Active driven LED matrices

• US 5,748,160 A
• Filed: 08/21/1995
• Issued: 05/05/1998
• Est. Priority Date: 08/21/1995
• Status: Expired due to Term

• Current Assignee: Universal Display Corporation
• Original Assignee: Mororola Incorporated
• Inventors: Lee, Hsing-Chung, Shieh, Chan-Long, So, Franky
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): WU, XU MING
• Application Number:
  US08/517,222
• Time in Patent Office: 988 Days
• Field of Search: 345/82, 345/83, 345/39, 345/63, 345/147, 345/210, 345/211, 345/208
• US Class Current: 345/82
• 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 2300/0804 Sub-multiplexed active matrix panel, i.e. wherein one active driving circuit is used at pixel level for multiple image producing elements
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 2310/0256 with the purpose of reversing the voltage across a light emitting or modulating element within a pixel
• 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 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2330/02 Details of power systems and of start or stop of display operation
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/2025 the sub-frames having all the same time duration
• CPC Class Codes: G09G 3/2081 with combination of amplitude modulation and time modulation space and time error diffusion G09G3/2066
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across 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 matrix of light emitting devices including a voltage source constructed to repetitiously supply a multi-step voltage waveform and a matrix of rows and columns of pixels, each pixel being connected to the voltage source. A method of driving the matrix including addressing each of the pixels of the matrix by supplying scan and image data activating signals to each of the pixels, the image data activating signal being used to activate a pixel by completing a current path from the pixel to a return for the voltage source, and activating the voltage source to repetitiously supply multi-step waveforms of voltage and sequentially supply each step of each of the multi-step voltage waveforms to the pixels, and addressing each of the pixels in the matrix for each step supplied.

Claims

1. Active drive apparatus for a matrix of light emitting devices comprising:

a voltage source constructed to repetitiously supply a multi-step voltage waveform when activated;

a matrix including a plurality of rows of light emitting devices and a plurality of columns of light emitting devices, each light emitting device having a first contact connected to the voltage source and a second contact;

a plurality of semiconductor switches, one each associated with each light emitting device, each semiconductor switch having a first current carrying terminal connected to the second contact of the associated light emitting device and a second current carrying terminal connected to a common terminal, each semiconductor switch further having first and second activating input terminals, and each semiconductor switch being constructed to complete a circuit between the first and second current carrying terminals only when activating signals are supplied to both of the first and second activating input terminals; and

a column driver circuit having a plurality of column outputs one each associated with each column of light emitting devices, all of the first activating terminals of each semiconductor switch associated with the light emitting devices in each specific column of light emitting devices being connected together and to the associated column output of the plurality of column outputs;

a row driver circuit having an output all of the second activating terminals of each semiconductor switch associated with the light emitting devices in each specific row of light emitting devices being connected together and to the output of the row driver circuit;

timing circuitry connected to the voltage source, the column driver circuit and the row driver circuit, the timing circuit being constructed to control the row driver circuit to provide an activating signal to each row in sequence and to control the column driver circuit to provide an activating signal to each column for each activating signal applied to a row, each activation or addressing of all of the light emitting devices in the matrix being a sub-frame; and

the timing circuit being further constructed to control the column and row driver circuits and the voltage source and to supply a next sequential step of the multi-step voltage waveform each time a sub-frame is completed, a frame being completed when all of the multi-step voltages of the waveform are supplied.

2. Active drive apparatus for a matrix of light emitting devices as claimed in claim 1 wherein the multi-step voltage waveform which the voltage source is constructed to repetitiously supply includes a plurality of ascending steps of voltage, each representing a level of a multi-bit gray scale.

3. Active drive apparatus for a matrix of light emitting devices as claimed in claim 1 wherein the light emitting devices are current driven devices.

4. Active drive apparatus for a matrix of light emitting devices as claimed in claim 3 wherein the light emitting devices are organic light emitting diodes.

5. Active drive apparatus for a matrix of light emitting devices as claimed in claim 1 wherein each of the plurality of semiconductor switches includes a first transistor with current carrying electrodes forming the first and second current carrying terminals of the semiconductor switch, and a control electrode.

6. Active drive apparatus for a matrix of light emitting devices as claimed in claim 5 wherein each of the plurality of semiconductor switches further includes a second transistor with a first current carrying electrode connected to the control electrode of the first transistor, a second current carrying electrode forming the first activating input terminal of the semiconductor switch, and a control terminal forming the second activating input terminal of the semiconductor switch.

7. Active drive apparatus for a matrix of light emitting devices as claimed in claim 1 wherein each of the column driver circuits is a digital driver.

8. Active drive apparatus for a matrix of light emitting devices as claimed in claim 1 wherein all of the second activating terminals of each semiconductor switch associated with the light emitting devices in each specific row of light emitting devices are connected together and to an output of a shift register.

