Operating Manual Vol 1 - ES Documentation

SMIQArbitrary Waveform Generator ARB2.21 Arbitrary Waveform Generator ARBThe option SMIQB60, a two-channel ARB generator, is an integrated I/Q modulation source of theSMIQ. Thus, arbitrary modulation signals such as COFDM, multicarrier or noise can be generated. Thesoftware WinIQSIM enables the calculation of modulation signals and the loading of these signals intothe instrument. Furthermore, signals which were calculated by a mathematical program such as Matlabmay be transferred.2.21.1 FunctionConventional ARB generators substantially consist of an output memory with series-connected D/Aconverter and analog filter. Due to the limited number of filters and their steepness the sampling rateoften has to be set considerably higher than required by Nyquist's theorem, in order for the aliasingeffects to be sufficiently suppressed by the analog filter. Fig. 2-214 shows these ratios for a 1-MHzsinewave signal. If a filter provides a cutoff-frequency of 11 MHz, a sampling rate of at least 12 MHzmust be selected to make sure that the aliasing effects are suppressed sufficiently.Fig. 2-214Signal flow of ARB generator1125.5555.03 2.341 E-9