[time-nuts] Stepping up the output of an OCXO

[Dr Bruce Griffiths]

Dr Bruce Griffiths wrote:
> Didier Juges wrote:
>   
>> Bruce,
>>
>> In cases where the output signal does not need to be a sinewave, how would a common base amplifier compare to a fast comparator and if necessary a digital buffer as necessary to deliver the necessary power level? If this is designed to drive a mixer, a square wave may actually be better than a sine wave (lower conversion loss), and I would venture that the isolation (at least load independence) in most comparators is much better than that of a monolithic amplifier. 
>>
>> Didier
>>     
Didier

Perhaps the major reason that comparators and logic gates have inferior 
phase noise than linear amplifiers is that comparators do not use 
negative feedback (except for some Plessey comparators that used series 
shunt feedback in the signal path). A comparator that employed negative 
feedback in a limiting preamp would be expected to have a lower phase 
noise than that of the comparator without the preamp. The critical 
region is around the input signal zero crossing, if RF feedback is 
effective noise around this transition then the effective noise of the 
following comparator should be suppressed.

Unfortunately AFAIK there is no data on the phase noise properties of 
the Plessey comparators, nor has anyone tried using a limiting preamp 
with RF feedback.

Bruce