# Crystal Motional Parameters

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 for each crystal holder type

Overall statistical analysis of unloaded crystal Qs

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

## 4 thoughts on “Crystal Motional Parameters”

1. Kurt Wessendorf says:

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.

2. George says:

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?

3. George Robinson says:

But how to measure a 32767Hz watch crystal that has 30kΩ motional resistance, with a 50Ω VNA ?