GROL Semiconductor and Tube Components 3

Question 1

For normal operation of a JFET, the gate-source junction must be:

Accepted Answer

Reverse biased to control the depletion region width and channel conductivity

Answer

A JFET uses reverse bias on the gate-source P-N junction to widen the depletion region into the channel, narrowing the conductive channel and reducing drain current without drawing significant gate current.

Question 2

An N-channel enhancement-mode MOSFET (E-MOSFET) differs from a depletion-mode MOSFET in that it:

Accepted Answer

Has no pre-formed channel and requires a positive VGS above threshold voltage to induce a conducting inversion layer

Answer

Enhancement-mode MOSFETs are 'normally off' devices with no implanted channel; a gate voltage above threshold attracts electrons to form an inversion layer between drain and source.

Question 3

Which diode type is used as a voltage-variable capacitor in voltage-controlled oscillators (VCOs) and electronically tunable filters?

Accepted Answer

Varactor (varicap) diode

Answer

A reverse-biased varactor diode's junction capacitance varies predictably with the applied reverse voltage, enabling electronic tuning of resonant circuits without mechanical adjustments.

Question 4

A tunnel diode exhibits a negative-resistance region in its I-V characteristic because:

Accepted Answer

Heavy P+ and N+ doping creates a very thin junction through which electrons tunnel quantum-mechanically at low forward voltages; current decreases past the peak as tunneling probability falls

Answer

Degenerate (very heavy) doping thins the depletion region enough for quantum tunneling; as forward bias increases past the peak, energy alignment for tunneling is lost, causing current to drop — negative resistance.

Question 5

The wide intrinsic (I) layer in a PIN diode is primarily included to:

Accepted Answer

Minimize junction capacitance at RF and microwave frequencies, enabling the device to function as a voltage-controlled switch or attenuator

Answer

The I layer widens the depletion region to minimize capacitance at RF frequencies; DC forward bias controls the conductivity of the I layer, making the PIN diode an effective microwave switch.

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(GROL) General Radiotelephone Operator License Practice Test

GROL Semiconductor and Tube Components 3