Passive crystal oscillator is a passive oscillator, which does not need external power supply to maintain oscillation. Its oscillation frequency is determined by the physical size and material characteristics of the crystal (generally passive crystal oscillation is adopted).
Active crystal oscillator is an active oscillator, which needs external power supply to provide energy to maintain oscillation. It usually includes crystal oscillator chip and external circuit, which generates stable oscillation signal through feedback mechanism.
Crystal oscillator placement rule：
- Close Placement: Place the crystal oscillator package and related transistors, amplifiers or microcontrollers as close as possible to reduce the length of connecting lines and the delay and loss of signal transmission.
- Interference isolation: keep the crystal oscillator circuit at a certain distance from high-frequency and high-current parts (such as processor and clock generator) to reduce the influence of electromagnetic interference on the crystal oscillator.
- Short circuit of ground wire: ensure that the ground wire of crystal oscillator is the shortest and most direct path, and avoid crossing with other signal lines to reduce the noise of ground wire.
- Reduce the loop: avoid forming a large loop around the crystal oscillator and its related circuits, because the loop will cause electromagnetic radiation and mutual interference, which will affect the stability and performance of the crystal oscillator.
- Common-mode interference: isolate the signal lines of crystal oscillator and its related circuits from other signal lines as far as possible to reduce the influence of common-mode interference on crystal oscillator signals.
- Differential wiring: differential signal transmission is used to reduce the interference and loss of crystal oscillator signals and improve the anti-interference ability.
- Prevention of crosstalk: in PCB layout, avoid the interference between crystal oscillator signal lines and other signal lines, especially the intersection with high-frequency signal lines.
- Electromagnetic compatibility: Follow the design principle of electromagnetic compatibility (EMC), reduce the interference of electromagnetic radiation and sensitive signals through reasonable layout and grounding design, and ensure the stability and reliability of crystal oscillator circuit.
- Keep the temperature stable: try to place the crystal oscillator in a position that is not easily affected by external temperature changes, and avoid the vicinity of heat sources or areas with poor ventilation.
