PORTLAND, Ore. — Let's face it: Most of the time our mobile devices are idle. No matter how addicted you've become to checking for messages, surfing the web, listening to music, or playing games, most of the time it's waiting for you to activate it. However, during this idle time your unit is not totally off. If Bluetooth is turned on, for instance, it has to wake up every few seconds to make sure no paired device is wishing to transfer data. Likewise, it has to periodically check for button clicks, WiFi activity, and for battery supervision functions.
During those operations SiTime Corp. of Sunnyvale, Calif., claims its new, high-precision, real-time clock can save 50 percent or more of the power usually expended during idle time, at least doubling the battery life during those periods.
SiTimes super-accurate temperature compensated MEMS oscillator (TCXO) helps extend battery life of wearables by allowing smaller sampling windows for sensors, Bluetooth, WiFi, et. al.
"These power savings might not amount to much for a device with a big battery, but for Internet of Things and wearable devices with tiny batteries, their lifetime can be significantly extended with our new SiT1552 MEMS 32 kHz TCXO [Temperature Compensated Oscillator] real-time clock," Piyush Sevalia, executive vice president of marketing, told EE Times.
Every mobile device has a 32 kHz real-time clock to keep track of time, telling its device when to wake up and perform its duties. Most of these real-time clocks have a precision of 100 to 250 parts per million (PPM), which is adequate to keep a device from seeming unresponsive or sluggish. However, for real-time devices like Bluetooth accessories, even 20 PPM means that the software designers have to include buffer time to make sure the external device is connected properly before data is transferred.
In essence, this means the software designers add extra time at the beginning of a wakeup operation to make sure both devices are communicating, then more extra time at the end of an operation before the device is put back in idle mode to make sure all the data was transferred. However, with SiTimes SiT1552 TCXO real-time clock, its accuracy is within 5 PPM -- the lowest in the industry -- permitting the software writers to drastically cut down those buffer periods, thus saving power and extending battery life, especially for wearables.
"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 us.
SiTimes temperature controlled MEMS oscillator (TCXO) uses a unique 3-D chip stack with the tiny 125 micron thick MEMS die flipped and mounted between the solder bumps on the bottom of the application specific integrated circuit (ASIC) containing the electronics.
The SiT1552 TCXO uses the same TempFlat technology used in its SiT15xx -- a 20 to 100 PPM part announced last year. By adding on-chip temperature sensor and an analog temperature-to-digital converter (ADC) SiTime was able to increase precision to plus or minus 5 PPM. The SiT1552 TCXO real-time clock also claims the smallest footprint of any TCXO today, a 1.5 x 0.8 x 0.55 millimeter 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 x 400 x 125 microns -- that it fits between the solder balls on the bottom of the application-specific integrated circuit (ASIC) containing the electronics.
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, Advanced Technology Editor, EE Times
Story updated: 6/4/2014, 200 percent changed to 50 percent, in second paragraph. -- EE Times