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The Solutions & Reasons for Making the Crystal Oscillator Working

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The Solutions & Reasons for Making the Crystal Oscillator Working

  • Jun 14, 2019
The importance of a crystal is equal to the heart of mankind. The crystal oscillator in the motherboard suddenly does not work, it is really anxious, the crystal oscillator is usually stopped for what reason.

Crystal oscillator can not solve the solution:

1, the material parameter selection error causes the crystal to not vibrate


This problem occurs more in the load capacitance of the crystal, why is the load capacitance easy to make a mistake? In the use of passive crystal oscillators, the external components usually need external capacitors and other components, so that the passive crystal oscillator can normally start to work for the IC. Here, we need to note that the unit of the external capacitor is also PF, and the load capacitance unit of the crystal oscillator is also PF. When the supplier asks about the load capacitance, it is easy to confuse the parameters of the two, so the parameters are not Matching will naturally cause the crystal oscillator to not start properly, or the frequency accuracy will be biased, and it will easily stop the vibration when the crystal oscillator performance is stable.

2, the internal wafer is broken or damaged, resulting in no vibration

This problem occurs mostly in cylindrical crystal oscillators, 49/S crystal oscillators, ceramic plug-in crystal oscillators, etc. Therefore, the series of crystal oscillators have no fixed braids, and they are all packaged in transparent bags. It is easy to be damaged during transportation, or the wafers inside the crystals are damaged due to factors such as falling and impact during use, resulting in the crystals not vibrating.

3, the oscillation circuit does not match, causing the crystal to not vibrate

Three indicators affecting the oscillation circuit: frequency error, negative impedance, and excitation level.

The frequency error is too large, causing the actual frequency to shift to the nominal frequency and causing the crystal to not vibrate. This is also a lot of purchases do not understand, the same frequency, the same package of crystal oscillators will have different unit prices, because the higher the accuracy of the crystal oscillator, which means the better product performance. Do not blindly pursue the price of crystal oscillators, and ignore the quality of crystal oscillators!

Solution: Choose the right PPM value for the product.


Negative impedance

If the negative impedance is too large or too small, the crystal will not vibrate. Solution: If the negative impedance is too large, the value of the crystal external capacitors Cd and Cg can be increased to reduce the negative impedance. If the negative impedance is too small, the values of the external capacitors Cd and Cg can be adjusted to increase the negative. Sexual impedance. In general, the negative impedance value should satisfy not less than 3-5 times the nominal maximum impedance of the crystal.


Excitation level

If the excitation level is too large or too small, the crystal will not vibrate. Solution: Adjust the excitation level of the oscillator output to the crystal oscillator by adjusting the size of Rd in the circuit. In general, the smaller the excitation level, the better the processing power consumption, and the stability of the oscillating circuit and the lifetime of the crystal oscillator.

4, the crystal inside the crystal wafer with impurities or dust, etc. will also cause the crystal to not vibrate

One of the processes of the crystal oscillator is a wafer-plated electrode, that is, a gold layer or a silver electrode is plated on the wafer, which requires completion in a 10,000-class clean room. If dust particles in the air are attached to the electrodes, or if gold residue remains on the electrodes, the crystal will not vibrate.

5, the crystal oscillator leaks and causes no vibration

During the process of the crystal oscillator, the internal vacuum is required to be filled with nitrogen gas. If the pressure seal is poor, the crystal gas is not tightly leaked; or the crystal oscillator is exposed during the welding process due to the mechanical stress of the product during the process of cutting the foot. Poor air tightness; both will cause the crystal oscillator to not vibrate.

6, the temperature is too high or too long when welding

For example, the 32.768 KHz in-line type of crystal oscillator requires solder with a melting point of 178 ° C. The temperature inside the crystal oscillator exceeds 150 ° C, which may cause deterioration of the crystal characteristics or no vibration. When soldering the pins, it is within 5 seconds at 280 °C or within 10 seconds at 260 °C. Do not solder directly at the root of the lead. This will also result in deterioration of the crystal characteristics or no vibration.

7. Improper storage environment causes deterioration of crystal oscillator performance and causes no vibration

Prolonged use or storage under conditions of high temperature or low temperature or high humidity may cause deterioration of the electrical properties of the crystal oscillator, which may result in no vibration.

8, MCU quality problems, software problems, etc. cause the crystal oscillator to not vibrate

Solution: At present, the MCU in the market has new products, refurbished goods, dismantled goods, and OEM goods. If there is no certain industry experience or choose a regular supplier, it is very easy to buy non-genuine. Such a circuit is prone to problems, resulting in an unstable operation of the oscillating circuit. In addition, even if it is a genuine MCU, if there is a problem with the programming program, it may cause the crystal to not start.

9, EMC problems cause the crystal to not vibrate

Solution: In general, metal-encapsulated products are superior to ceramic package products in anti-electromagnetic interference. If the EMC on the circuit is large, metal-encapsulated products should be used as much as possible. In addition, do not take the signal line under the crystal to avoid interference.

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