The principle of phase-locked loop frequency control

QWE4562009

The principle of phase-locked loop frequency control [Copy link]

The principle of phase-locked loop frequency control

Phase-locked loop frequency automatic tracking-------Use the phase-locked loop to ensure that it works at the desired frequency point

How do you understand the following two paragraphs?

The phase detector is a phase comparison device, which compares the phase of the input signal and the output signal of the voltage-controlled oscillator, and generates an error voltage corresponding to the phase difference. The phase is a time relationship, while the error voltage is an amplitude relationship. There is an X-axis and a Y-axis. How does the Y-axis amplitude affect the X-axis phase?

After the phase detector is a loop filter, which is used to filter out the high-frequency components and noise in the output signal of the phase detector to ensure the performance required by the loop and increase the stability of the system. The voltage-controlled oscillator is controlled by the voltage output of the filter, so that the frequency of the voltage-controlled oscillator approaches the frequency of the input signal, that is, the beat frequency is lowered until the frequency difference is eliminated and locked. When the phase-locked loop starts working, the frequency of the input signal is usually different from the oscillation frequency of the voltage-controlled oscillator when no control voltage is applied. Since there is an inherent frequency difference between the two signals, the phase difference between them is bound to change continuously and exceed 2 degrees. The characteristic of the phase detector is based on a phase difference of 20,000 as a period. As a result, the error voltage output by the phase detector swings within a certain range. Under this error voltage control, the frequency of the voltage-controlled oscillator also changes within the corresponding range. If the frequency of the voltage-controlled oscillator can be changed to be equal to the frequency of the input signal, it is possible to stabilize at this frequency. After reaching stability, the frequency difference between the input signal and the output signal of the voltage-controlled oscillator is zero, the phase no longer changes with time, and the error voltage is a fixed value. At this time, the loop enters the locked state. -------This is about the working principle of the phase-locked loop and how to stabilize the frequency point, but I don't understand what it means

Anyone who knows please give me some pointers

btty038

Receiving systems in the RF and microwave world

QWE4562009

btty038 posted on 2022-6-22 22:13 Receiving system in the field of RF and microwave

I don't understand how this is a closed loop control frequency