JP2000047639A - Led display unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED display unit in which character information and picture information are displayed by inputting gradation data from the external and especially, plural compensation data, that reduce the dispersion of each light emitting diode, are constituted by a relatively simple circuit. SOLUTION: The LED display unit has an LED display panel, on which LEDs are arranged in a dot matrix shape, and light turning-on means that dynamically drives each LED in accordance with inputted gradation data. The light turning-on means adjusts the turning-on of the LEDs by supplyng the turning-on signal to a gradation driver. The signal is based on the multiplied value of two corrected values. The first corrected value is provided by first luminance correcting means which are connected in series and correct the output levels to LEDs in a common manner to rows and columns. The second corrected value is provided by a second luminance correcting means that adjusts individual the output levels of LEDs corresponding to the rows and the columns of the LED display panel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED display unit capable of displaying character information, video information, and the like by externally inputting gradation data, and more particularly to a plurality of correction data for reducing variations among light emitting diodes. And an LED display unit that can be configured with a relatively simple circuit.

[0002]

2. Description of the Related Art A full-color LED display unit can be realized by using light emitting diodes (hereinafter, also referred to as LEDs) capable of emitting RGB (red, green, and blue) light. One full-color dot is formed by each light-emitting diode using three or more types of light-emitting elements that emit light of RGB. The light emitting diodes constituting one dot are arranged close to each other to such an extent that color mixing occurs from a desired visual recognition position. By arranging the dots in a matrix, an LED display unit can be configured. LED display unit is RGB
The light emission color can be freely changed by adjusting the brightness of each of them.

For example, when all the light emitting diodes are turned on at the same time, white light can be displayed by color mixture. When the red and blue light emitting diodes are turned on, magenta, yellow in red and green, and cyan in green and blue.

In the LED display unit, each light emitting diode is turned on and off within a predetermined cycle by a built-in lighting means. When the lighting means adjusts the lighting time of the light emitting diode, the brightness perceived by the eyes, that is, the substantial light emission luminance of the light emitting diode can be adjusted. The longer the lighting time of the light emitting diode, the brighter the eyes. Conversely, if the lighting time is shortened, it will appear dark.

In a dynamically driven LED display, the lighting means includes a pulse width modulation circuit for outputting a pulse width corresponding to the input gradation data. The lighting time is calculated based on the input gradation data, and the length of the pulse width is specified based on the calculated lighting time. The pulse from the pulse width modulation circuit switches the LED driving circuit including the gray scale driver and the scanning driver at regular intervals in synchronization with the reference clock to turn on the light emitting diode. Each light emitting diode is sequentially turned off according to the pulse width. For example, L
The ED drive circuit turns on the light emitting diode when the input pulse is "High" and turns off the light when the pulse is "Low".
The shorter the High time, the lower the visible brightness of the light emitting diode. Conversely, a light emitting diode with a long lighting time feels bright to the eyes, so that the light emitting diode can be brightly lit in proportion to the gradation data. The light emitting diodes of RGB are also turned on. Thus, the LED display can display various images in full color or multi-color based on desired gradation data.

[0006]

However, usually,
The LED display is composed of a plurality of LED display units. As the LED display unit, for example, 256 × 3 light emitting diodes are used for each of RGB for even one unit using 16 vertical and 16 horizontal light emitting diodes. In addition, LED display is LE
When 30 D display units are arranged vertically and 40 units are arranged horizontally, a total of about 310,000 light emitting diodes are used. Therefore, it is extremely difficult to make the characteristics of each light emitting diode uniform.

Each of the light emitting elements constituting the light emitting diode has a size of about 200 to 400 μm. For example, even if light-emitting elements formed simultaneously from a 2-inch semiconductor wafer are used, the brightness, wavelength, and the like vary. Similarly, different semiconductor wafers tend to form light emitting elements with further variations in luminance and the like. These are considered to be due to various causes such as the flow rate and temperature distribution of the reaction gas at the time of forming the LED chip, and it is currently difficult to form a large number of light emitting elements having exactly the same characteristics. Such a variation in the light emitting elements causes unevenness in brightness in an LED display using the above number of light emitting diodes. The uneven brightness reduces the quality of the display screen.

In order to reduce variations in light emitting diodes, light emitting diodes of each emission color can be level-selected by luminance. However, equalizing the total brightness of each light emitting diode constituting the LED display causes a significant increase in cost. Further, when the brightness is further finely adjusted using the selected light emitting diodes, the uneven brightness becomes more conspicuous. Therefore, there is a problem that it is necessary to select light emitting diodes at a finer level.

