I am new to cadence virtuoso/spectre. I want to design an ADC for which I have written some components through verilog A containing their respective noise models implemented through white_noise and flicker_noise functions.
Now how to activate those sources in spectre simulation ? It's only active in small signal analysis as far as I know. However I want noise to be present along with the main signal so that I can measure SNR etc using calculator function.So which type of analysis to use: tran or noise ? and how (few lines of analysis statement will help)
Moreover, from cadence virtuoso manual I found that we can perform small signal analysis during transient analysis, by using below command:
Name tran stop=stop actimes=time acnames=name
However I got a syntax error of "ERROR (SPECTRE-16062): Output of circuit is not specified." on running below code snippet on a simple test circuit :
tran tran stop=4u write="spectre.ic" writefinal="spectre.fc" \
annotate=status maxiters=5 actimes=[2u] acnames=[noise1]
noise1 noise start=2u stop=2.1u
finalTimeOP info what=oppoint where=rawfile
I stuffed another "info what=oppoint" statement between 2nd and 3rd line, still same error. Here my understanding is tran analysis stops at 2u and till 2.1 the simulator will run noise analysis (if wrong please correct me). I am still trying to debug this and it may be a plain syntax error. However can someone please answer above questions and guide me through the right approach.
Thanks a lot!
I'm not quite sure how you're managing to model the flicker and white noise of the devices in the ADC without a good understanding of the noise mechanisms, but maybe you have a better understanding than your questions suggest?
Obviously you can also have "noise" caused by signal integrity issues (e.g. parasitic coupling from unwanted signals onto critical nodes). But maybe if you class the ADC as "properly designed" you wouldn't get this?
In general you can use the frequency domain output of small signal noise analysis to compute noise figures for linear circuits. For example, if you have an amplifier, it's an effective way of measuring noise. If however the circuit has some kind of sampling behaviour, or translates signals from one frequency to another (such as a sample and hold, or a mixer, or an ADC), then you need to do some kind of simulation that will take that into account. As I mentioned before, pss/pnoise can be an effective way to do this for circuits which have a periodic response - the non-linearity (which is what causes the frequency translation) is captured in the pss, which finds the periodic steady state (a kind of periodic operating point), and then the pnoise is a small-signal analysis around this periodic operating point.
So the noise output is not just there for information - it is useful for many classes of circuit,