9. Active drive apparatus for a matrix of light emitting devices comprising:

a voltage source having a plurality of outputs and constructed to repetitiously supply a multi-step voltage waveform sequentially on each of the outputs when activated;

a matrix including a plurality of rows of pixels and a plurality of columns of pixels, each pixel including a plurality of light emitting devices with a first light emitting device of the plurality of light emitting devices having a first contact connected to a first output of the plurality of outputs of the voltage source and a second light emitting device of the plurality of light emitting devices having a first contact connected to a second output of the plurality of outputs of the voltage source, and the first and second light emitting devices of each pixel each having a second contact; and

a plurality of semiconductor switches, one each associated with each pixel, each semiconductor switch having a first current carrying terminal connected to the second contacts of each of the first and second light emitting devices of the associated pixel and a second current carrying terminal connected to a common terminal, each semiconductor switch further having first and second activating input terminals, and each semiconductor switch being constructed to complete a circuit between the first and second current carrying terminals only when activating signals are supplied to both of the first and second activating input terminals.

10. Active drive apparatus for a matrix of light emitting devices as claimed in claim 9 wherein each of the light emitting devices in each pixel are constructed to produce a different color of light.

11. Active drive apparatus for a matrix of light emitting devices as claimed in claim 9 wherein each of the pixels includes three light emitting devices, each constructed to produce a different color of light.

12. Active drive apparatus for a matrix of light emitting devices as claimed in claim 11 wherein the three light emitting devices of each pixel are constructed to produce red, green and blue color light, respectively.

13. Active drive apparatus for a matrix of light emitting devices as claimed in claim 9 wherein all of the second activating terminals of each semiconductor switch associated with the pixels in each specific row of pixels are connected together and to an output of a shift register.

14. Active drive apparatus for a matrix of light emitting devices as claimed in claim 13 including in addition timing circuitry connected to the voltage source, the column driver circuits and the shift register, the timing circuit being constructed to switch the voltage source to the first output of the plurality of outputs of the voltage source and to control the shift register to provide an activating signal to each row in sequence and to control each column driver circuit to provide an activating signal to each column in sequence for each activating signal applied to a row while the voltage source is supplying a multi-step voltage waveform sequentially on the first output and to switch the voltage source to the second output of the plurality of outputs of the voltage source and to control the shift register to provide an activating signal to each row in sequence and to control each column driver circuit to provide an activating signal to each column in sequence for each activating signal applied to a row while the voltage source is supplying a multi-step voltage waveform sequentially on the second output, each activation of all of the first light emitting devices in the matrix being a first sub-sub-frame of a sub-frame, each activation of all of the second light emitting devices in the matrix being a second sub-sub-frame of a sub-frame, and each activation of all of the pixels in the matrix being a sub-frame.

15. Active drive apparatus for a matrix of light emitting devices as claimed in claim 14 wherein the timing circuit is constructed to control the voltage source to supply a next sequential step of the multi-step voltage waveform each time a sub-frame is completed, a frame being completed when all of the multi-step voltages of the waveform are supplied to all of the outputs of the plurality of outputs of the voltage source.

16. A method of driving a matrix of light emitting devices comprising the steps of:

providing a voltage source constructed to repetitiously supply a multi-step voltage waveform when activated;

providing a matrix including a plurality of rows of pixels and a plurality of columns of pixels, each pixel having a first contact connected to the voltage source and a second contact;

addressing each of the pixels of the matrix by supplying scan and image data activating signals to each of the pixels of the matrix, the image data activating signal being used to determine when a pixel is activated by completing a current path from the second contact of each pixel to a return for the voltage source; and

activating the voltage source to repetitiously supply multi-step waveforms of voltage and sequentially supply each step of each of the multi-step voltage waveforms to the pixels, and addressing each of the pixels in the matrix for each step supplied.

17. A method of driving a matrix of light emitting devices comprising the steps of:

providing a voltage source having a plurality of outputs and constructed to repetitiously supply a multi-step voltage waveform sequentially on each of the outputs when activated;

providing a matrix including a plurality of rows of pixels and a plurality of columns of pixels, each pixel including a plurality of light emitting devices with a first light emitting device of the plurality of light emitting devices having a first contact connected to a first output of the plurality of outputs of the voltage source and a second light emitting device of the plurality of light emitting devices having a first contact connected to a second output of the plurality of outputs of the voltage source, and the first and second light emitting devices of each pixel each having a second contact connected to a common terminal;

addressing each of the pixels of the matrix by supplying scan and image data activating signals to each of the pixels of the matrix, the image data activating signal being used to determine when a pixel is activated by completing a current path from the common terminal to a return for the voltage source;

activating the voltage source to supply a multi-step waveform of voltage to the first output of the plurality of outputs of the voltage source and addressing each of the pixels in the matrix for each step of the multi-step voltage waveform; and

activating the voltage source to supply a multi-step waveform of voltage to the second output of the plurality of outputs of the voltage source and addressing each of the pixels in the matrix for each step of the multi-step voltage waveform.