Micropower MEMS oscillator for wearables, IoT and mobile

June 22, 2015 // By Steve Taranovich, EDN
SiTime recently announced a new family of µPower (micropower) MEMS oscillators for the wearable, IoT and mobile markets. The SiT8021 oscillator is the first device in this family.

The company claims that the device consumes 90% lower power, is 40% smaller, and 70% lighter than existing quartz devices. This product enables long battery life as well as the small size and weight for smart watches, fitness bands, tablets, smart phones, portable audio and accessories.

I spoke to Piyush Sevalia, Executive Vice President of Marketing for SiTime to get some more insight into the product as well as the market for which this MEMS oscillator was developed. Sevalia told me that they craft the IC in 180 nm CMOS, so the analogue portion of the IC is 1.5 x 0.8 mm while the MEMS is 0.4 x 0.4 mm. The oscillator typically drives low power microcontrollers, audio interfaces, glue logic (CPLD), SoCs and USB charging.

To generate a MHz frequency from an oscillator, a designer may use a kHz reference or a MHz reference. The benefit of using a kHz reference is that it consumes much lower power. The SiT8021 uses a 524 kHz MEMS resonator and uses a highly optimised PLL for performance. Battery-operated devices will run longer between charges with the 100 µA operating power dissipation of this oscillator. The oscillator can use only 1.8V operation for battery powered applications. The MEMS oscillator is capable of driving two loads. The device has programmable output drive strength for best EMI or driving multiple loads.

This MEMS oscillator is based on SiTime’s TempFlat MEMS technology and has ±100 PPM frequency stability; quoted failure rate at 1.6 DPPM is 30x better than quartz. The oscillator chip can withstand 20 k-g shock resistance and 70 g vibration resistance. Don’t try that with a quartz oscillator.

In quartz crystal technology, physics dictates that the lower the frequency, the larger the crystal resonator. MEMS resonators do not have the same constraint; they are 1000 to 3000 times smaller than typical quartz resonators.

Because SiTime’s MEMS resonators are fully encapsulated in silicon and