Liquid crystal display
An LCD includes a liquid crystal panel having a TFT substrate, a CF substrate, and a liquid crystal layer interposed between the two substrates; a TFT ambient light photosensor having a semiconductor layer for detecting external light; a photodetector unit having a capacitor 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 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 that is in contact with the liquid crystal layer, and the surface of the photodetector unit except for the semiconductor layer and its periphery is covered by a light-shielding layer. Malfunction or reduced sensitivity of an ambient light photosensor due to light from backlights is prevented with a simple structure.
1. A liquid crystal display comprising:
a liquid crystal panel including an active matrix substrate, an opposed substrate, and a liquid crystal layer interposed between the two substrates;
a photodetector unit including:
an ambient light photosensor having a semiconductor layer for detecting external light,
a first capacitor electrically connected to the ambient light photosensor, a charged voltage on the first capacitor being lowered by leakage current caused by ambient light,
a switching element for charging a predetermined reference voltage on the first capacitor while the switching element is turned on, and
a light sheilding layer; and
an ambient light photosensor reader unit for reading the charged voltage on the first capacitor, wherein
the photodetector unit is disposed on a first surface of the active matrix substrate that is in contact with the liquid crystal layer,
the switching element is provided in a region other than the ambient light photosensor and the ambient light photosensor reader unit,
the light shielding layer entirely covers, in the photodetector unit, the first capacitor and the switching element, which are disposed on a periphery of the ambient light photosensor and entirely covered by the light-shielding layer, which is formed between the liquid crystal layer and the first capacitor,
the light shielding layer is a top layer of the photodetector unit without overlapping the semiconductor layer of the ambient light photosensor, and
an ambient brightness is detected by reading the voltage charged on the first capacitor at a time when a predetermined time period has been elapsed after the switching element is turned off.
2. 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.
3. The liquid crystal display according to claim 1 , wherein the ambient light photosensor is a thin-film transistor that is manufactured together with another thin-film transistor serving as the switching element in a process for manufacturing the active matrix substrate.
4. The liquid crystal display according to claim 1 , further comprising:
an illuminating unit for illuminating the liquid crystal panel; and
a 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.
5. 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.
6. The liquid crystal display according to claim 1 , wherein
the ambient light photosensor includes a first gate electrode,
the switching element includes a second gate electrode,
the first capacitor includes a first terminal, and
the first terminal, the first gate electrode, and the second gate electrode are arranged apart from each other in a same layer.