat top interval is longer than the 0 100 risetime of the preamplifier output pulses by at least 1 decimation period Gap Time 2 P SLOWGAP 125 ns gt pulse risetime 2P 125 ns or 2 Dix SLOWGAP 1 125 ns gt pulse risetime 5 10 3 Setting the fast filter parameters FASTLEN FASTGAP The fast filter is also trapezoidal but has a decimation of 0 for all FiPPI designs The values of FASTLEN and FASTGAP are given for Tp fast peaking time and Tg fast gap time in psec FASTLEN 8 T p FASTGAP 8 T g Typical values of these parameters are FASTLEN 4 and FASTGAP 0 5 10 4 Setting Thresholds THRESHOLD MINWIDTH BASETHRESH BASETHRADJ SLOWTHRESH FIPCONTROL Note BASETHRESH is NOT used in the decimation 0 FiPPI i e peaking time range 0 75 3 usec for the standard 8MHz pipeline clock or peaking time range 0 375 1 5 usec for a 16MHz pipeline clock Instead THRESHOLD is used to discriminate both for and against events X rays are identified when a filter output goes above an active threshold Thresholds can be applied to the fast THRESHOLD intermediate BASETHRESH BASETHRADJ and energy filters SSLOWTHRESH though 72 Micro Digital X ray Processor Technical Reference Ma
36. CR This phenomenon it should be noted is a characteristic of all x ray detection circuits whether analog or digital and is not specific to the DXP Of the detected x rays some fraction will also satisfy both fast and slow channel pileup tests and have their values of Vx captured and placed into the spectrum This number is the output count rate which we refer to as the OCR The DXP normally returns in addition to the collected spectrum the REALTIME for which data was collected the fast channel LIVETIME for which the fast channel was below threshold and thus ready to detect a subsequent x ray together with the number FASTPEAKS of fast peaks detected and the number of Vx captured events EVTSINRUN From these values both the OCR and ICRm can be computed according to Equation 4 11 These values can then be used to make deadtime corrections as discussed in the next section ICRm FASTPEAKS LIVETIME OCR EVTSINRUN REALTIME Equation 4 11 Note The fast channel LIVETIME should only be used to determine the input count rate according to Equation 4 11 Specifically it is NOT related to the energy filter livetime and should not be interpreted as the inverse of the processor deadtime The DSP does calculate the energy filter livetime ELIVETIME however it is only an approximation The most accurate deadtime measurement is obtained from ICRm and OCR in Equation 4 11 as discussed in 4 11 4 10 Throughput 8 6 2009 Figure 4 12 shows
37. EAD4 IDMA data address I O line 33 EAD3 IDMA data address I O line 35 EAD2 IDMA data address I O line 37 EAD1 IDMA data address I O line 39 EADO IDMA data address I O line LSB 41 GND Internal ground connection 43 EWR IDMA write strobe Active LO 45 ESel IDMA device select INPUT must be asserted LO for IDMA use 47 ERdy IDMA data ready Active LO OUTPUT 49 ERD IDMA read strobe Active LO Even numbered pins top to bottom along the left side of the connector as shown in Figure C 3 2 AVDD Positive DC supply voltage for analog signal conditioner Regulated 5 0V or unregulated 5 5V if on board regulator present 4 AVSS Negative DC supply voltage for analog signal conditioner Regulated 5 0V or unregulated 5 5V if on board regulator present 6 3 3VCC 3 3V DC supply for on board digital components 8 GND Internal ground connection 10 SPORT_RFS DSP serial port receive frame sync line ADSP218x SPORT 12 SPORT_RDATA _ DSP serial port receive data line ADSP218x SPORT 14 GND Internal ground connection 16 SPORT_TFS DSP serial port transmit frame sync line ADSP218x SPORT 18 SPORT_TDATA DSP serial port transmit data line ADSP218x SPORT 20 GND Internal ground connection 22 SPORT_CLK DSP serial port clock line ADSP218x SPORT 24 GND Internal ground connection 26 Aux3 Auxiliary configurable digital I O line connects to FiPPI 28 Aux2 Auxiliary co
38. F13 2630SCFR Figure C 2 Connector locations and part numbers top side 4 x 0 120 diameter i e Board to Board Port S0 conductor 0 5mm pitch ft N Hirose SMT Receptacle P N DF12 SODS 0 5V Hirose Mating Header P N DF12 5 0 SODP 0 5V lt c lise MIRRORED VIEW looking down through the board at bottom side components 0 175 0 175 N standard width Figure C 3 Connector locations and part numbers bottom side 8 6 2009 81 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 J1 Analog Input 2 pin compact right angle header or thru hole LEMO Note 1 Hirose P N DF13 2P 1 25H mating P N DF13 2S 1 25C crimp contact P N DF13 2630SCFR Pin Name Description 1 SIGNAL Preamplifier output signal 2 GND Internal ground connection Note 1 Customers wishing to use an SMA input cable are advised that this capability is provided by means of the MicroComU companion board See the separate MicroComU Technical Reference Manual Also contact XIA in order to get quotes for the appropriate variant of the microDXP board J12 Flex Cable Port 30 conductor 0 5mm locking flex cable connector carries power communications and auxiliary digital I O Hirose P N FH12 30S 0 5SH e g flat flex cable Parlex P N 0 5MM 3
39. Hirose SMT connector P N FH12 30S 0 5SH Parlex flat flex cable P N 0 SMM 30 x B pin 1 1 395 mere Fate eb AS GHD af f Preamplifier Type Selector Switch The only hardware setting on the microDXP board is the preamplifier type selector switch The location of the miniature two position slide switch S1 is displayed in Figure C 2 The two positions are silkscreen labeled RAMP and OFFSET for reset type and RC feedback preamplifiers respectively Connector Locations and Pinouts Two connectors carry all electronic signals to and from the microDXP standard assembly as depicted in Figure C 2 A 2 conductor 1 25mm pitch connector carries the analog signal from the preamp The mating connector is a crimp type socket that accommodates 26 30AWG stranded wire A single 30 conductor 0 5mm pitch flat flex interconnect carries all communications power and auxiliary I O to and from the microDXP The flex cable provides for two dimensions of freedom but does require alignment along the axis that bisects all of the contacts The most likely error would be misalignment of this interconnect or a reversal of the pinout Table C 1 details the pin assignments of the flex interconnect wat oie StvRANP OFFSET s a E a C Li amie Sid aiar Ri f STGNAL oo Analog input 2 conductor 1 25am pitch Hirose SMT header P N DF13 2P 1 25H 1 640 Hirose mating connector P N DF1i3 2S 1 25C Hirose crimp contacts P N D
40. If the 27 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 checkbox is unchecked press the Update button to manually update the spectrum and statistics The RS 232 command to read the MCA spectrum is 0x02 Please refer to the RS 232 Command Specification for details 2 6 4 Reading and Calculating the Run Statistics The read run statistics command retrieves the fast filter livetime LIVETIME the realtime REALTIME the number of input counts FASTPKS and the number of output counts EVENTSINRUN These parameters can be used to directly calculate the input count rate ICR output count rate OCR and the deadtime percentage pgaprime ICR FASTPKS LIVETIME OCR EVENTSINRUN REALTIME YopeapTiME OCR ICR Realtime and livetime are expressed in units of 500 ns Note The LIVETIME corresponds to the fast filter NOT the energy filter and thus does not alone determine the relationship between input and output count rates i e the deadtime percentage In microManager the spectrum and statistics can be updated automatically or manually Check the Continuous checkbox for automatic updates If the checkbox is unchecked press the Update button to manually update the spectrum and statistics The RS 232 command to read the run statistics is 0x06 Please refer to the RS 232 Command Specification for details 2 6 5 Specifying fixed run lengths By default the microDXP
41. Interfaces for Production Recently the MicroComU companion board has been introduced in order to provide customers with a USB 2 0 high speed interface to the microDXP and power supply generation for the microDXP all in a form factor close to the size of the microDXP itself We are interested in how well the new MicroComU board satisfies customer requirements and or what improvements are desired 1 4 5 The Accelerated DevelOPmenT ADOPT Program The ADOPT program is a support plan for users developing custom software using any of our driver libraries It is intended for those who wish to get direct access to the XIA software team and obtain hands on training in the use of XIA software tools as a method of reducing overall software development time The standard ADOPT package provides 12 months of support divided as follows e 1 month on site support and priority phone email support e 11 months priority phone email support The specific number of hours for on site support and priority phone email support depend on the driver library being used Typically the 16 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 person who will be doing the majority of the development will visit XIA for a hands on tutorial with the XIA software team The visitor will be encouraged to work at XIA for anywhere from a few days to two weeks depending on the specific situation and complexity of the project By w
42. S 232 serial port or PDA Legend lt Routing Adapter O Customer designed hardware L XIA and 3rd party hardware Figure 1 2 A general purpose spectrometer incorporating the microDXP A simple user designed routing adapter interface connects the microDXP to the host computer PDA and power supplies The microDXP power supplies and routing adapter together constitute a spectrometer that can be connected to virtually any controller with RS 232 communications Note The microCOM interface board included with the RS232 Rapid Development Kit falls into this category though its large form factor nearly prohibits commercial use However the recently released 8 6 2009 8 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 MicroComU board included with the USB Rapid Development Kit may also be used for this purpose 1 1 3 3 Example 3 Dedicated Spectrometer Using RS232 This example considers a materials sorting application where objects with certain pre defined alloy ratios X Y and Z are to be separated from others An x ray source irradiates incoming samples and incident x rays are collected by a solid state detector connected to the microDXP The microDXP is configured to assert a combination of its auxiliary digital I O lines whenever the peak ratio X Y or Z is detected The digital I O lines drive electromechanical or pneumatic components in real time to execute the appr
43. SPORT interface is a interface candidate in multi microDXP systems and is available with either interface connector option see 3 7 below 3 5 3 DMA Port Parallel Direct Memory Access DMA provides the highest bandwidth communications path to the DSP data memory Transfer rates up to 16 Mbytes sec are possible The DMA bus is available to the host computer PDA only if the high speed board to board interface option see 3 7 2 below is chosen 3 5 4 DSP Code Variants The FiPPI pipeline topology for RC type preamplifiers is different than for reset type preamplifiers thus two standard code variants are offered for each FiPPI decimation Additionally special data acquisition modes e g time resolved spectroscopy multi SCA s etc require variation in the DSP code Please contact XIA to discuss this development 3 6 PIC MicroConitroller 8 6 2009 The PIC microprocessor serves as the system controller carrying out procedures to boot the board loading appropriate DSP code from memory and running acquisition routines In addition the PIC handles I O including RS 232 standard communications and an I C bus for controlling dedicated peripheral devices 3 6 1 RS 232 Serial Port The RS 232 serial port is the default communications interface for the microDXP and is wired to both the flex cable connector and the high speed DMA port connector Though relatively slow 115 kbaud the RS 232 port is in fact adequate for most ap
44. TERF 5 5 3 Baseline Histogram As part of the baseline processing all valid baseline samples are entered into the baseline histogram which occupies 1024 words of data memory The baseline histogram can be very useful in monitoring or evaluating the performance of the microDXP as discussed in the Rapid Development Kit Manual The parameter BASESTART contains the pointer to the location of the histogram in data memory and the length nominally 1K is contained in the parameter BASELEN The baseline histogram is centered about a zero baseline The parameter BASEBINNING determines the granularity of the histogram 2 B ASEBINNING baseline values are combined into one bin of the baseline histogram The default value of BASEBINNING is 2 i e the baseline value is divided by 4 to determine the bin All valid baseline values are included in the histogram even if there is a baseline cut see 5 5 5 below in use The baseline histogram is only filled during a normal data acquisition run when the DSP is idle the baseline average is calculated but the histogram is not filled Since the baseline histogram is stored in data memory 16 bit words are used to record the bin contents As a result the histogram overflows quite often the time to overflow depends on the baseline sample rate typically several 100 kHz and the width of the baseline distribution When the DSP detects an overflow all bins are scaled down by a factor of 2 and histogramming
45. TFS DSP serial port transmit frame sync line ADSP218x SPORT 28 GND Internal ground connection 29 SPORT_RDATA DSP serial port receive data line ADSP218x SPORT 30 SPORT_RFS DSP serial port receive frame sync line ADSP218x SPORT Table D 1 Pin assignments for the 30 conductor flat flex interconnect 8 6 2009 82 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 J11 Board to Board Port 50 conductor 0 5mm mezzanine board to board receptacle carries power communications and auxiliary digital I O Hirose P N DF12 50DS 0 5V microCOM MicroComU mating header P N DF12 5 0 50DP 0 5V Pin Name Description Odd numbered pins top to bottom along the right side of the connector as shown in Figure C 3 1 3 3VCC 3 3V DC supply for on board digital components 3 3 3VCC 3 3V DC supply for on board digital components 5 4 3 3VCC 3 3V DC supply for on board digital components 7 GND Internal ground connection 9 EAD15 IDMA data address I O line MSB 11 EAD14 IDMA data address I O line 13 EAD13 IDMA data address I O line 15 EAD12 IDMA data address I O line 17 EAD11 IDMA data address I O line 19 EAD10 IDMA data address I O line 21 EAD9 IDMA data address I O line 23 EAD8 IDMA data address I O line 25 EAD7 IDMA data address I O line 27 EAD6 IDMA data address I O line 29 EAD5 IDMA data address I O line 31
46. UMGENSET and GENVERSION used internally GENVERSION 16 0 Version of the GENSET used internally MCALEN Number of spectrum bins MCALIMLO Lowest spectrum bin allows offset spectrum MCALIMHI Highest spectrum bin BASEBINNING Number of bins baseline values combined into one bin in baseline histogram power of 2 BLCUT Baseline cut value in percentage of peak value in baseline histogram Standard value is 5 Expressed as x 32768 BINMULTIPLE MCA bin size in terms of the minimum BINGRANULAR Bin granularity as defined in command 0x83 0 very fine etc GAINBASE 16 bit GAINDAC base setting Higher value higher gain This value is modified per peaking time by the GAINTWEAK table in the PARSET 8 6 2009 78 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 Appendix C PARSET Version 1 Specification 8 6 2009 These are all the parameters that are stored and retrieved for each peaking time ID Parameter Format Description 0 NUMPARSET Number of PARSET parameters NOT including NUMPARSET and PARVERSION used internally 1 PARVERSION PARSET version number used internally 2 BINSCALEXP Energy scaling factor internally calculated 3 BINSCALE Energy scaling factor proportional to SLOWLEN 4 FIPSCALE Controls FiPPI energy scalin
47. VAL Parameter Tracking DAC value 12 bit parallel TDACWIDTH Parameter Track DAC pulse width 50 ns units TDQPERADC Calibration TDQPERADCE Calibration ASC Control Parameters and Calibrations RC feedback variants OFFSETDAC Parameter Current offset DAC value 16 bit serial DAC range 0 65535 OFFSETSTEP Parameter Offset DAC step size TAURC Parameter Preamplifier decay constant in 25 ns units RCF variant only RCFCOR Calibration Preamplifier decay correction RCF variant only Miscellaneous Constants SPECTSTART Constant Address of MCA spectrum in program memory SPECTLEN Constant Length of MCA spectrum buffer BASESTART Constant Address of baseline histogram in data memory offset by 0x4000 BASELEN Constant Length of baseline histogram EVTBSTART Constant Address of event buffer in data memory offset by 0x4000 EVTBLEN Constant Length of baseline histogram HSTSTART Constant Address of history buffer in data memory offset by 0x4000 HSTLEN Constant Length of history buffer NUMSCA Parameter Number of SCA regions defined mapping variants only SCAxLO x 0 23 Parameter Lower MCA channel for SCA region x mapping variants only SCAXHI x 0 23 Parameter Upper MCA channel for SCA region x mapping variants only USER1 USER8 User User variables Host software can use these for any purposes Table 5 4 Summary of DSP parameter definitions 5 10 1 Specifying fixed run lengths PRESET PRESETLENO 1 By default the
48. a x ray events measured with the DXP 4C As Figure 4 10 makes clear there is a linear correlation between the step height from the trapezoidal filter and the ADC amplitude for pulses of a given energy This is due to the fact that the exponential decay causes a deficit in the measured step height which grows linearly with the distance from the asymptotic ADC offset at zero count rate The DSP reads these two values for each event that passes the FiPPI s trigger criteria and makes a correction of the form E k Sx ky Vx lt Sg k Vg gt Equation 4 9 Here the quantities Sx and Vx are the step height and ADC amplitude measured for the step and the corresponding values with the B subscript are baseline values which are measured frequently at times when there is no trigger The brackets lt gt indicate that the baseline values are averaged over a large enough number of events to not introduce additional noise in the measurement The constant k the DSP parameter called RCFCOR is inversely proportional to the exponential decay time this correction factor is a constant for a detector channel at a fixed gain and shaping time The constant k is effectively a gain factor and is taken into account with a detector gain calibration The parameter RCFCOR is a function of the digital filter parameters SLOWLEN SLOWGAP and DECIMATION and the preamplifier decay time the DSP parameter TAURC The user entered decay time TAURC is
49. acquires data until a stop command is received from the host Alternatively the microDXP can automatically terminate data acquisition runs based upon the realtime livetime or the number of input or output counts exceeding a preset value Note Although the realtime and livetime are expressed in measured accurately to units of 500 nanoseconds the process that monitors the realtime and livetime is only updated every 500 microseconds Similarly the input and output counts are tallied every 500 microseconds The result is that a preset of 100 000 input counts may terminate with a slightly larger number of input events than 100 000 Nonetheless the run statistics see 2 6 4 above are all mutually consistent and accurate In microManager select the desired Preset Run Type from the drop down list and enter the desired value in the Preset Value field The RS 232 command to control preset run settings is 0x07 Please refer to the RS 232 Command Specification for details 28 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 2 7 Diagnostic Tools The microDXP provides for diagnostic features including ADC trace readout baseline trace and histogram readout and DSP parameters readout 2 7 1 ADC Trace Readout An 8000 point digital trace of the signal at the ADC is available for readout as a diagnostic aid Remember that this signal is NOT the raw preamplifier signal but has been conditioned as described i
