Main characteristic parameters of MOSFET

Main characteristic parameters of field-effect transistors

DC parameters of field-effect transistor

1. Pinch off voltage Up

Under the condition that UDS is a fixed value, when ID equals a small current value (a few microamperes), the bias voltage UGS applied to the gate is the pinch off voltage. It is suitable for junction field-effect transistors and depletion type insulated gate field-effect transistors.

2. Turn on voltage UT

Under the condition of a fixed UDS value, the UGS that forms a conductive channel between the S and D poles is the turn-on voltage. It is only applicable to enhanced insulated gate field-effect transistors.

3. Saturation current IDSS

Under the condition of UDS=0, the channel current when the voltage applied between the drain and source is greater than the pinch off voltage is called saturation current, which is suitable for depletion type insulated gate field-effect transistors.

4. DC input resistor RGS

The ratio of the voltage Ucs applied to the input terminal of the field-effect transistor (i.e. between the gate and source) to the gate current flowing through it is called the DC input resistance. The DC input resistance of insulated gate field-effect transistors is more than two orders of magnitude higher than that of junction field-effect transistors. The DC input resistance of junction field-effect transistor is 1 X 10 8 Ω, while the DC input resistance of insulated gate field-effect transistor is above 1 X 10 12 Ω.

5. Leakage source breakdown voltage BVDS

The UDS value that causes a significant increase in ID during the process of increasing leakage and voltage is called the leakage source breakdown voltage. BVDS has determined the operating voltage of field-effect transistors.

6. Gate source breakdown voltage BVGS

For junction field-effect transistors, the UGS value at which the reverse saturation current begins to increase sharply is the gate and breakdown voltage. For insulated gate field-effect transistors, it is the voltage that causes the breakdown of the SiO2 insulation layer.

Micro variation parameters of field-effect transistors

<1. transconductance gm

When the drain source voltage UDS is constant, the ratio of the small change in drain current ID to the small change in gate source voltage that causes this change is called transconductance, that is

Transconductance is a parameter that measures the control ability of gate source voltage UGS on drain current ID in field-effect transistors, and is also an important parameter for measuring the amplification effect of field-effect transistors.

<2. Leakage source dynamic resistance rDS

The ratio of the small change in UDS to the change in ID when the grid voltage is constant is called the dynamic internal resistance rDS of the drain source

The value range of rDS is generally from several thousand ohms to several hundred thousand ohms.

Other parameters of field-effect transistor

① Inter electrode capacitance. There are inter electrode capacitances between the three electrodes of a field-effect transistor, namely gate capacitance CGS, gate drain capacitance CGD, and gate drain capacitance CDS. CGS and CGD are generally 1-3 pF, while CDS is approximately 0.1-1 pF.

② Maximum leakage source current IDM

It refers to the maximum current allowed to pass through the drain source of a field-effect transistor.

③ Field effect transistor dissipated power PD

It refers to the power dissipated during the operation of field-effect transistors.

④ Low frequency noise coefficient NF
The noise of field-effect transistors is caused by the irregularity of internal carrier motion. Its existence will cause an amplifier to experience irregular voltage or current changes atthe output even when there is no signal input.