I am looking for ways to reduce the third harmonic from the output of a differential amplifier. Are there any papers detailing distortion analysis? any good books which relate to this topic that anyone can recommend?

Any help will be deeply appreciated!

A possibly more useful response...

Distortion can occur throughout the circuit, but it is likely to be either at the input or at the output. Improving distortion first requires deciding where the dominant source is.

Odd harmonic distortion is often caused by output load currents. Change the load impedance and see what happens.

Output distortion is often dependent on output stage bias current. Try experimenting with the bias.

Input distortion in a feedback amplifier implies that you have too much error voltage applied to the input stage, given its construction. Higher bias current can help, you can also improve distortion by degenerating the input, but these also change open loop gain.

In a feedback amplifier, higher open loop gain will usually decrease distortion whether the source is at the input or output. The trick, of course, is how to increase the open loop gain and retain stability.

Steve

raja.cedt wrote on Jun 23^rd, 2009, 7:55am:

This changes a load line for output transistor, so it is quite natural that odd harmonics depends on output load current.

sos wrote on Jun 23^rd, 2009, 4:55am:

Berti wrote on Jun 24^th, 2009, 6:20am:
Who refers to SC circuits in this thread ?
And even for SC circuits, we can define load line and current.

raja.cedt wrote on Jun 24^th, 2009, 6:26am:
Output impedance of OPAmp is not zero actually.

And apart from final output of OPAmp, there are loads in voltage gain stages in every OPAmp.

aaron_do wrote on Jun 24^th, 2009, 7:10am:
I think odd harmonics of V-I converters is dominated by input nonlinearity not output.

raja.cedt wrote on Jun 24^th, 2009, 6:26am:


My suggesting output load current assumed you had a load. If there is no load, other sources of distortion are at fault.

Steve