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Which of the following statements about FM detection using PLL circuit are correct?
S1: At the error amplifier output, we get demodulated FM output.
S2: FM signal is applied to the input of the PLL.

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RRB JE ECE 22 Apr 2025 Shift 2 CBT 2 Official Paper
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  1. Only S1
  2. Neither S1 nor S2
  3. Only S2
  4. Both S1 and S2

Answer (Detailed Solution Below)

Option 4 : Both S1 and S2
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Detailed Solution

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The correct answer is: 4) Both S1 and S2

Explanation:
S1: At the error amplifier output, we get a demodulated FM output.
True. In a Phase-Locked Loop (PLL) used for FM detection:

The error amplifier (or phase detector output) produces a voltage proportional to the phase difference between the input FM signal and the VCO signal.

Since frequency modulation (FM) is the derivative of phase modulation, this voltage directly represents the demodulated message signal.

S2: The FM signal is applied to the input of the PLL.
True. The FM signal is fed into the PLL's input (phase detector). The PLL locks onto the carrier frequency and tracks the frequency variations (modulation), allowing demodulation.

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Q1.Which of the following statements about FM detection using PLL circuit are correct? S1: At the error amplifier output, we get demodulated FM output. S2: FM signal is applied to the input of the PLL.
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