Liquid crystal display device having stabilized drive circuit

• US 7,042,430 B2
• Filed: 03/18/2003
• Issued: 05/09/2006
• Est. Priority Date: 03/18/2002
• Status: Expired due to Fees

• Current Assignee: Panasonic Liquid Crystal Display Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Hitachi Device Engineering Co., Ltd., Hitachi, Ltd.
• Inventors: Isami, Hironobu, Matsumoto, Katsumi, Takemoto, Iwao
• Primary Examiner(s): Lefkowitz, Sumati
• Assistant Examiner(s): Beck, Alexander S.
• Application Number:
  US10/389,801
• Publication Number:
  US 20040004595A1
• Time in Patent Office: 1,148 Days
• Field of Search: 345/87, 345/89, 345 98-100, 345204-206, 345/690
• US Class Current: 345/89
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2310/0259 with use of an analog or digital ramp generator in the column driver or in the pixel circuit
• CPC Class Codes: G09G 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• 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: G09G 3/3677 suitable for active matrices only
• CPC Class Codes: G09G 3/3688 suitable for active matrices only

Abstract

A liquid crystal display device has a liquid crystal display panel and a drive circuit for supplying gray scale voltages to pixels in the liquid crystal display panel. The drive circuit selects desired gray scale voltage levels from a gray scale voltage varying with time in a staircase fashion, in accordance with display data, and supplies the selected gray scale voltage levels to the pixels. The drive circuit includes a stabilizer circuit provided to a gray scale voltage line for supplying the gray scale voltage varying with time.

Claims

1. A liquid crystal display device comprising:

a liquid crystal display panel including a first substrate, a second substrate, a liquid crystal composition sandwiched between said first substrate and said second substrate, a plurality of pixels arranged in a matrix configuration on said first substrate, a plurality of video signal lines for supplying video signal voltages to said plurality of pixels; and

a drive circuit for supplying video signal voltages to said plurality of video signal lines,

wherein

said drive circuit includes a selector circuit which receives display data signals, a gray scale voltage varying with time periodically, and time control signals varying in synchronism with said gray scale voltage, and selects a voltage level of said gray scale voltage in accordance with said display data signals in cooperation with said time control signals;

said selector circuit has a plurality of display data signal lines coupled thereto for receiving said display data signals, and is composed of a plurality of series combinations of a plurality of processing circuits each disposed between two adjacent ones of said plurality of display data signal lines, and each of said plurality of processing circuits is composed of a parallel combination of a display data switching element and a time signal switching element, with a control terminal of said display data switching element being supplied with a corresponding one of said display data signals, and with a control terminal of said time signal switching element being supplied with a corresponding one of said time control signals; and

a stabilizer circuit is provided to a gray scale voltage line for supplying said gray scale voltage such that a change in voltage or current is suppressed under varying loads on said gray scale voltage line.

2. A liquid crystal display device according to claim 1, wherein said display data switching element is formed of a transistor of a same conductivity type as that of a transistor forming said time signal switching element.

5. A liquid crystal display device according to claim 1, wherein said stabilizer circuit includes a constant-current circuit.

3. A liquid crystal display device comprising:

a liquid crystal display panel including a first substrate, a second substrate, a liquid crystal composition sandwiched between said first substrate and said second substrate, a plurality of pixels arranged in a matrix configuration on said first substrate, a plurality of video signal lines for supplying video signal voltages to said plurality of pixels; and

a drive circuit for supplying video signal voltages to said plurality of video signal lines,

wherein

said drive circuit includes a selector circuit which receives display data signals, a gray scale voltage varying with time periodically, and time control signals varying in synchronism with said gray scale voltage, and selects a voltage level of said gray scale voltage in accordance with said display data signals in cooperation with said time control signals,

said selector circuit has N display data signal lines coupled thereto for receiving said display data signals, and has N time control signal lines coupled thereto for receiving said time control signals, and is composed of a plurality of decoder columns each composed of a plurality of processing circuits connected in series and each disposed between two adjacent ones of said plurality of display data signal lines,

each of said plurality of processing circuits is composed of a parallel combination of a display data switching element and a time signal switching element, with a control terminal of said display data switching element being coupled to a corresponding one of said N display data signal lines, and with a control terminal of said time signal switching element being coupled to a corresponding one of said N time control signal lines, said N display data make 2^N different combinations by selecting a number of from zero to N of said display data switching elements, assigning said selected number of said display data switching elements to be turned OFF and turning ON the remainder of said display data switching elements in each of said plurality of decoder columns,

each of said 2^N different combinations being uniquely in synchronism with one level of said gray scale voltage,

said time control signals uniquely determine one level of said gray scale voltage by turning ON a time control signal switching element constituting said parallel combination with said turned-OFF display data switching element, and

a stabilizer circuit is provided to a gray scale voltage line for supplying said gray scale voltage such that a change in voltage or current is suppressed under varying loads on said gray scale voltage line.

4. A liquid crystal display device according to claim 3, wherein said display data switching element is formed of a transistor of a same conductivity type as that of a transistor forming said time signal switching element.

6. A liquid crystal display device according to claim 3, wherein said stabilizer circuit includes a constant-current circuit.