MEMS oscillator extends wearable battery life

"We weren't aware of this as a problem when we started talking to our customers about a TCXO version of our real-time clock, but they immediately told us about how a high-precision, real-time clock could significantly extend battery life—especially on wearables," Sevalia told EE Times.

Figure 2: SiTime's temperature controlled MEMS oscillator (TCXO) uses a unique 3-D chip stack with the tiny 125? MEMS die flipped and mounted between the solder bumps on the bottom of the application specific integrated circuit (ASIC) containing the electronics. Source: SiTime

The SiT1552 TCXO uses the same TempFlat technology used in its SiT15xx—a 20ppm to 100ppm part announced last year. By adding on-chip temperature sensor and an analogue temperature-to-digital converter (ADC) SiTime was able to increase precision to plus or minus 5ppm. The SiT1552 TCXO real-time clock also claims the smallest footprint of any TCXO today, a 1.5mmx0.8mmx0.55mm chip scale package (CSP), one sixth the size of quartz crystals. And it consumes less than one microAmp of power. The MEMS chip is so small and thin—400?x400?x125?—that it fits between the solder balls on the bottom of the application-specific integrated circuit (ASIC) containing the electronics.

Figure 3: The SiT1550 system block diagram. Source: SiTime

The SiT1552 is also marketed to device makers that need accuracy over long periods, such as smart meters, which need to stay accurate for 20 years or more. The device has a lifetime of 500 million hours and is covered by SiTime's lifetime replacement warranty, as are all its timing chips. The SiT1552 is in mass production now, and so far SiTime has shipped 220 million total timing chips since its founding in 2005.

- R. Colin Johnson
??EE Times

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