Apart from this, a method of electrically correcting the luminance variation of the LED display can be considered. As a method for electrically correcting the luminance variation, the luminance variation can be corrected by adjusting the amplitude value and the pulse width of the current output flowing through the light emitting diode by performing the electrical correction with the lighting means. Specifically, the luminance correction data is transferred and written together with the display data from the storage means electrically connected to the driving circuit for driving each light emitting diode.
The storage means is, for example, a non-volatile ROM (Read Only Memory).
The luminance correction data can be held using y) or the like.

In accordance with the lighting operation of each display line of the LED display, correction data is sequentially transferred from the storage means to the drive circuit to perform correction. When there are a plurality of light-emitting diode luminance corrections for each characteristic, such as dot variation, panel-to-panel variation, and RGB-to-RGB variation, each correction data is calculated by the CPU or the like on the data and gradation data held in the storage means. Then, each light emitting diode is turned on by lighting means which can be finely adjusted.

However, the dot luminance correction is to control each light emitting diode individually. On the other hand, the inter-panel correction or the like controls each light emitting diode in common. Therefore, in order to simultaneously perform the individual correction means such as the dot luminance correction and the common correction means, the number of bits that can be simultaneously corrected by the number of columns or rows of each light emitting diode is relatively large. Requires an arithmetic unit. Therefore, the number of bits to be corrected for each LED increases as the type of data to be corrected increases,
There is a problem that the lighting means is complicated as the time constraint increases. In particular, an arithmetic circuit having a larger number of bits has a much larger cost difference than an arithmetic circuit having a smaller number of bits. As described above, the arithmetic circuit used for the lighting means for driving each LED has the number of light-emitting diodes in each column or row × the number of types to be corrected × L even when dynamically driven.
The number of ED display units is required. Therefore, as the number and types of data to be corrected increase, the LE becomes extremely large.
The cost of the entire D display is extremely high.

The inventor of the present invention has found that as a result of various experiments,
Each correction value is divided into a correction for each LED and a correction to be performed in common for a certain group of LEDs, and common correction means are connected in multiple stages while maintaining the correction ratio for each LED, so that each correction value can be relatively easily configured. It has been found that the correction can be made accurately, and the present invention has been accomplished.

While maintaining the ratio of the dot-luminance-corrected data corrected by the second luminance correction means, the first luminance correction means performs surface luminance correction, coarse correction, and the like. In other words, different types of correction can be performed in multiple stages while maintaining the correction ratio instead of the correction amount. Therefore, light emission can be performed for each light emitting diode while maintaining the respective correction ratios. Further, the correction can be performed with a relatively simple circuit configuration.

[0014]

SUMMARY OF THE INVENTION The present invention provides an LED display panel having LEDs arranged in a dot matrix, and a floor for supplying a lighting signal to each LED corresponding to each column or row of the LED display panel. An LED display unit having lighting means for dynamically driving each of the LEDs in accordance with the input gradation data by means of a tone driver and a scanning driver which scans individual LEDs corresponding to each row or column.

In particular, the lighting means is commonly used for each column or row.
Correction values from a plurality of connected first brightness correction means for correcting the output level to D and second brightness correction means for adjusting the output level of each LED corresponding to each column or row of the LED display panel The lighting of the LED is adjusted by causing the gradation driver to supply a lighting signal based on the integrated value with the correction value from. Thereby, the light emitting diode can be turned on while maintaining each correction ratio. In addition, by using a relatively simple circuit configuration, not only the design becomes easy, but also the cost can be reduced.

In the LED display unit according to a second aspect of the present invention, the second luminance correcting means is a dot luminance correcting means, and the plurality of first luminance correcting means are LE.
D panel-to-panel correction means for adjusting the mutual output level between display panels, coarse correction adjustment means for adjusting the output level corresponding to each type of LED chip, luminance correction adjustment means for adjusting the output level of the entire LED display, saturation It comprises at least two combinations selected from gamma correction means for adjusting the output level in accordance with the luminance. Thereby, an extremely high quality image can be provided as the whole LED display.

