Introduction to FET
Field Effect Transistor (FET). A few carriers participate in heat conduction, which is also called multipolar crystal tube. It belongs to the voltage controlled semi superconductor device. There are many advantages such as high output resistance (10 ^ 8~10 ^ 9 Ω), low noise, low power consumption, large static range, easy integration, no secondary breakdown scene, wide sea area for insurance tasks, etc. Now, bipolar crystal tubes and power crystal tubes have been changed to become stronger partners.
1： FET is a voltage control device, which controls ID (drain DC) through VGS (gate source voltage);
2： The output DC electrode of FET is small, so its output resistance is large.
3： It uses a few carriers to conduct heat, so its measurement stability is good;
4： The electric shrinking coefficient of the shrinking path formed by it is smaller than that of the shrinking path formed by the triode;
5： The field effect tube has strong radiation resistance;
6： Because there is no shot noise caused by the dispersion of minority carriers with mixed activities, because the noise is low.
Task principle of FET
In a word, the task principle of FET is "the ID between drain and source that passes through the channel, which is used to master the ID by the electrode voltage of the reverse bias caused by the pn structure between the electrode and the channel". More precisely, the amplitude of ID passing through the circuit, that is, the channel cross-section, is the reason for the change of the reverse bias of the pn junction and the expansion of the depletion layer. In the non full sea area with VGS=0, the indicated expansion of the transition layer is not very large. According to the magnetic field of the VDS added between the drain and the source, some electrons in the source sea area are pulled away by the drain, that is, there is DC ID activity from the drain to the source. A moderate layer extending from gate pole to drain pole forms a blocking type for all channels, with full ID. This form is called pinching. This means that the transition layer blocks all the channels, and no DC power is cut off.
Because there is no self movement of electrons and holes in the transition layer, it is almost insulating in the real form, and it is difficult for DC to move. However, at this time, the magnetic field between the drain and source is actually that two transition layers contact the drain and close to the lower part of the gate pole, because the high-speed electrons pulled away by the drift magnetic field pass through the transition layer. Because of the intensity of the drift magnetic field, the full scene of ID has hardly changed. Secondly, VGS changes to a negative position, making VGS=VGS (off). At this time, the transition layer generally changes to cover the shape of the whole sea area. Moreover, the magnetic field bulk of VDS is added to the transition layer to pull the electrons to the magnetic field at the drift position. As long as the magnetic field is very short near the source pole, the DC current can not be sluggish.
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