Electromagnetic compatibility spread spectrum device and method of generating spread spectrum clock signal

Abstract

The invention relates to the technical field of electromagnetic compatibility, and particularly relates to an electromagnetic compatibility spread spectrum device, which comprises a spread spectrum unit and a spread spectrum frequency adjusting unit, wherein the spread spectrum unit is connected with a clock source for carrying out phase modulation on clock signals according to the spread spectrum frequency and outputting a spread spectrum clock signal; and the spread spectrum frequency adjusting unit is connected with the spread spectrum unit for setting the spread spectrum frequency of the spread spectrum unit. The invention also relates to a method of generating the spread spectrum clock signal. The method comprises steps: S1, the spread spectrum frequency is set; and S2, phase modulation is carried out on the received clock signal according to the spread spectrum frequency, and the spread spectrum clock signal is outputted. Through designing the spread spectrum device for restraining EMI transmission of a crystal oscillation circuit and the method of generating the spread spectrum clock signal, signal spectrum amplitude of crystal oscillation clock fundamental and harmonic waves is reduced, EMI transmission of the clock source is thus restrained, and signal integrity is kept; and the spread spectrum device can be directly arranged on the crystal oscillation circuit, the structure is simple, and the cost is low.

Description

technical field [0001] The invention relates to the technical field of electromagnetic compatibility, in particular to an electromagnetic compatible spread spectrum device and a method for generating a spread spectrum clock signal. Background technique [0002] With the development of intelligent and high-speed electronic products, electromagnetic compatibility has become an important indicator for evaluating the quality of electronic products. According to the definition of electromagnetic compatibility by the International Electronics Commission standard IEC, it mainly includes two parts: EMI (electromagnetic emission) and EMS (electromagnetic immunity). Such as figure 1 As shown, the crystal oscillator circuit is always used as the core functional device of electronic products to generate clock signals. It is directly connected to the MCU and is also the main source of EMI emission. Therefore, the EMI suppression of the crystal oscillator clock is particularly important....

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Problems solved by technology

[0003] The existing EMI suppression schemes for crystal oscillator clocks mainly include three traditional methods: grounding, shielding, and filtering. However, the above-mentioned methods may cause unsatisfactory suppression effects due to some external factors, specifically:

[0004] 1. Grounding, grounding may introduce the clock signal interference of the crystal oscillator into the ground plane and cause negative effects;

[0005] 2. The metal shielding cover is used to shield the crystal oscillator circuit. Although the metal shielding cover can suppress the emission of the crystal oscillator, due to the trend of miniaturization and integrated design of electronic products, and the PCB wiring is intricate, the crystal oscillator interference is easy to pass through the PCB wiring. The crosstalk between emits

[0006] 3. Filtering the crystal oscillator circuit can reduce the output amplitude of the crystal oscillator clock and reduce EMI emissions, but the existence of the filter circuit will change the signal waveform of the crystal oscillator clock signal, such as the rising and falling edge times of the crystal oscillator clock signal, destroying the clock signal The signal integrity of the signal affects the stability of the system

[0007] Although the above-mentioned traditional rectification methods can reduce EMI emissions to a certain extent, because they do not suppress EMI at the source of the clock, it takes a lot of time to check the propagation path of crystal oscillator clock emissions, and a lot of time is spent in the EMI rectification process

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