Question
What type of semiconductor device is designed for use as a voltage-controlled capacitor?
Answer Options
- A) Varactor diode
- B) Tunnel diode
- C) Silicon-controlled rectifier
- D) Zener diode
Correct Answer: A
Explanation
Every PN-junction diode, when reverse biased, exhibits capacitance. This capacitance is primarily due to the non-conductive depletion region acting as an insulator between the two conductive layers (P and N), essentially forming a capacitor. The width of this depletion region is directly related to the magnitude of the reverse-bias voltage.
By manipulating the doping and geometry of the junction, engineers created a device specifically designed to exploit this characteristic. The Varactor diode (or voltage-variable capacitance diode) is optimized for use as a voltage-controlled capacitor. Increasing the reverse-bias voltage widens the depletion region, decreasing the capacitance, which allows it to be used for electronic tuning in VCOs, frequency multipliers, and resonant circuits.
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