JP2001147675A - Display unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure of display unit capable of performing a uniform screen display without a large reduction in brightness. SOLUTION: This display unit comprises a transmission type liquid crystal for displaying a horizontal synchronizing signal at the same time, plural back- light units which are constituted of plural LED groups LW1-LE8 arranged in the horizontal direction and arranged in the vertical direction, a counter for frequency-dividing the horizontal synchronizing signal supplied to the transmission type liquid crystal and outputting a count value of the frequency-divided signal, and a decoder for outputting signals to turn on only the LED groups corresponding to the count value of the counter, and brings only the LED groups into lighting state, which are positioned on the rear side of the line of the transmission type liquid crystal currently displaying.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a display using an ED (light emitting diode).

[0002]

2. Description of the Related Art A transmissive liquid crystal is mainly used as a display element of a display, but a backlight unit is arranged behind the transmissive liquid crystal in order to visually observe the contents displayed on the transmissive liquid crystal. Need to be done. As a light source of the backlight unit, an LED, a CFL tube, an EL luminous body, or the like can be used. However, recently, LEDs have become mainstream in small display devices.

As shown in FIG. 8, for example, a backlight unit of such a small display includes a box-shaped housing having a bottom and a substantially rectangular shape in plan view, and about 5 to 10 vertically and 10 to 15 horizontally. And a diffusion plate attached to the housing so as to close an opening of the housing. Usually, all the LEDs incorporated in the backlight unit are driven by a DC power supply and are turned on at the same time.

For example, when a backlight unit is configured by arranging eight LEDs vertically and 16 horizontally in a matrix, a total of 128 LEDs are turned on at the same time. As the current flowing through the LED increases, the brightness increases, the luminance characteristics improve, and ideal display is possible. In addition, a method in which the LEDs incorporated in the backlight unit are simultaneously turned on is the most advantageous in terms of brightness characteristics. However, since about 100 LEDs are densely arranged in the backlight unit, the backlight unit is used. The temperature of the backlight unit itself becomes extremely high, which adversely affects circuit components disposed around the backlight unit, and also causes a problem that the backlight unit itself is destroyed by heat.

One of the measures against heat generation of this backlight unit is as follows.
One method is to use a current-limiting resistor to limit the current flowing through the LED to suppress heat generation of the LED. FIG.
Is a circuit diagram showing an example of a display device using a current limiting resistor. The display device includes a transmission type liquid crystal (LCD), a CPU for controlling the display of the LCD and a lighting state of a backlight unit, a backlight unit, and a CPU. And a driving circuit for driving the LED of the backlight unit in response to the above signal. The drive circuit includes an NPN transistor and a current limiting resistor connected to the collector of the NPN transistor and configured by a variable resistor or a fixed resistor.
The base of the PN transistor is connected to the signal output terminal of the CPU, and the emitter is connected to the low potential side of the DC power supply.

In the backlight unit shown in FIG. 9, the anodes of all the built-in LEDs are connected to the high potential side of the DC power supply, and the cathodes of all the LEDs are connected to the DC power supply via a current limiting resistor and an NPN transistor. It is connected to the low potential side.

[0007] In the display shown in FIG.
For turning on (signal in High state) is NP
When output is made to the N transistor, the NPN transistor is turned on, and all LEDs are turned on. But,
In the case of the display shown in FIG. 9, since the number of LEDs to be turned on simultaneously is large, it is necessary to use a high-wattage resistor as the current limiting resistor, and the resistor generates heat.
It was not an ideal measure.

As another countermeasure against the heat generation of the backlight unit, there is a method of shortening the time for turning on the LED. A display that takes this measure is, for example, FIG.
0, a transmission type liquid crystal (LCD), and L
CPU for controlling display of CD and lighting state of backlight unit, backlight unit, oscillation circuit controlled by CPU, drive circuit for inputting output signal of oscillation circuit and driving LED of backlight unit And The drive circuit shown in FIG. 10 includes only NPN transistors, the base of which is connected to the output terminal of the oscillation circuit, the collector is connected to the cathodes of all LEDs of the backlight unit, and the emitter is a DC power supply. Is connected to the low potential side of The anodes of all the LEDs of the backlight unit are connected to the high potential side of the DC power supply. Further, the oscillation circuit outputs an oscillation signal having a predetermined duty ratio of a predetermined frequency while the signal for turning the LED on is input from the CPU, and outputs a signal for turning off the LED from the CPU. It is configured to output a signal in a low state during input.

[0009] In the display shown in FIG.
The oscillation circuit outputs an oscillation signal having a predetermined frequency and a predetermined duty ratio to the NPN transistor while a signal indicating that D is turned on is output to the oscillation circuit. This allows
Since all the LEDs are turned on when the oscillation signal is in the High state, all the LEDs blink while the CPU outputs a signal to turn the LEDs on.
As a result, the time for turning on the LED can be shortened and the heat generation can be suppressed, but in the case of this measure,
There is a feature that flicker easily occurs on the screen.

[0010]

In the display device shown in FIG. 10, for example, one line of the LED of the backlight unit is arranged corresponding to the LCD area for eight continuous lines, and The LCD is configured to illuminate the LCD, wherein the LED is driven by an oscillating signal while the LCD
Are driven line by line in order from the top of the screen according to the horizontal synchronization signal, and display is performed. Usually, the signal for driving the LED and the signal for driving the LCD are not synchronized, and the
Blinks rapidly so that flicker is not noticeable, but the screen may appear to be wavy because it is not synchronized with the LCD display.

