Question

A PLL can be used to modulate

• A. PAM signals
• B. PCM signals
• C. FM signals
• D. DSB-SC signals

Hint:

Remember that a PLL is fundamentally a frequency-tracking loop.
Thus, it is naturally suited for frequency modulation (FM) and frequency demodulation applications.
For amplitude-based systems like AM, PAM, and DSB-SC, other circuits are preferred.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to identify which type of analog or digital modulation can be generated using a Phase-Locked Loop (PLL).

Step 2: Detailed Explanation:

• A Phase-Locked Loop (PLL) is a feedback control system that consists of a phase detector, a low-pass filter, and a Voltage-Controlled Oscillator (VCO).

• The primary function of a PLL is to generate an output signal whose phase is related to the phase of an input signal.

• A PLL is widely used for frequency demodulation (FM demodulation) because the error voltage at the input of the VCO tracks the frequency variations of the incoming FM wave.

• Conversely, a PLL can also be configured to perform frequency modulation (FM modulation).

• By applying a modulating baseband signal directly to the control voltage input of the internal VCO, the output of the VCO becomes a frequency-modulated (FM) signal.

• PAM (Pulse Amplitude Modulation) and PCM (Pulse Code Modulation) are pulse modulation techniques that require sampling, quantization, and encoding, which cannot be performed directly by a standard PLL.

• DSB-SC (Double Sideband Suppressed Carrier) is an amplitude modulation scheme requiring a balanced modulator or multiplier, which is structurally distinct from the frequency-tracking nature of a PLL.