Projection-type liquid crystal display device

• US 6,072,458 A
• Filed: 04/24/1997
• Issued: 06/06/2000
• Est. Priority Date: 07/29/1996
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Sugiura, Hiroaki, Ishida, Kozo, Tamano, Kouhei, Asakawa, Katsumi, Yoshikawa, Shigeharu, Ishitani, Hiroaki
• Primary Examiner(s): Hjerpe, Richard A.
• Assistant Examiner(s): Dinh, Duc Q.
• Application Number:
  US08/842,400
• Time in Patent Office: 1,139 Days
• Field of Search: 345/101, 345/102, 345/1-3
• US Class Current: 345/101
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 3/36 using liquid crystals
• CPC Class Codes: G09G 3/3607 for displaying colours or for displaying grey scales with a specific pixel layout, e.g. using sub-pixels display of colours in flat matrix panels other than liquid crystal displays G09G3/2003; grey scales specific for television H04N3/127
• CPC Class Codes: G09G 3/3655 Details of drivers for counter electrodes, e.g. common electrodes for pixel capacitors or supplementary storage capacitors
• CPC Class Codes: H04N 9/3105 for displaying all colours simultaneously, e.g. by using two or more electronic spatial light modulators simultaneous projection in colour photography G03B33/10; beam splitting or combining systems per se G02B27/10
• CPC Class Codes: H04N 9/3144 Cooling systems cooling of liquid crystal cells in general G02F1/133382; cooling of projectors not peculiar to the presence of an electronic spatial light modulator G03B21/16

Abstract

A projection-type liquid crystal display device having a light source for emitting a luminous flux; a liquid crystal light valve for modulating the luminous flux emitted by the light source means; a liquid crystal drive circuit for applying the common voltage to the common electrode and the video signal to the source electrode; a projection lens for projecting the luminous flux modulated by the liquid crystal light valve onto a screen; a liquid crystal temperature detector for detecting temperature in the vicinity of the liquid crystal light valve; and a controller. The controller controls the common voltage and/or the source voltage on the basis of values detected by the liquid crystal temperature detector in such a way that fluctuation in the light transmittance of the liquid crystal light valve means is reduced.

Claims

1. 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; and

a 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-Δ

t), where Δ

t is a specified unit of time, is represented by D(t-Δ

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 |D(t)-D(t-Δ

t)|>

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 |D(t)-D(t-Δ

t)|≦

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; and

when, during an iteration of said first processing, |D(t)-D(t-Δ

t)|≦

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 |D(t)-(t'"'"')| 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 |D(t)-D(t'"'"')| 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.

2. 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; and

a 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 a common voltage amplitude at value T detected by said temperature detecting means, where T is a currently set value, is represented by A(T), the optimum value of said common voltage amplitude at value D(t) detected by said liquid crystal temperature detecting means is represented by A(D(t)), and a specified reference value is represented by Ath,

when 0<

A(T)-A(D(t))<

Ath, said common voltage amplitude is changed from A(T) to A(T-1);

when 0<

A(D(t))-A(T)<

Ath, said common voltage amplitude is changed from A(T) to A(T+1); and

when |A(T)-A(D(t))|≧

Ath, said common voltage amplitude is set to A(D(t)).

3. 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 the luminous flux emitted by said light source means;

a liquid crystal drive means for applying the common voltage to said common electrode and the video signal to said source electrode;

a projection means for projecting the 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; and

a control means for controlling voltage of said video signal 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 vale means is reduced;

wherein;

if the value detected by said liquid crystal temperature detecting means at time (t-Δ

t), where Δ

t is a specified unit of time, is represented by D(t-Δ

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 |D(t)-D(t|Δ

t)|>

Dth, said control means controls a video signal voltage 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 aid liquid crystal light valve means is reduced, and when |D(t)-D(t-Δ

t)|<

Dth, a first processing is carried out repeatedly in such a way that said video signal voltage is held unchanging and constant;

a value D(t'"'"') detected when a final change in said video signal voltage has been effected is stored; and

when, during an iteration of said first processing, when |D(t)-D(t-Δ

t)|≦

Dth and said video signal voltage is subjected to said first processing for a specified number of iterations, in such a way that said video signal voltage is held constant and unchanging, when an absolute value |D(t)-D(t'"'"')| of a change from detected value D(t) at time after which the subsequent specified period has elapsed and stored value of D(t'"'"') is greater than a specified reference value Dth'"'"', said video signal voltage applied to said source electrode is controlled according to the detected value D(t), and when the absolute value |D(t)-D(t'"'"')| is equal to or less than said reference value Dth'"'"', said video signal voltage is subjected to a second processing in such a way that said video signal voltage is held constant and unchanging.

4. 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 the luminous flux emitted by said light source means;

a liquid crystal drive means for applying the common voltage to said common electrode and the video signal to said source electrode;

a projection means for projecting the 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; and

a control means for controlling voltage of said video signal 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 vale means is reduced;

wherein

if said brightness at value T detected by said temperature detecting means, where T is a currently set value, is represented by B(T), the optimum value of said brightness at value D(t) detected by said liquid crystal temperature detecting means is represented by B(D(t)), and a specified reference value is represented by Bth,

when 0<

B(T)-B(D(t))<

Bth, said brightness is changed from B(T) to B(T-1),

when 0<

B(D(t))-B(T)<

Bth, said brightness is changed from B(T) to B(T+1), and

when |B(T)-B(D(t))|≧

Bth, said brightness is changed from B(t) to B(D(t)); and

if said contrast at value T detected by said temperature detecting means, where T is a currently set value, is represented by C(T), the optimum value of said contrast at value (d(t) detected by said liquid crystal temperature detecting means is represented by C(D(t)), and a specified reference value is represented by Cth,

when 0<

C(T)-C(D(t))<

Cth, said contrast is changed from C(T) to C(T-1),

when 0<

C(D(t))-C(T)<

Cth, said contrast is changed from C(T) to C(T+1), and

when |C(T)-C(D(t))|≧

Cth, said contrast is changed from C(T) to C(D(t)).