An Integrated Readout Circuit for a Transcutaneous Oxygen Sensing Wearable Device

Abstract

This paper presents an integrated readout dedicated to sensing transcutaneous oxygen, a first of its kind. The readout circuit employs a fluorescence-based method to sense the oxygen molecules diffusing through the skin. The system uses a platinum porphyrin thin film, a blue light-emitting diode (LED) that excites the thin film, and a photodiode (PD) that captures the red light emitted from the thin film. The presence of oxygen quenches the intensity and the lifetime of red light. The readout integrated circuit (IC), which is integrated in a 0.18 µm 5 V CMOS process, excites the thin film and senses the current flowing through the PD. The analog front-end converts the detected current to a voltage while providing a variable gain of $59\ \mathrm{k}\Omega-0.94\ \mathrm{M}\Omega$. The LED driver circuit generates current as high as 40 mA. To decrease the power consumption of the readout, the LED can be pulsed at 16 $u\mathrm{s}$ intervals (based on the $1.7\ \mathrm{k}\Omega$ input impedance of the transimpedance amplifier and 20 pF PD capacitance). The readout IC consumes 631 $\mu \mathrm{W}$ power and occupies 1.04 mm2. This paper also shows ex vivo measurements.