SMIQB60 Arbitrary Waveform Generator for SMIQ
Contents
1. 0 0 20 201 20 20 oo A0 40 40 40 60 60 60 60 80 a 80 80 0 10 oo wm 0 10 0 T MHz Fig 2 12 Building a sinewave with SMIQB60 Upper row time domain Lower row frequency domain In Fig 2 12 the function principle is shown for a 1 MHz sinewave signal In the leftmost figure the 1 MHz sinewave and the aliasing products resulting from the sample rate of 3 MHz are shown The digital interpolation filter suppresses parts of the aliasing products which leads to a higher effective sample rate and therefore more values in the time domain The D A conversion weights the signal with a sin fsampie fsampe function The analog filter suppresses the remaining aliasing products The interpolation filter technique significantly saves memory It usually leads to lower oversampling values than with conventional ARBs The interpolation filter is designed in a way that it starts suppressing at 0 375 fsampe See Fig 2 13 The sample rate fsampie is set by Choosing an oversampling value O aS fsampie O fsym where the symbol rate of the 7 Rohde amp Schwarz SM IQB60 Arbitrary Waveform Generator modulated signal is defined by the application Choosing O sets both the sample rate and the passband range of the interpolation filter Fig 2 13 Schematic characteristics of the interpolation filter in SMIQB60 In general oversampling has to be selected so that the bandwidth of the int2. PEY me 1125 5555 03 Wie 230m SMA 038 gt ROHDE amp SCHWARZ SIGNAL GENERATOR soon a WCOMAS SUE F200 000 000 0 fee 2 000 000 000 0 o i Br f n x W gt Ld 2 4 4 o a C i hy WN W Products Vector Signal Generator SMIQ SMIQB60 Arbitrary Waveform Generator for SMIQ Application Note The SMIQB60 option is an internal two channel arbitrary waveform generator based on the modulation coder SMIQB20 SMIQB60 uses an innovative interpolation filter technique to increase memory capacity Waveforms can be calculated and transmitted with the external PC Software WinlQSIM and stored in the non volatile memory of SMIQ Stored waveforms can be recalled by SMIQ without using WinlQSIM ROHDE amp SCHWARZ Subject to change Dr Ren Desquiotz Hans J rg Strufe 08 2002 1GP45_ 1E Contents 1 Introduction 1GP45_1E SM IQB60 Arbitrary Waveform Generator AOU CUON erna E E E AAE 2 Function Principles of SMIQB60 0 ccc cc ec cce ee cceceeeeeeneeeeaneeeeans 3 Conventional arbitrary waveform generators cccccceeeeeeee sees 3 Functioning of an interpolation filter eccceeseeceeaeeeeeaeees 4 SMIQEGO CONCEDE ssccceccccosusncnsesxedeccncusdianaseeyceackexeniestitestouyiveatewetaveoeh T SMIQBGO OPEratON o 2 2cdb dcstateseseendsenasdaiessecemndasaeohuaoacaniusareeneasinensiaiane 10 Generating waveforms with WinlQSIM sssssannnnsssnrnn
3. by I t coswyt Q t 1 sin wast y with lt lt 1 This leads to the following result for the RF signal s t COS Wo i Was t Asin wo WM t o where the second term describes the spurious signals The parameters A are A tango a IG bo A and can be obtained from the data sheet values for imbalance magnitude and group delay They depend on the frequency offset from the 13 Rohde amp Schwarz SM IQB60 Arbitrary Waveform Generator center frequency The resulting expected spurious signals are shown in Fig 3 6 Actually the typical performance of SMIQB60 is far better when the SMIQB60 and Q outputs are calibrated For a well calibrated unit image suppression values of 50 to 60 dB can be achieved for offsets up to 10 MHz see Fig 3 6 REW 30 kHz RF Att 20 dB Ref Lvl VBW 2 kHz Mixer 20 dBm 0 dBm SWT 1 05 s Unit 58 dB pected spurious xp r data sheet values L nay Wu Center 2 GHZ 2 5 MHz Span 25 MHz l in O Eue eE a er if fag E FARK ENNR E Date 6 AUG 2002 14 53 33 Fig 3 6 Typical image suppression values of SMIQB60 with the improvements measured with a CW multi carrier signal 24 carriers 500 kHz spacing all placed above the center frequency In this example an image suppression of 58 dB is obtained for freque
