am
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Hi,
Let me start by clarifing my understanding of pnoise calculations:
1. pnoise with noisetype=correlations I thought that in this case the simulator would compute: E{X(relharmnum*fund+df) * conjugate(X(relharmnum*fund+df+cycles*fund))}
2. pnoise with noisetype=sources In this case I expected the simulator to simply compute: E{X(relharmnum*fund+df) * conjugate(X(relharmnum*fund+df))}
Under this assumptions pnoise with noisetype=correlations and with cycles=0 would be exactly the same as pnoise with noisetype=sources.
Well, I have written an simple behavioral model to check this (first I did an AM modulator and then a PM modulator), and in fact this is the case in my simple test circuit.
Then, I tried this with a simple VCO circuit (a simple amplifier and an LC tank). In this case I run the circuit in autonomous mode and now the values of the pnoise with noisetype=sources and pnoise with noisetype=correlations and cycles=0 are very much different.
I would also like to clarify that I was careful in the following aspects: - in pnoise with noisetype=sources I square the result (in order to compute power) and then compare it to the other simulation - since the output of the VCO is differential and in order to avoid errors with factors of two, I convert the differential signal to a single ended signal with a simple behavioral model.
At the end I am left with a discrepancy between the two results. I beleive the one with noisetype=sources is right.
So, 1. Am I wrong in my understanding of pnoise? 2. Is there something different in the way pnoise works in an autonomous circuit considering that my test case worked fine?
Thanks,
AM
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