Published:2011/6/8 22:13:00 Author:leo | Keyword: The high input resistance amplifier circuit formed by FET | From:SeekIC
The picture 1 shows a high input resistance amplifier circuit. The picture 1(a) is the sourcing follower circuit formed by FET. The voltage gain of the follower: Av=gmRL/(l+gmRL); gm is mutual conductance; RL is sourcing load resistance. If Ac needs to be near 1, FET with bigger gm value is needed with the resistance value RL as big as possible. In order to increase the RL value, constant sourcing current formed by VT2 is adopted.
The picture1 (b) is the high input resistance circuit formed by FET. R1 is the grid offset deciding resistance. The current pass through R1 is usually very small. So the resistance is super high in the circuit.The Picture1 (c) is the circuit connected to operational amplifier. It is made up of two simple FET. RP1 is used to investigate the offset voltage.
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