AS
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I have a rather fundamental question regarding Monte-Carlo simulation using Spectre. And I would like to use a Band-gap circuit as a reference design, as it would include a Bjt, resistor and MOS elements in the same design, and maybe designers have different experiences with those elements. The models support simulation of process and mismatch (globalmc_localmc) and the simulated variation (with sufficient no. of samples) in the band-gap voltage should cover 3-Sigma variation seen at the foundry. (Also, this is common with designers from a lot of big semicon companies; no one I came across uses the correlation parameter between devices for simulation as described by Don O’Riordan in "Recommended Spectre Monte Carlo Modeling Methodology".) Now, my question is with so much variation covered under-the-hood by the same model(globalmc_localmc), what kind of process variation/mismatch is getting simulated and are different devices correlated to each other? For example, can there be a case where the differential pair of op-amp in BGR have the two devices at extreme process corners with x%-mismatch on top (should be an impossible event even with lot/wafer/die/intra-die variations)? Is there any correlation between a fast MOS corner and fast BJT/min resistor corner. I know this has a lot to do with foundry data but would appreciate if someone could shed some light here?
Thanks, Aman
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