Semiconductor and Tube Components Flashcards
7 cards from real GROL practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Semiconductor and Tube Components flashcards as text
For normal operation of a JFET, the gate-source junction must be:
Answer: Reverse biased to control the depletion region width and channel conductivity
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.
An N-channel enhancement-mode MOSFET (E-MOSFET) differs from a depletion-mode MOSFET in that it:
Answer: Has no pre-formed channel and requires a positive VGS above threshold voltage to induce a conducting inversion layer
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.
Which diode type is used as a voltage-variable capacitor in voltage-controlled oscillators (VCOs) and electronically tunable filters?
Answer: Varactor (varicap) diode
A reverse-biased varactor diode's junction capacitance varies predictably with the applied reverse voltage, enabling electronic tuning of resonant circuits without mechanical adjustments.
A tunnel diode exhibits a negative-resistance region in its I-V characteristic because:
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
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.
The wide intrinsic (I) layer in a PIN diode is primarily included to:
Answer: Minimize junction capacitance at RF and microwave frequencies, enabling the device to function as a voltage-controlled switch or attenuator
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.
The lower forward voltage drop (~0.3 V) of a Schottky diode compared to a silicon P-N diode (~0.7 V) is due to:
Answer: The thermionic emission mechanism at the metal-semiconductor interface, which has a lower barrier potential than a P-N homojunction
Current in a Schottky diode flows by majority-carrier thermionic emission over a metal-semiconductor barrier that is lower than a silicon P-N junction, and there is no minority carrier storage, yielding very fast switching.
In a JFET datasheet, IDSS is defined as:
Answer: Drain current measured with gate shorted to source (VGS = 0), representing the maximum drain current for a depletion-mode device
IDSS (Drain current, Source shorted to gate) specifies the drain current when VGS = 0 V and is used as the reference maximum current from which transconductance curves are plotted.