According to a third aspect of the present invention, there is provided an LED display unit, wherein the lighting means switches the gradation driver according to the gradation data and controls the lighting time of each LED to adjust the luminance. The first brightness correction means and the second brightness correction means have means for adjusting the brightness of each LED by sequentially changing the constant current from the reference constant current source based on each correction means. This allows the LED to emit light with each correction ratio being positioned with a relatively simple configuration. In particular, when the gradation data is modulated by the pulse width modulation circuit, the gradation data and a plurality of correction data can be processed simultaneously. Therefore, time constraints can be reduced.

[0018]

Embodiments of the present invention will be described below in detail. FIG. 6 is a schematic perspective view in which an LED display unit 600 is configured using a chip type LED 601 in which LED chips capable of emitting light of the three primary colors of light, RGB, respectively, are arranged at one place. 8x chip type LED 601 on the substrate as 1 dot
An LED display panel 602 is arranged in a dot matrix of eight.

The LED display panel 602 has a substrate 6 on which a driving circuit for driving each LED is disposed on the back surface.
03 and a pin 604. L
The LED display unit 600 includes an ED display panel 602 and lighting means including a drive circuit. The LED display units are arranged vertically and horizontally as desired, and can constitute an LED display as a whole (not shown). Display data from various data sources such as various VTRs and DVDs is transmitted to each LE via a controller.
It is supplied to the D display unit 600. The LED display unit that has received the display data displays an image or the like by driving the lighting means based on the data to light each LED.

The light emitting diode may be one in which an LED chip capable of emitting light of each of RGB is arranged on one LED, or an LED for each of RGB in which at least one LED chip is arranged is placed close to one dot. It may be configured. Further, as the shape of the light emitting diode, various types such as a bullet type, a chip type LED, and a type in which a bare chip is directly arranged on a panel can be used. Furthermore, when full color display is not performed, various types such as an LED using one type of LED chip and an LED using two types of LED chips can be selected.

The LED display unit of the present invention comprises:
An example of a dynamic driving method in which brightness is adjusted by the emission time of three LED chips that emit RGB light to display one dot of full color will be described. Needless to say, the present invention can be applied to a static drive system. Fig. 1
And outputting a pulse width corresponding to the gradation data from a current output unit and a pulse width modulation circuit for creating a pulse corrected by the first luminance correction unit and the second luminance correction unit as shown in FIG. And a driving circuit for driving.

As shown in FIG. 2, the lighting means of the present invention comprises a first brightness correction means and a second brightness correction means connected in multiple stages to a reference constant current source.
Is connected to the drive circuit. The driving circuit is constituted by a gradation driver and a scanning driver, and can turn on the LED by switching. The first luminance correction means is a panel-to-panel correction means for commonly determining the mutual output ratio between the LED display units with respect to the total current output as the input gradation data, L
LE configured by connecting multiple ED display units
A luminance correction unit for adjusting the output level of the entire D display, and a gamma correction unit for commonly adjusting the output level in accordance with the saturation luminance. It should be noted that the difference in characteristics due to the semiconductor material and structure of each of the RGB LED chips is represented by R
It is also possible to suitably use a coarse correction means for performing common correction for each GB. The second brightness correction means is a dot brightness correction means for individually adjusting brightness for each LED.

The first luminance correction means is formed in a plurality of layers for commonly adjusting the output level to the LED, and is connected from the reference constant current source in the above-described order. The reference constant current supplied from the reference constant current source is supplied to the LED via the second brightness correction means.
The first brightness correction means individually adjusts the dot brightness of each LED constituting the display unit and outputs the adjusted brightness to the LED. The output value from the reference constant current source is determined by the first luminance correction means formed in multiple stages.
Can be set in common. By performing dot brightness correction for each channel by the second brightness correction means, the output value corrected from the reference constant current source becomes a constant current output for each LED while maintaining the ratio of each correction data.

The dot luminance correcting means as the second luminance correcting means is provided with an operation circuit corresponding to each LED of each column or row arranged in a dot matrix.
The dot brightness correction means includes a current mirror circuit or the like, as shown in FIG. 3, and a constant current output unit which receives an output from a common reference constant current source and determines an output value. It consists of a corresponding SW circuit section.
As shown in FIG. 3 represented by 8ch to 16ch, it can be constituted by a plurality of constant current output circuits. In the correction data, the least significant bit (LSB) to the most significant bit (MSB)
The configuration is such that the ratio of the current output matches the bit according to the bit of B). The divided constant current outputs are finally united into one through the SW circuit unit to become a constant current output for one channel. The constant current output divided in the channel according to each bit value of the dot luminance correction data is turned on / off, and
Output value is determined. A similar relationship operates between a plurality of output channels.

