This crystal ladder filter calculator is a simple tool for dimensioning crystal
bandpass filters composed by 2 to 8 identical quartz crystals and some
Quartzes are used in their fundamental mode (even if they are overtone) in
their series resonance (even if they were designed for parallel mode
The series and parallel resonance of the crystals must be precisely known, as well as the crystal's series capacitance Cs. Those values cannot be found on datasheets with the necessary accuracy and need to be manually measured with the method described before. It's also important to select crystals with very similar characteristics (the resonance frequencies should be within 100 Hz).
If no bandpass ripple is allowed the filter will be of Butterworth type and the transitions between pass-band and stop-band will not be very fast and the ultimate attenuation (horizontal asymptote) will be poor. If some bandpass ripple is allowed the filter will be of Chebytheff type with much better stop-band characteristics.
The number of poles of the filter equals the number of crystals and depends on how many identical crystals one happens to have.
The target bandwidth is the bandwidth the filter should pass: the maximum possible bandwidth depends on all the data entered and is usually only a few kHz.
Hitting the "Calculate" button will start the simulation.
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