DA converter circuit, liquid crystal driver circuit, liquid crystal display apparatus, and method for designing DA converter circuit

• US 20090295838A1
• Filed: 05/28/2009
• Published: 12/03/2009
• Est. Priority Date: 05/29/2008
• Status: Abandoned Application

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Tanigawa, Akira
• Application Number:
  US12/453,973
• Publication Number:
  US 20090295838A1
• Time in Patent Office: Days
• US Class Current: 345/690
• 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 3/3688 suitable for active matrices only

Abstract

A DA converter circuit configured to output a gray scale voltage to a liquid crystal display panel is disclosed, wherein the gray scale voltage is generated from reference voltages fewer than gray scales of the liquid crystal display panel and it is still to be able to prevent deterioration in display quality of the liquid crystal display panel. A DA converter circuit of at least one embodiment includes: a reference voltage generator circuit for generating reference voltages; a selector circuit for selecting one or two reference voltages from the reference voltages in according to the inputted gray scale value; and a voltage follower circuit for outputting the gray scale voltage that is the one reference voltage thus selected or a mean value of the two reference voltages thus selected. Reference voltages are generated, in at least one embodiment, as a variety of gray scale voltages.

Claims

1. A DA converter circuit for outputting a gray scale voltage to a liquid crystal display panel in accordance with a gray scale value externally inputted to the DA converter circuit, where the gray scale voltage and the gray scale value are of n gray scales and n is a natural number of 2 or more, the DA converter circuit comprising:

a generating section for generating m reference voltages, which are different from each other, where m is a natural number less than n;

a selecting section for selecting one or two reference voltages from the m reference voltages in according to the inputted gray scale value; and

an output section for outputting the gray scale voltage that is the one reference voltage thus selected or a mean value of the two reference voltages thus selected,

the generating section generating the reference voltages in such a manner that, respectively for each end portion of a voltage range of the gray scale voltages of n gray scales, the generating section generates i reference voltages, where i is a natural number less than m and is as many as a variety of gray scale voltages that the output section is capable of outputting for each end portion respectively, and for a center portion of the voltage range, the generating section generates m−

i reference voltages.

2. The DA converter circuit as set forth in claim 1, wherein:

the selecting section selects one reference voltage if a gray scale value corresponding to a gray scale voltage in any one of the end portions is inputted; and

the selecting section selects one or two reference voltages if a gray scale value corresponding to a gray scale voltage in the center portion is inputted.

3. The DA converter circuit as set forth in claim 1, wherein:

the generating section includes j resistor elements connected in series, where j is a natural number not less than m−

1, but less than n−

1; and

the m reference voltages are outputted from the j resistor elements respectively.

4. The DA converter circuit as set forth in claim 3, wherein:

the selecting section includes;

switching elements for respectively switching over connection of the output section between the resistor elements; and

spare switching elements spared for a case where the number of the reference voltages outputted from the generating section for each end portion respectively is increased, the spare switching elements for respectively switching over connection of the output section between that resistor elements which respectively output reference voltages newly added by the increase of the number of the reference voltages.

5. A liquid crystal driver circuit for driving a liquid crystal display panel, the liquid crystal driver circuit comprising:

a DA converter circuit for outputting a gray scale voltage to the liquid crystal display panel in accordance with a gray scale value externally inputted to the DA converter circuit, where the gray scale voltage and the gray scale value are of n gray scales and n is a natural number of 2 or more,

the DA converter circuit including;

a generating section for generating m reference voltages, which are different from each other, where m is a natural number less than n;

a selecting section for selecting one or two reference voltages from the m reference voltages in according to the inputted gray scale value; and

an output section for outputting the gray scale voltage that is the one reference voltage thus selected or a mean value of the two reference voltages thus selected,

the generating section generating the reference voltages in such a manner that, respectively for each end portion of a voltage range of the gray scale voltages of n gray scales, the generating section generates i reference voltages, where i is a natural number less than m and is as many as a variety of gray scale voltages that the output section is capable of outputting for each end portion respectively, and for a center portion of the voltage range, the generating section generates m−

i reference voltages.

6. A liquid crystal display apparatus comprising a liquid crystal display panel and a liquid crystal driver circuit for driving the liquid crystal display panel,

the liquid crystal driver circuit including:

a DA converter circuit for outputting a gray scale voltage to a liquid crystal display panel in accordance with a gray scale value externally inputted to the DA converter circuit, where the gray scale voltage and the gray scale value are of n gray scales and n is a natural number of 2 or more, the DA converter circuit including;

a generating section for generating m reference voltages, which are different from each other, where m is a natural number less than n;

a selecting section for selecting one or two reference voltages from the m reference voltages in according to the inputted gray scale value; and

an output section for outputting the gray scale voltage that is the one reference voltage thus selected or a mean value of the two reference voltages thus selected,

the generating section generating the reference voltages in such a manner that, respectively for each end portion of a voltage range of the gray scale voltages of n gray scales, the generating section generates i reference voltages, where i is a natural number less than m and is as many as a variety of gray scale voltages that the output section is capable of outputting for each end portion respectively, and for a center portion of the voltage range, the generating section generates m−

i reference voltages.

7. A method for designing a DA converter circuit for outputting a gray scale voltage to a liquid crystal display panel in accordance with a gray scale value externally inputted to the DA converter circuit, where the gray scale voltage and the gray scale value are of n gray scales and n is a natural number of 2 or more,

the DA converter circuit including:

a generating section for generating m reference voltages, which are different from each other, where m is a natural number less than n;

a selecting section for selecting one or two reference voltages from the m reference voltages in according to the inputted gray scale value; and

an output section for outputting the gray scale voltage that is the one reference voltage thus selected or a mean value of the two reference voltages thus selected,

the generating section generating the reference voltages in such a manner that, respectively for each end portion of a voltage range of the gray scale voltages of n gray scales, the generating section generates i reference voltages, where i is a natural number less than m and is as many as a variety of gray scale voltages that the output section is capable of outputting for each end portion respectively, and for a center portion of the voltage range, the generating section generates m−

i reference voltages,

the method comprising;

a first calculating step for calculating the gray scale voltage to be outputted from the output section, which gray scale voltage is the one reference voltage thus selected or the mean value of the two reference voltages thus selected;

a second calculating step for calculating a difference between the mean value thus calculated and an ideal gray scale voltage value for a gray scale value corresponding to the mean value, the ideal gray scale voltage value being obtained in advance; and

a voltage range determining step for determining the end portions and center portion of the voltage range according to the voltage difference thus calculated.