[Amps] grounded-gate power MOSFET

[Radio WC6W]

On Fri, 14 May 2004 11:23:42 +0200 Angel Vilaseca <avilaseca at 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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