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Design of Readout Circuit with Dual Slope Correction for photo sensor of LTPS TFT-LCD  

Woo, Doo-Hyung (School of Information, Communications & Electronic Engineering, The Catholic University of Korea)
Publication Information
Journal of the Institute of Electronics Engineers of Korea SD / v.46, no.6, 2009 , pp. 31-38 More about this Journal
Abstract
To improve the image quality and lower the power consumption of the mobile applications, it is the one of the best candidate to control the backlight unit of the LCD module with ambient light. Ambient light sensor and readout circuit were integrated in LCD panel for the mobile applications, and we designed them with LTPS TFT. We proposed noble start-up correction in order to correct the variation of the photo sensors in each panel. We used time-to-digital method for converting photo current to digital data. To effectively merge time-to-digital method with start-up correction, we proposed noble dual slope correction method. The entire readout circuit was designed and estimated with LTPS TFT process. The readout circuit has very simple and stable structure and timing, so it is suitable for LTPS TFT process. The readout circuit can correct the variation of the photo sensors without an additional equipment, and it outputs the 4-levels digital data per decade for input luminance that has a dynamic range of 60dB. The readout rate is 100 times/sec, and the linearity error for digital conversion is less than 18%.
Keywords
readout circuit; ambient light sensor; two point correction; LTPS TFT; LCD;
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