August 13, 2021
As the heart of the circuit, the crystal oscillator has an extremely important role. It is widely used in various electronic products and equipment. If it does not vibrate, the entire device will not work properly. The following briefly introduces the reason why the crystal does not vibrate daily:
The wrong selection of material parameters causes the crystal oscillator to fail to oscillate
For example: a certain MCU needs to match the 6PF 32.768KHz, and the result is 12.5PF, which causes no vibration.
Solution: Replace the specifications and models that meet the requirements. If necessary, please confirm with the original manufacturer.
The internal crystal is broken or damaged, causing no vibration
For example: damage during transportation, drop, impact and other factors in the course of use cause damage to the internal crystal of the crystal oscillator, which causes the crystal oscillator to fail to vibrate.
Solution: Replace the good crystal oscillator. Usually need to pay attention to: the foam bag should be thicker during transportation to avoid damage in the middle; avoid falling, heavy pressure, impact, etc. during the manufacturing process. Once the above conditions occur, it is forbidden to use it again.
The mismatch of the oscillation circuit causes the crystal oscillator to fail to oscillate
Three indicators that affect the oscillation circuit: frequency error, negative impedance, and excitation level.
(1) The frequency error is too large, causing the actual frequency to deviate from the nominal frequency and causing the crystal oscillator to fail to oscillate.
Solution: Choose a product with a suitable PPM value.
(2) Too large or small negative impedance will cause the crystal oscillator to fail to oscillate.
Solution: The negative impedance is too large, you can increase the value of the crystal oscillator external capacitors Cd and Cg to reduce the negative impedance; if the negative impedance is too small, you can reduce the value of the crystal oscillator external capacitors Cd and Cg to increase the negative 性impedance. Generally speaking, the negative impedance value should be no less than 3-5 times the nominal maximum impedance of the crystal oscillator.
(3) Excessive or too small excitation level will also cause the crystal oscillator to fail to oscillate
Solution: Adjust the excitation level of the oscillator circuit to the crystal oscillator output by adjusting the size of Rd in the circuit. Generally speaking, the smaller the excitation level, the better. In addition to low processing power consumption, it is also related to the stability of the oscillation circuit and the service life of the crystal oscillator.Do not solder directly to the root of the pin, as this will also cause deterioration of the crystal characteristics or failure to oscillate.
Impurities or dust attached to the crystal crystal inside the crystal oscillator will also cause the crystal oscillator to fail to vibrate.
For example, one of the crystal oscillator manufacturing processes is the plating of electrodes on crystals, that is, a layer of gold or silver electrodes are plated on the crystals, which requires operations to be completed in a 10,000-level dust-free workshop.
If dust particles in the air are attached to the electrode, or there are gold slag and silver slag remaining on the electrode, it will also cause the crystal oscillator to fail to vibrate.
Solution: Replace with a new crystal oscillator. When choosing a crystal oscillator supplier, you need to consider the manufacturer's equipment, workshop environment, process and process capabilities, which are related to the quality of the product.
The crystal oscillator fails to vibrate due to air leakage
For example: during the manufacturing process of the crystal oscillator, it is required to evacuate the inside and then be filled with nitrogen. If the compression seal is not good, the crystal oscillator is not airtight and leaks; or the crystal oscillator is caused by the mechanical stress of the product in the process of cutting the foot during the welding process. The crystal oscillator has poor airtightness; all will cause the crystal oscillator to fail to vibrate.
Solution: Replace the good crystal oscillator. During the manufacturing process and welding process, work must be standardized to avoid product damage caused by misoperation.
The temperature is too high or the time is too long during welding, resulting in abnormal internal electrical performance indicators of the crystal oscillator and causing the crystal oscillator to fail to oscillate
For example: Taking 32.768KHz in-line type as an example, it is required to use solder with a melting point of 178°C. If the temperature inside the crystal oscillator exceeds 150°C, it will cause deterioration of the crystal oscillator characteristics or failure to oscillate. When soldering leads, within 5 seconds at 280°C or within 10 seconds at 260°C.
Solution: The operation must be standardized during the welding process, and the welding time and temperature settings must meet the requirements of the crystal oscillator.