The constant current output for one channel is divided into more than the number of bits of the dot luminance correction data, and the current value output by the input from the same reference constant current source is output corresponding to the bit of the correction data. Is done. A similar relationship operates between a plurality of output channels. That is, the input correction data is processed using an 8-bit arithmetic circuit, and a switching element connected to the plurality of current mirror circuits is driven to obtain a constant current corresponding to the correction data.

On the other hand, the first correction means differs in the number of bits according to various correction characteristics, but can be configured in almost the same manner. The first luminance correction means is, for example, an inter-panel correction means is an 8-bit correction means,
The luminance correction means of the entire display is composed of 8-bit correction means and the gamma correction means is composed of 8-bit correction means.
As the first luminance correction means, the amount of constant current supplied for each type of RGB LEDs is adjusted in common.

The inter-panel correction means adjusts the brightness between the panels constituting the LED display with the output value of the reference constant current source as a reference (100%). Processing is performed using an 8-bit arithmetic circuit, and a switching element connected to the current mirror circuit is driven.

Further, the luminance correction adjusting means adjusts the output level (constant current) of the entire LED display based on the constant current in which the luminance between the LED display panels is adjusted. An R LED is shown as an example. The value of the reference constant current source is set to the upper limit (100%).
LED between individual ratios divided by 8 bits between%
Adjust the brightness of. Similarly with GB, LED
Brightness variation between display panels can be corrected. Next, based on the adjusted constant current, the constant current amount of each LED is commonly adjusted by a correction unit that corrects the luminance of the entire LED display as one of the first luminance correction units.

Subsequently, based on the adjusted constant current,
As one of the first luminance correction means composed of multiple stages, each of the L-values is corrected by a correction value corresponding to the saturation luminance by a gamma correction means.
Adjust the constant current of the ED. Finally, the second brightness correction means can adjust the current value supplied to the LED at individual intervals divided by 8 bits with the limited maximum current value as a reference (100%), so that the dot brightness correction means can be adjusted. Is configured. Thus, the constant current amount corrected based on each correction value is output from the constant current output circuit to the drive driver via the first brightness correction means. Therefore, the correction is performed by another correction unit while maintaining the ratio of the correction value for the dot luminance correction. That is, the constant current values corrected by the correction means have an integration relationship that maintains the correction ratio. Therefore, each correction is performed while maintaining the luminance ratio of the corrected dot luminance of each LED. Also,
Since it does not simultaneously perform a plurality of luminances, an arithmetic circuit having a small number of bits can be used, so that the circuit configuration can be extremely simplified and the cost can be reduced.

FIG. 5 shows an example of the corrected output of the present invention.
FIG. 5 shows an output example of eight light-emitting diodes connected in one column in one type of LED constituting a dot arranged in a dot matrix. For simplicity, an example is shown in which only the inter-panel correction as the first luminance correction means and only the dot luminance correction means as the second luminance correction means. When the current supplied to each LED is 100%, no correction is performed. Here, of the power supplied to each LED, the dot current correction for each LED can be performed by reducing the total current amount corresponding to the dotted arrow or increasing the total current amount corresponding to the correction. Specifically, a 100% current flows through the output 1 LED without performing dot correction. At the output 2, a current corresponding to 90% before the correction flows by the dot luminance correction. At the output 3, a current corresponding to 80% before the correction flows by the dot luminance correction. In this manner, dot luminance correction is similarly performed from output 1 to output 16. Next, the current corresponding to the solid arrow is reduced by the inter-panel luminance correction, or is increased to the total current amount corresponding to the correction. This LED
In the display unit, half output is suppressed as the inter-panel luminance correction. Specifically, dot brightness correction for the dotted arrow is performed by the second brightness correction unit. In addition, the inter-panel luminance correction for the solid arrow is performed by the first luminance correction unit. As a result, the output 1 is suppressed to 50% of the output before each correction. A shaded current flows as the corrected output value. On the other hand, in the output 2, the current that has become 90% due to the dot luminance correction is suppressed to half, that is, 45% by the inter-panel luminance correction. The output 3 is suppressed to 40% of the output before each correction. In this way, the same amount of current as the inter-panel luminance correction of output 1 is not similarly reduced from output 2, output 3... Output 8, but the rate at which each LED whose dot luminance has been corrected emits light is maintained. The luminance correction between panels is performed as it is. Therefore, even if the dot brightness correction and the inter-panel brightness correction are performed, the correction can be performed accurately and easily at the same time. Therefore, it is possible to provide an LED display unit or the like that does not need to perform dot luminance correction again after the inter-panel luminance correction and can obtain accurate light emission from input data. Similarly, coarse correction, gamma correction, and the like can be performed. Note that dot luminance correction can be performed after panel-to-panel luminance correction as long as each luminance correction ratio can be maintained.

