Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-07-06
2003-04-08
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S076000, C345S077000, C345S078000, C345S204000, C345S214000, C345S215000, C315S169100, C315S169200, C315S169300
Reexamination Certificate
active
06545652
ABSTRACT:
This application is based on applications No. 11-194551 filed in Japan on Jul. 8, 1999, No. 11-302493 filed in Japan on Oct. 25, 1999, and No. 11-303134 in Japan on Oct. 25, 1999, the contents of which incorporated hereinto by references.
BACKGROUND OF THE INVENTION
The present invention relates to a display apparatus provided with a plurality of light emitting devices such as light emitting diodes arrayed in a matrix A display panel, and to its method of operation.
Currently, bright red, green, and blue (RGB) light emitting diodes (LEDs) of 1000 mcd or more have been developed, and fabrication of large-scale LED displays has become possible. These LED displays have features such as low power consumption, lightness in weight, and the possibility for thin panel display. Further, demand for large-scale displays, which can be used out doors, has increased dramatically.
Practical large-scale LED displays are configured to fit the installation space by assembling a plurality of LED units. An LED unit is formed from a dot matrix array of RGB LEDs arranged on a substrate board.
Further, an LED display is provided with a driver circuit capable of driving each individual light emitting diode. Specifically, each LED control device, which transmits display data to each LED unit, is connected to the LED display, and a plurality of LED units are connected to form one large-scale LED display. The number of LED units used increases as the LED display becomes larger in scale. For example, a large-scale display can use 300 vertical×400 horizontal, or 120,000 LED units.
The LED display uses a dynamic driver system as its driver method, and specifically, the display is connected and driven as described below.
For example, in an m×n dot matrix LED unit, each LED anode in each line is connected to a common source line, and each LED cathode in each column is connected to a common current line. The m-line common source lines are sequentially turned on for display with a prescribed period. For example, m-line common source line switching is performed via decoder circuitry based on the address signal.
However, when LEDs connected to a selected common source line were activated in related art apparatus, charge accumulated in non-activated LEDs connected to unselected common source lines. When these common source lines were then selected, excess current developed as a result of charge built-up during their inactive period. As a result of this problem, LEDs controlled to be off emitted low levels of light and sufficient image contrast could not be obtained. These types of effects caused display quality degradation.
Thus, the first object of the present invention is to reduce the effects of accumulated charge and provide a high quality image display apparatus and its method of operation.
Further, in an LED display, corrected image data are typically used for each LED device to display a high quality image. This is because device-to-device LED variation in brightness, for example, is relatively large.
More specifically, the control circuit has a read-only-memory (ROM) correction data memory section to store correction data corresponding to each LED device. Corrected image data based on the correction data stored in ROM has been used for display.
However, since correction data were stored in ROM in related art apparatus, correction data could not be re-written. Consequently, related art apparatus had the problem that it was necessary to provide a re-writable memory device separate from ROM when different correction data were required.
Thus, the second object of the present invention is to provide an image display apparatus which can store a plurality of correction data in one correction data memory section.
Further, to accurately represent image data on an LED display, the light emission characteristics (driving current vs. brightness characteristics) of each LED device in the image display apparatus must be uniform. However, since LEDs are fabricated on wafers by semiconductor technology, light emission characteristic variation results from fabrication lot-to-lot, wafer-to-wafer, and chip-to-chip. Therefore, it is necessary to correct image data amplitude to compensate for light emission characteristic differences of the LED for each pixel.
An example of related art image data correction is described as follows.
Turning to
FIG. 12
, a block diagram of an embodiment of a related art LED display is shown. In
FIG. 12
,
101
is an m-line n-column LED matrix,
107
is a control circuit,
105
is a microprocessor unit (MPU),
106
is a ROM to store correction data,
102
is a common driver circuit,
103
are horizontal driver circuits,
109
are correction circuits to correct image data, and
110
are random access memory (RAM) to temporarily store correction data. The horizontal driver circuits
103
, correction circuits
109
, and RAM
110
are integrated in LED driver integrated circuits (IC's)
104
(k) provided for each column of the LED matrix (k=1 to n).
First, prior to display illumination, correction data for the m×n pixels stored in ROM are transferred to a high speed buffers. RAM
110
are used as the high speed buffers. Correction data transfer is accomplished as follows. First, correction data held in ROM
106
are read out by the MPU
105
. The MPU
105
sequentially selects LED driver IC's
104
(k) via the address bus
111
and sequentially outputs one columns-worth, or m-pixels, of correction data corresponding to each selected column. The correction data output is input to each LED driver IC
104
(k) via the correction data bus
112
and stored in RAM
110
internal to the LED driver IC
104
(k).
When LEDs are illuminated, correction data stored in RAM
110
are sequentially read out by correction circuits
109
. The value of input image data (IMDATA) is increased or decreased for each pixel based on the correction data to achieve image data correction. Corrected image data are output to the driver circuits
103
, and the driver circuits
103
produce driving current for each LED based on the corrected image data.
However, in the related art LED display described above, a total of m×n pixels-worth of correction data must be stored in the buffers, or RAM
110
, and as display pixel count increases, very large RAM capacity becomes necessary. Further, the operation of correction data read-out from RAM
110
to the correction circuits
109
becomes complicated as the amount of RAM increases. In addition to these problems, both the address bus
111
and the data bus
112
must branch to, and connect with, each of the n driver IC's
104
(1 to n), thereby making wiring complex and peripheral circuitry large in area.
Thus, the third object of the present invention reflects consideration of these problems, and is to provide an image display
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.
SUMMARY OF THE INVENTION
The image display apparatus of the present invention is provided with a dot matrix of light emitting devices, driver circuitry, and a switching circuit section. The dot matrix is a plurality of light emitting devices arranged in a matrix of m-lines and n-columns. One terminal of each light emitting device in each column is connected to a current line, and the other terminal of each light emitting device in each line is connected to a common source line. Driver circuitry controls the display drive to be in an active or inactive state depending on an input illumination signal. In the display drive active state, driver circuitry controls connection of one end of each common source line and each current line according to input display data. The switching circuit section floats the other end of each common source line in the active state and connects the other end of all common source lines to ground in the inactive state.
In this image display apparatus, charge accumulated at light emitting devices and their periphery in the active state, is
Hjerpe Richard
Nguyen Jennifer T.
Nichia Corporation
Wenderoth , Lind & Ponack, L.L.P.
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