[time-nuts] Re: Collector current that minimizes BJT noise

[ghf at hoffmann-hochfrequenz.de]

I confess to sloppy wording:
In the FET section, replace gain by gm.

Now that I send the correction: Bob Widlar did not like
JFETs too much. He designed a bipolar opamp with bias
currents better than the FET ones at high temperatures.
(LM108 IIRC)

I've played a bit in LTspice with his input circuit.
He ran the input transistors with Vce abt= Vbe. That results
in small bias currents and allows the use of super-beta
transistors that cannot withstand much voltage.

I was surprised by the good low noise properties.
The circuit at the top left creates a noisy Vcc to see
how much noise can be tolerated there. Q4 and Q5 are parked
there only for quick exchange.

Gerhard
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