Low-Noise and Process Variation-Tolerant Readout Circuit for Electrochemical Sensors

This study describes the design and development of a low-noise and process variation-tolerant potentiostat readout integrated circuit optimized for electrochemical sensors in biomedical applications. Accurate and fast detection by electrical signals, particularly for pathogenic viruses, is critical in the biomedical field. Therefore, design criteria for biosignal sensing architectures emphasize high precision and low noise to ensure high reliability. The proposed potentiostat readout circuit integrates key components, such as a control amplifier (CA), transimpedance amplifier (TIA), 12-bit R-2R digital-to-analog converter (DAC), 12-bit SAR analog-to-digital converter (ADC), relaxation oscillator, clock divider, current/voltage reference, and serial peripheral interface. The chopping technique is adopted to mitigate the 1/f noise. The low-frequency noise is substantially reduced by implementing chopper stabilization in the CA and TIA. High-precision DACs are required because various waveforms, including dc, triangular, and ramp functions, are utilized for electrochemical measurement. In this design, dynamic element matching is applied to DACs with high precision. This approach can reduce the intrinsic mismatch in the R-2R DAC, thereby improving the offset error and spurious-free dynamic range from −1.4 least significant bit (LSB) and 74 dB to −0.5 LSB and 79 dB, respectively. The readout circuit was fabricated using a standard 180-nm CMOS process and can measure sensor currents in the range of <inline-formula> <tex-math notation="LaTeX">$\pm 20~\mu $ </tex-math></inline-formula>A, achieving a linearity performance of 0.9998. The input-referred noise, as measured, is 6.65 pARMS in the frequency range of 0.5–400 Hz, and the total current consumption of the circuit is <inline-formula> <tex-math notation="LaTeX">$339.6~\mu $ </tex-math></inline-formula>A at a supply voltage of 3.3 V.