--- On Sat, 4/13/13, Andy <Andrew.Ingraham@...> wrote:
From: Andy <Andrew.Ingraham@...>
Subject: Re: [LTspice] Re: inverting opamp simulation: rapid component variation
To: LTspice@...
Date: Saturday, April 13, 2013, 8:13 PM
?
> Hello Helmut. Thank you for your example. I have no issue in performing transient.
Question is how do I simulate this behavior in terms of frequency response.
The quickest way to get a frequency response is to use an .AC
analysis, rather than .TRANsient. Then you can sweep and plot output
amplitude versus frequency.
The thing to always remember about .AC analysis, is that it is a
"small-signal" analysis, and the entire circuit is first linearized at
the operating point. If there is anything nonlinear in your circuit,
its effects would be ignored.
For the op-amp circuit, if you want to see the response from resistor
R2 to the output, that should work. But if you want to do something
like look at the frequency response between the source VDC and the
output, while R2 varies sinusoidally, that would not work because R2
modulates the response, i.e., its effect on VDC (and vice-versa) would
be nonlinear.
The other possible problem with .AC analysis is getting a modulated
resistance that works in AC analysis too.
Sometimes you just need to use a transient analysis. Then you can use
the .STEP command to vary the frequency in steps.
Andy
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