4. market Option SMIQK15 covers several OFDM based standards such as HiperLAN 2 and WLAN 802 11a The option contains the WinlQOFDM software for calculating OFDM signals WinlIQOFDM is used together with WinlQSIM Option SMIQK16 covers the WLAN standard IEEE802 11b 1xEV DO option SMIQK17 is an enhanced version of the 1x mode of the North American standard cdma2000 for the third generation mobile radio 3G 1xEV DO stands for cdma2000 1x Mode Evolution Data Only This enhanced version of the cdma2000 standard allows packet oriented data transmission at a data rate of up to 2 4 Mbps in the 1 25 MHz wide cdma2000 1x channel Option SMIQK18 contains the WLAN standard IEEE802 1 1a All those signals can be calculated with WinlQSIM WinlQOFDM for OFDM right away However the keycode options are required if the signals are downloaded to SMIQB60 18 Rohde amp Schwarz SM IQB60 Arbitrary Waveform Generator GG Basic unit FJ Hardware option J Software option Fig 5 1 Excerpt from SMIQ options map SMIQB60 and related options 1GP45_1E 19 Rohde amp Schwarz SM IQB60 Arbitrary Waveform Generator 6 Software cal_igskew tor SMIQB60 Calibration 1GP45_1E New SMIQ units delivered with firmware 5 85 HX or later are calibrated in the factory to obtain the improved dynamic range with SMIQB60 SMIQs with SMIQB6O0 delivered before the release of firmware 5 85HX can be calibrated with the cal_iqgskew software to get the i
5. 7 References SM IQB60 Arbitrary Waveform Generator 1 2 Vector Signal Generator SMIQ Data Sheet Rohde amp Schwarz 2002 PD 757 2438 25 Vector Signal Generator SMIQ Operating Manual Rohde amp Schwarz 2002 PD 1125 5610 12 8 Ordering information Vector Signal Generator R amp S SMIQ02B 300 kHz to 2 2 GHz 1125 5555 02 R amp S SMIQ03B 300 kHz to 3 3 GHz 1125 5555 03 R amp S SMIQO03HD 300 kHz to 3 3 GHz 1125 5555 33 R amp S SMIQ04B 300 kHz to 4 4 GHz 1125 5555 04 R amp S SMIQO6B 300 kHz to 6 4 GHz 1125 5555 06 R amp S SMIQO6ATE 300 kHz to 6 4 GHz 1125 5555 26 Options R amp S SMIQB11 Data Generator 1085 4502 04 R amp S SMIQB12 Memory Extension 1085 2800 04 R amp S SMIQB20 Modulation Coder 1125 5190 02 R amp S SMIQB60 Arbitrary Waveform Generator 1136 4390 02 WinlQSIM options incl WinlQSIM R amp S SMIQK11 Digital Standard IS 95 option 1105 0287 02 SMIQB60 required R amp S SMIQK12 Digital Standard cdma2000 1105 0435 02 option SMIQB60 required R amp S SMIQK13 Digital Standard WCDMA 1105 1231 02 Mode TDD 3GPP option SMIQB60 required R amp S SMIQK14 Digital Standard TD SCDMA 1105 1383 02 option SMIQB60 required R amp S SMIQK15 OFDM Signal Generation 1105 1531 02 option SMIQB60 required R amp S SMIQK16 Digital Standard IEEE 802 11b 1154 7700 02 option SMIQB60 required R amp S SMIQK17 Digital Standard 1xEV DO 1154 7800 02 option SMIQB60 required R amp S SMIQK18 Digital Standard IEE
6. E 802 11a 1154 7952 02 option SMIQB60 required ROHDE amp SCHWARZ ROHDE amp SCHWARZ GmbH amp Co KG MuhldorfstraRe 15 D 81671 M nchen P O B 80 14 69 D 81614 M nchen Telephone 49 89 4129 0 Fax 49 89 4129 13777 Internet http www rohde schwarz com This application note and the supplied programs may only be used subject to the conditions of use set forth in the download area of the Rohde amp Schwarz website 1GP45_1E 23 Rohde amp Schwarz
7. ER Hi BERT 2 rg OUTPUT OM TIME 1 LF OUTPUT CCDF P S OFF TIME 1 Fig 3 4 Trigger settings in ARB menu of SMIQ For example to generate a slot trigger for a W CDMA signal with 3 84 Mcps the following values have to be set tsiot Slot time tchip Chip time ta Sample time OV Oversampling A W CDMA frame is 10 ms long As this system has 15 slots each slot has a length of 666 67 us The chip rate multiplied by the frame length gives the number of chips per frame 38400 This divided by the number of slots gives the value for chips per slot 2560 OV 2 tchip OV ta siot 2560 e tcnip gt tst 5120 ta On Time 500 for example gt Off Time 5120 On Time 4620 The trigger signals can be delayed with respect to the waveform by setting the parameter TRIGGER OUT 1 or 2 DELAY in the ARB menu This can be used for compensating different delay times for the signal and control paths of a measurement setup for example Start I l On Time l Off Time 1 Delay Fig 3 5 Trigger delay on and off times for SMIQB60 trigger 12 Rohde amp Schwarz 1GP45_1E SM IQB60 Arbitrary Waveform Generator Dynamic range From SMIQ firmware 5 85HX the dynamic range of SMIQB60 has been improved significantly Extended calibration gives better image suppression This has advantages for the following applications e improved Error Vector Magnitude EVM for IEEE 802 11a e improved Error Vector Magnit
