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This answer led to the conclusion that it is unclear what the meaning of the frequency listed by crystal manufacturers actually means.

Given this graph on page 79 of this ECS Crystals Application Note enter image description here

there seems to be three obvious possibilities:

fs - the series resonant frequency

fa - the antiresonant frequency

fL - some value in the area of usual parallel resonance

In the case of fL the frequency specification itself would depend on load capacitance (see Figure E in this application note).

Here are some typical datasheets that turn up on the manufacturer's websites:

They seem to leave the meaning of the frequency ambiguous.

So, my question is this:

What is the meaning of the nominal frequency specified by manufacturers of crystals?

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alx9r
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2 Answers2

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I think your second app note from ECS explains it: it is the frequency the crystal oscillates at when put into an (parallel) oscillator circuit, with the load capacitance specified by the manufacturer. (see page 85, "load capacitance")

This means you are right in that the frequency depends on the load capacitance - which is why it is specified in the data sheets.

But there are also crystals which are used in series oscillator, the you have no capacitance, and the specified crystal frequency is the series resonant frequency (fs).

hli
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When you order a crystal, you specify how it is to be used. The factory then cuts and trims the crystal to operate at the desired frequency, under those conditions. The reverse is true. If you were to buy an off the shelf crystal, the circuit you put it in should match the crystal "type" if you expect it to operate at the correct frequency. This matters in radio applications, but not so much for microprocessors. That's why the subject is relatively unfamiliar.

gbarry
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