JPH09265273A - Display device and driving method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust surface luminances of the whole display device while having a multilevel displaying function in a pixel unit by multiplying surface luminance adjustment data to multilevel input data and controlling the lighting cumulative time of an LED by the calculation result. SOLUTION: Decoder for X line display 12 controls a transformation RAM 20 so as to determine an LED lighting cumulative time in accordance with a data quantity from write data to be stored in the X-Y transformation RAM 20. Moreover, the decoder 12 controls the output circuit of the RAM 20 to output a signal having the LED lighting cumulative time as a pulse width with one output line among 16 lines of output lines according to respective X lines X1∼X16. Further, a counter 13' transmits a timing signal to a decoder for X line display 12 so as to perform the changeing over of the 16 lines of output lines in synchronization with the can clock from a scan clock terminal 46 and the horizontal synchronizing signal from a horizontal synchronizing signal terminal 44. Thus, the surface luminance adjusting function of a low-speed display clock which has the multilevel displaying function of the pixel unit and which is of high accuracy and is miniaturized is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to surface luminance of a display device having gradation in pixel units effective for displaying indoor and outdoor information (hereinafter, "surface luminance" means luminance of a display surface of the display device).
It is about adjustment.

[0002]

2. Description of the Related Art In recent years, in the field of indoor and outdoor information display, there is a demand for a light emitting diode (hereinafter, light emitting diode is referred to as LED) display device having gradation in each pixel. Since the LEDs constituting the LED display device have different characteristics between the current and the brightness for each individual product, these LEDs are selected in advance in a specific brightness range under certain conditions, and a large number of these LEDs are selected.
Are assembled into one LED display device. Therefore, when a large screen is configured with LED display devices, display devices having a plurality of surface luminances are mixed, and the variation in the brightness is conspicuous among the LED display devices. For this reason, conventionally, it is necessary to have a function of adjusting the surface brightness for each LED display device.

A conventional LED display device will be described below. Generally, there are a dynamic lighting system and a static lighting system as a lighting drive system of the LED display device.
Since only the pulse lighting and the DC lighting are different, the dynamic lighting method will be described here.

FIG. 6 is a perspective view of a conventional general LED display device viewed from the front and the back. The LED display device main body includes a reflector 22, an LED display substrate 23, and a drive circuit board 2.
It consists of 6. The drive circuit board 26 has a mounting boss 24, a signal connector 27, a power connector 28, and a surface brightness adjusting volume resistor 19. A large number of LEDs 21 are inserted in a matrix on the LED display board 23.
To connect the display board 23 and the drive circuit board 26, 16 pins 29 are used on each of the two sides of each board.

A conventional general LE having the above structure
The operation of the surface brightness adjusting function of the D display device will be described below. The explanation is for the sake of simplification 16 × 16 in single color display
Do this with a dot matrix LED display.

At present, in order to change the surface brightness of the LED display device, a method of controlling the lighting time of the LED to be long or short within the display time of one Y line (duty variable method), L
A method of changing the current value flowing in the ED (current variable method),
Alternatively, there is a method of changing display / non-display in display screen units (frame thinning method).

FIG. 8 shows a conventional example of a block system diagram of the variable duty system, and FIG. 9 shows the operation. This will be described below with reference to FIGS. 8 and 9. The variable duty method is the LED display unit 1, X (X1, X2, ..., X16) line 2, Y
(Y1, Y2, ..., Y16) line 3, current limiting resistors (R1, R2, ..., R16) 4, X line driver 5, Y line driver 7, shift register / latch 9, Y line decoder 10. And pulse duty circuit 1
6. The LED display unit 1 is X-shaped as shown in FIG.
1, X2, ..., X16 line and Y1, Y2, ...
The LEDs are arranged in matrix between the Y16 lines. The X1 ..., X16 lines are connected to the X line driver 5 via the current limiting resistors R1, R2 ,. The X line driver 5 is controlled by the shift register / latch circuit 9 and the pulse duty circuit 16. Y1 ..., Y16 line is Y
It is connected to the line driver 7. The Y line driver 7 is controlled by the output of the Y line decoder 10. FIG. 9 (a)
Is a drive pulse waveform of the Y1 line, FIG. 9B is a drive pulse waveform of the Y2 line, and FIG. 9C is an X line erase signal.

