It can be seen from the working principle of the above MOS tube that the gate g and the source s of the MOS tube are insulated. Due to the existence of SiO2 insulating layer, there is an equivalent capacitance between the gate g and the source s, and the voltage VGS generates an electric field, resulting in the generation of source drain current. At this time, the gate voltage VGS determines the drain current. Controlling the gate voltage VGS can control the drain current ID. This leads to the following conclusions:

1) MOS transistor is a device that controls current by changing voltage, so it is a voltage device.

2) The input characteristic of MOS pipeline is capacitive, so the input impedance is very high.

4. Voltage polarity and sign rules of MOS tubes