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https://designers-guide.org/forum/YaBB.pl Simulators >> Circuit Simulators >> Discrepancy between liberal and moderate in the simulation of a SC delta sigma https://designers-guide.org/forum/YaBB.pl?num=1514166904 Message started by polyam on Dec 24th, 2017, 5:55pm |
Title: Discrepancy between liberal and moderate in the simulation of a SC delta sigma Post by polyam on Dec 24th, 2017, 5:55pm Hi, I am trying to simulate a 2nd order SC delta-sigma modulator. Whole blocks are implemented through either macro-models or Verilog-A modules. Specifically, OTAs are modeled with macro models and switches are the Verilog-A modules. The sampling frequency is fs= 5.12 MHz and BW=20MHz. 1ms simulation is carried out to get 4096 points. I've also set strobe period and strobe delay to Ts=1/fs and Ts/2-epsilon, respectively. When I use the liberal mode, I get what I expect BUT when I switch to moderate mode the performance goes down and I cannot figure out what the reason is. :o Please check out both PSDs in liberal and moderate modes. Thanks |
Title: Re: discrepancy between liberal and moderate in the simulation of a SC delta sigma Post by polyam on Dec 24th, 2017, 5:55pm PSD moderate |
Title: Re: Discrepancy between liberal and moderate in the simulation of a SC delta sigma Post by sheldon on Dec 27th, 2017, 10:10am Polyam, These results are the FFT results, not the PSD. You will need to use a different simulation setup, run longer simulation, and use a different measurement to perform a PSD. These results are expected and correct. The moderate error preset has higher simulation accuracy tolerances than the liberal error preset. The moderate error preset results are showing the noise shaping of the quantization noise. Try running a 16,384 point FFT with the moderate error preset. In that case, the quantization noise floor should be ~6dB lower for the 16384 point FFT. Sheldon |
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