Buck Converter Drops Static Power To 217 nW

In many medical monitoring systems, each patient wears several sensors.

In many medical monitoring systems, each patient wears several sensors. Those sensor nodes transmit specific physiological signals in a group of small monitoring systems. The sensed data is collected wirelessly by the central health server. Because each sensor node works as a micro system, it must be sustained for a long time without changing the battery. To achieve high conversion efficiency over a wide load range, a battery-free, nano-power buck converter with dynamic on/off time (DOOT) control was recently proposed by Ming-Wei Lee from Taiwan’s Industrial Technology Research Institute (ITRI) together with Chen-Chih Huang and Yin-Hsi Lin from Realtek Semiconductor Corp. and Tzu-Chi Huang, Chun-Yu Hsieh, Yao-Yi Yang, Yu-Huei Lee, Yu-Chai Kang, and Ke-Horng Chen from National Chiao Tung University.

Their DOOT control can predict the on/off time at different input voltages without a power-consuming zero-current-detection (ZCD) circuit. To adapt to the fluctuations in a harvesting system, the proposed α-calibration scheme guarantees accurate ZCD over process, voltage variation, and temperature (PVT) in the DOOT.

For its part, the adaptive-phase-lead (APL) mechanism improves the inherent propagation delay that arises due to a low-power and non-ideal comparator. As a result, load regulation is improved by as much as 30 mV. In addition to consuming low static power, the nano-power bias circuit generates a 1-V reference voltage.

The test chip was implemented in 0.25-μm CMOS with a die area of 0.39 mm2. Experimental results showed 95% peak efficiency, static power of 217 nW, and load regulation of 0.1 mV/mA. See "A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting with α-Calibrated Dynamic On/Off Time and Adaptive Phase Lead Control," IEEE Journal Of Solid-State Circuits, April 2012, p. 852.

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