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User`s Manual PIXIE-4

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1. ADC units 30 28 75 80 85 90 95us Time Figure 6 4 A y ray event displayed over a longer time period to show baseline noise and the effect of preamplifier decay time With a RC type preamplifier the slope of the preamplifier is rarely zero Every step decays exponentially back to the DC level of the preamplifier During such a decay the baselines are obviously not zero This can be seen in Figure 6 4 where the filter output during the exponential decay after the pulse 1s below the initial level Note also that the flat top region 1s sloped downwards Using the decay constant t the baselines can be mapped back to the DC level This allows precise determination of y ray energies even if the pulse sits on the falling slope of a previous pulse The value of t being a characteristic of the preamplifier has to be determined by the user and host software and downloaded to the module 28 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved 6 4 Thresholds and Pile up Inspection As noted above we wish to capture a value of V for each y 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 t
2. XIA 2008 All rights reserved 8 Using Pixie 4 Modules with Clover detectors When working with clover detectors the Pixie 4 can be operated in a specific clover mode In this mode the DSP will calculate the pulse height for each channel as m normal operation and in addition for events with hits in more than one channel calculate the sum of individual channel energies The result the full energy of gamma rays scattered within the clover detector 1s binned in an additional addback spectrum In the current implementation of the clover mode the spectrum length 1s fixed to 16K The clover mode applies only to MCA runs not list mode runs The clover mode is enabled by setting the corresponding checkbox in the Pixie Viewer s Module Control Register panel There is also the option of binning only those events in the individual channel spectra that do not have multiple hits Additional clover functions are under development 43 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved 9 Troubleshooting 9 1 Startup Problems The following describes solutions to common startup problems l Computer does not boot when Pixie module is installed in chassis This 1s usually caused by an incorrect clock setting on the Pixie module The module needs to have a valid clock to respond to the computer s scanning of the PCI bus Computer reports new hardware found needs driver files Whenever a Pixie module is install
3. Pixie 4 modules in the chassis it will detect new hardware and try to find drivers for it A Pixie 4 module will be detected as a new device every time it is installed in a new slot While there 1s no required order of installation of the driver software the following sequence is recommended users with embedded host computer skip to step 4 1 If you have a remote controller first install the driver software for the controller itself Unless directed otherwise by the manufacturer of the controller this can be done with or without the controller and Pixie 4 modules installed in the host computer and or chassis If the modules are installed ignore attempts by Windows to install drivers until step 7 NI controllers come with a multi CD package called Device Driver Reference CD for simplicity it is recommended to install the software on these CDs in the default configuration 2 Unless already installed power down the host computer install the controller in both the host computer and chassis and power up the system again chassis first 3 Windows will detect new hardware the controller and should find the drivers automatically Verify in Window s device manager that the controller 1s properly installed and has no resource conflicts 4 Install Igor Pro 5 Install the Pixie 4 software provided by XIA see section 2 2 3 6 Unless already installed power down the host computer install the Pixie 4 modules in the chassis and po
4. Pixie module at a time The number of that module is displayed at the top right corner of the Control Panel inside the Module control Next to the Module control 1s the Channel control which indicates the current channel the Pixie Viewer is interacting with Proceed with the steps below to configure your system Note The More Less button next to the Help button on the bottom of the Pixie Control Panel can be used to hide some controls This may be helpful to those first time Pixie users who only need to use those major controls in the beginning W Pied Run Control Calibrate Run Module 0__ K Channei 0 Te Analog Signal Conditioning Decay Time Gain Vf T Tau ps 50 000 Tel Auto Find Ofset M Figure 2 2 The Pixie 4 Run Control Panel Calibrate tab shown 1 In the Calibrate tab click on the Oscilloscope button This opens a graph that shows the untriggered signal input Click Refresh to update the display The pulses should fall in the display range If no pulses are visible or if they are cut off out of the display range click Adjust Offsets to automatically set the DC offset There is a control called Offset on the Oscilloscope which can be used to set the DC offset level for each channel If the pulse amplitude is too large to fall in the display range decrease the Gain in the Calibrate tab of t
5. in Figures 7 1 a and 7 2 a Connect pin 2 of JP2 the clock input with a shunt to pin 3 of JP2 which is labeled LOC This will use the on board clock crystal as the clock source 7 1 2 Daisy chained Clock Mode The preferred way to distribute clocks between modules is to daisy chain the clocks from module to module where each module repeats and amplifies the signal This requires one master module located in the leftmost slot of the group of Pixie 4 modules with the same jumper settings as an individual module see Figures 7 1 a and 7 2 a Configure the other modules in the chassis as clock repeaters by setting the jumpers as shown in Figures 7 1 b and 7 2 b 1 e remove all shunts from JP 1 and JP2 and set a shunt on JP3 located on top of the clock crystal U2 Note that the clock output is always enabled 1 e every board independent of its clock mode sends out a clock to its right neighbor as long as it has a clock itself Thus make sure that no other module sits to the right of a Pixie module that uses the PXI LBRO line on the PXI backplane for other purposes 7 1 3 Bussed Clock Mode If there have to be gaps between a group of Pixie 4 modules the daisy chained clock distribution will not work since the chain 1s broken In this case the modules can be configured for bussed clock mode To do so configure one module in any slot as the bussed 33 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved clo
6. left The leftmost module issues the combined OR to a bussed PXI line The chassis has to be configured such that the leftmost segment drives all other segments to the right The Pixie 4 modules can be set up to operate in this mode using the chassis control panel of the 36 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved Pixie Viewer The PXI backplane buffering has to be set up with the tools provided by the chassis manufacturer the lines named PXI TRIGO fast trigger PXI TRIGI event trigger and PXI TRIG2 synchronization have to be set up to be driven from the leftmost segment 7 2 4 Trigger Distribution between PXI chassis In principle it is possible to distribute triggers between several chassis with Pixie 4 modules using XIA s PXI PDM module Please contact XIA for details 7 3 Run Synchronization It is possible to make all Pixie 4 modules in a system start and stop runs at the same time by using a wired OR SYNC line on the PXI backplane In all modules the variable SYNCHWAIT has to be set to 1 If the run synchronization is not used SYNCHWAIT must be set to 0 The variable is set by checking the corresponding checkbox in the Run tab of the Pixie Viewer The run synchronization works as follows When the host computer requests a run start the Pixie 4 s DSP will first execute a run initialization sequence clearing memory etc At the beginning of the run initialization the DSP causes the SYNC line to be driven lo
7. low 1 e logic 1 1s OV 38 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved 7 6 Coincident Events 7 6 1 Coincidences Within a Module In any given event a single Pixie 4 module will have up to four channels with a hit i e a valid local pulse without pileup The four channels thus form one of 16 possible Hit Patterns stored in the lower 4 bits of a DSP parameter In this representation the Hit Pattern ranges from no channel hit 0000 over only channel 1 hit 0010 to all four channels hit 1111 For each event the Hit Pattern is checked against the user defined Coincidence Pattern to determine if it 1s acceptable Local Test If acceptable the event is recorded and processed if not the event is rejected and data acquisition continues lee Module Register Panel m m Gel w w w w Gel SR SR WW IS S Figure 7 3 Coincidence Pattern and Coincidence Window Settings in the Pixie Viewer 39 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved The user can define the Coincidence Pattern to accept one or more hit patterns For example in the Module Register Edit Panel of the Pixie Viewer there are 16 checkboxes for the 16 possible hit patterns and selecting one sets the corresponding bit in the coincidence pattern In the example shown in Figure 7 3 accepting only Hit Pattern 0001 makes the Coincidence Pattern 0x0002 Several of the check boxes can be set at the same ti
8. low logic 0 3 The module in slot 2 typically XIA s PXI PDM module uses the up to 48 bit hit pattern from up to 12 modules slots 3 14 to make an accept reject decision If the hit pattern is acceptable the TOKEN line is left pulled up If not acceptable the TOKEN line is driven low logic 0 The decision criteria is based on a user defined control word downloaded to the PXI PDM by its neighboring Pixie 4 module The acceptance decisions implemented in the current PDM firmware are described in detail in the Pixie Viewer online help For example if the control word is 0x13 0x14 0x15 etc events are only acceptable if at least 3 4 5 etc channels are hit In case of 0x0200 channel 0 but not 1 2 and 3 must be hit in each module 0 and 1 The current firmware does not claim to cover all cases Please contact XIA to request additional cases or to obtain verilog source code to write custom PDM firmware 4 Each module after waiting 100ns for the global accept reject decision to be made captures the status of the TOKEN line and puts it in the event hit pattern The hit pattern also contains the status of the backplane STATUS line the result of the local coincidence test and the status of the front panel input at this moment Depending on user settings the event will be recorded or discarded if the TOKEN and or LOCAL bits are set in the hit pattern A full implementation of this feature thus requires an additional module in slot 2
9. module configured as PXI clock master shown in Figure 7 2 f a XIA PXI PDM power and logic module or any other suitable custom module The PXI clock master has to be configured as shown in Figure 7 2 f The PXI clock slaves are configured by connecting pin 2 on JP and JP2 together PXT to clock input as shown in Figures 7 1 e and 7 2 e Always make sure that there is no shunt on JP3 in order to disconnect from the incoming daisy chained clock else there will be a conflict between the two clock signals 7 2 Trigger Distribution 7 2 1 Trigger Distribution Within a Module Within a module each channel can be enabled to issue triggers Two kinds of triggers are distributed First a Fast Trigger indicating the trigger filter just crossed the threshold which is used to start pileup inspection and to stop the FIFOs for waveform acquisition among other things Second an Event Trigger indicating that pileup inspection was passed 1 e validating the event as acceptable The Event Trigger also tells the DSP that data is ready for readout in the Trigger Filter FPGA If channels are put in group trigger mode each trigger enabled channel issues both kinds of triggers to the central Communication FPGA which builds an OR of all triggers and sends it 34 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved back to all channels The channels then use the distributed fast triggers and event triggers instead of their own
