Another neat fet amplifier app note



Called, LSK489 Application Note, and written by Bob Cordell, it is well worth a look.

Amongst the many things I had not seen before (although sadly this is not saying much, considering the poor state of my amplifier knowledge), is the source-follower in Figure 3C (not shown here) which increase input impedance at the cost of only two resistors.

The diagram show is a differential buffer where each jfet is connected to a pnp bipolar in a complementary feedback pair – increasing transconductance and reducing distortion. “Notice that the pnp transistors are actually connected as a differential pair, providing additional common-mode rejection,” says Mr Cordell.

In this application, it is used to boosts the input impedance of a power amplifier.



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