[time-nuts] ? phase comparison or other device

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Jun 30 19:54:11 EDT 2007


John Miles wrote:
>> The output of an opamp is always referenced to its power supply,
>> regardless of the configuration.  If the power supply is noisy,
>> the output is noisy.
>>     
>
> Beyond a few kHz this may be true, but at lower frequencies even a low-grade
> opamp has excellent rejection of power supply noise.  A good opamp data
> sheet will characterize the PSRR versus frequency.
>
> -- john, KE5FX
>   
John

Only when the opamp is operating within its linear region, not when the 
output is saturated.
Opamp saturation has been proposed as a good method of reducing the 
output noise of an opamp when an amplifier is overdriven.
This is clearly not true when power supply noise is significant, as is 
almost always the case.

Bruce




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