A Multi-sensing ISFET Array for Simultaneous In-pixel Detection of Light, Temperature, Moisture and Ions

This paper presents a multi-sensing pixel capable of sensing ion concentration, temperature, moisture and light from the same spatial point. The presented pixel is composed of an ISFET chemical sensor, a light sensor, a moisture sensor and a temperature sensor, all implemented in standard CMOS technology in a compact pixel. All sensing modalities are acquired simultaneously and modulated onto a single waveform using multi-frequency PWM modulation, overcoming the associated transmission overhead. Furthermore, ISFET non-idealities such as trapped charge are compensated through a global DAC, balancing the input linear OTA, while the light sensor dark current is mitigated in-pixel by subtracting its influence using a reference photodiode. The proposed pixel occupies 50x50 mu m(2), and it is integrated as part of a 4x4 multi-sensing array, along with on-chip biasing, instrumentation and digital control. To the best of our knowledge, this architecture represents the first multi-sensing architecture capable of extracting four features from the same spatial point simultaneously, enabling ISFET-based platforms to sense both the chemical signal and the external conditions influencing its measurement.