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Re: 3rd harmonic distortion

Rolf, I received your E-mail. I will attempt to send you the info I have. The analysis was developed for an advanced course by Dr. R.G. Meyer and Dr. Don Pederson, (and perhaps others as well) as working notes for a course in nonlinear circuit analysis in the early 1970's. Subsequently, Dr. Meyer wrote the book: 'Analysis and Design of Analog Integrated Circuits' , a very good textbook, BUT it is for an other course and it covers only the usual aspects of negative feedback, known to almost everyone interested in this subject.
The cancellation of 3'rd harmonic distortion by local feedback is, however, on page 94 of 'Analog Integrated Circuits for Communication' by Don Pederson and K. Mayaram. You might find this textbook in your university library.
In 1973, I did ask Dr. Meyer, privately, whether higher orders were easily cancelled as well, but he said that he did not know of any approach at the time. I am not surprised at this time after rereading the class notes on the subject, because:
"The term involving a(3) in (1.42) is due to third order distortion in the forward amplifier. The term involving a(2) is due to second order distortion in the forward amplifier being fed back and combining with the fundamental signals to produce third order distortion. Thus the error signal S(e) contains second order distortion as well as linear terms. These two combine in the second order nonlinearity to produce third order distortion. This process is called second order interaction. It is interesting to note that if a(3) is zero, but a(2) is non-zero, then b(3) will be finite. That is, even if the original amplifier had no third order distortion, the application of feedback can create third order distortion via second order interaction. ..."
The basic equation relating to the above commentary is:

b(3) = {a(3)[ 1+a(1)f ] - 2a(2)squared times f } / [ 1+a(1) times f ] to the fifth power



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  • Re: 3rd harmonic distortion - john curl 12:25:17 12/29/04 (0)


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