JP3125711B2 - LED display unit and LED constant current driver circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED driver circuit and an LED display unit which can display character information and video information by inputting display data from the outside. The present invention relates to an LED driver circuit, an LED display unit, and the like, in which luminance variation between units is small.

[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. In this LED display unit, one full-color dot can be constituted by a 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 so close to each other that color mixing occurs. The LED display unit having this structure can change the emission color by adjusting the brightness of RGB. For example, when all the light emitting diodes are turned on, white light can be displayed. When the red and blue light emitting diodes are turned on, magenta, yellow in red and green, and cyan in green and blue. Furthermore, the brightness of each light emitting diode can be adjusted to provide various light emitting colors.

In the LED display unit, the light emitting diodes are turned on at regular intervals by lighting means. When the lighting circuit adjusts the time within a certain period in which the light emitting diode is turned on, the brightness perceived by the eyes, that is, the substantial light emission luminance of the light emitting diode can be adjusted. One of the light emitting diodes within a certain period
The longer the lighting time, the brighter the eyes. Conversely, if the lighting time is shortened, it will appear dark.

[0004] The lighting means calculates the lighting time of the light emitting diode based on the input gradation data. In order to specify the lighting time of the light emitting diode, the lighting circuit includes a pulse width modulation circuit that outputs a pulse having a time width corresponding to the input gradation data and / or a pulse width modulation circuit that has a height corresponding to the input gradation data. An amplitude modulation circuit for outputting a pulse is provided. The output pulse of the pulse width modulation circuit or the pulse amplitude modulation circuit is input to an LED drive circuit for lighting the light emitting diode of the lighting means, and the pulse signal causes the LED drive circuit to switch to light the light emitting diode. In the pulse width modulation circuit, for example, in an LED drive circuit, the input pulse is “H”.
The light-emitting diode is turned on at the time of "high" and turned off at the time of "Low".

[0005] The gradation data input to the pulse width modulation circuit or the pulse amplitude value modulation circuit is information for determining the brightness of the light emitting diode. The pulse width modulation circuit increases the time width of the output pulse as the input grayscale data becomes brighter. By increasing the time width of the output pulse, the lighting time of the light emitting diode can be increased in proportion to the gradation data. Similarly, the pulse amplitude value modulation circuit, as the input grayscale data becomes brighter,
Increase the height of the output pulse. The height of the output pulse can be increased in proportion to the gradation data. A light emitting diode having a long lighting time and a high lighting luminance feels bright to the eyes, so that the light emitting diode can be brightly lit in proportion to the gradation data. The RGB light emitting diodes are similarly driven, and the brightness is adjusted in proportion to the input gradation data. An LED display that adjusts the brightness of each of the RGB LEDs in proportion to the gradation data can display full color.

[0006] LED display units in which light emitting diodes are arranged in a dot matrix form are 16 units in length,
Even one unit using 16 horizontal light emitting diodes has R
256 × 3 light emitting diodes are arranged for each of GB. In a display device in which a plurality of LED display units having such a configuration are electrically connected, variation in luminance among the light emitting diodes poses a problem. In order to prevent these adverse effects, the light emitting diodes of each emission color can be level-selected by luminance. However, uniforming the total brightness of each light emitting diode constituting the display device causes a significant increase in cost. Further, when the brightness is further finely adjusted by using the selected light emitting diodes according to the gradation data, the uneven brightness becomes more noticeable. Therefore, it becomes necessary to select light emitting diodes at a finer level.

[0007] 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 a storage device electrically connected to a driving IC for driving each light emitting diode.
The storage device includes, for example, a nonvolatile ROM (Read Only Mem
ory) is used to hold the luminance correction data. Correction can be performed by sequentially transferring correction data from the storage device to the drive IC in accordance with the lighting operation of each display line of the LED display. In the dot brightness correction, the dot brightness variation can be reduced by performing the correction by determining the adjustment amount for each current output to each light emitting diode.

