CAD:Transient gm

I had an older post on sweeping and plotting the transistor operating points for DC sweeps, etc., for the Spectre simulator.

As Dai Zhang (Electronic devices) asked me – what about transient sweeps – she did inform me about “infotimes” in the transient options for spectre. That seems to work quite well, see for example

However, as tips for you others I compile some ideas on how to do this (first of all, use an ocean script, that kind of solves all problems. However, sometimes the GUI makes a little bit more sense … so what to do then…):


Start by defining those time points where you want to evaluate the operating point

(setq tStart 0n)
(for m 0 (floor (setq tStop 1m)/(setq tStep 10u))
(printf "%3.1e " tStart+m*tStep))
(printf "\n")

take that line and paste it into the GUI transient options infotimes field. It could however be hard to get access to one line neatly in the CIW. You could then emacs (yeah, no vi) the log file and find the text string to paste into the GUI.


Save the state (as a cell view or library), then open the analyses.state (in the cell view state mode) file and change the row:

analysis(tran options infotimes) ()

to contain your line of time points. They should be separated by a “” in a list, so for example:

analysis(tran options infotimes) ("10n" "20n" "30n")

Save the file and reload the state.


First, create your list of points, say (paste into CIW):

(setq timeList (list))
(setq tStart 0n)
(for m 0 (floor (setq tStop 1m)/(setq tStep 10u))
(setq timeList
(append timeList
(list (sprintf nil "%3.2e" tStart+m*tStep)))))

Then use the quick-and-dirty (there are neater ones, of course… Andrew Beckett knows) paste this into the CIW, provided that you have the ADE for this simulation active:


Sometimes, cadence is a bit dodgy and you need to open the analyses form and close it, just to make it understand that something has changed.

2 thoughts on “CAD:Transient gm

  1. Pingback: Plotting MOS device parameters as function of time (revisited) | Mixed-Signal Comments

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