why does a precision full wave rectifier give unequal amplitudes for different half-cycles? How to eliminate this problem?

 

Do you have a particular precision rectifier circuit in mind?

Can you attach it?

hgmjr

 

why does a precision full wave rectifier give unequal amplitudes for different half-cycles? How to eliminate this problem?

Probably because it is autumn, and because birds fly generaly east.

Would you care to post some schematic or are we supposed to guess??

 

The signal may simply be offset by some DC bias, or have unequal excursions.

 

Maybe your feedback resistors are mismatched. Maybe your diodes are mismatched. Maybe the universe sneezed. Maybe you should post a schematic.

 

Typically, the full-wave rectifier is composed of two stages. One is a summer, the other is a half-wave rectifier. You are summing the original signal with the rectified version. If these resistors are not matched, then you run into trouble. Use a potentiometer, this will allow you to adjust it with the oscilloscope.

Steve

 

This is the circuit that I was referring to.

R3 R4 R5 must be precision resistors!

 

The half-cycle amplitudes will be unequal at frequencies higher than about 1kHz if you use lousy old 741 or LM358 opamps. A TL072 dual opamp works pretty well up to 10kHz or 20kHz in that circuit.