The PLL consists of a phase detector, low pass filter, error amplifier, and voltage controlled oscillator (VCO). The phase detector compares the input signal frequency to the VCO output frequency and generates an error voltage if they differ. This error voltage is filtered and amplified to control the VCO frequency, shifting it toward the input signal frequency, forming a feedback loop that locks the VCO frequency to the input signal frequency.

1. PHASE LOCKED LOOP

2. Basic Operation of PLL

3.  It consist of
1. Phase detector
2. Low pass filter
3. Error Amplifier
4. Voltage Controlled Amplifier (VCO)
VCO:
 It’s a free running multivibrator, operates at a set frequency 𝑓𝑜 called free running
frequency, determined by external timing capacitor & resistor.
 Shifted either side by dc control voltage Vc.
 Frequency deviation is directly proportional to dc control voltage and hence it is
called a voltage controlled oscillator(VCO).

4. Phase Detector:
 Compares the input signal Vs of frequency 𝑓𝑠 the output of the VCO.
 If differ in frequency and phase an error voltage Ve is generated.
 This is basically a multiplier and produces the sum (𝑓𝑠 + 𝑓𝑜) and difference (𝑓𝑠 − 𝑓𝑜)
at its output.
Low Pass Filter:
