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PAC simulation results

mxm14 over 2 years ago

Hello I m trying to understand how PAC simulations work..

So I use this simple circuit with a switch that commute at 1Mhz, and applied a 1V PAC signal on V0

I launched a PSS and then PAC simulation with input sweep from 0 to 500kHz.

I obtained the following result:

- in blu is the out spectrum obtained from the PSS ( square wave from 0 to 1)

- then there are the result of the PAC

I was expecting the sidebands at the same magnitude of the squarewave spectrum components, but I see that they have half of the magnitude. WHy this happens?

Thank you in advance.

Andrew Beckett over 2 years ago

Why would you expect to have the full energy in both sidebands? It's being sampled...

If you apply a 200kHz sine wave with 1V amplitude and run a transient simulation for 1/200k (5u) with strobeperiod set to 1/200k/256 and then perform a DFT over the 5u with 256 samples, you'll see the same result. I'm not sure why you'd expect it not to behave this way since this is what the circuit does!

Andrew
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ShawnLogan over 2 years ago in reply to Andrew Beckett

Dear mxm14,

I had started a quick example when I read Andrew's response and thought I would continue the effort to illustrate the sideband energy as a function of harmonic. I also varied the amplitude of your 1 VAC PAC input to show the impact of the modulation index (1 VAC => modulation index of 100%) on the ratio. I hope between Andrew's post and this example, you might better understand the simulation results you obtained.

Shawn

pac_sideband_amplitude_ratio_030523v1p0.pdf
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mxm14 over 2 years ago in reply to ShawnLogan

Thank you Andrew and Shawn!
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