Electromagnetic Compatible Spread Spectrum Device and Method for Generating Spread Spectrum Clock Signal

Abstract

The invention relates to the technical field of electromagnetic compatibility, in particular to an electromagnetically compatible spread spectrum device, a spread spectrum unit connected to a clock source, which is used to phase modulate a clock signal according to the spread frequency, and output a spread spectrum clock signal; The frequency adjustment unit is connected with the frequency spreading unit, and is used for setting the spreading frequency of the frequency spreading unit. It also relates to a method for generating a spread frequency clock signal, comprising the steps of: S1, setting the spread frequency; S2, performing phase modulation on the received clock signal according to the spread frequency, and outputting the spread frequency clock signal. The present invention reduces the signal spectrum amplitude of the fundamental wave and harmonics of the crystal oscillator clock by designing a spread spectrum device for suppressing the EMI emission of the crystal oscillator circuit and a method for generating a spread spectrum clock signal, thereby suppressing the EMI emission of the clock source and maintaining the signal integrity. Integrity; at the same time, the spread spectrum device can be directly arranged on the crystal oscillator circuit, with simple structure and low cost.

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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