Peak Detector circuit

[Ankita Pasad]

Hello all,

I want a circuit which gives accurate value of the peak of input sinusoidal wave (zero DC offset) as DC output. The one which I am currently using, a very common approach, gives an error offset of about 0.2 V which is too high for my experiment.

Here are the specifics:

opamp - TL081

C - 10nF

diode - IN914

frequency of operation - 30kHz

(there does not seem to be a problem with opamp gain bandwidth product or slew rate)

Any kind of help will be highly appreciated. 

Regards,

Ankita

​

[Yash Bhalgat]

Maybe you could amplify your sinusoidal signal before giving it to Vin. That would reduce percentage error. And then again "deamplify" your Vout by the same ratio?

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Yash Bhalgat,

Electrical Engineering, IIT Bombay

[Neeraj Babu]

This reduction in voltage may be due to the loading imposed by the measuring instrument. You can put another voltage follower at the output and measure voltage at the output of the follower.. Also use a bigger  capacitance if it don't hurt your application

[Ankita Pasad]

Yes I tried adding a buffer as well, it made no difference.Also no change with bigger capacitance. The output remains the same whether measured with a DMM or atmega32 adc.

[Satishwar Kedas]

https://www.youtube.com/watch?v=jllsqRWhjGM

hope this helps..

[Ashish Goyal]

I think saturation is an issue here. You might add another opamp (not a buffer) such that capacitor gets charged whenever the opamp tries to go in saturation. This is widely used.

Ashish Goyal

U.G. Department of Electrical Engineering

Music Secretary, Hostel 2, IIT Bombay

[Neeraj Babu]

This error can be due to the non idealities of the OPAMP . 0.2V is too big to be true, but around 0.1V may be possible in case of OPAMPs with BJT stages. BJT drive stages are employed to increase the speed, but this may lead to lot of loss of precision. In your OPAMP, the input bias current comes to around 0.4nA which is quite high and the offset volt is also around 30mV. 

You can do two things here.

1. Apply offset and bias nulling by known techniques for the same OPAMP

2. Go for a better OPAMP say OPA320 which has just 0.9pA bias current and 150uV offset. Go for precision OPAMPS. 

Neeraj Babu .C

MTech - Electronic Systems

Research Assistant - Wadhwani Electronics Lab

Department of Electrical Engineering

IIT Bombay

Ph:91-22-2576-4449

Mob:9167516136

http://www.ee.iitb.ac.in

http://wel.ee.iitb.ac.in/

[Ankita Pasad]

Yes the problem is due to opamp going in negative saturation. Will try that!

I had tried offset bias nulling - no change.

Will try better opamps if nothing else works.

[Ankita Pasad]

It is a nice video!

So this is the circuit which came to rescue (googled it). D2 helps the opamp not to go to negative saturation by restricting the voltage at point B to Va--0.7.

​

Specs:

R = 2.2 kohm

D1, D2 - IN4148

C = 100nF

Thank you all for your inputs.

Regards,

Ankita