Energy Micro claims quarter power for ARM-based MCU

Norwegian startup Energy Micro has launched the first of its microcontrollers aimed at low-power systems.

Instead of opting for the Cortex-M0, favoured by NXP Semiconductors for microcontrollers that can run at less than 200mW/MHz, Energy Micro has gone for the more complex M3, claiming that it offers better code density and efficiency thanks to a slightly larger instruction set.

“We knew about the M0 before we started,” said Geir Førre, founder and CEO of Energy Micro. “By the time we took the peripherals into account, there would only have been a 25 per cent difference in the power consumption. We could have chosen to save that 25 per cent but the M0 is a 30 per cent less efficient core than the M3.

“And the M0 needs more memory space because you have a reduced instruction set. But we believe that the M0 is a good core for embedded designs where you can benefit from the low gate count.”

Through a combination of low-energy circuit techniques and hardware-assisted sleep and snooze modes, Førre claimed the company’s microcontrollers consume a quarter of the power of existing designs, based on a benchmarks in which a battery powered device wakes up periodically to process data and then sleep until the next event. The company used an on-chip oscillator to reduce the wake-up time to around 2µs and introduced a ‘peripheral reflex system’ in which peripherals co-operate without intervention from the processor core to increase the amount of time that much of the device is asleep.

“Many microcontrollers have these functions but they are hardwired. Ours is completely flexible,” claimed Førre, adding that the peripherals are coordinated by a state machine.

One of the peripherals is a low-energy LCD controller that consumes 900nA in a mode that updates the display periodically. “We are very proud of this,” said Førre. “We haven’t seen any standalone LCD controller with these numbers. The only one we know of is one made specifically for watches, which is 1.5µA.”

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