Power supply and reference voltage circuit for TFT LCD source driver

• US 20020175662A1
• Filed: 05/24/2002
• Published: 11/28/2002
• Est. Priority Date: 05/24/2001
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Sakurai, Takaaki, Watanabe, Yoshiteru, Yana, Toshiyuki, Karube, Satoshi
• Granted Patent: US 6,963,323 B2
• Time in Patent Office: Days
• US Class Current: 323/312
• CPC Class Codes: G09G 2330/02 Details of power systems and of start or stop of display operation
• CPC Class Codes: G09G 3/3696 Generation of voltages supplied to electrode drivers

Abstract

A liquid crystal power supply is provided which generates a high-precision drive power supply voltage supplied to a driver circuit by using a low-precision reference voltage generating circuit. The power supply circuit includes a DC/DC converter which generates a voltage having a size based on an oscillation signal from a power supply voltage and outputs the generated voltage as a drive power supply voltage; a stabilized power supply circuit which generates a highest-level reference potential for generating a gray-scale voltage in a driver circuit; a comparison unit which outputs a difference voltage according to a difference between the drive power supply voltage and the highest-level reference potential; an internal reference voltage generating unit; an error amplifying unit which amplifies a difference between the reference voltage and the difference voltage; and a PWM conversion unit which outputs an oscillation signal in response to the amplified difference.

Claims

1. A power supply circuit, comprising:

a drive power supply voltage generating circuit for generating a drive power supply voltage for a driver circuit for use in a display device; and

a reference voltage generating circuit for generating a reference voltage for use in generating a gray-scale voltage in said driver circuit,

wherein feedback control is performed to maintain a specified relation between said drive power supply voltage and said reference voltage.

2. The power supply circuit according to claim 1,

wherein said drive power supply voltage generating circuit includes:

a voltage output circuit for outputting said drive power supply voltage while changing an output value thereof in response to an inputted control signal; and

a comparison circuit for comparing said drive power supply voltage and said reference voltage to output a signal in response to a result of the comparison as said control signal.

3. The power supply circuit according to claim 1,

wherein said reference voltage generating circuit generates said reference voltage by a stabilized power supply circuit.

4. The power supply circuit according to claim 2, wherein said comparison circuit includes a difference amplifying circuit for outputting, as said control signal, a signal based on a difference voltage between a feedback voltage generated by a comparison between said drive power supply voltage and said reference voltage and a reference voltage generated independently of said drive power supply voltage and said reference voltage.

5. The power supply circuit according to claim 2,

wherein said comparison circuit includes a difference amplifying circuit for outputting, as said control signal, a signal based on a difference voltage between a first feedback voltage generated from said drive power supply voltage and/or said reference voltage and a second feedback voltage generated from said drive power supply voltage and/or said reference voltage.

6. The power supply circuit according to claim 1,

wherein said reference voltage generating circuit generates said reference voltage from said drive power supply voltage.

7. The power supply circuit according to claim 1,

wherein said reference voltage generating circuit generates a voltage corresponding to a maximum potential among a plurality of reference potentials required for generating a gray-scale voltage in said driver circuit, and outputs the generated voltage as said reference voltage.

8. The power supply circuit according to claim 1,

wherein said reference voltage generating circuit generates a voltage corresponding to a maximum potential among a plurality of reference potentials required for generating a gray-scale voltage in said driver circuit, and generates said plurality of reference potentials based on the generated voltage.

9. The power supply circuit according to claim 2,

wherein said voltage output circuit includes:

a pulse width modulation (PWM) controller for outputting pulse signals, each having a width different from the other, in response to control signals outputted from said comparison circuit; and

a DC/DC converter controlled by said pulse signals.

10. A power supply circuit, comprising:

a drive power supply voltage generating circuit for generating a drive power supply voltage for a driver circuit for use in a display device; and

a reference voltage generating circuit for generating a reference voltage for use in generating a gray-scale voltage in said driver circuit,

wherein said drive power supply voltage generating circuit generates said drive power supply voltage with said reference voltage as a reference.

11. The power supply circuit according to claim 10,

wherein said drive power supply voltage generating circuit includes:

a voltage output circuit for outputting said drive power supply voltage while changing an output value thereof in response to an inputted control signal; and

a comparison circuit for comparing said drive power supply voltage and said reference voltage with to output a signal in response to a result of the comparison as said control signal.

13. The driver circuit voltage generating method according to claim 12, further comprising:

a comparing step of comparing said drive power supply voltage and said reference to output a control signal in response to a result of the comparison,

wherein said drive power supply voltage generating step changes a value of said drive power supply voltage in response to said control signal.

14. The driver circuit voltage generating method according to claim 13,

wherein said reference voltage generating step includes a step of stabilizing said reference voltage.

15. The driver circuit voltage generating method according to claim 13,

wherein said reference voltage generating step includes a reference potential generating step of generating a voltage corresponding to a maximum potential among a plurality of reference potentials required for generating gray-scale voltages in said driver circuit, outputting the generated voltage as said reference voltage, and generating said plurality of reference potentials based on said reference voltage.

17. The display device according to claim 16,

wherein said power supply circuit includes a drive power supply voltage generating circuit for generating said drive power supply voltage, and a reference voltage generating circuit for generating said reference voltage, and

said drive power supply voltage generating circuit includes a voltage output circuit for outputting said drive power supply voltage while changing an output value thereof in response to an inputted control signal, and

a comparing circuit for comparing said drive power supply voltage and said reference voltage with each other to output a signal in response to a result of the comparison as said control signal.

18. The display device according to claim 17,

wherein said reference voltage generating circuit generates said reference voltage by a stabilized power supply circuit.

19. The display device according to claim 17,

wherein said reference voltage generating circuit generates a voltage corresponding to a maximum potential among said plurality of reference potentials, and outputs the generated voltage as said reference voltage.

20. The display device according to claim 19, further comprising:

a reference potential generating circuit for generating said plurality of reference potentials based on said reference voltage.

12. A driver circuit voltage generating method, comprising:

a reference voltage generating step of generating a reference voltage for use in generating a gray-scale voltage in a driver circuit for use in a display device; and

a drive power supply voltage generating step of generating a drive power supply voltage of said driver circuit with said reference voltage as a reference.

16. A display device, comprising:

a display panel including a plurality of pixels arrayed in a matrix, said display panel being for displaying an image by said plurality of pixels;

a driver circuit for outputting a gray-scale voltage to said plurality of pixels based on a plurality of reference potentials; and

a power supply circuit for outputting a drive power supply voltage for said driver circuit and a reference voltage for deciding said plurality of reference potentials,

wherein said power supply circuit performs feedback control to maintain a specified relation between said drive power supply voltage and said reference voltage.