[time-nuts] Low noise power supplies?

[Bruce Griffiths]

Poul-Henning Kamp wrote:
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> In message<BAY162-W38A3AC22812AC79A0FBFC6DF1D0 at phx.gbl>, Tom Knox writes:
>    
>> Starting with a hp supply this finesse regulator will really clean
>> up the output. http://www.wenzel.com/documents/finesse.html
>>      
> I've played with that, and it can do impressive things.
>
> However, to big caveats:
>
> 1.  It's very temperature sensitive so on average you only get tens
>      of dB, not hundred dB damping.
>
> 2.  Noise which comes in from the load gets amplified.
>
>
>    
With some care its possible to make the emitter current of the shunt 
transistor approximately PTAT so that, at least for small signals the 
temperature dependence of the rejection is reduced significantly.

Its also possible to build a feedback style shunt regulator that has 
considerably higher supply rejection than the Wenzel circuit using an 
opamp and a shunt transistor together with a small resistance in series 
with one of the supply leads.

Bruce