50. al event energy which can lead to peak shifting at high event rates The cut is expressed as a fraction of the peak value of the baseline distribution by default the baseline cut is set to 5 The cut values are based on the baseline histogram and are recalculated every time the histogram overflows every few seconds The DSP searches on either side of the peak of the baseline distribution for the first bin whose contents are less than the cut 05 by default times the peak value these bin numbers are used to calculate the actual baseline cut The cut fraction is stored in the parameter BLCUT expressed in 16 bit fixed point notation Interpreted as an integer BLCUT cut fraction 2 15 the default 5 cut corresponds to BLCUT 1638 decimal or 666 hex The actual cut values determined by the DSP code are stored in BLMIN and BLMAX The baseline cut is enabled or disabled by setting or clearing a bit 10 in the RUNTASKS parameter 5 6 Interrupt Routines 8 6 2009 There are several tasks performed under interrupt control within the DSP on the microDXP The event interrupt routine which just transfers event data from the FiPPI to an internal buffer is described above in Section 5 4 above There are two other interrupt routines the ASC interrupt is used to keep the analog signal within the input range of the ADC and the timer interrupt is 66 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6
51. ard temperature is 0x41 Please refer to the RS 232 Command Specification for details 2 2 Global Settings and the GLOBSET 8 6 2009 The GLOBSET specified in Appendix A contains global settings including detector preamplifier settings and system settings There is only one GLOBSET these settings are used for all peaking times and MCA formats The GLOBSET includes detector preamplifier settings advanced processor settings run control settings and diagnostic control settings In microManager GLOBSET settings are accessed via the Detector and Advanced tabs of the Settings panel Because these settings are global changes are simultaneously applied and saved to nonvolatile memory via the Apply And Save button 19 Micro Digital X ray Processor Technical Reference Manual Note The microDXP must have appropriate firmware for the preamplifier type used In addition the HARDWARE must also be set to the appropriate preamplifier type via a miniature DIP switch S1 Set S1 to RAMP for reset type preamplifiers Set S1 to OF FSET for RC type preamplifiers 8 6 2009 mdo microDXP MAN 1 1 2 2 2 1 Preamplifier Settings The microDXP s analog signal conditioner must be configured for the specific detector preamplifier that is used in order for the downstream digital processing pipeline to operate correctly The microDXP must have firmware pre loaded in non volatile memory that is appropriate for the preamplifier
52. ation and Implementation Methods This chapter provides an in depth discussion of x ray pulse processing theory both generally and as implemented in the microDXP The topics include how digital filters work x ray detection thresholds baselines pileup inspection and input and output count rates Topics are covered to illustrate the theoretical issues practical implementation and how to adjust parameters to obtain best performance The acronym DXP stands for Digital X ray Processor and refers to XIJA s standard digital processing technology which is included in many XIA products including the microDXP 4 1 X ray Detection and Preamplifier Operation 8 6 2009 Energy dispersive detectors which include such solid state detectors as Si Li HPGe HgI2 CdTe and CZT detectors are generally operated with charge sensitive preamplifiers When an x ray is absorbed in the detector material it releases an electric charge Qx E e where the material constant is the amount of energy needed to form an electron hole pair Qx is integrated onto the preamplifier s feedback capacitor C to produce the voltage Vx Qx Cf Ex eCf Measuring the energy Ex of the x ray therefore requires a measurement of the voltage step Vx in the presence of the amplifier s noise o Figure 4 1 and Figure 4 3 depict reset type and RC type charge sensitive amplifiers respectively In both figures the detector D is biased by voltage source HV either p
53. cessor Technical Reference Manual mdo microDXP MAN 1 1 2 1 1 3 2 Example 2 General Purpose Spectrometer Using RS232 and Custom Breakout Board In this example the microDXP acts as a general purpose spectrometer connected as a peripheral device under the control of a host computer or PDA No specialized data acquisition modes are required thus no firmware development is necessary Some user hardware design is however required XIA non recurring engineering NRE required NONE User development required 1 To connect to the external host only a simple routing adapter interface unit is required to break out the microDXP high density internal connection to standard RS 232 and power connections At a minimum this interface is a wire harness but could entail a printed circuit board with a small number of passive components 2 Power supplies for the microDXP must be provided Optional voltage regulators for the analog circuitry are included on the microDXP for systems in which high quality power supplies are not available 3 Some additional mechanical design i e enclosure design may be necessary MicroDXP board dimensions and mounting information the connector locations and specifications and the power supply specifications are all found in Appendix D of this manual x ray O signal lt Detector Preamp VNA te i A i Power Supply i 1 j 1 1 oogocoocococoo goocogcooocooean ooooooooooo0000 R
54. cification This section describes the first steps that should be taken to design hardware for a system incorporating the microDXP XIA engineers will provide limited assistance with the actual design depending on the support agreement Board Dimensions and Mounting The microDXP measures 3 375 x 2 125 as shown in Figure C 1 with 0 120 non plated mounting holes inset by 0 175 symmetrically with respect to each of the four corners These mounting holes are intended for use with 4 40 or equivalent screws An alternate board form factor includes 0 1875 blank PCB rails on the two long sides The rails were included for systems where the microDXP board is to be mounted in a slot The overall dimensions for the slot mounted board are thus 3 375 x 2 500 4 x 0 120 diameter _ _ _ 02s ________ 0 175 0 175 standard width optional rail 169 R72 U yie_SisRAMP OFFSET ere TPL REIR 28 1 Fee eee ee gt 7 eno Sy SND yes E LE ee Ld pao EEr Gay boos a Standard width 2 125 inches Alternate width 2 500 inches 2 125 2 500 Symmetric around standard boarc 0 1875 inch rail both sides uDXP rev B digital xray orocesso optional rail 3 375 gt Figure C 1 Dimensions and mounting hole locations 8 6 2009 80 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 Flex Cable Port 30 conductor 9 5mm pitch
55. continues The baseline distribution should be very Gaussian the width of the distribution reflects the electronic noise in the system including the effects of the energy filter A tail on the positive side of the distribution indicates the presence of energy in the baseline resulting from undetected pileup or energy depositions that did not satisfy the trigger threshold The tail should be very small compared to the peak of the histogram it will grow with rate If this tail is too large it can have a noticeable effect on the baseline mean leading to negative peak shifts Under these circumstances enabling the baseline cut is useful in eliminating the bias A tail on the low energy side of the baseline distribution is usually caused by baseline samples just after a preamplifier reset the effects of the reset can last quite a while tens of microseconds especially for optical reset preamplifiers It is usually best not to take data while the reset is in effect the dead time associated with a reset can be adjusted using the parameter RESETWAIT which sets the dead time in units of 250 65 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 5 5 4 Residual Baseline When operating with a reset type preamplifier the raw baseline measured in the FiPPI which is just the output of the energy filter comes from two sources the detector preamplifier and the slope generator in the microDXP itself At high rates
56. ctral data are desired for many different time or spatial points 5 5 Baseline Measurement 8 6 2009 The DSP collects baseline data from the FiPPI whenever there are no events to process both during a run and between runs when there are never events to process The DSP keeps a running average of the most recent baseline samples this average is written back into the FiPPI where it is subtracted from the raw energy filter value to get the true energy The baseline data read from the FiPPI is just the raw output of the energy filter One bit of the baseline register is used to indicate whether the sample occurred while an event was in progress in which case it is not used Two methods are available to determine the average baseline value By default an infinite impulse response IIR filter is used where the baseline average is calculated by combining a new baseline sample with the old average using weights x and 1 x respectively where x is typically 1 128 By setting the appropriate bit in the parameter RUNTASKS see below a finite impulse response FIR filter is used where the baseline mean is just the straight average of the N most recent baseline samples Both averaging methods are described in more detail in the following sections The baseline mean is stored with 32 bit precision in the parameters BASEMEANDO high order word and BASEMEAN 1 5 5 1 IIR Infinite Impulse Response Filter By default the baseline mean is calc
57. current GENSET table is Ox8E Note that this command does not save the setting to nonvolatile memory Please refer to the RS 232 Command Specification for details 2 3 6 Saving the Current GENSET to Non Volatile Memory The RS 232 command to save the current GENSET table is 0x8F Please refer to the RS 232 Command Specification for details 2 4 Spectrometer Settings and PARSETs 8 6 2009 For a given FiPPI decimation i e peaking time range and pipeline clock speed the slow filter length SLOWLEN sets the peaking time In practice other FiPPI control parameters as well as other DSP parameters such as the analog gain may also be require adjustment for optimal performance at each peaking time To avoid repeating the optimization procedure five sets of parameters and thus five optimized peaking times are available for each FiPPI decimation The PARSET specified in Appendix C is a table of peaking time related spectrometer parameters e g filter values thresholds pileup inspection settings etc Parameters within the PARSET can be modified and stored such that a calibrated spectrum is achieved whenever the peaking time PARSET is subsequently selected The PARSETs are stored in the nonvolatile flash memory Five 5 PARSETs are available for each FiPPI decimation purchased 23 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 see 1 1 2 4 Up to three FiPPI decimations and thus a ma
58. d the MCA are cleared Otherwise the run is treated as a continuation of the previous run Note that for a run continuation no gain or FiPPI changes are performed In either case the run number parameter RUNIDENT is incremented 62 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 5 4 2 Event Interrupt When the FiPPI detects a good event it triggers a high priority interrupt in the DSP Upon receiving the interrupt the DSP immediately reads the event energy from the FiPPI into an internal circular buffer and increments the write pointer into that buffer The normal event loop compares the write pointer to the read pointer to determine that there is a new event to process 5 4 3 Event Loop The processing that takes place during a normal collection run is very simple in order to allow high event rates The structure of the event loop is illustrated below in pseudocode while RunInProgress if EventToProcess ProcessEvent else CollectBaseline endif RunFinish goto IdleLoop The run can be stopped by the host or can be stopped internally for fixed length runs see 5 10 1 below The event processing involves either binning the energy into an MCA or determining whether the event falls into a defined SCA window depending upon the DSP code variant If there is no event to process the DSP reads a baseline value from the FiPPI see below for a detailed descript
59. de Variants cceccccccseeeeeeceeeeeceeeeeeaeeeeeeeseeeeseaeeeeneeeeaes 34 3 5 The Digital Signal Processor DSP cccceeeeceeeeeeeeeeeeeeeeseeeeeseaeeeseaeeeeneeees 34 3 5 1 FLASH Mem Ory irii Sneep a aaau oaair aaia Mets 34 3 5 2 Serial Port SPORT nisione ai aaeoa aina aai uais 35 353 DMA POM ooann aa cians Miele aneeeeieag sie dee eneleeviaies 35 3 5 4 DSP Code Variants cececcccceceeeeeeneeceeeeeeeaeeeeaaeeeeeeeseeeeseaeeeeeeeeaes 35 3 6 PIG MicroControlle i ccc c2dettaeivtnee edit dade aaaeaii eae iene 35 3 6 1 RS 232 SerialPort arrine e ndings 35 3602 ANC Seral BUS iaia a A A aN 36 363 TiC Meimiohy sctechcohinden a e E NN a 36 3 6 4 IC Temperature Sensor sss isssiisssiisesereessrirsrrreerrresrrressrreeesrrees 36 3 6 5 PIC Qode Variants i i aneii eaaa a a ae aia tetas 36 3 7 Interface to Host Computer PDA ssessssssesressrrssrssrssrrssrrssrrssrrssrnssrissressrnnt 37 3 7 1 Flex Cable Interface eeececccccseeeenceceeeeeeeaeeeenaeeseneeseeeesaeeneaeeesaes 37 3 7 2 High Speed Interface cececceecceeeeeceeececeeeeeeeaeseeneeseeeeessaeeeenaeenenees 37 4 Digital Filtering Theory of Operation and Implementation Methods 39 4 1 X ray Detection and Preamplifier Operation cccccsceeereeseeeeeesteeeeneeees 39 4 1 1 Reset Type Preamplifiers 0 cece eceeeeeeeneeeeeeeeeeeeenaeeeeeenaeeeeeeaaes 39 4 1 2 RC Type Preamplifiers 0 ccccccsceeesceceeeeseeeeeeeeeeeeees
60. ds on the chosen pipeline clock speed FiPPI ADC codes Peaking times Peaking times Decimation pre averaged available available with 8MHz clock with 16MHz clock 0 0 0 75 1 125 1 5 2 25 0 375 0 5625 0 75 3 1 125 1 5 1 2 1 5 2 25 3 4 5 6 0 75 1 125 1 5 2 25 3 2 3 4 5 6 9 12 1 5 2 25 3 4 5 6 3 8 6 9 12 18 24 3 4 5 6 9 12 4 16 12 18 24 36 48 6 9 12 18 24 Table 1 3 Firmware peaking time range options For each FiPPI decimation five sets of DSP parameters or PARSETs are stored in non volatile memory corresponding to the five available peaking times This allows for the procedural separation of parameter optimization and data acquisition During the setup process the parameters for each peaking time are optimized once and saved and are then automatically retrieved whenever the peaking time is selected for acquisition Parameter set storage and retrieval is described in further detail the Getting Started section below 1 1 2 5 Gain and Calibration Options Two gain configurations are available as hardware options With the fixed gain option a user selected analog gain is implemented in the on board circuitry The gain tolerance will typically be at the one percent level typically an energy calibration must be handled offline by the host software Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 The variable
61. e Range Current min Current max Description 3 3V 150mV 100mA 130mA Decent switching supply 5 0V 100mV 25mA 30mA Linear or high quality switching 5 0V 100mV 25mA 30mA Linear or high quality switching Unregulated Supply Option lt 100mV pk pk noise Voltage Range Current min Current max Description 3 3V 150mV 100mA 130mA Decent switching supply 5 5V to 6 0V 25mA 35mA Decent switching supply 5 5V to 6 0V 25mA 35mA Decent switching supply Table D 3 Power supply specifications for the microDXP Clock Speed Voltage Current Power Comment MHz Supply mA mW 8 VCC 89 7 296 0 3 3V digital includes ADC 8 V 20 3 101 5 5V analog includes VGA 8 V 23 3 116 5 5V analog includes VGA 514mW Total power consumption at 8MHz 16 VCC 103 0 339 9 3 3V digital includes ADC 16 V 20 3 101 5 5V analog includes VGA 16 V 23 3 116 5 5V analog includes VGA 557 9mW Total power consumption at 16MHz Table D 4 Power consumption by pipeline clock speed The optional variable gain stage draws approximated 12 5mA 8 6 2009 85 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 Appendix E RS 232 Communications This appendix describes the basic microDXP RS 232 command and response protocol Please refer to the RS 232 Com
62. e idle phase Event interrupts are enabled when the FiPPI detects an event it interrupts the DSP which quickly responds and reads the energy value from the FiPPI into an internal buffer in data memory The events in the buffer are then used to build the x ray spectrum or fill regions of interest In a special run the action is determined by the value of the parameter WHICHTEST The special runs include calibration tasks such as collecting an ADC trace as well as ways of putting the DSP code into a special state such as putting it into a dormant state to allow reprogramming the FiPPI on the fly Special runs normally end automatically and the DSP returns to the idle state After the initialization phase the Timer interrupt is enabled This interrupt is used to handle the housekeeping type chores such as updating the statistics during a run controlling the rate LED and handling fixed length runs The Timer interrupt occurs with a period of 500 usec 8 6 2009 61 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 If the DSP encounters an error condition the DSP turns on the red status LED and waits for the host to set the parameter RUNERROR to 0 after finding and fixing the problem that resulted in the error condition Each phase of the DSP program is discussed in more detail below 5 3 Initialization The DSP code starts running immediately after the power is turned on During the initializat
63. e period defined by RESETINT has expired see also 2 2 1 3 3 2 1 2 RC Feedback Preamplifiers RC feedback preamplifiers inherently produce a smaller dynamic range At low rates the preamplifier output decays to baseline after each event producing a voltage range on the order of a single event at higher rates successive events add up however the larger the sum the steeper the decay slope back to baseline The result as of course intended is to yield a full scale signal that increases only logarithmically with count rate Another consideration with RC feedback preamplifiers is the DC offset Although many such preamplifiers produce a ground referenced output many do not Both problems are solved in the microDXP by adding a digitally controlled DC offset voltage to the input signal The offset DAC is used both to 32 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 subtract the DC shift that results when running at high rates and to account for any DC offset voltage in the preamplifier output signal 3 2 2 Nyquist Criterion The Nyquist criterion states that there should be no frequency component in the signal that exceeds half of the sampling frequency Frequencies above this value are aliased into the digitized signal at where they are indistinguishable from original components at those frequencies In particular high frequency noise would appear as excess low frequency noise spoiling the spectr
