What is a Oscillator?

The oscillator circuits that form the basis of oscillators include RC oscillators that output sine waves in the low frequency range, LC oscillation circuits that output sine waves in the high frequency range using resonance phenomena, and crystal oscillation circuits. Here, we will mainly explain the crystal oscillator circuit.

1. Crystal unit
A crystal resonator is a pure reactance element with almost no loss in terms of electrical characteristics. This reactance is inductive (a characteristic of the coil) only in a very narrow frequency range, so connecting a capacitor to the crystal will determine the resonant frequency within that frequency range. If the coil is replaced with a crystal resonator in the Colpitts oscillator configuration, which is a typical LC oscillator, the crystal oscillates only within a narrow range where the crystal resonator exhibits inductive properties.

2. Ceramic resonator
Crystal resonators are expensive to manufacture because the oscillation frequency is determined by processing mineral crystal with high precision. Therefore, ceramic oscillation circuits using relatively inexpensive ceramic resonators are also used. Ceramic resonators also exhibit inductive reactance in certain frequency ranges, but the characteristics are not as steep as crystal resonators, so the disadvantage is that the oscillation frequency is less accurate.

3. Crystal unit for watches
The oscillation frequency of crystals and ceramic resonators ranges from several hundred kHz to several tens of MHz, but some crystal resonators for watches have a frequency of 32.768kHz. Frequency accuracy is extremely important in oscillation circuits for watches, so ceramic resonators are not used, but crystal resonators are used. This is because quartz crystals can provide high frequency accuracy.

summary
Crystal oscillator: Has highly accurate frequency characteristics and is expensive.
Ceramic resonator: Low cost, but lower frequency accuracy than crystal resonator.
Crystal units for watches: 32.768kHz crystal units are used for watches that require high precision.
In this way, crystal oscillation circuits and ceramic oscillation circuits are appropriately selected according to their characteristics and costs, and are applied to a variety of devices.

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