8. Output gt gt Ae gt Converter gt 45kHz 12MHz gt Amgifier DSP TRIGOUT_1 D gt Trigger Unt gt TRIGOUT_2 DATAIN TRIGGERIN Fig 2 14 Basic block diagram of SMIQB6O0 The I Q samples are loaded by the host computer via the DATA IN interface to the DSP which passes them into a non volatile FLASH RAM The latter is organized in 22 blocks of 64ksamples each At least one block is occupied by each waveform If a waveform is selected the I Q samples are loaded into the output memory They are convolved with a correction filter which compensates in particular the Si frequency response of the D A converter The maximum absolute value of the I Q output signal is 0 5 V at 50 Q 0 dB in Normal mode This is the nominal output of the I Q modulator The output level can be varied in Manual mode between 6 dB and 3 dB in order to optimize the ACP in various channel offsets For measurements in alternate channels the output signal can be increased above OdB to slightly overdrive SMIQ s I Q modulator This may produce more intermodulation distortion but intermodulation will mostly affect the adjacent channels In ther alternate channels the performance will be better because signal to noise ratio is increased The range above 0 dB is not specified signal frequencies above 10 MHz may lead to a limitation The internal calibration of the SMIQB60 which is performed automatically with calibration of the vector modulation corre
9. automatic calibration fails or does not work try the manual calibration instead During the calibration process cal_iqskew gives a status report in a separate window Manual calibration This function gets up all the necessary SMIQ settings however the spectrum analyzer is not set Use this function for analyzers that are not covered by the automatic calibration Start the function by clicking on the Manual Calibration button Then set your analyzer so that you can see the signal output of the SMIQ and the residual sidebands Recommended settings are Center Frequency 2 0 GHz Span 30 MHz Reference Level 10dBm 21 Rohde amp Schwarz SM IQB60 Arbitrary Waveform Generator set the resolution and video bandwidth of the analyzer so that you can clearly identify the carriers of the test signal and the residual sidebands see the diagram in Fig 6 3 Manual Calibration Watch the SMIG output with an analyzer and adjust the IQ skew value below such that the residual sideband carers are minimized Analyzer settings Center Frequency 2 0 GHz Span 30 MHz Ref Level 10 dEm Peery vi rl ee ee MTTtii a ia vv 6 LiL Store Calibration Data Close Fig 6 3 Manual calibration with cal_iqskew Set the parameter IQ Skew so that the sidebands are minimized Then click on the Store Calibration Data button to store the calibration value Quit Exits the program 1GP45_1E 22 Rohde amp Schwarz
10. cts offset and gain errors to a minimum 9 Rohde amp Schwarz SM IQB60 Arbitrary Waveform Generator 3 SMIQB60 Operation 1GP45_1E Generating waveforms with WinlQSIM SMIQB60 is supported by WinlQSIM from version 3 30 Waveforms can be loaded via the IEC IEEE bus into the FLASH memory an individual Operating menu can set numerous SMIQ parameters WinlQSIM provides predefined settings for bit and symbol clock for generating trigger signals slot and frame trigger and the restart signal for the Bit Error Rate Tester SMIQB21 Waveforms generated for AMIQ can also be loaded into SMIQB60 Calculating