64. e running baseline average Note that all captured baseline values are included in the Baseline Histogram however so that it is always a valid representation of the system s behavior 4 4 3 Baseline Averaging in the DXP A running average of baseline measurements is computed which is then subtracted from sampled peak values to compute the energy of corresponding incident x rays The number of baseline samples averaged is set in microManager as Number of Baselines to Average In the DSP this is converted into the parameter BLFILTER according to the equation baseline samples averaged 32768 BLFILTER Decimation Baseline Samples to BLFILTER Average DSP Parameter 0 64 512 2 128 256 4 256 128 Table 4 1 Typical values used for baseline averaging The best value for each decimation should be determined empirically though the general trend illustrated in the table i e larger number to average for higher decimations should be followed Physically the baseline is a measure of the instantaneous slope volts sec for a pulsed reset detector and a measure of the DC offset for an RC feedback preamplifier For a perfect detector and preamplifier the baseline value is independent of time In fact the variation in leakage current of the 47 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 detector and offset drift and 1 f noise of the preamplifier contribute to
65. eeeeeeeeeeeeeeeeeeeeeeeeseeeeeeeseeeeeeeseeeaeens 80 Preamplifier Type Selector Switch ccceceececeeeeeeeeeeeeeeseeeeeseaeeeseaeeeeeeeees 81 Connector Locations and PiNOUtS ccceeeceeeeeeeeeeeeeaeeeeeeeseeeeeseaeeeeaaeeeeeees 81 Power Supplies enes hee As deed tages letra ied Aaa anaa iaeoe ga aa eee 84 Appendix E RS 232 Communications ccccecceeeeeeeceeeeeeeeeeeeeseeeeseaeeeeneeee 86 mdo microDXP MAN 1 1 2 iii Micro Digital X ray Processor Technical ReferenceManual mdo microDXP MAN 1 1 2 Safety Please take a moment to review these safety precautions They are provided both for your protection and to prevent damage to the Micro Digital X ray Processor uDXP and connected equipment This safety information applies to all operators and service personnel Power Source The microDXP requires several DC voltage supplies to operate In such cases where the user will provide their own power supplies they must conform to the specifications contained in section Appendix D of this manual to avoid damaging the microDXP and connected equipment and nullifying the product warranty We recommend that new users purchase either the microDXP RS232 Rapid Development Kit or the microDXP USB Rapid Development Kit The RS232 kit includes a wall mount power supply intended to operate from a mains supply voltage of 120VAC at 60Hz The included microCOM interface circuit board provides linear regulation of the DC v
66. eeesseaeeseneeeeaes 40 4 2 X ray Energy Measurement amp Noise Filtering ec eeeeeeeeeeeneeeeeeeneeeeeenaes 41 4 3 Trapezoidal Filtering in the DXP cccccceeeesecceceeeeeeeeeeaeeeeeeeeeseeseneeeeeeeees 44 4 4 Baseline ISSUGS 2 3 cecscce2ecssecue consebedsevpce a CEAR PCAN NEKANE An AN EEANN EEOAE KATES ENGS 45 4 4 1 The Need for Baseline Averaging sssesrssssrrsseerrssrerrssrrrrssrrrns 45 4 4 2 Raw Baseline Measurement sssissssreseerrsssrrrssrirrssrirnssrnnnsrnnn 47 4 4 3 Baseline Averaging in the DXP eeccceeeeseeeeeenneeeeeeeaeeeeeenaeeeeeenaes 47 4 5 X ray Detection amp Threshold Setting eeeeeeeeeeeeeeeeeeresresrssrrssrrssressn 48 8 6 2009 ii Micro Digital X ray Processor Technical ReferenceManual 8 6 2009 4 6 Peak Capture Methods ccceccceceeeceeseeeeeeeeseeeeecaeeesaaeeeeeeeseaeeeseaeeeeaeeeneees 49 4 6 1 The Slow Filter Gap Length eecceeeeeeeeeeeeeeeeeeeeeeseeeeeseaeeseeeeeaes 49 4 6 2 Peak Sampling vs Peak Finding cc cccccecesseeeeeeeeeeeeeeesaeeeeeeteaes 50 4 7 Energy Measurement with Resistive Feedback Preamplifiers 0 52 48 Pile up INSpeCUON 400 ti a A ei ain te eines 54 4 9 Input Count Rate ICR and Output Count Rate OCR 0 0 0 ecsseeeeenees 56 AI Throughput cn tidal ate ie eA ain te 56 4 11 Dead Time Corrections 0 ccccccccceeseeeeeeeeeceeeeeeeaeeeeaeeseeeeeseaeeeeaaesseneeenaes 58 microDXP DSP Code Descript
67. elected in microManager and should normally not be adjusted by the user PEAKINT is also a pileup inspection parameter as will be discussed in further detail in 4 8 Peak finding method used in Decimation 2 4 amp 6 FiPPls Peak value within this i Ready for next interval is sampled x ray pulse Preamp Output Signal lt lt PEAKINT Slow Filter Output KH SLOWLEN gt SLOWGAP Figure 4 7 For decimations 2 and 4 the slow filter output is monitored and the peak value is selected For decimation 0 the slow filter output is instead sampled a fixed time after the x ray is detected This method is referred to as peak sampling An 8 6 2009 50 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 additional Peak Sampling timer is started when an x ray step is detected which expires after PEAKSAM decimated clock cycles PEAKSAM must be less than PEAKINT and should typically be set such that the sample point lies in the flat top region of the slow filter output SLOWLEN lt PEAKSAM lt SLOWLEN SLOWGAP Equation 4 7 The precise setting has a strong effect on energy resolution and should be determined empirically for each new detector More on this below Peak sampling method used in the Decimation 0 FiPPI Preamp Output Signal Slow Filter Output K PEAKSAM KH PEAKINT kK SLOWLEN Slow Filter Ready for next Sampled Here x ray pul
68. er For the complete command set please refer to the RS 232 Command Specification available at http www xia com microDXP html XIA offers the Accelerated DevelOPmenT ADOPT support option at an additional fee to advanced users and OEM customers ADOPT is described in 1 4 5 1 3 4 Firmware Firmware refers to the PIC DSP and FiPPI FPGA configuration code that is stored in non volatile memory on the microDXP One PIC file one DSP file and up to three FiPPI files can be stored For simplicity XIA provides complete firmware updates in files of the form update_name xup The XUP utility in microManager supports firmware backup and update functions The XUP utility also supports parameters settings import and export to aid in the production of multiple identical systems The FiPPI and DSP are discussed in chapter 3 and chapter 5 The XUP utility is described in 1 4 1 1 and in the Rapid Development Kit Manual 8 6 2009 13 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 1 4 Support Check for firmware and software updates at http www xia com micro DXP html 8 6 2009 A unique benefit of dealing with a small company like XIA is that the same people who designed them often provide the technical support for our sophisticated instruments Our customers are thus able to get an in depth technical advice on how to fully utilize our products within the context of their particular ap
69. erties is thus 2L G This raises several important points in comparing the noise performance of the DXP to analog filtering amplifiers First semi Gaussian filters are usually specified by a shaping time Their peaking time is typically twice this and their pulses are not symmetric so that the basewidth is about 5 6 times the shaping time or 2 8 times their peaking time Thus a semi Gaussian filter typically has a slightly better energy resolution than a triangular filter of the same peaking time because it has a longer filtering time This is typically accommodated in amplifiers offering both triangular and semi Gaussian filtering by stretching the triangular peaking time a bit so that the true triangular peaking time is typically 1 2 times the selected semi Gaussian peaking time This also leads to an apparent advantage for the analog system when its energy resolution is compared to a digital system with the same nominal peaking time One extremely important characteristic of a digitally shaped trapezoidal pulse is its extremely sharp termination on completion of the basewidth 2L G This may be compared to analog filtered pulses which have tails which may persist up to 40 of the peaking time a phenomenon due to the finite bandwidth of the analog filter As we shall see below this sharp termination gives the digital filter a definite rate advantage in pileup free throughput In practice it is also important to realize that implementing an energy f
70. es with all DXP instruments Handel provides an interface that is versed in lay spectroscopic units eV microseconds etc while still allowing for safe direct access to the DSP The trade off for this ease of use is size The Handel library is on the order of 2 Mbytes Though microManager does currently use the Handel driver we are in the process of refining Handel to work more efficiently with the microDXP and thus are not yet offering Handel to microDXP users In fact the feature omissions in this release are due primarily to Handel and not to the microDXP hardware or firmware Please contact XIA for further information 1 3 3 Physical Interface The physical interface to the microDXP may be either an RS232 COM port or a USB 2 0 port The MicroComU companion board is required in order to use USB communications Regardless of physical interface the microDXP is controlled directly via the RS 232 command set This is the lowest level of access currently supported and is appropriate for OEM customers who wish to design embedded systems incorporating the microDXP Such users are encouraged to at first get up and running with microManager and may in fact find it useful in the long run to use microManager for board configuration and their own software simply for data acquisition in the field Keep in mind that certain configuration procedures namely firmware updates via the XUP specification can only be executed using microManag
71. eshold settings Settings for the current PARSET can be tested by pressing the Apply button and saved to nonvolatile memory via the Save button The RS 232 command to modify thresholds is 0x86 Note that this command does not save the change to nonvolatile memory To do so it is necessary to subsequently save the current PARSET as described below Please refer to the RS 232 Command Specification for details 2 4 7 Reading the Current PARSET The RS 232 command to read the current PARSET table is 0x8C Note that this command does not save the setting to nonvolatile memory Please refer to the RS 232 Command Specification for details 2 4 8 Saving the Current PARSET to Non Volatile Memory In microManager all changes to the current PARSET can be saved to nonvolatile memory via the Save button The RS 232 command to save the current PARSET table is 0x8D Please refer to the RS 232 Command Specification for details 2 5 Repetitive Configuration of Identical Systems 8 6 2009 In cases where many microDXPs are to be configured identically or nearly identical it is very desirable to carbon copy user settings that have been optimized This procedure is supported in microManager Note that gain variations between modules make fine gain tuning necessary for each microDXP 2 5 1 Create Master Parameter Set In microManager select Firmware gt Create Master Parameter Set to save all parameters to XUP file format Select
72. etime In particular as described in 3 the DSP is not live while an x ray pulse is being processed during preamplifier resets or during ASC out of ranges in the latter case both because it is adjusting the ASC and because the ADC inputs to the FiPPI are invalid Thus the DXP measures livetime more accurately than an external clock which is insensitive to resets and includes them as part of the total livetime While the average number of resets sec scales linearly with the count rate in any given measurement period there will be fluctuations in the number of resets which may affect counting statistics in the most precise measurements 8 6 2009 33 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 3 4 1 FiPPl Decimation FiPPI s are distinguished also by decimation Decimation refers to pre averaging of the ADC signal prior to the FPGA processing pipeline Each decimation accommodates a specific range of peaking times i e shaping or integration times Up to three 3 FiPPI configuration files can be stored in the microDXP s nonvolatile memory When the peaking time is changed such that a range boundary is crossed the host software downloads the appropriate FiPPI configuration to the MicroDXP FiPPI ADC Samples Peaking Time Peaking Time Decimation in Average Range 16MHz Range 8MHz Pipeline Clock Pipeline Clock 0 1 125 ns 750 ns 250 ns 1
73. fer to this filtering procedure as Decimating by N By feeding the decimated data in an Equation 4 4 filter we now obtain peaking times that are extended to L D It is important 43 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 to understand that no data are lost in this procedure we have merely rearranged the order of the summations represented in Equation 4 3 By extension a Decimation N FiPPI is one that decimates the data by N before applying the energy filter The common decimation values in the microDXP are 0 2 and 4 corresponding to averaging times of 125 ns 500 ns and 2 0 us The associated peaking time ranges are 0 75 3 0 us 3 0 12 0 us and 12 0 48 0 us Note This assumes the standard 8MHz pipeline clock For a 16MHz pipeline clock optional the averaging times and peaking time ranges are exactly one half of above values 4 3 Trapezoidal Filtering in the DXP 8 6 2009 From this point onward we will only consider trapezoidal filtering as it is implemented in the DXP according to Equation 4 3 and Equation 4 4 The result of applying such a filter with Length L 20 and Gap G 4 to the same data set of Figure 4 4 is shown in Figure 4 5 The filter output Vx is clearly trapezoidal in shape and has a risetime equal to L a flattop equal to G and a symmetrical falltime equal to L The basewidth which is a first order measure of the filter s noise reduction prop
74. fying option M Transferring data to from these memory spaces is done through the DSP s built in DMA port which does not interfere with the DSP program operation 3 5 1 FLASH Memory A new feature implemented on the microDXP is the inclusion of on board non volatile memory which allows for firmware storage and retrieval 34 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 The flash memory accessed by the DSP used to store FiPPI configuration codes and parameter sets called GENSETS and PARSETS The FiPPI is thus configured and optimized independently with only a short command issued from the host Parameter sets simplify data acquisition procedures The DXP works well only if the internal parameters that govern digital filtering peak detection and pileup inspection are properly set For the lay user the optimization process can become overwhelming The new approach is to optimize the relevant parameters for each peaking time only one time and store the entire parameter in a unique location in the flash memory The exact state can be subsequently reproduced simply by selecting the saved parameter set The flash memory can be updated with new FiPPI code via the RS 232 SPORT or IDMA ports 3 5 2 Serial Port SPORT The Analog Devices DSP synchronous serial port or SPORT supports a variety of serial data communications protocols and offers a maximum transfer rate of approximately 1Mbyte sec The
75. g depends on SLOWLEN 5 BLFILTER Baseline filter average length 32768 BLFILTER 6 SLOWLEN Slow Filter Ramp length 7 SLOWGAP Slow Filter gap 8 PEAKINT Minimum spacing between pulses 9 FASTLEN Fast filter ramp length 10 FASTGAP Fast filter gap 11 THRESHOLD Fast filter threshold corresponding to the current GENSET 12 MINWIDTH Minimum time above threshold for fast filter 13 MAXWIDTH Maximum time above threshold for fast filter detects fast filter pileup 14 SLOWTHRESH Energy filter threshold corresponding to the current GENSET only needed for light elements normally set to 0 to disable 15 BASETHRESH Intermediate filter threshold corresponding to the current GENSET Needs to be set properly to get good baselines 16 BASTHRADJ Parameter used for future auto adjustment of BASETHRESH 17 PEAKSAM Energy Sampling point 18 GAINTWEAKO If non zero this per GENSET 22 GAINTWEAK4 parameter modifies the GAINBASE setting in the GENSET to arrive at 79 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 the GAINDAC setting E g If GENSET 3 is in use GAINDAC GAINBASE GAINTWEAK 3 23 THRESHOLDO Per GENSET fast filter threshold 27 THRESHOLD4 values 23 BASETHRESHO Per GENSET baseline filter 27 BASETHRESH4 threshold values 23 SLOWTHRESHO Per GENSET slow filter threshold 27 SLOWTHRESH4 values Appendix D MicroDXP Hardware Spe
76. g time range five 5 tables of parameters are stored in nonvolatile memory Each PARSET corresponds to a peaking time In microManager PARSET settings are accessed via the Acquisition tab of the Settings panel PARSETs 0 4 can be selected via the Peaking Time drop down list Modifications to spectrometer settings for the selected PARSET can be tested by pressing the Apply button and saved to nonvolatile memory via the Save button The RS 232 command to select a PARSET is 0x82 Note that this command simply retrieves one of five tables of spectrometer settings from nonvolatile memory Please refer to the RS 232 Command Specification for details 2 4 3 Filter Parameters Although the peaking time itself cannot be edited several digital filter parameters are available for modification Please refer to Chapter 4 for a thorough discussion of digital filtering with the DXP In microManager the filter parameters are accessed via the Acquisition tab of the Settings panel Press the Edit Filter Parameters button and modify settings in the associated dialog Modifications for the selected PARSET can be 24 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 tested by pressing the OK button and saved to nonvolatile memory via the Save button The RS 232 command to modify filter parameters is 0x8B Note that this command does not save the change to nonvolatile memory To do so it is necessary
77. gh there may be excessive deadtime and attenuation of higher energy x rays The ADC range is one 1 Volt full scale Two guidelines are suggested for the internal gain setting 74 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 1 This is appropriate when there is a single peak of interest Set the gain such that the typical pulse height is between 2 and 10 of the ADC range 2 This is appropriate when looking at a fixed energy range with no particular peak of interest Set the gain such that the maximum energy pulses are around 200 displayed vertical units in the ADC Trace readout The parameter GAINDAC sets the internal amplifier gain The overall gain can be expressed as follows 9 Gtot Gin Gyar Gpase where Gin the nominal input stage gain Gin 1 is modified by the resistive divider created by the output impedance of the preamplifier and the input impedance of the microDXP to the value Gin Gyar variable gain setting 0 36 to 36 depending on GAINDAC setting Gbase reference gain 1 87 The total internal gain ranges from 0 67 Vapc Vinpur to 67 3 Vapc Vinput The digital gain control is a 16 bit DAC that sets the gain of a linear in dB variable gain amplifier The gain setting accuracy is approximately one bit or 0 00061 dB 0 007 The relationship between Gyar and GAINDAC is Gain in dB GAINDAC 65536 40 dB Gyar 10 Gain in dB 20 The output
78. hich refers to pileup in the slow channel This occurs when the rising or falling edge of one pulse lies under the peak specifically the sampling point of its neighbor Thus peaks 1 and 2 are sufficiently well separated so that the leading edge point 2a of peak 2 falls after the peak of pulse 1 Because the trapezoidal filter function is symmetrical this also means that pulse 1 s trailing edge point 1c also does not fall under the peak of pulse 2 For this to be true the two pulses must be separated by at least an interval of L G 2 Peaks 2 and 3 which are separated by only 1 8 us are thus seen to pileup in the present example with a 2 0 us peaking time This leads to an important first point whether pulses suffer slow pileup depends critically on the peaking time of the filter being used The amount of pileup which occurs at a given average signal rate will increase with longer peaking times We will quantify this in 4 10 where we discuss throughput Because the fast filter peaking time is only 0 4 us these x ray pulses do not pileup in the fast filter channel The DXP can therefore test for slow channel pileup by measuring for the interval PEAKINT after a pulse arrival time If no second pulse occurs in this interval then there is no trailing edge pileup PEAKINT is usually set to a value close to L G 2 1 Pulse 1 passes this test as shown in the figure Pulse 2 however fails the PEAKINT test because pulse 3 follows in 1 8
