Bill wrote:
Low noise voltage at the cost of noise current which is around 1000 times that
of low noise JFETs.
Sure, but the noise resistance (input termination at which voltage
noise and current noise contribute equally to the output noise) is
still around 400 ohms -- anything lower and the input current noise
is not much of a factor. For a 10 MHz distribution amp, this
condition is very likely to be met.
The discussion suggest that opamps contribute to the sideband phase noise
of the signal. I am interested in the mechanism that adds this phase noise.
It would have to be a small shift in either gain (changing Miller
capacitance) or
an internal capacitance in the opamp.
As you suspected, the primary mechanism is usually modulation of
transistor capacitances by noise. Another is general component
noise. Three good references are:
Walls, et al., Origin of 1/f PM and AM Noise in Bipolar Junction
Transistor Amplifiers;
Ferre-Pikal, et al., Guidelines for Designing BJT Amplifiers with Low
1/f AM and PM Noise; and
Ascarrunz, et al., PM Noise Generated by Noisy Components.
I think Bruce has these linked on his pages at Didier's (KO4BB) site
(http://www.ko4bb.com/~bruce/).
Best regards,
Charles
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