An Integrated Multipurpose Low-Power Electrochemical Readout Interface with On-Chip Input Waveform Generator

This brief implemented a multimodal time-based bidirectional wide-range electrochemical readout. The proposed design uses a chopper-stabilized, low-noise potentiostat circuit and a delay chain-based time-to-digital converter (TDC) to improve the accuracy and the conversion rate. In this design, an on-chip waveform generator creates area-efficient, multi-rate ramp signals for cyclic voltammetry (CV), fast-scan cyclic voltammetry (FSCV), and several derived waveforms like square wave voltammetry (SWV) etc. The significant non-faradaic background current problem in the FSCV process is solved with an analog background subtraction technique by utilizing a pseudo-differential sensing scheme and a class-AB common-mode rejection circuit. The wide-range, low-input-impedance current conveyor circuit based on a regulated current mirror diminishes the nonlinearity effect of the current-to-frequency converter. The system is developed using a $0.18-\mu\mathrm{m}$ CMOS process, and the design provides a $20-\mathrm{pA}$ resolution of current within the range of $-12.5\mu\mathrm{A}$ to $12.5\mu\mathrm{A}$ with an R
²
linearity of 0.99995 while absorbing $30\mu\mathrm{W}$. The power efficiency and sensing current dynamic range are 0.83 and 116 dB. The resulting input-referred current noise is $20-{\mathrm {pA_{rms}}}$.