A Direct Current-to-Digital Converter IC for Luminescence-Based Detection Toward an Energy Efficient Transcutaneous Carbon Dioxide Sensor Wearable.

Continuous monitoring of arterial carbon dioxide is critical for assessing respiratory function and detecting ventilation inefficiencies. Arterial blood gas analysis, the clinical gold standard, is invasive and limited to intermittent measurements in hospital settings. Transcutaneous carbon dioxide sensing offers a noninvasive alternative by measuring carbon dioxide diffusing through the skin, which strongly correlates with arterial carbon dioxide. However, conventional transcutaneous sensors require bulky bedside monitors and heating elements, making them unsuitable for wearable applications. This work presents the first integrated circuit implementation of a ratiometric time-domain dual lifetime referencing technique using a direct current-to-digital converter architecture designed for energy-efficient wearables. The proposed design achieves 0.15-nA/cnt resolution over a 30-μA input range at 88-μW power consumption. With the proposed I-DAC current-scaling technique, the system maintains a luminescence ratio error of ≤0.5% across a wide input range.