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Re: That's what I was thinking....

Hi,

I spent a little time with Spice this evening. Used a DN2540 FET
model in a local feedback circuit. Wanted to see if varying level
of local feedback increased high order harmonics.

I veried feedback from none (infinite), 1Meg, 500K, 200K, 100K, 50K.
Adjusted input signal and bias so that output stayed the same as
feedback resistor was changed.

The result was as you said, and what Cheever fig 2-15 says.
It is interesting that as feedback increases, 2nd marches steadily
downward. So much for the usefullness of THD.

An active load (current source) non feedback stage seems to be a
better substitute...all harmonics start out at a lower level.
Using another DN2540 as a current source, I was able to cancel even
harmonics at one setting (in simulation).

I'd never heard that a transistor could have its 3rd cancelled.
Will have to try this (simulated).

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