A 7 μW Offset- and Temperature-Compensated pH-to-Digital Converter

This paper demonstrates a micropower offset- and temperature-compensated smart pH sensor, intended for use in battery-powered RFID systems that monitor the quality of perishable products. Low operation power is essential in such systems to enable autonomous logging of environmental parameters, such as the pH level, over extended periods of time using only a small, low-cost battery. The pH-sensing element in this work is an ion-sensitive extended-gate field-effect transistor (EGFET), which is incorporated in a low-power sensor front-end. The front-end outputs a pH-dependent voltage, which is then digitized by means of a co-integrated incremental delta-sigma ADC. To compensate for the offset and temperature cross-sensitivity of the EGFET, a compensation scheme using a calibration process and a temperature sensor has been devised. A prototype chip has been realized in a 0.16 μm CMOS process. It occupies 0.35 × 3.9 mm2 of die area and draws only 4 μA from a 1.8 V supply. Two different types of custom packaging have been used for measurement purposes. The pH sensor achieves a linearity of better than ±0.1 for pH values ranging from 4 to 10. The calibration and compensation scheme reduces errors due to temperature cross-sensitivity to less than ±0.1 in the temperature range of 6°C to 25°C.

[1]  Christofer Toumazou,et al.  An Integrated ISFETs Instrumentation System in Standard CMOS Technology , 2010, IEEE Journal of Solid-State Circuits.

[2]  Cecilia Jiménez-Jorquera,et al.  ISFET Based Microsensors for Environmental Monitoring , 2009, Sensors.

[3]  Jikun Huang,et al.  Food losses and waste in the context of sustainable food systems , 2014 .

[4]  D. Cumming,et al.  Design of a Single-Chip pH Sensor Using a Conventional 0 . 6-m CMOS Process , 2004 .

[5]  T. Unander,et al.  Designing of RFID-Based Sensor Solution for Packaging Surveillance Applications , 2011, IEEE Sensors Journal.

[6]  Dermot Diamond,et al.  Development of an autonomous, wireless pH and temperature sensing system for monitoring pig meat quality. , 2005, Meat science.

[7]  L. P. Yu,et al.  Effects of Postmortem pH and Temperature Muscle Structure and Meat Tenderness , 1986 .

[8]  D. Cumming,et al.  Design of a single-chip pH sensor using a conventional 0.6-/spl mu/m CMOS process , 2004, IEEE Sensors Journal.

[9]  Wen-Yaw Chung,et al.  Titanium Nitride Membrane Application to Extended Gate Field Effect Transistor pH Sensor Using VLSI Technology , 2001 .

[10]  Christofer Toumazou,et al.  A biochemical translinear principle with weak inversion ISFETs , 2005, IEEE Transactions on Circuits and Systems I: Regular Papers.

[11]  Kazuaki Sawada,et al.  A Miniature Integrated Multimodal Sensor for Measuring pH, EC and Temperature for Precision Agriculture , 2012, Sensors.

[12]  Gerard C.M. Meijer.  Thermal sensors based on transistors - ScienceDirect , 2018 .

[13]  P. K. Chan,et al.  A CMOS ISFET Interface Circuit With Dynamic Current Temperature Compensation Technique , 2007, IEEE Transactions on Circuits and Systems I: Regular Papers.

[14]  P. K. Chan,et al.  An Intelligent ISFET Sensory System With Temperature and Drift Compensation for Long-Term Monitoring , 2008, IEEE Sensors Journal.

[15]  Kazuo Nakazato,et al.  An Integrated ISFET Sensor Array , 2009, Sensors.

[16]  Wen-Yaw Chung,et al.  A novel pH sensitive ISFET with on chip temperature sensing using CMOS standard process , 2001 .

[17]  R. Hoofman,et al.  A 7μW pH-to-digital converter for quality monitoring of perishable products , 2013, 2013 Transducers & Eurosensors XXVII: The 17th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS & EUROSENSORS XXVII).

[18]  Frank Devlieghere,et al.  Intelligent food packaging: the next generation , 2014 .

[19]  Gabor C. Temes,et al.  Theory and applications of incremental ΔΣ converters , 2004, IEEE Trans. Circuits Syst. I Regul. Pap..

[20]  Danny Wen-Yaw Chung,et al.  New ISFET interface circuit design with temperature compensation , 2006, Microelectron. J..