What is the role of the phase-locked loop _ the main role of the phase-locked loop _ what is the phase-locked loop

A phase-locked loop is a circuit or module that is used in a communication receiver to process a received signal and extract phase information from a clock. Or, for the received signal, a clock signal is copied so that the two signals are synchronized (or coherent) from a certain point of view. Since the imitation clock signal has a certain phase difference with respect to the clock signal in the received signal due to the locking situation (i.e., after the capture is completed), it is aptly called a phase locker. Under normal circumstances, the three components of the phase-locked loop and the corresponding operating mechanism are: 1 phase detector: used to determine the amplitude of the phase difference between the clock signal output by the phase locker and the clock in the received signal; Adjustable phase/frequency modulation clock generator: used to properly adjust the frequency or phase of the clock output signal inside the phase locker according to the signal output by the phase detector, so that the phase locker completes the above fixed phase difference function; Loop Filter: Used to filter and smooth the output signal of the phase detector. In most cases, it is a low-pass filter that filters out the effects of data changes and other unstable factors on the entire module. As can be seen from the above, there are roughly the following block diagrams: ┌─────┐┌─────┐┌───────┐→─┤ phase detector ├─→─┤loop filter├ ─→─┤Controlled Clock Generator├→┬─→└──┬──┘└─────┘└───────┘│↑??↓└─────── ───────────────────┘ Visible, is a negative feedback loop structure, so generally known as phase-locked loop () phase-locked loops have many types, can be digital It can also be analog or hybrid, and can be used to recover the carrier or to recover the baseband signal clock.

Automatic variable mode control digital phase locked loop schematic

How the phase-locked loop works

The phase-locked loop is a module related to the clock of the chip. For example, a digital chip must have a clock signal (acting like a clock, allowing each module of the chip to adjust its working progress in its changes). It is better to replace a large circuit with a wire.

The phase-locked loop is a ring that can “lock” the phase. The more specific point is explained as follows: The simplest phase-locked loop is two ports, a reference input clock, and an output clock generated by the internal module of the phase-locked loop. It is useful to talk about its module composition, the most important ones include phase frequency detector and voltage controlled oscillator. Using the phase discriminator to compare the error between the input reference clock and the clock generated by the voltage controlled oscillator in frequency and phase to generate a correspondingly controlled voltage, the control voltage controls the voltage controlled oscillator, and then adjusts the input of the voltage controlled oscillator. The clock signal eventually makes the output clock's frequency exactly the same as the phase and input clock. In fact, this is a module-level negative feedback.

Multiplier for multiplier:

Above the phase-locked loop is the simplest use of the phase-locked loop. The phase-locked loop also has a multiplier function because the output clock is generated by its own internal voltage-controlled oscillator. If a divider is added, the input reference clock is used. In comparison, a clock signal with a frequency plus N times is obtained, and of course the phase is synchronized with the reference clock.

Phase-locked loop modulation and demodulation:

The phase-locked loop is to get the same frequency signal, it is also in the radio frequency, modulation and demodulation, I don't know if you have used an old-fashioned TV set, there is an adjustment button to adjust the TV screen up and down, since the phase-locked loop The problem is solved, and now the TV does not have that adjustment button.

The role and application of phase-locked loop in analog signals

After the baseband signal is transmitted by the high frequency carrier, it is required to multiply the signal at the receiving end by the same phase as the carrier to demodulate.

Due to the frequency error generated by the transmitting device, even if the carrier frequency is known to be 900 MHz, the receiving end cannot directly demodulate with 900 MHz. To get the exact carrier frequency, a phase-locked loop is used to generate the same frequency signal.

For digital signals, some transmission methods do not have a synchronous clock. It is necessary to recover the clock from the data, and a phase-locked loop is also used.

You said that the wire for eliminating frequency error should be used in analog signals. The problem is that you can't demodulate yourself by using the received signal directly. What is needed is a sinusoidal signal that produces a carrier frequency. The error is also for the carrier frequency

Small class of knowledge: Why not replace a phase-locked loop with a wire?

Its working principle and role are roughly said. It seems that some friends have asked, "If you eliminate the frequency error, it is not better to use a good wire directly, the cost is lower, such a problem." Is it that a wire seems to be more than a phase-locked loop? So good? .

The digital chip has the concept of a clock tree. Now, for example, a wire replaces the phase-locked loop. The chip starts to send a set of data to the chip on the rising edge of the clock. The internal clock circuit leads to the internal sequential circuit. The actual clock used is delayed, which in turn causes a data drift phenomenon. But with a phase-locked loop, we can connect one of the branches of the clock tree to the phase-locked loop, so that the phase frequency of the clock tree tip is consistent with the reference signal, there will be no data drift, so the phase-locked loop Not a wire can be substituted.

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