DC Biasing for JFET and MOSFET

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Questions and Answers

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

  • Has an IDSS parameter
  • Has no structural channel (correct)
  • Can only operate in depletion mode
  • Operates in both enhancement and depletion modes

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

  • The IDSS parameter affects the operation
  • It operates in depletion mode
  • A channel is formed with increased conductivity
  • No channel is formed (correct)

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

  • Remains constant
  • Increases (correct)
  • Decreases
  • Is not affected

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

<p>n-channel requires a positive VGS while p-channel requires a negative VGS (D)</p> Signup and view all the answers

Which configuration describes an Enhancement MOSFET used as a switch?

<p>Normally off configuration (D)</p> Signup and view all the answers

Which technologies are EMOSFET technologies developed for higher power dissipation?

<p>LD MOSFET, VMOSFET, TMOSFET (C)</p> Signup and view all the answers

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

<p>Saturation region (B)</p> Signup and view all the answers

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

<p>Q-point (C)</p> Signup and view all the answers

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

<p>Active region (B)</p> Signup and view all the answers

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

<p>Loadline (C)</p> Signup and view all the answers

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

<p>hf (C)</p> Signup and view all the answers

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

<p>Both junctions are reverse biased. (C)</p> Signup and view all the answers

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

<p>IGFETs (A)</p> Signup and view all the answers

How does a Depletion MOSFET differ from JFET?

<p>It has no PN junction structure. (A)</p> Signup and view all the answers

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

<p>Operation modes - depletion and enhancement (A)</p> Signup and view all the answers

In which mode is the Depletion MOSFET normally operated?

<p>Depletion mode (B)</p> Signup and view all the answers

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

<p>More conduction electrons are attracted to the channel. (B)</p> Signup and view all the answers

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

<p>Depletion mode (B)</p> Signup and view all the answers

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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.

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