The correction data input to the first and second luminance correction means may be stored in a storage means such as a ROM or a RAM in advance even if the correction data is configured to be externally input. Can also. As an example of correction data input to the brightness correction means from the outside, each correction data is transferred from a controller arranged outside the LED display unit and is sequentially transferred to an adjacent correction register. Similarly, the RGB gradation data is input to the respective constant current drive circuits. In addition, the next L
The ED display unit transfers and outputs gradation data and correction data. The gradation data register is provided for each LED constituting the column. The grayscale data is sequentially shifted by the shift register in synchronization with the transfer clock (not shown) for each column.
Transferred as D lighting data. The transferred data of each column is latched and held by a latch circuit by a latch signal.

A count clock is input from a circuit for generating a gray scale reference clock to the gray scale clock counter, and each held display data value is compared with a counter output value by a comparator circuit. When the value of the display data matches the count output value, a matching signal for turning off the LED is output to each LE.
Occurs every D.

When the BLANK signal is released, the drivers of the LEDs in each column are turned on, and the LEDs are maintained in a lit state. By the time the next BLANK signal arrives, the grayscale drivers in that column are all turned off on the basis of the above-mentioned coincidence signal to be turned off.
That is, between the BLANK signals, pulses representing display data corrected by the first and second brightness correction means for each LED synchronized with the counter output are output. The constant current output is supplied to the LED as display data corrected by the first correction means and the plurality of second correction means. When a plurality of LED display units are electrically connected, the above operation is performed for each LED display unit, and a desired image can be obtained.

[0034]

【The invention's effect】 [Brief description of the drawings]

FIG. 1 shows a schematic block diagram inside an LED display unit of the present invention.

FIG. 2 is a schematic diagram showing a rate of luminance correction by first and second luminance correction means of the present invention.

FIG. 3 is a schematic circuit configuration diagram showing first and multi-stage second luminance correction means of the present invention.

FIG. 4 shows a block diagram of lighting means in the LED display unit of the present invention.

FIG. 5 is a schematic diagram showing an example of a current value corrected by the first and second brightness correction units of the present invention.

FIG. 6 is a schematic perspective view showing an LED display unit of the present invention.

[Explanation of symbols]

600 LED display unit 601 Chip type LED 602 LED display panel in which chip type LEDs are arranged in a dot matrix 603 Board on which a driving circuit for driving each LED is arranged on the back surface 604 ... pin

Claims (3)

[Claims] 1. An LED display panel in which LEDs are arranged in a dot matrix form, a gradation driver for supplying a lighting signal to each LED corresponding to each column or row of the LED display panel, and a gradation driver for each row or column. With a scan driver that scans the corresponding individual LEDs,
An LED display unit having lighting means for dynamically driving each of the LEDs in accordance with the input gradation data, wherein the lighting means is connected to a plurality of columns or rows in such a manner as to correct the output level to the LEDs in common for each column or row. And a correction value from the second brightness correction means for adjusting the output level of each LED corresponding to each column or row of the LED display panel. An LED display unit which adjusts lighting of an LED by supplying a lighting signal to a gradation driver. 2. The method according to claim 1, wherein the second brightness correction means is a dot brightness correction means, and the plurality of first brightness correction means are inter-panel correction means for adjusting mutual output levels between LED display panels. At least two selected from coarse correction adjustment means for adjusting the output level corresponding to the LED chip, luminance correction adjustment means for adjusting the output level of the entire LED display, and gamma correction means for adjusting the output level corresponding to the saturation luminance. The LED display unit according to claim 1, wherein the LED display unit comprises a combination of species. 3. The lighting device according to claim 1, wherein the lighting unit switches a gradation driver in accordance with the gradation data and controls a lighting time of each LED to adjust luminance. 2. The LED display unit according to claim 1, wherein the second brightness correction means adjusts the brightness of each LED by sequentially changing the constant current from the reference constant current source based on each correction means.