Next, the shift register / latch 9 is in a state in which all the LEDs constituting the LED display device can be turned on, that is, the output of the shift register / latch 9 is X1, X2,
The description will be made assuming that the level of all X16 lines is "L". Further, in order to explain the surface brightness adjusting function in an easy-to-understand manner, the following description will be given with the Y1 line at the "H" level.

At this time, the L connected to the Y1 line
The ED can be turned on by the X line erase signal "
The period of L "level, that is, the period of t3-t1. On the other hand, the output of the X line driver is the pulse duty circuit 1
6 changes in synchronization with the output of 6. When the surface brightness adjustment volume resistor 19 is maximum (minimum resistance value), the output of the duty circuit 16 becomes the signal shown in (d), the waveform of the X1 line becomes (e), and it is connected to the X1 line. The LED can be turned on during the period of t3-t1. When the scale of the surface brightness adjustment volume resistor is minimum (resistance value is maximum), the output of the pulse duty circuit becomes the signal shown in (f), the waveform of the X1 line becomes (g), and it is connected to the X1 line. It is during the period of t3 to t2 that the LED can be turned on. When the scale of the surface brightness adjustment volume resistor is changed from maximum to minimum, the pulse duty circuit output changes from "H"
The time to change to L ″ accordingly changes from t1 to t2. The LED 211 in FIG. 7 is actually turned on at Y1.
This is a period in which the line is "H" and the X1 line is "L". From this, by changing the scale of the surface brightness adjusting volume resistor, the lighting time of the LED 211 in FIG. 7 can be changed. This operation is for all LEs that make up the LED display device.
The surface brightness can be adjusted because the process is performed simultaneously with D. A conventional method for controlling the brightness of LEDs arranged in a matrix by controlling the duty of a pulse waveform is proposed in, for example, Japanese Patent Laid-Open No. 63-287997.

As a method different from such a conventional example, a conventional variable current method is also known. FIG. 10 shows a block diagram of the conventional example, and FIG. 11 shows the operation.

A description will be given below with reference to FIGS. 10 and 11. The current variable method is different from the duty variable method in the following points. In the current variable system, the X line constant current driver 6 is used instead of the duty variable system X line driver 5. Further, the variable duty type pulse duty circuit 16 of FIG. 8 is omitted in the variable current type of FIG. The other configuration is the same as that of the variable duty method.

The LE connected to the Y1 line in FIG.
It is the X line erase signal “D” that can be turned on.
The LED connected to the X1 line can be turned on within the L "level period and the period from t2 to t1. Like the Y1 line, the LED can be turned on within the" L "level period of the X line erase signal. During the period from t2 to t1, when the scale of the surface brightness adjustment volume resistor is maximum (minimum resistance value), X
The waveform of the 1st line becomes the voltage level a (V) shown in (d), and when the surface brightness adjustment volume resistor is minimum (the resistance value is maximum), the waveform of the X1 line becomes the voltage level b ((e). V). When the surface brightness adjustment volume resistor changes from the maximum to the minimum, the voltage level of the X1 line changes from a (V) to b (V) according to the change of the surface brightness adjustment volume resistor scale. The current value flowing through the LED 211 changes according to the change of the scale of the volume resistor. In the variable duty method of the above-mentioned Japanese Patent Laid-Open Publication, the lighting time is controlled with a constant current flowing through the LED, but in the variable current method, the lighting time does not change.
The current flowing through D changes. Since this operation is performed simultaneously for all the LEDs that constitute the LED display device, the surface brightness can be adjusted. A method of adjusting the light emission brightness of the LEDs by changing the drive current for the LEDs arranged in a matrix is described in, for example, Japanese Utility Model Application Laid-Open No. 5-27789.

As a conventional example different from the above, a frame thinning method is also known. FIG. 12 shows a block diagram of the conventional example, and FIG. 13 shows the operation.

A description will be given below with reference to FIGS. 12 and 13. The frame thinning method differs from the duty variable method in the following points. In the frame thinning method, the pulse duty circuit 16 of the variable duty method of FIG. 8 is replaced with a frame control circuit 17.

