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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