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Jun 3rd, 2023, 3:23pm
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Question about discrepancy between PNOISE and NOISE analysis (Read 76 times)
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Question about discrepancy between PNOISE and NOISE analysis
Mar 27th, 2023, 10:05am
First time posting here so please bear with me if my formatting looks terrible.

A little bit of background…I have a circuit that has an autonomous output waveform as it is the result of periodically charging and discharging a capacitor. There are no driven sources in the schematic. I have a transient testbench where I use acnames to break and run noise analysis. I have utilized the “@sigoutCross” function to define the threshold crossing at 0.5V that the noise analysis is to be performed. That is done using acnames. At exactly 0.5V on the first rising edge crossing noise is to be performed. Which is the yellow curve in the plot I have attached, this looks like what I expected.

Since I need to evaluate the impact of noise around the trip point, I have set up the PSS/PNOISE analysis as well. However, this is in a separate test within that same testbench so I can make use of the calcVal() function. I have verified that the PSS transient waveform looks correct, it is one cycle of operation. The “VAR(“period_calc”) function is defined in a separate test, I run transient to extract the period of the signal since it is not a known parameter to me and it is called using the calcVal() function. The PNOISE analysis (red plot) does not look correct to me as it is 500x higher than what I calculated in NOISE analysis. Is there something obvious that I am doing wrong?

Rather than fail spectacularly at formating my images, I decided to upload them as a PDF. Hope that is alright.

Thanks in advance!
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