Drive circuit for display device

• US 20030030603A1
• Filed: 08/05/2002
• Published: 02/13/2003
• Est. Priority Date: 08/09/2001
• Status: Active Grant

• Current Assignee: HannStar Display Corporation
• Original Assignee: NEC Corporation
• Inventors: Shimoda, Masamichi
• Granted Patent: US 6,809,706 B2
• Time in Patent Office: Days
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0465 Improved aperture ratio, e.g. by size reduction of the pixel circuit, e.g. for improving the pixel density or the maximum displayable luminance or brightness
• CPC Class Codes: G09G 2300/0814 used for selection purposes, e.g. logical AND for partial update
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• 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 2320/0295 by monitoring each display pixel
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements

Abstract

A drive circuit drives a display device including a plurality of pixels arranged as a matrix. Luminous elements are provided for the individual pixels. In this circuit, the luminous element and a drive transistor for driving the luminous element in each of the pixels are serially connected between a first power supply and a second power supply. A first switching transistor supplies the gate of the drive transistor with a control signal for controlling the drive transistor. A differential amplifier compares a voltage at a connection point between the luminous element and the drive transistor, and a control voltage which is input in the differential amplifier so as to control the luminance of the pixel, thereby generating a control signal. The control signal is supplied to the gate of the drive transistor via the first switching transistor. A hold capacitor holds a voltage between the gate and the source of the drive transistor. Thus, the drive circuit does not present a luminance unevenness, enables a high gradation display, prevents a decrease of the yield and the aperture ratio, and decreases the price and the power consumption.

Claims

1. A drive circuit which drives a display device with a plurality of pixels arranged as a matrix and luminous elements being provided for the individual pixels, the drive circuit comprising:

drive transistors provided for the individual luminous elements and driving said luminous elements, said luminous element and said drive transistor in each of the pixels being serially provided between a first power supply and a second power supply;

a first switching transistor provided in each of the pixels for supplying a gate of said drive transistor with a control signal for controlling said drive transistor; and

a differential amplifier for comparing a voltage of a connection point between said luminous element and said drive transistor in each of said pixels, and a control voltage input in said differential amplifier and indicating luminance of the pixel, and, thereby generating said control signal, wherein

said control signal is supplied for the gate of said drive transistor through said first switching transistor.

2. The drive circuit for driving a display device according to claim 1, further comprising a second switching transistor for supplying said differential amplifier with said voltage of said connection point between said luminous element and said drive transistor in each of said pixels.

3. The drive circuit for driving a display device according to claim 1, wherein both of said first switching transistor and said second switching transistor are controlled by the same second control signal.

4. The drive circuit for driving a display device according to claim 1, further comprising a hold capacitor holding a voltage between the gate and the source of said drive transistor.

5. The drive circuit for driving a display device according to claim 2, further comprising a hold capacitor holding a voltage between the gate and the source of said drive transistor.

6. The drive circuit for driving a display device according to claim 3, further comprising a hold capacitor holding a voltage between the gate and the source of said drive transistor.

7. The drive circuit for driving a display device according to claim 1, further comprising a circuit for canceling an input offset which is provided for said differential amplifier.

8. The drive circuit for driving a display device according to claim 2, further comprising a circuit for canceling an input offset which is provided for said differential amplifier.

9. The drive circuit for driving a display device according to claim 3, further comprising a circuit for canceling an input offset which is provided for said differential amplifier.

10. The drive circuit for driving a display device according to claim 1, wherein said differential amplifier is formed on a same substrate as the pixel.

11. The drive circuit for driving a display device according to claim 2, wherein said differential amplifier is formed on a same substrate as the pixel.

12. The drive circuit for driving a display device according to claim 3, wherein said differential amplifier is formed on a same substrate as the pixel.