Search

This paper presents a performance analysis of a system for electrochemical impedance spectroscopy (EIS). The system, composed by an analog front-end (AFE) and a custom microcontroller (MCU) board, performs the impulse response (IR) measurement of linear and time-invariant (LTI) systems with pseudo-random excitation signals. As a novelty, a specific AFE for the interfacing of two-terminal resistive and capacitive sensors is covered in detail. The paper proposes, for the first time, a mathematical model to predict the impact of the main noise sources in the measured IR. Thanks to the proposed approach, the AFE and the system’s parameters can be properly designed in order to reduce the error, thus, minimizing the energy-per-error figure of merit (FOM) as well. The AFE is realized as discrete-components circuit and it has been included in a custom MCU-based measurement system as an expansion module. The predicted results from the mathematical model, in terms of noise power, SNR, and measurement error are validated through system-level simulation and experimental measurements. The system performs the IR measurement with 1023 points, showing root-mean-square (RMS) measurement errors of 1% and 1.4% for the tested ADC sampling frequencies of 62.5 kHz and 125 kHz, respectively. These lead to excellent FOM values of 128.9 mJ $\cdot $ %2 and 252.6 mJ $\cdot $ %2 that outstand the state of the art. [ABSTRACT FROM AUTHOR]

An energy-efficient, wide dynamic-range (DR) CMOS analog front-end (AFE) for chemiresistive sensors is presented. The circuit is specifically designed for the Metal Oxide (MOX) gas sensors, a special technology of chemiresistive sensors, broadly diffused in modern portable devices due to their low-cost and simplicity of use. Energy efficiency is mandatory for the AFE in order to prolong the battery life that supply these devices. The proposed circuit implements the resistance-to-time (R-to-T) conversion of the sensor’s resistance by adopting a relaxation oscillator-based architecture. A limiting resistor in series with the sensor is introduced for reducing the circuit’s energy-per-measurement (EpM), while mitigating the error due to the sensor’s parasitic capacitance. The analysis of the circuit is presented with emphasis on the design trade-off between error due to the sensor’s parasitic capacitance and power consumption on one side and read-out sensitivity on the other. The chip prototype is realized in AMS $0.35 ~\mu m$ process and has been tested in the DR between $100\Omega $ and $4.7M\Omega $ with an accuracy less than 0.1% and a precision less than 0.029%. The efficacy of the presented AFE is proved by adopting the circuit in a real chemical environment with a commercial sensor. The proposed AFE shows a maximum EpM of $296nJ$ which is three times better than the state of the art. [ABSTRACT FROM AUTHOR]