JP3666271B2 - Display device and driving method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a display device installed indoors and outdoors, and more particularly to a full-color light emitting display device that drives light emitting diodes arranged on a screen by a dynamic lighting method and a driving method thereof.
[0002]
[Prior art]
A full-color display panel using light-emitting diodes (hereinafter referred to as “LEDs”) installed indoors or outdoors has three light-emitting diodes of red (R), green (G), and blue (B). A color image is formed as a pixel. In such a full-color image, fine brightness control for each LED is required in addition to dimming control for adjusting the brightness of the entire screen and gradation control for each dot. In addition, in order to improve the quality of an image, for example, an LED panel having a small square shape with a side length of about 64 mm in units of 16 × 16 dots is used to cope with image densification.
[0003]
As described above, in dimming the entire screen or controlling the luminance of the LED, it is necessary to drive the LED with a small circuit configuration. The LED lighting drive method includes a dynamic lighting method and a static lighting method. In order to reduce the circuit size, it is generally more advantageous to use the dynamic lighting method than the static lighting method.
[0004]
FIG. 4 is an example of a driving circuit of a static lighting system, and FIG. 5 is a timing chart thereof.
[0005]
A power supply (VLED) 51 for one LED 50 is connected, and a constant current driver IC 52 is connected to the ground side. In this circuit configuration, the least significant bit of the display data for one line of the image display unit is sent to the constant current driver IC 52. When data for one line is sent and latched, lighting is performed for a pulse width corresponding to each bit. Next, the data of the next bit is sent to the constant current driver IC 52 during this pulse width lighting. Each time the display of the pulse width corresponding to each bit is switched, the enable signal of the constant current driver IC 52 is made inactive and the display is turned off for latching in order to stabilize the display. When the latch is applied, the enable signal of the constant current driver IC 52 is activated and the next display is started.
[0006]
Thus, in the case of the static lighting method, gradation display is performed by repeating the above operation for each of the least significant bit to the most significant bit using the constant current driver IC 52.
[0007]
[Problems to be solved by the invention]
On the other hand, in the case of the dynamic lighting method, it is necessary for a plurality of dots corresponding to the duty to share the X line defined as the horizontal arrangement of display pixels in this specification. For this reason, a switch for selecting a Y line defined as a vertical array orthogonal to the X line is added to the drive circuit of the static lighting system.
[0008]
That is, the display data sent to the constant current driver IC for the X line is sent alternately as odd-numbered data and even-numbered data in the case of 1/2 duty, for example, and as a switch for the Y line accordingly. A PNP power transistor or a P-channel FET is used to switch between odd and even stages for display.
[0009]
However, large-capacity PNP power transistors or P-channel FETs tend to be unsuitable for high-speed switching because they have a longer turn-off time than NPN transistors or N-channel FETs. For this reason, when high-frequency switching is performed by the dynamic lighting method, the turn-off is not completed during the Y-line switching mask period, and a timing that a plurality of Y lines are in an on state occurs. Therefore, although the LED of the dot sharing the X line should not be lit up originally, these LEDs are lit up weakly, causing a light leakage phenomenon.
[0010]
Thus, when driving LEDs such as full-color LED display devices at a high frequency, it is difficult to obtain sufficient luminance, for example, the PNP transistor or P-channel FET must be made small. On the other hand, in order to ensure sufficient luminance, the LED drive frequency must be lowered to reduce the displayable gradation.
[0011]
The problem to be solved by the present invention is to provide a display device which can eliminate the obstacle to the turn-off time of the transistor in the dynamic lighting system, can operate with high luminance and high-speed display clock, and is miniaturized.
[0012]
[Means for Solving the Problems]
According to the display device of the present invention, a display unit in which display pixels are arranged in a matrix and a display pixel of the display unit based on input display data are dynamically generated with respect to a horizontal X line and a vertical Y line orthogonal thereto. a control circuit for outputting a lighting signal, and a independent X-line drive circuit connected to the Y-line drive circuit to said control circuit, said X-line driving circuits is a signal for designating the X line A constant current driver IC is provided as an element to be driven , and the Y line driving circuit includes a first transistor for driving the display pixel with a current from a power source by a signal designating the Y line, the first transistor, A second transistor connected to ground between the display pixels, and the control circuit supplies the constant current when lighting the display pixels. In the mask period in which the driver IC is activated, the first transistor is turned on to light the display pixel, and the constant current driver IC is later deactivated and the first transistor is turned off. The second transistor is turned on to ground between the first transistor and the display pixel, and when the mask period ends, the second transistor is also turned off .
