You say that the output voltage level is proportional with the phase difference. From my understanding after half-an-hour search in datasheets and sample circuits on the webthis IC has two inputs; pins 2 and 3. Dec Part and Inventory Search. Heat sinks, Part 2: As the external signal sources frequency SLOWLY moves up, for instance, the onboard VCO will sense an instantaneous phase error between its two inputs, and automatically try to correct the phase error. Distorted Sine output from Transformer 8. Hierarchical block is unconnected 3.

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The device being cheap can be used in applications where cost is considered. In order to understand let us simplify this block diagram further to get the following. 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.


Phase Lock loop (PLL) LM565 Circuit

But how can you compare the phases of two signals if their frequencies are different? From my signal courses I remember that in order to talk about the phase difference of two signals their magnitude spectrum must be same. I understand that it is related with the operation of the IC. Can you explain it please? If both frequencies are not yet synchronized a so called "pull-in" action takes place, which simply means that the VCO frequency moves towards the reference frequency - under the condition, that the frequency difference is nor too large this defines the "pull-in-range".


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. As a result, the phase lock will attempt to compensate and multiply the incoming frequency 16 fold. If the inputs signal changes, the phase detector will recognise the change in frequency and force the VCO to change the output accordingly, such that the output is equal to the new input frequency, thereby eliminating the error value from the phase comparator. The range of frequencies over which the PLL will track an input signal and remain locked is the lock frequency.

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