Can we use a MOSFET/FET as amplifier at the first stage? [RF transceiver]

tindel

Joined Sep 16, 2012
936
Horses for courses - Power MOSFETs in TO220 or bigger have a few nF gate capacitance, RF DG MOSFETS like the BF991 etc have a few pF capacitance.
I stand corrected. Looks like a good transistor for RF... I'm a bit confused about the two gates though... Is that an 'OR' configuration. Either Vgs going high turns on the FET?
 

bertus

Joined Apr 5, 2008
22,270
Hello,

The second gate of a dual gate mosfet can be used as a multiplier.
You can use the voltage in the second gate as an AGC signal or mixing signal, as shown in the link I posted earlier.

Bertus
 

ian field

Joined Oct 27, 2012
6,536
I stand corrected. Looks like a good transistor for RF... I'm a bit confused about the two gates though... Is that an 'OR' configuration. Either Vgs going high turns on the FET?
Its pretty much 2 FETs in a casc-o-de configuration.

The bottom FET is in common source configuration, and the top one is grounded gate.

Bipolar (and sometimes MOSFETs) were used like this for high resolution in CRT video amplifiers because they give pretty amazing bandwidth.

With DG MOSFETs; the upper gate is frequently used for injecting the AGC voltage.
 
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