What is mos tube

The mos tube is a metal-oxide-semiconductor field effect transistor, or a metal-insulator-semiconductor. The source and drain of the MOS tube can be reversed. They are all N-type regions formed in the P-type backgate. In most cases, the two zones are the same, even if the two ends are reversed, it will not affect the performance of the device. Such devices are considered to be symmetrical.

The bipolar transistor amplifies a small change in the current at the input and outputs a large current change at the output. The gain of a bipolar transistor is defined as the ratio of the output to the input current (beta). Another type of transistor, called a field effect transistor (FET), converts the change in input voltage into a change in output current. The gain of a FET is equal to its transconductance, defined as the ratio of the change in output current to the change in input voltage. Commonly used in the market are N-channel and P-channel. For details, refer to the picture on the right (N-channel depletion MOS transistor). The common P-channel is a low-pressure mos tube.

The FET affects the current flowing through the transistor by projecting an electric field on an insulating layer. In fact no current flows through this insulator, so the GATE current of the FET tube is very small. The most common FET uses a thin layer of silicon dioxide as an insulator under the GATE pole. Such a transistor is called a metal oxide semiconductor (MOS) transistor, or a metal oxide semiconductor field effect transistor (MOSFET). Because MOS tubes are smaller and more power efficient, they have replaced bipolar transistors in many applications.

Mos tube advantage

1. Can be applied to zoom in. Since the input impedance of the FET amplifier is high, the coupling capacitor can have a small capacity and it is not necessary to use an electrolytic capacitor.

2. Very high input impedance is ideal for impedance transformation. Commonly used in the input stage of multi-stage amplifiers for impedance transformation.

3. Can be used as a variable resistor.

4. Can be conveniently used as a constant current source.

5. Can be used as an electronic switch.

6. Flexibility in circuit design. The gate bias can be positive or negative, the transistor can only operate under forward bias, and the tube can only operate with a negative bias. In addition, the input impedance is high, which can reduce the signal source load and is easy to match with the previous stage.