signals in WinlQSIM works as usual see the WinlQSIM user manual or online help system for details Communication with SMIQB6O0O is done via the SMIQ ARB menu The different functions of this menu are also described in the WinlIQSIM documentation Here we shall only mention two functions If the waveform contains too many samples for the SMIQB60 RAM WinlQSIM gives a warning when the transmission to SMIQB60 is started e If the original oversampling value is bigger than 2 WinlQSIM suggests a new value and the transmission is aborted nally i Error Number of samples out of specified range Number of samples out of range r864 Maximum number of samples for SMG is 524216 Reduce oversampling oversampling 5 suggested Transmission will be stopped Fig 3 1 WinlQSIM recommends lower oversamplin
11. equency spectrum of Fig 2 9 leads to the time signal displayed in Fig 2 10 looking exactly like the sine wave with a sample rate of 12 MHz see Fig 2 3 O 0 1 0 2 03 0 4 0 5 0 6 0 7 0 8 0 9 1 tis Fig 2 10 1 MHz sinewave with 3 MHz sample rate in time domain after applying the interpolation filter of Fig 2 8 Actually the interpolation filter takes away some signal energy However we are still in the digital world so this problem can be eliminated with sufficient calculation accuracy 1GP45_1E 6 Rohde amp Schwarz 1GP45_1E SM IQB60 Arbitrary Waveform Generator The interpolation filter increases the effective sample rate by a factor of four To put it another way we can obtain an effective sample rate of 12 MHz by sampling with 3 MHz applying the interpolation filter and using up four times less samples SMIQB60 concept polation Filter Fig 2 11 Schematic of the SMIQB60 ARB In the SMIQB60 ARB the interpolation filter is inserted between the RAM and the D A converters It has two functions e The interpolation filter allows low nominal sample rates which uses up less RAM capacity e The interpolation rate of the filter is automatically set in a way that aliasing products of the signals are shifted into the stopband range of the antialiasing filters Waveform RAM interpolator D A Converter Output ES 1 05 zal Ot of Ml lh Lait Cram 0
12. ererrrrrenne 10 Programming triggers with WinlQSIM 0 0 ceeceeeeeeeee eee 11 GICK SII Satcher T E tle tigenes E E aiuesdacetens 11 ARB menu in SMIQ ersen enre ira EE EA ERE EE SIET 12 ONN a Or E ccieoe 13 AS UO A E E EA EE EEE EE 14 PAO UC AUO S eenn e E E teers eronceasagucataeege dun maces 15 CW multi carrier signals ccc ccc ceeccccee ee eeeeeseeeeeesaeeseeeaneeeenans 15 Digital StANdAMS ccc cece cee ceeeeeeee ee eeeeeeeeeeaeeeeeaeeeeeaeeeeaneeeeaanes 15 CGSN cl Caen eee eee eee eee eer eee ree 16 P DO ee eee oer ee eer er ee ee ee ee eee 16 ealan z DSR Sea eee neta Ont er een een nae race eter en tenes EE 16 cdma2000 TASA rene ee err aE ey ee ee S 17 W CDMA OG FDD acteeccaceteaccadtosacecnsnausictbesecaceeeeaeqaidiaren ss 17 Additional Options related to SMIQB60 0 ce eccee neces cena eens 18 Software cal_iqskew for SMIQB60 Calibration 20 installing Cal TOS ROW eener A N EEE 20 Bleee nE lt 0 o E E E E E TE E 20 Calibrating SMIQBOO ssccscencccasawncnocacwsonsbasnmctendatendlanerodaasmsonncadunenseanste 21 EUPEN SEUD ae N 21 Automatic calibration 00 ccccceccceeceeeeeeeeeeeaeeeeeeeeaeeeeeaees 21 Manual Calibration ccc ccc ccccecce ee eeeeeeeeee cess eeeneeeeneeeaneeeas 21 a nn reer ne ee en 22 BR SS teeters rescence tissu decease T EAA EE 23 Ordering information cc ccc ccceeeccce ce eece ee eeeeeeeeeeaeeeesaeeeesneeeeenneeeens 23 The SMIQ option SMIQB60 i