10. more since the noise 1s averaged over longer periods This can help to remove tails on the peaks A long trigger flat top will help to trigger on slow rising pulses and thus result in a sharper cut off at the threshold in the spectrum 3 6 4 Decay Time The preamplifier decay time x is used to correct the energy of a pulse sitting on the falling slope of a previous pulse The calculations assume a simple exponential decay with one decay constant A precise value of t 1s especially important at high count rates where pulses overlap more frequently If t is off the optimum peaks in the spectrum will broaden and if t 1S very wrong the spectrum will be significantly blurred The first and usually sufficiently precise estimate of t can be obtained from the Auto Find routine in the Calibrate tab Measure the decay time several times and settle on the average value Fine tuning of t can be achieved by exploring small variations around the fit value 22 39 This 1s best done at high count rates as the effect on the resolution 1s more pronounced The 12 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved value of t found through this way is also valid for low count rates Manually enter t in the Calibrate tab take a short run and note the value of t that gives the best resolution Pixie users can also use the Manual Fit routine to manually find the decay time through exponentially fitting the untriggered input signals Another tool i
11. 1 XIA 2008 All rights reserved noise at longer filter rise times The fast filter has a filter length Lr O lus and a gap Gr 0 1us The slow filter has L 1 2us and G 0 35us The arrival of the y ray step in the preamplifier output 1s detected by digitally comparing the fast filter output to THRESHOLD a digital constant set by the user Crossing the threshold starts a counter to count PEAKSAMP clock cycles to arrive at the appropriate time to sample the value of the slow filter Because the digital filtering processes are deterministic PEAKSAMP depends only on the values of the fast and slow filter constants and the rise time of the preamplifier pulses The slow filter value captured following PEAKSAMP is then the slow digital filter s estimate of Vx ADC units 56 58 60 62 64 66 68us Time Figure 6 6 A sequence of 3 y ray pulses separated by various intervals to show the origin of pileup and demonstrate how it 1s detected by the Pixie 4 The value V captured will only be a valid measure of the associated y ray s energy provided that the filtered pulse is sufficiently well separated in time from its preceding and succeeding neighbor pulses so that their peak amplitudes are not distorted by the action of the trapezoidal filter That 1s if the pulse 1s not piled up The relevant issues may be understood by reference to Figure 6 6 which shows 3 y rays arriving separated by various intervals The fast filter has a filter l
12. 9 or 515 CHANHEADLEN 2 and the two words are Table 4 7 Channel header for compression 3 format CHAN_TRIGTIME CHAN ENERGY Energy 19 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved 5 Hardware Description The Pixie 4 is a 4 channel unit designed for gamma ray spectroscopy and waveform capturing It incorporates four functional building blocks which we describe below This section concentrates on the functionality aspect Technical specification can be found in section 1 2 Figure 1 shows the functional block diagram of the Pixie 4 Input AO MCA List mode 250K x 32 XC2S200 Analog Signal Conditioning PLX 9054 POM EPGA SP FPGA Trigger bus XC2S200 XC28S200 Input A3 IDMA DSP Local data bus 2185 cPCI bus Figure 5 1 Functional block diagram of the Pixie 4 front end data acquisition and signal processing card 5 1 Analog Signal Conditioning Each analog input has its own signal conditioning unit The task of this circuitry is to adapt the incoming signals to the input voltage range of the ADC which spans 2V Input signals are adjusted for offsets and there is a computer controlled gain stage of switched relays This helps to bring the signals into the ADC s voltage range and set the dynamic range of the channel A fine tuning of the gain is achieved by multiplying the calculated energy values with digital gain factors in the digital signal processor DSP 20 PIXIE 4 User s Manua
13. All rights reserved 10 3 Control and Status Register Bits Table 9 4 Control and Status Register of the Pixie 4 System FPGA Set to to start data acquisition or 0 to stop Automatically cleared when DSP de asserts Active to end run Unused Reserved for future use PClactive Set to reserve external memory I O for host Unused Reserved for future use 0x0010 DSPReset Write only Set to reset DSP processor to initiate program download 0x0020 SynchCtrl Read only If low module is busy with run initialization has filled its I O buffer with data or 1s finished with the run 0x0040 Unused Reserved for future use 0x0080 Unused Reserved for future use 0x0100 SynchFlag Read only Reserved for future use 0x0200 Live Read only If zero DSP is taking data 0x0400 Unused Reserved for future use 0x0800 Unused Reserved for future use 0x1000 Unused Reserved for future use 0x2000 Active Read only If set there 1s a run in progress 0x4000 LAMState Read only If set LAM is set internally 0x8000 Unused Reserved for future use 47 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved
14. E 4 User s Manual V1 61 XIA 2008 All rights reserved The communication FPGA links the PCI slave with the DSP and the on board memory The host can read out the memory without interrupting the operation of the DSP This allows updates of the MCA spectrum while a run is in progress The communication FPGA also distributes triggers and coincidence signals to other modules using the PXI backplane connections 23 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved 6 Theory of Operation 6 1 Digital Filters for y ray Detectors Energy dispersive detectors which include such solid state detectors as Si Li HPGe Hot CdTe and CZT detectors are generally operated with charge sensitive preamplifiers as shown in Figure 6 1 a Here the detector D is biased by voltage source V and connected to the input of preamplifier A which has feedback capacitor Cr and feedback resistor Ry The output of the preamplifier following the absorption of an y ray of energy Ex in detector D is shown in Figure 6 1 b as a step of amplitude V on a longer time scale the step will decay exponentially back to the baseline see section 6 3 When the y ray 1s absorbed in the detector material it releases an electric charge Qx Ex where s is a material constant Qx 1s integrated onto Cr to produce the voltage Vx Q Cr Ex eCr Measuring the energy Ex of the y ray therefore requires a measurement of the voltage step V in the presence of the amplif
15. E IV ECS AIR E 14 AND CISC Mode A CN 14 2 1 39 Fast List Mode EE 16 4 2 OUtput Data SUC UTE a 17 ql MCA TATS 6 Sr Ati EE 17 2 2 2 BE ER EE 17 5 Hardware Desc ipl O ities se eat etre es ea ewe ee tutus 20 5 1 Analog Signal Conditioning sse eee eene eene 20 3 2 Real time Processtmp UMIS aoo PIER vox a a Doc es DRM SRR eee 21 5 3 Digital Signal Eroeessopt Debatte gege 22 5 4 ENEE ee e 22 6 TOCO Or Te memmemteere eeesen meee neeresae re Penner rr nary nmr Reenter nee rere oa Enea 24 6 1 Digital Filters Tor ysray Re 24 6 2 Trapezoigal Filtering am the PIKEM anaana a te he a ever Lens 26 6 3 Baselines and Preamplifier Decay Times us ioo de te TE Saca etd 27 6 4 Thresholds and Pile up Inspecton 29 6 5 EE 3l 7 Operating Multiple Pixie 4 Modules Synchronously oo0s0ooeooonnenenenenssssssssss 32 7 1 COCK DISCIDUIO EE 32 T nasadgabe OC H 33 ii PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved 10 1 10 2 10 3 Daisvsehamed C lock MOUE EE 33 Bussed lock IMOde v cemere e aie o re RT e du ares ties ae Aes ateendnirebet 33 Eege 34 TYAS SE r DSO e E 34 Trigger Distribution Within a Module 34 Trigger Distribution Between Modules nnnn nnnnnnnnnesessosseeeeteereennesssssssssssssssene 36 R n Sy NC ht Oni Za e EEN 37 Extetial Gaie Ga CV ClO EE 38 EE 38 Cottcident E EE 39 Coincidences Withimca Module sioe r 39 Coincidences Between Modules ee Zeen de dee 40 Using Pixie 4 Modules with Cl
16. K channels The Pixie 4 supports coincidence spectroscopy and can recognize complex hit patterns Data readout rates through the CompactPCT PXI backplane to the host computer can be over 100Mbytes s The PXI backplane is also used to distribute clocks and trigger signals between several Pixie 4 modules for group operation With a large variety of CompactPCT PXI processor controller or I O modules being commercially available complete data acquisition and processing systems can be built in a small form factor 1 1 Features e Designed for high precision y ray spectroscopy with HPGe detectors e Directly compatible with scintillator PMT combinations Nal CsI BGO and many others e Simultaneous amplitude measurement and pulse shape analysis for each channel e Input signal decay time as fast as 150ns and up to 10ms exponentially decaying e Wide range of filter rise times from 27ns to 109us equivalent to 12ns to 5Ous shaping times e Programmable gain and input offset e Excellent pileup inspection double pulse resolution of 50 ns Programmable pileup inspection criteria include trigger filter parameters threshold and rejection criteria e Digital oscilloscope and FFT for health of system analysis e Triggered synchronous waveform acquisition across channels modules and crates e Dead times as low as 1 us per event are achievable limited by DSP algorithm complexity Events at even shorter time intervals can be extracted via off
17. User s Manual Digital Gamma Finder DGF PIXIE 4 Version 1 61 May 2008 XIA LLC 31057 Genstar Road Hayward CA 94544 USA Phone 510 401 5760 Fax 510 401 5761 http www xia com Disclaimer Information furnished by XIA is believed to be accurate and reliable However XIA assumes no responsibility for its use or for any infringement of patents or other rights of third parties which may result from its use No license is granted by implication or otherwise under the patent rights of XIA XIA reserves the right to change the DGF product its documentation and the supporting software without prior notice Table of Contents i ON N ee l 1 1 FS AUS its aya Eege ATEN l PEOS a T T O eU 2 2 SENE U EE 3 2 1 DCODS Ol DOCUMEN EE 3 22 lasta haton sse aon lteter teat ob tb t Hia tur tua ad al bu ued Had uestis 3 22 Jat wagte Seis EE 3 22 LEE Ee 3 22 9 PAKS User Ue aCe ee ee 4 2 3 CS BUI e o EEEN EAE eegen 4 3 Navigating the Dixie EE 8 3 1 EEN 8 32 SODE S NE ONERE RENE NONE RENTRER TENERENT TONERS 8 3 3 E eaeentomerncte rar eee tat ba ur adam er OY apnd eee Mayr tea en eer ar eee myn pd 9 3 4 hime 10 39 AVON RM CR E E 10 3 6 Optimizing Paramet c usce ab Ue EOM cause PRI EDU E to oaa Pu a 11 ZO NOS CE 11 2 02 Teroy Brei EE 11 3 6 3 Threshold and Trigger Filter Parameter 12 3 0 4 VEER 12 4 Data Runs and Data Structures cete o on eege dee Cantus ences 14 4 1 RUN FV E 14 e
