The respective characteristics of FETs and transistors

The respective characteristics of FETs and transistors

1. The source S, gate G, and drain D of the FET correspond to the emitter E, base B, and collector C of the triode, respectively, and their functions are similar.

    2. FET is a voltage control current device, controlled by vGS iD, its amplification coefficient gm is generally small, so the amplification ability of FET is poor; transistors are current-controlled current devices that control iC by iB (or iE).

    FETs

    FETs

    3. The FET gate hardly takes current (ig»0); When the triode is working, the base always draws a certain current. Therefore, the gate input resistance of FETs is higher than that of transistors.

    4. The FET is conducted by multiple sons; Triode has two kinds of carriers, multi-son and oligonut, participating in conduction, and the concentration of oligospermia is greatly affected by temperature, radiation and other factors, so the FET has better temperature stability and strong radiation resistance than transistors. In the case of large changes in environmental conditions (temperature, etc.), FETs should be selected.

    5. When the FET is connected to the source metal and the substrate, the source and drain can be used interchangeably, and the characteristics change little; When the collector and emitter of the transistor are used interchangeably, their characteristics vary greatly, and the β value will be greatly reduced.

    6. The noise figure of FET is very small, and FET should be selected in the input stage of low-noise amplification circuit and circuit requiring high signal-to-noise ratio.

    7. FETs and transistors can be composed of various amplification circuits and switching circuits, but because the former manufacturing process is simple, and has the advantages of low power consumption, good thermal stability and wide working power supply voltage range, it is widely used in large-scale and ultra-large-scale integrated circuits.

    8. The transistor on-resistance is large, the FET on-resistance is small, only a few hundred milliohms, in the current electrical device, generally use the FET as a switch to use, his efficiency is relatively high.

    Comparison of FETs and bipolar transistors

    FETs are voltage control devices, and the gate basically does not take current, while transistors are current control devices, and the base must take a certain current. Therefore, in the case of a very small rated current of the signal source, FETs should be selected.

    FETs are polyon conductive, and both carriers of a transistor participate in conduction. Since the concentration of low birthrate is sensitive to external conditions such as temperature and radiation, it is more appropriate to use FETs for occasions where the environment changes greatly.

    In addition to being used as an amplifier device and controllable switch like transistors, FETs can also be used as voltage-controlled variable linear resistors.

    The source and drain of FETs are structurally symmetrical and can be used interchangeably, and the gate-source voltage of depleted MOS transistors can be positive or negative. Therefore, the use of FETs is more flexible than transistors.