Jpn. J. Appl. Phys. 47 (2008) pp. 1919-1923 |Previous Article| |Next Article| |Table of Contents|
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Ambient Light Sensing Circuit with Low-Temperature Polycrystalline Silicon p–Intrinsic–n Diode and Source Follower for Auto Brightness Control
Division of Electrical and Computer Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Korea
(Received July 11, 2007; accepted September 22, 2007; published online March 21, 2008)
An ambient light sensing function, which is one of several value-added functions in system-on-panel (SoP), can contribute to low power consumption and improve visibility by auto brightness control. However, it is very challenging to read the photo-leakage current of p–intrinsic–n (PIN) diode directly, which is generally used as a photodetector in SoP. Therefore, we propose an ambient light sensing circuit using low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) and the PIN diode, which can output analog voltage converted from the photo-leakage current of the PIN diode. Through the measurement of the proposed circuits under ambient light variations from 0 to 2000 lx, we confirmed that the proposed ambient light sensing circuits can perform sensing and readout operations accurately. The dynamic range of the proposed circuit is 35 dB and the maximum variation of the output voltage among eight samples is ±45 mV.
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