13. erpolation filter W exceeds that of the modulated signal Ws Wr gt Ws This leads to the following equation for derivation see the mathematical appendix provided with this application note Wg Ws Q fsa mple fs ym The following value is obtained for the digital standard W CDMA with the baseband filter Vcos a 0 22 a nET s ym 2 thus with Wi fsampie 0 375 Due to the reduced oversampling the duration of the signal increases with a constant number of sampling values Accordingly the number of sampling values decreases with constant signal duration Usually with conventional ARBs the minimum oversampling is limited to 4 Then a W CDMA frame with 38400 chips requires 153600 samples A conventional ARB with 512 ksamples memory could take signals with up to 3 frames In SMIQB60 WCDMA signals with up to 8 frames are possible 512k 38400 1 63 8 375 Fig 2 14 shows the basic block diagram of the SMIQB60 ARB 1GP45_1E 8 Rohde amp Schwarz 1GP45_1E SM IQB60 Arbitrary Waveform Generator Pp our Interpolator DIA Filter Output gt Ae f gt Converter gt 45kHz 12M gt Amplifier 12 FLASH RAM lt p evcomRAM I Ook 1 5MSanples 512kSamples Synthesizer 32 24 40 v A IOUT v v Interpolator D A Filter
14. g if the number of samples is too high for SMIQB60 RAM e If the original oversampling value is 2 WinlQSIM offers downsampling to a value between 1 and 2 remember that the effective sample rate is increased by SMIQB60 s interpolation filter method E WwinlQSIM 7 AHIO Warning Sith Warning Number of samples out of specified range Number of samples out of range 786432 Maximum number of samples for SMIG ts 524276 Down sampling possible resulting oversampling 1 333150 down sampling factor 0 666575 ai down sampling me 4 p M Show this warning nest time Fig 3 2 If the number of samples is too high and oversampling is already 2 WinlQSIM offers downsampiling 10 Rohde amp Schwarz SM IQB60 Arbitrary Waveform Generator Programming triggers with WinlQSIM WinlQSIM supports predefined trigger signal generation menu SMIQ ARB gt Trigger Output Settings e Bit clock e Symbol clock e Slot clock e Frame clock e Restart clock e g for usage of SMIQB21 Bit Error Rate Tester e User PULSE definable on and off time Trigger Out Model w Trigger Out2 Model v Current Mode M ode4 am I I I Iaa Bit Clack BIT_CLK C Symbol Clock SMB_CLE Slot Clack SLOT_CLE Frame Clock FRAM CLE f Restart Clock SEQUENZ ON time 2 samples User PULSE z2 p OFF time a2 samples Fig 3 3 SMIQB6O trigger menu in WinlQSIM The availability of t
15. he shown trigger signals depends on the system used e g no slot clock for IS 95 The trigger signals are time synchronous with the I Q output signals Clock Settings SMIQB60 can be driven by either an internal or external clock With internal clock operation the sample clock signal is available at the BIT CLOCK connector on the front panel of SMIQ For external clock operation a clock signal TTL level must be fed into the SYMBOL CLOCK connector on the front panel of SMIQ 1GP45_1E 11 Rohde amp Schwarz 1GP45_1E SM IQB60 Arbitrary Waveform Generator ARB menu in SMIQ Stored waveforms can be handled via the SMIQ user interface without any external device In addition ARB hardware parameters such as operation mode outputs or clock rate can be set The CCDF of a loaded waveform can also be displayed Furthermore triggers can be programmed manually The trigger generator consists of programmable counters which generate a periodic sequence with a pulse duty cycle of On Time Off Time with settable start delay The settable resolution for this trigger is the sample rate 1 ta 30 0 dEm 30 0 dEm FREQUENCY J LEVEL H TRIGGER OUT1 POL NEG J ANALOG MOD f H TRIGGER OUT2 POL FOS MEG VECTOR MOD TRIGGER OUT1 DELAY o DIGITAL MOD A TRIGGER OUT2 DELAY o DIGITAL STD _ TRIGGER OUT1 MODE CURRENT USER ON TIME 1 NOISE DIST 3 OFF TIME 1 H FADING SIM I TRIGGER OUT2 MODE CURRENT US
