FET operating characteristics

        One: The field effect tube is a voltage control device, which controls ID (drain direct current) through VGS (gate-source voltage);

        Two: The DC electrode of the output end of the field effect tube is small, so its output resistance is very large.

        Three: It uses minority carriers to conduct heat, so its measurement stability is better;

        Four: The electrical reduction factor of the reduced path formed by it is smaller than that of the reduced path formed by the triode;

        Five: The field effect tube has strong anti-radiation power;

        Six: Because there is no shot noise caused by the dispersal of minority children, because the noise is low.

    The mission principle of the field effect tube

        In a word, the mission principle of the field effect tube is "the ID of the channel between the drain and the source, and the reverse biased electrode voltage formed by the pn between the electrode and the channel is used to control the ID". More precisely, The amplitude of the ID traversed by the circuit, that is, the channel cross-sectional area, is controlled by the change in the reverse bias of the pn junction and the expansion of the depletion layer. In the non-saturated sea area where VGS=0, the expansion of the transition layer indicated is not very large. According to the VDS magnetic field applied between the drain and the source, some electrons in the source sea area are pulled away by the drain, that is, from the drain. There is direct current ID activity towards the source. The moderate layer that expands from the gate to the drain makes the entire channel a blocking type, and the ID is full. This form is called pinch off. This symbolizes that the transition layer obstructs the entire channel, and the direct current is not cut off.

        Because there is no free movement of electrons and holes in the transition layer, there are almost insulating characteristics in the real state, and general direct current is also difficult to move. However, at this time, the magnetic field between the drain and the source is actually the two transition layers contacting the drain and the lower part of the gate, because the high-speed electrons pulled by the drift magnetic field pass through the transition layer. Due to the intensity of the drift magnetic field, the ID is almost unchanged. Secondly, VGS changes to a negative position, let VGS=VGS(off), at this time the transition layer generally changes to cover the shape of the whole sea area. In addition, the large magnetic field of VDS is applied to the transition layer, which pulls electrons to the magnetic field of the drift position, as long as it is close to the source electrode, which makes the direct current not sluggish.