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Crystal load and frequency tolerance

Calculate crystal load capacitors and convert between frequency variation and parts per million.

Inputs

All three sections calculate independently.

Crystal load capacitors
pF
pF
pF
pF
Parts per million to hertz
Hz
ppm
Hertz to parts per million
Hz
Hz

Result

Enter your values to calculate a result.

Crystal load capacitors
Crystal load capacitors

The two capacitors contribute a series capacitance across the crystal. Stray capacitance adds to that value. Use the crystal datasheet load capacitance when choosing the capacitors.

Illustration only. Not to scale.

Calculated load capacitance

N/A

Suggested C1 and C2N/A
Frequency variation from toleranceN/A
Upper frequency limitN/A
Lower frequency limitN/A
Entered frequency differenceN/A
Frequency difference in ppmN/A
Method and assumptions

Crystal load: Cload = C1×C2/(C1+C2) + Cstray. The suggested value for each capacitor assumes C1 = C2 and uses 2(Cload − Cstray).

Parts per million to hertz: Δf = f×ppm/1e6. Hertz to parts per million: ppm = Δf/f×1e6.

  • Crystal load capacitance should be checked against the crystal datasheet.
  • Stray capacitance includes package, pads and PCB routing.

Match the crystal’s specified load

Enter the crystal’s specified load capacitance and your estimated stray capacitance. The calculator suggests a starting value for C1 and C2. Adjust the capacitor values until the calculated load matches the datasheet.