On Fri, 14 May 2004 11:23:42 +0200 Angel Vilaseca <avilaseca@bluewin.ch>
writes:
> Hi,
>
<snip>
>
> My question is: Could a gate-grounded circuit help with the
> power-MOSFET
> input matching problem?
>
> More generally: Has someone already tried to build a grounded-gate
> power MOSFET amplifier?
>
>
>
> Angel Vilaseca HB9SLV
>
>
Hi Angel,
You would still have the horrific input capacitance in GG and an even
lower impedance to drive.
I've been contemplating a cascode connection to alleviate the input
capacitance using a low voltage (25V) FET for the input device connected
to a 500V FET, with the gate biased to 15V or so, to complete the
cascode.
The low voltage input FET has 1/10 or so of the capacitance of the HV
part. If the HV FET's have a 200V Drain supply the output impedance will
be in the vicinity of 50 ohms which will be easier to match to the load
than a typical transistor circuit.
I've seen cascodes of similar design used for driving CRT's and other
things but, never for RF power. There may, or may not, be a reason why
not... :-)
73 & Good morning,
Marv WC6W
*
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