18. V1 61 XIA 2008 All rights reserved MCA histograms for all four channels You can deselect other channels while working on only one channel You can do a Gauss fit on a peak by entering values in the Min and Max fields as the limits for a Gauss fit You can also use the mouse to drag the Cursor A and B in the MCA spectrum to the limits of the fit Click Fit to select one or all channels and to perform the fit Enter the true energy value in the Peak field to calibrate the energy scale At this stage you may not be able to get a spectrum with good energy resolutions You may need to adjust some settings such as energy filter rise time and flat top etc as described in section 3 6 7 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved 3 Navigating the Pixie Viewer 3 1 Overview The Pixie Viewer consists of a number of graphs and control panels linked together by the main Pixie Run Control panel The Pixie Run Control panel is divided into 4 tabs corresponding to the 4 topics summarized below The Settings tab contains controls used to initialize the module and the file and directory settings The Calibrate tab contains controls to adjust parameters such as gain DC offset preamplifier decay time histogram control The Run tab is used to start and stop runs and in the Analyze tab are controls to analyze save and read spectra or event traces At the bottom of the panel is a More button which wil
19. ame action as a shaping amplifier The important difference is in the type of filter used In a digital application it is easy to implement finite impulse response filters and we use a trapezoidal filter The flat top will typically cover the rise time of the incoming signal and makes the pulse height measurement less sensitive to variations of the signal shape Secondly the RTPUs contain a pileup inspector This logic ensures that if a second pulse is detected too soon after the first so that it would corrupt the first pulse height measurement both pulses are rejected as piled up The pileup inspector is however not very effective in detecting pulse pileup on the rising edge of the first pulse 1 e 1n general pulses must be separated by their rise time to be effectively recognized as different pulses Therefore for high count rate applications the pulse rise times should be as short as possible to minimize the occurrence of pileup peaks in the resulting spectra If a pulse was detected and passed the pileup inspector a trigger may be issued That trigger would notify the DSP that there are raw data available now If a trigger was issued the data remain latched until the RTPU has been serviced by the DSP The third component of the RTPU is a FIFO memory which 1s controlled by the pile up inspector logic The FIFO memory is continuously being filled with waveform data from the ADC On a trigger it 1s stopped and the read pointer is positione
20. be wider by one filter clock cycle than that minimum but at least 3 filter clock cycles Note that a filter clock cycle ranges from 0 026 to 0 853us depending on the filter range so that it is not possible to have a very short flat top together with a very long filter rise time The Pixie Viewer provides a tool which automatically scans all possible combinations of energy filter rise time and flat top and finds the combination that gives the best energy resolution This tool can be accessed by clicking the Optimize button on the Settings tab Please refer to the Online Help documentation for more details 3 6 3 Threshold and Trigger Filter Parameters In general the trigger threshold should be set as low as possible for best resolution If too low the input count rate will go up dramatically and noise peaks will appear at the minimum edge of the spectrum If the threshold is too high especially at high count rates low energy events below the threshold can pass the pile up inspector and pile up with larger events This increases the measured energy and thus leads to exponential tails on the ideally Gaussian peaks in the spectrum Ideally the threshold should be set such that the noise peaks just disappear The settings of the trigger filter have only minor effect on the resolution However changing the trigger conditions might have some effect on certain undesirable peak shapes A longer trigger rise time allows the threshold to be lowered
21. ck master as shown in Figures 7 1 c and 7 2 c 1 e set one shunt to connect pins 2 and 3 on JP2 and a second shunt to connect Pinl of JP1 and JP2 together OUT to BUS The clock master will drive the clock signal to a line that is bussed to all others slots in the chassis The drive strength is limited to 3 4 modules All other modules should be configured as clock slaves 1 e set a shunt to connect pin 1 and 2 of JP2 BUS to clock input as shown in Figures 7 1 d and 7 2 d Note that the bussed clock line does usually not connect over a PCI bridge in chassis with more than 8 slots whereas daisy chains usually do Always make sure that there is no shunt on JP3 in order to disconnect from the incoming daisy chained clock else there will be a conflict between the two clock signals 7 1 4 PXI Clock Mode A further option for clock distribution 1s to use the PXI clock distributed on the backplane The PXI clock is driven by default by the PXI backplane at a rate of 10 MHz too slow to run the Pixie 4 modules However clock signals are individually buffered for each slot and clock skew between slots 1s specified to be less than Ins making it the preferred distribution path for sensitive timing applications If a custom backplane provides 37 5 MHz or if a module in slot 2 overrides the default signal from the backplane this clock can be used as an alternative setting for Pixie 4 modules Such a module can be a Revision C Pixie
22. d 7 Operating Multiple Pixie 4 Modules Synchronously When many Pixie 4 modules are operating as a system it may be required to synchronize clocks and timers between them and to distribute triggers across modules It will also be necessary to ensure that runs are started and stopped synchronously in all modules All these signals are distributed through the PXI backplane T 1 Clock Distribution In a multi module system there will be one clock master and a number of clock slaves or repeaters The clock function of a module can be selected by setting jumpers JP1 JP2 and JP3 near the back of the board Pin 2 of JP2 1s the input to the board s clock distribution circuitry It can be connected with a shunt to several other pins thus choosing a particular clock distribution mode The preferred clock distribution is the PXI clock mode is the chassis supports it else the daisy caned clock mode These jumpers differ slightly for modules of Revision B and Revision C D The clock functions themselves as described below are identical and compatible for both revisions Pixie 4 Revision B sg ES ee ee es LOC LOC PXI JP1 JP2 JP1 JP2 JP1 JP2 JP1 JP2 JP1 JP2 a Individual or b Clock c Bussed clock d Bussed clock e PXI clock clock master repeater mode master mode slave mode slave mode mode Figure 7 1 Jumper Settings for different clock distribution modes of Revision B modules In a group of modules there will be one daisy chained c
23. d such that it points to the 2 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved beginning of the pulse that caused the trigger When the DSP collects event data it can read any fraction of the stored waveform up to the full length of the FIFO 5 3 Digital Signal Processor DSP The DSP controls the operation of the Pixie 4 reads raw data from the RTPUs reconstructs true pulse heights applies time stamps prepares data for output to the host computer and increments spectra in the on board memory The host computer communicates with the DSP via the PCI interface using a direct memory access DMA channel Reading and writing data to DSP memory does not interrupt its operation and can occur even while a measurement is underway The host sets variables in the DSP memory and then calls DSP functions to program the hardware Through this mechanism all gain and offset DACs are set and the RTPUs are programmed in this way The RTPUS process their data without support from the DSP once they have been set up When any one or more of them generate a trigger an interrupt request 1s sent to the DSP It responds with reading the required raw data from the RTPUs and storing those in an intermediate buffer It then returns from the interrupt routine without processing the data to minimize the DSP induced dead time The event processing routine works from the data in the buffer to generate the requested output data There are differen
24. ectra for each channel are 16K long and compressed into the first 64K of the external memory The remaining 64K of the external memory contains a 256 x 256 bin two dimensional spectrum custom code required 4 2 2 List Mode Data The list mode data 1n external memory consists of 32 local I O data buffers The local I O data buffer can be written by the DSP in a number of formats User code should access the three variables BUFHEADLEN EVENTHEADLEN and CHANHEADLEN in the configuration file of a particular run to navigate through the data set It should only be read when the run has ended The 32 buffers in external memory follow immediately one after the other The data organization of one I O buffer is as follows The buffer content always starts with a buffer header of length BUFHEADLEN Currently BUFHEADLEN is six and the six words are Table 4 2 Buffer header data format 0 BUF NDATA Number of words in this buffer BUF MODNUM Module number Modulenumber 17 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved Following the buffer header the events are stored in sequential order Each event starts out with an event header of length EVENTHEADLEN Currently EVENTHEADLEN 3 and the three words are Table 4 3 Event header data format 0 EVT PATTERN Hit pattern Bit 15 0 gate pattern hit pattern status read pattern EVT TIMEHI Event time high word EVT TIMELO The hit patt
25. ed 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 Eqn 6 2 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 6 2 Trapezoidal Filtering in the Pixie 4 From this point onward we will only consider trapezoidal filtering as it is implemented in the Pixie 4 according to Eqn 6 2 The result of applying such a filter with Length L lus and Gap G 0 4us to a y ray event 1s shown in Figure 6 3 The filter output 1s clearly trapezoidal in shape and has a rise time equal to L a flattop equal to G and a symmetrical fall time equal to L The basewidth which 1s a first order measure of the filter s noise reduction properties is thus 2L G 26 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved This raises several important points in comparing the noise perfor
26. ed in a slot of the chassis for the first time it is detected as new hardware even if Pixie modules have been installed in other slots previously Point Windows to the driver files provides with the software distribution Drivers are installed but module does not boot The Modules require driver version 3 20 0 0 or 4 1 0 0 provided by XIA not 4 4 0 0 When starting the Pixie Viewer IGOR reports compile error For IGOR to start up properly a number of driver files have to be in the correct locations In particular the file pixie xop has to be located 1n the Igor Extensions folder usually C Program Files Wavemetrics gor Pro gor Extensions in a default installation When starting up modules in the Pixie Viewer downloads are not successful This can have a number of reasons Verify that The files and paths point to valid locations run the UseHomePaths macro The slot numbers entered in the Startup panel match the location of the modules After starting up modules the ADC traces show only rectangular waves This problem can be caused by downloading the wrong Communication FPGA file e g a Rev B file to a Rev C module Verify the file names are correct 44 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved 10 Appendix A This section contains hardware related information 10 1 Jumpers Table 9 1 Analog conditioning selection jumpers on Pixie 4 modules x 1 4 for channel 0 3 Remove only