16. ming Especially for multi carrier signals AMIQ with its large RAM capacity might be the better solution in general Nevertheless SMIQB60 can be successfully used in many situations where digitally modulated signals are required The following tables give an overview of SMIQB60 s capacity for different digital communication standards 15 Rohde amp Schwarz SM IQB60 Arbitrary Waveform Generator GSM EDGE Symbol rate 270 833 ksps Symbols per frame 4 616 ms 1250 Channel spacing 200 kHz Number of carriers maximum number of frames 209 1 frame Limitation through max clock rate of 40 MHz NADC Symbol rate 24 3 ksps Symbols per frame 40 ms 972 Channel spacing 30 kHz 269 oS max 217 1 frame Limitation through memory size of 512 kSamples cdmaOne IS 95 Chip rate 1 2288 Mcps Chips per Frame 80 ms 98304 Channel spacing 1 25 MHz Number of carriers maximum number of frames 1 Downsampling used Limitation through memory size of 512 kSamples 1 Downsampling used Limitation through memory size of 512 kSamples 1GP45_1E 16 Rohde amp Schwarz SM IQB60 Arbitrary Waveform Generator cdma2000 1X 3X Chip rate 1 2288 Mcps 3 6864 Mcps Chips per frame 80 ms 98304 respectively 294912 Channel spacing 1 25 MHz 3 75 MHz 1X mode like cdmaOne Number of carriers maximum number of frames 2 1 Downsampling used Limitation through memory size of 512 kSamples 3 1 Downsampling
17. mproved dynamic range with SMIQB60 SMIQ Firmware 5 85HX or later is a prerequisite to perform the calibration Installing cal_iqskew Extract the zip archive to a directory on your PC and start the setup exe Follow the instructions for installing the software Calibration setup Connect the SMIQ to be calibrated and a suitable spectrum analyzer via GPIB to the PC on which cal_iqskew is installed As spectrum analyzer we recommend R amp S FSIQ FSU or FSU However other spectrum analyzers can also be used PC with cal_iqskew GPIB SMIQ Spectrum Analyzer e g FSU Fig 6 1 Setup for IQ skew calibration 20 Rohde amp Schwarz 1GP45_1E SM IQB60 Arbitrary Waveform Generator Calibrating SMIQB60 After connecting the instruments start cal_iqskew The main menu appears SMIQ B60 IQ Skew Calibration 1 0 M E Equipment setup Manual calibration Cuit Fig 6 2 The main menu of the cal_iqskew program Equipment setup Specify the GPIB addresses of the SMIQ and the spectrum analyzer here Automatic calibration Runs the entire calibration procedure automatically All necessary SMIQ and analyzer settings are done by the software This function works with R amp S FSEx FSIQ FSU FSQ and FSP analyzers With other analyzers it might work but there is no guarantee that the automatic calibration runs perfectly or runs at all If the
18. ncy offsets up to 10 MHz The curve denotes the image suppression obtained from the SMIQ data sheet values Calibration New SMIQ units delivered with firmware 5 85 HX or later are calibrated in the factory to obtain the improved dynamic range with SMIQB60 Older SMIQs equipped with SMIQB60 can be calibrated by the user to get the improved dynamic range with SMIQB60 Installation of firmware 5 85HX is prerequisite For the calibration we provide the free software cal_iqskew delivered with this application note The software is described in section 6 1GP45_1E 14 Rohde amp Schwarz 4 Applications 1GP45_1E SM IQB60 Arbitrary Waveform Generator CW multi carrier signals A classical application for an arbitrary waveform generator is the generation of CW multi carrier signals As there is no modulation present the sequences can be kept rather short With its maximum clock rate of 40 MHz SMIQB60 can cover a wide range of signal scenarios The well balanced and Q channels lead to signals of high quality as shown in the previous section Digital standards For modulated signals the sequence length of the stored signal plays an important role In many cases the signal contains a large number of symbols for bit error tests and similar measurements for example For spectral measurements the number of symbols is less important For multi carrier signals however large bandwidths require high sample rates and this is memory consu
