Multicolor display system

• US 5,134,387 A
• Filed: 11/06/1989
• Issued: 07/28/1992
• Est. Priority Date: 11/06/1989
• Status: Expired due to Term

• Current Assignee: Texas Digital Systems, Inc. (NCR Voyix Corporation)
• Original Assignee: Texas Digital Systems, Inc. (NCR Voyix Corporation)
• Inventors: Smith, George C., Bower, Robert Jr.
• Primary Examiner(s): Weldon, Ulysses
• Assistant Examiner(s): CHOW, DOON Y
• Application Number:
  US07/432,566
• Time in Patent Office: 995 Days
• Field of Search: 340/701, 340/702, 340/703, 340/762, 340/782, 340/815.03, 340/793, 340/767, 358/56
• US Class Current: 345/83
• CPC Class Codes: G09F 9/33 being semiconductor devices, e.g. diodes
• CPC Class Codes: G09G 2300/0452 Details of colour pixel setup, e.g. pixel composed of a red, a blue and two green components
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/32 semiconductive, e.g. using light-emitting diodes [LED]

Abstract

A multicolor display system comprised of a matrix of light-emitting diodes (LEDs). Each display dot or pixel is comprised of one red LED and one green LED. The display data is stored in a selected one or more discrete locations of a random access memory as a bit map, depending upon the desired display color. Each memory location is associated with a particular primary color "field" (e.g., red or green). The bit map indicates which of the LEDs is ON and which is OFF in order to display selected data. The data associated with each field is displayed sequentially during a display cycle so that the relative mixture of red fields and green fields determines the resulting display color. The duty cycle of each LED is therefore controlled in software, which reduces the need for complex hardware such as voltage drivers and counters needed in prior art multicolor display systems.

Claims

1. A multicolor display system, comprising, in combination:

a plurality of display elements, each of which includes a plurality of electrically activatable light-emitting devices for emitting light of respective primary colors;

display activation means for activating a selected one or more of the display elements by periodically activating a selected one or more of the corresponding light-emitting devices at an activation frequency such that an image displayed by the activation of said selected one or more of the display elements appears to a human eye to be continuously displayed, a time period equal to the reciprocal of the activation frequency being a refresh cycle of the display system;

storage means for storing a plurality of discrete codes, each of said discrete codes corresponding to a discrete time interval of said refresh cycle and indicating whether or not each of the light-emitting devices of a particular primary color is to be activated during the corresponding discrete time interval, the light-emitting devices of each primary color being activatable during a plurality of discrete time intervals of the refresh cycle, consecutive ones of the discrete time intervals corresponding to each primary color being punctuated by at least one intermediate discrete time interval corresponding to another primary color; and

control means responsive to each of the discrete codes for controlling said display activation means to activate each of said selected one or more of said light-emitting devices during a selected one or more of said discrete time intervals, the intensity of the color emitted by each of said selected one or more of said light-emitting devices being partially defined during each discrete time interval corresponding to the primary color of the corresponding light-emitting device such that the intensity of the color of each of the selected one or more of the light-emitting devices is separately definable during the refresh cycle from the intensity of the color of any other of the selected one or more of said light-emitting devices of the same primary color, the color of each of the selected one or more of the display elements being defined by the number of discrete time intervals of the refresh cycle that each of the light-emitting devices of the corresponding display element is activated, said control means providing separate color control of each display element such that an image is displayable which appears to the human eye to be continuously displayed in a plurality of colors.

2. The display system of claim 1 wherein said storage means includes a plurality of discrete storage locations, each of said storage locations being adapted for storing a corresponding discrete code.

3. The display system of claim 1 wherein said plurality of display elements is comprised of M×

N number of display elements arranged in a matrix of M number of columns and N number of rows, M and N being integers, said display system further including first driver means for applying a discrete electrical signal to each of said M columns in accordance with each of the discrete codes and second driver means for sequentially scanning the N rows.

4. The system of claim 3, wherein said first driver means is comprised of first latch means for temporarily storing display data and M number of electrical current supply devices connected between said first latch means and the respective M columns for supplying electrical current to the display elements of the respective columns, said current supply devices being controlled by the first latch means to supply electrical current to a selected one or more of the columns in accordance with the display data stored in the first latch means, said second driver means being comprised of second latch means for applying a scanning signal in sequence to the N rows and N groups of switching devices connected between the second latch means and the respective N rows for selectively activating and deactivating the display elements of the respective rows, the individual switching devices of each group being coupled to the light-emitting devices of the respective primary colors in the corresponding row so that the light-emitting devices of each primary color are separately controllable.

5. The system of claim 4, wherein each display element is comprised of P number of light-emitting diodes for emitting light of respective P number of primary colors, the respective anodes of the light-emitting diodes in the same column being commonly coupled to the corresponding current supply device, the respective cathodes of the light-emitting diodes of a particular primary color in the same row being commonly coupled to the corresponding switching device.

6. The system of claim 5, wherein each current supply device is comprised of a current supply transistor, the base of which is connected to the first latch means, the emitter of which is coupled to the respective anodes of the light-emitting diodes of the corresponding column and the collector of which is connected to a source of working electrical current.

