EPSON crystal oscillator safeguards automotive electronics

Jul 22,2024
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What are the main EMI issues in automotive electronic systems?

At present, in electric vehicles (EVs), hybrid electric vehicles (HEVs), and traditional fuel vehicles, the functions of body entertainment systems and electronic assistance systems are increasing, gradually becoming the mainstream and standard in the industry. This also reflects the increasing complexity of electronic components and circuits inside vehicles. In order to meet diverse functional requirements, engineers need to design more compact solutions. Meanwhile, due to the requirement for high sensitivity, the application of high-speed signals has become very widespread. Therefore, in the process of circuit design, reducing the size and size of related circuits, including the power supply part, becomes crucial. However, power supplies that meet product requirements often have higher switching frequencies, which exacerbates electromagnetic interference (EMI) issues.

With the increasing complexity and density of automotive electronic systems, how to effectively reduce the impact of EMI in the early stages of design has become a key factor that engineers must consider.

How to reduce the impact of electromagnetic interference?

In addition to power supply, several points closely related to EMI electromagnetic interference are clock, wiring, and shielding, all of which may lead to exceeding EMI indicators. In practical operation, relevant institutions have issued regulations on electromagnetic compatibility (EMC), which includes two requirements: on the one hand, it refers to the requirement that the electromagnetic interference generated by the equipment in the environment during normal operation cannot exceed a certain limit; On the other hand, it refers to the device having a certain degree of immunity to electromagnetic interference present in the environment, that is, electromagnetic sensitivity.

Multiple methods can be adopted, such as shielding, filtering, isolation, ferrite magnetic rings, signal edge control, and adding power and GND layers in the PCB. These methods can be flexibly selected in practical applications, but each has its own advantages and disadvantages. For example, shielding as a mechanical method, although simple, is costly and not suitable for handheld and portable devices. Filtering and signal edge control are effective for low-frequency signals, but their effectiveness is limited in the currently widely used high-speed signal environment. In addition, using passive components such as EMI/RFI filters increases costs, while reducing EMI through LAYOUT techniques is relatively time-consuming and has limited improvement effects.

Given that clock signals are typically the highest frequency and steepest edge signals in circuit systems, most EMI issues are closely related to them. Therefore, in the case where the circuit board has already been formed, the Spread Spectrum Crystal Oscillator (SSXO) has become an effective method to reduce EMI.

What is a spread spectrum oscillator?

Spread spectrum crystal oscillator is a special type of crystal oscillator that mainly relies on spread spectrum technology. This technology has a wide range of applications in anti-interference communication. By frequency modulation, narrow bandwidth energy is dispersed to a wider bandwidth range, thereby reducing spikes and dispersing energy to a wider range. The programmable features not only meet the requirements of fast delivery, but also reduce the printed circuit board area used for EMI suppression due to the small size selection, saving product costs and time to market.

By dynamically adjusting the clock frequency, the effective reduction of electromagnetic radiation power has been achieved, thereby reducing the impact of EMI (electromagnetic interference) on automotive electronic systems. Compared to other EMI suppression technologies, the main advantage of the spread spectrum crystal oscillator lies in its systematic nature. All clock and timing signals generated by the spread spectrum crystal oscillator are modulated at the same ratio, which enables the entire system to achieve significant EMI improvement.

Epson recommends the 9101 series, which is a programmable crystal oscillator. SG-9101CGA code X1G005281xxxx00 car grade crystal oscillator adopts a 2.5x2.0mm package and is produced using PLL technology. The frequency range of this oscillator can be selected from any frequency point between 0.67M and 170MHz, with a step size of 1ppm. It uses standard CMOS output and a maximum output load of 15pF, with good frequency stability. Power consumption as low as 0.3 μ A, operating temperature as high as 125 ℃, compliant with RoHS requirements and AEC-Q100 standards, suitable for application in automotive electronic devices.