Low-Power MEMS Clocks Deliver Stratum 3/OCXO Accuracy And Performance For Less
The SiT530x Stratum 3-compliant silicon microelectromechanical-systems (MEMS) timing solutions from SiTime Corp. can replace oven-controlled crystal oscillators (OCXOs) and temperature-controlled crystal oscillators (TCXOs). The SiT5301 and SiT5302 target telecom and networking infrastructure such as SONET-based and Synchronous Ethernet-based core and edge routers, wireless basestations, Internet protocol (IP) timing, and Smart Grid applications (see the figure).
The family combines Stratum 3 stability with small size, low-voltage/power operation, and programmable features that let you quickly and easily customize and differentiate your products. Telcordia’s Stratum 3 timing standards require clock oscillator frequency stability of 0.1 to 0.28 ppm (100 to 280 ppb) over temperature and less than 4.6 ppm over 20 years. The only oscillators currently capable are quartz crystal TCXOs and OCXOs. The oven-controlled oscillators are best but are larger and require more power because of the oven heater.
SiTime has found a way to stabilize its MEMS clocks for Stratum 3 service. The company uses a 48-MHz MEMS oscillating element and a phase-locked loop (PLL) multiplier to bump the output up to the desired higher value as needed. The SiT5301 provides frequencies in the 1- to 60-MHz range with a precision and accuracy to six decimal places. The SiT5302 provides outputs in the 60- to 220-MHz range with the same accuracy. Virtually any telecom or networking frequency is available.
The ability to replace a quartz TCXO or OCXO with a MEMS device is a real timing breakthrough. Designers now have another option that is smaller with lower cost and lower power consumption. Also, the SiT530x family meets or exceeds Telcordia GR-1244 Stratum 3 frequency stability specifications for the most stringent timing applications:
- ±0.1-ppm frequency stability over commercial temperature (0°C to 70°C)
- <±0.37-ppm 24-hour holdover stability
- ±4.6-ppm frequency stability over 20 years
Available in a 2520 compatible package, the SiT530x is the industry’s smallest ±100-ppb solution. This is a 60% reduction in size compared to any other Stratum 3 TCXO and 10 times smaller than an OCXO. The family is available in 3225, 5032, and 7050 packages as well.
Furthermore, the family boasts the widest frequency range, 1 to 220 MHz, with six digits of accuracy, enabling designers to easily program custom frequencies and develop systems with better performance and reliability. And unlike quartz, the SiT530x oscillators have no activity dips, which enable a more stable reference clock and superior system performance over temperature.
The devices’ operating voltage of 2.5 V to 3.3 V supports all telecom and networking systems-on-a-chip (SoCs), ASICs, and FPGAs and eliminates level translation. The clocks also offer 500 fs of typical integrated RMS phase jitter (12 kHz to 20 MHz) to meet the stringent requirements of telecom and networking applications.
The family’s SoftEdge configurable rise/fall time control improves trace impedance matching and reduces electromagnetic interference (EMI). Its available voltage control with a pull range of up to ±12.5 ppm suits in-system calibration and fine-tuning over time. Also, its outstanding silicon reliability of 500 million hours of mean time before failure (MTBF) is 10 times better than quartz. And, its 50,000-g shock and 70-g vibration resistance is 10 times better than quartz.
Samples will be available in December 2011 to qualified customers. Production is planned for the first half of 2012. Pricing is available upon request.
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