How to use an oscilloscope to measure whether a crystal oscillator starts to oscillate

Crystal oscillator

KDS crystal oscillator DSB221SDN

When I tested this board, I found that a board always burned into the program.遂 Check it out:

1, power, no problem

2. Using an oscilloscope to measure whether the crystal oscillator starts up, found a strange problem. The 24MHz sine wave on the XOUT side appears, and XIN is not? Why is it not?

So I can't change the main chip. QFP128 didn't work before. It's very easy to disassemble it now. Thanks to the guidance of my colleagues. (Small, I don't dare to install the most common patch before).

But after changing the chip, although I can program the program, but I measured the crystal, or XIN, XOUT. It can be confirmed that the chip is working normally. Why can't the crystal oscillator start? The circuit is correct and you can only check if the oscilloscope has a problem.

The probe is self-calibrated on the oscilloscope, and the 5V 1KHz square wave is normal. Where is the problem? Is it not an energy crystal? Impossible, I used to measure it before.

I found the X1 file for the probe. I tried to change the X10 file. I suddenly found out that the start-up waveform was there. Strange, why is XIN not available in X1, and X10?

From the probe, I found it on the Tektronix website that it was related to the capacitance of the probe.

The characteristic parameters of the oscilloscope probe are:

correspond:

P2200 x 10X/1X 200MHz/6MHz 10MO/1MO 16pF/95pF 300V/150V

Here the Typical input C is very important. It is 95pF at 1X. The size of this capacitor affects the oscillation of the crystal. The matching capacitance of the crystal oscillator is 30pF. Therefore, the waveform detected by XIN is normal and will not affect the chip operation. If you want to measure the vibration, apply a probe with a small capacitance, such as 10X. Of course, the quality of the crystal oscillator itself is also critical.

Similarly, from the above analysis, from the accuracy point of view, strictly speaking, the waveform measured by the oscilloscope is distorted, not the actual value. Of course, for the crystal oscillator, regardless of whether or not the capacitor is added, and how much capacitor is added, the shape quality of the waveform is affected, and the frequency is not affected. So the system will work normally.