Dear MaryEm, [quote userid="504246" url="~/cadence_technology_forums/f/custom-ic-design/43969/isf-function-extraction-in-cadence-virtuoso/1373744"]If Spectre ppv plot gives the net result, I am not sure how it combines the different ISFs. Based on what algorithm.?[/quote] I'm not sure I was clear, the ISF (or equivalently ppv) is the phase variation that is produced is a result of the all the individual noise components in the steady-state solution computed in a large-signal sense (i.e., including folding noise). There is only a single ISF. [quote userid="504246" url="~/cadence_technology_forums/f/custom-ic-design/43969/isf-function-extraction-in-cadence-virtuoso/1373744"]"Efficient Calculation of the Impulse Sensitivity Function in Oscillators" by Salvatore Levantino in which they use both Transient Method and PXF analysis method with some post processing. At the end they obtain "two separate ISF plots" from each of the methods. So, for their oscillator design one knows where the exact contribution is coming from. [/quote] The purpose of the Levantino paper is to show a number of computational methods provide the same basic result. It is totally unrealistic to assume the output noise of an oscillator is due to a single source of charge injection. The spectre pnoise analysis is designed to study the phase noise of an actual VCO or oscillator and hence the ppv represents this capability. [quote userid="504246" url="~/cadence_technology_forums/f/custom-ic-design/43969/isf-function-extraction-in-cadence-virtuoso/1373744"]If Spectre ppv plot gives the net result, I am not sure how it combines the different ISFs. Based on what algorithm.?[/quote] It does not as I mentioned above. It computes the ppv based on the total output noise produced by all device noises and their folding due to the large signal steady-state response of the nodes you specify as the outputs in the pss/pnoise GUI dialog boxes. Maryem, I might suggest you please refer to the Cadence documentation of the pss and pnoise analyses. I get the impression you may not understand these two analyses. Shawn
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