oscillator , crystals, resonators
Zap-o
Posts: 452
So whats the differences between oscillator, crystals, and resonators. I am looking at keeping time for several hours using the propeller and need someone to break down the differences between these items.
Thanks in advanced.
Thanks in advanced.
Comments
Electronic oscillators are usually intended to produce a repetitive waveform (often sinusoidal) of reasonably constant (and sometimes variable by a control) amplitude and frequency.
Many electronic oscillators have their frequency controlled by a circuit element (or sometimes a subcircuit consisting of several elements like inductors, capacitors, or resistors)·whose electrical characteristics vary greatly at different frequencies, and the oscillator is designed to take advantage of this to control its oscillation frequency.
If that frequency-controlling circuit element is resonant at some particular frequency, the design of the oscillator circuit is usually made easier.· Therefore most electronic oscillators use resonant circuit elements as frequency-controlling elements.· Such elements are called resonators.
Resonators are known (and used) of several types.· One of these, very common, is a quartz crystal that resonates by vibrating physically -- ringing like a bell, basically, but at higher frequency than most bells, anywhere from several thousand to several million vibrations per second.· An electronic oscillator that is controlled by such a quartz crystal is called a crystal oscillator.· There are several different ways to design a crystal oscillator.
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· -- Carl, nn5i@arrl.net
A crystal is made from a crystal of quartz cut to a specific size that vibrates at a specific frequency. This frequency changes slightly over time as the crystal "ages" and crystal manufacturers can characterize this aging pretty accurately. The frequency also changes with temperature changes as the crystal expands and contracts and this is fairly predictable and can be compensated for if you know the temperature.
A resonator is similar to a crystal, but is made from ceramic. It's typically less accurate and drifts more with time and temperature than a crystal.
An oscillator is the circuit used to produce a signal at a single frequency based on some kind of frequency control like a crystal or resonator.
Crystals were generally considered to be more accurate than resonators, but resonators have pretty much caught up with crystals - unless you have a crystal in a controlled oven to make the temperature stable.
Oven controlled crystals are super accurate, but also quite expensive. Ocillators are either crystal controlled and merely output more power or a cleaner wave or both OR they tend to wander much more than crystal or resonator control.
Resonators are pretty much the dominant choice as crystals at higher frequencies [noparse][[/noparse]above 20Mhz} can be driven to two different harmonics and one of the two is not what you want. The test equipment to properly tune a crystal the right harmonic is too expensive for a hobbyist.
Going to a higher frequency doesn't increase the time keeping accuracy, but does increase the power consumption of the microprocessor. So a 32K clock crystal is just as accurate as a 50mhz crystal. The faster one will allow you to do more tasks through an interrupt scheme.
The Propeller does fine with a slower crystal - 4Mhz or so. You may not want to bother with a resonator as there is no issue of a 2nd harmonic at that speed.
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Ain't gadetry a wonderful thing?
aka G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan
Post Edited (Loopy Byteloose) : 8/10/2009 5:58:33 PM GMT
Crystals are available for fundamental operation at 40 MHz.
Leon
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Amateur radio callsign: G1HSM
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