Liquid crystal display

Abstract

A liquid crystal display (LCD) 1 according to an embodiment of the present invention includes a liquid crystal panel having a TFT substrate 2, a CF substrate 25, and a liquid crystal layer 14 interposed between the two substrates; a TFT ambient light photosensor having a semiconductor layer 19L for detecting external light; a photodetector unit LS1 having a capacitor Cw in which a predetermined reference voltage is charged and a voltage charged by leakage current of the TFT ambient light photosensor is lowered; and an ambient light photosensor reader unit Re1 for reading a voltage charged in the capacitor for a predetermined read period. The photodetector unit is disposed on a first surface of the TFT substrate 2 that is in contact with the liquid crystal layer, and the surface of the photodetector unit except for the semiconductor layer 19L and its periphery is covered by a light-shielding layer 21. It is therefore possible to provide an LCD in which malfunction or reduced sensitivity of its ambient light photosensor due to light from its backlights is prevented with a simple structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.

FIG. 1 shows an example of the voltage-current curve of a TFT ambient light photosensor.

FIG. 2 is a circuit diagram of a photodetector unit using the TFT ambient light photosensor.

FIG. 3 shows the voltage-time curve at both ends of a capacitor included in the circuit diagram of FIG. 2 with different brightness levels.

FIG. 4 is a plan view schematically showing an active matrix substrate seen through a color filter substrate included in a liquid crystal display (LCD) according to an embodiment of the invention.

FIG. 5 is a sectional view along line X-X of FIG. 4.

FIG. 6 is a plan view showing a single pixel seen through a color filter substrate included in a semi-transmissive LCD.

FIG. 7 is a sectional view along line A-A of FIG. 6, with the color filter substrate included.

FIG. 8 is a sectional view showing an ambient light photosensor and a switching element on a thin-film transistor (TFT) substrate.

FIG. 9 is a circuit diagram showing a photodetector unit and an ambient light photosensor reader unit.

FIG. 10 is a timing chart showing output waveforms of the components shown in FIG. 9.

FIG. 11 is a block diagram of a controller.

FIG. 12 is a sectional view schematically showing a TFT ambient light photosensor included in a known LCD.

Claims

1. A liquid crystal display comprising: a liquid crystal panel having an active matrix substrate, a opposed substrate, and a liquid crystal layer interposed between the two substrates;an ambient light photosensor having a semiconductor layer for detecting external light;a photodetector unit having a first capacitor in which a predetermined reference voltage is charged and a voltage charged by leakage current of the ambient light photosensor is lowered; andan ambient light photosensor reader unit for reading a voltage charged in the first capacitor for a predetermined read period;the photodetector unit being disposed on a first surface of the active matrix substrate that is in contact with the liquid crystal layer, and the surface of the photodetector unit except for the semiconductor layer and a periphery thereof being covered by a light-shielding layer.

2. The liquid crystal display according to claim 1, wherein the photodetector unit and the ambient light photosensor reader unit are provided to the first surface of the active matrix substrate that is in contact with the liquid crystal layer, and in the photodetector unit and the ambient light photosensor reader unit, the surface of the photodetector unit except for the semiconductor layer and a periphery thereof is covered by a light-shielding layer.

3. The liquid crystal display according to claim 1, wherein the light-shielding layer is made of a resin material containing a light-shielding material that shields light.

4. The liquid crystal display according to claim 1, wherein the ambient light photosensor of the photodetector unit is a thin-film transistor that is manufactured together with another thin-film transistor serving as a switching element for the liquid crystal display in a process for manufacturing the active matrix substrate.

5. The liquid crystal display according to claim 1, further comprising: an illuminating unit for illuminating the liquid crystal panel; anda controller unit for controlling the illuminating unit in accordance with an output from the ambient light photosensor reader unit; the controller unit including a threshold memory and a comparator,in normal operation mode, the comparator comparing an output from the photodetector unit and a threshold stored in the threshold memory, and a comparison result being used for controlling on/off of the illuminating unit, and in default mode, the ambient light photosensor being irradiated with reference light, and an output from the photodetector unit being stored in the threshold memory.

6. The liquid crystal display according to claim 1, wherein the liquid crystal panel is one of a transmissive liquid crystal display panel and a semi-transmissive liquid crystal display panel.