Which of these functions can be performed by a phase-locked loop?
Wide-band AF and RF power amplification
Frequency synthesis and FM demodulation✓الإجابة الصحيحة
Photovoltaic conversion and optical coupling
Comparison of two digital input signals and digital pulse counting
الشرح
Putting a programmable divider inside a phase-locked loop makes the VCO run at an exact multiple of the reference, which is frequency synthesis. Locking the loop to an incoming FM signal makes the VCO control voltage follow the deviation, which recovers the audio, so the same loop can demodulate FM.