The LE connected to the Y1 line in FIG.
The state in which D can be turned on is during the period from t1 to t0 when the output of the frame control circuit 17 is "H". At the time when one screen is completed, all Y lines (Y1, ..., Y1
6) ends the output once, the period is t2-t0.
Period. When the scale of the surface brightness adjusting volume resistor is maximum, the output waveform of the frame control circuit 17 becomes (d) and all the screens are displayed. When the scale of the surface brightness adjusting volume resistor is medium (surface brightness is 50%), the output waveform of the frame control circuit becomes (i), and display / non-display is repeated for each screen. That is, the first screen (t2-t0
During the period), and the next screen (period between t3 and t2) is not illuminated. When the scale of the surface brightness adjustment volume resistor changes from the maximum to the minimum, the output waveform of the frame control circuit changes according to the change of the surface brightness adjustment volume resistor scale, and the display / non-display ratio changes in screen units. . The surface brightness is adjusted by changing the display / non-display ratio.

[0016]

In each of the variable duty method, the variable current method, and the frame thinning method described in the above "Prior Art", the data given to each pixel is "bright" and "dark". Is a binary value, and is not a multivalued one that can display gradation. On the other hand, as a display device capable of displaying gradation in pixel units, for example, Japanese Patent Laid-Open No. 5-265
There is a display device proposed in the 399 publication. However, Japanese Patent Laid-Open No. 5-265399 does not show a method for adjusting the surface brightness of the entire display device.

Therefore, it is desired to construct a display device which has a gradation display function for each pixel and which can adjust the surface luminance of the entire display device.

However, there are the following problems to realize gradation display in pixel units with the conventional configurations.

In the variable duty system, the unit of the lighting time of the LED constituting the LED display device is shorter by a multiple corresponding to the number of gradations than that of the conventional LED display device having no gradation display (1 in case of 256 gradations). / 256)), and it is difficult to obtain stability and accuracy of operation. When a general-purpose constant current driver IC is adopted in the variable current system, there is a difficulty in downsizing the LED display device, and it is necessary to limit the selection of IC parts. In the frame thinning method, it is necessary to increase the speed of the display clock signal in order to improve the accuracy of brightness adjustment (accuracy of 1/32, that is, 3.1%).
In the case of the surface brightness adjustment resolution of (3), there is a problem that the display clock needs to be 32 times faster than in a system without a gradation control function).

The present invention solves the problems of each method in the above-mentioned prior art. In a display device having a gradation display function for each pixel, a high precision, miniaturization, and a surface brightness adjusting function of low speed display clock operation are provided. Aim to achieve.

[0021]

In a display device of the present invention, a display section in which pixels are arranged in a matrix, a multiplier for multiplying gradation input data and surface brightness adjustment data,
A control means for controlling the light emission (lighting) accumulated time of each pixel of the display section by the calculation result of the multiplier is provided, the gradation of each pixel is controlled by the gradation input data, and the surface brightness adjustment data is controlled by the surface brightness adjustment data. The surface brightness of the entire display device is adjusted.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A display device according to a first aspect of the present invention includes a display section in which display pixels are arranged in a matrix, a multiplier for multiplying gradation input data and surface brightness adjustment data, and Control means for controlling the light emission accumulated time of each display pixel of the display section by the calculation result of the multiplier, controlling the gradation of each display pixel by the gradation input data, and displaying by the surface brightness adjustment data. The feature is that the surface brightness of the entire device is adjusted.

A display device according to a second aspect of the present invention is the display device according to the first aspect, characterized in that the light emitting element forming the display pixel is a light emitting diode.

A display device according to a third aspect of the present invention is the display device according to the first aspect, wherein a level detection block for detecting that the voltage obtained from the surface tone adjustment volume resistor is at a certain level or higher, An edge detection block that controls the start and stop of the counter at the next stage by detecting the rising and falling edges of this level detection, a counter block that counts the number of clocks from the start to the stop, and its count data temporarily. It is characterized in that it is composed of a latch block held in.

A display device according to a fourth aspect of the present invention is the display device according to the first aspect, wherein the light emission pattern on the display / non-display time axis of the display pixel is 1 depending on the change amount of the surface luminance adjustment data. It is characterized in that it has a function of changing the brightness of the entire display surface while maintaining the gradation operation for each display pixel unit by repeating the control at least twice within the display screen.