27. ength Lf 0 1us and a gap Gr 0 1 us The slow filter has L 1 2us and G 0 35us Because the trapezoidal filter 1s a linear filter its output for a series of pulses is the linear sum of its outputs for the individual members in the series Pileup occurs when the rising edge of one pulse lies under the peak specifically the sampling point of its neighbor Thus in Figure 6 6 peaks 1 and 2 are sufficiently well separated so that the leading edge of peak 2 falls after the peak of pulse 1 Because the trapezoidal filter function is symmetrical this also means that pulse Us trailing edge 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 Peaks 2 and 3 which 30 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved are separated by less than 1 0 us are thus seen to pileup in the present example with a 1 2 us rise time This leads to an important point whether pulses suffer slow pileup depends critically on the rise time of the filter being used The amount of pileup which occurs at a given average signal rate will increase with longer rise times Because the fast filter rise time 1s only 0 1 us these y ray pulses do not pileup in the fast filter channel The Pixie 4 can therefore test for slow channel pileup by measuring the fast filter for the interval PEAKSEP after a pulse arrival time If no second pulse occurs in this interval then there is no t
28. ern 1s a bit mask which tells which channels were read out plus some additional status information as listed in table 4 4 After the event header follows the channel information as indicated by the hit pattern in order of increasing channel numbers For example if bits 3 0 1001 the event header is followed by data from channel 0 then channel 3 Table 4 4 Hit E bit description If set indicates that data for channel 0 3 have been recorded 4 Logic level of FRONT panel input 5 Result of LOCAL coincidence test 6 Logic level of backplane STATUS line 7 Logic level of backplane TOKEN line 7 result of global coincidence test see section 7 If set indicates that channel 0 3 has been hit in this event i e if zero energy reported is invalid or only an estimate 12 15 Logic level of the GATE input of channel 0 3 for rev D modules only The data for each channel are organized into a channel header of length CHANHEADLEN which may be followed by waveform data CHANHEADLEN depends on the run type and on the method of data buffering 1 e 1f raw data 1s directed to the intermediate Level 1 buffer or directly to the linear buffer Offline analysis programs should therefore check the value of RUNTASK which 1s reported 1n the buffer header All currently supported data formats are defined below 1 For List Mode or Fast List Mode either standard or compression 1 RUNTASK 256 257 512 or 513 CHANHEADLENCSO and the ni
29. fferent settings for different detectors and applications Parameter files are saved and loaded with the g PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved corresponding buttons in the Settings tab After loading a settings file the settings are automatically downloaded to the module At module initialization the settings are automatically read and applied to the Pixie module from the current settings file Internally the module parameters are handled as binary numbers and bitmasks The Settings tab gives access to user parameters in meaningful physical units Values entered by the user are converted by the Pixie Viewer to the closest value in internal units Refer to the Online Help for detailed descriptions of the parameters 3 3 Calibrate The Calibrate tab is used to calibrate or diagnose the system You can adjust the Gain and DC Offset on the channel by channel basis You can use the automatic Tau Finder routine to find the Decay Time of the preamplifier You can also control the histogram by setting the cut off energy and binning factor imi Pizxie4 Run Control E x Calibrate Run X Analyze Medie Ei Channei 0 Je Analog Signal Conditioning Decay Time Histogram Control I iain Vv 1 3144 TRUM Tau us 50 000 E AN tien ere Minimum Energy oS Offset v 0 9026 Binning Factor 1 Iei Figure 3 2 The Calibrate tab of the Pixie 4 Ru
30. he Pixie Control Panel If the pulses are 5 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved negative toggle the Trigger positive checkbox in the Channel CSRA Edit Panel which can be accessed by clicking on the Edit button next to Channel on the Settings tab Bele L n 0 053333 10 Li 0 053333 40 Le oss 10 Show Filters FFT Display BE H O 0S3333 10 C un E f Figure 2 3 Oscilloscope Panel with typical pulses from a pulser In the Calibrate tab input an estimated preamplifier exponential RC decay time for Tau and then click on Auto Find to determine the actual Tau value for the current channel of the current module Repeat this for other channels if necessary You can also enter a known good Tau value directly in the control Save the modified parameter settings to file To do so click on the Save button on the Settings tab to open a save file dialog Create a new file name to avoid overwriting the default settings file Click on the Run tab set Run Type to 0x301 MCA Mode Poll time to 1 second and Run time time out to 30 seconds or so then click on the Start Run button A spinning wheel will appear occasionally in the lower left corner of the screen as long as the system is waiting for the run to finish After the run is complete select the Analyze tab and click on the MCA Spectrum button The MCA spectrum shows the 6 PIXIE 4 User s Manual
31. he Pixie module 4 1 2 List Mode Runs If on the other hand you want to operate the Pixie in multi parametric or list mode and collect data on an event by event basis including energies time stamps pulse shape analysis values and wave forms you should start a list mode run In list mode you can still request histogramming of energies e g for monitoring purposes In the current standard software one pulse shape analysis value is a constant fraction trigger time calculated by the DSP the other is reserved for user written event processing routines Other routines exist to e g calculate rise times and or to characterize pulses from phoswich detectors 4 1 2 1 Compressed Data Formats The output data of list mode runs can be reduced by using one of the compressed formats described below The key difference is that as less data is recorded for each event there 1s room for more events in the I O data buffer of the Pixie 4 module and less time 1s spent per event to read out data to the host computer For example 1f you need individual energies and time stamps but no waveforms select energy and time only instead of general purpose in the Pixie Viewer In this mode raw data from the energy filters and waveforms are temporarily stored in an intermediate buffer and only results are written to the output buffer In compressed list mode runs the following points are to consider e When using a runtype that computes results of pulse sha
32. id conflicts in driving the backplane The option 1s enabled in software by setting the corresponding checkbox in the Pixie Viewer s Chassis Setup Panel Setting it for one module will automatically disable it for all other modules Each channel can be programmed individually to require the presence of a GFLT in order to latch event data This is achieved by setting the corresponding checkbox in the Pixie Viewer s Channel Control Register panel 7 5 External Status A second function for the Pixie 4 s front panel input is to contribute to a wired OR backplane line called Status Several modules can be enabled to contribute to the Status line The backplane status line will be logic 1 whenever the DSP OUT input of any enabled module is high 3 3V The status of this line is read as part of the event acquisition and is stored in the list mode data The third function for the Pixie 4 s front panel input is to contribute one Front bit in the event hit pattern If the front panel 1s not used as Veto or Status input this allows recording of an externally created logic level in each module individually For example each module may be assigned to a detector or radiation source that 1s enabled disabled individually and so the status of that detector 1s recorded in the event data stream Notes The front panel input can be used for Veto Status and Front at the same time if necessary The wired OR backplane lines are of type active
33. ier noise o as indicated in Figure 6 1 b 4 Preamp Output mV 0 00 0 02 0 04 0 06 a b Time ms Figure 6 1 a Charge sensitive preamplifier with RC feedback b Output on absorption of an y ray 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 6 1 b into either triangular or semi Gaussian pulses whose amplitudes with respect to their baselines are then proportional to V and thus to the y ray s energy Digital filtering proceeds from a slightly different perspective Here the signal has been digitized and is no longer continuous Instead it is a string of discrete values as shown in 24 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved Figure 6 2 Figure 6 2 is actually just a subset of Figure 6 1 b in which the signal was digitized by a Tektronix 544 TDS digital oscilloscope at 10 MSA megasamples sec 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 6 2 averages are computed over the two regions marked Length the Gap region is omitted because the signal is changing rapidly here and
34. if you require attenuation Attenuation will be 1 7 5 1f JPx02 1s set JPx02 Set for input impedance of 50Q If not set input impedance is 5KQ Revision B only Set to VGA to enable contributions of the variable gain amplifier to the overall system gain for fine tuning of the gain This might increase the signal noise and is currently not supported by software Table 9 2 On board jumper settings for the clock distribution on Pixie 4 modules Clock mode JP1 and JP2 PCB Reference single Module Connect pins 2 and 3 of JP2 not set LOC to IN Clock Master Clock Repeater Bussed Clock Connect pins 2 and 3 of JP2 not set LOC to IN Master Connect pinl JP1 to pin 1 JP2 OUT to BUS Bussed Clock Connect pins 1 and 2 of JP2 not set BUS to IN Slave Clock Slave with Connect pin2 JP1 to pin 2 JP2 not set PXI to IN PXI clock Clock Master for Connect pin2 JP1 to pin 2 JP2 not set PXI to IN PXI clock Connect pin3 JP to pin 3 JP2 LOC to BP Revision C only 45 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved 10 2 PXI backplane pin functions Table 9 3 Pins of the J2 backplane connector defined in the PXI standard used by the Pixie 4 Pins not listed are not connected except for pull ups to 5V recommended by the PXI standard number name revised in version 1 5 6 pC TRIGO Fast Trigger TRIG4 LBRS Right neighbor SE WEE eae GATE input channel 2 pec d 46 PIXIE 4 User s Manual V1 61 XIA 2008
35. ignal is driven low by the module that issues a trigger All other modules detect the lines being low and send the triggers to all channels In other words the backplane line carries a system wide trigger that essentially acts as a 5 input to the trigger OR in the Communication FPGA of each module Each module can be enabled to share triggers over the backplane lines or not In this way a trigger group can be extended over several modules or each module can form its local sub group 7 2 3 Trigger Distribution across PXI segment boundaries In PXI chassis with more than 8 slots the PCI bus as well as the PXI bussed backplane lines are divided into segments with not more than 8 slots While the PCI bus is bridged between the segments the PXI bussed backplane lines are usually only buffered from one segment to the next 1 e the line in one segment drives the line in the neighboring segment Since this buffer is essentially a one way communication though the direction may be selectable no wire OR can be build across the segment boundary Note Sometimes there is no connection at all For applications with more than 7 modules the Pixie 4 have to be operated in a chained OR mode where trigger signals are passed from module to module using the PXI nearest neighbor lines which are not interrupted by the segment boundaries In this mode each module ORs the trigger signal from its right neighbor with its own contributions and passes it to the
