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Phase Noise Setup doesn't work in port/vsource

VIP of NH

I'm simply simulating pss and pnoise for a port/vsource, with added phase noise "freq, noise(dBc)" pairs.

In my testbench, there's only the vsource and it's labelled output, and gnd. 

In ade, I setup pss output as voltage between vsource positive and vsource negative(gnd), no input.

But the simulation result in Direct Plot -> pnoise -> Phase Noise gives me a straight line with same value for all frequencies.

Then it means either the added Phase Noise pairs don't work, or there's sth wrong with my simulation.

Could you please tell me why?

Thank you very much.

Here's my testbench and vsource setup (when I use port, the setup is almost the same, only with a 50 Ohm impedance for the port)

Here's the ade setup for pss and pnoise:

Here's the simulation result plot of phase noise:

 

Parents

  • Thank you Andrew!
    Actually I initially tried 300ns tstab, which is long enough to lock the loop (verified by transient sim), but pss/voltage/time gave bad result as mentioned (not oscillating).
    After that I just wanna see whether pss went weird, that's why I changed to 20ns tstab, which I knew the loop won't locked and pss should not converge. However, it can still converge......
    I'm using a simple cross-couple NMOS-pair LC oscillator, which outputs sine wave with some distortion.

    After your reply, I tried setting pss "No. of Harmonic" to 1640. But it still gave the same result. I also tried running transient to 300ns first, then running pss with "transient's .fc file" as initial condition (ic: all), and setting pss tstart to be 300ns. However, pss/voltage/time of VCO output is still the previous wrong result, a "white noise shape plot" around 0.5V........Then I'm just really confused. I think at least it should be an oscillating plot, because I've given the transient final condition to the pss, in which the VCO is oscillating.

    Another thing I tried is using verilog-A VCO with tstab=300ns, and pss seems to work good with it. When I plot pss/voltage/time for VCO output and control voltage, they all seem correct (control voltage indicates lock state). So it seems pss doesn't like my transistor-level VCO, although transient can get along with it :(

    Just to make sure:
    If I set pss/tsart to 300ns, or I set pss/tstab to 300ns, with a beat period of 10ns, when I plot pss/voltage/time, should the x-axis be from 300ns to 300ns+10ns? Or from 0 to 10ns? I though it should be a one period plot after achieving static state, which is from 300ns to 300ns+10ns. But it always plot from 0.


    Thanks

Reply

  • Thank you Andrew!
    Actually I initially tried 300ns tstab, which is long enough to lock the loop (verified by transient sim), but pss/voltage/time gave bad result as mentioned (not oscillating).
    After that I just wanna see whether pss went weird, that's why I changed to 20ns tstab, which I knew the loop won't locked and pss should not converge. However, it can still converge......
    I'm using a simple cross-couple NMOS-pair LC oscillator, which outputs sine wave with some distortion.

    After your reply, I tried setting pss "No. of Harmonic" to 1640. But it still gave the same result. I also tried running transient to 300ns first, then running pss with "transient's .fc file" as initial condition (ic: all), and setting pss tstart to be 300ns. However, pss/voltage/time of VCO output is still the previous wrong result, a "white noise shape plot" around 0.5V........Then I'm just really confused. I think at least it should be an oscillating plot, because I've given the transient final condition to the pss, in which the VCO is oscillating.

    Another thing I tried is using verilog-A VCO with tstab=300ns, and pss seems to work good with it. When I plot pss/voltage/time for VCO output and control voltage, they all seem correct (control voltage indicates lock state). So it seems pss doesn't like my transistor-level VCO, although transient can get along with it :(

    Just to make sure:
    If I set pss/tsart to 300ns, or I set pss/tstab to 300ns, with a beat period of 10ns, when I plot pss/voltage/time, should the x-axis be from 300ns to 300ns+10ns? Or from 0 to 10ns? I though it should be a one period plot after achieving static state, which is from 300ns to 300ns+10ns. But it always plot from 0.


    Thanks

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