A display device driving method according to a fifth aspect of the present invention is a display device having a display section in which display pixels are arranged in a matrix for display control by an X line input terminal and a Y line input terminal. The multiplication output of the digital gradation input data corresponding to the display pixel and the digital surface brightness adjustment data of the brightness of the entire display surface is used as the display input data for the X
It is characterized by inputting to the line input terminal.

According to a sixth aspect of the present invention, there is provided a display device driving method according to the fifth aspect, wherein 1 is added to the display input data.

According to a seventh aspect of the present invention, there is provided a display device driving method according to the fifth aspect, wherein display input data is dispersed in a predetermined unit within a switching cycle time range of Y line input data. Is characterized by.

According to the eighth aspect of the present invention, there is provided a display device driving method according to the seventh aspect, wherein a predetermined unit corresponds to an X line erase signal.

[0030]

Embodiments of the present invention will be described below with reference to FIGS.

In the block system diagram of FIG. 1 and the timing chart of FIG. 2, the maximum luminance is turned on when the gradation input data is 8 bits and the display gradation number is 8 bits (256 gradations) (pixel gradation input data: FFH (16 The explanation will be given by taking the case of H.S. 255)) as an example.

As shown in FIG. 7, the inside of the LED display unit 1 of FIG. 1 has X1, X2, ..., X16 lines and Y1, Y.
The LEDs are arranged in a matrix form between 2, ..., Y16 lines. The X line 2 in FIG. 1 is shown in FIG.
X1, X2, ..., X16 of each line, and Y
Line 3 is also composed of lines Y1, Y2, ..., Y16 in FIG. X line (X1, X2, ..., X
16) 2 is a current limiting resistor (R1, R2, ..., R1)
6) It is driven by the X line driver 5 via 4. The Y line (Y1, Y2, ..., Y16) 3 is driven by the Y line driver 7. One line in the Y line driver 7 is selected by the Y line decoder 10.

The voltage obtained from the surface brightness adjusting volume resistor 19 is input to the A / D conversion circuit 14 via the terminal 43, and is converted into an 8-bit digital value by the A / D conversion circuit 14. The output of the A / D conversion circuit 14 is the 8-bit surface luminance input data, and the input from the gradation input data terminal 42 is the gradation input data.
Multiply by 8. The 8-bit data from the multiplier 18 is X
Output as write data to the -Y conversion RAM 20. The XY conversion RAM 20 stores the 8-bit write data and converts the array into display data.

The X-line write decoder 11 X-writes the above 8-bit write data into the XY conversion RAM 20.
An address is designated in the XY conversion RAM for storing in correspondence with X1, X2, ..., X16 of the line. The counter 13 is controlled by a clock, a horizontal synchronizing signal, and a vertical synchronizing signal, and gives a timing signal to the X-line writing decoder 11.

The X-line display decoder 12 controls the XY conversion RAM 20 so as to determine the LED lighting cumulative time corresponding to the data amount from the 8-bit write data stored in the XY conversion RAM 20. At the same time, a signal with the LED lighting cumulative time as the pulse width is
The operation of controlling the output circuit of the XY conversion RAM such that the output circuit of one of the 16 output lines corresponds to each of the X1, X2, ..., X16 lines of the X line. I do. The counter 13 'sends timing signals to the X-line display decoder 12 so that the 16 output lines can be switched in synchronization with the scan clock from the scan clock terminal 46 and the horizontal sync signal from the horizontal sync signal terminal 44. give.

The erase control circuit 15 generates the X-line erase signal shown in FIG. 2F and is synchronized with the scan clock. The Y line erase signal of FIG. 2E is a horizontal sync signal (b) input from the horizontal sync signal terminal 44.
Although shown in the same polarity as Y1, Y2, ...
When adding to the Y16 line, reverse it.

The timing control circuit 34 generates a timing for fetching data from the XY conversion RAM into the buffer 8 while the X-line erase signal is at "H" level.

FIG. 3 shows an example of the configuration of the A / D conversion circuit 14 of FIG. 1 and peripheral circuits. The A / D conversion circuit includes a level detection block 30, an edge detection block 31, a counter block 32, and a latch block 33.

