A Phase Lock Loop PLL is an electronic circuit, which locks the phase of the input signal with that of the output by keeping them synchronised. It achieves this through a closed loop feedback mechanism that compares the input signal with the output and makes the necessary corrections so that the phase remains synchronous. The values of the components may have changed during design, so please use the full schematic in the final draft of the circuit diagram. The job of a PLL is to track an incoming frequency and match the phase precisely. However, in this circuit the feedback loop has a divided-by counter, which returns the feedback signal that is 16 fold less.
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The device mainly consists of two components, one is voltage controller oscillator and other is phase detector. The device being cheap can be used in applications where cost is considered. In the device pin 2 and pin3 are inputs where we can connect the input analog signal but usually pin 3 will be grounded and pin2 is used as input.
The input signal goes in to the phase detector along with VCO feedback and this phase detector compares whether both signal are in same phase or frequency. If they are in phase or frequency the PD provides zero voltage output and if phase or frequency is present the PD provides positive output voltage. This output voltage of PD is given to amplifier to amplify the voltage signal and the amplified voltage is given to VCO, which generates waveform whose frequency depends on magnitude of the given input voltage.
Now consider no input is given, under such case the VCO will be in free running mode generating signal whose frequency is determined by the capacitor and resistor connected at the pin 8 and pin 9. When a signal is given at the input, the frequency of both input signal and the VCO output is compared. The VCO will increase or decrease the signal frequency depending of the fed voltage of amplifier. Once the adjustment is done both the input signal frequency and VCO frequency will match.
This is how a phase locked loop works , the VCO output signal frequency will always tries to keep up with the input signal frequency. Subscribe to stay updated with industry's latest Electronics components and news. Pin Configuration LM is a 14 pin device and the function of each pin is stated below. In order to understand let us simplify this block diagram further to get the following.
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