MOS tube (field effect transistor) amplifier circuit and principle

Crystal oscillator

MOSFET imported original FET

Photocoupler

The field effect transistor amplifier is a voltage control device, which has the advantages of high input impedance and low noise, and is widely used in electronic circuits, and in particular, the preamplifier display has the above requirements. According to the two types of FETs - junction field effect transistors and insulated gate field effect transistors can form corresponding FET amplifiers. The equivalent circuit and performance index calculation expressions of three basic configuration amplifiers are given below as an example. See Table 5.2-7. The picture shows that the FET has a positive control effect similar to that of a transistor. It can also form three basic amplifiers: common source, common drain, and common gate.

1. Bias circuit Because different types of FETs work in the amplification region, the polarity of the gate voltage is required to be different. For example, the junction field effect transistor requires the polarity of the gate source and the drain source voltage to be opposite, and the added MOS transistor requires The gate source and the drain-source voltage have the same polarity. As for the gate bias polarity of the depletion mode MOS transistor, it can be positively biased, zero-biased or negatively biased.

According to these characteristics, there are two main types of bias circuits for single-supply: (1) Self-biasing circuit self-biasing for junction and depletion MOS tube amplifying circuits, Figure 5.2-6 shows N-channel Junction field effect transistor self-biasing circuit.

Figure 5.2-6 Self-biasing circuit gate-source voltage is UGS=RID (2) Hybrid bias circuit Hybrid bias circuit is used for various FET amplifiers. The hybrid bias circuit of the N-channel enhancement type MOS tube amplifying circuit is shown in Figure 5.2-7.

Figure 5.2-7 Mixed bias circuit 2, field effect transistor three basic configuration amplifier equivalent circuit and performance index calculation formula (see Table 5.2-7)

Gate source voltage is