The level detection block 30 detects the voltage level of the terminal CRin and outputs a "H" level signal when the voltage level is higher than a certain level. The edge detection block 31 detects the rising and falling edges of the level detection output, and starts and stops the counter 32 at the next stage. The counter counts the number of clocks from start to stop and outputs it to the latch block 33 as 8-bit data. When the surface brightness adjustment volume resistor 19 is changed, the time until the voltage at the terminal CRin reaches the maximum voltage changes as shown in FIG. 4C, and the number of clocks from the start to the end of the count changes. The brightness adjustment data (output data of the latch block) also changes. The signal waveforms at the points in FIGS. 3A to 3E are respectively shown in FIG.
Through (e). The period shown as “count (medium)” and “count (large)” at the bottom of FIG. 4E indicates a period in which the counter 32 counts corresponding to the surface brightness adjustment (medium) or (large). ing. By calculating (multiplying) the output data of the A / D conversion circuit and the gradation input data, the surface brightness can be adjusted for each LED display device. A / D conversion can be performed using a gate array instead of the A / D conversion circuit of FIG.

FIG. 5 shows gradation input data, surface brightness adjustment data, and calculation results (display data) of these. In this example, 8 bits are used as the gradation input data, 8 bits are used as the surface brightness adjustment data, and the upper 8 bits of 16 bits are practically used to save the cost as the operation result. When actually used, the number of bits of display data may be determined in consideration of the balance between cost and performance. By the above calculation, the display input data, which is the calculation result, changes according to the surface brightness adjustment data. However, one problem here is that accuracy is always deteriorated by 1/256 = 0.4% as a result of adopting only the upper 8 bits of 16 bits as described above. To prevent this, a method of adding 1 to the input data in advance is effective.

LE screen with a refresh rate of 60 Hz
When displayed on the D display, one screen is switched at an interval of 16.6 ms of the vertical synchronizing signal as shown in FIG. Since one screen consists of 16 lines, the lighting time of one line is 1/16 times the vertical sync signal, that is, the horizontal sync signal is 1.0.
The interval is 38 ms.

In FIG. 2, the Y1 line can be turned on (c)
It becomes 1.038 ms while the Y line erase signal (e) is at the "L" level. The output of the X line driver 5 also changes in synchronization with the X line erase signal (f). When the surface brightness adjusting volume resistor is maximum, the pixel gradation input data becomes the display data as it is, so the output of the X line becomes (g). However, X1, X2, ... X16 in FIG.
When added to the line, the polarity is opposite to that of (g). The same applies to (h) and (i) below. The minimum lighting time of the X line is 4.055 μs in the case of 256 gradations, and the cumulative lighting time of one line is 1.038 ms (= 256 × 4.0).
55 μs). When the surface brightness adjusting volume resistor is set to the center (50% of the maximum brightness), the dot gradation input data is calculated as the surface brightness data, and the output of the X line is alternately turned on as shown in (h). In this case, the cumulative lighting time for one line is 0.519 ms (= 128 × 4.055 μs). Similarly, when the surface luminance is 25% which is the maximum, the output of the X line is lit every 4 times as shown in (i).
The cumulative lighting time for one line is 259.52 μs (= 64 ×
4.055 μs). In this embodiment, in order to prevent display flicker, the lighting / non-lighting states of the LEDs are dispersed with respect to time except when the brightness is maximum. As another method, a method may be used in which the first is continuously displayed within the display time of one line of horizontal synchronization and then the first display is made non-display. Further, in order to prevent display flicker, the above 1
The same line may be repeated several times with a line display time of 1.038 ms to increase the number of scans in a pseudo manner. In this way, the lighting pattern can be changed according to the amount of change in the surface brightness adjusting volume resistor, and the surface brightness can be changed by changing the cumulative lighting time.

In the actual gradation operation, the pixel gradation input data is freely changed, but all the pixel gradation input data handled by one LED display device is multiplied by the same surface luminance data. The cumulative lighting time is changed for all the pixels of the LED display device at a ratio corresponding to the surface luminance data.
Therefore, the surface brightness can be adjusted without impairing the gradation function operation in pixel units.

