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how to measure delay of the circuit in cadence..

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vrunda

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hi,
i had done the 8bit priority encoding based comparator in cadence and performed the transient analysis. i need to measure the delay of the circuit. can anyone tell me the method or procedure to find the delay of the circuit in cadence spectre..

thanking u
vru
 
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dick_freebird

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In the ADE you'd use calculator to find your output
transition timepoint (using cross() function) and the
input transition preceding it, and subtract. That
calculator expression will also work in Ocean. I do
not use bare Spectre.
 

vrunda

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thank u very much. when i have many inputs and single output can i follow the same procedure.. is that method gives correct value of the delay?
 

dick_freebird

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As a rule, testing likes to change only one input at a time.
But learning which change is the worst case, required you
to have gone through them all.

If you are wanting to run a pattern, I would recommend you
do it as a rack of parametric analyses rather than one long
simulation, to make it simpler in the data collection - 2^n
runs of one cycle apiece, all with a single transition are
easier to deal with than having to keep on changing the
time window and so on. Which you might do in Ocean, but
interactively w/ Calculator would be very tedious. You can
then printvs all the 2^n results and sort them to find the
worst, and know which code transition is the worst case.

Of course a simple ripple count may not exercise the worst
transition either; that does not hit any:any by a long shot.
You might need to use some veriloga or cutely-parameterized
source expressions and nest two 2^n loops ("from_code" and
"to_code") to exercise everything.

Most often I add a "raster" source on the same timescale
as the inputs, turn the output into an eye digram and pick
off the rightmost transition by eyeball. Which is OK for me,
but maybe not you and whoever's breathing on you.
 

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