Question
What is a phase-locked loop?
Answer Options
- A) An electronic servo loop consisting of a ratio detector, reactance modulator, and voltage-controlled oscillator
- B) An electronic circuit also known as a monostable multivibrator
- C) An electronic servo loop consisting of a phase detector, a low-pass filter, a voltage-controlled oscillator, and a stable reference oscillator
- D) An electronic circuit consisting of a precision push-pull amplifier with a differential phase input
Correct Answer: C
Explanation
A Phase-Locked Loop (\text{PLL}) is a fundamental electronic circuit widely used in communications for frequency synthesis, modulation, and demodulation. It is a closed-loop negative feedback system designed to ensure that one oscillator (the Voltage-Controlled Oscillator, \text{VCO}) precisely tracks the frequency and phase of a second, highly stable reference signal.
A \text{PLL} is defined as an electronic servo loop consisting of a phase detector, a low-pass filter, a voltage-controlled oscillator, and a stable reference oscillator. The phase detector compares the \text{VCO} frequency (or a divided version) to the reference frequency, generating an error voltage that, after filtering, controls the \text{VCO} to lock it exactly to the reference frequency and phase.
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