Constant output opamp?

[varunperumal]

Hi all,

I need help with making an op-amp circuit. I am trying to amplify a sine wave of varying frequency. I am looking to get the same peak-peak amplified output whatever the amplitude of the input signal is (within limits). Is there any standard way to do this, to dynamically alter the gain?

Any suggestions are greatly appreciated. I am trying to do this in a fairly complicated way, i was wondering if there are any standard solutions to this.

Thanks in advance,
Varun

 

[Reloadron]

I don't get it? You want output the same amplitude as input so you want unity gain? What frequencies?

Ron

 

[audioguru]

Design the opamp to have a voltage gain of 1. Then the output (up to saturation) will be the same amplitude as the input.

Do not exceed the max allowed input common mode voltage range of the opamp. You might need to attenuate the input to half then use a voltage gain of 2 for the opamp.

 

[varunperumal]

Hi all,

Thanks for your reply. What i meant was not a unity gain configuration.

Say there was a signal of peak to peak 500mV- i want it to be amplified to 5v, say there is another case where the input signal is of 200mV i want it to be amplified to the same 5V as well, and so on with any other input signal voltage.

Thanks
-Varun

 

[Nigel Goodwin]

You want AGC (automatic gain control) - it's usually done with FET's and rectifiers, altering the gain of the opamp dependng on the output level.

 

[varunperumal]

Thanks a lot! now i know what to google for.