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Cadence virtuoso tool related

salamkgp

I am using Cadence virtuoso 6.1.5. I am required to measure the SNR  at the input and output of some Analog Circuits simulated at Nyquist rate, using Spectral Analysis. When measured for an ideal sinusoidal source (from analogLib) with simple resistive load (and capacitive load), I was getting less than 50 dB. Kindly help me in doing the proper settings of the tool, so that the SNR for the ideal source may be high (expected to be above 180 dB).

  • Andrew Beckett

    OK, it threw me because the question above bears no resemblance to the question that arrived by email, so presumably you've edited it.

    Anyway, how are you measuring the SNR? Are you using PSS? The fourier analyser component in analogLib? Using the DFT from the calculator? Rather than give a full tutorial covering everything that you  might be trying, tell me what you're doing, and I can give more targeted advice.

    Regards,

    Andrew.

  • salamkgp

    Sir, I am using the measurement tool for spectrum available with Cadence Virtuoso ADE. I am not doing the PSS analysis. After running the transient simulation, transient domain waveform can be given to the spectrum with proper start/stop time, sample count/freq, selecting the window type as rectangular, we can plot the FFT. It will display the SNR, SINAD, ENOB, SFDR etc..


    I have applied a sinusoidal input from AnalogLib_hspice with amplitude 1V, frequency (100MHz * 8191/16384). Run for FFT is plotted with start/stop time of 0/163.84u. screenshot is inserted with this reply.

  • Andrew Beckett

    Does the fact that you're using analogLib_hspice mean that you're using HSPICE as the simulator? If so, I probably can't advise you on the best simulator settings.

    With spectre, I'd recommend you set the transient analysis option strobeperiod to match the sample points - i.e. 163.84u/16384 - or 10n.

    There are various other strategies for doing this, but that would work well. With spectre that would cause the simulator to solve at (at least) the strobe points, which tends to remove interpolation error during sampling.

    Regards,

    Andrew.

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