IEEE Trans Biomed Circuits Syst. 2020 Jun;14(3):463-476. doi: 10.1109/TBCAS.2020.2977960. Epub 2020 Mar 3.
This paper presents a CMOS ion-sensitive-field-effect-transistor (ISFET) array with superior offset distribution tolerance, resolution and linearity for long-term bacterial metabolism monitoring. A floating gate ISFET is adopted as the sensing front end to maximize ion sensitivity and support ultra-long-term measurement. To solve the DC offset issue induced by trapped chargers and drifts in each ISFET sensor, a complementary readout scheme with column offset compensation is proposed. P-type and N-type source followers are combined to cover a wide range of input DC offsets while maintaining small area and high linearity. The DC offset is digitally compensated during signal readout to facilitate global amplification and quantization. Fabricated in 0.18 μm standard CMOS process, the ISFET array can tolerate an offset distribution beyond power supply with a linear pH-to-output response. Due to high ion sensitivity and low circuit noise, the whole system achieves a high resolution of 0.017 pH. The proposed ISFET system has successfully demonstrated an accurate pH monitoring of normal Escherichis coli growth for 11 hours and its response to antibiotics, showing long-term bacterial metabolism monitoring capability.
本文提出了一种具有优异失调分布容限、分辨率和线性度的 CMOS 离子敏感场效应晶体管（ISFET）阵列，可用于长期细菌代谢监测。采用浮栅 ISFET 作为传感前端，以最大限度地提高离子灵敏度并支持超长测量。为了解决每个 ISFET 传感器中由于俘获电荷和漂移引起的直流失调问题，提出了一种具有列偏移补偿的互补读出方案。采用 P 型和 N 型源跟随器组合，可覆盖宽输入直流偏移范围，同时保持小面积和高线性度。在信号读出过程中进行直流偏移数字补偿，以方便全局放大和量化。该 ISFET 阵列采用 0.18μm 标准 CMOS 工艺制造，可容忍超出电源范围的失调分布，并具有线性 pH 至输出响应。由于高离子灵敏度和低电路噪声，整个系统实现了 0.017 pH 的高分辨率。所提出的 ISFET 系统成功地演示了对正常大肠杆菌生长 11 小时的精确 pH 监测及其对抗生素的响应，展示了长期细菌代谢监测能力。