[0013]
In such a configuration, if a discharge circuit is added to the common transistor of the Y-line driving circuit, the switching of the common transistor can be accelerated and the light leakage of the LED can be prevented. High quality full color display can be realized while maintaining the above.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
According to the first aspect of the present invention, a display unit in which display pixels are arranged in a matrix, and a display pixel of the display unit based on input display data are arranged in a horizontal X line and a vertical Y line perpendicular thereto. for comprises a control circuit for outputting a dynamic lighting signals, each independent X-line drive circuit are connected and the Y-line drive circuit to said control circuit, said X-line driving circuits specifies the X line A constant current driver IC is provided as an element driven by a signal , and the Y line driving circuit includes a first transistor for driving the display pixel by a current from a power source by a signal designating the Y line, and the first transistor A second transistor connected to ground between the transistor and the display pixel, and the control circuit is configured to turn on the display pixel when turning on the display pixel. In a mask period in which the current driver IC is activated, the first transistor is turned on to light the display pixel, and the constant current driver IC is later deactivated and the first transistor is turned off. The second transistor is turned on to ground between the first transistor and the display pixel, and when the mask period is completed, the second transistor is also turned off. It has an effect that it is possible to realize a high-speed display clock operation while at the same time encouraging higher luminance and smaller size of a possible display device.
[0015]
The invention according to claim 2 is the display device according to claim 1, wherein the light emitting element constituting the display pixel is a light emitting diode, and can emit light that can be turned on and off at a higher speed than an LCD or a CRT. By utilizing the characteristics of the diode, a display capable of high-speed pulse control is obtained.
[0016]
According to a third aspect of the present invention, in the display device according to the first or second aspect, the display input data corresponding to the display pixel is input as X line data, and a signal for designating a Y line synchronized with the X line data is specified. This is a driving method of a display device that is driven by dynamic lighting, and has the effect that full color display with sufficient luminance can be achieved without causing light leakage which was unavoidable in the dynamic lighting system.
[0017]
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. In this embodiment, the case of a dynamic lighting display method with a duty of 1/2 will be described.
[0018]
FIG. 1 is a block system diagram of a dynamic lighting system according to the present invention.
In FIG. 1, a timing controller 2 and a dot gradation / luminance variation correction are input to an input terminal 1 to which a data input clock and a display clock, a vertical synchronization signal, a horizontal synchronization signal, display data and other control signals are input. A control circuit 5 and a data selector 6 are connected to each other. The timing controller 2 is connected to an address generator 3 and includes a dot gradation / luminance variation correction control circuit 5 that receives a signal from the timing controller 2 and a RAM 4 that receives a signal from the address generator 3. And an E2PROM 7 between the dot gradation / luminance variation correction control circuit 5.
[0019]
A display data output circuit 8 is provided on the output side of the RAM 4, and a group of LEDs on the display screen that is conducted to an LED power source (shown as “VLED”) is orthogonal to the horizontal X line of the display pixel, respectively. An X-line drive circuit 9 and a Y-line drive circuit 10 are provided for driving separately from the vertical Y lines. An output signal from the display data output circuit 8 can be input to the drive circuits 9 and 10 of these X and Y lines, and the LEDs arranged on the display panel 11 of the display device are driven by these drive circuits 9 and 10. Make it possible.
[0020]
FIG. 2 is a driving circuit diagram of a dynamic lighting system using the X line driving circuit 9 and the Y line driving circuit 10.
[0021]
In FIG. 2, a power source 14 is connected to the first LED 12 and the second LED 13, and a constant current driver IC 15 is connected to the ground side. In this circuit, the constant current driver IC 15 is included in the X-line driving circuit 9, and the Y-line driving circuit 10 includes first and second transistors Q1 and Q2, and third and fourth transistors Q3 and Q3 for discharging. Q4 is connected to the ground side.
[0022]
In the above configuration, the timing controller 2 determines which position on the display unit the display data is based on the vertical synchronization signal and the horizontal synchronization signal from the input terminal 1. A signal from the timing controller 2 is input to an address generator 3 which designates an address in the RAM 4.
[0023]
On the other hand, the display data input from the input terminal 1 is corrected by the dot gradation / luminance variation correction control circuit 5 based on the correction data of the LED in the E2PROM 7 designated by the data selector 6. The corrected data is written to an address in the RAM 4 designated in advance by the address generator 3.
[0024]
Since the display data can be output at the time when the display data for one screen is created, a flag notifying the end of writing is set. When the write end flag is set, the display data output circuit 8 starts outputting display data to the X-line driving circuit 9 in accordance with the data written in the RAM 4 in synchronization with the display clock. The least significant bit of the corrected display data of the odd number of stages for one line of the display unit is sent to the constant current driver IC. When an odd-stage data for one line is sent and latched, the X-line drive circuit 9 becomes displayable.