36. in a file with name extension set after each run if you select Auto store settings on the Record panel 3 5 Analyze The Analyze tab 1s used to investigate the spectrum or to view list mode traces It also shows the run statistics such as run time event rate and live time and input count rate for each channel You can perform Gauss fits on peaks to find the resolution and calibrate the energy 10 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved spectrum by entering a known energy value for a fitted peak You can also view individual event trace and its energy from a standard list mode run ioj xl Settings Calibrate Run X Analyze Module 0 i Chane J Hun Statistics Sun Time HI En Live Time E Input Count Rate cps me 0 6044 2594 ist Mode races 1 0 60845 3357 7 Event Rate eps 2840 2 List Mode Spectrum z 0 60856 0 3 0 60856 Update More Statistics H Figure 3 4 The Analyze tab of the Pixie 4 Run Control Panel 3 6 Optimizing Parameters Optimization of the Pixie 4 s run parameters for best resolution depends on the individual systems and usually requires some degree of experimentation The Pixie Viewer includes several diagnostic tools and settings options to assist the user as described below 3 6 1 Noise For a quick analysis of the electronic noise in the system you can view a Fourier transform of the incoming signal by selecting Oscil
37. ith adjustable threshold Rise time and flat top set independently from 26ns to 413ns Trigger Data Outputs Spectrum 1024 32768 channels 32 bit deep 4 2 billion counts bin Additional memory for sum spectrum for clover detectors Statistics Real time live time input and throughput counts Event data Pulse height energy timestamps pulse shape analysis results waveform data and ancillary data like hit patterns PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved 2 Setting Up 2 1 Scope of Document The scope of this document is Pixie 4 modules with serial numbers 105 through 129 Revision B serial numbers 130 through 249 Revision C and serial numbers 250 299 Revision D 2 2 Installation 2 2 4 Hardware Setup The Pixie 4 modules can be operated in any standard 3U CompactPCI or PXI chassis Chassis following only the CompactPCI standard can be used to operate modules individually To operate several modules together a backplane following the PXI standard has to be present Put the host computer or remote controller in the system slot of your chassis Place the Pixie 4 modules into any free slots with the chassis still powered down then power up the chassis Pixie 4 modules are not hot swappable If using a remote controller be sure to boot the host computer after powering up the chassis 2 2 2 Drivers When the host computer 1s powered up the first time after installing the controller and
38. l V1 61 XIA 2008 All rights reserved The ADC is not a peak sensing ADC but acts as a waveform digitizer In order to avoid aliasing we remove the high frequency components from the incoming signal prior to feeding it into the ADC The anti aliasing filter an active Sallen Key filter cuts off sharply at the Nyquist frequency namely half the ADC sampling frequency Though the Pixie 4 can work with many different signal forms best performance is to be expected when sending the output from a charge integrating preamplifier directly to the Pixie 4 without any further shaping 5 2 Real time Processing Units The real time processing units RTPUs one per two channels consist of a field programmable gate array FPGA which also incorporates a FIFO memory for each channel The data stream from the ADCs is sent to these units at the full ADC sampling rate Using a pipelined architecture the signals are also processed at this high rate without the help of the on board DSP Note that the use of one RTPU for two channels allows sampling the incoming signal at twice the regular ADC clock frequency If both channels are fed the same input signal the RTPU can give the second ADC a clock with a 180 degree phase shift thus sampling the signal twice in one clock cycle Special software 1s required to combine the two input streams into one contact XIA for details The real time processing units apply digital filtering to perform essentially the s
39. l make all advanced panel controls visible as well For initial setup and normal operation these controls are not important Below we describe the concepts and principles of using the Pixie Viewer Detailed information on the individual controls can be found in the Online Help for each panel 3 2 Settings The Pixie Viewer comes up in exactly the same state as it was when last saved to a file using File gt Save Experiment However the Pixie module itself loses all programming when it is switched off When the Pixie 1s switched on again all programmable components need code and configuration files to be downloaded to the module Clicking on the Start System button in the main Pixie Run Control panel performs this download imi Pixie4 Run Control E Biel x Settings Run Module oS Channel oS Filter File Tools en Pulse Shape Analysis Energy Filter Trigger Filter 1 Trace length us 4 000 Je WER sz Je oso Je Extract Delay us 1 000 Te Flat Top uz 173 Je open Je Registers E PSA Start us O e ax FFFE T ox 0084 Threshold 25 Je PSA End ps 0 000 e Figure 3 1 The Settings tab of the Pixie 4 Run Control Panel The Pixie 4 being a digital system all parameter settings are stored in a settings file This file is separate from the main IGOR experiment file to allow saving and restoring di
40. large coincidence window intentionally set by the user the value entered by the user is never decreased automatically Notes 1 Any added coincidence window width will increase the time required to process an event and thus reduce the maximum count rate 2 In run types 0x100 0x300 pulses contributing during the readout of data after the end of the coincidence window are lost The readout may take several microseconds longer if waveforms are to be recorded 3 The cut off at the end of the coincidence window 1s precise to within 13 3ns 2 Filter Range e g 100ns in range 3 7 6 2 NEW Coincidences Between Modules If more than one module is operated in the same PXI chassis acceptance of events can also be subject to the results of a system wide global coincidence test The result of the global test 1s distributed over the TOKEN backplane line This module coincidence test takes place in the following steps 40 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved 1 After receiving a valid event trigger and waiting for the user defined coincidence window each module sends its channel hit pattern to slot 2 of the chassis using the PXI STAR trigger line 2 Each module determines the result of the local coincidence test based on its own 4 channels If enabled to do so it signals the test result on the TOKEN line If the local test passed the TOKEN line is left pulled up 3 3V logic 1 else the TOKEN line is driven
41. legacy run type and only marginally faster slightly shorter dead time from event processing than a normal list mode run recording waveforms of zero length To make it faster a number of steps are omitted during data acquisition For example the live time and other run statistics are not updated during the run and no channel or module coincidences are tested Also at high count rate when the intermediate buffer for event processing fills faster with raw data than being emptied by the processing routine output data can be corrupted as checks for this condition are omitted It is therefore important to always keep the input rate below the average processing rate Table 4 1 Summary of run types and data formats Run Type DSP Variables List Mode Energies time stamps 6 PSA values and RUNTASK 256 standard wave forms in List mode block MAXEVENTS lt calculate gt Spectra in MCA block CHANHEADLEN 9 List Mode Energies time stamps and 6 PSA values in RUNTASK 257 Compression 1 List mode block MAXEVENTS calculate Spectra in MCA block CHANHEADLEN 9 List Mode Energies time stamps and 2 PSA values in RUNTASK 258 Compression 2 List mode block MAXEVENTS calculate Spectra in MCA block CHANHEADLEN 4 List Mode Energies and time stamps in List mode block RUNTASK 259 Compression 3 Spectra in MCA block MAXEVENTS lt calculate gt CHANHEADLEN 2 Fast List Mode Energies time stamps and 6 PSA val
42. line ADC waveform analysis l PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved e Digital constant fraction algorithm measures event arrival times down to a few ns accuracy e Supports 32 bit 33 MHz PCI data transfers 7100 Mbytes second 1 2 Specifications Front Panel I O Signal Input 4x 4 analog inputs Selectable input impedance 50Q and 5kQ 5V pulsed 2V DC Selectable input attenuation 1 7 5 and 1 1 Logic Input Output General Purpose I O connected to programmable logic Rev C D only Currently can be either used as input for global backplane signals Veto or Status or as an input for module specific logic level reported in the data stream determined waveform acquisition one for event triggers Global logic level from backplane used for coincidence tests Synch Wired or SYNC signal distributed through PXI backplane to synchronize timers and run start stop to 50ns Global logic level to suppress event triggering Channel Gate Individual GATE to suppress event triggering for each channel with use of PXI PDM Rev D only PCI 32 bit 33MHz Read Write memory readout rate to host over 100 Mbytes s Digital Controls Gain Analog switched gain from 0 97 to 11 25 in max 10 steps Digital gain adjustment of up to 10 in 15ppm steps Offset Shaping Digital trapezoidal filter Rise time and flat top set independently 27ns 109us in small steps Digital trapezoidal trigger filter w
43. local triggers to capture data In this way one channel can cause data to be acquired at the same time in all other channels of the trigger group The DSP then reads data from all participating channels and stores it as one event record Each channel trigger enabled or not always also generates a hit flag if pileup inspection was passed and DSP readout is conditional to this flag Even in group trigger mode some data 1s captured based on the channel s local trigger For example the pulse height of a pulse is best determined based on the trigger from the pulse itself not from a common group trigger that may be delayed if several channels in a group are trigger enabled always the ast fast trigger before the first event trigger 1n this event 1s the one that counts The following table lists which quantities are based on local or group trigger in group trigger mode If not in group trigger mode all quantities are based on local triggers Note that for the trigger timing to be correct all channels in a trigger group should be set to the same energy filter rise time and flat top Furthermore to capture the energy of delayed channels ensure that the coincidence window see section 7 6 1s long enough to include the maximum expected delay Bal Ben DO TL Hit and trigger Based on local trigger Based on last group trigger Based on last group trigger enabled unless local trigger only option selected Always read out Alwa
44. lock master a in the leftmost position and several repeaters b OR one bussed clock master c and several bussed clock slaves d Modes a b and c d can not be mixed Mode e can only be used with a backplane providing 37 5 MHz instead of the usual 10M Hz Jumper JP3 is located near the chip U2 it has no label 32 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved Pixie 4 Revision C D Left M JP3 B JP3 H JP3 H JP3 H JP3 k JP3 T ON T ON T ON T ON T ON T ON aA aA aA aA aA aA O LOC a Q O em u z z emm z a z sex F Ww 0 Oo d a a Individual b Clock c Bussed d Bussed e PXI clock f PXI clock or clock repeater clock master clock slave slave mode master mode master mode mode mode mode slot 2 only Figure 7 2 Jumper Settings for different clock distribution modes of Revision C modules In a group of modules there will be one daisy chained clock master a in the leftmost position and several repeaters b OR one bussed clock master c and several bussed clock slaves d OR one PXI clock master f in slot 2 and several PXI clock slaves e Modes a b c d or e f can not be mixed Mode e can also be used with a custom module in slot 2 or a backplane providing 37 5 MHz instead of the usual 10MHz 7 1 1 Individual Clock mode If only one Pixie 4 module is used in the system or if clocks between modules do not have to be synchronized the module should be set into individual clock mode as shown
