chopper amplifier, feedback feasible?

[Roger Bourne]

Hello all,

I want to implement a chopper amplifier (differential input, single
output) into a follower topology. Since a chopper amplifier works by
square wave modulating the input (chopping, originally by a mechanical
switch), amplifying the resultant AC signal,
and then synchronously detecting the amplified signal.... (copied this
bit from another post), is a follower topology (minus input shorted
with output) feasible with a chopper amplifier, or will the feedback
destroy basic chopper amplifier principle?

In other words, can a chopper amplifier be operated only in "open-
loop" mode (no feedback), or can the chopper amplifier replace op-amps
in typical op-amp topologies, meaning that it can handle feedback.

I am using the chopper amplifier to remove a signal's flicker noise.
This is why I am employing the chopper amplifier in a follower
topology.

Any help will be appreciated.


Regards,
-Roger

 

[Robert Latest]

I want to implement a chopper amplifier (differential input, single
output) into a follower topology. Since a chopper amplifier works by
square wave modulating the input (chopping, originally by a mechanical
switch), amplifying the resultant AC signal,
and then synchronously detecting the amplified signal.... (copied this
bit from another post), is a follower topology (minus input shorted
with output) feasible with a chopper amplifier, or will the feedback
destroy basic chopper amplifier principle?

In other words, can a chopper amplifier be operated only in "open-
loop" mode (no feedback), or can the chopper amplifier replace op-amps
in typical op-amp topologies, meaning that it can handle feedback.

I am using the chopper amplifier to remove a signal's flicker noise.
This is why I am employing the chopper amplifier in a follower
topology.

Any help will be appreciated.

I'm not sure if you have got the concept straight. Besides, I can't see how
any kind of amplifier can help you "remove" any kind of noise from a signal.
If all you want is an amp with very low 1/f noise, maybe a chopper
stabilized opamp is what you need.

robert

 

[Roger Bourne]

I'm not sure if you have got the concept straight. Besides, I can't see how
any kind of amplifier can help you "remove" any kind of noise from a signal.
If all you want is an amp with very low 1/f noise, maybe a chopper
stabilized opamp is what you need.

robert- Hide quoted text -

- Show quoted text -

I just read some more on chopper amps (....prompted by your
comment ). I get it now, chopper amps remove/attenuate the 1/f
noise contribution of the amp only. Hmmm..... I guess I will have to
find a way to introduce the the chopper amp in the feedback loop that
is responsible for producing the very-noisy 1/f signal. That should
not be too difficult (i hope) since the noisy signal stems from an op-
amp in follower configuration. That brings me back to my original
question, can chopper amps function with feedback ?


-Roger

 

[Robert Latest]

On 5 Apr 2007 08:04:31 -0700,

That should
not be too difficult (i hope) since the noisy signal stems from an op-
amp in follower configuration. That brings me back to my original
question, can chopper amps function with feedback ?

Without knowing any more about the kind of signal being processed, this
brings me back to my original suggestion: Read up on chopper-stabilized
opamps (very different from chopper amps which have gone out of fashion
decades ago). Possibly you can just replace your noisy opamp follower
by dropping in a chopper stabilized one and be done.

When doing research on this, you can also look for "zero drift" opamps
which is another name for the same thing. LT have a few cute app notes
on their site (www.linear.com).

robert