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YOU ARE HERE: HOME > OSCILLATORS
> CRYSTAL OSCILLATORS
Crystal oscillators are oscillators where the primary frequency determining
element is a quartz crystal. Because of the inherent characteristics of the
quartz crystal the crystal oscillator may be held to extreme accuracy of
frequency stability. Temperature compensation may be applied to crystal
oscillators to improve thermal stability of the crystal oscillator.
Crystal oscillators are usually, fixed frequency oscillators where stability
and accuracy are the primary considerations. For example it is almost impossible
to design a stable and accurate LC oscillator for the upper HF and higher
frequencies without resorting to some sort of crystal control. Hence the reason
for crystal oscillators.
The frequency of older FT-243 crystals can be moved upward by crystal
grinding.
I won't be discussing frequency sythesisers and direct digital synthesis
(DDS) here. They are particularly interesting topics to be covered later.
This is a typical example of the type of crystal oscillators which may be
used for say converters. Some points of interest on crystal oscillators in
relation to figure 1.
Figure 1 - schematic of a crystal oscillator The transistor could be a general purpose type with an Ft of at least 150 Mhz
for HF use. A typical example would be a 2N2222A.
The turns ratio on the tuned circuit depicts an anticipated nominal load of
50 ohms. This allows a theoretical 2K5 ohms on the collector. If it is followed
by a buffer
amplifier (highly recommended) I would simply maintain the typical 7:1 turns
ratio. I have included a formula for determining L and C in the tuned circuits
of crystal oscillators in case you have forgotten earlier tutorials. Personally
I would make L a reactance of around 250 ohms. In this case I'd make C a smaller
trimmer in parallel with a standard fixed value.
You can use an overtone crystal for the crystal and set L * C for the odd
particular multiple of overtone wanted in your crystal oscillators.
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www.electronics-tutorials.com/oscillators/crystal-oscillators.htm
Updated 15th May, 2000
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crystal oscillators page What are crystal oscillators?
A practical example of a Crystal Oscillator
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Related topics on crystal oscillator
broad
band amplifiers
buffer
amplifiers
colpitts
oscillators
crystal
grinding
emitter
degeneration
hartley
oscillator
negative
feedback
oscillator
basics
voltage
controlled oscillators
oscillator
drift
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