W
Walter Harley
 Jan 1, 1970
 0
I'm trying to analyze a trivial commonsource amplifier based on an IRFP9240
power Pchannel MOSFET (datasheet at
http://www.irf.com/productinfo/datasheets/data/irfp9240.pdf).
The circuit is simply this:
24V


..
  Load
  100R
''


+
> IRFP9240
Vin +


===
GND
Now, I know that voltage gain = gm * Rd. But how do I find gm? I'm
interested in the condition where the MOSFET will be operating in its linear
region, with Vgs close to Vt; Vds around 1V, Id around 200mA.
The datasheet specifies forward transconductance of 4.2S, but that's at 7.2A
and 50V, in the saturation region. The transfer characteristic curves only
go down to 400mA, and anyway they're at 50V also. Similarly, the output
characteristic curves don't show the region I'm interested in.
Given the available data, how can I determine the transconductance at the
operating point of interest?
Thanks for any help!
power Pchannel MOSFET (datasheet at
http://www.irf.com/productinfo/datasheets/data/irfp9240.pdf).
The circuit is simply this:
24V


..
  Load
  100R
''


+
> IRFP9240
Vin +


===
GND
Now, I know that voltage gain = gm * Rd. But how do I find gm? I'm
interested in the condition where the MOSFET will be operating in its linear
region, with Vgs close to Vt; Vds around 1V, Id around 200mA.
The datasheet specifies forward transconductance of 4.2S, but that's at 7.2A
and 50V, in the saturation region. The transfer characteristic curves only
go down to 400mA, and anyway they're at 50V also. Similarly, the output
characteristic curves don't show the region I'm interested in.
Given the available data, how can I determine the transconductance at the
operating point of interest?
Thanks for any help!