Patent ID: 6072458
Filing Date: 2000-06-06
Classification: G09G,H04N

Abstract:
A projection-type liquid crystal display device comprising:a light source means for emitting a luminous flux;a liquid crystal light valve means, which has a common electrode to which a common voltage is applied and a source electrode to which a video signal is applied, for modulating said luminous flux emitted by said light source means;a liquid crystal drive means for applying said common voltage to said common electrode and said video signal to said source electrode;a projection means for projecting said luminous flux modulated by said liquid crystal light valve means onto a screen;a liquid crystal temperature detecting means for detecting temperature in the vicinity of said liquid crystal light valve means; anda control means for controlling said common voltage on the basis of values detected by said liquid crystal temperature detecting means in such a way that fluctuation in a light transmittance of said liquid crystal light value means is reduced;wherein:if the value detected by said liquid crystal temperature detecting means at time (t-.DELTA.t), where .DELTA.t is a specified unit of time, is represented by D(t-.DELTA.t), the value detected by said liquid crystal temperature detecting means at time t is represented by D(t), and a specified reference value is represented by Dth,when .vertline.D(t)-D(t-.DELTA.t).vertline.>Dth, said control means controls a common voltage amplitude on the basis of said values detected by said liquid crystal temperature detecting means in such a way that fluctuation in the light transmittance of said liquid crystal light valve means is reduced, and when .vertline.D(t)-D(t-.DELTA.t).vertline..ltoreq.Dth, a first processing is carried out repeatedly in such a way that said common voltage amplitude is held unchanging and constant;a value D(t') detected when a final change in said common voltage amplitude has been effected is stored; andwhen, during an iteration of said first processing, .vertline.D(t)-D(t-.DELTA.t).vertline..ltoreq.Dth and said common voltage amplitude is subjected to said first processing for a specified number of iterations in such a way that said common voltage amplitude is held constant and unchanging, when an absolute value .vertline.D(t)-(t').vertline. of a change from detected value D(t) at time after which the subsequent specified period has elapsed and stored value D(t') is greater than a specified reference value Dth', said common voltage amplitude is controlled according to the detected value D(t), and when the absolute value .vertline.D(t)-D(t').vertline. is equal to or less than said reference value Dth', said common voltage amplitude is subjected to a second processing in such a way that said common voltage amplitude is held unchanging and constant.