Five things to consider when choosing a crystal oscillator: Page 3 of 4

October 03, 2016 // By Steve Fry, Greenray Industries, Inc.
Most electronic systems require some sort of oscillator as a critical functional block in their design. Some typical uses would include: a clock for a digital system that synchronizes the operation, a stable RF signal for a receiver or transmitter, an accurate frequency reference for precision measurements or a real time clock for accurate timekeeping. The specifications for the system and how the oscillator needs to function will determine most of the parameters of the device.

Voltage Controlled Crystal Oscillator (VCXO): In some applications it is desirable to be able to tune or adjust the frequency of the oscillator in order to phase lock it to a reference in a phase locked loop or possibly to modulate the waveform. A VCXO provides this capability via an Electronic Frequency Control (EFC) voltage input. The tuning range specification for a VCXO may vary from ±10ppm to ±100ppm or even higher for some specialized devices.

TCVCXO and VCOCXO: A TCXO or OCXO will often include an EFC input voltage. This allows adjustment in order to calibrate the output frequency precisely to a nominal value.

Figure 1: Generic oscillator block diagrams.

Figure 2: Frequency versus temperature stability of crystal oscillator types.

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