Patent ID: 8102361
Filing Date: 2012-01-24
Classification: G09G

Abstract:
1. A liquid crystal display for adjusting a brightness of a backlight of a liquid crystal display panel in accordance with an illuminance of external light, comprising: an external light sensing circuit including: a pulse width modulation (PWM) duty controller for detecting the illuminance of the external light by using a time taken for the output voltage to exceed a predetermined reference voltage, and controlling a duty ratio of a pulse width modulation signal used for controlling the brightness of the back light in accordance with a detected illuminance of the external light, wherein a control signal applied to a gate electrode of the photosensor is generated at a first logic level during a sensing permitting period from a starting point of a write-ON period for charging the capacitor until a specific time point within a write-OFF period for discharging the capacitor, and the control signal is generated at a second logic level for detrapping electric charges trapped in a dielectric layer in the gate electrode due to the first logic level during a sensing blocking period from the specific time point until a finishing point of the write-OFF period, wherein an amplitude of the control signal and a length of a maintenance period of the second logic level of the control signal are varied according to an amount of electric charges trapped in the dielectric layer in the gate electrode and a sensing speed and a sensing sensitivity for sensing the illuminance of external light.