45. loscope gt FFT Display in the Calibrate tab The graph shows the FFT of the untriggered input sigal of the Oscilloscope By adjusting the dT control in the Oscilloscope and clicking the Refresh button you can investigate different frequency ranges For best results remove any source from the detector and only regard traces without actual events If you find sharp lines in the 10 kHz to 1 MHz region you may need to find the cause for this and remove it If you click on the Apply Filter button you can see the effect of the energy filter simulated on the noise spectrum 3 6 2 Energy Filter Parameters The main parameter to optimize energy resolution is the rise time of the energy filter Generally longer rise times result in better resolution but reduce the throughput Optimization should begin with scanning the rise time through the available range Try 2us 4us 8us 11 2us take a run of 60s or so and note changes in energy resolution Then fine tune the rise time 11 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved The flat top usually needs only small adjustments For a typical coaxial Ge detector we suggest to use a flat top of 1 2us For a small detector 20 efficiency a flat top of 0 8us is a good choice For larger detectors flat tops of 1 2us and Tous will be more appropriate In general the flat top needs to be wide enough to accommodate the longest typical signal rise time from the detector It then needs to
46. mance of the Pixie 4 to analog filtering amplifiers First semi Gaussian filters are usually specified by a shaping time Their rise time 1s 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 rise time Thus a semi Gaussian filter typically has a slightly better energy resolution than a triangular filter of the same rise 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 rise time a bit so that the true triangular rise time 1s typically 1 2 times the selected semi Gaussian rise 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 rise time One 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 whose tails may persist up to 4096 of the rise 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 ADC units 9 5 10 0 10 5 11 0 11 5 12 0 12 bus Time Figure 6 3 Trapezoidal filtering of a preamplifier step with L 1us and G 0 4us 6 3 Baselines and Preamplifier Decay Times Figure 6 4
47. me for instance to accept any pattern with two or more channels If all checkboxes are set any possible Hit Pattern 1s acceptable and the Coincidence Pattern is OXFFFF Each channel with a pulse above threshold whether trigger enabled of not contributes to the hit pattern the moment the pulse is validated as not piled up e an energy filter time after rising edge of pulse The hit pattern 1s read for comparison with the coincidence pattern about 50 ns after the first pulse 1s validated If several channels contribute to an event the minimum coincidence window the time period in which delayed channels can contribute to the hit pattern is thus 50ns When sharing triggers over the backplane it takes longer to route the triggers to all modules so the minimum width is 300ns A difference in peaking times between channels will cause even channels with simultaneous pulses to contribute to he hit pattern at different times The Pixie Viewer thus calculates the required additional window width to compensate for any such difference displays it and ensures that the additional window width is at least this value If longer delays between channels are expected from the physics of the experiment this added width can be increased up to a value of 870 microseconds 16 bit counter If the required additional with 1s later decreased by reducing the difference in peaking times a smaller coincidence window 1s possible However to avoid modifying a
48. mer s Manual for details 37 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved 7 4 External Gate GFLT Veto It is common in larger applications to have dedicated external electronics to create event triggers or vetoes While the Pixie 4 does not currently accept an external fast trigger it does accept a global first level trigger GFLT This signal acts as a validation for an event already recognized by the Pixie 4 Based on multiplicities and other information the dedicated trigger logic needs to make the decision whether to accept or reject a given event If that decision can be made within a filter rise time of all Pixie 4 channels involved then the GFLT input can be used To accept signals the GFLT signal applied to the Pixie 4 must be logic 0 0V at the time when the event data are latched in the RTPUs This happens not before a filter rise time has passed since the event arrival and not later than a rise time plus the flat top Therefore the trigger logic should generate a GFLT pulse that is logic 0 during the filter flat top The GFLT signal 1s distributed through the PXI backplane Using XIA s PDM module or a custom board external signals can be connected to the backplane In addition the Pixie 4 front panel input labeled DSP OUT sic can be used to send the signal to the backplane The input signal must be LVTTL i e logic 0 OV logic 1 3 3V Only one module within a chassis may use this option to avo
49. n Control Panel The Calibrate tab also has an Oscilloscope button linking to a diagnostic graph The Oscilloscope shows a graph of ADC samples which are untriggered pulses from the signal input The time intervals between the samples can be adjusted for intervals greater than 0 147us the samples will be averaged over the interval The main purpose of the Oscilloscope is to make sure that the signal is in range in terms of gain and DC offset The Oscilloscope is also useful to estimate the noise in the system Clicking on the FFT Display button opens the ADC Trace FFT where the noise spectrum can be investigated as a function of frequency This works best if the Oscilloscope trace contains no pulses 1 e with the detector attached but no radioactive sources present 9 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved 3 4 Run The Run tab is used to start and stop runs There are two major run types List mode runs and MCA runs MCA runs only collect spectra List mode runs acquire data on an event by event basis List mode runs come in several variants Before you start a run you need to select the run type polling time the time interval for polling the run status run time for MCA runs and time out limit and the number of spills repeated runs for list mode runs WW Pixie4 Run Control ej Run Medie ei Channel 0 E Run Control l Synchronization Run type 0x100 General Purpose w Simultaneously star stop mod
50. nd future updates rely on this Feel free however to add folders and subfolders at your convenience 2 3 Getting Started To start the Pixie Viewer double click on the file Pixie4 pxp in the installation folder After IGOR loaded the Pixie Viewer the Start Up panel should be prominently displayed in the middle of the desktop Flease specify the modules Number of Pied Modules D Je Offline Analysis Start Up Sustem Help Figure 2 1 The Pixie 4 Start Up Panel 4 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved In the panel first select the number of Pixie 4 modules in the system Then specify the slot number in which each module resides Click on the Start Up System button to initialize the modules This will download DSP code and FPGA configuration to the modules as well as the module parameters If you see messages similar to Module 0 in slot 5 started up successfully in the IGOR history window the Pixie 4 modules have been initialized successfully Otherwise refer to the troubleshooting section for possible solutions If you want to try the software without a chassis or modules attached click on the Offline Analysis button After the system is initialized successfully you will see the main Pixie Control Panel from which all work is conducted The tabs in the Control Panel are arranged in logical order from left to right For most of the actions the Pixie Viewer interacts with one
51. ne words are Table 4 5 Channel header possibly followed by waveform data 0 LCHAN NDATA Number of words for this channel CHAN TRIGTIME 1 Fast trigger time 2 CHAN ENERGY Enmgy 3 CHAN XIAPSA XIAPSAvale 4 CHAN USERPSA User PSA value N A s SCHAN REALTIMEHI High word ofthe eal ine 18 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved Any waveform data for this channel would then follow this header An offline analysis program can recognize this by computing N WAVE DATA CHAN NDATA 9 If N WAVE DATA is greater than zero it indicates the number of waveform data words to follow In the current software version the XIA PSA value contains the result of the constant fraction trigger time computation CFD The format 1s as follows the upper 8 bit of the word point to the ADC sample before the CFD counted from the beginning of the trace The lower 8 bits give the fraction of an ADC sample time between the sample and the CFD time For example if the value is 0x0509 the CFD time is 5 9 256 ADC sample steps away from the beginning of the recorded trace For compression 2 List Mode or Fast List Mode RUNTASK 258 or 514 CHANHEADLEN 4 and the four words are Table 4 6 Channel header for compression 2 format CHAN_TRIGTIME CHAN ENERGY CHAN XIAPSA XIA PSA value CHAN USERPSA User PSA value For compression 3 List Mode or Fast List Mode RUNTASK 25
52. o digital conversion process the system is dead to other events which can severely reduce system throughput Even single channel analyzer 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 take the filter sums reconstruct the energy Vx and add it to the spectrum In the Pixie 4 the filter sums are continuously updated by the RTPU see section 5 2 and only have to be read out by the DSP when an event occurs Reconstructing the energy and incrementing the spectrum is done by the DSP so that the RTPU 1s ready to take new data immediately after the readout This usually takes much less than one filter rise time so that no system deadtime is produced by a capture and store operation This is a significant source of the enhanced throughput found in digital systems 3 32x10 31 30 ADC units 2 Time Figure 6 5 Peak detection and sampling in the Pixie 4 The peak detection and sampling in the Pixie 4 1s handled as indicated in Figure 6 5 Two trapezoidal filters are implemented a fast filter and a slow filter The fast filter is used to detect the arrival of y rays the slow filter is used for the measurement of Vx with reduced 29 PIXIE 4 User s Manual V1 6
53. of the chassis receiving hit patterns over the PXI STAR Trigger lines making a coincidence decision and signaling the result on the TOKEN line This can be XIA s PXI PDM module or any other compatible PXI module A limited coincidence decision can be made with Pixie 4 modules only e g one or more master modules inhibiting acquisition in all other modules based on their local hit pattern In the Pixie Viewer the module coincidence is configured in the Chassis Register Panel Fig 7 4 With the checkboxes in the Module Coincidence Setup block each module can be set to accept events if a only the local coincidence test is passed check local b only the global coincidence test 1s passed check global c either the local OR the global coincidence test 1s passed check global and local d the global test AND all relevant local tests pass check global and local adds to global Other checkboxes and controls define 1f a module sends its hit pattern to slot 2 if a module is writing the global coincidence control word to a neighboring PDM and the control word to write 4 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved W Chassis Register Panel Backplane Options Module Trigger share mode Front panel drives GFLT line fone module only Front panel contributes to STATUS line twire OR Module writes control pattern ta POM to immediate lett Send local hit pattern ta POM in slot 2 POM control patte
