The method of measuring crystal oscillator output frequency
In general, the crystal output frequency is measured with the frequency meter.
A frequency meter is an electronic measuring instrument that specializes in
measuring the output frequency accuracy of a crystal oscillator when it is operating.
Among the common electronic frequency measurement instruments,
the oscilloscope measurement accuracy is low and the error is large.
Although the spectrum meter can accurately measure the crystal frequency and display the spectrum,
the measurement speed is slow and cannot capture the real-time change of the crystal oscillator frequency.
The frequency meter can quickly and accurately capture the changing state of
the output frequency when the crystal oscillator is working. Therefore, the frequency meter has a wide range of applications.
The use of the frequency meter is described as follows.
For example: test the output frequency of 27.000 MHZ on the board.
To the circuit board power.The frequency meter to power on, open the power switch,
the general frequency meter is divided into KHZ and MHZ two files, now set to MHZ file.
The frequency converter probe attached to the metal clip clamps the board grounding parts.
With the probe gently touch the crystal frequency output feet or input feet soldering parts.
Observe the frequency meter display, then the crystal will show the working frequency, such as 27.000063 or 26.999592.
Attention
If the frequency meter does not display a stable frequency of around 27.000000.
For example, if it shows 16.987564 or 29.034321 and keeps changing, it means that the frequency meter has not yet
captured the crystal frequency. We could try to use the frequency meter probe to re-contact the crystal pins.
If the above method still fails to capture the crystal frequency,
please try to perform a shutdown and reboot action on the frequency amount.
For the frequency meter probe itself load capacitance problem, try to choose a smaller capacitance value of the probe,
such as 12PF probe is far better than 6PF probe better use. The smaller the capacitance value of the probe,
the more accurate the measured crystal frequency. Because the frequency meter probe itself has a load capacitance,
plus the board's stray capacitance and other effects on the crystal frequency,
the measured crystal frequency is a little more positive than the actual frequency.
Therefore, according to actual experience, it is recommended that the measured crystal frequency is slightly more negative,
which proves that the actual output frequency of the crystal is closer to the actual frequency.