Crystal oscillator, or crystal oscillator, plays a vital role in modern electronic design. It is responsible for generating accurate clock signals and is the core component for maintaining the synchronous operation of digital circuits. In the process of printed circuit board (PCB) design, the layout position of the crystal oscillator, especially whether it should be avoided to be placed on the edge of the PCB board, is a topic worthy of in-depth discussion. It will be evaluated from the following points of view!
- Consideration of stability
The core function of the crystal oscillator is to provide a highly stable and accurate frequency reference. It is the "heart" of the system clock. Therefore, ensuring the stability of its operation is the primary consideration. Therefore, the crystal oscillator cannot be placed on the edge of the PCB, which will reduce the risk of interference from external physical factors. For example, mechanical vibration or impact force, don't underestimate this insignificant force, which may cause serious degradation of equipment performance or functional failure. (Such as communication equipment, precision measuring instruments, etc.)
- Electromagnetic compatibility (EMC)
Electromagnetic compatibility is a measure of whether electronic equipment can work normally in an electromagnetic environment without interfering with other equipment. It is also an indicator of its anti-interference ability. When the crystal oscillator is working, it not only generates electromagnetic radiation, but also receives surrounding electromagnetic waves. If it is placed at the edge of the board, the distance between the crystal oscillator and the outside world is shortened, making it more susceptible to external electromagnetic interference (EMI), such as wireless signals, power line noise, etc. These interferences may cause the crystal oscillator frequency to drift and affect the accuracy of the system timing. In addition, the crystal oscillator at the edge of the board may also become the source of electromagnetic interference to the outside world.
When the crystal oscillator is placed in the middle of the PCB or away from the edge of the PCB, due to the existence of the working ground (GND) plane in the PCB, most of the electric field is controlled between the crystal oscillator and the working ground, that is, inside the PCB. The electric field distributed to the reference ground will be greatly reduced, resulting in reduced radiation emissions and better compliance with EMC regulations.
- Signal integrity and wiring optimization
In high-speed digital circuits, signal integrity refers to the ability of a signal to be received correctly without distortion during transmission. The quality of the connection between the crystal oscillator and the IC related to the system clock directly affects the quality of the clock signal. If the crystal oscillator wiring is too long, it will not only increase the delay of signal transmission, but also may introduce adverse effects such as reflection and crosstalk, reducing signal integrity. The ideal wiring strategy is to keep the distance between the crystal oscillator and the associated components as short as possible, and the wiring is simple and direct to reduce signal attenuation and distortion.
- Considerations of manufacturing and maintainability
From a manufacturing perspective, the edge position of the PCB may pose a challenge to automated assembly processes (such as SMT mounting). Components in the edge area are more susceptible to mechanical positioning deviations, which increases assembly difficulty and reduces production efficiency. In addition, the edge position is not conducive to manual soldering or troubleshooting, especially in mass production. Any factors that affect manufacturing efficiency need to be carefully considered.