DC Biasing for JFET and MOSFET

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18 Questions

What is a key characteristic of an Enhancement MOSFET (E-MOSFET) in terms of its operation mode?

Has no structural channel

What happens when the gate voltage is below the threshold in an n-channel Enhancement MOSFET?

No channel is formed

How does the conductivity of the channel in an Enhancement MOSFET change with an increase in gate-source voltage?

Increases

Which statement is true about the gate voltage required for an n-channel E-MOSFET and a p-channel E-MOSFET to operate?

n-channel requires a positive VGS while p-channel requires a negative VGS

Which configuration describes an Enhancement MOSFET used as a switch?

Normally off configuration

Which technologies are EMOSFET technologies developed for higher power dissipation?

LD MOSFET, VMOSFET, TMOSFET

In which region of transistor action are both junctions forward biased?

Saturation region

What is the term used to describe the operating point of a transistor with time-varying sources out of the circuit?

Q-point

Which region of transistor action involves the base-emitter junction being forward biased and the collector-base junction being reverse biased?

Active region

What is the straight line drawn on the collector curves between the cut-off and saturation points of a transistor called?

Loadline

Which H-parameter represents the short circuit forward current gain of a Bipolar Junction Transistor (BJT)?

hf

What happens to a transistor in the cut-off region?

Both junctions are reverse biased.

Which term is sometimes used to refer to MOSFETs due to the presence of an insulated gate?

IGFETs

How does a Depletion MOSFET differ from JFET?

It has no PN junction structure.

What is the primary difference between Depletion MOSFET and Enhancement MOSFET?

Operation modes - depletion and enhancement

In which mode is the Depletion MOSFET normally operated?

Depletion mode

What happens when a positive gate voltage is applied to an Enhancement Mode MOSFET?

More conduction electrons are attracted to the channel.

What configuration is a normally-on switch when using a D-MOSFET?

Depletion mode

Study Notes

Enhancement MOSFET (E-MOSFET)

• Operates only in enhancement mode, with no depletion mode. • No structural channel and no IDSS parameter. • An n-channel E-MOSFET requires a positive gate voltage above threshold to induce a channel. • A layer of negative charges (inversion layer) is created in the substrate portion adjacent to the SiO2 layer. • A p-channel E-MOSFET requires a negative VGS.

E-MOSFET Characteristics

• Conductivity of the channel is enhanced by increasing the gate-to-source voltage. • No channel is formed for gate voltage below the threshold. • Configured as a switch, the device is normally off.

E-MOSFET Technologies

• LD MOSFET, VMOSFET, and TMOSFET are E-MOSFET technologies for higher power dissipation.

Amplifiers

Classification of Amplifiers

• Voltage Amplifier: voltage controlled source, e.g., Op-amps. • Current Amplifier: current controlled source, e.g., BJTs.

BJT Transistor Biasing

Regions of Transistor Action

• Active region: base-emitter junction is forward biased, collector-base junction is reverse biased. • Saturation region: both junctions are forward biased. • Cut-off region: both junctions are reverse biased.

Loadline and Q-Point

• Loadline: a straight line drawn on the collector curves between the cut-off and saturation points. • Q-point (Quiescent point): the operating point of the transistor with time-varying sources removed.

BJT Small Signal Analysis

Transistor Hybrid Equivalent Circuit

• hi: short circuit input impedance. • hr: open circuit reverse voltage gain (voltage feedback ratio). • hf: short circuit forward current gain.

Field Effect Transistors (FETs)

MOSFET

• A type of FET with an insulated gate, sometimes called IGFET. • Two basic types: Depletion MOSFET (D-MOSFET) and Enhancement MOSFET (E-MOSFET).

Depletion MOSFET (D-MOSFET)

• Drain and source are diffused into substrate material, connected by a narrow channel adjacent to the insulated gate. • Operated in depletion mode or enhancement mode. • Normally operated in depletion mode, and configured as a switch, it is normally-on.

Test your knowledge on DC biasing techniques used for Junction Field Effect Transistors (JFET) and Metal Oxide Semiconductor Field Effect Transistors (MOSFET). Understand how to set up proper biasing for optimal transistor operation.

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