An LTPS Ambient Light Sensor System with Sensitivity Correction Methods in LCD

Takashi NAKAMURA  Masahiro TADA  Hiroyuki KIMURA  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E102-C   No.7   pp.558-564
Publication Date: 2019/07/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.2018CTP0004
Type of Manuscript: Special Section PAPER (Special Section on Analog Circuits and Their Application Technologies)
Category: 
Keyword: 
LTPS,  ambient light sensor,  p-i-n diode,  optical sensor,  

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Summary: 
An integrated ambient light sensor (ALS) system in low-temperature polycrystalline silicon (LTPS) thin-film-transistor liquid-crystal-displays (TFT-LCDs) is proposed and prototyped in this study. It is designed as a 4-bit (16-step-grayscale) ALS and includes a noise subtraction circuit, a comparator as an analog-to-digital converter (ADC), 4-bit counters, and a parallel-to-serial converter. LTPS lateral p-i-n diodes with a long i-region are employed as photodetectors in the system. An LSI source driver is mounted on the LCD panel with a sensor control block which provides programmable clocks and reference voltages to the ALS circuit on the glass substrate for sensitivity tuning. The reliability tests were conducted for 300 hours with 30000 lux illumination at 70 °C and at -20 °C. The observed deviations of the ALS values for dark, 1000 lux, and 10000 lux were within ±1.