Hi Maktoomi
Helmut example is absolutely right. This is because a quick analysis of the circuit you have given shows the following:-
Vo/Vin = R2(f)/R1 . It follows that Vo= [R2(f)/Rin]*Vin = Iin*R2(f)
Now Vo = Iin*R2(f) shows the variation of the output with increasing frequency for a simulation time of 100mS. It does not take a lot of imagination to deduce that if your inverting amplifier can be represented by a single exponential lag, Vo will follow the response shown by Helmut's example and then its envelope will roll off at 20dB per decade at high frequencies at the half power point. You can sketch this manually when you know the frequency response of the inverting amplifier you want to use from the data sheet. (refer to Bode). Once you define your R2 the rest is easy.
Best regards,
Michael P Kiwanuka
To: LTspice@...
From: amaktoomamu@...
Date: Sat, 13 Apr 2013 16:46:27 +0000
Subject: [LTspice] Re: inverting opamp simulation: rapid component variation
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.
I want to see how output varies if the rate of variation of R2 keeps on increasing. So, I wish to get a plot Vout vs frequency, where frequency shows the rate of fluctuation of R2.
Higher the frequency on horizontal scale, more rapid the variation in the value of R2.
Any help/suggestions would be greatly appreciated. (This is a part of a paper that I aim at submitting in conference).
PS: I have posted similar question in edaboard to get help in manual analysis of this problem.( more details: )
--- In LTspice@..., "Helmut" <helmutsennewald@...> wrote:
--- In LTspice@..., "MOHAMMAD A MAKTOOMI" <amaktoomamu@> wrote:
Hi,
In an inverting amplifier(Uploaded File:
),
suppose R2 fluctuates very rapidly (say at 10KHz or even
higher, may be due to some environmental condition).
How do I simulate this behavior, given input is some fixed
dc voltage and opamp is 741 type (I have not attached any
specific opamp model so far, use what you have).
I am basically interested in perhaps frequency response-
I want to see how output varies if rate of variation of R2
keeps increasing.
Hello,
I have uploaded an example with a time-variable resistance.
R=1k+5k*(V(ctrl)+1)
Files > Temp > ni-opamp_.asc
Best regards,
Helmut
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