A 2.2 mu W,-12 dBm RF-Powered Wireless Current Sensing Readout Interface IC With Injection-Locking Clock Generation

Abstract

This paper presents a wireless-powering current-sensing readout system on a CMOS platform for portable electrochemical measurement. The wireless sensing system includes energy-efficient power management circuitry, a sensor readout interface, and a backscattering wireless communication scheme. For power-and-area-constrained bio-sensing applications, the proposed readout circuitry incorporates an ultra-low-power potentiostatic system that generates a current according to the electrochemical reaction, as well as an oscillator-based time-to-digital converter instead of a voltage-domain analog-to-digital converter. To avoid a bulky battery and power-hungry clock reference, the chip is wirelessly powered and injection-locked by the modulated radio waves, which includes a 918 MHz carrier signal mixed with a 3.2 MHz modulated signal. The chip, implemented using a 0.18-mu m CMOS process, occupies a silicon area of 1 mm(2). The proposed design achieves a sensitivity of 289 Hz/nA and an R-2 linearity of 0.997 over a current range of 200 nA while consuming 2.2 mu W at a supply voltage of 0.8 V. The chip, integrated with a PCB antenna, has minimum sensitivities of -12 dBm and -25 dBm for RF-powering and injection-locking mechanisms, respectively.