Typical applications of PLL are: Frequency Synthesis ..
some quotations from his article "The Basics of PLL Frequency Synthesis".
THE BASICS OF PLL FREQUENCY SYNTHESIS …
A circuit for studying the 565 is shown at the right. Note that both inputs are returned to ground through 470Ω resistors, so there is no trouble with bias currents to the bases, and the input from the function or signal generator is through a coupling capacitor. Set the signal source for a sine wave output, and an amplitude of about 2 V peak-to-peak. It must be at least 1 V p-p for the PLL to work. Connect scope leads as shown, Ch 1 at the input, and Ch 2 at the VCO output. Connect a frequency counter to the input, and measure the VCO control voltage with the DMM at pin 7. Don't try to measure the VCO gain as we did for the 4046--pin 7 has a limited range of voltages for which the circuit will function, and we will make this measurement another way. Turn the power on, then the counter and the signal source. Vary the frequency until the PLL locks, which will happen around 25-30 kHz. Observe that the following range is greater than the capture range. To narrow the capture range, connect a resistance between pins 6 and 7. Leaving this open, as we have, makes the capture range as large as possible. Shorting it makes the range as small as possible. Measure the VCO control voltage at pin 7 while varying the frequency. I found from 7.99 V at 35.5 kHz to 9.87 V at 20.2 kHz, which was about the maximum lock-in range in this case. As you vary the frequency, note the phase relation between the input and the VCO output, which changes as expected for a Type I phase detector.
If the reference signal moves away in frequency, the phase detector generates a train of short pulses, charging (or discharging) the capacitor to the new voltage needed to put the VCO back into lock.
The second-order PLL, serves as the basis for all PLL synthesizer designs and technology.
AD9910 Datasheet and Product Info | Analog Devices
The reference frequency, ƒREF, is typically a precision frequency source such as a crystal oscillator or a rubidium reference.
There are basically three different types of synthesizers: direct, indirect and direct digital synthesis (DDS).
An alternative to re-tuning the VCO is to have several VCO's and have the microprocessor switch the appropriate one into circuit for the desired frequency range.
You now should have a very good idea of the way PLL frequency synthesis systems work.
AD5933 Datasheet and Product Info | Analog Devices
The most important part of the feedback loop for the designer is the loop filter. It is basically a low-pass filter with a corner frequency that should be well below the signal frequencies, so that the control voltage to the VCO is relatively steady. However, the PLL must be able to respond to changes, so the corner frequency should be above the frequency of those changes. Quite often, we want a PLL that responds rather slowly, to provide a flywheel action that damps out noise and unwanted variations. It is a delicate matter of compromise, and the designer's tool is the loop filter.
The phase-locked loop (PLL) is a device with many interesting applications, including frequency synthesis, FM demodulation, and television sweep circuits. Its operation seems nearly miraculous, but feedback makes the job easy, and it is an excellent example of feedback in action. Phase-locked loops, despite their importance and interest, are usually not treated in a university electronics course, though they are very much electronics and help the understanding greatly.
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Phase-locked loop - Wikipedia
PLL frequency synthesizer tutorial ..
[TI] Fractional Integer-N PLL Basics
Phase Locked Loop ( PLL )/Frequency Synthesis - …
1989) and Gernsback Publishing (No longer in business).
Ron Bertrand VK2DQ, some quotations from his article "The Basics of PLL Frequency Synthesis".
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