[time-nuts] re low noise regulators

[Bruce Griffiths]

A more accurate summary of the noise characteristics of voltage
regulators is something like (neglecting the effects of excessive noise
on the regulator input voltage):

1) For all regulators when the reference isn't low pass filtered the
reference noise dominates the output noise. Even when the reference
noise is low pass filtered it dominates the regulator output noise at
low frequencies.

2) When the reference is low pass filtered the error amplifier noise
dominates the midband regulator output noise.

3) The regulator output noise scales with output voltage. However a
capacitor bypassing one of the output voltage setting resistors in a
conventional voltage regulator circuit can reduce the midband output noise.

Using the 723 regulator as an example: