# Integrator in feedback.

1. Nov 13, 2008

### matheinste

Hello all

I have come across a circuit of a standard differential amplifier with an integrator in one of the feedback paths. I have no idea what its function is. I suppose some sort of frequency gain discrimination Any ideas?

Matheinste

2. Nov 13, 2008

### Staff: Mentor

Seems like an integrator in the feedback path would result in a differentiation transfer function. Are there multiple feedback paths? Can you post a copy of the circuit and put its application into context?

EDIT -- Duh, I just noticed that you said there were multiple feedback paths. I need to read posts a bit slower, it appears. So my guess is that the overall transfer function needed a differentiator term on that variable that is being fed back through the integrator, and different transfer functions on the other feedback paths. Sounds like an interesting circuit -- can you post more details?

Last edited: Nov 13, 2008
3. Nov 13, 2008

### Averagesupernova

It might just be a crude filter.

4. Nov 14, 2008

### matheinste

Hello all.

It seems that in the application in which this circuit is used a ramp is generated by the integrator which modulates a sine wave applied to the input. This sine wave is of a very much lower frequency than the repetition rate of the ramp. After further analogue and software processing, the fequency and amplitude of the input sinewave is reovered. Why it is done this way i have still to find out.

Matheinste.

5. Nov 16, 2008

### matheinste

Hello all.

I have now found out that the operation described in my last post is a failure mode and not how the circuit should behave.

The integrator in the feedback loop is just a low pass filter.

What is he advantage of the filter being in the feedback loop.

Matheinste.

6. Nov 16, 2008

### Staff: Mentor

This is starting to sound like a homework/coursework question. If it is, I can move it to the Homework Help forums here at the PF.

7. Nov 17, 2008

### matheinste

Hello berkeman

While i may be guilty of laziness, I am 60 years old and stopped doing homework 40 years ago.

Thanks to everyone for their replies.

Matheinste.

8. Nov 17, 2008

### Staff: Mentor

I didn't say anything about laziness...didn't mean to imply that at all. I was just asking for more information and input from you. It's pretty hard to try to answer your questions without a full circuit diagram showing the parts that you are wondering about.