As described above, when the luminance variation of each light emitting diode is reduced, the variation of the light emission luminance of each LED display unit becomes conspicuous. If there is a variation in surface luminance between the LED display units, unevenness of (surface) luminance such as a tile shape is identified, and the quality of the LED display is greatly reduced. The surface luminance between such LED display units can be electrically corrected similarly to the dot luminance. That is, the lighting means of the LED display unit has a current output section for supplying a current to each light emitting diode at a time. In the surface luminance correction, it is conceivable to perform the surface luminance correction by adjusting the current output unit by the common amount for each LED display unit. As described above, by adjusting the amount of current output to each light emitting diode and the like, correction of surface luminance can be realized.

[0009]

However, if the surface luminance correction and the dot luminance correction are simply performed simultaneously, a new variation or the like is inevitably generated.
Specifically, as shown in FIG. 5, the amplitude value, which is the pulse height of the current output to each light emitting diode, is reduced to a required level amount in accordance with the variation in dot luminance to reduce the variation, thereby correcting the dot luminance. I do. Further, the total current output of the lighting means is reduced by a common amount for each LED display unit for surface luminance correction. In this case, even if the variation of the dot brightness of each light emitting diode is corrected, the correction balance between the dots is lost by performing the surface brightness correction, and the resetting is performed.

On the other hand, as shown in FIG. 6, there is a method of changing the maximum number of gradations of the display data according to the correction amount of the dot luminance within the gradation expression range of the display data as a means of luminance correction by adjusting the current pulse width. is there. FIG. 6 shows an example in which there are 256 gradations when no correction is performed. In the case of this method, there is a problem that the final gradation expression range after luminance adjustment is narrowed. When the final gradation expression range is narrowed, the gradation expression step becomes apparent. Therefore, when the LED display is driven, the color reproducibility is deteriorated and the display quality is restricted.

As shown in FIG. 7, a method of increasing the number of display data bits and increasing or decreasing the data in accordance with the dot luminance correction amount while maintaining the number of display gradations within the range of the maximum number of gradations is also conceivable. However, in this method as well, if the common output of each unit is reduced as the surface luminance correction to the current output of each light emitting diode, the surface luminance correction is performed even if the dot luminance variation of each light emitting diode is corrected. Is lost, and the setting is reset. Therefore, an object of the present invention is to provide an LED driver unit, an LED display unit, and the like that can accurately and easily perform dot luminance correction and surface luminance correction.

[0012]

SUMMARY OF THE INVENTION The present invention is connected to an LED display panel and changes a pulse width according to input data.
L having lighting means for causing the LED to emit light through the adjustment circuit
It relates to an ED display unit. In particular, the lighting means of the present invention, the first luminance correction means for adjusting the current values of the individual to the output level corresponding to each dot of the LED display panel, the output level of each Dots were maintained at the same ratio A second brightness correction means for adjusting the output level with the current amplitude value in common for each dot as it is .

In the LED display unit according to the second aspect of the present invention, the first luminance correction means is weighted by a dot luminance correction register.

According to a third aspect of the present invention, there is provided an LED constant current driver circuit which increases / decreases a constant current based on surface luminance correction data which can be externally input to a reference constant current source determined by an external resistor. An adjustment circuit, a current mirror circuit for distributing the constant current of which the surface luminance has been corrected to each dot composed of LEDs, and a constant current output value of each dot based on dot correction data that can be input from the outside. And a circuit for correcting the

[0015]

The configuration example of the present invention maintains the light emission ratio (the same ratio as the output level) for each dot (for each LED) adjusted by the dot brightness correction means. While maintaining the light emission ratio for each dot instead of the dot correction amount for each dot, the LED
The output level of each display unit is corrected by the surface luminance correcting means. As a result, the surface luminance can be corrected without the output level of each dot adjusted once being deviated. Therefore, the dot luminance and the surface luminance can be corrected more accurately and easily at the same time.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The inventor of the present invention
It has been found that the luminance variation is greatly reduced by the specific dot luminance and surface luminance correction, and the present invention has been accomplished.

According to the present invention, the surface luminance is corrected by the second luminance correcting unit while the ratio of the data subjected to the dot luminance correction by the first luminance correcting unit is maintained. That is, another correction can be performed while maintaining the correction ratio instead of the correction amount. Therefore, the ratio after the correction by the surface luminance correction does not change. As a result, even if the dot luminance correction and the surface luminance correction are performed, each LE maintaining the respective correction ratio is maintained.
Light emission for each D can be performed.

