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regarding PSS and PAC analysis

Erez Zolkov

Hello.

I'm trying to simulate an N path filter circuit.

I used to deal with analog circuits and not RF ciruits, so im always used to run an AC analysis that follows a DC operating point analysis.

to my understanding, regarding LPTV systems PSS is equivalent to finding the DC operating point, and PAC is equivalent to finding the AC response (for different harmonies).

That being said, I am confused regarding what should be the input when I set the PSS analysis.

Say my LO is at 1 GHZ, what should be the proper Vin I need to set? at what frequency, if any? if I assume the input is always gonna be small signal, should I even provide other DC than zero?

I tried setting Vin to zero DC, then to 1Ghz sinus at different amplitudes, and even at other frequencies. each time, i'm getting different PAC frequency responses.

See the attached circuit schematic (I assume this is a common topology). 

Thanks in advance.

  • If you're simulating the small-signal response, then you don't need (or want) a large signal sine wave at the input. If you do that, you'd be looking at the small signal response with an interferer. I'm not familiar with this type of circuit, but I suspect having a large signal input at the same frequency as the switching clock would not be a good idea (for aliasing reasons).

    You could compare the response of (say) a 1.1GHz input sine wave with PSS running with a fundamental of 100MHz (don't run pac) - you'd be able to see the signal level arising from your 1.1GHz input signal at various output frequencies (e.g. 900Mhz, 100MHz, 1.1GHz and so on), and then you could run your PSS with the 1GHz clock alone (no large signal for the input), with a 1GHz PSS fundamental, and apply a PAC Magnitude instead at 1.1GHz and compare the response. I would imagine with such an ideal circuit they should be the same.

    Unless you need a bias level, your input signal for the 1GHz PSS with PAC should be 0V DC, with the PAC magnitude set appropriately to the small signal level you want (in this case you could set it to 1 and then you'll see the gain, but it might be easier to set it to the expected amplitude so you can compare with your large signal sine wave sims).

    Regards,

    Andrew.

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