Crystal Parameters Explained

See also: Crystal Summary and  Crystal Specifications

Below we give a brief explanantion of the more popular terms used when describing the specifications of quartz crystals. If you need further explanation, our engineers will be happy to help.

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Frequency

The nominal frequency of the crystal. This is expressed in kilohertz (kHz) for frequencies less than 1.0MHz, and Megahertz (MHz) for frequencies of 1.0MHz and over. Frequencies may be specified to seven significant figures. If less are specified, then we may assume any digits that follow are zero.

Calibration Tolerance

Also known as adjustment tolerance. This is specified in parts per million (ppm), normally at 25C (room temperature).

Temperature Stability

The frequency deviation in ppm over the operating temperature range. The type and angle of cut of the crystal blank affects the way the crystal behaves over temperature. The type of cut (SL, DT, AT etc) will be determined mainly by the specified frequency. The precise angle of cut will be determined by the specified stability and operating temperature range.

Operating Temperature Range

This is the temperature range over which the quoted temperature stability is specified, in C. Most types of crystals will operate over a much wider range, but the stability may not be within the specified values. This wider range is called the operable temperature range.

Storage Temperature Range

The temperature range in which the crystal can be stored without damage, i.e. it will resume operation as normal once it is restored to within its operable temperature range.

Equivalent Series Resistance (ESR)

For crystal units designed to operate at series resonance, ESR is the equivalent ohmic resistance of the unit when operating in the specified crystal impedance meter adjusted for the rated drive level and tuned to the specified crystal frequency.

Load Capacitance (CL)

This is an external capacitance which sets a point on the reactance curve at which the crystal will resonate. It is normal to refer to crystals which are operated with a small (say 10 ~ 150pF) value of CL as ‘parallel resonant’ and to those which are not as ‘series resonant’.

Shunt Capacitance (C0)

The ‘static capacity’ or shunt capacity of the electrodes, the holder, and the leads. It is usually measured with an ungrounded case.

Aging

The crystal frequency will change over a period of time, with the amount of change being dependent on a number of factors. The greatest change occurs within the first sixty days. Typically, resistance weld crystals age by a maximum of 3ppm in the first year, reducing by 50 ~ 70% in each subsequent year.