precision rectifier

[AN920]

Your function generator may have a dirty/noisy offset pot. You don't need much offset to mess up the result. Have you tried making R3 variable and adjust for balance?

 

[MNA]

You don't need much offset to mess up the result.

sorry but i didn't get it?

Have you tried making R3 variable and adjust for balance?

No i haven't tried it yet but i think it has nothing to do with the waveform which is a result of some dc offset....
But i will make it variable because of the 1% tolerance factor....
i have checked the resistor values with the multimeter and then with those values i simulated the circuit...it is still not making such a big difference......


shouldn't the generator give 0 dc offset when the offset knob is closed/not pulled out(default)?..... why is it not giving 0 dc offset?.....

 

[AN920]

I am trying to say that very little DC offset on the input will make the peaks uneven.

Read your generators instruction manual to find out where is the cal position. Some generators will have a internal adjustment to calibrate the DC offset zero position. That may be out of calibration. More expensive digital synthesized generators will be auto cal'd by the uP and offset will be very close (within uV's) to zero.

Just checked my digital generator and the offset is 11uV. I think this will be equal to 1LSB of the internal DAC

 

[MNA]

ok I'll check that....
Thanx

 

[LostViking]

As AN920 is indicating the generators output does not appear stabile. It seems to drift over temp/time. Will the real world input also drift? That will cause a constant problem. What MIGHT be required is to sample the difference in peaks and use that as a correction voltage to control the offset circuit. This will keep the output centered.