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https://designers-guide.org/forum/YaBB.pl Analog Verification >> Analog Performance Verification >> Transient noise of a vsource component https://designers-guide.org/forum/YaBB.pl?num=1452089303 Message started by mtytgat on Jan 6th, 2016, 6:08am |
Title: Transient noise of a vsource component Post by mtytgat on Jan 6th, 2016, 6:08am Hi, I want to perform a transient noise simulation in Cadence (because I want to include non-linear effects) but I keep getting a slight underestimation of the noise. This is my test-case: A vsource from analogLib, connected to a 1M resistor, which generates no noise. In the vsource, I specify 1 noise/freq pair: Freq 1 = 1, Noise 1 = 1. This should give me a flat noise PSD of 1V**2/Hz. In the tran analysis, I specify: Stop Time = 0.1m Transient Noise: Noise Fmax = 1G Noise Update = fmax Noise contribution = on, Instance list = the vsource component All the rest default The simulation runs without warnings or errors. As a result, I plot the transient waveform at the vsource output, and from it, I calculate the noise PSD in V/sqrt(Hz): sqrt(((rms(tran_out)**2) / VAR("BW"))) where tran_out is the transient waveform and BW is a variable for the bandwidth. The result should be 1, as specified in the vsource. It is always smaller however. No matter which parameter I change, it is between 5-20% below the expected value. When I increase the length of the tran simulation, I would expect that the extreme values in the transient voltage will increase, because the noise is supposed to be a gaussian process, so the probablility of larger extreme values should increase with simulation time. This does not happen however. I have a feeling that the output signal is somehow limited, which could result in a lower rms value of the noise. The regular noise analysis does give me the correct result. Does anyone have any idea what could cause this underestimation of the transient noise? Thanks a lot! M |
Title: Re: Transient noise of a vsource component Post by sheldon on Nov 18th, 2016, 9:54am Greetings, The noise update method noisefmax is not recommended. What is the value of Bandwidth? If you plot noise as a function of bandwidth what happens? Have tried adding a shunt capacitor to define a bandwidth and then check over the RC bandwidth. Then look at the relationship between the RC bandwidth vs. noisefmax. It is expected that as the noisefmax increases for a fixed RC bandwidth the noise should approach the ideal value. Sheldon |
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