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DSP-integrated SoC prolongs wearables' battery life

Posted: 08 May 2014 ?? ?Print Version ?Bookmark and Share

Keywords:wearable? battery? DSP?

Wearable devices end up kept in the chest too soon, due mainly to poor battery life. Developers point their finger at the dearth of optimised wearable hardware that meet the design prerequisites (see Optimised SoCs key to wearables success).

With that in mind, if they were to develop their own wearable SoCs, what should be their priority?

On a system level, system designers first and foremost need to rethink displays. Will Strauss, president of Forward Concepts, said the biggest power drain in a cell phone is the screen. Switching "to black and white to save power when colour is not needed" is one idea. Other power wasters include "keeping WiFi on when you're not near a hotspot."

On a silicon level, Linley Gwennap, principal analyst at Linley Group Inc., calls "higher power in the application processor" the main culprit in power drain. "Processors with four or eight cores, particularly big cores, are much more power hungry than the single- and dual-core processors from a couple of years ago." Choosing a low-power processor (CPU and/or DSP) combined with wireless communications (e.g., Bluetooth, WiFi, cellular) should be a high priority in wearable SoCs, he says.

Eran Briman, VP of marketing at Ceva, told EE Times, "Today's IoT and wearable devices are underserved by inappropriate solutions." For the moment, we should forget about using a multi-core app processor to do everything, he said. Adopting a multi-functional DSP core in combination with a small MCU/CPU is one way to design a new wearable SoC.

Last week at the Linley Mobile Conference, Ceva pitched its TeakLite-4 DSP v2 architecture with 50 new instruction sets. It now can handle Bluetooth connectivity (Classic or Low Energy). That connectivity comes on top of the same single DSP core running other functions, including audio and voice software packages, always-on user interface (UI) functions, and a full suite of sensor-fusion capabilities, according to Briman.

The basic principle behind the DSP+MCU idea is to let the DSP handle the always-listening chores. The DSP triggers an MCU to wake up when necessary, thus saving the system's overall power.

In essence, Gwennap said, Ceva's DSP platform supports "always-on functions and low-power connectivity. Those are the two capabilities that are critical in wearable devices."

Let DSP listen all the time

Let's take a closer look at the tasks that consume most of the power during screen-off. According to Briman, these include Bluetooth Low Energy, sensor fusion, always-listening (voice) and always-watching (face, gesture) functions. If a single DSP corerunning at extremely low powercan do all that, it "dramatically lowers the cost, complexity, and power consumption of chip designs for IoT, wearables, and wireless audio devices," according to Ceva.

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