Ask for advice on the problem that the crystal oscillator does not work, and I don t understand the

The working principle of the crystal oscillator is based on the piezoelectric effect. When a voltage is applied to the two poles of the wafer, the crystal will be deformed; Conversely, if an external force deforms the wafer, a voltage is generated on the metal sheet at the poles. If an appropriate alternating voltage is applied to the wafer, the wafer will resonate (the resonant frequency is related to the inclination angle and thickness of the quartz bevel).

Operating in a resonant state provides stable, accurate single-frequency oscillations. Crystal oscillator uses a crystal that can convert electrical energy and mechanical energy into each other, and under normal working conditions, the absolute accuracy of ordinary crystal oscillator frequency can reach 50 parts per million. Taking advantage of this feature, the crystal oscillator can provide relatively stable pulses, which are widely used in the clock circuit of microchips.

1. Due to the thin thickness of the chip itself, when the excitation power is too large, the internal quartz chip will be damaged, resulting in vibration stopping.

2. In the leak detection process, that is, in the environment of alcohol pressurization, the crystal is easy to collide with the shell, that is, the chip and the shell are easy to collide when vibrating, so that the crystal is prone to vibration and vibration or vibration stopping.

3. When pressurizing, the inside of the crystal requires vacuum nitrogen, if the pressure sealing is poor, that is, the sealing of the crystal is not good, under the condition of alcohol pressurization, it will be manifested as air leakage, which is called double leakage, which will also lead to vibration stopping.

4. The active load will reduce the q value (i.e., the quality factor), so that the stability of the crystal will decrease, and it is easy to be affected by the surrounding active components, and it will be in an unstable state, and the phenomenon of vibration and vibration will occur.

5. When the crystal frequency drifts and exceeds the crystal frequency deviation range too much, the center frequency of the crystal cannot be captured, resulting in the chip not vibrating.

6. Because the crystal is prone to mechanical stress and thermal stress when cutting feet and soldering, and the solder temperature is too high and the action time is too long, it will affect the crystal, which is easy to cause the crystal to be in a critical state, so that there is a phenomenon of vibration and vibration, or even vibration.

7. During soldering, when the tin wire penetrates through the small holes on the circuit board, resulting in the pin and shell being connected together, or the crystal is in the manufacturing process, the tin dot on the pin on the base is connected to the shell and a single leak, which will cause a short circuit and cause vibration stopping.

Crystal oscillators, which are used to generate pulses, have their theoretical roots in "high-frequency electronic circuits".

In "high-frequency electronic circuits", high-frequency oscillators, transmitting, receiving, modulating, demodulating, and other theories and circuits are discussed.

The oscillation frequency of a high-frequency oscillator depends on the value of LC in the circuit, and the crystal oscillator acts as L.

The shape of the quartz crystal determines the frequency oscillation when it represents l, and this value is extremely stable, so crystal oscillators are widely used.

If you are not majoring in electronic information engineering, you generally do not need to engage in circuit design, and you generally do not need to study the principle of crystal oscillator.

Work is carried out by the piezoelectric effect of quartz.

The working principle is: electrodes are plated on both sides of the quartz crystal sheet, and a certain voltage is added to the two electrodes, because quartz has a piezoelectric effect, the voltage is formed, and the deformation will naturally occur, so as to provide a sinusoidal waveform to the IC. After passing through the IC's internal shaping and PLL circuits, a square wave is generated and then fed to the subordinate circuit.

A passive crystal oscillator is a crystal that must be combined with peripheral circuits to form an oscillator to output a signal of a specific frequency, and this oscillator needs to provide power. For example, MCU can use passive crystal oscillator because it has a circuit that constitutes an oscillator integrated inside, and the crystal is not well integrated, so it has to be externalized.

The passive crystal oscillator needs the peripheral circuitry to drive its operation, generating a clock output, and the signal level is variable, that is, it is determined according to the starting circuit.

The main principles are the piezoelectric effect and the inverse piezoelectric effect.

Passive crystal oscillator (X-TAL).

It is a silica wafer that is coated with a layer of conductive medium (mostly gold and silver) on the surface, and the crystal oscillator has a unique electromechanical effect.

Output a certain amount of power (50uw 100uw) to the 1 pin of the crystal oscillator

Pins are mostly grounding points.

Realize the transformation of electromechanical effects.

To put it simply.

Input force, generate vibration, output electrical signal.

The crystal oscillator is not energized and has a frequency. If a probe with a high input impedance is used, the measured value will be low, because the probe has equivalent capacitance (pf level), and direct contact methods such as probes will definitely introduce capacitive effects, so that the frequency of harmonic orange guessing is low. Therefore, please use the induction method to test the draft test, and the spectrum analyzer can be received by a self-made coil antenna, and the test error is minimal.

Frequency distribution histogram several important data methods:

Mean: The area of each small rectangle of the frequency distribution histogram * the sum of the abscissa of the midpoint of the base edge.

Median: Divides the histogram of the frequency distribution into two equal parts of the recessa parallel to the y-axis.

mode: The abscissa of the midpoint of the base edge of the highest rectangle in the frequency distribution histogram.

Addendum: In the graph, the area of each rectangle is equal to the mega-osmosis: the frequency of the corresponding groups.

Short-circuit R5 should do the trick. If it still doesn't work, you have to pay attention to the IC power supply, maybe it is more suitable to adjust to 60K crystal oscillation.

