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Common Crystal Oscillator Anomalies

The author:admin Number of visits: Date:2020-12-28 13:38

1. The crystal oscillator when the vibration is depressed ------ A: the crystal oscillator load and the capacitance at both ends of the mismatch caused by the frequency deviation is too large;B: The crystal oscillator itself has problems, parasitic & impedance value fluctuates greatly & internal solder joint is not firm, etc.

2. crystal oscillator on the plate is not good, electric hot air or removed to install it again can ------ is mainly crystal load and capacitance at both ends of the mismatch caused by frequency deviation is too large.Electric heating is actually equivalent to changing the stray capacitance of the line.

3. The matching between the crystal load and the capacitance at both ends of the crystal oscillator ------- Cl =(C1*C2)/(C1+C2)+C"Where, Cl: load capacitance value of crystal oscillator;C1, C2: capacitance values at both ends of the crystal oscillator;C ": Line stray capacitanceThe main function of the crystal oscillator matching capacitor is to match the crystal oscillator and the oscillator circuit, so that the circuit is easy to start vibration and in a reasonable excitation state, and also has a certain "fine tuning" effect on the frequency.To MCU, correct selection of capacitance matching crystals, the key is to fine-tune the crystal incentive status, avoid or owe incentives, the former makes crystal easy to aging influence service life and cause the oscillation circuit EMC characteristics become worse, while the latter is not easy to rev up, work is not stable, so it is important to correctly choose matching crystal capacitors.

4.32768Hz crystal oscillator time deviation: the time deviation is mainly due to the frequency deviation. If the frequency deviation of 1PPM is converted to 0.0864s throughout the day, the time deviation is 0.0864s.So if time error is needed to achieve accuracy, it is better to weld the capacitance at both ends of the crystal oscillator according to the normal ratio. At the same time, the crystal oscillator supplier should help to find the best PPM value of 0 error through QWA detection, and specify the supply frequency range according to the standard of 0 error.

5.32768Hz crystal oscillator welding: 1). When encountered, the shell of 32768Hz crystal oscillator is welded to the plate to realize signal shielding and anti-interference.As a result, the welding time will be too long to melt the solder joints inside the crystal oscillator, and the internal structure of the chip will tilt against the shell and cause a short circuit.The best method is to have two pinholes on the PCB board using copper wire to bind the crystal oscillator.Or use a rubber binder.2). Bend at will when the crystal oscillator bends its feet.The best bending is done by pinching the outer shell of a cylindrical crystal with your fingers;Use forceps to clamp the lead more than 3mm from the bottom of the base of the crystal. Use forceps to clamp the bent lead to 90° without pulling the lead too hard.Strictly pulling the lead may cause the glass at the root of the lead to break, resulting in air leakage and damage to electrical performance.If the air leaks the crystal oscillator is basically useless.

6. Because there is dirt such as soldering flux when welding, we choose to use ultrasonic cleaning PCBA board: ultrasonic cleaning or ultrasonic welding will affect and damage the internal structure of quartz crystal and even chip damage.

7. Crystal vibration time is long, the boot is weak, shut down and then start vibration, power consumption of large finished battery is not durable, this is mainly caused by the resistance of crystal oscillator is too large, the crystal oscillator can not start vibration under low voltage.


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