79. how the values of ICRm and OCR vary with true input count rate for the DXP and compare these results to those from a common analog shaping amplifier plus SCA system The data were taken at a synchrotron source using a detector looking at a CuO target illuminated by x rays slightly above the Cu K absorption edge Intensity was varied by adjusting two pairs of crossed slits in front of the input x ray beam so that the harmonic content of the x ray beam striking the detector remained constant with varying intensity 56 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 NOTE The DXP s peaking time is twice as long as the analog system peaking time in this comparison and yet the throughput is nearly the same Output Count Rate kcps 200 e DXP OCR DXPICR Analog OCR Analog ICR Zoe 150 True ICR oa a 100 a oO ICR OCR Plot kfig 960922 l l l f f f f 0 50 100 150 200 Input Count Rate kcps Figure 4 12 Curves of ICRm and OCR for the DXP using 2 us peaking time compared to a common analog SCA system using us peaking time Table 4 3 Comparing the deadtime per event for the DXP and an analog shaping amplifier Notice that that the DXP produces a comparable output count rate even though its peaking time is nearly twice as long 8 6 2009 Functionally the OCR in both cases is seen to initially rise with increasing ICR and then saturate at higher
80. ifier slope value at the start of data taking runs to assure optimum starting parameter values 4 Collect data a Read energy values Ex from the FiPPI under interrupt control and store them in DSP buffer memory in less than 0 25 us b Adjust the ASC control parameters under interrupt control to maintain its output within the ADC s input range c Process captured Ex values to build the x ray spectrum in DSP memory d Sample the FiPPI slow filter baseline and build a spectrum of its values in order to compute the baseline offset for Ex values Several DSP program variants are available to cover a range of applications The standard program provided with the microDXP is for typical x ray fluorescence spectroscopy using a reset type preamplifier Additional program variants are available for other applications including hardware diagnostics and other specialized measurements e g e X ray mapping e Quick XAFS scanning e Switching between multiple spectra synchronously with an experimentally derived signal e g Phased locked EXAFS e Time resolved spectroscopy e g multi channel scaling 8 6 2009 59 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 Standard variants available to all users via our website are described in 5 11 Several other variants have been developed for particular customers and may be made available upon request By convention the DSP programs are na
81. ilter in a Decimation N FiPPI sets certain limitations on the practical flat top lengths that can be obtained in trapezoidal filters Because the decimation process is uncorrelated with the arrival of x rays the gap G must be 3 or greater to assure that the filter s peak truly represents the x ray s energy Therefore the minimum Decimation N gap time is G 2N At where At is the ADC s sampling interval With the microDXP s At 125 ns sampling interval for instance the smallest useful flat top in Decimation 4 is 6 0 us Note Again this assumes the standard 8MHz pipeline clock For a 16MHz pipeline clock optional the sampling interval and gap time would be exactly one half of above values Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 6 Filtered Step S kfig 960920 4 os ontee ve eo gepe o eo on e e ee o pi of ao eee oo S 2 a o 0 hoonononoonpon000 PY q noonoo lt j L gt Hoooopoonon2000 O L G 2 lt 2 Lee ee S lt 2L4 G gt Preamp Output mV Filter Output mV 24 26 28 30 32 Time us Figure 4 5 Trapezoidal filtering the Preamp Output data of Figure 4 4 with L 20 and G 4 4 4 Baseline Issues 8 6 2009 4 4 1 The Need for Baseline Averaging Figure 4 6 shows the same event as is Figure 4 5 but over a longer time interval to show how the filter treats the preamplifier noise in regions when no x ray pul
82. impedance Rour of the preamplifier creates a resistive divider with the microDXP input impedance R 1 0kQ and thus affects the input gain term Gjin Gin Rour 1 0kQ 1 0kQ Rour 5 11 Standard Program Variants 8 6 2009 5 11 1 MCA acquisition with reset type preamplifiers Variant 0 is the standard firmware variant supplied with the microDXP as described in this manual It is intended for use with reset type preamplifiers described in 4 1 1 Note To use this variant the Ramp Offset switch S1 see Appendix D should be in the Ramp position 5 11 2 MCA acquisition with RC type preamplifiers This firmware variant is intended for use with resistive feedback preamplifiers described in 4 1 2 Additional parameters described in 4 7 75 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 TAURC Exponential decay time in 50 ns units RCFCOR Correction factor calculated automatically at start of run if TAURC not 0 Note To use this variant the Ramp Offset switch S1 see Appendix D should be in the Offset position 8 6 2009 76 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 Appendices Appendix A GLOBSET Specification ID Parameter Format Description 0 NUMGLOBSET 16 0 Number of GLOBSET parameters NOT including NUMGLOBSET and GLOBVERSION used internally 1 GLOBVERSION 16 0
83. in the decimation 0 firmware The resolution can nonetheless be improved in most cases by reducing the number of baseline samples in the average 4 5 X ray Detection amp Threshold Setting 8 6 2009 Before capturing a value of Vx we must first detect the x ray X ray steps in the preamp output are detected by digitally comparing the output of a trapezoidal filter to a threshold In the DXP up to three trapezoidal filters are implemented fast intermediate and slow each with a threshold that can be individually enabled or disabled A fast filter very quickly detects larger x ray steps A slow energy filter averages out the most noise and can thus detect smaller x ray steps but has a response that is much slower An intermediate filter used in decimations 2 and 4 only is a derivative of the slow filter that provides a balance between the speed of the fast filter and the noise reduction of the slow filter The fast filter is used solely for x ray detection i e a threshold crossing initiates event processing Its short basewidth 2L G means that successive pulses that would pile up in slower filters can be resolved in the fast filter and rejected from the spectrum see Figure 4 11 below Conversely little noise reduction is achieved in the fast filter thus the fast threshold cannot be set to detect particularly low x ray energies The intermediate filter is used for all decimations other than 0 Its threshold is applied as pa
84. in units of 50 ns clock ticks At the start of an acquisition run the DSP calculates RCFCOR using the following approximate expression 53 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 RCFCOR 27 LEN GAP TAURC LEN GAP 2 3 2 F Equation 4 10 The above expression is valid for peaking times less than about TAURC 2 Alternatively RCFCOR can be determined empirically in a special test run from a linear fit of data as in Figure 4 10 4 8 Pile up Inspection 8 6 2009 The captured value Vx see Figure 4 6 will only be a valid measure of t its associated x ray s energy provided that its filtered pulse is sufficiently well separated in time from its preceding and succeeding neighbor pulses so that its peak amplitude is not distorted by the action of the trapezoidal filter on those neighbor pulses That is if the pulse is not piled up The relevant issues may be understood by reference to Figure 4 11 which shows 5 x rays arriving separated by various intervals Because the triangular filter is a linear filter its output for a series of pulses is the linear sum of its outputs for the individual members in the series In Figure 4 11 the pulses are separated by intervals of 3 2 1 8 5 7 and 0 7 us respectively The fast filter has a peaking time of 0 4 us with no gap The slow filter has a peaking time of 2 0 us with a gap of 0 4 us The first kind of pileup is slow pileup w
85. included in the histogram 8 6 2009 o sqrt of 141 128 o Equation 4 6 This results in less than 0 5 eV degradation in resolution even for very long peaking times when resolutions of order 130 eV are obtained 4 4 2 Raw Baseline Measurement The output of the baseline filter either the energy filter itself or a derivative of it is sampled periodically in the explicit absence of an x ray step defined by a baseline threshold In practice the DXP initially makes a series of Np baseline measurements to compute a starting baseline mean It then makes additional baseline measurements at quasi periodic intervals to keep the estimate up to date These values are stored internally and can be read out to construct a spectrum of baseline noise referred to as the Baseline Histogram This is recommended because of its excellent diagnostic properties When all components in the spectrometer system are working properly the baseline spectrum should be Gaussian in shape with a standard deviation reflecting op Deviations from this shape indicate various pathological conditions which may also cause the x ray spectrum to be distorted and therefore have to be fixed The situation is remedied by removing cutting outlying samples from the baseline average described below If the maximum in the baseline distribution lies at Ep then captured baseline values that deviate from Ep by more than AEt and AE respectively are not included in th
86. ines that the slope must be changed to match the rate the SlopeDAC value is modified by a constant fraction of the parameter SLOPEVAL determined by the value of the parameter SGRANULAR By default the slope adjustment granularity is 5 which is a good compromise between adjusting the slope quickly to match quickly changing input rates and being able to set the SlopeDAC just right For an RC feedback detector the offset added to the input signal is adjusted such that the signal stays in range as much as possible 5 6 2 Timer Interrupt Every 500 usec the DSP is interrupted to take care of the regular maintenance type tasks These tasks include 1 Update the run statistics EVTSINRUN LIVETIME REALTIME and FASTPEAKS only during a run 2 Control the Rate LED This LED flashes whenever a reset is detected reset detector only and during a run the color indicates the current output input ratio By default the LED flashes green for OCR ICR gt 0 5 flashes yellow green plus red for 0 5 gt OCR ICR gt I e and flashes red for OCR ICR lt 1 e The thresholds are determined by the parameters YELTHR and REDTHR 67 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 3 Handle fixed length runs During a fixed length run the current value of EVTSINRUN output events FASTPEAKS input events LIVETIME or REALTIME is compared to the desired run length Once the value exceeds the desired value the ru
87. ion sccsseccsseceeeeeeseeeseseeeenseeeseeeseseaesnseeeeeeneess 59 5 1 Introduction and Program OVErView ccceecceceeeeeeeeeeeeeeeeeeeesaeeeeeaeeeeeeeee 59 52 Progrant FION segs eects duce asvcehs seaaues Saal cate ted Due based Meme pt tanaihs ceded tassel fied 60 By IMMA ZATION ss os eed oc sch Fa sess ha anc A aA AEEA OA 62 5 4 Event Processing e A aiani nedcuneg ot camcnete adi ES MOFARE RAEE PEART TIRE RREA 62 SA RU Oa a a a a a E eer 62 Da2 Event INOU rre a ani a ASAR 63 DAS Event Ooms nuen E E A TARSA 63 5 4 4 Spectrum Binning cceccccecceceeeceeeeeeeeeeeceeeeeeaeeseneeceeeeeseaeeeeaeesenees 63 S45 SCAIMADDING a a cbs huts ee ea a a ue slate eta erik cates 63 5 5 Baseline Measurement ccceeeeececeeeeeeeeeeeeneeeeeeeeeeeeeaeeeeseeaeeeeeeseeeeeeenenaeees 64 5 5 1 IIR Infinite Impulse Response Filter eee ceeeeeeeeeeeeeeeneeeeeeeaes 64 5 5 2 FIR Finite Impulse Response Filter ee eeeeeeeeneeeeeeeneeeeeeaaes 65 5 5 3 Baseline Histogram siooni a E O SS 65 5 5 4 Residual Baseline ec nirin nnana aiK EEA EARE S EE ERR 66 5 55 Baseline GUte aea aa aa ae ie aaea aa ES RESE 66 5 6 Interrupt ROUES Ar rE A A TRAA 66 56 ASCMOnNtnNg siaaa r a A E taateeea ee 67 562 Tiner Interrupt asysek eects sees yeaa che Abaca TAO 67 57 Error Handing ras n EEA ONNA 68 5 8 Specifying Data Acquisition Tasks RUNTASKS c cccesseeessesteeeeeeteeees 68 5 9 Special Tasks WHICHTEST
88. ion of the baseline processing Once the run is over the statistics are finalized and the DSP returns to the idle state where it continuously samples baseline and waits for a command to start a new run 5 4 4 Spectrum Binning The primary event processing task is to use the energies measured in the FiPPI to build up a full energy spectrum MCA The MCA bin width is determined by the analog gain the FiPPI filter length and the binning parameter BINFACT1 The DSP determines the spectrum bin by multiplying the FiPPI energy output by 1 BINFACT1 If the bin is outside the range determined by the parameters MCALIMLO and MCALIMHI the event is classified as an underflow or overflow Otherwise the appropriate bin is incremented A 24 bit word is used to store the contents of each bin allowing nearly 16 8 million events per MCA channel 5 4 5 SCA Mapping An alternate variant of the DSP code allows the user to define up to 24 SCA regions and count the number of events that fall into each region The regions are defined in terms of MCA bin number and can overlap A useful method for defining the SCA windows is to take a run with the full MCA 63 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 spectrum and use the spectrum as an aid in choosing the limits for each SCA The reduced amount of data storage in SCA mapping mode is very useful in time resolved spectroscopy or scanning applications where separate spe
89. ion of x ray rays Note that the steps have a rising edge so that the signal polarity is positive Figure 4 2 depicts the large signal saw tooth waveform that results from successive x ray steps followed by the reset Note that the units here are Volts and milliseconds vs millivolts and microseconds in the previous figure Preamp Output V H enlarged view 0 50 100 150 Time ms Figure 4 2 The large signal reset waveform for a reset type preamplifier with positive signal polarity as displayed on a real oscilloscope Note that the large signal character is not displayed in the microDXP diagnostic ADC readout e g used in microManager s ADC Trace diagnostic tool looks quite different because of the dynamic range reduction carried out in the ASC as described in 3 2 1 4 1 2 RC Type Preamplifiers Figure 4 3a is a simplified schematic of an RC type preamplifier wherein Cr is discharged continuously through feedback resistor Rr The output of an RC type preamplifier following the absorption of an x ray of energy Ex in detector D is again a voltage step of amplitude Vx The continuous discharge of Cr through Re results in an exponential voltage decay after the x ray step with decay constant t where 8 6 2009 40 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 a t RfCf Equation 4 1 In practice the decay time may depend on subsequent circuitry i e if a pole zero ca
90. ion phase several tasks are performed 1 2 Setup internal DSP control registers Zero spectrum and data memory then initialize parameters to default values Set ASC DACs to initial default values Initialize FiPPI and download default filter parameters Perform initial calibrations for controlling the ASC a Find the SlopeDAC setting corresponding to zero slope b Measure conversion factor used to calculate the contribution of the slope generator to the FiPPI baseline Enable the ASC and timer interrupts After the interrupts are enabled the DSP is alive and ready to take data After completing the initialization phase the DSP enters the idle phase In the idle phase the DSP continuously samples the FiPPI baseline and updates the baseline subtraction register in the FiPPI so that the FiPPI is always ready to take data as soon as a run is started There are two primary tasks performed during a normal data acquisition run event processing and baseline measurement These tasks are described in detail below 5 4 Event Processing 8 6 2009 5 4 1 Run Start Prior to the start of a normal the run the DSP performs several tasks Sets the stored gain by setting the GAINDAC Sets the stored polarity Downloads FiPPI parameters SLOWLEN SLOWGAP etc stored in the current PARSET to obtain the desired peaking time Updates the internal calibrations with the new gain and FiPPI values If desired the run statistics an
91. ithin the ASC input range In practice the large signal dynamic range can be reduced by a factor of 8 to 16 thus reducing the required number of bits necessary to achieve the same resolution from 14 to 10 31 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 Preamp Output V 1 0 T ADC Min naput SOsC CS S lt C lt C lt CStSt F 0 0 7 Preamp i ADC Max Input Amplified Sawtooth Subtracted Data Output 1 0 7 2 2 0 7 A p Sawtooth Function 3 0 7 Resets 2295 es SSeS ee E i Level Preamp Sawtooth kfig 960923 I T I I 0 1 2 3 4 5 Time ms Figure 3 2 A saw tooth function having the same average slope as the preamp output is subtracted from it and the difference amplified and offset to match the input range of the ADC Occasionally as also shown in Figure 3 2 fluctuations in data arrival rate will cause the conditioned signal to pass outside the ADC input range This condition is detected by the FiPPI which has digital discrimination levels set to ADC zero and full scale which then interrupts the DSP demanding ASC attention The DSP remedies the situation by quickly closing the reset switch During this time data passed to the FiPPI are invalid Preamplifier resets are detected similarly When detected the DSP responded by resetting the current integrator until the signal comes back into range Note Data acquisition is halted until the tim
92. l a e aa a a aee aai pEr Eaa Aa dae vi T UNO GU CON srs naa a aa A a cocesacucccesnecudensee 1 1 1 MicroDXP OVEWVIEW diriche dinari aniidae neieiet 1 LET Features ieur i tii EAE A 1 1 1 2 Options and Specifications eee cecececeeeeeeee sees ceeeeeseeeeseaeeseneeeeaes 3 1 1 3 Application Examples serani 6 1 2 Hardware Requirements ccccceeeeceeeceenneeeeeenaeeeeeeaeeeeeeaaeeeeeeaeeeeeeaeeeeneaaes 10 1 2 1 Host Computer or PDA 0 cccccceceeeeeeeeeeeneeeeaeeeeeeeseeeeeseaeeesaeeeeeeeees 10 1 2 2 Detector Preamplifier eee cceeeeneeeeeeeneeeeeeeeeeeeeeaeeeeetaeeeeeenaeeeeneaa 10 1 2 3 Power Requirement ccccceceeeeeeeeeeeneeeeeeeaeeeeeeaeeeeesaeeeeeeaeeeeneaa 11 1 2 4 Operating ENVirOnMent 0 cccccceeceeceeeeneeeeeeeeeeeeeseeeeeseaeeeseaeeeeeeeees 12 1 2 5 Regulatory Compliance 0 ccccceceeeeeceee cess eeeeeseeeeeseaeeesaeeeeeeeeed 12 1 3 Software OVerViOW ceccececesseeeeceeceeeeeaaeceeaeeceeeeecaaeeeeaaesseneesnaeeesaeseeaaeesnees 12 1 3 1 User Interface e g microManager eee eeeeeeeeeeteeeeeenteeeeeenaeeeeeene 12 1 3 2 Device Drivers e g Handel ecececcecceeeeeeeeeceeeeeeeeeeeseseeneeeeeeees 13 1 3 3 Physical Merate neacsas i ie e E a i a 13 V 3 4 JFINMNWANG arrire iii a E AE ia Ei A 13 VA SUP POM a r E O ER a ET Weveg dinetceduades 14 1 4 1 Software and Firmware Updates ccccccccssccecesseeeeessteeeesesteeeeeees 14 1 4 2 Related Documentation
93. l mdo microDXP MAN 1 1 2 End Users Agreement 8 6 2009 XIA LLC warrants that this product will be free from defects in materials and workmanship for a period of one 1 year from the date of shipment If any such product proves defective during this warranty period XIA LLC at its option will either repair the defective products without charge for parts and labor or will provide a replacement in exchange for the defective product In order to obtain service under this warranty Customer must notify XIA LLC of the defect before the expiration of the warranty period and make suitable arrangements for the performance of the service This warranty shall not apply to any defect failure or damage caused by improper uses or inadequate care XIA LLC shall not be obligated to furnish service under this warranty a to repair damage resulting from attempts by personnel other than XIA LLC representatives to repair or service the product or b to repair damage resulting from improper use or connection to incompatible equipment THIS WARRANTY IS GIVEN BY XIA LLC WITH RESPECT TO THIS PRODUCT IN LIEU OF ANY OTHER WARRANTIES EXPRESSED OR IMPLIED XIA LLC AND ITS VENDORS DISCLAIM ANY IMPLIED WARRANTIES OF MERCHANTABILITYOR FITNESS FOR A PARTICULAR PURPOSE XIA LLC S RESPONSIBILITY TO REPAIR OR REPLACE DEFECTIVE PRODUCTS IS THE SOLE AND EXCLUSIVE REMEDY PROVIDED TO THE CUSTOMER FOR BREACH OF THIS WARRANTY XIA LLC AND ITS VENDORS WILL NOT BE LIABLE FOR
