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genyap1

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israel

PXF and PAC possible inconsistency
Feb 17^th, 2015, 7:47am

Good day.

I have posted the same question on cadence community forums; sorry if you bump into it twice.

I am trying to simulate power supply noise propagation through an amplifier stage. The amplifier is driven by a large signal, which is the PSS beat. The circuit is slightly non-linear (THD around 30dB). I use harmonic balance for PSS engine. Now I add power supply interference (small signal); I try it in two different ways:

1) Run PAC analysis, with the only PAC source being power supply voltage source, look at the output spectrum (differential voltage).

2) Run PXF (differential voltage output) and look at the transfer function from the said power supply voltage source.

I deem the two analyses should have given same spectra, but they don't. In fact, the base harmonic (i.e. number "0") is exactly identical, all the others as not.

Can anyone please explain that to me?

Many thanks,

Yevgeny.

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smlogan

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Boston, MA

Re: PXF and PAC possible inconsistency
Reply #1 - Feb 17^th, 2015, 10:20am

I just provided the following response on the Cadence forum.

[i][i][i]Dear Yevgeny,

> I deem the two analyses should have given same spectra, but they don't. In fact, the base harmonic

> (i.e. number "0") is exactly identical, all the others as not.

My understanding is that a PAC analysis maps a given input frequency (in this case the power supply modulation frequency) to the various output frequencies it will produce due to amplifier. You do note that the THD of the amplifier is better than 30 dB. Howver, I assume that is the THD from the amplifier input - not from an input on the supply rail. Hence, my guess is you observe significant sidebands at the amplifier output due to the supply noise modulation frequency.

A PXF analysis maps an output harmonic back to the input frequencies that are required to generate that output harmonic. Hence, the two analyses, from my understanding, will not produce the same output spectra. PAC provides information on the output frequencies produced from a given input - and PXF provides insight on the input frequencies required to produce a given output frequency.

Let me know your thoughts, or if I misinterpreted your question![/i][/i][/i]

Shawn

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Shawn

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Frank Wiedmann Community Fellow Offline Posts: 678 Munich, Germany	Re: PXF and PAC possible inconsistency Reply #2 - Feb 19^th, 2015, 12:31am This discussion was continued in the Cadence forum and resulted in an even more detailed explanation by Andrew Beckett, which can be found at http://community.cadence.com/cadence_technology_forums/f/33/t/31596.
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