[time-nuts] Effect of EFC noise on phase noise

Charles Steinmetz csteinmetz at yandex.com
Tue Aug 2 04:21:35 EDT 2016


Gerhard wrote:

> The preamp will be classical.  Some JFETs in parallel  *  *  *
> Cascode with a Zetex bipolar (or whatever they are called now).
>      *  *  *
> Without the cascode, the 1 MHz is not possible. It does not help that
> the feedback limits the voltage excursions on the drain.

As you recognize, these FETs need significant drain-source voltage to 
give their promised performance (8v at the absolute minimum, IMO, and 
they really should have 10v).  You might try a folded cascode topology 
(sometimes called a "reverse cascode") to increase the D-S voltage.  It 
is a little more complicated, but should not have any material impact on 
the noise figure if it is done properly.

Best regards,

Charles




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