Appendix 1 Quartz oscillator types. Terasync

Below we will present different types of quartz oscillators and their key parameters.

XO – uncompensated Crystal Oscillator. Frequency stability of tens to hundreds PPM in the temperature ranges, aging of a few PPM per year. The cost is around and usually below 1 US$ per piece. Size can be as small as 2x2mm.

TCXO - Temperature Compensated Crystal Oscillator. The quartz is wired with an additional circuitry that compensates (up to some degree) the frequency changes caused by the ambient temperature variations. High end TCXO can cost up to 20 US$, with frequency stability of ±0.28 PPM vs. temperature range, low aging of around 0.1-0.2 PPM per year. The size is usually 5x7mm, can be 5x3.2mm. Low end TCXO are priced from a few US$ up to 10 US$, with a typical frequency stability vs. temperature from 0.5 to a few PPM, and aging that can be close to 1 PPM per year.

The power consumption of XO and TCXO oscillators is relatively low, and rarely surpasses 30-50 mW.

OCXO – Oven Controlled Crystal Oscillator. This device differs significantly from the lower stability crystal oscillators. The crystal is placed in the oven that heats it to the temperature (around 80-90°C) where the frequency stability is the best. The price range of OCXO is also different and varies around 50-100 US$. The frequency stability vs. temperature is in order of magnitude of ±0.01 PPM, while the yearly aging is usually less than ±0.1 PPM. OCXO of significant quality is much bigger than the simpler oscillators. Even for small devices the size is around 25x22 mm, with a height of about 10-15 mm. Additionally, the current consumption is quite high, especially a few minutes after the power on (warm up). The typical values are 2-3 W consumption at warm up, and around 1 W at steady state. The power consumption of the OCXO is also very dependent on the ambient temperature (at low temperatures the oven works harder).

DOCXO – Double Oven Controlled Crystal Oscillator. This is more sophisticated device than OCXO, as there are two ovens – one inside another. It allows minimizing the temperature variations at the crystal itself, thus achieving very high frequency stability vs. temperature - of around ±0.001 PPM. The aging is also low, close to 0.05 PPM per year. This stability comes with a price though, as the cost of DOCXO can reach a few hundreds of US$. The power consumption is usually a few times more than that of OCXO. Even miniature DOCXO is quite bulky - 36x27x20 mm.

OCXO and DOCXO internal temperature is high, and their complexity is also higher than that of TCXO. Therefore, the MTBF of ovenized oscillators is generally lower. Not every manufacturer can produce high quality ovenized oscillators that will work reliably over time and comply with the long term aging specifications.

The oscillator parameters affect the normal solution performance up to some degree, but more important, they define the equipment behavior in case of failure.

Table 1 Quartz oscillator types summary