A 2.2 <inline-formula> <tex-math notation="LaTeX">$\mu\text{W}$</tex-math> </inline-formula>, <inline-formula> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula>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- $\mu\text{m}$ CMOS process, occupies a silicon area of 1 $\text{mm}^{2}$ . 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 $\mu\text{W}$ 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.