Display driver circuits

• US 20050007353A1
• Filed: 10/23/2002
• Published: 01/13/2005
• Est. Priority Date: 10/31/2001
• Status: Active Grant

• Current Assignee: Cambridge Display Technology Limited (Sumitomo Chemical Company Limited)
• Original Assignee: Cambridge Display Technology Limited (Sumitomo Chemical Company Limited)
• Inventors: Smith, Euan C., Routley, Paul R.
• Granted Patent: US 7,456,812 B2
• Time in Patent Office: Days
• US Class Current: 345/204
• CPC Class Codes: G09G 2300/0417 Special arrangements specific to the use of low carrier mobility technology
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/088 using a non-linear two-terminal element
• CPC Class Codes: G09G 2310/0262 The addressing of the pixel, in a display other than an active matrix LCD, involving the control of two or more scan electrodes or two or more data electrodes, e.g. pixel voltage dependent on signals of two data electrodes
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 2360/148 the light being detected by light detection means within each pixel
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: H10K 59/13 comprising photosensors that control luminance
• CPC Class Codes: H10K 59/65 OLEDs integrated with inorganic image sensors

Abstract

Display driver circuitry for electro-optic displays, in particular active matrix displays using organic light emitting diodes. The circuitry includes a driver to drive an electro-optic element in accordance with a drive voltage, a photosensitive device optically coupled to the electro-optic display element to pass a current dependent upon illumination reaching the photosensitive device, a first control device coupled between the photosensitive device and a data line and responsive to a first control signal on a first control line to couple the photosensitive device to the data line, and a second control device coupled between the photosensitive device and the driver and responsive to a second control signal on a second control line to couple the photosensitive device to the driver. The circuit can be operated in a number of different modes and provides flexible control of an electro-display element such as an organic LED pixel.

Claims

1. Display element driver circuitry for driving an element of an electro-optic display, the circuitry having first and second control lines and a data line, the circuitry comprising:

a driver to drive the electro-optic display element in accordance with a drive voltage;

a photosensitive device optically coupled to the electro-optic display element to pass a current dependent upon illumination reaching the photosensitive device;

a first control device coupled between the photosensitive device and the data line and responsive to a first control signal on the first control line to couple the photosensitive device to the data line; and

a second control device coupled between the photosensitive device and the driver and responsive to a second control signal on the second control line to couple the photosensitive device to the driver.

2. Display element driver circuitry as claimed in claim 1, further comprising a storage element coupled to the second control device to memorize a drive voltage for the driver.

3. Display element driver circuitry as claimed in claim 2, wherein the storage element comprises a capacitor.

4. Display element driver circuitry as claimed in claim 3, wherein the driver comprises a field effect transistor (FET) and the capacitor comprises a gate capacitance of said FET.

5. Display element driver circuitry as claimed in claim 1, wherein said first and second control devices each comprise a FET switch.

6. An active matrix display comprising a plurality of electro-optic display elements, each display element having associated display element driver circuitry as claimed in claim 1.

7. An active matrix display as claimed in claim 6, further comprising a switch to selectively couple said data line to a data line driver and to a signal sense circuit.

8. An active matrix display as claimed in claim 6, further comprising control circuitry to drive said first and second control lines to operate the display in a plurality of modes.

9. An active matrix display as claimed in claim 8, wherein said modes include an ambient light compensate mode in which said control circuitry controls the display element driver circuitry to measure an ambient light level before writing data to the display.

10. An active matrix display as claimed in claim 8, wherein said modes include current driver mode in which the brightness of a said display element is set by a reference current on said data line.

11. An active matrix display as claimed in claim 8, wherein said modes include a first voltage drive mode in which the brightness of a said display element is set by a voltage on said data line.

12. An active matrix display as claimed in claim 8, wherein said modes include a second voltage drive mode in which the brightness of a said display element is set by a voltage on said data line and in which said second control line is driven to couple said photosensitive element and said driver whilst said display element is on.

13. An active matrix display as claimed in claim 8, further comprising a pattern sense input mode in which said control circuitry controls the display element driver circuitry to input a light pattern from said display using a plurality of said photosensitive devices associated with a corresponding plurality of said display elements.

14. Display element driver circuitry as claimed in claim 1, wherein a said electro-optic display element comprises an organic light emitting diode.

15. A method of operating display element driver circuitry as claimed in claim 1, the method comprising:

controlling said circuitry to couple said photosensitive device to said data line;

measuring a light level using said photosensitive device;

controlling said circuitry to couple said driver to said data line; and

driving said data line with a signal dependent upon said measuring.

16. A method of operating display element driver circuitry as claimed in claim 1, the method comprising:

controlling said first and second control lines to assert and de-assert said first and second control signals together; and

driving said data line with a reference current to set a brightness for said display element when said driver, said photosensitive device and said data line are all coupled.

17. A method of operating display element driver circuitry as claimed in claim 1, the method comprising:

controlling said first and second control lines to assert and de-assert said first and second control signals together; and

driving said data line with a reference voltage to set a brightness for said display element when said driver, said photosensitive device and said data line are all coupled.

18. A method as claimed in claim 16, further comprising:

controlling said circuitry to couple said photosensitive device to said data line;

measuring a light level using said photosensitive device; and

controlling said circuitry to couple said driver to said data line; and

wherein said driving drives said data line with a signal dependent upon said measuring.

19. A method of operating display element driver circuitry as claimed in claim 1, the method comprising:

controlling said second control line to assert said second control signal to couple the photosensitive device to the driver;

controlling said first control line to couple the photosensitive device to the data line to select the display element;

driving said data line with a reference voltage to set a brightness for said display element when said driver, said photosensitive device and said data line are all coupled; and

controlling said first control line to decouple the photosensitive device from the data line to deselect the display element whilst maintaining said second control signal to maintain the coupling of said photosensitive device to said driver.

20. A method of operating an active matrix display as a light pattern sensor, the active matrix display comprising a plurality of display elements, each display element having associated display element driver circuitry as claimed in claim 1, the method comprising:

controlling the display element driver circuitry of a plurality of said display elements to couple the photosensitive device of each display element to the corresponding data line; and

reading light pattern data from the display using the data line of each photosensitive device.

22. A method as claimed in claim 15, further comprising writing an initial dark level signal to the display element or pixel prior to said measuring.

23. An active matrix display as claimed in claim 6, wherein said electro-optic display element comprises an organic light emitting diode.

24. A method as claimed in claim 17, further comprising:

controlling said circuitry to couple said photosensitive device to said data line;

measuring a light level using said photosensitive device; and

controlling said circuitry to couple said driver to said data line; and

wherein said driving drives said data line with a signal dependent upon said measuring.

25. A method as claimed in claim 18, further comprising writing an initial dark level signal to the display element or pixel prior to said measuring.

21. A method of controlling the light output from a pixel of an active matrix electroluminescent display, the pixel including an electroluminescent display element and a light sensor optically coupled to the electroluminescent display element to provide an optical feedback path for controlling the electroluminescent display element light output, the method comprising:

measuring an ambient light level using the light sensor; and

writing a light level signal to the pixel modified to compensate for said ambient light level.

26. A method as claimed in claim 21, further comprising writing an initial dark level signal to the display element or pixel prior to said measuring.