23.2 A 1.1nW energy harvesting system with 544pW quiescent power for next-generation implants

Abstract

This paper presents a nW power management unit (PMU) for an autonomous wireless sensor that sustains itself by harvesting energy from the endocochlear potential (EP), the 70-100 mV electrochemical bio-potential inside the mammalian ear. Due to the anatomical constraints inside the inner ear, the total extractable power from the EP is limited to 1.1-6.25 nW. A nW boost converter is used to increase the input voltage (30-55 mV) to a higher voltage (0.8 to 1.1 V) usable by CMOS circuits in the sensor. A pW Charge Pump circuit is used to minimize the leakage in the boost converter. Further, ultra-low-power control circuits consisting of digital implementations of input impedance adjustment circuits and Zero Current Switching circuits along with Timer and Reference circuits keep the quiescent power of the PMU down to 544 pW. The designed boost converter achieves a peak power conversion efficiency of 56%. The PMU can sustain itself and a duty-cyled ultra-low power load while extracting power from the EP of a live guinea pig. The PMU circuits have been implemented on a 0.18µm CMOS process.

A Sub-nW 2.4 GHz Transmitter for Low Data-Rate Sensing Applications

“…Here, P TX,leak is the transmitter leakage power, E b is the energy required to transmit a single bit, N is the number of bits per packet (programmable from 8–128 bits based on a binary counter), and T pkt,int is the time interval between packets (programmable from 40–360 s based on a counter that is driven by the 12.8 Hz on-chip oscillator found in the boost converter control circuitry [10]). Based on this equation, the transmitter must not only have extremely low leakage power, it also must be very energy efficient during active-mode in order to achieve the necessary overall power goal, otherwise the effective bit rate (i.e.…”

“…The transmitter receives its supply voltage, V DD , from an on-chip boost converter whose details are discussed in [10]. The value of V DD is set by a balance between the amount of energy extracted from the EP and the power of the load circuits.…”

“…In this system, the boost converter requires 544 pW of quiescent power [10]; leaving approximately 250 pW of transmitter power budget after taking into account the overhead of other peripheral circuits and adding some power budget safety margin. Given the extreme power budget limit, the transmitter is designed and optimized to operate over short transmission distances (1 m) in order to limit the requisite output power.…”

“…This paper describe the details of the transmitter, antenna, and kick-start rectifier, while details of the biology and overall system operation can be found in [8], and details of the boost converter can be found in [10]. …”

Ultra-low-power circuit techniques for mm-size wireless sensor nodes with energy harvesting

“…Fig. 3 plots the change in power consumption of low-power LSI chips reported from 2007 to 2014 at ISSCC and VLSI Circuits [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37], which are the most popular international conferences in the semiconductor industry. It is found that there are three domains: milliwatt, microwatt, and nanowatt.…”