54. out time 4 1 2 3 Multiple Spills Runs can be resumed by the host after the data is read out In a resumed run run statistics are not cleared at the beginning of the run Le it is possible to combine several buffer readouts spills into one extended run In the Pixie Viewer this 1s done automatically when requesting several spills 15 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved Note that for runs with several modules the buffer ordering in the data depends on the readout option In mode 1 the data file begins with the first buffer readout of module 0 followed by first buffers of module 1 module 2 module N then the second buffers of modules 0 to N and so forth In readout mode 2 list mode runs are repeated 32 times before readout Therefore the data file will begin with the first 32 buffer readouts of module 0 followed by the first 32 buffers of module 1 module 2 module N then a second 32 buffers of module 0 to N and so forth In mode 3 list mode runs are repeated 16 times before readout Therefore the data file will begin with the first 16 buffer readouts of module 0 followed by the first 16 buffers of module 1 module 2 module N then a second 32 buffers of module 0 to N and so forth 4 1 3 Fast List Mode Runs In Fast List Mode data are collected on an event by event basis but waveforms are not read The output can again be stored in standard or compressed format This 1s mainly a
55. over detectors esses 43 LroublesBOOU f c actis edv netu quei e haus testo ng eene n RN m eue und iin metet 44 EE 44 EIER eg 45 EE ees 45 Pr backplane PIM TUNC et EE 46 Control and Status Register TEE 47 111 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved 1 Overview The Digital Gamma Finder DGF family of digital pulse processors features unique capabilities for measuring both the amplitude and shape of pulses in nuclear spectroscopy applications The DGF architecture was originally developed for use with arrays of multi segmented HPGe gamma ray detectors but has since been applied to an ever broadening range of applications The DGF Pixie 4 is a 4 channel all digital waveform acquisition and spectrometer card based on the CompactPCT PXI standard for fast data readout to the host It combines spectroscopy with waveform digitizing and on line pulse shape analysis The Pixie 4 accepts signals from virtually any radiation detector Incoming signals are digitized by 14 bit 75 MSPS ADCs Waveforms of up to 13 us in length for each event can be stored in a FIFO The waveforms are available for onboard pulse shape analysis which can be customized by adding user functions to the core processing software Waveforms timestamps and the results of the pulse shape analysis can be read out by the host system for further off line processing Pulse heights are calculated to 16 bit precision and can be binned into spectra with up to 32
56. pe analysis PSA computations make sure the total combined trace length from all four channels is less than 52 l4 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved microseconds because the intermediate buffer used to temporarily store the trace data 1s limited to 4k samples e If no PSA is required reduce the trace length to zero to avoid unnecessary data transfer time e When the intermediate buffer is filled with events not yet processed for output data new events are reyected Whenever a new event occurs the DSP first checks if there is enough room left in the intermediate buffer then transfers the data from the FPGAs into its intermediate buffer or rejects it Consequently if the combined trace length is more than 26 microseconds only one event at a time can be stored This means that the effective dead time for an event is increased by the processing time If the combined trace length is such that N gt 2 events fit into the intermediate buffer the processing time does not add to the dead time as long as the average event rate 1s smaller than the processing rate and no bursts of more than N events occur 4 1 2 2 Data Readout Options List mode runs halt data acquisition either when the local I O data buffer is full or when a preset number of events are reached The data has then to be read out by the host PC Runs can be resumed for longer data acquisitions as described in 4 1 2 3 There are three options for the da
57. pt behind time variant filters is that since the y rays arrive randomly and the lengths between them vary accordingly one can make maximum use of the available information by setting the length to the interpulse spacing In principal the very best filtering 1s 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 W sets on a pulse by pulse basis The Pixie 4 takes a different approach because it was optimized for very high speed operation It implements a fixed length filter with all W values equal to unity and in fact l computes this sum afresh for each new signal value k Thus the equation implemented is Wms TK 6 2 i k 2L G 1 i k L 1 where the filter length is Land the gap is G The factor L multiplying V arises because the sum of the weights here is not normalized Accommodating this factor 1s trivial 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 industry s standard for high rate processing In the second place one can show theoretically that 1f the noise in the signal is white De Gaussian distribut
58. railing edge pileup PEAKSEP is usually set to a value close to L G 1 Pulse 1 passes this test as shown in Figure 6 6 Pulse 2 however fails the PEAKSEP test because pulse 3 follows less than 1 0 us Notice by the symmetry of the trapezoidal filter if pulse 2 1s rejected because of pulse 3 then pulse 3 is similarly rejected because of pulse 2 6 5 Filter Range To accommodate the wide range of filter rise times from 0 053 us to 106 us the filters are implemented in the RTPUs or FPGA configurations with different clock decimations filter ranges The ADC sampling rate is always 13 3ns but in higher clock decimations several ADC samples are averaged before entering the filtering logic In filter range 1 2 samples are averaged 2 samples in filter range 2 and so on Since the sum of rise time and flat top is limited to 127 decimated clock cycles filter time granularity and filter time are limited to the values are listed in Table 6 1 Table 6 1 RTPU clock decimations and filter time granularity Filter granularity 1 0 0267 1s 3 387 us 0 0533us 0 08us 2 0 533us 6 773us 0 1067us 0 16us 4 0213us 2709s Lies 064us 5 042607 54187us 08533ps 1 28ps 6 08533us 108 373 ss All filter ranges are implemented in the same FPGA configuration Only the FILTERRANGE parameter of the DSP has to be set to select a particular filter range 3 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserve
59. rn SUUUU OxO000 UU Module Coincidence Setup Module di T Accept event if local hit pattern passes local test LJ LJ LJ al Accept event if global hit pattern passes global test fin POW LJ LJ LJ Module s local test adds to global test local fail causes global fail LJ LJ LJ Coincidence Pattern for local test rom Module Register BEES EE STR Ts E Use Ree Coincidence Window far both tests fram Module Register 13 13 13 gt Figure 7 4 Module coincidence setup in the Pixie Viewer Examples 1 To require a local coincidence of channels 0 1 2 3 or both as above set the coincidence pattern to 0x9008 in the ModuleRegisterPanel and check only the local test box in the Chassis RegisterPanel 2 To require coincidence of channels 0 and in Module 0 and no other channel module matters in the ModuleRegisterPanel set the coincidence pattern in Module 0 to 0x8888 and in all other modules to OxFFFF In the Chassis Register Panel check the global test box for all modules and the local adds to global box for module 0 No PXI PDM is required 3 To require at least 3 channels to be active in all modules use a PDM module in slot 2 and set the PDM control pattern to 0x0013 for the module in slot 3 Make sure the Module writes control pattern box 1s checked for this module and the Send local hit pattern to PDM box is checked for all modules Then check the global test box for all modules 42 PIXIE 4 User s Manual V1 61
60. s the Optimize routine Similar to the routine for finding the optimal energy filter times this routine can be used to automatically scan a range of decay times and find the optimal one Please refer to the Online Help documentation for more details 13 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved 4 Data Runs and Data Structures 4 4 Run Types There are two major run types MCA runs and List mode runs MCA runs only collect spectra List mode runs acquire data on an event by event basis but also collect spectra List mode runs come in several variants see below The output data are available in three different memory blocks The multichannel analyser MCA block resides in memory external to the DSP There is a local I O data buffer for list mode data located in the DSP consisting of 8192 16 bit words and an extended I O data buffer for list mode runs in the external memory holding up to 32 local buffers 4 1 1 MCA Runs If all you want to do 1s to collect spectra you should start an MCA run For each event this type of run collects the data necessary to calculate pulse heights energies only The energy values are used to increment the MCA spectrum The run continues until the host computer stops data acquisition either by reaching the run time set in the Pixie Viewer or by a manual stop from the user the module does not stop by itself Run statistics such as live time run time and count rates are kept in t
61. shows an event over a longer time interval and how the filter treats the preamplifier noise in regions when no y ray pulses are present As may be seen the effect of the filter 1s 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 from which the y ray peak amplitude V is to be measured The fluctuations in the baseline have a 27 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved standard deviation o which is referred to as the electronic noise of the system a number which depends on the rise time of the filter used Riding on top of this noise the y ray peaks contribute an additional noise term the Fano noise which arises from statistical fluctuations in the amount of charge Qx produced when the y ray is absorbed in the detector This Fano noise or adds in quadrature with the electronic noise so that the total noise o in measuring V 1s found from oi sqrt of oe 3 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 contribution should be essentially negligible Achieving this in the mixed analog digital environment of a digital pulse processor is a non trivial task however 32 31