FIG. 2 shows an output example for explaining the output correction of the present invention.
Shown in FIG. 2 shows an output example of 16 light emitting diodes connected in one column in one type of LED constituting a dot arranged in a dot matrix. Each LED
Is 100% when 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, for the output 1 LED, 100
% Current flows. 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 surface luminance correction, or the current is increased to the total current amount corresponding to the correction. In this LED display unit, the output is suppressed to half as the surface luminance correction. Specifically, dot brightness correction for the dotted arrow is performed by the first brightness correction means. Further, the second brightness correction unit performs surface brightness correction for the solid arrow. 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 surface luminance correction. The output 3 is suppressed to 40% of the output before each correction. In this way, the same amount of current as that for the surface luminance correction of output 1 is not similarly reduced from output 2, output 3... Output 16, but the ratio of light emission of each LED whose dot luminance has been corrected is maintained. Performs surface luminance correction. Therefore, even if the dot luminance correction and the surface luminance correction are performed, the corrections can be performed accurately and simply 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 surface luminance correction or the like and can obtain accurate light emission from input data. Note that dot brightness correction can be performed after surface brightness correction as long as each brightness correction ratio can be maintained.

[0019]

An embodiment of the present invention will be described below with reference to the drawings. It goes without saying that the present invention is not limited to only specific examples. Multicolor LE
FIG. 1 shows a D display unit.

FIG. 1 shows RGB arranged close to each other.
(Red-based 106, Green-based 107, Blue-based 108) LEDs and LED lighting means for lighting the LEDs of the respective colors. The LED emits light of RGB color 3
The pieces are arranged close to each other so that mixed color light emission is possible.
The LEDs for each LED display constitute one dot by three RGB, and are arranged in a 16 × 16 matrix, for example. This LED display unit is RG
A dynamic driving method is adopted in which the brightness is adjusted by the emission time of the three LEDs emitting B light to display one full-color dot. The lighting means includes a dot brightness correction means 101 for correcting dot brightness, and a surface brightness correction means 1 for correcting surface brightness.
02, and a pulse width modulation circuit 103 that creates a pulse obtained by correcting display data based on each correction value, and a driver that drives each LED with an output from the pulse width modulation circuit. The driver drives the gradation driver 104 based on the corrected data output, and scans the
Is turned on as desired.

FIG. 3 shows an example of an internal block diagram of the LED constant current driver constituting the lighting means. Each display data is
Each of the RGB display data is input to each constant current drive circuit. The display data is sequentially transferred and output to the next horizontal row. The display data register is provided for each L constituting a column.
There is ED part. The display data is sequentially transferred as LED lighting data for each column by a shift register in synchronization with a transfer clock (not shown). The data in each column transferred is
The signal is latched and held by the latch circuit by the latch signal.

On the other hand, a count clock from a circuit for generating a gray scale reference clock is input to a 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 match signal for turning off the LED is generated for each LED.

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, a current representing the dot luminance of each LED and the display data corrected for the surface luminance synchronized with the counter output is output.

According to the present invention, a reference constant current source for surface luminance correction for determining a common output ratio for each LED display unit with respect to a total current output as input gradation data, and an output of the reference constant current source. It has a constant current output circuit for dot brightness correction corresponding to each current output on a one-to-one basis. Here, the surface luminance correction data is configured to be input from the outside. The surface luminance correction data is transferred from the outside and sequentially transferred to an adjacent surface luminance correction register. Further, the output of the reference constant current source that has been subjected to constant current adjustment based on the surface luminance data from the surface luminance correction register is input to the constant current circuit for dot luminance correction data.
Further, the dot luminance correction data is input to the dot luminance correction register and is sequentially transferred to the adjacent dot luminance correction data.

The dot luminance correction circuit is constituted by a current mirror circuit or the like, and has a constant current output section whose output value is determined by receiving an output from a common reference constant current source, and a SW circuit section corresponding to each bit of the dot luminance correction data. Consisting of It can be composed of a plurality of constant current output circuits as shown in FIG. The constant current output for one channel is
A constant current output circuit is divided into more than the number of bits of the dot luminance correction data, and a current value output by an input from the same reference constant current source is weighted in accordance with the correction data bit.

