What Are TCXO / OCXO / VCXO?
TCXO, OCXO and VCXO are special types that improve the stability or controllability of an ordinary crystal oscillator. They're used where precise frequency is required.
Why Special Types?
An ordinary crystal's frequency drifts somewhat with temperature. Applications like communications, GPS and measurement can't tolerate even this small drift; so oscillators with improved stability were developed.
| Type | Method | Stability |
|---|---|---|
| TCXO | Temperature compensation | High |
| OCXO | Constant temperature (oven) | Very high |
| VCXO | Voltage adjustment | Adjustable |
TCXO and OCXO
TCXO (temperature-compensated) corrects the temperature drift with an internal circuit; it's low-power. OCXO (oven-controlled) holds the crystal at a constant temperature to give the highest stability, but consumes more power and needs a warm-up time.
VCXO
VCXO (voltage-controlled) is a crystal oscillator whose frequency can be finely adjusted with an externally applied voltage. It's used in PLL and synchronization circuits.
Where Is It Used?
TCXO: phones, GPS, radios. OCXO: base stations, measurement instruments, reference clocks. VCXO: PLLs, data synchronization and frequency adjustment.
Common Mistakes
- Over-specifying: putting an OCXO on a simple job brings needless power and cost.
- Warm-up time: an OCXO needs time to reach full accuracy.
- Power budget: an OCXO may not suit a battery-powered device.
Frequently Asked Questions
Which is the most stable?+
Why is a VCXO adjustable?+
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