19. s an internal 2 channel arbitrary waveform generator ARB based on the modulation coder SMIQB20 Waveforms can be calculated and transmitted with the external PC Software WinlQSIM and stored in the non volatile memory of SMIQ Stored waveforms can be recalled by SMIQ without using WinlQSIM SMIQB60 provides arbitrary I Q signals to drive SMIQ s I Q modulator This is the main purpose of SMIQB60 although the I Q signals are also available at SMIQ s and Q outputs SMIQ is based on a concept providing considerable improvements compared to conventional arbitrary waveform generators This concept is outlined in section 2 Sections 3 and 4 describe SMIQB60 operation and applications 2 Rohde amp Schwarz SM IQB60 Arbitrary Waveform Generator 2 Function Principles of SMIQB60 1GP45_1E Conventional arbitrary waveform generators HHE Fig 2 1 Conventional ARB A conventional arbitrary waveform generator ARB basically consists of an output memory a D A converter and an analog filter see Fig 2 1 D A Converter fy ith 60 B0 B vif dB oO gt ho D lj O EP a D D D ey K Tr X 0 10 fiMHZz Fig 2 2 Building a sinewave with a conventional ARB Upper row time domain Lower row frequency domain Fig 2 2 shows how a signal is generated with a conventional ARB A sinewave with frequency 1 MHz is taken as example The sinewave is represented b
20. tiples of the sampling frequency The aliasing products are located at 12 1 MHz 24 1 MHz and so on N Q 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 1 ties Fig 2 6 1MHz sinewave with 3 MHz sample rate time domain Fig 2 6 shows the same 1 MHz sine wave signal This time it is sampled with a sample rate of 3 MHz a value every 333 ns 0 8 0 6 0 4 0 2 Q 1 2 3 4 Ss 6 T 8 9 10 11 12 13 14 15 16 EMHZ Fig 2 7 1 MHZ sinewave with 3 MHz sample rate frequency domain This results in a spectrum as shown in Fig 2 7 The fundamental is still at 1 MHz but the aliasing products are now at 3 1 MHz 6 1 MHz and so on 5 Rohde amp Schwarz SM IQB60 Arbitrary Waveform Generator 5 6 Y 8 9 10 11 12 13 14 15 16 tiMHz Fig 2 8 The interpolation filter suppresses a part of the aliasing products By applying a digital interpolation filter all unwanted aliasing products are suppressed see Fig 2 8 In this example only the frequencies within the marked area are passing the filter which means that the filter provides an oversampling of 4 3 MHz 4 12 MHz T f_sf2 fs 0 8 0 6 0 4 0 2 Q 1 2 3 4 S5 S ri 8 9 10 3 12 13 14 15 16 HFMHZ Fig 2 9 Spectrum of the 1 MHz sinewave with 3 MHz sample rate after applying the interpolation filter from Fig 2 8 As result we have exactly the same frequency spectrum as for a 12 MHz sample rate compare Fig 2 9 with Fig 2 5 The fr
21. ude EVM for WCDMA multi carrier signals e better dynamic range for all I Q signals that are not symmetric to the center frequency To evaluate the signal quality produced by SMIQB60 we can take CW carriers with offset from the RF center frequency wo If a carrier is generated at o m Spurious signals at o my are caused by deviations from the ideal balanced I Q signal i e different magnitude and or group delay for and Q In the case of group delay the spurious signals increase with increasing offset from the center frequency That means these effects are most important for wideband signals The spurious signals are called images and the difference in power between the wanted signal and the spurious is the image suppression Deviations from the ideal I Q signal can result from either not totally balanced SMIQB60 outputs or imbalance of the I Q modulator itself The measurement cannot distinguish between the two cases Actually the I Q modulator s contribution is smaller The SMIQ data sheet states the following values IQ imbalance Magnitude typ 0 05 dB up to 10 MHz Group delay typ 0 5 ns up to 10 MHz These values contain both the contributions from the ARB and the I Q modulator The resulting spurious signals are calculated as follows The complete calculation can be found in the mathematical appendix provided with this application note The non ideal I Q signal for a CW carrier at o my can be described
