Fantastically Clean Differential Oscillators
Posted By: Aaron Partridge

SiTime is now sampling our new generation of high-frequency differential oscillators, the SiT9121 and 9122. These are designed for high speed serial interfaces, such as SONET, that require high clock frequencies and waveforms with fantastically clean edges.

At the very highest data rates even slight noise in the transmit or receive clocks can degrade data fidelity. And because of this the cleanliness standards on these clocks are very tight. The primary spec is that the jitter integrated from 12 kHz to 20 MHz must be less than one picosecond (one trillionth of a second). SiTime has the only MEMS oscillators capable of meeting this spec. In fact, SiTime’s new oscillators beat this by a factor of two, delivering clocks with only a half-picosecond integrated jitter.

In quartz, oscillators that can beat a picosecond are often called “extremely low jitter”. The extremely is well deserved – it is a very low number. For example, in half a picosecond light travels only 150 microns in a vacuum. An electrical signal in a copper wire travels at about half the speed of light. Thus a clock signal traveling in a printed circuit board goes about 75 microns in a half picosecond. That is roughly the width of a human hair.

So think of what these oscillators are doing. They are producing electrical waves that travel out from their pins, across PC boards, and into application ICs. These waves move at half the speed of light while their edges are where they should be to the width of a human hair. Pretty amazing!


Feb 11, 2022

Jan 11, 2022