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Design >> Analog Design >> Need help in designing an opamp circuit
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Message started by pt3rg on Oct 29^th, 2003, 5:54am

Title: Need help in designing an opamp circuit
Post by pt3rg on Oct 29^th, 2003, 5:54am

I need help in designing an opamp circuit with the following features:
A difference of 45.9mV for the Vin will result in a 0.1V difference for the Vout.

For example, if Vin=4.1V and Vout =5V
a change in Vin = 4.05V will make Vout = 4.9V

It doesn't matter what are the values of Vin and Vout, it's the difference that's important.

Title: Re: Need help in designing an opamp circuit
Post by Paul on Oct 30^th, 2003, 1:06am

If I understand correctly, you want to track changes of Vin over time. You could do this using a switched-capacitor structure calculating Vin(k)-Vin(k-1) and amplifying this difference. Is discrete-time operation acceptable for your application?

Generally speaking, a high-pass topology would reject the DC component of your input and amplify the high-frequency components.

Paul

Title: Re: Need help in designing an opamp circuit
Post by Ken Kundert on Oct 30^th, 2003, 9:51am

The way I understand his post is that he wants a unity gain amplifier with a built-in 100mV offset. To do so, you could configure a unity gain amplifier that has a resistor in the feedback, then build a current source that pulls a fixed current through that resistor. In that way, the feedback voltage will always be offset from the output voltage by a fixed amount, and so the output would have a fixed offset from the input.

-Ken