As described above, the embodiment of the present invention is as follows.
Although a display device using LEDs as pixels has been described, the present invention is not limited to this embodiment, and other light emitting elements such as plasma displays and incandescent lamps may be used as pixels.

[0045]

As described above, according to the present invention, since the gradation input data is multiplied by the surface brightness adjustment data, and the cumulative lighting time of the LED can be controlled by the calculation result, the gradation display function can be provided for each pixel. While having it, the effect that the display device which can adjust the surface brightness of the whole display device can be constituted is acquired.

According to the invention of claim 4 or 7,
In addition to the above effect, display flicker can be prevented by changing the light emission pattern of the display pixel on the display / non-display time axis.

[Brief description of drawings]

FIG. 1 is a block system diagram of an LED display device of the present invention.

FIG. 2 is a timing chart of the LED display device of the present invention.

FIG. 3 is an example of a configuration and peripheral circuit diagram of an A / D conversion circuit in the LED display device of the present invention.

FIG. 4 is a timing chart of an A / D conversion circuit in the LED display device of the present invention.

FIG. 5 is an explanatory diagram of gradation input data, surface brightness adjustment data, and calculation results of these in the LED display device of the present invention.

6A is a front perspective view of the LED display device. FIG. 6B is a rear perspective view of the LED display device.

FIG. 7 is a layout diagram of LEDs arranged in a matrix on an LED display section.

FIG. 8 is a block system diagram of a variable duty system.

FIG. 9 is a timing chart of a variable duty method.

FIG. 10: Block diagram of variable current method

FIG. 11 is a timing chart of a variable current method.

FIG. 12 is a block diagram of a frame thinning method.

FIG. 13 is a timing chart of the frame thinning method.

[Explanation of symbols]

 1 LED display section 2 X line 3 Y line 4 Current limiting resistor 5 X line driver 6 X line constant current driver 7 Y line driver 8 Buffer 9 Shift register / latch 10 Y line decoder 11 X line writing decoder 12 X line display Decoder 13 Counter 14 A / D conversion circuit 15 Erase control circuit 16 Pulse duty circuit 17 Frame control circuit 18 Multiplier 19 Surface brightness adjustment volume resistor 20 XY conversion RAM 21, 211 LED 22 Reflector 23 LED display substrate 24 Fixed Boss 26 Drive circuit board 27 Signal connector 28 Power connector 30 Level detection block 31 Edge detection block 32 Counter block 33 Latch block

Claims (8)

[Claims] 1. A display unit in which display pixels are arranged in a matrix, a multiplier for multiplying gradation input data and surface brightness adjustment data, and a light emission of each display pixel of the display unit based on a calculation result of the multiplier. A control means for controlling the cumulative time,
The gradation of each display pixel is controlled by the gradation input data,
A display device, wherein the surface brightness of the entire display device is adjusted by the surface brightness adjustment data. 2. The display device according to claim 1, wherein the light emitting element forming the display pixel is a light emitting diode. 3. A level detection block for detecting that the voltage obtained from the surface brightness adjustment volume resistor is above a certain level, and detecting the rising and falling edges of this level detection to start the next stage counter. 2. The display device according to claim 1, further comprising an edge detection block for controlling stop, a counter block for counting the number of clocks from the start to the stop, and a latch block for temporarily holding count data thereof. . 4. A gradation operation for each display pixel is performed by repeatedly controlling a lighting pattern on the display / non-display time axis of the display pixel at least twice in one display screen according to a change amount of the surface brightness adjustment data. The display device according to claim 1, further comprising a function capable of changing the brightness of the entire display surface while holding the display. 5. A display device having a display unit in which display pixels are arranged in a matrix for display control with an X line input terminal and a Y line input terminal, wherein digital gradation input data corresponding to the display pixels and the entire display surface are provided. A method for driving a display device, wherein the output of multiplication of the brightness of the digital surface brightness adjustment data is input to the X-line input terminal as display input data. 6. The method of driving a display device according to claim 5, wherein 1 is added to the display input data. 7. The method of driving a display device according to claim 5, wherein the display input data is dispersed in a predetermined unit within a switching cycle time range of Y line input data. 8. The method of driving a display device according to claim 7, wherein the predetermined unit corresponds to an X-line erase signal.