# How gain is changed in this Op-AMP integrator? Hi, I am simulating this circuit for personal development. The gain of the integrator can be calculated using the following formula:

Gain = -Rf/R1 (1/(1+(2 x pi x f x C1 x Rf)))

But, how to calculate the gain of this circuit when diodes are introduced for rectification. I tried for some time. But couldn't get the result I see on simulation. How to calculate the gain of this circuit and output voltage(both Vrms and Vdc) with that gain?

Also, if anybody explains how this circuit works, it will be helpful for me.

• Ignore the capacitors. Analyze the circuit assuming the op amp output is positive. Analyze the circuit assuming the op amp output is negative. The op amp negative terminal is always at ground potential. Assume the diodes are shorts when forward biased and opens when reversed biased. – user69795 Dec 10 '20 at 5:07
• @user69795, can you be more specific? – CNA Dec 10 '20 at 12:59

## 1 Answer

When the input is negative, the op amp output is positive. D3 is ON. The circuit is an inverting amp with a gain of 1.4. When the input is positive, the output is negative. D2 is ON. The circuit has no gain. The op amp output is then a half wave rectified signal. R5 and C3 are a low pass filter. C2 also acts as a low pass, when the op amp has positive outputs.

• If so, how should i calculate the output voltage? – CNA Dec 13 '20 at 4:03