Crystal Parameters Glossary and Specification Guide

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.

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

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.

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.

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.

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.

This is an external capacitance which sets a point on the reactance curve at which the crystal will resonate. Crystals used in this way are referred to as  ‘parallel resonant’. Alternatively crystals may be used at the point that their reactance is at or close to zero, these are referred to as  ‘series resonant’.

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

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.

To express normal parameters concisely we use a standard notation of the form:

A/B/C/D-E

where:

A = Calibration tolerance, expressed in parts per million (ppm)

• eg. 30/50/10/30-F denotes a crystal with ±30ppm calibration tolerance
  
  

B = Temperature stability over the temperature range, expressed in parts per million (ppm)

• eg. 30/50/10/30-F denotes a crystal with ±50ppm over temperature range
  
  

C = Negative end of operating temp range, which is normally symmetrical about +25°C 

0 = 0 to +50°C
10 = -10 to +60°C
20 = -20 to +70°C
30 = -30 to +80°C
40 = -40 to +90°C
55 = -55 to +105°C

• eg. 30/50/10/30-F denotes operating temperature range -10+60°C

If the operating temperature range is not symmetrical about +25°C we will specify both upper and lower limits i.e. ‘-55+125’. Ovened Crystals are signified by showing the oven temperature here and the figures ‘00’ for temperature stability.

D = Circuit condition

A number = parallel resonance with a load capacitance in pF.
SR = Series Resonance.

• eg. 30/50/10/30-F denotes 30pF load capacitance
  
  

E = Operating mode of crystal

F = fundamental mode
3 = third overtone
5 = fifth overtone
7 = seventh overtone mode
9 = ninth overtone mode

• eg. 30/50/10/30-F denotes fundamental mode

Frequency and holder style are shown separately as are any special parameters such as C1,C0,L1, etc.

• 30/50/10/30-F denotes a crystal with ±30ppm calibration tolerance, a temperature stability of ±50ppm over temperature range -10+60°C, 30pF load capacitance and operating in fundamental mode.
  
  
• 05/10/20/SR-3 denotes a crystal with ±5ppm calibration tolerance, a temperature stability of ±10ppm over temperature range -20+70°C, series resonant and operating in third overtone mode.