Question
What characteristic of a PIN diode makes it useful as an RF switch?
Answer Options
- A) Extremely high reverse breakdown voltage
- B) Ability to dissipate large amounts of power
- C) Reverse bias controls its forward voltage drop
- D) Low junction capacitance
Correct Answer: D
Explanation
A PIN diode is a specialized structure with an intrinsic (I) region between the P and N semiconductor layers. When forward biased, the intrinsic region floods with charge carriers, making it act like a low-value resistor (an RF short circuit). When reverse biased, the intrinsic region is depleted of charge carriers, making it act like an insulator (an RF open circuit).
For effective operation as an RF switch or attenuator, the diode must not interfere with the RF signal when it is in the ‘off’ (reverse-biased) state. The characteristic that makes it excellent for this is low junction capacitance. This low capacitance ensures that the diode acts as a very high impedance (an excellent open circuit) at RF, allowing minimal RF energy to leak through when the switch is nominally open.
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