Crystal Units FAQ


Please let me know a cause and measures for oscillation stop.

Please check oscillation frequency or waveform to make sure driving of oscillation circuit or frequency you want.

Please refer how to check oscillation frequency or waveform below.

If you confirm that oscillation circuit does not work, please check below points to make sure the cause.

2-1. IC setting
Some ICs require to be programmed or reset to enable oscillation circuit.
Please check if any required setting is done.

2-2. Checking function of C-MOS inverter as amplifier
Please make sure that C-MOS inverter for oscillation circuit works as inverting amplifier.
Feedback resistor (Rf) is important as bias resistor to make inverting amplifier with C-MOS inverter.
Please check Rf is integrated in IC or added on oscillation circuit.
If inverting amplifier works, DC voltage level at input / output of C-MOS inverter should be 1/2 voltage applied to C-MOS inverter.

2-3. Checking crystal unit characteristics
Please check "R1" and "fL" are within specification.
Network analyzer or impedance analyzer is necessary to check those.

2-4. Checking oscillation margin
If characteristics of crystal unit is normal, it is possible that insufficient oscillation margin causes the oscillation stop.
Please refer "What is oscillation margin" and "How to check oscillation margin" below.

We propose over 5 times of oscillation margin based on R1 specification.
We explain how to make oscillation margin large below.

  1. To change external capacitance small
    Oscillation margin will be high with small external capacitance.
    Lower external capacitance makes high impedance at output of C-MOS inverter.
    Mentioned high impedance leads high negative resistance of oscillation circuit and increases oscillation margin.
    After you change external capacitance small, please check actual oscillation frequency is within frequency range you want. Actual oscillation frequency becomes high with small external capacitance.

  2. To change damping resistance small
    Oscillation amplitude is attenuated by damping resistor. Oscillation margin can be increased to change damping resistance small because of higher negative resistance.
    After you change damping resistance small, please check drive level is within crystal unit's spec, because drive level becomes high with smaller damping resistance.

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