Worst case AC analysis

[aislam]

Hello!

I am trying to do worst case analysis on the frequency response of a circuit - essentially, how does the 3 dB cutoff frequency of the magnitude response vary as the component tolerances change.

Nominally, the attn is -7.7 dB at 1 Hz (almost DC). At 3.03 Hz, the attn is -10.7 dB - so this is the nominal -3 dB cutoff frequency for my circuit. Now I hope to see how the attenuation varies at 3.03 Hz as the component tolerances are applied in a worst case scenario.

I used Collate: Frequency, Frequency: 3.03 and Direction: High (and later repeat with Low). In both cases, the component values were not adjusted at all by the simulation. It reports that the nominal run IS the worst case run.....

What is going on? Please advise (circuit attached).

Thanks,

Anik

[Tien_P]

Hi Anik,

I don't know why but the exrpession V(2)-V(5) is causing the simulation error, select the "simulation" tab on the spreadsheet view to view the error.  If you select node 5 or 2 as the output, you will see a response, make sure you uncheck the "expression' checkbox.