Electronics notes/frequency generation
|This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)|
Oscillators, resonators, crystals, and such.
- clock source (for digital elements, digital communication)
- reference clock
- signal generator
In basic electronics you mostly see ceramic resonators (cheap, can be used when timing is not critical), basic quartz crystal oscillators (more accuracy than resonators), and corrected quartz crystal oscillators (more accuracy than basic quartz; necessary for some applications)
Accuracy refers to how much it adheres to specification, and how much it may vary (e.g. due to temperature).
- ceramic resonators are less accurate than crystals, but good enough whenever timing need not be that accurate
- frequency tolerance: on the order of 0.5% (5000ppm) (7.2min/day)
- crystal oscillators - piezoelectric quartz.
- frequency tolerance: on the order order of ~0.001% (~10ppm) (~0.86sec per day)
- Tunable within a small range of frequencies
- Fairly cheap
- not accurate enough for certain some applications (such as some radio transmission, long-term timekeeping, stability under varying temperatures)
- Low-Frequency Oscillator (LFO) - designs that generates a waveform below ~20 Hz. Used in synthesizers and such.
- Surface acoustic wave (SAW) oscillators - quartz crystals that achieve higher frequencies though a standing-wave construction. More expensive, but necessary for devices that
- frequency tolerance: on the order of 0.0001
- harmonic/linear, oscillator (waveform like a sine wave) 
- relaxation oscillator (waveform like a sawtooth) 
- TCXO (temperature-compensated crystal oscillator)
- less than 5 PPM, down to 0.1 PPM is theoretically possible. A little more complex than basic crystals.
- TCXO often implies analog TCXO (sometimes ATCXO)
- DTCXO is digital TCXO
- MCXO (microcontroller-compensated crystal oscillator)
- refers to designs that are more stable and avoid more noise and drift (useful when supporting less predictable things like uCs) (verify)
- Down to 0.1PPM