The two inputs to a phase detector in PLL are _________.

Question

Question

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RRB JE CBT 2 (Electronics Engineering) ReExam Official Paper (Held On: 04 Jun, 2025)

low pass filter output and feedback voltage from a voltage controlled oscillator
amplifier output and feedback voltage from a voltage controlled oscillator
input voltage and feedback voltage from a voltage controlled oscillator
input voltage and amplifier output

Answer 1

The two inputs to a phase detector in a Phase-Locked Loop (PLL) are the input voltage and feedback voltage from a voltage controlled oscillator.

Explanation:

Phase Detector (PD): This component compares the phase of two input signals.
- One input is the reference signal (or input voltage).
- The other input is the feedback signal (typically the output of the Voltage Controlled Oscillator or VCO).
Low-Pass Filter (LPF): The output of the phase detector (which is a voltage proportional to the phase difference) goes through a low-pass filter to remove high-frequency components and produce a smooth DC voltage.
Voltage Controlled Oscillator (VCO): The filtered DC voltage (error voltage) from the LPF controls the frequency of the VCO. The VCO's output frequency changes to minimize the phase difference between its output and the input reference signal, thereby "locking" the loop.