Types of MOSFETsECE 2204

Types of MOSFETS

n-channel Enhancement Mode

(nMOSFET)

p-channel Enhancement Mode

(pMOSFET)

n-channel Depletion Mode

(nMOSFET)

p-channel Depletion Mode

(pMOSFET)

MOSFETsEnhancement mode Depletion mode

• Also known as Normally Off transistors.▫ A voltage must be

applied to the gate of the transistor, at least equal to the threshold voltage, to create a conduction path between the source and the drain of the transistor before current can flow between the source and drain.

• Also known as Normally On transistors.▫ A voltage must be

applied to the gate of the transistor, at least equal to the threshold voltage, to destroy a conduction path between the source and the drain of the transistor to prevent current from flowing between the source and drain.

Cross-Sectional View of n channel Enhancement Mode Transistor

oxide

Before electron inversion layer is

formed

After electron inversion layer is

formed

p channel Enhancement Mode Transistor

n channel Depletion Mode Transistor

p channel Depletion Mode Transistor

Symbols for n channel Enhancement Mode MOSFET

VGS ≥ 0V, VDS ≥ 0V

VTN is positive

Symbols for p channel Enhancement Mode MOSFET

VGS ≤ 0V, VDS ≤ 0V

VTP is negative

Symbols for n channel Depletion Mode MOSFET

Symbols for p channel Depletion Mode MOSFET

PSpice MOSFET Symbols• The IRF150 is an nMOS and the IRF9140 is a

pMOS. Both are enhancement mode transistors.▫ The body terminal is connected to the source

terminal on the FET.▫ “M” is used to denote that the device is a MOSFET.

Family of iD Versus vDS Curves:Enhancement-Mode nMOSFET

VDS ≥ VGS – VTNVDS ≤ VGS – VTN

Pinch-off/Saturation

Triode/Nonsaturation

Family of iD Versus vDS Curves:Depletion-Mode nMOSFET

Assuming that VTN < -1V

For this course

•I am going to emphasize the operation and applications of Enhancement Mode FETs