Drive circuit and image forming apparatus using the same

• US 20050179626A1
• Filed: 01/31/2005
• Published: 08/18/2005
• Est. Priority Date: 02/12/2004
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Nakajima, Yoshinori, Kondo, Shigeki, Yuki, Osamu
• Granted Patent: US 7,502,000 B2
• Time in Patent Office: Days
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than one capacitor
• CPC Class Codes: G09G 2300/0861 with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes
• CPC Class Codes: G09G 2300/088 using a non-linear two-terminal element
• CPC Class Codes: G09G 2310/0254 Control of polarity reversal in general, other than for liquid crystal displays
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3241 the current through the light-emitting element being set using a data current provided by the data driver, e.g. by using a two-transistor current mirror

Abstract

In a pixel circuit that accumulates a display signal Vsig in a capacitor and supplies a display current to a light-emitting element using a TFT serving as a drive transistor in order to correct fall of a luminance due to aged deterioration of the light-emitting element, the pixel circuit supplies the display current to a gate of a TFT and sets a source of the TFT to a value obtained by deducting a threshold value of the TFT from an anode potential of the light-emitting element with respect to the display current using a variable bias voltage to thereby extract an amount of an increase of a voltage due to the aged deterioration of the light-emitting element as a source-to-drain current of the TFT. The pixel circuit feeds the source-to-drain current from the capacitor as a correction signal and adjusts a gate potential of the TFT serving as the drive transistor to thereby correct the display current and correct a luminance of the light-emitting element.

Claims

1. A drive circuit comprising a drive transistor for feeding to a load a drive current corresponding to an input signal, wherein

the drive circuit has a correction circuit that supplies a correction signal corresponding to an impedance of the load to a gate of the drive transistor to correct the drive current to be fed to the load by the drive transistor.

2. The drive circuit according to claim 1, wherein the load is a light-emitting element, and the drive circuit feeds an electric current to the light-emitting element, detects a voltage between both terminals of the light-emitting element to detect an impedance of the light-emitting element, and performs the correction on the basis of a result of the detection.

3. The drive circuit according to claim 1, wherein the load is a light-emitting element, one terminal of the light-emitting element is connected to a gate of a transistor for correction, and when a predetermined potential Ps is set to a value calculated by deducting a threshold voltage Vth of the transistor for correction from a terminal potential Pi of the light-emitting element with respect to a drive current, the drive circuit sets a source potential of the transistor for correction to the predetermined potential Ps to thereby generate a voltage corresponding to an impedance of the light-emitting element as a source-to-drain current of the transistor for correction.

4. The drive circuit according to claim 3, wherein the drive circuit inputs the source-to-drain current of the transistor for correction to the gate of the drive transistor as the correction signal.

5. The drive circuit according to claim 3, wherein the drive circuit sets the source potential of the transistor for correction using a nonlinear element having a variable bias voltage or diode characteristic.

6. The drive circuit according to claim 3, wherein it is possible to multiply the correction signal with a coefficient according to a setting for a size of the transistor for correction.

7. An image forming apparatus comprising:

a pixel circuit group in which plural pixel circuits, which include a light-emitting element and a drive transistor for feeding a drive current corresponding to an input signal to the light-emitting element, are arranged, wherein

each of the pixel circuits has a correction circuit that supplies a correction signal corresponding to an impedance of a load to a gate of the drive transistor and corrects the drive current to be fed to the light-emitting element by the drive transistor.

8. The image forming apparatus according to claim 7, wherein the light-emitting element is an organic electroluminescent element.

9. The image forming apparatus according to claim 8, wherein

the pixel circuit group is arranged in a two-dimensional matrix shape, and

the image forming apparatus includes:

a display unit that forms an image in the pixel circuit group according to light emission of the light-emitting element;

a line drive circuit that supplies an image signal to the pixel circuit group;

an image data supply circuit that supplies image data to the line drive circuit; and

a decoder that decodes compressed image data stored in a storage medium and supplies the decoded image data to the image data supply circuit.

10. The image forming apparatus according to claim 8, further comprising:

a photosensitive member;

a charging device for charging the photosensitive member;

an exposure device that has the pixel circuit group arranged at least in a one-dimensional matrix shape and is used for forming a latent image on the photosensitive member according to light emission of the light-emitting element;

a developing device;

a line drive circuit that supplies an image signal to the pixel circuit group; and

an image data supply circuit that supplies image data to the line drive circuit.

11. A drive circuit comprising a drive transistor for feeding a drive current corresponding to an input signal to a load, wherein

the drive circuit has a correction circuit that supplies a correction signal corresponding to an amount of deterioration of the load to a gate of the drive transistor to correct the drive current to be fed to the load by the drive transistor.

12. A drive circuit comprising:

a drive transistor for feeding a drive current corresponding to an input signal to a load;

a storage capacitor that is connected to a control electrode of the drive transistor and used for retaining an input signal;

a detection circuit for detecting a resistance of the load; and

a correction circuit that feeds back a result of the detection by the detection circuit to the drive transistor to correct a drive current to be fed to the load by the drive transistor.

13. The drive circuit according to claim 12, wherein

the detection circuit includes a second capacitor that is connected to a terminal, which is connected to the load, via a switching transistor, and

the correction circuit includes a transistor for correction that has a control electrode connected to the second capacitor and is used for changing a potential of the control electrode of the drive transistor.

14. An image forming apparatus comprising a pixel circuit group in which plural pixel circuits, which include a light-emitting element serving as a load and the drive circuit according to claim 12, are arranged, wherein

the pixel circuit group is arranged in a two-dimensional matrix shape, and

the image forming apparatus includes:

a display unit that forms an image in the pixel circuit group according to light emission of the light-emitting element;

a line drive circuit that supplies an image signal to the pixel circuit group;

an image data supply circuit that supplies image data to the line drive circuit; and

a decoder that decodes compressed image data stored in a storage medium and supplies the decoded image data to the image-data supply circuit.

15. An image forming apparatus comprising a pixel circuit group in which plural pixel circuits, which include a light-emitting element serving as a load and the drive circuit according to claim 12, are arranged, comprising:

a photosensitive member;

a charging device for charging a photosensitive member;

an exposing device that has the pixel circuit group arranged at least in a one-dimensional matrix shape and is used for forming a latent image on a photosensitive member according to light emission of the light-emitting element;

a developing device;

a line drive circuit that supplies an image signal to the pixel circuit group; and

an image data supply circuit that supplies image data to the line drive circuit.