Design cuts Bluetooth transceiver power in half

By Nick Flaherty www.flaherty.co.uk

Researchers at Tokyo Institute of Technology (Tokyo Tech) have developed a Bluetooth Low-Energy transceiver with the lowest ever power consumption for applications in the Internet of Things (IoT).

Figure 1. A photograph of the chip. The chip was designed using standard 65-nanometer CMOS technology.

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When transmitting, the transceiver consumes 2.9 milliwatts (mW) and when receiving, it consumes 2.3 mW, less than half the power consumed by previous transceivers (see Table 1).

"Our research grew out of this need for connectivity," said Kenichi Okada of Tokyo Institute of Technology, Japan. "In an IoT world, trillions of devices will be used. To extend battery life and aim for maintenance-free operations, reducing power consumption is vital."

The BLE transceiver has a receiver sensitivity of -94dBm and high interference tolerance of other signals in the 3.4Gz band with the low power. It uses an all-digital phase-locked loop (ADPLL), that is less susceptible to noise compared to its analogue counterpart. The transceiver was designed in a 65nm CMOS process.

In another study focusing on ADPLL, the researchers achieved a figure of merit4 (FoM) of -246dB, one of the best obtained so far. The FoM is an important metric for evaluating the trade-off between performance and power consumption.

In future, Okada says: "The PLL could operate on just 0.65 mW, and studies are underway to reduce our transceiver's power consumption

Table 1. A performance comparison of BLE transceivers

	Tokyo Tech ISSCC 2018	Renesas ISSCC 2015	Dialog ISSCC 2015	Texas Instruments CC2540	Nordic nRF51822
Transmitter	2.9	7.7	10.1	63	32
Receiver	2.3	6.3	11.2	58	39

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