SimElectronics™

N-Channel MOSFET - Model N-Channel MOSFET using Shichman-Hodges equation

Library

Semiconductor Devices

Description

The N-Channel MOSFET block uses the Shichman and Hodges equations [1] for an insulated-gate field-effect transistor to represent an N-Channel MOSFET.

The drain-source current, I_DS, depends on the region of operation:

In the off region ( ) the drain-source current is:
In the linear region ( ) the drain-source current is:
In the saturated region ( ) the drain-source current is:

In the preceding equations:

K is the transistor gain.
V_DS is the positive drain-source voltage.
V_GS is the gate-source voltage.
V_th is the threshold voltage.

The block models gate junction capacitance as a fixed gate-drain capacitance C_GD and a fixed gate-source capacitance C_GS. If you select Specify using equation parameters directly for the Parameterization parameter in the Junction Capacitance tab, you specify these values directly using the Gate-drain junction capacitance and Gate-source junction capacitance parameters. Otherwise, the block derives them from the Input capacitance C_iss and Reverse transfer capacitance Crss parameter values. The two parameterizations are related as follows:

C_GD = Crss
C_GS = C_iss – Crss

Dialog Box and Parameters

Main Tab

Parameterization

Select one of the following methods for block parameterization:

Specify from a datasheet — Provide the drain-source on resistance and the corresponding drain current and gate-source voltage. The block calculates the transistor gain for the Shichman and Hodges equations from this information. This is the default method.
Specify using equation parameters directly — Provide the transistor gain.

Drain-source on resistance, R_DS(on)

The ratio of the drain-source voltage to the drain current for specified values of drain current and gate-source voltage. R_DS(on) should have a positive value. This parameter is only visible when you select Specify from a datasheet for the Parameterization parameter. The default value is 0.025 Ω.

Drain current, Ids, for R_DS(on)

The drain current the block uses to calculate the value of the drain-source resistance. I_DS should have a positive value. This parameter is only visible when you select Specify from a datasheet for the Parameterization parameter. The default value is 6 A.

Gate-source voltage, Vgs, for R_DS(on)

The gate-source voltage the block uses to calculate the value of the drain-source resistance. V_GS should have a positive value. This parameter is only visible when you select Specify from a datasheet for the Parameterization parameter. The default value is 10 V.

Gain K

Positive constant gain coefficient for the Shichman and Hodges equations. This parameter is only visible when you select Specify using equation parameters directly for the Parameterization parameter. The default value is 5 A/V².

Gate-source threshold voltage Vth

Gate-source threshold voltage V_th in the Shichman and Hodges equations. For an enhancement device, V_th should be positive. For a depletion mode device, V_th should be negative. The default value is 1.7 V.

Ohmic Resistance Tab

Source ohmic resistance: The transistor source resistance. The default value is 0.001 Ω. The value must be greater than or equal to 0.
Drain ohmic resistance: The transistor drain resistance. The default value is 0.001 Ω. The value must be greater than or equal to 0.

Junction Capacitance Tab

Parameterization

Select one of the following methods for capacitance parameterization:

Specify from a datasheet — Provide parameters that the block converts to junction capacitance values. This is the default method.
Specify using equation parameters directly — Provide junction capacitance parameters directly.

Input capacitance C_iss

The gate-source capacitance with the drain shorted to the source. This parameter is only visible when you select Specify from a datasheet for the Parameterization parameter. The default value is 350 pF.

Reverse transfer capacitance Crss

The drain-gate capacitance with the source connected to ground. This parameter is only visible when you select Specify from a datasheet for the Parameterization parameter. The default value is 80 pF.

Gate-source junction capacitance

The value of the capacitance placed between the gate and the source. This parameter is only visible when you select Specify using equation parameters directly for the Parameterization parameter. The default value is 270 pF.

Gate-drain junction capacitance

The value of the capacitance placed between the gate and the drain. This parameter is only visible when you select Specify using equation parameters directly for the Parameterization parameter. The default value is 80 pF.

Ports

The block has the following ports:

G: Electrical conserving port associated with the transistor gate terminal.
D: Electrical conserving port associated with the transistor drain terminal.
S: Electrical conserving port associated with the transistor source terminal.

References

[1] H. Shichman and D. A. Hodges. "Modeling and simulation of insulated-gate field-effect transistor switching circuits." IEEE J. Solid State Circuits, SC-3, 1968.