The least significant bit (LSB) of the correction data
, The ratio of the current output according to the bit of the most significant bit (MSB) matches the weight of the bit. The weighted and divided constant current outputs are finally united into one and become a constant current output for one channel. Since the weighted divided constant current outputs use a common reference constant current source, the output current value can be increased or decreased at the same ratio while maintaining the weighting relationship. C according to each bit value of the dot luminance correction data
The constant current output divided in h turns on / off, and the output value of ch is determined. As a result, the constant current output circuits in one channel are combined into one before the output terminal and output to the final output stage as a corrected constant current value. The same operation is performed between a plurality of output channels, and each constant current value can be increased or decreased in accordance with the input of the common reference constant current source while maintaining the ratio between the respective channels after the set dot luminance correction. . On the other hand, the output value of the reference constant current source is determined by the surface brightness correction data.
h can be commonly set. The constant current output for each LED is reflected on the dot luminance correction data and the surface luminance correction data. The constant current output is turned off by the coincidence signal from the comparator. Therefore, the LEDs in each row can be dynamically driven according to the corrected display data.

The LED is turned on as display data corrected for dot brightness and surface brightness by the constant current output. When a plurality of LED display units are electrically connected, a display device can be similarly configured. In a display device in which a plurality of LED display units are electrically connected, the above operation is performed for each LED display unit to obtain a desired image.

[0028]

The LED display unit and the like according to the present invention can correct the current amplitude value at the same ratio of the entire current output while maintaining the luminance variation correction ratio between dots. Therefore, the dot luminance variation correction and the surface luminance variation correction can be both more accurately, easily, and accurately performed. In particular, by using the LED display unit according to the first aspect of the present invention, it is possible to reproduce display data obtained by performing dot luminance correction and surface luminance correction accurately and simply.

With the LED display unit according to the second aspect of the present invention, the dot luminance correction ratio can be maintained more easily.

By using the LED constant current driver circuit according to the third aspect of the present invention, it is possible to reproduce display data in which dot luminance correction and surface luminance correction have been performed accurately and simply.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an LED display unit used in the present invention.

FIG. 2 is an explanatory diagram illustrating output correction according to the present invention.

FIG. 3 is a block diagram of a constant current drive circuit according to the present invention.

FIG. 4 is a functional block diagram illustrating weighting of dot luminance correction according to the present invention.

FIG. 5 is an explanatory diagram showing output correction by current amplitude adjustment shown for comparison with the present invention.

FIG. 6 is an explanatory diagram showing output correction by current pulse width adjustment shown for comparison with the present invention.

FIG. 7 is an explanatory diagram showing output correction by enlarging the number of data bits for comparison with the present invention.

[Explanation of symbols]

 101: dot brightness correction means 102: surface brightness correction means 103: pulse width modulation circuit 104: gradation driver 105: scanning driver 106: red LED forming one dot 107: Green LED constituting one dot 108: Blue LED constituting one dot

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G09G 3/32 G09G 3/20

Claims (3)

(57) [Claims] 1. An LED display panel and the LED
It is connected to the display panel Pal according to the input data
There is a lighting means for emitting an LED through a width modulation circuit.
An LED display unit, comprising: a first brightness correction means for individually adjusting a current value of an output level corresponding to each dot of the LED display panel;
If, LED display units characterized by having a second luminance correction means for adjust a current amplitude value output levels the output level to each dot commonly maintained at the same ratio for each Dots. 2. The LED display unit according to claim 1, wherein said first brightness correction means is weighted by a dot brightness correction register. 3. An LED constant current driver circuit capable of driving a plurality of LEDs, wherein a reference constant current source determined by an external resistor is increased or decreased based on surface luminance correction data which can be input from outside. A constant current adjustment circuit, a current mirror circuit for distributing a constant current corrected for surface luminance to each dot composed of LEDs, and a constant current output value of each dot based on dot correction data that can be input from outside LE having a circuit for individually correcting
D constant current driver circuit.