[time-nuts] TADD-1 Design (was Re: Stepping up the output of an OCXO

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Feb 5 17:28:41 EST 2007

Christopher Hoover wrote:
> Agreed, that that regulator doesn't have sufficient margin for the entire
> TADD-1.
> I was suggesting using the low-noise high PSRR linear reg only to establish
> the bias level.  
> There are indeed better parts.  This one looks pretty good for an
> integration solution (not include three C's):
> http://datasheets.maxim-ic.com/en/ds/MAX6126.pdf
> This app note, which filters the MAX6126 with an additional pass transistor
> and opamp, shows how to get down to 6 nv/sqrt(hz):
> http://www.maxim-ic.com/appnotes.cfm/appnote_number/3657

A simpler solution should be possible.
Since both the input and the outputs are transformer coupled, the 
circuit ground plane could sit at half the supply voltage.
There need be little dc current flowing into or out of the circuit 
ground plane so a simple resistive divider should suffice to bias it at 
the desired voltage.
If all RF loads within the circuit are returned to the circuit ground 
plane then most of the resistive dividers used to set opamp input dc 
levels can be eliminated.

This complicates testing in that either a floating dc input supply would 
be necessary or differential probes with adequate common mode rating 
would be required.


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