Operating Manual Vol 1 - ES Documentation

Arbitrary Waveform Generator ARBSMIQThis conception has been considerably improved in the option SMIQB60. The modulation signal isinterpolated to a higher sampling rate by means of a very steep-edged, digital interpolation filter and isthen output. The interpolation rate is set by the SMIQB60 automatically such that aliasing of theinterpolated sampling rate is suppressed by the analog filter. This procedure offers the followingadvantages to the user:1. Oversampling has to be selected such that the bandwidth of the interpolation filter exceeds that ofthe modulation signal. The following equation applies:ov * int_bw >= mod_bw,ov == Oversampling,int_bw == 0.375, standardized bandwidth of the interpolation filter,mod_bw == bandwidth of the modulation signal standardized to symbol rateThe following value is thus obtained for the digital standard W-CDMA with the baseband filter √cos,α = 0.22:(1+ α)0.61mod_bw = = 0.61, => ov >= = 1.63.20.3752. Due to the reduced oversampling, the duration of the signal increases with constant number ofsampling values. Accordingly, the number of sampling values decreases with constant signalduration. Usually, with conventional ARB generators, the minimum oversampling is limited to 4. Thus,provided that the above parameters of the W-CDMA system apply, the 512 ksamples of the SMIQB60correspond to 4/1.63 * 512 = 1256 kSamples memory in a conventional ARB generator.The block diagram in Fig. 2-215 roughly illustrates the structure of the ARB generator.Interpolatorup14D/AConverterFilter45kHz, 12MHzOutputAmplifierQ_OUTQ_MOD12FLASH RAM1.5MSamplesWaveform RAM512kSamplesup*clockClockSynthesizer32 2412DSPInterpolatorup14D/AConverterFilter45kHz, 12MHzOutputAmplifierI_OUTi_MODDATA INTRIGGER INTrigger UnitTRIGOUT_1TRIGOUT_2Fig. 2-215Block diagram SMIQB601125.5555.03 2.342E-9