I am a beginner in TX IC design. Now I am using virtuoso IC18.104.22.168 and MMSIM101 to simulate a RF modulator. I need to test its linearity and EVM. So I want to perform the envlp analysis. However I met a problem:
First I use the ppwlf to source my saved matlab ASCII data file, and then feed to a verilogA block written by myself, which transforms the pwl waveform to the thermometer coded waveform. I need it as switching input signal to my modulator(kind of switching PA). For simplicity, I just use 1LSB to do single bit test. However, the envlp results show that the voltage spectrum after my verilogA decoder is all 0 level. The pwl input signal spectrum of the decoder is all right. I also did a comparison simulation, feed my modulator directly with ppwlf source, the signal will not be pulled all down to 0, and the specturm of the input is OK. But I think this PWL signal is not the signal I want. I simulated my circuit using transient analysis, it works. Does envlp only support PWL waveform as input? Can it be thermometer coded waveform? Does anybody know how to solve this problem?