I am designing a transimpedance amplifier - current in, voltage out.
I want to measure the group delay - is this the derivative of the phase of S21 or of S21/(1-S11).
Also what does the cadence calculator groupdelay function measure and how would I use it to measure the group delay of this amplifier ?
Did you search for groupDelay in the documentation (in current versions you can use the search box in the Help menus inside Virtuoso)? It explains exactly how it is calculated (it takes an AC signal; it doesn't use s-parameters).