Ever tried searching through your datasheets for the motional parameters of that quartz crystal you just bought? Good luck! Vendors simply don’t specify these parameters to general end users, and for most applications that’s OK. But for high Q oscillator and filter design, measuring and matching crystals can be important.
This video discusses crystal motional parameters, how to measure them with a crystal impedance meter, and finally examines the measured values of 150+ real world crystals.
Below are some interesting correlations/statistics gathered from the measured data; raw measurement data is available here.
Average C0 capacitance for each crystal holder type
Average motional resistance vs frequency
Average motional inductance vs frequency
Average unloaded Q vs frequency
Average unloaded Q for each crystal holder type
Unloaded Q of glass-sealed crystals vs average unloaded Q
Overall statistical analysis of unloaded crystal Qs
References and additional reading:
| Description | Reference |
|---|---|
| Crystal motional parameters and relevant equations | Understanding Quartz Crystals and Oscillators, Ramon M. Cerda, Chapter 1.27 |
| Measuring quartz crystal parameters | Measurement of the equivalent circuit of a quartz crystal, Omicron Lab |
| Crystal measurements with a VNA | Crystal Bandpass Filters, W0QE |
| Crystal measurements with a Spectrum Analyzer | Crystal Parameters — Experiments with a Tracking Generator + Spectrum Analyzer, QRP HomeBuilder |
| Comparison of crystal measurement techniques | Crystal Motional Parameters: A Comparison of Measurement Approaches, Jack R. Smith, K8ZOA |
| Crystal test fixture design | Assembly and Usage Notes for K8ZOA Crystal Test Fixture Revised for Version 1.2 PCB, Jack R. Smith, K8ZOA |
Hi Craig, could we discuss your Pierce Oscillator Youtube explaination sometime? I have been working in this field for >30 years and I would like to see if I can provide some input to you that I believe more thoroughly explains the Pierce oscillator you described. There is a common error that occurs in the explaination that can be shown in the math, which is much more typically correct, it’s the expalination that can have problems.
Absolutely, I’d love to! Shoot me an email: cheffner@devttys0.com
Did you ever measure one of those 32768Hz crystals for RT Clocks? What are their typical parameters?
I am trying to build a 32768Hz tone detector with such crystal and I am kind of stumped because my VNA shows -50dB attenuation in the passband and -80dB in the stopband when swept as suggested in your video. …while using 50 Ohm I/O with the trivial Test Fixture “C” shown here: http://www.cliftonlaboratories.com/Documents/Crystal%20Motional%20Parameters.pdf
Could my VNA be blowing the crystal up?
But how to measure a 32767Hz watch crystal that has 30kΩ motional resistance, with a 50Ω VNA ?