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
What is the primary purpose of the screen grid in a tetrode vacuum tube?
Answer: To reduce interelectrode capacitance between control grid and plate
The screen grid is held at a positive DC voltage and electrostatically shields the control grid from the plate, greatly reducing Miller capacitance and improving high-frequency gain.
The amplification factor (μ) of a vacuum tube is defined as:
Answer: The magnitude of plate voltage change per unit grid voltage change needed to keep plate current constant
μ equals ΔVp/ΔVg (with opposite sign) at constant plate current and also equals the product of transconductance (gm) and plate resistance (rp).
In an NPN bipolar junction transistor operating in the active (linear) region, the junction biasing is:
Answer: Emitter-base junction forward biased and collector-base junction reverse biased
In the active region the forward-biased emitter-base junction injects minority carriers into the base, while the reverse-biased collector-base junction sweeps them into the collector.
The DC current gain parameter hFE of a BJT is defined as the ratio of:
Answer: Collector current to base current
hFE (also called β) equals IC/IB and typically ranges from about 20 to 500 for silicon transistors; it quantifies how much the base current is amplified at the collector.
A reflex klystron differs from a two-cavity klystron in that it uses:
Answer: A single resonant cavity with a repeller electrode that returns velocity-modulated electrons for a second pass through the gap
The reflex klystron uses one resonant cavity; a negative-voltage repeller reflects the velocity-modulated beam back through the same gap, producing oscillation without a second cavity.
The suppressor grid of a pentode vacuum tube is held at cathode potential in order to:
Answer: Repel secondary electrons emitted from the plate back to the plate rather than allowing them to reach the screen grid
Secondary electrons emitted from the plate would be attracted to the positive screen grid in a tetrode, causing the kink in the characteristic curve; the suppressor's near-cathode potential repels them back to the plate.
A common-emitter BJT amplifier stage produces an output voltage signal that is:
Answer: 180° out of phase with the input signal (inverted)
When input base-emitter voltage increases, collector current increases, increasing the voltage drop across the collector load resistor and therefore decreasing the collector output voltage — a phase inversion.