Crystal UnitsDrive level

Basic Knowledge of Crystal Units

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No. Item Title Contents
1 Outline Drive level Drive level indicates power consumption by crystal unit while oscillation circuit works.
It is important for crystal to keep within drive level specification.
Excessive drive level might cause unexpected change of frequency and equivalent series resistance.
2 Measure Calculation Drive level could be calculated as follows.
Drive level = I2・R1
I: Drive current [Effective value]
R1: Equivalent series resistance of crystal unit
Drive current is a current through crystal unit while the oscillation circuit works. Drive current could be measured on actual oscillation circuit.
R1 could be measured by network analyzer and so on.
Measurement
example
  1. Measurement equipment and device
    • PCB
    • Crystal unit (with equivalent circuit constants data)
    • Oscilloscope, Current probe
  2. Solder a lead wire to crystal and set a current probe as figure shown in below.
  3. Supply power voltage to PCB and observe drive current waveform on oscilloscope
  4. Caluculate effective value of drive current
    If waveform is sine wave or similar, effective value is caluculated by Ip-p /2√2
    With digital oscilloscope, effective value could be read by function of oscilloscope.
  5. Drive level is caluculated by above formula.
3 Judgement
Measured drive level should not exceed drive level specified in crystal specification.
Oscillation circuit: Normal condition
Connecting current probe