How to determine whether the crystal oscillator is oscillating?
1、Use an oscilloscope to view the waveform Using an oscilloscope to view the waveform is the most direct method. Because the duty cycle of the crystal oscillator waveform is 50%, the average voltage measured is about 1/2Vcc.
The crystal oscillator waveform is generally a sine wave or a square wave. When the output waveform is a square wave, the rising edge is generally steeper and contains more high-frequency signals. At this time, it is necessary to ensure that the test bandwidth is sufficient. The theoretical value is that the bandwidth is twice the frequency of the measured signal. When testing the square wave, the bandwidth should be 10 times the frequency of the measured signal. In addition to the bandwidth, when testing the crystal oscillator, there is another point that should be paid attention to: the crystal oscillator is sensitive to capacitive loads, and the probe capacitance is relatively large, which is equivalent to a heavy load connected in parallel in the crystal oscillator circuit, which can easily cause the circuit to stop oscillating and fail to obtain correct measurement results. Therefore, when testing the crystal oscillator, it is necessary to ensure sufficient bandwidth and a smaller input capacitance.
2、Use the voltage range of a digital multimeter to measure voltage. The passive crystal oscillator has two pins: the frequency input pin and the frequency output pin. If the crystal oscillator has started oscillating, it means that there must be a voltage difference between the two pins, so that the current flowing through can generate excitation power for the chip. Therefore, we can use the DC voltage range of the multimeter to measure the voltage of the two pins of the crystal oscillator. When starting oscillating, the voltage across the crystal oscillator is generally half of the chip power supply voltage Vcc. But here we should note that if the chip is bad, it is impossible to capture the correct clock signal that the crystal oscillator is providing to it. In this case, we are prone to misjudging whether the crystal oscillator has started oscillating.
3、Use a frequency meter to test When using a frequency meter to measure the crystal oscillator frequency output pin, if there is a normal waveform (commonly a square wave, the temperature compensated crystal oscillator has a clipped sine wave output) or a normal frequency signal output, it can be regarded as the crystal oscillator has started oscillating normally.
4、Finally, the method of judging whether the crystal oscillator has started oscillating by listening to the sound is not reliable. Because the oscillation frequency of the crystal is far beyond the upper limit of the frequency that the human ear can hear, sometimes it is a problem to be able to hear it, indicating that the crystal quality is poor. More often, a normally working crystal will not emit any sound that can be heard by the human ear. Sometimes the sound comes from external circuit components. Crystal oscillators are essential electronic components in circuits, and are mainly used for wireless data transmission and timing.
With the rapid development of domestic 5G and new energy industries, the demand for domestic crystal oscillators has grown rapidly, and domestic manufacturers are striving to catch up and accelerate the process of domestic substitution. Yangxing Technology is one of them.