MOSFETs: Depletion-Type vs Enhancement-Type - Parameters, Characteristics, and Handling, Slides of Electronics

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Department of Electrical Engineering

MOSFET’s

Enhancement-Type

MOSFET

Basic Construction

Four most IMPORTANT parameters

 VGS (Gate to Source / Gate Voltage)

 VTN ( Voltage at which Induced electron inversion

layer forms)

 VDS (Drain to Source)

 VDS (Sat) (Saturation Drain to Source)

Electron inversion layer

The magnitude of the

current is a function of

the amount of charge

in the inversion layer,

which in turn is a

function of the applied

gate voltage

• When VGS > VTN and VDS= Some small Voltage

 When V GS is fixed and V DS is increased

If VGS is held fixed at some value such as

8V andVDS is increased from 2 to 5

V, the voltage VGS will drop from- 6 to

-3V and the gate will become less and

less positive with respect to the

drain

Characteristic curves

WhenVDS <VDS(Sat)

WhenVDS >V DS (Sat)

Where,

Kn= Conduction parameter

Example

Ideal MOSFET Current–Voltage

Characteristics—PMOS Device

Symbols

 N-Channel

 P- Channel

Depletion MOSFET’s

n-Channel Depletion-Mode MOSFET

 When VGS = 0 V

 When Gate Terminal is at Negative Potential

Transfer characteristics