Using Spread Spectrum Crystal Oscillators to Reduce EMI Electromagnetic Interference and Solve the Problem of EMC Radiation Exceeding Standards

May 13,2024
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By using spread spectrum crystal oscillators to reduce EMI electromagnetic interference, the problem of excessive EMC radiation can be solved. How to reduce EMI electromagnetic interference? What to do if the EMC radiation exceeds the standard after installing the crystal oscillator? How to solve problems such as excessive frequency doubling radiation of crystal oscillators.

With the increasing demand for EMC electromagnetic compatibility in electronic devices, how to reduce EMI electromagnetic interference when designing circuits should be a headache for many engineers. The points closely related to EMI electromagnetic interference are the clock, power supply, wiring, and shielding, all of which may cause EMI indicators to exceed the standard. In practical operation, relevant organizations issue electromagnetic compatibility EMC specifications, which include two requirements: on the one hand, it means that the electromagnetic interference generated by the equipment to the environment during normal operation cannot exceed a certain limit; On the other hand, it refers to the equipment having a certain degree of immunity to electromagnetic interference present in the environment, that is, electromagnetic sensitivity.

Traditional elimination of EMI electromagnetic interference requires the addition of magnetic beads, filters, grounding circuits, and metal covers in the circuit, which is known as shielding. If it is a power and wiring issue, adjusting the circuit design to meet these standards may be challenging and costly, especially in today's electronic systems where processor speed and data rate are being improved. As the product shrinks, the challenge of reducing power consumption and combating EMI becomes more complex. Traditional containment techniques, such as shielding, have become more expensive and impractical.

Due to the high cost and space occupation of mechanical solutions, the use of spread spectrum technology has become a common means of reducing EMI electromagnetic interference. Moreover, in many cases, during EMI testing, certain frequency points may exceed the standard. After a long period of investigation into the cause, the power supply, clock, and PCB wiring were investigated, and ultimately it was found that the problem was often with the clock. A basic principle of EMC design is to reduce EMI electromagnetic interference at the source of the PCB. The principle of spread spectrum technology is to modulate the output signal to spread the electromagnetic interference of the output signal to a larger spectrum. Applied to digital cameras, projectors, photocopiers, scanners, monitoring systems, electronic music devices, and car navigation.

On this issue, Epson has provided us with a solution. The Epson spread spectrum crystal oscillator SG-9101 series is a programmable crystal oscillator that reduces EMI electromagnetic interference by adjusting the clock frequency. The programmable frequency range is 0.67MHz~170MHz (1ppm per step), and the spread frequency range is ± 0.25%~+4%. The new SG-9101 product provides a wider operating temperature range and reduces current consumption by 50%. When using SG-9101, you can choose to pair it with an existing SG-Writerl dedicated burner to define the center frequency of the SG-9101 crystal oscillator that can reduce electromagnetic interference (EMI).

The consumption current of SG-9101 series spread frequency quartz oscillators has been significantly reduced by 75% compared to current products. The spread spectrum clock crystal oscillator of SG-9101 provides several types of modulation methods, which can achieve modulation with 6 values of+0.5%, ± 0.75%,+1%,+1.5%,+2%, and 0.25%. Practice has shown that the introduction of spread spectrum clock crystal oscillator modulation results in very small clock signal jitter. SG-9101 effectively reduces the electromagnetic radiation power and EMI interference by dynamically changing the clock frequency, thereby solving the problem of excessive EMC radiation. The EPSON spread spectrum crystal oscillator specification sheet can be found in the table below:

Compared to other EMI electromagnetic interference suppression technologies, the systematic characteristics of the spread spectrum oscillator are its main advantage, and all clock and timing signals generated by the spread spectrum oscillator are also modulated at the same ratio. This brings significant EMI improvement effects to the entire system. In EMC testing, changing only one capacitor or programmable digital input can adjust the frequency modulation (spread spectrum percentage). The programmable characteristics of spread spectrum crystal oscillators enable the use of this technology in product design and EMC testing, and can also reduce the printed circuit board area used for EMI electromagnetic interference suppression. Another benefit of using spread spectrum crystal oscillators is that programmable electromagnetic interference suppression and timing functions can be further integrated into the same product, thereby solving the problem of excessive EMC radiation. Another benefit is that it can accelerate the launch of wireless and portable application products into the market.