62. ssibly to obtain energy estimates on piled up pulses 35 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved Note that since the timing of the group trigger is not precise with respect to the non triggering pulse the energy reported is only a rough estimate It might help to set the flat top time to a large value to make the capturing of the energy filter less time sensitive Waveforms The waveforms are always captured based on the last group trigger for this event Channels without hit are read out only if the read always option is set for this channel Timestamp Normally in acquisitions with shared group triggers all channels record the identical timestamp of the last group trigger for this event Since waveforms are captured based on the group trigger this ensures that within a data record traces and timestamps are correlated However if no waveforms are recorded there 1s no time of arrival information of possible delays between channels from the timestamps alone In this case setting the local trigger only option a module wide option preserves the time difference information by recording timestamps for each channel based on its local trigger only 7 2 2 Trigger Distribution Between Modules Both fast triggers and event triggers can also be distributed over the PXI backplane Each trigger uses a common backplane line for all modules which is set up to work as a wired OR Normally pulled high the s
63. t implementations of the intermediate buffer for the different run types In standard list mode runs intermediate and I O buffer are the same to avoid moving long waveforms inside the DSP In other run types the intermediate buffer 1s circular old data 1s overwritten once it has been processed If the circular buffer fills up before the data can be processed no further raw data 1s read from the RTPUs In this scheme the greatest processing power is located in the RTPUs Implemented in FPGAs each of them processes the incoming waveforms from its associated ADC in real time and produces for each valid a event a small set of distilled data from which pulse heights and arrival times can be reconstructed The computational load for the DSP is much reduced as it has to react only on an event by event basis and has to work with only a small set of numbers for each event 5 4 PCI Interface The PCI interface through which the host communicates with the Pixie 4 is implemented in a PCI slave IC together with an FPGA The configuration of this PCI IC is stored in a PROM which is placed in the only DIP 8 C socket on the Pixie 4 board The interface conforms to the commercial PCI standard It moves 32 bit data words at a time The interface dos not issue interrupt requests to the host computer Instead for example to determine when data is ready for readout the host has to poll a Control and Status Register CSR in the communication FPGA 22 PIXI
64. ta readout mode with different consequences for the readout dead time Modes 2 and 3 are only available for module revisions C and D 1 The default readout option available for all module revisions is to simply fill and read the local I O buffer However data readout from the local I O buffer is relatively slow and since acquisition is halted during the readout the readout dead time is relatively large 30ms per module and buffer 2 A more efficient readout mode is to transfer the data is to the external memory when the local buffer is full and resume the run right away This 1s repeated 32 times until the external memory is full and only then the run is halted and data is read out by the host PC in a fast block read 30ms per 32 buffers and module about 550us between buffers 3 A third readout mode is to transfer the data 1s to the external memory when the local buffer 1s full and resume the run as 1n mode 2 but after 16 times a flag 1s raised to the host PC to read out the external memory while new data 1s stored in the other half of the external memory This allows almost uninterrupted data acquisition Readout dead time between buffers is about 550 us and readout time for 16 buffers is again 30ms Note that at high cont rates and or for uncompressed data runs with long waveforms 16 buffers may fill up faster than 30ms Readout mode 3 is only efficient as long as the time to half fill the external memory 1s longer than the read
65. their difference taken as a measure of Vx Thus the value V may be found from the equation V 2 WV WV 6 1 i before i after 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 e e e etm SS Ta Kapen m Length Gap Preamp Output mV 20 22 24 26 28 30 Time us Figure 6 2 Digitized version of the data of Figure 6 1 b in the step region The primary differences between different digital signal processors lie in two areas what set of weights 1W is used and how the regions are selected for the computation of Eqn 6 1 Thus for example when larger weighting values are used for the region close to the step while smaller values are used for the data away from the step Eqn 6 1 produces cusp like filters When the weighting values are constant one obtains triangular 1f the gap 1s zero or trapezoidal filters The concept behind cusp like filters 1s that since the points nearest the step carry the most information about its height they should be most strongly weighted in the averaging process How one chooses the filter lengths results in time variant the lengths vary 25 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved from pulse to pulse or time invariant the lengths are the same for all pulses filters Traditional analog filters are time invariant The conce
66. ues in RUNTASK 512 standard List mode block MAXEVENTS lt calculate gt Spectra in MCA block CHANHEADLEN 9 Fast List Mode Energies time stamps and 6 PSA values in RUNTASK 513 Compression 1 List mode block MAXEVENTS lt calculate gt Spectra in MCA block CHANHEADLEN 9 Fast List Mode Energies time stamps and 2 PSA values in RUNTASK 514 Compression 2 List mode block MAXEVENTS lt calculate gt Spectra in MCA block CHANHEADLEN 4 16 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved Fast List Mode Energies and time stamps in List mode block RUNTASK 515 Compression 3 Spectra in MCA block MAXEVENTS calculate CHANHEADLEN 2 MCA Mode Spectra in MCA block RUNTASK 769 MAXEVENTS 0 4 2 Output Data Structures 4 2 1 MCA Histogram Data The MCA block is fixed to 32K words 32 bit deep per channel 1 e total 128K words The MCA block resides in the external memory which can be read out via the PCI data bus at rates over 100Mbytes s If spectra of less than 32K length are requested only part of the 32K will be filled with data This data can be read even when a run is in progress to get a spectrum update In clover mode spectra for each channel are 16K long and compressed into the first 64K of the external memory An additional 16K addback spectrum containing the sum of energies in events with multiple hits is accumulated m the second 64K of the external memory In 2D mode sp
67. ules Stal Pun Run time fe 10000 00 l Pell Time d 0 10 Je SOS olone EN he TE List mode spill settings Output File Ema Humber of spills ooo Timeout z enn Je _ 32 buffers per spill Deed Events buffer L1 OR double butters Run number 2 Je Figure 3 3 The Run tab of the Pixie 4 Run Control Panel In a multi module system you can set all modules to start and stop simultaneously and to reset the timers in all modules with the start of the next data acquisition run by selecting the two options in the Synchronization group You can choose a base name and a run number in order to form an output file name The run data will be written to a file whose name is composed of both The run number is automatically incremented at the end of each run if you select Auto update run number on the Record panel but you can set it manually as well Data are stored in files in either the MCA folder if the run is a MCA run or the PulseShape folder if the run is a List mode run These files have the same name as the output file name but different extension For list mode runs buffer data are stored in a file with name extension bin For both list mode runs and MCA runs MCA spectrum data are stored in a file with name extension mca if you select Auto store spectrum data on the Record panel Module settings are stored
68. w At the end of the initialization the DSP enters a waiting loop and allows the SYNC line to be pulled high by pullup resistors As long as at least one of all modules 1s still in the initialization the SYNC line will be low When all modules are done with the initialization and waiting loop the SYNC line will go high The low gt high transition will signal the DSP to break out of the loop and begin taking data If the timers in all modules are to be synchronized at this point set the variable INSYNCH to 0 by checking the corresponding checkbox in the Run tab of the Pixie Viewer This instructs the DSP to reset all timers to zero when coming out of the waiting loop From then on they will remain in synch if the system 1s operated from one master clock Whenever a module encounters an end of run condition and stops the run it will also drive the SYNC line low This will be detected in all other modules and in turn stop the data acquisition Note that 1f the run synchronization 1s not operating properly and there was a run start request with SYNCHWAIT 1 the DSP will be caught in an infinite loop This can be recognized by reading the variables INSYNCH and SYNCHWAIT If after the run start request the DSP continues to show INSYNCH 0 and SYNCHWAIT 1 it is stuck in the loop waiting for an OK to begin the run Besides rebooting there is a software way to force the DSP to exit from that loop and to lead it back to regular operation See the Program
69. wer up the system again chassis first 7 Windows will detect new hardware the Pixie 4 modules and should find the drivers automatically If not direct it to the drivers directory in the Pixie 4 3 PIXIE 4 User s Manual V1 61 XIA 2008 All rights reserved software distribution installed in step 5 Verify in Window s device manager that the modules are properly installed as Custom OEM PCI 9054 Boards and have no resource conflicts Currently the driver must be version 4 1 2 2 3 Pixie User Interface The Pixie Viewer XIA s graphical user interface to set up and run the Pixie 4 modules is based on WaveMetrics IGOR Pro To run the Pixie Viewer you have to have IGOR Version 4 0 or higher installed on your computer By default the IGOR Pro should be installed at C Program Files WaveMetrics IGOR Pro Folder The CD ROM with the Pixie 4 software distribution contains 1 an installation program Setup exe 2 the Pixie 4 software in the folder XIA Pixie4 and its subfolders The Pixie 4 software can be installed by running its installation program Follow the instructions shown on the screen to install the software to the default folder selected by the installation program or to a custom folder This folder will contain the IGOR control program Pixie4 pxp online help files and 5 subfolders Configuration DSP Firmware MCA and PulseShape Make sure you keep this folder organization intact as the IGOR program a
70. ys read out Always read out Hit but not Based on local trigger Based on last group trigger Based on last group trigger trigger enabled unless local trigger only option selected Always read out Always read out Always read out Not hit Based on group trigger if Based on last group trigger Based on last group trigger no pulse or estimate energy option unless local trigger only pileup selected else zero option selected Only read if read Only read if read always Only read if read always always option selected option selected option selected Energy The pulse height of a pulse 1s best determined based on the trigger from the pulse itself not from a common group trigger that may be delayed Even if a channel is not trigger enabled energy filter values are latched some time after the local trigger filter crosses the user defined threshold The channel 1s then marked as hit for the DSP to read out Even channels without hit are read out 1f the read always option is set for this channel In this case the channel s energy is usually reported as zero since there was no valid local trigger to capture the value of the energy filter However since the energy filter is computed continuously setting the estimate energy option cause the energy filter value to be captured based on the last group trigger This might be useful for channels with occasional very small pulses below the threshold or po

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