94. le command Five 5 sets of MCA parameters or spectrum formats can be stored and later retrieved with a single command Note The microManager software currently supports only one MCA set XIA provides the microManager software application for microDXP parameter set configuration intended for use both in evaluation and production phases A small and powerful RS 232 data acquisition command set Custom OEM Features Customized firmware development for special applications such as time resolved spectroscopy multiple SCA s and pulse shape analysis Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 Note The hardware options included with your microDXP are specified on the information sheet included with the shipment 8 6 2009 e Flexible auxiliary digital I O 4 general purpose lines a Gate signal to externally control data acquisition the emerging industry standard VC bus interface and an external interrupt line e Several assembly options are offered that exclude various hardware and software features in order to reduce the cost for dedicated applications further details in the following section 1 1 2 Options and Specifications The microDXP hardware is both powerful and flexible In many cases particularly for dedicated embedded systems much of the microDXP s resources will not be used XIA is pleased to offer a number of assembly options that will produce the best value for a
95. ltage Range Current min Current max Description 3 3V 150mV 100mA 130mA Decent switching supply 5 5V to 6 0V 25mA 35mA Decent switching supply 5 5V to 6 0V 25mA 35mA Decent switching supply Table 1 1 Power supply options and specifications for the microDXP For both variants the onboard digital circuitry draws from a 3 3V supply input with on board regulators employed to produce 2 5V for the DSP and 3 0V for the ADC The ripple requirements for this supply are not particularly stringent though excessive radiated noise is to be avoided Ifa switching supply is used it should be well shielded from and properly grounded with respect to the microDXP 1 1 2 3 Pipeline Clock Speed Choice The DSP operates with a 32MHz clock and a clock divider produces either 16MHz or 8MHz for the more power hungry ADC and the FiPPI Filter Pulse Pileup Inspector Simply put the clock speed determines the scale of available peaking times see Table 1 3 below with a faster clock producing shorter peaking times and thus a higher output count rate or OCR Note however that a higher clock speed will result in slightly increased power consumption The following table illustrates these points Clock Speed Sampling Period Maximum OCR Power Consumption 8 MHz 125 ns 164 000 cps 514 mW 16 MHz 62 5 ns 328 000 cps 558 mW Table 1 2 Data pipeline ADC and FiPPI clock speed options Micro Digital X ray Process
96. mand Specification a separate document for a detailed presentation of all RS 232 commands DXP related documents are available online at www xia com DXP_Resources html The general structure for commands and responses is as follows Esc Command Ndata 2 bytes datal dataN xor CS where Esc Escape ASCII 0x1B as a command start byte Command Single byte for command number allowing up to 255 commands See the tables below for command definitions Ndata Number of data bytes to follow Two bytes low byte first datal dataN The data bytes xor CS Exclusive or checksum bitwise xor of all bytes except for the initial Esc If the checksum is not correct an error response is returned The format of responses echo the format of commands that is they start with the 1 Esc character and pass back the command to which it is responding followed by appropriate data and checksum The first data byte of all responses is the return status which is zero for a successful command In case of an error only the error byte is returned no other data bytes are sent The command for starting a run is given below as an example Command Ox1B 0x00 0x01 0x00 0x01 0x00 the escape character the command the low byte that sets the number of data bytes the high byte that sets the number of data bytes the data byte new run clear the
97. med NAMEmmnn HEX where NAME is the variant name listed in the table mm and nn are major and minor version numbers respectively The hex file format is in ASCII with the parameter table at the top followed by the code generated by the Analog Devices 218x development system The internal data memory area is subdivided into three sections The first section starting at location 0x4000 contains DSP parameters and constants both those used for controlling the DSP s actions and those produced by the DSP during normal running These parameters and their addresses are listed and described in the following sections When these parameters are referred to they will be denoted by all capital letters e g RUNTASKS The locations of parameters can and for forward compatibility should be determined from the symbol table The second section of data memory contains acquired monitoring data such as the baseline event histogram The third section of internal data memory is used as a circular buffer for storing events from the FiPPI Note that future hardware revisions may eliminate the need for this buffer area in which case it could be switched to more histogramming area 5 2 Program Flow 8 6 2009 The flow of the DSP program is illustrated in Figure 5 1 It is essentially identical for all program variants The structure is very simple after initialization the DSP enters an idle phase waiting for a signal from the host to start a run Du
98. microDXP Digital X Ray Processor Technical Reference Manual Version 1 1 2 August 6 2009 MicroDXP Hardware Revision E Micromanager Software Revision 2 3 x XIA LLC 31057 Genstar Rd Hayward CA 94544 USA Tel 510 401 5760 Fax 510 401 5761 http www xia com Information furnished by XIA LLC XIA is believed to be accurate and reliable However no responsibility is assumed by XIA for its use nor for any infringements of patents or other rights of third parties which may result from its use No license is granted by implication or otherwise under any patent or patent rights of XIA XIA reserves the right to change specifications at any time without notice Patents have been applied for to cover various aspects of the design of the DXP Digital X ray Processor Micro Digital X ray Processor Technical ReferenceManual mdo microDXP MAN 1 1 2 SAL CLY AE EEA cane A cane denatanszace es seesecneahavetcusccesaaauhvacesn cuter sucthesehenetceasscuassizestascreuaseecns iv PowerSource sidni eai ia a aa a a aati Medel iv Detector and Preamplifier Damage eee ceeeeeeeeeeeneeeeeeaeeeeeeaaeeeeeeaaeeeeeeaaeeeeeeaas iv Servicing ANd Cleaning ccecececeececeeeeeeeeeeeeeeeceaeeeceaeseeaaeseeeeeseaeeesaeeseaeeseeneesaas iv End Users Agreement c ecccceseeeceeeseeeeeensceeeeenseeeeensneeeeenseeeeeensneeeeensneeeeenseeeeenseeeenenss v Contact Informations a a a a a ea aaa v Manual Conventions a rrr rE nde aaa e aae ne
99. n about the current state of the PIC DSP and data acquisition run 18 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 The RS 232 command to read board information is 0x4B Please refer to the RS 232 Command Specification for details 2 1 2 Serial Number In microManager the serial number is automatically read at startup It is displayed along the bottom of the window The RS 232 command to read the serial number is 0x48 Please refer to the RS 232 Command Specification for details 2 1 3 Firmware Version In microManager this command is omitted All the version information is embedded in the board information command described above The RS 232 command to read the firmware version information is 0x4D Please refer to the RS 232 Command Specification for details 2 1 4 Idle and Sleep Modes If the Idle Mode is enabled the microDXP will enter a low power state a specified time after the end of a run Several different subsystems can be manually powered down via the Sleep Mode command to conserve energy The sleep mode can not be changed in microManager The RS 232 command to change the Idle Mode is 0x46 The RS 232 command to change the Sleep Mode is 0x47 Please refer to the RS 232 Command Specification for details 2 1 5 On Board Temperature The microDXP hardware includes an I2C thermometer The temperature reading is not accessible in microManager The RS 232 command to read the on bo
100. n is ended 5 7 Error Handling When the DSP detects an error in the operation of the microDXP the red Status LED is turned on and the source of the error is stored in the parameter RUNERROR The possible values for RUNERROR are listed below RUNERROR Value Meaning 0 No Error 1 FiPPI communication error 2 ASC setup failure 3 5 Reserved 6 TrackDAC calibration error Table 5 1 Identification of DXP errors according to the DSP parameter RUNERROR A FiPPI communication error could mean that the FiPPI configuration was not successful An ASC calibration error can indicate a hardware problem or possibly that a jumper is not set properly for example the DSP code for reset preamplifiers will generate an error if the jumper is set to run in OFFSET mode Once the source of the error has been located and cleared the host can set RUNERROR to 0 to force the DSP to exit the error loop and reinitialize the system Note that all system settings are saved when initialization is performed coming out of the error loop Of course another valid method for clearing the error is to re download the DSP code after fixing the problem 5 8 Specifying Data Acquisition Tasks RUNTASKS Many aspects of the operation of the microDXP are controlled by individual flag bits of the parameter RUNTASKS The meaning of each RUNTASKS bit is described below Bit Meaning if set 1 Meaning if cleared 0 0 Reserved set to 0
101. n section 3 2 In microManager select the ADC tab in the Data Acquisition panel Enter the desired value in the Sampling Interval field The minimum value is 0 125 microseconds Press the Read ADC button to refresh the display Press the Save ADC to save the data to file in ASCII format The RS 232 command to read the ADC is 0x11 Please refer to the RS 232 Command Specification for details 2 7 2 Baseline Diagnostics An 8000 point digital trace of the running baseline average is available for readout as a diagnostic aid A histogram of instantaneous baseline samples is also available Refer to sections 4 4 and 5 5 for discussion of baseline acquisition and averaging In microManager select the Baseline tab in the Data Acquisition panel Press the Get Baseline button to display the baseline histogram Press the Get Baseline History button to display the baseline average vs time Press the Save Baseline to save the data to file in ASCII format The RS 232 command to read the baseline histogram is 0x10 The RS 232 command to read the baseline history is 0x12 Please refer to the RS 232 Command Specification for details 2 7 3 DSP Parameters Readout In microManager the spectrum and statistics can be updated automatically or manually Check the Continuous checkbox for automatic updates If the checkbox is unchecked press the Update button to manually update the spectrum and statistics The RS 232 command to read the run s
102. n this example the microDXP microComU board set acts as a general purpose spectrometer connected as a peripheral device under the control of a host computer No specialized data acquisition modes are required thus no firmware development is necessary No user hardware design is required All required power is drawn from the USB port XIA non recurring engineering NRE required NONE User development required ALMOST NONE 1 It may be necessary to design an enclosure x ray Detector Preamp w Wwr aa microDXP ah Host Computer Power Supply Legend customer designed hardware none xa and 3rd party hardware Figure 1 1 A general purpose spectrometer incorporating the microDXP and MicroComU companion board The board set communicates with a host PC using USB 2 0 The board set derives all necessary power supplies from the USB port In this example the MicroComU board acts as both a carrier and companion board for the microDXP Power for the MicroComU microDXP board set may be taken from the USB port as shown in the example above or may be provided externally as with the AC wall adapter provided with the USB Rapid Development Kit MicroComU board dimensions and mounting information the connector locations and specifications and the power supply specifications are all found in the separate MicroComU Technical Reference Manual available at http www xia com microDXP html 8 6 2009 7 Micro Digital X ray Pro
103. n to energy resolution Where analog shaping amplifiers typically have a pole zero adjustment to cancel out the exponential decay the DXP uses a patented exponential decay correction to achieve good energy resolution without a pole zero correction Figure 4 9 and Figure 4 10 illustrate the method used The first shows the output voltage of a RC feedback preamplifier with a x ray or y ray step of amplitude A appearing at t 0 V is the voltage just before the step pulse arrives and V is the asymptotic value that the signal would decay to in the absence of steps ty is the earliest time used in the slow filter L and G are the length and gap of the trapezoidal filter in clock units and At is the clock period In addition to the normal slow filter measurement of the step height the ADC amplitude Vp is made at time tp In the following discussion it is assumed that the signal rise time is negligible t t tp gt lt GAt t Figure 4 9 RC preamplifier output voltage An x ray step of amplitude A occurs at time t 0 52 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 10000 aka T TT l T ToT FOU V Faas ea Fae ear oe ICR 41 kcps 8000 ieee Zr K Sige a 6000 xK n 4000 2000 Ge escape 0 ee peaks ogo ete el Pe EN BP 0 4000 8000 12000 Amplitude Figure 4 10 Correlation between step size and amplitude for Zr K
104. ncellation circuit is used thus t may not be directly related to the feedback elements of the front end The point of this simplified model is that the resulting waveform is a single pole RC decay The discussion in 4 2 through 0 assumes a reset type preamplifier but is mostly applicable to RC type preamplifiers 4 7 describes the few key differences in the processing of RC type preamplifier signals b Preamp Output mV 60 0 30 100 150 200 250 Time ps Figure 4 3 a RC type charge sensitive preamplifier with a positively biased detector b Output on absorption of an x ray Note that the step has a falling edge thus the signal polarity is 4 2 X ray Energy Measurement amp Noise Filtering 8 6 2009 Reducing noise in an electrical measurement is accomplished by filtering Traditional analog filters use combinations of a differentiation stage and multiple integration stages to convert the preamp output steps such as shown in Figure 4 1b into either triangular or semi Gaussian pulses whose amplitudes with respect to their baselines are then proportional to Vx and thus to the x ray s energy Digital filtering proceeds from a slightly different perspective Here the signal has been digitized and is no longer continuous but is instead a string of discrete values such as shown in Figure 4 4 The data displayed are actually just a subset of Figure 4 3b which was digitized by a Tektronix 544 TDS digital oscillosc
105. nfigurable digital I O line connects to FiPPI 30 Aux Auxiliary configurable digital I O line connects to FiPPI 32 Aux0 Auxiliary configurable digital I O line connects to FiPPI 34 Gate Inhibits data acquisition active low 36 SCE IC clock 38 SDA TC data line 40 GND Internal ground connection 8 6 2009 83 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 42 RX B RS 232 microDXP receive host microDXP 44 TX B RS 232 microDXP transmit microDXP host 46 GND Internal ground connection 48 EA D IDMA address HI data LO selector INPUT 50 ExtInt External interrupt line active low Table D 2 Pin assignments for the 50 conductor board to board interconnect Note Excessive ripple on the analog supplies gt 20mVpp can seriously degrade system performance If 5 0V is supplied directly either linear regulated or high quality switching supplies should be used 8 6 2009 Power Supplies The microDXP requires three supply voltages to operate A supply voltage of 3 3V is used to directly power most on board digital circuitry with minimal LC filtering at the board entry point On board voltage regulators also generate from this supply 3 0V for the ADC and 2 5V for the DSP The total current requirement depends on the selected clock speed ranging from 80mA to 130mA The ripple requirements for this supply are not particularly stringent
106. nsed summary of the RS 232 command and response protocol Users who wish to develop the configuration routines into their software should refer to the RS 232 Command Specification a separate document for a detailed presentation of all RS 232 commands DXP related documents are available online at http www xia com microDXP html 2 1 Board State and Configuration 8 6 2009 The microDXP boots itself upon power up and is shortly thereafter ready to acquire data with the same set of operating parameters used in the previous run The first time the microDXP is powered on detector and preamplifier related parameters should be modified unless the default parameters have been factory set to match the detector and preamplifier Once these settings have been saved to non volatile on board memory they will automatically load during subsequent boot operations 2 1 1 Board Information and Status General information about the hardware and firmware and current board status can be retrieved In microManager select View gt Board Info to display the Board Information dialog 2 1 1 1 Board Information In microManager press Read Information to display information about the hardware and firmware configuration variants and versions The RS 232 command to read board information is 0x49 Please refer to the RS 232 Command Specification for details 2 1 1 2 Board Status In microManager press Read Status to display informatio
107. ntribution should be essentially negligible Achieving this in the mixed analog digital environment of a digital pulse processor is a non trivial task however In the general case the mean baseline value is not zero This situation arises whenever the slope of the preamplifier signal is not zero between x ray pulses This can be seen from Equation 4 3 When the slope is not zero the mean values of the two sums will differ because they are taken over regions separated in time by L G on average Such non zero slopes can arise from various causes of which the most common is detector leakage current When the mean baseline value is not zero it must be determined and subtracted from measured peak values in order to determine Vx values accurately If the error introduced by this subtraction is not to significantly increase ot then the error in the baseline estimate op must be small compared to Ge Because the error in a single baseline measurement is Ge by definition this means that multiple baseline measurements will have to be averaged This number Np is the Baseline Average For example if Ng 128 measurements are averagedthen the total noise will be as shown in Equation 4 6 46 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 Applying a Baseline Cut can improve performance when the Baseline Histogram is non Gaussian Outlying data points are cut from the running Baseline Average though still