The crystal oscillation does not vibrate, and it often causes the machine to stop running completely, which makes everyone very annoyed, but I don't know how to start, the following Yangxing Technology gives a few examples to share with you, what to do when the crystal oscillation does not vibrate:

1. No vibration, it will affect the circuit on the motherboard after the whole board is not reset, and the vibration waveform is abnormal, which may directly cause the motherboard to boot up.

Timed blocking phenomenon.

Example 1: A motherboard that has been put back by the tester several times. The cause of the failure is determined to not turn on. It was later confirmed. The board is unstable to boot most of the time.

It can be turned on, sometimes it is not turned on, and when it is not turned on, there is no reset of the whole board (and no vibration). It will return to normal after replacing the crystal oscillator. (This is crystal oscillator operation.)

Unstable) When the M crystal oscillator is used for nvidia electrical timing, 25m no vibration will affect no power, or power off or no power on, and unilateral vibration will also cause power-on power-off phenomenon. When 25M is used for the network card chip, the network card will not be caught if it does not vibrate. It is rare to have phenomena such as not connecting to the network or not lighting up the network lights.

Example 2: A NF520T motherboard, unable to catch the network card, the side volume of 25M crystal oscillator at both ends, found that there is voltage but no waveform, after replacing the crystal oscillator, the fault disappears. A colorful CN61G motherboard, the fault phenomenon is not to turn on the digital card display FF, two or three maintenance measurements have not found any problems.

This board is a short-term board, and the BGA has been replaced, and it cannot be repaired when the sound is intelligent. Put it at your desk. After plugging in the power for the fourth time, the power was cut off, and then he suddenly woke up.

Measured 25m without vibration, just replace it.

3. The crystal oscillator period is wrong. It will directly affect the accuracy of the motherboard system clock, and there will be the problem that the clock is not accurate, which is the same as the mobile phone.

Not allowed. For motherboards with Intel, AMD, ATI chips; If the crystal oscillator does not vibrate, it will cause the motherboard to not power on or the whole board will not reset after powering on. For NVIDIA chips, the motherboard crystal does not vibrate, and there will be a digital card that runs CF or 45 (side).

Example 3: The boot digital card runs 45, and the measurement is not vibrational. The resistance of the continuous crystal oscillator to the ground is low by measuring the diode.

And the resistance values of both are similar. The OK plate crystal oscillator is 670 ohms and 775 ohms respectively (there is no need to remember its resistance value in maintenance, and you can refer to the OK board when it is not accurate).

The internal circuit contact of the crystal oscillator is not good, try another one.

What do you ask about the mold vibrating all the time after it has stopped? Here's how to fix this situation:

1. Disconnect the power supply or battery: If you are using a battery or an external power supply, you can disconnect the power supply or battery first to avoid damage to the equipment or accidents.

2. Check the equipment: check the appearance of the crystallizer to see if there are loose parts or broken parts. If you find a fault with a rough belt, you can try to tighten the loose parts with a wrench, screwdriver and other tools or replace the broken parts.

3. Clean the equipment: remove the dust and dirt inside and outside the mold. Wipe the surface of the mold with a clean cloth to keep the equipment clean and in good working order.

I know that the role of the crystal oscillator is to provide the basic clock signal to the system. Often, a system shares a single crystal oscillator, making it easy for all parts to stay in sync.

The crystal oscillator is combined with the internal circuit of the single-chip microcomputer to generate the necessary clock frequency of the single-chip microcomputer, and the execution of all instructions of the single-chip microcomputer is based on this basis. The crystal oscillator is like a traffic light on the road, providing a certain frequency rhythm for the normal driving of vehicles on the road.

1. Using an oscilloscope to see the waveform is the most straightforward.

It is also possible to measure the voltage with the voltage of the digital multimeter, because the duty cycle of the crystal oscillator waveform is 50%, so the average voltage measured is about 1 2vcc, for 51 single-chip microcomputer, when using external program memory, you can also measure the voltage or waveform of the PSEN pin or P0 port pin, only the crystal oscillator circuit works normally, those pins will have signal output, but now it is rare to use off-chip extended memory, so the voltage or waveform at both ends of the crystal can be measured, but when the crystal oscillator circuit is poorly designed, The introduction of test equipment has the potential to cause vibration stoppage.

2. The voltage difference between the two ends of the crystal is not the average voltage difference.

Although in fact, due to the influence of external circuits, the voltage at the two ends of the crystal may be different, but this is not the basis for judging whether the crystal oscillator vibrates, nor is it the condition for the normal operation of the crystal oscillator circuit. As for one high and one low no work, it means that one end is VCC or close to VCC, and the other end is 0 or close to 0, at this time, of course, the crystal oscillator circuit does not vibrate, otherwise the 50% duty cycle potential will pull the average voltage to about 1 2VCC, but this expression is not accurate, and the technology should be described quantitatively and accurately as much as possible.

3. It is unreliable to listen to the sound to judge whether the crystal oscillator is vibrating.

The oscillation frequency of the crystal far exceeds the upper limit of the frequency that the human ear can hear, and sometimes it is problematic to be able to hear, indicating that the crystal quality is not good, and more often, the normal working crystal will not emit sound that can be heard by any ear, and sometimes the sound comes from external circuit components.

4. The two signal input pins of the single-chip microcomputer are 19 pins (XTAL1) and the other is 18 pins (XTAL2), which correspond to the internal circuit of the single-chip microcomputer is a high-gain amplifier.

When the outside is connected to the crystal oscillator, the 19 pins correspond to the input of the high-gain amplifier, and the 18 pins correspond to the output of the high-gain amplifier, so when you measure, there should be a signal at the high-gain output end, that is, 18 pins.