7. The display system of claim 6, further including a current limiting resistor in series between each of the current supply devices and the respective anodes of the light-emitting diodes of the corresponding column

8. The display system of claim 6, wherein each switching device is comprised of a current sink transistor, the base of which is connected to the second latch means, the emitter of which is grounded and the collector of which is coupled to the respective cathodes of the light-emitting diodes of the corresponding primary color in the corresponding row.

9. The display system of claim 1 wherein said storage means includes a plurality of discrete storage locations, each of said storage locations being adapted for storing a particular one of said discrete codes, each discrete time interval being associated with a corresponding discrete storage location and being further associated with a particular one of said primary colors such that only light-emitting devices of the particular primary color are activatable during the corresponding discrete time interval.

10. The display system of claim 9 wherein each primary color is associated with an equal number of discrete time intervals of the refresh cycle.

11. The display system of claim 1 wherein each of said discrete time intervals represents a discrete color field, the time duration of each field corresponding to a particular primary color being different from the time duration of each of the other fields corresponding to the same particular primary color such that the human eye can detect 2ⁿ number of different intensities of each primary color, where n is the number of fields associated with each primary color during the refresh cycle.

12. A method of controlling the color of a multicolor display system having a plurality of display elements, each of which has a plurality of electrically activatable light-emitting devices for emitting light of respective primary colors, said method comprising the steps of:

dividing a predetermined time period corresponding to a refresh cycle of the display elements into a plurality of discrete time intervals, said refresh cycle representing a time period between successive activations of a selected one or more of said display elements such that an image displayed by the activation of said selected one or more of the display elements appears to a human eye to be continuously displayed, each of said time intervals corresponding to a particular one of said primary colors, the light-emitting devices of each primary color being activatable during a plurality of discrete time intervals of the refresh cycle, consecutive ones of the discrete time intervals corresponding to each primary color being punctuated by at least one intermediate discrete time interval corresponding to another primary color;

providing a plurality of discrete codes, each of said discrete codes corresponding to a discrete time interval of said refresh cycle and indicating whether or not each of the light-emitting devices of a particular primary color is to be activated during the corresponding discrete time interval; and

controlling the activation of the display elements in accordance with the discrete codes by periodically activating a selected one or more of the light-emitting devices during a selected one or more of the discrete time intervals, the intensity of the color emitted by each of the selected one or more of the light-emitting devices being partially defined during each discrete time interval corresponding to the primary color of the corresponding light-emitting device such that the intensity of the color of each of the selected one or more of the light-emitting devices is separately definable from the intensity of the color of any other of the selected one or more of the light-emitting devices of the same primary color, the color of each activated display element being defined by the number of discrete time intervals of the refresh cycle that each of the light-emitting devices of the corresponding display element is activated, to provide separate color control of each display element such that an image is displayable which appears to the human eye to be continuously displayed in a plurality of colors.

13. The method of claim 12 wherein said display system includes storage means having a plurality of discrete storage locations, each of said storage locations being adapted for storing a corresponding discrete code, said method including storing each of said discrete codes in a corresponding one of said discrete storage locations.

14. The method of claim 12 wherein said plurality of display elements is comprised of M×

N number of display elements, M and N being integers, said display elements being arranged in a matrix of M columns and N rows, said controlling including applying respective discrete electrical signals to said M columns in accordance with said discrete codes and sequentially scanning said N rows.

15. The method of claim 12 wherein each primary color is associated with an equal number of discrete time intervals of the refresh cycle.

16. In a multicolor display system having a plurality of display elements, each of which has a plurality of electrically activatable light-emitting devices for emitting light of respective primary colors, control means for selectively activating and deactivating the light-emitting devices in accordance with predetermined display parameters, and memory means having a plurality of discrete storage locations, a method of controlling the color of each of the display elements, comprising the steps of:

dividing a predetermined time period corresponding to a refresh cycle of the display elements into a plurality of discrete time intervals, said refresh cycle representing a time period between successive activations of a selected one or more of said display elements such that an image displayed by the activation of said selected one or more of said display elements appears to a human eye to be continuously displayed, each of said time intervals corresponding to a particular one of said primary colors, the light-emitting devices of each primary color being activatable during a plurality of discrete time intervals of the refresh cycle, consecutive ones of the discrete time intervals corresponding to each primary color being punctuated by at least one intermediate discrete time interval corresponding to another primary color;

providing a plurality of discrete codes, each of said discrete codes corresponding to a discrete time interval of said refresh cycle and indicating whether or not each of the light-emitting devices of a particular primary color is to be activated during the corresponding discrete time interval;

allocating each of the discrete storage locations to a particular one of said discrete time intervals and storing the corresponding discrete code in the corresponding discrete storage location; and

,

controlling the activation of the display elements in accordance with the discrete codes by periodically activating a selected one or more of the light-emitting devices during a selected one or more of the discrete time intervals, the intensity of the color emitted by each of the selected one or more of the light-emitting devices being partially defined during each discrete time interval corresponding to the primary color of the corresponding light-emitting device such that the intensity of the color of each of the selected one or more of the light-emitting devices is separately definably from the intensity of the color of any other of the selected one or more of the light-emitting devices of the same primary color, the color of each activated display element being defined by the number of discrete time intervals of the refresh cycle that each of the light-emitting devices of the corresponding display element is activated, to provide separate color control of each display element such that an image is displayable which appears to the human eye to be continuously displayed in a plurality of colors.

17. The method of claim 16 further including the step of allocating to each primary color an equal number of discrete time intervals of the refresh cycle.