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-μm 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 μW 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.

CMOS Interfaces for Internet-of-Wearables Electrochemical Sensors: Trends and Challenges

“…Another well known continuous time amperometric readout technique is based on current mirror amplifiers [129,130,134,[136][137][138][139], such as those shown in Figure 12. A closer look at the configurations in Figure 10 reveals that the potentiostatic control amplifier A 1 provides the current to the sensor, so it can be copied and eventually amplified by simple current mirror configurations.…”

“…I-to-f potentiostats: the readout current is converted to a square-wave signal whose frequency is proportional to the current amplitude [136][137][138][139]151]; 3.…”

“…Here, I W is injected into the the I-to-f modulator through a current amplifier potentiostat such as those of Figure 12. Similarly, the circuit in Figure 16b integrates I W alternatively on two nominally identical capacitors C 1 and C 2 [138,139]. Here, the use of a single comparator triggering at a fixed voltage makes the modulated square wave insensitive to comparator offset (and to its temperature drift).…”