# Will crystal oscillator draw current?

1. ## Will crystal oscillator draw current?

im using a crystal oscillator in my embedded system design. i wonder if crystals draw current. if yes , how much?

i have attached datasheet of the crystal im using here.

https://www.digikey.com/product-deta...1-1-ND/7645323

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2. ## Re: will crystal oscillator draw current?

The commonly understood technical terms are "crystal" for the pure resonator device and "crystal oscillator" for the crystal supplemented by an oscillator circuit. The shown device is a crystal, it needs an oscillator circuit to generate a clock signal, e.g. the built-in oscillator circuit of a microcontroller.

The crystal itself doesn't "draw current" because only AC voltage is applied to it (not counting the small AC losses of the crystal), the oscillator circuit however consumes supply current.

If your "embedded system" doesn't provide an oscillator circuit to operate the crystal, you should use a crystal oscillator device instead, e.g. this one https://www.digikey.com/product-deta...6-1-ND/1237033

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3. ## Re: will crystal oscillator draw current?

thanks for elaborate explanation FvM

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4. ## Re: will crystal oscillator draw current?

The crystal itself doesn't "draw current" because only AC voltage is applied to it (not counting the small AC losses of the crystal), the oscillator circuit however consumes supply current.
The crystal is a basic resonant device. You can compare it to a pendulum, or a tuning fork or a mass attached to a spring. As a physical model, all are equivalent.

All of these oscillators are physical devices and they have dissipation. In other words, they do not oscillate for ever. A crystal oscillator is the same.

Even for an ideal oscillator, if you couple it to a load, the load takes energy from the oscillator and there must be a driver that feeds energy to the oscillator to make up the loss.

An ideal oscillator has exactly one natural frequency: the Q is infinite. All real oscillators are coupled to a load (or even a measuring device) and that reduces the Q: we want the coupling as small as possible.

Just like a watch or a wall clock. You have to wind it regularly to make up the loss.

So does the crystal: it consumes some energy to keep on oscillating. The higher the Q, the lower the energy consumption.

This energy goes into the crystal as dissipation: the crystal vibrates and produces acoustic waves that are responsible for the loss.

The higher the loss, the lower the Q. For good crystals, you mount them is a vacuum tube with a very fine suspension that also acts as support.

The atomic clocks use a low pressure gas that use molecules as the oscillator. They have very high Q. Their Q is limited by the uncertainty principle (ignoring collisions).

The current drawn by the crystal is equal to the dissipation (internal) plus the load (driver circuit).

Theoretically, the crystal is working as a forced vibration close to its natural frequency.

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