[0025]
The display data output circuit 8 waits for this timing and activates the enable signal of the constant current driver IC 15, and at the same time outputs a signal designating an odd-numbered Y line to the Y line driving circuit 10. As a result, the odd-numbered Y-line PNP transistor Q1 is turned on, and the first LED 12 lights up for a pulse width corresponding to each bit. During this pulse width, even-stage corrected data for one line is sent to the shift register.
[0026]
When the display of the pulse width corresponding to each bit in the odd-numbered stage is finished, the enable signal of the constant current driver IC 15 is made inactive to stabilize the display, and an off signal is also output to the transistors Q1 and Q2. At this timing, the display data output circuit 8 turns on the discharge NPN transistors Q3 and Q4. The NPN transistors Q3 and Q4 do not need to pass a large amount of current, so that a high-speed response type can be used. When the discharge transistors Q3 and Q4 are turned on, the collector potentials of the PNP transistors Q1 and Q2 of the Y-line drive circuit 10 are forcibly grounded regardless of their original natural potential drop. Therefore, the PNP transistor Q1 can be sufficiently discharged within the time period when the constant current driver IC is inactive, and the anode potential of the LED of the display unit can be lowered to a potential at which the LED is not turned on.
[0027]
In this state, when the display data output circuit 8 latches the constant current driver IC 15, the X-line driving circuit 9 is in an even-stage displayable state. Similarly, the display data output circuit 8 waits for this timing to activate the enable signal of the constant current driver IC and simultaneously turns off the discharge transistors Q3 and Q4. When the discharge transistors Q3 and Q4 are turned off at this timing, the timing of the transistors Q1 and Q2 of the Y-line driving circuit 10 is turned off and the discharge path through the reverse voltage of the LED is cut off. Therefore, the timing at which a reverse voltage is simultaneously applied to the first LED 12 and the second LED 13 does not occur.
[0028]
Thereafter, the display data output circuit 8 outputs a signal designating the Y line to the Y line driving circuit 10. Thereby, the transistor Q2 of the even-numbered Y line is turned on, and the second LED 13 is lit for a pulse width corresponding to each bit. At this time, since the collector potential of the transistor Q1 of the odd-numbered PNP is sufficiently lower than the potential at which the LED is lit, the odd-numbered first LED 12 is not lit.
[0029]
By repeating this operation up to the most significant bit, the odd-numbered and even-numbered mask periods in the timing chart shown in FIG. 3 are switched reliably, so that gradation display is alternately performed for the odd-numbered and even-numbered LEDs.
[0030]
【The invention's effect】
In the present invention, since the PNP power transistor switches at a sufficient speed when switching the common line, the display device is dynamically lit while maintaining sufficient high frequency and brightness of the display surface necessary for full color display without causing light leakage. Can be driven. Therefore, even for a large-screen display device in which a large number of LEDs are arranged, the drive circuit can be reduced in size, and a display form corresponding to the gradation difference of the image can be obtained at a high frequency, enabling high-quality image display. It becomes.
[Brief description of the drawings]
FIG. 1 is a block system diagram of an LED display device of the present invention. FIG. 2 is a display data driving circuit diagram of the LED display device of the present invention. FIG. 3 is a timing chart of the LED display device of the present invention. Display data drive circuit diagram in display device [FIG. 5] Timing chart in conventional LED display device [Explanation of symbols]
1 Input terminal 2 Timing controller 3 Address generator 4 RAM
5 dot gradation / brightness variation correction control circuit 6 data selector 7 E2PROM
8 Display Data Output Circuit 9 X Line Drive Circuit 10 Y Line Drive Circuit 11 Display Panel 12 First LED
13 Second LED
14 Power supply 15 Constant current driver IC
Q1, Q2, Q3, Q4 transistors

Claims (3)

A display unit in which display pixels are arranged in a matrix, and a control circuit that outputs a dynamic lighting signal for a horizontal X line and a vertical Y line orthogonal to the display pixel of the display unit based on input display data And an X-line driving circuit and a Y-line driving circuit that are independently connected to the control circuit,
Wherein X line driver circuits is as an element for driving the signal specifying the X line, with a constant-current driver IC,
The Y line drive circuit is connected to ground a first transistor that drives the display pixel with a current from a power source by a signal designating the Y line, and between the first transistor and the display pixel. With a second transistor
The control circuit activates the constant current driver IC when lighting the display pixel, turns on the first transistor to light the display pixel, and later deactivates the constant current driver IC. In the mask period in which the first transistor is turned off, the second transistor is turned on to ground between the first transistor and the display pixel, and when the mask period ends, the second transistor is turned on. Display device with a function to turn off The display device according to claim 1, wherein the light emitting element constituting the display pixel is a light emitting diode. 3. The display device according to claim 1, wherein display input data corresponding to the display pixel is input as X line data, and the display is driven by dynamic lighting based on a signal designating a Y line synchronized with the X line data. Device driving method.

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