±1ppb/°C 156.25MHz mems oscillator for SerDes and 800G links

SiTime has introduced SiT5977, a ±1ppb/°C mems-based 156.25MHz oscillator for network timing in data centres.

It is “capable of driving 800G and higher links via 80fs phase jitter and LVDS outputs,” according to the company.

Inside the tiny package, which measures 3.5 x 5mm, is what is claimed to be “the world’s most accurate silicon temperature sensor”.

This sensor consists of two micro-machined resonators fabricated on the same die, one with flat frequency characteristic over temperature, and the other sensitive to temperature changes – physically, the mems resonator die is mounted on top of a CMOS die for the electronics.

“The ratio of frequencies between these two resonators provides an accurate reading of the resonator temperature with 30µK resolution,” said SiTime. “This design eliminates thermal gradients between the resonator and the temperature sensor – there is no lag between the mems resonator and the mems temperature sensor as both resonators are physically located on the same die substrate and therefore have 100% thermal coupling.”

The resulting measured temperature is used as an input to a digital compensation system built around a fast PLL-based fractional-n synthesiser to reduce jitter.

“The compensation runs at 100s of Hz [and] achieves dynamic performance that is far superior to any quartz TCXO,” claimed the company.

Control loop pull-in range is ±400ppm, and tuning resolution is 0.05 part-per-trillion. Control is though I2C.  or SPI.