The MOS field effect transistor is a metal-oxide-semiconductor field effect transistor, abbreviated as MOSFET (Metal-Oxide-Semiconductor Field-Effect-Transistor, that is, a field-effect transistor of a metal-oxide-semiconductor), which belongs to the insulated gate type. There is a silicon dioxide insulating layer between the metal gate and the channel, so it has a very high input resistance (up to 1015Ω). It is also divided into N-channel tube and P-channel tube. Usually, the substrate (substrate) and the source S are connected together.

According to the different conduction mode, MOSFET is divided into enhancement type and depletion type. The so-called enhanced type refers to: when VGS=0, the tube is in an off state; after adding the correct VGS, the majority of carriers are attracted to the gate, thereby "enhancing" the carriers in this area and forming a conductive channel Tao. The depletion type means that when VGS=0, a channel is formed, and when the correct VGS is added, the majority of carriers can flow out of the channel, thus "depleting" the carriers and turning the tube off.

Taking the N channel as an example, it is made on a P-type silicon substrate with two source diffusion regions N+ and drain diffusion regions N+ with a high doping concentration, and then the source S and the drain D are led out respectively. The source and the substrate are connected internally, and the two always maintain the same potential. The direction of the potential is from the outside to the inside, which means from the P-type material (substrate) to the N-type channel. When the drain is connected to the positive pole of the power supply and the source is connected to the negative pole of the power supply and VGS=0, the channel current (that is, the drain current) ID=0. With the gradual increase of VGS, attracted by the positive voltage of the gate, negatively charged minority carriers are induced between the two diffusion regions, forming an N-type channel from the drain to the source. When VGS is greater than the tube When the turn-on voltage VTN (usually about +2V) is reached, the N-channel tube begins to conduct, forming a drain current ID.
 

• South grid voltage UG
• Control its drain current ID
• High input impedance
• Low noise
• Large dynamic range
• Low power consumption
• Easy to integrate
 

•  Field effect tube can be used for amplification. Because the input impedance of the field effect tube amplifier is very high, the         coupling capacitor can have a smaller capacity, and it is unnecessary to use an electrolytic capacitor.
•  The high input impedance of the field effect tube is very suitable for impedance transformation. It is often used for impedance          conversion in the input stage of a multi-stage amplifier.
•  The field effect tube can be used as a variable resistor.
•  The field effect tube can be conveniently used as a constant current source.
•  The field effect tube can be used as an electronic switch.
 

Before measuring, short-circuit the human body to ground before touching the pins of the MOSFET. It is best to connect a wire to the wrist to connect with the earth, so that the human body and the earth maintain an equipotential. Separate the pins again, and then remove the wires.
 

2. Determine the electrode:

Set the multimeter to the R×100 gear, and first determine the grid. If the resistance of a pin and other pins are both infinite, it proves that this pin is the grid G. Exchange the test leads and measure again, the resistance value between S-D should be several hundred ohms to several thousand ohms. The black test lead is connected to the D pole and the red test lead is connected to the S pole at the time with the smaller resistance value. For the 3SK series products produced in Japan, the S pole is connected to the shell, so it is easy to determine the S pole.

3. Check the amplification capability (transconductance):

Hang the G pole in the air, connect the black test lead to the D pole, and the red test lead to the S pole, and then touch the G pole with your finger, the needle should have a larger deflection. The double-gate MOS field effect transistor has two gates G1 and G2. In order to distinguish, you can touch the G1 and G2 poles with your hands, and the G2 pole is the one with the larger deflection of the hand to the left.
 

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