Do you know all the important knowledge points of MOS tube?

1. MOS tube description.

The MOS tube is also called a field effect tube, which is an insulating field effect tube in an integrated circuit. On a semiconductor device with a certain structure, silicon dioxide and metal are added to form a gate. The source and drain of the MOS tube are both N-type regions formed in the P-type backgate, and they can be reversed.

2. MOS tube structure characteristics.

When a unipolar transistor is turned on, only carriers of one polarity participate in the conduction. The conduction mechanism is the same as that of a low-power MOS tube, but the structure is different. The low-power MOS tube is a lateral conductive device, and the power MOSFET usually adopts a vertical conductive structure. , Improve the withstand voltage and current capability of MOSFET devices.

The main feature is that there is a silicon dioxide insulating layer between the metal gate and the channel, so it has a very high input resistance, and an n-type conductive channel is formed in the two high-concentration n-diffusion regions when it is turned on. The n-channel enhancement mode MOS tube must be forward biased on the gate, and only when the gate-source voltage is greater than the threshold voltage can there be an n-channel MOS tube generated by the conductive channel.

3.1 Input & output characteristics of MOS tube.

In a circuit with a common source connection, the source and the substrate are separated by a silicon dioxide insulating layer, so the gate current is zero.

3.2 The conduction characteristics of the MOS tube.

The MOS tube is a switching element, which works in two states: off or on. The MOS tube is a voltage control element, and its working state is mainly determined by the gate-source voltage uGS.PMOS characteristics: Vgs will be turned on if it is less than a certain value, which is suitable for the situation when the source is connected to VCC. However, due to the large on-resistance and high price, NMOS is generally used in high-end drives.

The characteristics of NMOS: Vgs is greater than a certain value, it will be turned on, suitable for the situation when the source is grounded, as long as the gate voltage reaches 4V or 10V.

4. MOS tube working principle.

(With N-channel enhancement mode MOS field effect transistor) It uses VGS to control the amount of "induced charge" to change the condition of the conductive channel formed by these "induced charges", and then achieve the purpose of controlling the drain current. 

When the electrode voltage changes, the amount of charge induced in the channel also changes, and the width of the conductive channel also changes accordingly, so the drain current ID changes with the change of the gate voltage.