Design of an Ultraviolet Light Intensity Monitor for Personally Wearable Devices

Abstract

In this paper, an ultraviolet (UV) light intensity monitor was newly fabricated for personally wearable devices of monitoring environmental UV light intensity. It was realized by using a UV light sensor and a proposed UV light sensor transducer. The proposed UV light sensor transducer can linearly convert UV light intensity into an output of duty cycle. The proposed UV light intensity to duty cycle conversion was less susceptible to noise than the conversion of UV light intensity to analog voltage. In addition, a calibratable technique was also proposed to solve the intrinsic nonlinearity of the output resistance of the monitor's operational amplifier and the resistance of switches. All the functions of the UV light sensor and the proposed UV light sensor transducer were validated by measurements. After calibration, the UV light intensity was in the range of 1.49-8 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and the corresponding range of the duty cycle was in the range of 68%-42%. The measured maximum linear error was 0.79%. The measured sensitivity was -3.99%/mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and the chip area was 1.016× 1.01 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The proposed chip can be suitable for personally wearable devices of monitoring UV light intensity.