[time-nuts] OP-Amps for 10MHz distribution...?

[Charles P. Steinmetz]

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