Question
What is used to control the attenuation of RF signals by a PIN diode?
Answer Options
- A) Forward DC bias current
- B) A variable RF reference voltage
- C) Reverse voltage larger than the RF signal
- D) Capacitance of an RF coupling capacitor
Correct Answer: A
Explanation
A PIN diode is used as an electronically controlled variable resistor or RF switch/attenuator. When reverse-biased, the diode is a high impedance (switch open). When forward-biased, the intrinsic (I) region is filled with charge carriers, and the diode becomes a low resistance (switch closed). The precise value of this resistance is adjustable, making it an attenuator.
The resistance of the PIN diode (and thus the level of attenuation it provides to an RF signal) is controlled by the amount of forward DC bias current applied. Increasing the DC bias current increases the number of carriers in the intrinsic region, which decreases the diode’s resistance, leading to lower RF attenuation. This variable resistor characteristic is exploited in AGC circuits and electronic RF attenuators.
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