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Error in PSS and PNoise simulation of a VCO followed by Frequency detector with 150MHz clock signal

Jayanta

Hello

I am facing difficulty in simulating phase noise of an oscillator circuit. The circuit consists of a Current starved VCO (2.4GHz) followed by a frequency sensor circuit. To the frequency sensor circuit I have given a 150 MHz clock frequency(reference). while running the PSS analysis it is showing an error that this is not an autonomous circuit instead it is a driven circuit because of that reference clock signal. After going through some forum I tried the PSS analysis with the oscillator mode unchecked and tstab as 800ns. but in this case it is not converging at all.

Kindly guide me as i am stuck at this point.

Thanks & Regards,

Jayanta

  • in reply to Jayanta

    Dear Jayanta,

    Jayanta said:
    I tried to overcome both the warnings. 1. Tried with giving manual Tstab of even 1us. 2. The harmonics also increased to 16 for tone 2. But still not converging. 

    Great - thank you for letting us know! It certainly seems as both of these values should be sufficient to address the two warnings in your spectre.out log file. Did th wirings change or were they eliminated with the increased value of Tstab and number of harmonics?

    I took some added time to review your GUI and log file and noticed a few items that I would suggest. Andrew may have other or more fruitful suggestions as he often does!

    1. I noticed you did not include a negative node for /VCO_OUTPUT in your harmonic balance GUI. I could see from what looks like your ADE-L or test configuration window you did include /gnd! as the second node in a different analysis. I would add your second output node (see Figure 1)

    2. If the "digital output" you note is a digital signal, it will clearly have more harmonic content than your near sinusoidal VCO. Yet, on the GUI panel, as shown by the note in I circled in Figure 1, the harmonic with the most harmonic content should be your first tone listed. In your GUI, it is the second tone listed. Perhaps you might change the order of your two tones so the one with the greatest harmonic content is listed as #1.

    3. Since you are still experiencing convergence issues, I would also consider setting errpreset to "conservative" in lieu of your "moderate" setting (Figure 1)

    4 You also did not check the radio button for the multi-tine harmonic balance option in the GUI (Figure 2)

    5. You might also considering reviewing the application note on multi-tone analyses at URL:

    support.cadence.com/.../ArticleAttachmentPortal

    I hope these provide some insight into your convergence problem!

    Shawn

    Figure 1

    Figure 2

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