OCXO: PPM vs. PPB vs. PPS Explained

This page compares OCXO (Oven Controlled Crystal Oscillator) specifications in terms of ppm, ppb, and pps. It describes these terms and their units used in the context of OCXO crystal oscillators.

OCXO ppm | Parts Per Million

The frequency stability of an oscillator, synthesizer, or frequency transceiver is often specified in parts per million (ppm). The term “ppm” is shorthand for “Parts Per Million.”

Image alt: ppm to Hz converter equation

The image above shows a formula to convert a ppm value to Hertz (Hz). ppm represents a part of a whole number, with units of 1/1,000,000.

Example: The accuracy of an oscillator is specified as 5 x 10^-6, or 5 ppm.

• This means the actual frequency of the oscillator can deviate by a factor of 5 ppm compared to its nominal frequency.

OCXO ppb | Parts Per Billion

The term “ppb” stands for “Parts Per Billion.”

ppb also represents a part of a whole number, but with units of 1/10⁹. One billion equals one thousand million.

Example: An oscillator’s accuracy might be 0.36 x 10^-9, or 0.36 ppb.

OCXO pps | Pulse Per Second

The term “pps” is short for “Pulse Per Second”.

Example: The accuracy of an OCXO in PPS is specified as < +/- 50 nsec (nanoseconds), etc.