CMOS RGB Colour Sensor with a Dark Current Compensation Circuit

This article presents the design and development of a Red, Green, Blue (RGB) Colour Sensor with a dark current compensation circuit. The presented design employs a new approach to eliminate the conventional low pass filter, where it is normally required to integrate the pulsating signal. his is accomplished by employing switched capacitor circuit techniques. A covered photodiode is used to derive a proportional to dark current common mode voltage or compensated common mode voltage, Vdvcm. The measured performance of the sensor when it was used as an optical feedback solution for a light emitting diode (LED) backlighting system was very promising. The colour point accuracy, Delta u 'v' = 0.002, while colour point drift over temperature was less than 0.008 at 50 degrees C. The maximum reduction of 36 mV output voltage error was observed when the Vdvcm was applied to the single to differential circuit. The overall power consumption of the fabricated sensor was 7.8 mW. The whole sensor design was implemented in 035 mu m CMOS technology. The Vdvcm concept can be applied to other similar circuitry such as temperature-sensitive circuits.