22. used Limitation through memory size of 512 kSamples 3X multi carrier mode Superoversampling 2 1 Downsampling used Limitation through memory size of 512 kSamples 3X direct spread mode 1 1 Downsampling used Limitation through memory size of 512 kSamples W CDMA 3GPP FDD Chip rate 3 84 Mcps Chips per frame 10 ms 38400 Number of carriers maximum number of frames 1 Downsampling used Limitation through max clock rate of 40 MHz 1 With superoversampling 1 and baseband oversampling 4 1GP45_1E 17 Rohde amp Schwarz SM IQB60 Arbitrary Waveform Generator 5 Additional Options related to SMIQB60 1GP45_1E Fig 5 1 on the next page shows the SMIQ option policy related to SMIQB60 The hardware options SMIQB20 Modulation Coder and SMIQB11 Data Generator are prerequisite for installing SMIQB60 SMIQB6O0 itself can be activated by keycode and contains the WinlQSIM software There are five additional keycode options for generating signals according to special digital communication standards cdmaOne or IS 95 option SMIQK11 is a common CDMA standard in the U S and in Korea cdma2000 option SMIQK12 is a 3G standard proposed by some big U S manufacturers It is a CDMA system with one or three carriers and is backward compatible with IS 95 Option SMIQK13 contains the TDD mode of W CDMA 3GPP TD SCDMA option SMIQK14 is a special W CDMA standard that has been developed for the Chinese
23. ximum to suppress all aliasing products see Fig 2 3 1 1 1 1 H 1 1 L 1 O 1 2 3 4 5 6 Ti 8 9 10 11 12 13 14 15 16 i MHz Fig 2 3 1 MHz sinewave signal with 12 MHz sample rate and 11 MHz filter cutoff Usually the antialiasing filters in ARBs are hardware filters with fixed passband and stopband range the signal calculation has to be adapted to the filter characteristics In our example the sample rate has to be at least 12 MHz to make use of the 11 MHz filter This can lead to high oversampling values and therefore to a large amount of sample values using up RAM capacity The ARB concept has been significantly improved in the SMIQB60 option The core of this improved concept is using a digital interpolation filter Functioning of an interpolation filter Q 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 1 tis Fig 2 4 1MHz sinewave with 12 MHz sample rate time domain Let us have a closer look at how an interpolation filter works with a simple example In Fig 2 4 a 1 MHz sine wave signal is shown This waveform is sampled with a 12 MHz sample rate which means a value every 83 3 ns 4 Rohde amp Schwarz 1GP45_1E SM IQB60 Arbitrary Waveform Generator O 1 2 3 4 5 6 rd 8 9 10 11 12 13 14 15 16 fifMHz Fig 2 5 1 MHz sinewave with 12 MHz sample rate frequency domain In Fig 2 5 the resulting frequency spectrum is displayed consisting of the fundamental at 1 MHz and the aliasing products symmetric to mul
24. y a sequence of sample values stored in the waveform RAM Mathematically this is described as a sequence of weighted Dirac pulses The time interval between two consecutive sample values is given by Tsampie 1 fsampie With fsampie being the sample rate This time signal and the resulting frequency spectrum are shown in the left column of Fig 2 2 A sequence of Dirac pulses in time domain gives a sequence of Dirac pulses in frequency domain The fundamental at fmog modulation frequency is repeated at fsample fmoa 2 fsampie fmoa ANd SO on These repetitions are called aliasing products As the sample rate is 12 MHz and fmog 1 MHz there are aliasing products at 11 and 13 MHz 23 and 25 MHz and so on Actually this is not quite the signal coming out of the D A converter As we want a continuous output signal every sample value has to be held for Tsampie Thus the signal from the D A converter is a sequence of rectangles with amplitudes 3 Rohde amp Schwarz 1GP45_1E SM IQB60 Arbitrary Waveform Generator given by the sample values and widths Tsampie This leads to an additional SIN fsampie fsampie factor in the spectrum as shown in the middle column As the fundamental contains all necessary information about the signal the aliasing products are normally suppressed by low pass filters to reduce the bandwidth of the signal chain see the right column in Fig 2 2 In our example the filter cutoff has to be at 11 MHz at ma
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