108. nual mdo microDXP MAN 1 1 2 in practice the energy threshold is rarely used The user will typically only adjust the fast filter threshold THRESHOLD All thresholds are scaled by their respective filter lengths Further they cannot be expressed in energy units until the DXP conversion gain see 5 10 6 below Gpxp number of ADC counts per keV at the DXP input is known For an energy threshold E in keV THRESHOLD Gpxp E n FASTLEN BASETHRESH Gpxp Ein SLOWLEN SLOWTHRES Gpxp Et h SLOWLEN THRESHOLD is set by the user A good procedure is to initially set the value too high Once a spectrum is observed reduce THRESHOLD until the zero energy noise peak starts to become significant and then raise it again until only a trace of the noise peak remains The MINWIDTH parameter is used for noise rejection It is the minimum number of time bins the fast filter is above threshold A typical value that works with FASTLEN 4 is MINWIDTH 4 Currently BASETHRESH must also be set by the user BASETHRESH will be automatically set by the DSP in the next release and applied to the intermediate filter as part of the baseline acquisition circuitry i e baseline measurements are taken when the signal is below this threshold BASETHRESH threshold crossings by default also trigger event processing effectively extending the detectable energy range significantly below the fast filter THRESHOLD The parameter BASETHRADJ controls the algorithm that calculates
109. o setup procedures and to parameter settings XIA s DXP software includes several consistency checks to help select the best parameter values However due to large number of possible combinations the user may occasionally request parameter values which conflict among themselves This can cause the DXP unit to report data that apparently make no sense such as bad peak resolution or even empty spectra Each time a problem is reported to us we diagnose it and include necessary modifications in the new versions of our DXP control programs as well as add the problem description to the FAQ list Submitting a problem report XIA encourages customers to report any problems encountered using any of our software Unfortunately due to limited resources XIA is unable to handle bug reports over the phone In most cases the XIA engineering team will need to review the bug information and run tests on their hardware before being able to respond All software related bug reports should be emailed to software_support xia com and should contain the following information which will be used by our technical support personnel to diagnose and solve the problem v Your name and organization v Brief description of the application type of detector relevant experimental conditions etc XIA hardware name and serial number Version of the library if applicable OS Description of the problem steps taken to re create the bug SN NNN Supporting data
110. oltages required by the microDXP The USB kit introduced August 2009 includes a wall mount power supply that can accommodate 100VAC to 240VAC at 47Hz to 63Hz In addition it can adapt to plug styles for North America Japan Europe UK and Australia The included MicroComU board generates the various DC voltages required by the microDXP Use of either evaluation kit with any other mains voltage or power supply could damage the unit and nullify the product warranty Refer to the Rapid Development Kit Manual for instructions on installing the power supply Detector and Preamplifier Damage The microDXP input impedance is 1kQ and should be compatible with most preamplifiers Please consult the documentation provided by the preamplifier manufacturer to confirm that such a load is acceptable Because the microDXP does not provide power for the detector or preamplifier there is little risk of damage to either resulting from the microDXP itself Nonetheless please review all instructions and safety precautions provided with these components before powering a connected system Servicing and Cleaning 8 6 2009 To avoid personal injury and or damage to the microDXP or connected equipment do not attempt to repair or clean the unit The microDXP hardware is warranted against all defects for 1 year Please contact the factory or your distributor before returning items for service Micro Digital X ray Processor Technical ReferenceManua
111. ometer s energy resolution 3 3 The Analog to Digital Converter ADC Signal digitization occurs in the Analog to Digital converter ADC which lies between the ASC and the FiPPI The ADC is a 12 bit device which is currently run at either 8 or 16MHz Although the chosen ADC supports both sampling rates because the Nyquist criterion must be satisfied in both cases i e 4MHz at 8MSA and 8MHz at 16MSA the passive components are different in each case Changing the pipeline i e ADC and digital filtering clock speed thus requires modification to the microDXP hardware Pipeline Clock ADC Sampling Nyquist Sample Period Speed Rate Frequency 8 MHz 8 MSA 4 MHz 125 ns 16 MHz 16 MSA 8 MHz 62 5 ns Figure 3 3 Nyquist frequencies and sample periods for the two pipeline clock speed offerings 3 4 The Filter Pulse Detector amp Pile up Inspector FiPPI The FiPPI is implemented in a field programmable gate array FPGA to accomplish the various filtering pulse detection and pileup inspection tasks discussed in chapter 4 As described there it utilizes up to three digital filters running simultaneously for the purposes of pulse detection pileup inspection and rejection noise reduction and peak selection The FiPPI also includes a livetime counter that is activated any time the DSP is enabled to collect x ray pulse values from the FiPPI and therefore provides an extremely accurate measure of the system liv
112. ope at 10 MSA million samples per second Given this data set and some kind of arithmetic processor the obvious approach to determining Vx is to take some sort of average over the points before the step and subtract it from the value of the average over the points after the step That is as shown in Figure 4 4 averages are computed over the two regions marked Length the Gap region is omitted because the signal is changing rapidly here and their difference taken as a measure of Vx Thus the value Vx may be found from the equation 41 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 V 2 WM wV i before i after Equation 4 2 Where the values of the weighting constants w determine the type of average being computed The sums of the values of the two sets of weights must be individually normalized N Length lt Gap Preamp Output mV O Digitized Step 960919 20 22 24 26 28 30 Time us Figure 4 4 Digitized version of one of the x ray steps of Figure 4 3b The primary differences between different digital signal processors lie in two areas what set of weights w is used and how the regions are selected for the computation of Equation 4 2 Thus for example when the weighting values decrease with separation from the step then the equation produces cusp like filters When the weighting values are constant one obtains triangula
113. opriate mechanical operation e g put the recognized object in the desired bin User controls are limited to starting and stopping the system and selecting one out of a small number of operating modes Power supplies for the microDXP are also included Finally an external data port e g RS 232 is also included so that ratios corresponding to new alloys can be defined and new firmware uploaded without dismantling the hardware or alternatively the microDXP could periodically be run in full MCA mode under computer control for diagnostic purposes This example demonstrates a system that uses a very small data acquisition command set i e start run and stop run but that conversely requires customizations to the microDXP as well as significantly more user designed hardware XIA non recurring engineering NRE required 1 Customized PIC microcontroller code is required to implement the I C peripheral device control 2 Customized PIC microcontroller code is required to implement high level data acquisition routines controlled through the user pushbutton interface 3 Customized DSP code is required for peak ratio calculations possibly implemented in lookup tables 4 Minimal FiPPI FPGA code modification is required to implement the auxiliary digital I O functionality User development required 1 A more advanced interface unit is required to break out the microDXP high density internal connection to standard RS
114. or Technical Reference Manual 8 6 2009 mdo microDXP MAN 1 1 2 1 1 2 4 Firmware Selection The term firmware refers both to code running on the DSP and the FPGA configuration code that comprises the Filter Pulse Pileup Inspector or FiPPI Updates to both the DSP and FPGA codes will be posted to the XIA website Please check the microDXP page at http www xia com microDxXP html The on board digital signal processor DSP monitors the analog circuitry manages spectrum scaling and binning and carries out various high level calculations The standard DSP code included with all orders will be sufficient to satisfy most users requirements In some cases custom DSP code may be provided for specialized applications The reconfigurable digital shaping triggering and pileup rejection algorithms are contained in a field programmable gate array FPGA Each complete configuration code is referred to as a FiPPI Filter Pulse Pileup Inspector FiPPIs are denoted by their decimation Each FiPPI uses a decimator circuit to pre average the ADC codes before trapezoidal shaping is applied The so called decimation determines the peaking time range supported by a particular FiPPI The microDXP hardware can store between one and three FiPPI decimations allowing great flexibility in choosing the proper peaking time range at the lowest cost Table 1 3 lists the peaking times offered for each FiPPI decimation the peaking time range of course depen
115. orking on site visitors will have access to live experimental setups on which they will be able to test their software Furthermore the XIA software team will be available to provide assistance and help immediately without the limitations of either email or phone For situations where more time is required additional hours of support may be purchased at XIA s standard consulting rate This program supports both our Handel and Xerxes driver libraries as well as custom driver development Please contact XIA to determine which driver library is right for your application software_support xia com 17 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 2 Using the microDXP Note Please refer to the Getting Started section of the Rapid Development Kit User Manual for detailed setup instructions This chapter provides a general outline of microDXP operational procedures XIA recommends using the microManager software as a microDXP configuration platform in all phases of production For a step by step Getting Started guide using microManager including hardware setup instructions please refer to the Rapid Development Kit User Manual Though microManager also supports microDXP data acquisition DAQ procedures many customers will necessarily use their own software when acquiring data The most common procedures are explained below at the RS 232 command level Please refer to Appendix E for a conde
116. ositive or negative and connected to the input of amplifier A Note that the signal polarity must be distinguished from the bias voltage polarity The signal polarity is positive if the voltage step Vx is a rising edge as displayed in Figure 4 1 Whether signal polarity is positive or negative depends upon the preamplifier s design and does not depend upon bias voltage polarity which is specified on the detector and is determined by its design 4 1 1 Reset Type Preamplifiers Figure 4 3a is a simplified schematic of a reset type preamplifier wherein Cy is discharged through the switch S from time to time when the amplifier s output voltage gets so large that it behaves nonlinearly Switch S may be an actual transistor switch or may operate equivalently by another mechanism In pulsed optical reset preamps light is directed at the amplifier A s input FET to cause it to discharge Cy In transistor reset preamps the input FET may have an additional electrode which can be pulsed to discharge Cr The output of a reset type preamplifier following the absorption of an x ray of energy Ex in detector D is a voltage step of amplitude Vx Two x ray steps are shown in Figure 4 3b as a step 39 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 a b Preamp Output mV 8 50 0 60 100 150 Time us Figure 4 1 a Reset type charge sensitive preamplifier with a negatively biased detector b Output on absorpt
117. ow accessed via quotations from other Tools Options sources Italics Italic text denotes a new peaking time refers to the term being introduced length of the slow filter or simply emphasis it is important first to set the energy filter Gap so that SLOWGAP to at least one unit greater than the preamplifier risetime lt Key gt Angle brackets denote a lt W gt indicates the W key lt Shift Alt Delete gt or lt Ctrl D gt key on the keybord not case sensitive A hyphen or plus between two or more key names denotes that the keys should be pressed simultaneously not case sensitive lt Ctrl W gt represents holding the control key while pressing the W key on the keyboard Bold italic Warnings and CAUTION Improper cautionary text connections or settings can result in damage to system components CAPITALS CAPITALS denote SLOWLEN is the length of DSP parameter names the slow energy filter vi Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 1 Introduction The Micro Digital X ray Processor microDXP is a high rate digitally based multi channel analysis spectrometer designed for energy dispersive x ray or y ray measurements in benchtop networked portable and embedded systems Its versatile analog front end accommodates most solid state and gas detectors and a wide range of common preamplifiers including pulsed optical reset transistor rese
118. plications As one of the oldest communications 35 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 standards RS 232 enjoys wide compatibility with existing devices and is supported by all x86 Personal Computers 3 6 2 1 C Serial Bus The I C serial protocol allows for several serial devices to share the same two wire bus through a device ID handshaking procedure I C devices are pre programmed with a four bit device ID e g 1001 is used for some digital temperature sensors appended with a 3 bit suffix that is typically set by hardwiring the appropriate pins to either the supply voltage or to ground Two TC devices are included on the microDXP itself described below and the bus is wired to both interface connectors to provide for microDXP control over or monitoring of other devices 3 6 3 1 C Memory A new feature implemented on the microDXP is the inclusion of on board non volatile memory which allows for firmware storage and retrieval The I C memory accessed by the PIC is used to store the DSP code and general system information The DSP is booted automatically upon power up The I C memory can be updated with new DSP code via the RS 232 serial port 3 6 4 1 C Temperature Sensor An IC temperature sensor is included on the microDXP The temperature measurement range is 55 C to 125 C with 1 C accuracy 3 6 5 PIC Code Variants Semi custom and custom PIC code
119. plications Please read through this brief chapter before contacting us XIA LLC 31057 Genstar Rd Hayward CA 94544 USA 510 401 5760 Hardware Support microDXP xia com Software Support software_support xia com 1 4 1 Software and Firmware Updates It is important that the DXP unit is being driven by the most recent software firmware combination since most problems are actually solved at the software level Please check for the most up to date standard versions of the microDXP software and firmware at http www xia com microDXP html Please contact XIA at microDXP xia com if you are running semi custom or proprietary firmware code Note it is not a bad idea to make backup copies of your existing software and firmware before you update 1 4 1 1 XUP Utility and Firmware Updates Firmware updates will be provided in the XUP format which is only supported by microManager MicroManager s XUP utility also supports the import and export of parameter settings to and from non volatile memory such that multiple identical systems can easily be configured 1 4 2 Related Documentation As a first step in diagnosing a problem it is sometimes helpful to consult the most recent data sheets and user manuals for a given DXP product available in the Adobe Portable Document Format PDF from the XIA web site Since these documents may have been updated since the DXP unit was purchased they may contain information that could help sol
120. r if the gap is zero or trapezoidal filters The concept behind cusp like filters is that since the points nearest the step carry more information about its height they should be more strongly weighted in the averaging process How one chooses the filter lengths results in time variant the lengths vary from pulse to pulse or time invariant the lengths are the same for all pulses filters Traditional analog filters are time invariant The concept behind time variant filters is that since the x rays arrive randomly and the lengths between them vary accordingly one can make maximum use of the available information by adjusting Length on a pulse by pulse basis In principal the very best filtering is accomplished by using cusp like weights and time variant filter length selection There are serious costs associated with this approach however both in terms of computational power required to evaluate the sums in real time and in the complexity of the electronics required to generate usually from stored coefficients normalized wi sets on a pulse by pulse basis A few such systems have been produced but typically cost about 13K per channel and are count rate limited to about 30 42 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 Decimation by N means to break up the data into sequential sums of length DERN Peaking Time ranges vs Decimation N 8MHz clock assumed N 0_ 0 75 3 00 us N 1 1 50 6 00
121. ring this idle phase the DSP is continuously collecting baseline events from the FiPPI as well as monitoring the Analog Signal Conditioner ASC to keep the ADC input signal in the proper range and to adjust the slope generator to match the current input rate When the Begin Run signal is received from the host through the CSR register the DSP first determines whether the run is a normal data acquisition run or a special run 60 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 DXP X10P DSP Code Flow Chart Startups Initlze vanabes Initial calibrations Begin monitoring ASC Erbie Tirer Interrupt Keep signal in ADC range Onternupt driven Emor Cordition Idle Loop Continuously rreseure beeelire Wait for Begin Runsigral RUNERROR 0 inter rel Run Test Seqrrent deterrined by WH CHTEST Eror Cordition Eror Loog Tum on Red STATUS LED Wait for RUNERROR 0 Specel Pun Bit of RUNTASKS Begin Normal Pun Eror Cordition Cowricad FIPA Pararreters Ferformgain Calibration Zr Statetice f nav run Tirer Interrupt Upciate Statistics Noerrral Run Colled cata werte Fill spectrum for Rte Collect beselire wente Upcate LEDs Handle fixed length runs Erd Run Fi nternal or fromtbet Finish Rurt Update Statistice Figure 5 1 DSP code flow diagram In a normal run ASC monitoring and baseline collection continue as in th
