tiger66 said:
Thanks for the response
I am trying to design a chopper stabilized amplifier and the last
stage is a LPF. The stage before LPF is a modulator and its output is
a modulated signal. So I try to use a LPF to keep the first harmonic
and filter the other harmonics of the signal coming out of the
modulator.
My input is a 1khz, 5V DC signal, so I think I should have a LPF with
cutoff frequency at 1kHz.
Can you example what do you mean by pass both outputs through it.
capacitor. The -ve pin of the opamp connects to one output of my
modulator and the +ve pin of the opamp connects to ground.
So, do you suggest that I should connect the other output from
modulator to the +ve pin of the opamp instead of the ground?
Thanks
Hmm, i just replaced a Chopper Op-amp on a voltage sensing board
at work, it just used a RC network to smooth off the edges.
In any case, i would try a simple common mode filter and check it
on the scope ..
I'm assuming that you must be using a very square wave signal that
you're trying to remove the harmonics that are getting generated from
it ?
Most likely, any filter you use is going to curve the left and right
shades.. if that is fine with you, i think maybe just having a non
inductive type resistor on each output would fix your problem.
a little by pass capacitance should be applied on the output side of
the R's
I'm thinking 100 Ohm R should do it with like a .001 uf by pass, but
that is just off the top of my head.
filters like Active types may tend to take your nice square wave and
truncate it. That has been my experience on that subject, it only makes
sense that it would do that. But then again, the idea i gave you above
may also give you some deforms thus giving you what i call a hook tooth
wave, in which case an inductor added to the scene can handle that.
I think you need to experiment a little.