The clock distributor is a logic circuit that sends the input clock pulse to each output after a certain frequency division. Its composition principle block diagram is composed of a modular M counter and corresponding decoding circuit, and can also be composed of a ring counter.

Basic structure of clock generator

Phase locked loop (PLL) is the core technology of clock generator. Modern clock generator only needs to provide a reference frequency by quartz crystal, and uses more than one PLL with different proportion of frequency division circuit to generate clock output of various frequencies, replacing multiple quartz crystals in traditional system.

The PLL part has two inputs, one is the reference frequency (Fref), the other is the feedback frequency (fvco), and the other is the output (fout). The relationship between the three can be expressed as follows.

Fout=(Fref·P)/(Q·N)

PLL is basically a negative feedback system. In the loop, the feedback signal is used to lock the frequency and phase of the output signal to the frequency and phase of the reference signal at the input. The phase frequency detector (PFD) compares the phase relation and frequency difference between the reference frequency (Fref) and the feedback frequency (fvco), and detects the phase difference and frequency difference between them, so as to affect the frequency output of the voltage controlled oscillator (VCO). When Fref / Q is ahead of fvco / P, the up high potential output accelerates the fout frequency; on the contrary, when Fref / Q is behind fvco / P, the DN high potential output slows down the fout frequency, and finally achieves the stable output state as shown in the formula. Therefore, the required output frequency can be obtained by adjusting the ratio of P, Q and R values of PLL external frequency division circuit.

The function of clock generator

1、 Provide the initialization clock signal when the motherboard starts, so that the motherboard can start;

2、 In order to coordinate the clock frequency of the memory chip, the system can provide all kinds of clock signals when the motherboard is running normally. If the clock generator chip or crystal oscillator is broken, the system may not be able to start or operate normally. The latter is manifested as sudden and inexplicable crash, sometimes normal operation, sometimes abnormal and so on. If you suspect that there is a problem with the clock generator on the motherboard, you’d better send it to a professional repair shop for repair.

The electronic components of the clock generator continuously generate voltage pulses with stable intervals, and all components in the product will operate synchronously with the clock. In short, digital products must have the control of clock to accurately process digital signals, just like the heartbeat of living things. If the clock is not stable, it will lead to the error of digital signal transmission, or the failure of normal operation of digital equipment.

The technology of clock generator is developing towards high frequency to meet the demand of PC market. By using the technology of non-volatile silicon oxide silicon oxide (SONOS), a 200MHz clock module with high efficiency can be made, and it can be programmed directly through the compiler of desktop platform. With the help of this compiler, system designers can set the input and output clocks without even being familiar with PLL technology, thus shortening the design time before the product is launched.

Editor Lynn

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