122. rt of the baseline acquisition circuitry i e baseline measurements are taken when the signal is below this threshold Intermediate threshold crossings by default also trigger event processing extending the detectable energy range significantly below the fast filter threshold Note that this threshold is initialized to the maximum i e most conservative value and should be adjusted downward by the user for best performance 48 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 After an x ray has been detected the step height is measured at the slow filter output Although its excellent noise reduction also allows detection of the very lowest energy x rays its slow response precludes an accurate determination of pulse pileup For this reason the slow threshold should be disabled in almost all cases 4 6 Peak Capture Methods As noted above we wish to capture a value of Vx for each x ray detected and use these values to construct a spectrum This process is also significantly different between digital and analog systems In the analog system the peak value must be captured into an analog storage device usually a capacitor and held until it is digitized Then the digital value is used to update a memory location to build the desired spectrum During this analog to digital conversion process the system is dead to other events which can severely reduce system throughput Even single channel anal
123. s to do this for transcendental equations to obtain ICR Then the spectrum can be corrected on a channel by channel basis using Equation 4 12 In experiments with a DXP prototype we found that for a 4 us peaking time for which the maximum ICR is 125 kcps we could correct the area of a reference peak to better than 0 5 between and 120 kcps 8 6 2009 58 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 5 microDXP DSP Code Description NOTICE if you are curious about how the DSP operates in controlling the DXP and processing data from the FiPPI then please read on You will also find this information useful if you wish to develop your own control code for the microDXP However in the latter case we strongly advise you to use XIA s support libraries Handel to interface between your program and the microDXP module 5 1 Introduction and Program Overview The following sections are intended to provide the DXP user with a good understanding of the various tasks performed by the DSP in the microDXP The DSP performs several functions 1 Respond to input and output calls from the host computer to start and stop data collection runs download control parameters and download collected data 2 Perform system calibration measurements by varying the various DAC settings under its control and noting the output change at the ADC 3 Make initial measurements of the slow filter baseline and preampl
124. se SLOWGAP Figure 4 8 For decimation 0 the slow filter output is sampled a fixed time after the x ray is detected 8 6 2009 PEAKSAM must be set properly to achieve optimum performance In our experience values at the low end i e PEAKSAM SLOWLEN tend to work better We recommend that you record the initial value of PEAKSAM and then change it in steps of 1 working out from the initial value Certain PEAKSAM values may cause the Saturn to crash Do not be alarmed just restart and be sure to enter a valid PEAKSAM value before proceeding Making a plot of energy resolution versus PEAKSAM will indicate the best value to select This determination need only be done for one peaking time per decimation The result can then be applied to any value of SLOWLEN and SLOWGAP using the following recipe PEAKSAM SLOWLEN SLOWGAP X Equation 4 8 51 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 4 7 Energy Measurement with Resistive Feedback Preamplifiers 8 6 2009 In previous sections the pulse height measurement was shown for the case of reset type preamplifiers The reset type scheme is most often used for optimum energy resolution x ray detectors Other detectors use an RC type preamplifier as described in 4 1 2 Resistive feedback is most often used for gamma ray detectors that cover a larger dynamic range and where the electronic noise is not as significant a contributio
125. ses are present As may be seen the effect of the filter is both to reduce the amplitude of the fluctuations and reduce their high frequency content This signal is termed the baseline because it establishes the reference level or offset from which the x ray peak amplitude Vx is to be measured The fluctuations in the baseline have a standard deviation og which is referred to as the electronic noise of the system a number which depends on the peaking time of the filter used Riding on top of this noise the x ray peaks contribute an additional noise term the Fano noise which arises from statistical fluctuations in the amount of charge Qx produced when the x ray is absorbed in the detector This Fano noise of adds in quadrature with the electronic noise so that the total noise of in measuring Vx is found from oO sqrt of oe Equation 4 5 45 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 6 Filtered Step L kfig 960920 4 S 2 E 5 Q 5 0 O 2 Filter Output mV 4 5 10 15 20 25 30 35 40 45 Time us Figure 4 6 The event of Figure 4 5 displayed over a longer time period to show baseline noise The Fano noise is only a property of the detector material The electronic noise on the other hand may have contributions from both the preamplifier and the amplifier When the preamplifier and amplifier are both well designed and well matched however the amplifier s noise co
126. ssued The microDXP can be configured to automatically terminate until a preset time or number of input or output counts has elapsed as described below in 2 6 5 In such cases the stop run command overrides the run preset In microManager simply press the Stop Run button The RS 232 command to stop a data acquisition run is 0x01 Please refer to the RS 232 Command Specification for details 2 6 3 Reading a Spectrum The read spectrum command supports readout of any contiguous region of the MCA data extending of course to the entire spectrum Each MCA bin is represented in DSP program memory as a 24 bit word i e 3 bytes supporting up to 16 777 215 counts per bin In some cases i e for short runs and or low count rates the upper bits of each bin word will always be zero The readout speed can be increased by opting to read out a fewer number of bytes per bin or DEPTH At DEPTH 2 up to 65 535 counts per bin are supported At DEPTH 1 up to 255 counts per bin are supported Note If the number of counts in a bin exceeds the DEPTH the resulting distribution will display sharp discontinuities The data is however always stored internally in the DSP at the full 24 bits It is thus not necessary to restart the run when the DEPTH is exceeded Simply change DEPTH and re read the spectrum In microManager the spectrum and statistics can be updated automatically or manually Check the Continuous checkbox for automatic updates
127. t Baseline intermediate and Energy slow filters respectively Please refer to section 5 10 4 for a thorough discussion of thresholds Each PARSET includes 5 different settings for THRESHOLD BASETHRESH and SLOWTHRESH corresponding to the 5 MCA formats or GENSETs In microManager the threshold values for the current PARSET and GENSET are accessed via the Acquisition tab of the Settings panel Enter the desired threshold settings Settings for the current PARSET can be tested by pressing the Apply button and saved to nonvolatile memory via the Save button The RS 232 command to modify thresholds is 0x86 Note that this command does not save the change to nonvolatile memory To do so it is necessary to subsequently save the current PARSET as described below Please refer to the RS 232 Command Specification for details 25 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 2 4 6 Fine Gain Trim To maintain calibration across all combinations of peaking times and MCA formats slight modifications to the analog gain are necessary The DSP PARSET parameter GAINTWEAK is combined with GENSET parameter GAINBASE to arrive at the final gain setting Each PARSET includes 5 different settings for GAINTWEAK corresponding to the 5 MCA formats or GENSETs In microManager the threshold values for the current PARSET and GENSET are accessed via the Acquisition tab of the Settings panel Enter the desired thr
128. t and resistive feedback types The microDXP offers complete computer PDA control over all available amplifier and spectrometer controls including gain if applicable filter peaking time and pileup inspection criteria As with all DXP instruments the firmware i e DSP Microcontroller and FPGA code can be upgraded in the field Unlike other instruments in the DXP family microDXP firmware and parameters are stored locally in non volatile memory The architecture supports custom auxiliary digital access including the industry standard I C serial bus and four configurable digital I O lines Finally the microDXP consumes less than 600mW of power The microDXP is thus a flexible cost effective OEM component that can form the core of a broad range of systems from basic XRF to the most demanding process and control applications emerging in research and industry 1 1 MicroDXP Overview 8 6 2009 The microDXP offers a set of standard and customizable features and options intended to address the design requirements of a wide range of complex spectroscopy data acquisition systems Application examples are given below in 1 1 3 1 1 1 Features The microDXP is the latest addition to the Digital X ray Processor DXP line of instruments from XIA The DXP is a digitally based spectrometer architecture that offers general control over all analog and digital settings as outlined in 1 1 1 1 below A unique feature of the microDXP is non volatile
129. t events seen Number of upset events seen Number of drift up events seen Number of drift down events seen Number of zigzag events seen Number of baseline events acquired Updating mean baseline value Which test segment to execute Which tasks will be executed in run sequence MCA binning factor Lower limit of MCA spectrum Upper limit of MCA spectrum ADC trace time factor Timeout for ASCSetup in tenths of seconds Medium rate throughput threshold for front panel LED High rate throughput threshold for front panel LED Preset type O none 1 real time 2 live time 3 output cts 4 input cts Preset run length FiPPI Digital Filter Event selection parameters SLOWLEN Parameter SLOWGAP Parameter PEAKINT Parameter FASTLEN Parameter FASTGAP Parameter THRESHOLD Parameter MINWIDTH Parameter MAXWIDTH Parameter BASETHRESH Parameter BASETHRADJ Parameter FIPCONTROL Parameter SLOWTHRESH Parameter PEAKSAM Parameter Baseline Related Parameters BLFILTER Parameter BLFILTERF Parameter BASEBINNING Parameter BLCUT Parameter BLMIN Calibration BLMAX Calibration Slow filter length Slow filter gap Peak interval Fast filter length Fast filter gap Threshold value for fast filter trigger range 1 255 0 disables Minimum peak width Maximum peak width Automatically set threshold for intermediate filter trigger range 1 255 0 disables both baseline and event discrimination use FIPCONTROL to disable event discrimina
130. t software and the RS 232 or USB port and firmware code consisting of PIC DSP and FPGA code that is stored and runs on the microDXP itself Firmware code is factory pre loaded into nonvolatile memory on the microDXP circuit board and can be updated in the field via the XUP utility in the microManager software 1 3 1 User Interface e g microManager The host software communicates with and directs the microDXP via a driver layer and displays and analyzes data as it is received XIA offers microManager as a general purpose configuration and data acquisition application MicroManager features full configuration of and control over the microDXP with intuitive data visualization unlimited ROI s regions of interest Gaussian fitting algorithms and the exporting of collected spectra for additional analysis Please refer to the Rapid Development Kit Manual for instructions on using microManager with the microDXP Some users may decide instead to develop their own software to communicate with the microDXP directly via the RS 232 port Please read 1 3 3 below for further details XIA offers the Accelerated DevelOPmenT ADOPT support option at an additional fee to such users ADOPT is described in 1 4 5 12 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 1 3 2 Device Drivers e g Handel XIA will in the near future provide source code for Handel its high level spectrometer driver layer that operat
131. tatistics is 0x06 Please refer to the RS 232 Command Specification for details 8 6 2009 29 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 3 MicroDXP Functional Description 3 1 Organizational Overview The DXP channel architecture is shown in Figure 3 1 The four major operating blocks are the Analog Signal Conditioner ASC Digital Filter Peak Detector and Pileup Inspector FiPPI Digital Signal Processor DSP and PIC microcontroller Also depicted are the ADC the two host interface connections a digital temperature sensor and the nonvolatile memory The functions of each block are summarized below This chapter does assume the reader has some familiarity with x ray pulse processing theory and electronic devices Please see Chapter 4 of this manual for a brief review ge ip ps sl Pm rm digital Filter Pulse detector and Pileup Inspector FiPPI ADT fast x N slow Sawtooth good Function Generator Gain DAC Slope DAC 4 Digital Signal Processor High Peak measure iy Speed MCA binning DMA ASC control i Port FiPPI config PIC MicroController System DSP boot procedures ja Flex Acquisition routine control Cable Firmware loader Power down mode control i Port IC and RS 232 communications Temperature Sensor Figure 3 1 Block diagram of the DXP channel architecture showing the major functional sections and interface port op
132. the intermediate filter threshold BASETHRESH which is used for both baseline and energy discrimination e g setting FIPCONTROL XXXX XXXX XXXX X110 enables event discrimination based on the fast filter THRESHOLD disables event discrimination based on the intermediate filter BASETHRESH and slow filter SLOWTHRESH however BASETHRESH still discriminates baseline measurements in the intermediate filter alternatively setting BASETHRESH to zero would disable both event and baseline discrimination regardless of the value of FIPCONTROL 5 10 5 Setting the Pile up inspection parameters MAXWIDTH PEAKINT MAXWIDTH is used to reject pulse pile up on a time scale that is comparable to FASTLEN as discussed in 4 8 A typical value is MAXWIDTH 2 FASTLEN FASTGAP N where N is in the range 4 8 If the signal rise time depends on the x ray energy e g bandwidth limited preamplifier or low field regions of the detector that are preferentially sampled at some energy this cut can bias the spectrum if it is too small PEAKINT is used to reject energy channel pulse pile up when the pulses are well resolved by the fast channel This value should be set as PEAKINT SLOWLEN SLOWGAP N where N 1 typically 5 10 6 Setting the Analog Gain GAINDAC The DXP internal gain is chosen to set the ADC dynamic range appropriately for the signals of interest If it is set too low the energy resolution may be compromised while if is set too hi
133. the desired filename and location and press Save 2 5 2 Download a Master Parameter Set In microManager select Firmware gt Download to write the parameters in the XUP file you created to a second microDXP Browse to the desired XUP file and location and press Download 26 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 2 6 Data Acquisition 8 6 2009 This section describes the most common data acquisition procedures The most common commands i e start stop run readout data are covered in Error Reference source not found Please refer to the RS 232 Command Specification a separate document for a detailed presentation of all RS 232 commands DXP related documents are available online at http www xia com microDXP html In microManager select the MCA tab in the Data Acquisition panel 2 6 1 Starting a Run Data acquisition runs can be configured to automatically terminate the run after a preset time or number of input or output counts has elapsed as described below in 2 6 5 By default i e PRESET 0 the run continues until a stop run command is issued see 2 6 2 In microManager simply press the Start Run button The RS 232 command to start a data acquisition run is 0x00 Please refer to the RS 232 Command Specification for details 2 6 2 Stopping a Run By default i e PRESET 0 a run in progress continues until a stop run command is i
134. the digital system is almost twice as high since it attains the same throughput for a 2 us peaking time as the analog system achieves for a 1 us peaking time The slower analog rate arises as noted earlier both from the longer tails on the pulses from the analog triangular filter and on additional deadtime introduced by the operation of the SCA In spectroscopy applications where the system can be profitably run at close to maximum throughput then a single DXP channel will then effectively count as rapidly as two analog channels 4 11 Dead Time Corrections The fact that both OCR and ICRm are describable by Equation 4 12 makes it possible to correct DXP spectra quite accurately for deadtime effects Because deadtime losses are energy independent the measured counts Nmi in any spectral channel i are related to the true number N j which would have been collected in the same channel i in the absence of deadtime effects by Nei Nm ICR Y OCR Equation 4 14 Looking at Figure 4 12 it is clear that a first order correction can be made by using ICRm in Equation 4 11 instead of ICR particularly for OCR values less than about 50 of the maximum OCR value For a more accurate correction the fast channel deadtime tgf should be measured from a fit to the equation ICRm ICT exp ICRy Taf Equation 4 15 Then for each recorded spectrum the associated value of ICRm is noted and Equation 4 15 inverted there are simple numerical routine
135. the new MicroComU companion board and microDXP USB Rapid Development Kit 1 1 2 2 Power Supplies Two power supply variants are available corresponding to whether on board regulators for the analog supply voltages are used or are bypassed The analog circuitry requires 5 0V either supplied directly or indirectly through on board LDO regulators Excessive voltage spikes and or ripple on the analog supplies gt 20mVpp can seriously degrade system performance If 5 0V is supplied directly either linear regulated or high quality switching supplies should be used If the on board LDO regulators are used a minimum of 5 50V is required and the ripple requirement can be relaxed a bit Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 If planning to use the MicroComU companion board choose the variant of the microDXP that uses its on board voltage regulators Aside from this the MicroComU board will take care of generating all required voltages for the microDXP at the specified currents and noise performance Regulated Supply Option lt 20mV pk pk noise Voltage Range Current min Current max Description 3 3V 150mV 100mA 130mA Decent switching supply 5 0V 100mV 25mA 30mA Linear or high quality switching 5 0V 100mV 25mA 30mA Linear or high quality switching Unregulated Supply Option lt 100mV pk pk noise Vo
136. tion only Coefficient for BASETHRESH auto set algorithm range 1 255 smaller values result in tighter thresholds FiPPI advanced control bitwise flag register bit O fast threshold 0 enabled bit 1 intermediate threshold 0 enabled bit 2 slow threshold 0 enabled Threshold for slow filter trigger range 1 255 0 disables Peak sampling time Filtering parameter for baseline IIR filtering Filtering parameter for baseline FIR filtering Baseline binning for histogram 0 finest to 6 coarsest DSP baseline cut cut at BLCUT FWHM units defined below Min baseline value accepted in average calculated from BLCUT Max baseline value accepted in average calculated from BLCUT ASC Control Parameters and Calibrations all variants POLARITY Parameter Preamplifier signal polarity O negative step 1 positive step 8 6 2009 70 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 GAINDAC Parameter Current Gain DAC value 16 bit serial DAC range 0 65535 ASC Control Parameters and Calibrations reset type variants RESETWAIT Parameter Quick Reset time 25ns units RESETINT Parameter Reset time 0 25 usec units SLOPEDAC Calibration Current Slope DAC value 16 bit serial DAC range 0 65535 SLOPEZERO Calibration Slope DAC zero value approximately center of range SLOPEVAL Calibration Absolute setting SLOPEDAC SLOPEZERO SGRANULAR Parameter Slope DAC step size TRKDAC
