P‐198L: Late‐News Poster: Integrated Ambient Light Sensor in LTPS AMLCDs

Abstract

Sensing ambient light in mobile applications allows reduced power consumption through backlight control. Integration of light sensors reduces module complexity and location of the sensors close to the pixel array simplifies integration in products.We describe an integrated ambient light sensor consisting of lateral pin diodes and digital read out circuit.

An ambient-light sensor system with startup correction for LTPS-TFT LCD

“…It is sufficient to measure each photo detector at two brightness conditions, A and B, due to their linear characteristics. Because neighboring photo detectors on the same glass show a similar characteristic curve, the dark condition (A) is commonly realized by a masked photo detector [4]. However, it is difficult to realize the bright condition (B) during the ALS system operation, so an additional test process is normally needed, and the test results should be memorized before the ALS system operation.…”

Ambient‐light sensor system with wide dynamic range enhanced by adaptive sensitivity control

“…For monolithic systems on glass substrates, low-temperature polycrystalline-silicon (LTPS) technologies have gained significant interest because they offer good mobility and stability. [2][3][4] However, the detection range for normal environmental illumination may be over three orders of magnitude (60 dB or 10 bits) from the darkest to the brightest region. The use of logarithmic light sensors can be the most appropriate solution for that purpose because it could easily represent the logarithmic characteristics of human brightness perception.…”

Current‐mode ambient‐light sensing circuit using p‐type low‐temperature polycrystalline‐silicon TFTs and p‐i‐m diodes

“…An ambient-light sensing function can contribute to lower power consumption and improved visibility by detecting ambient light and controlling the brightness of the display panel accordingly. [1][2][3][4][5] Several ambient-light sensors using polycrystalline-silicon (poly-Si) thin-film transistors (TFTs) and p-intrinsic-n (p-i-n) diodes have been reported. [1][2][3][4][5] However, the photoleakage current range of a p-i-n diode is several picoamps to several hundreds of picoamps in the low-ambient-light range because the p-i-n diode has thin thickness and low absorption efficiency compared to a photodiode used in a CMOS image sensor (CIS).…”

“…[1][2][3][4][5] Several ambient-light sensors using polycrystalline-silicon (poly-Si) thin-film transistors (TFTs) and p-intrinsic-n (p-i-n) diodes have been reported. [1][2][3][4][5] However, the photoleakage current range of a p-i-n diode is several picoamps to several hundreds of picoamps in the low-ambient-light range because the p-i-n diode has thin thickness and low absorption efficiency compared to a photodiode used in a CMOS image sensor (CIS). Therefore, it is very difficult to design a readout circuit that performs a very accurate readout operation with the small current of the p-i-n diode.…”

“…The analog voltage depends on C1, integration time, and the photoleakage current o f the p-i-m diode. At the end of the integration period, the increased V A(integration) can be expressed as (2) where ∆V is the voltage difference of C1 charged by the photoleakage current of the p-i-m diode during the integration period. Finally, in the sampling period, when the SW3 signal becomes "low" and the SW4 signal becomes "high," T6 turns on and T3 turns off, and then the current source (T1) is driven by V A(integration) .…”