137. tion that supports 10 MSA is quite expensive The alternative approach is to first reduce the dynamic range of the preamplifier output signal such that a moderately priced ADC can be used 3 2 1 1 Reset Type Preamplifiers For reset type preamplifiers the dynamic range reduction is accomplished using a novel dynamic range technology for which XIA has received a patent and which is indicated in Figure 3 2 Here a preamplifier output is shown which cycles between about 3 0 and 0 5 volts We observe that it is not the overall function which is of interest but rather the individual steps such as shown in Figure 4 2 of the next chapter that carry the x ray amplitude information Thus if we know the average slope of the preamp output we can generate a saw tooth function that has this average slope and restarts each time the preamplifier is reset as shown in Figure 3 2 If we then subtract this saw tooth from the preamplifier signal we can amplify the difference signal to match the ADC s input range also as indicated in the Figure The generator required to produce this saw tooth function is quite simple comprising a current integrator with an adjustable slope and a reset switch A DAC SLOPEDAC controls the current which sets the slope The DAC input value is set by the DSP which thereby gains the power to adjust the saw tooth generator in order to maintain the ASC output i e the Amplified Saw tooth Subtracted Data of Figure 3 2 w
138. tions 3 2 The Analog Signal Conditioner ASC The ASC has two major functions to reduce the dynamic range of the input signal so that it can be adequately digitized by a 12 bit converter and to 8 6 2009 30 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 reduce the bandwidth of the resultant signal to meet the Nyquist criterion based upon the ADC sample rate 3 2 1 Dynamic Range Reduction In many cases and particularly for reset type preamplifiers the full scale output voltage range is many times greater than the voltage step produced by a single x ray event see Figure 4 2 A high sampling rate is necessary to provide good pulse pileup detection as described in 4 8 and sufficient ADC resolution is required to accurately sample the noise prior to the digital filters For high count rates pulse pair resolution less than 200 ns is desirable which implies a sampling rate of 10 MSA or more In order to reduce the noise o in measuring Vx see Figure 4 1 and Figure 4 3 experience shows that o must be at least 4 times the ADC s single bit resolution AV1 This effectively sets the gain of the amplifier stages preceding the ADC Then if the preamplifier s full scale voltage range is Vmax it must digitize to N bits where N is given by N log 10 Vmax AV log 10 2 Equation 3 1 For a typical high resolution spectrometer N must at least 14 An ADC with 14 effective bits resolu
139. to accept a synchronization signal in a time resolved spectroscopy experiment or as outputs e g multiple SCAs 1 1 1 1 1 1 1 3 General Spectrometer Features Extremely compact unit replaces spectroscopy amplifier shaping amplifier and multi channel analyzer MCA at significantly reduced cost and power consumption Operates with a wide variety of x ray or y ray detectors using preamplifiers of pulsed optical reset transistor reset or resistor feedback types Multi channel analysis with up to 8K 8132 bins allowing for optimal use of data to separate fluorescence signal from backgrounds Instantaneous throughput up to 164 000 counts per second cps in the spectrum for the standard 8MHz pipeline clock speed up to 328 000 cps for the 16MHz pipeline clock option see 1 1 2 3 Digital trapezoidal filtering with programmable peaking times between 750 ns and 48 us for the standard 8MHz pipeline clock speed and between 375 ns and 24 us for the 16MHz pipeline clock option see 1 1 2 3 Digitally controlled internal gain requires variable gain option see 1 1 2 5 32dB range 16 bit precision Pileup inspection criteria computer settable including fast channel peaking time threshold and rejection criterion Accurate ICR and live time reporting for precise dead time corrections Embedded Systems Features Up to fifteen 15 sets of optimized spectrometer parameters can be stored and later retrieved with a sing
140. try s standard for high rate processing In the second place one can show theoretically that if the noise in the signal is white i e Gaussian distributed above and below the step which is typically the case for the short shaping times used for high signal rate processing then the average in Equation 4 4 actually gives the best estimate of V in the least squares sense This of course is why triangular filtering has been preferred at high rates Triangular filtering with time variant filter lengths can in principle achieve both somewhat superior resolution and higher throughputs but comes at the cost of a significantly more complex circuit and a rate dependent resolution which is unacceptable for many types of precise analysis In practice XIA s design has been found to duplicate the energy resolution of the best analog shapers while approximately doubling their throughput providing experimental confirmation of the validity of the approach A practical limitation on the implementation of Equation 4 4 is that two FIFO memories are required one of length L and one of Length L G Since memory space is limited in FPGAs we have restricted our designs to values of L G less than 32 Since the microDXP samples at 20 MSA this corresponds to a peaking time of about 1 5 us a significant limitation XIA overcomes this limitation by first decimating the data stream from the ADC by performing sequential sums of D data points where D 2N We re
141. type used i e reset type or RC feedback and parameters must be properly set based upon the following information which is normally included in the detector or preamplifier documentation or alternatively measured using an oscilloscope v The decay constant for RC type preamplifiers or the settling time of the reset transient for reset type preamplifiers v The preamplifier signal polarity Positive polarity means that an x ray produces a positive step in voltage at the preamplifier output The preamplifier s signal polarity unrelated to the detector s bias voltage polarity 2 2 1 1 Preamplifier Type Please refer to 4 1 for more detailed description of charge sensitive preamplifier topologies Briefly RC feedback preamplifiers use resistive feedback to provide a continuous discharge path for the feedback capacitor resulting in a characteristic decay time e g 501s Reset preamplifiers employ a switch to periodically discharge the capacitor very quickly resulting in a periodic staircase waveform with many x ray steps between each reset The microDXP must have DSP and FPGA code pre loaded in non volatile memory that is appropriate for the preamplifier type used In addition the microDXP hardware must be set type via a miniature DIP switch refer to Appendix D for the switch location Set to RAMP for reset type preamplifiers Set to OFFSET for RC feedback preamplifiers In MicroManager the preamplifier t
142. ulated using an infinite impulse response filter characterized in the following way lt Bi gt Spasi N Equation 5 1 Where lt Bi gt is the baseline mean after the i baseline sample Bi is the i baseline sample and lt Bi gt is the baseline mean before the i sample With this filter the most recent baseline samples are weighted the most but up to the precision of the stored mean value all baseline values have a small effect on the mean hence the infinite in the name The length of the filter is controlled by the parameter BLFILTER which holds the value 1 N in 16 bit fixed point notation which has 1 sign bit and 15 binary bits to the right of the decimal point Expressed as a positive integer BLFILTER 1 N 2 15 The default value for BLFILTER corresponds to N 64 Interpreting BLFILTER as an integer gives 1 128 2 15 2 9 256 64 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 5 5 2 FIR Finite Impulse Response Filter By setting the appropriate RUNTASKS bit it is possible to choose a finite impulse filter to calculate the baseline mean With this filter a straight average of the N most recent valid baseline samples is used to calculate the mean To implement this filter a buffer large enough to hold all N samples is necessary For this reason the length of the finite response filter is limited to 1024 The filter length is stored in the parameter BLFIL
143. uld be a much more complex and considerably more expensive task when compared with the other solutions proposed here 1 2 Hardware Requirements 1 2 1 Host Computer or PDA The microDXP can communicate with a host computer or PDA ina variety of ways The hardware supports RS 232 serial communications DSP serial communications and parallel IDMA access to the DSP The IDMA port allows a variety of interface options to be implemented such as the USB 2 0 high speed interface now implemented on the MicroComU companion board At present DSP serial communication is not yet supported A full description of the RS 232 command set can be found in the microDXP RS 232 Communications Specification available online at http www xia com microDXP html 1 2 2 Detector Preamplifier The microDXP accommodates nearly all detector preamplifier signals Preamplifier signal and The two primary capacitor discharge topologies pulsed reset and resistive power specifications must feedback are supported The voltage compliance range in the DXP analog be verified circuitry imposes in the following constraints 8 6 2009 10 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 Parameter Minimum Maximum Typical X ray pulse height 250uV 375mV 25mV Input voltage range 5V 5V Table 1 4 Analog input signal constraints for pulsed reset preamplifiers Parameter Minimum
144. urrently selected GLOBSET in nonvolatile memory The RS 232 command to set MCALEN is 0x85 Note that this command does not save the setting to nonvolatile memory Please refer to the RS 232 Command Specification for details 2 3 3 MCA Granularity Bin Width The granularity setting determines the hardware DSP scaling factor BINGRANULAR with four standard settings and a custom as outlined in table Error Reference source not found below The raw energy filter sample i e the energy is divided in the DSP by BINMULTIPLE The combination of MCA size and granularity must satisfy dynamic range constraints imposed by the digital filter pipeline If they do not a dead region will be included at the highest energies in the spectrum i e there is no possibility of getting counts in this region Recommended Absolute MAX BINGRANULAR BINMULTIPLE of MCA Bins of MCA Bins 4096 8192 0 1 2048 8192 1 2 1024 4096 2 4 512 2048 3 8 lt 512 4 Bin Size e g 128 e g 32 Table 2 1 Suggested Bin Granularity settings based upon the Number of MCA Bins Using a larger than recommended number of bins for a given granularity will result in extended range events if such x rays are present being displayed If greater than the absolute maximum the spectrum will include a high energy dead region In microManager BINGRANULAR is set via the Bin Granularity field in the Acquisition tab of the Settings
145. us which is less than PEAKINT 2 3 us Notice by the symmetry of the trapezoidal filter if pulse 2 is rejected because of pulse 3 then pulse 3 is similarly rejected because of pulse 2 Pulses 4 and 5 are so close together that the output of the fast filter does not fall below the threshold between them and so they are detected by the pulse detector as only being a single x ray pulse Indeed only a single though somewhat distorted pulse emerges from the slow filter but its peak amplitude corresponds to the energy of neither x ray 4 nor x ray 5 In order to reject as 54 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 many of these fast channel pileup cases as possible the DXP implements a fast channel pileup inspection test as well The fast channel pileup test is based on the observation that to the extent that the risetime of the preamplifier pulses is independent of the x rays energies which is generally the case in x ray work except for some room temperature compound semiconductor detectors the basewidth of the fast digital filter i e 2Lf Gf will also be energy independent and will never exceed some maximum width MAXWIDTH Thus if the width of the fast filter output pulses is measured at threshold and found to exceed MAX WIDTH then fast channel pileup must have occurred This is shown graphically in the figure where pulse 3 passes the MAXWIDTH test while the piled up pair of pulses 4 and
146. ving a problem in question All manuals datasheets and application notes as well as software and firmware downloads can be found on at http www xia com microDXP html In order to request printed copies please send an e mail to software_support xia com or call the company directly In particular we recommend that you download the following documents 14 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 8 6 2009 v Rapid Development Kit User Manual covers both the RS232 and USB Rapid Development Kits All users v MicroComU Technical Reference Manual Users interested in using the MicroComU companion board to generate the microDXP s power supplies and or communicate with the microDXP using a USB 2 0 high speed interface MicroDXP RS 232 Communications Specification Users who wish to develop their own software and or hardware 1 4 3 Email and Phone Support The microDXP comes with one year of email and phone support Support can be renewed for a nominal fee Please call XIA if your support agreement has expired The XIA Digital Processors DGF amp DXP are digitally controlled high performance products for X ray and gamma ray spectroscopy All settings can be changed under computer control including gains peaking times pileup inspection criteria and ADC conversion gain The hardware itself is very reliable Most problems are not related to hardware failures but rather t
147. wer consumption at 8MHz 16 VCC 103 0 339 9 3 3V digital includes ADC 16 V 20 3 101 5 5V analog includes VGA 16 V 23 3 116 5 5V analog 557 9 mW Total power consumption at 16MHz Table 1 6 Power consumption depends upon the pipeline clock speed 8 6 2009 11 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 1 2 4 Operating Environment e Temperature Range 0 C 50 C e Maximum Relative Humidity 75 non condensing e Maximum Altitude 3 000 meters e Pollution degree 2 e Not rated for use in high electromagnetic fields e Not rated for use in environments with measurable neutron flux Neutron flux will cause permanent damage to silicon crystals and permanently degrade or impair the performance of this system e The components on the microDXP board are not radiation hardened Although there should not be a problem operating them in environments with modest gamma or X ray flux above a certain level this radiation will start to cause bit errors in the digital components If necessary please contact XIA LLC to discuss a proposed radiation environment 1 2 5 Regulatory Compliance The microDXP board is RoHS compliant 1 3 Software Overview 8 6 2009 Up to three layers of software are used in a typical microDXP instrumentation system a user interface for data acquisition and control a driver layer that communicates between the hos
148. ximum of 15 optimized peaking times can be stored The PARSET further contains 5 sets of gain tweaking and threshold settings each corresponding to the 5 GENSETs or MCA formats Storing thresholds and gain settings for every combination of peaking time and MCA format eliminates the need for calibrating a given combination more than once The factory set default spectrometer settings should be adequate to acquire a recognizable spectrum To achieve optimal performance the spectrometer settings must be adjusted and stored to non volatile memory such that the optimized settings will be accessible in the future To maximize throughput the slow filter peaking time Tp should be chosen to be as short as possible to meet energy resolution requirements since the maximum throughput scales as 1 t p see 4 10 for a detailed discussion of throughput OCR max Me tg 0 37 tg 2 4 1 Selecting a FiPP Decimation The microDXP comes pre programmed with at least one and up to three FiPPI decimations or peaking time ranges In microManager the FiPPI decimation is accessed via the Acquisition tab of the Settings panel FiPPIs 0 2 can be selected via the Peaking Time Range drop down list Notice that the Peaking Time and other PARSET settings update when the new FiPPI decimation is selected The RS 232 command to select a FiPPI decimation is 0x81 Please refer to the RS 232 Command Specification for details 2 4 2 Selecting a PARSET For each peakin
149. ype corresponding to the loaded firmware is displayed in the Detector tab of the Settings panel 2 2 1 2 Decay Time TAURC If using an RC feedback type preamplifier you must set the DSP parameter TAURC where the decay time constant Trc is expressed in microseconds us TAURC TRC In microManager TAURC is set via the Decay Time field in the Detector tab of the Settings panel Simply enter the desired value in microsecond units and press the Apply And Save button The RS 232 command to set and save TAURC to nonvolatile memory is 0x89 Please refer to the RS 232 Command Specification for details 2 2 1 3 Reset Interval RESETINT If using a reset type preamplifier you must set the DSP parameter RESETINT to the reset delay time or reset interval This is the period after each preamplifier reset that the microDXP waits before re enabling data acquisition 20 Micro Digital X ray Processor Technical Reference Manual mdo microDXP MAN 1 1 2 RESETINT expressed in microseconds is set based on the settling time of the preamplifier reset transient waveform which typically ranges from hundreds of nanoseconds to hundreds of microseconds Setting the delay shorter than the transient settling time typically degrades the energy resolution and may even introduce reset artifact events into the spectrum Setting the delay longer than necessary introduces additional processor dead time which will reduce the data throughput at high count
150. yzer systems introduce significant deadtime at this stage since they must wait some period typically a few microseconds to determine whether or not the window condition is satisfied Digital systems are much more efficient in this regard since the values output by the filter are already digital values All that is required is to capture the peak value it is immediately ready to be added to the spectrum If the addition process can be done in less than one peaking time which is usually trivial digitally then no system deadtime is produced by the capture and store operation This is a significant source of the enhanced throughput found in digital systems Once an active threshold is exceeded the microDXP employs one of two methods to capture the slow energy filter output such that the best measure of V results For decimations other than 0 the slow filter output is monitored over a finite interval of time in the region of its maximum and the maximum value within that interval is captured This method is referred to as peak finding or max capture For decimation 0 the slow filter is sampled at a fixed time interval after the pulse is detected by the fast filter This method is referred to as peak sampling After describing in 4 6 1 below how to set the Gap parameter so that there will be a quality value of the energy filter to capture we describe the two methods in detail in 4 6 2 4 6 1 The Slow Filter Gap Length

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