[0011] Further, in the case of synchronizing, there is a problem that, depending on the method, while the LCD is displaying a certain area, no backlight is illuminated on that area at all. This will be described with reference to FIG.

FIGS. 11A and 11B are diagrams showing an example of a synchronous blinking method of a display. FIGS. 11A and 11B show the display of the first frame when the LED is switched on and off every eight lines of the LCD. Screen, the display screen of the second frame,
(C) is a diagram showing the relationship between each signal and the lighting state of the backlight. In (c), the diagram of (4) is LC
It is the diagram which showed the case where LED blinking was performed once for every one line of D.

The display shown in FIG. 11 has a backlight unit having a built-in 8-line LED arranged behind a 64-line LCD. One line of LED is arranged in a continuous 8-line LCD area. And one frame is displayed with one vertical synchronization signal as a trigger, and one line of the LCD is displayed with one horizontal synchronization signal as a trigger. Further, all the LEDs incorporated in the backlight unit are configured to be turned on at the same time. Also, FIGS. 11 (a) and (b)
The numbers 1 to 8 shown in FIG.
One screen area corresponds to screen areas 1 to 8 in order from the top of the screen.

As shown in FIG. 11 (1), when the on / off state of the backlight is switched every eight LCD lines from the top of the screen, as shown in (3), the screen area 1
The backlight is turned on while the LCD is displayed on the screen areas 3, 5, and 7, and the backlight is turned off while the LCD is displayed on the screen areas 2, 4, 6, and 8. Therefore, in the first frame, only the contents displayed in the screen regions 1, 3, 5, and 7 can be visually confirmed as shown in FIG. Also in the second frame, as shown in (b), only the contents displayed in the screen areas 1, 3, 5, and 7 can be visually checked. In other words, in the case of the display device shown in FIG. 11, the number of times that the backlight is lit per frame is an even number, so that the backlight is always turned off while the LCD displays the screen regions 2, 4, 6, and 8. , And a phenomenon occurs in which the contents displayed in the screen areas 2, 4, 6, and 8 cannot be visually confirmed. For this reason, there is a restriction that the number of times of lighting of the backlight per frame must be an odd number.

Further, as shown in FIG. 11 (4), LC
When the LED blinks once for each line of D, the problem of not being able to visually confirm the contents displayed on the screen areas 2, 4, 6, and 8 can be prevented, but one line is displayed on all the lines of the LCD. Since the backlight is turned on only for half the time, there is a problem that the luminance is greatly reduced.

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide a structure of a display device capable of displaying a uniform screen without greatly lowering the luminance. It is in.

[0017]

According to a first aspect of the present invention, there is provided a display device comprising: a transmissive liquid crystal which performs display on a line-by-line basis in accordance with a horizontal synchronization signal; A backlight unit in which a plurality of LED groups constituted by a plurality of LEDs are vertically adjacent to each other, and a frequency division of a horizontal synchronization signal supplied to the transmissive liquid crystal, and outputs a count value of the frequency-divided signal. A counter to
A decoder for outputting a signal so that only the LED group corresponding to the count value output from the counter is turned on, and only the LED group located on the back side of the line of the transmissive liquid crystal being displayed. Is turned on.

According to a second aspect of the present invention, there is provided a display device, comprising: a transmissive liquid crystal for displaying a line by line in accordance with a horizontal synchronizing signal; and a plurality of LEDs arranged behind the transmissive liquid crystal and arranged in a horizontal direction. A backlight unit configured by vertically adjoining a plurality of LED groups configured by a plurality of LEDs, a counter that divides a horizontal synchronization signal supplied to the transmissive liquid crystal, and outputs a count value of the divided signal, A decoder that outputs a signal so that only the LED group corresponding to the count value output from the counter is turned on,
Only the LED group located on the back side of the line of the transmissive liquid crystal on which display is performed is turned on, and the other LEs are turned on.
It is characterized in that the D group is turned on and off.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the display of the present invention will be described with reference to the circuit diagram of FIG. The display shown in FIG. 1 is a transmission type liquid crystal (LCD), a CPU for controlling the display of the LCD and a lighting state of the backlight unit, a backlight unit, and a frequency dividing horizontal synchronizing signal supplied to the LCD. H is applied only to the counter that outputs the count value and the output terminal corresponding to the count value output from the counter.
It includes a decoder that outputs a signal in the high state, and a plurality of driving circuits that are connected to each output terminal of the decoder and that drive LEDs of each line of the backlight unit.
The drive circuit is composed of NPN transistors, and each NPN transistor
The collectors of the transistors are respectively connected to the cathodes of all the LEDs arranged in the corresponding line of the backlight unit, and the emitter of each NPN transistor is
It is connected to the low potential side of the DC power supply.

Further, in the backlight unit shown in FIG. 1, LEDs are arranged in one line in a horizontal direction in each line, and a plurality of series circuits are formed by connecting in series every four adjacent LEDs. A series circuit is connected between a high potential side of a DC power supply and a collector of an NPN transistor corresponding to each line. As described above, a plurality of LEDs arranged on the same line are connected in series, and the circuit is connected to the high potential side of the DC power supply and the NPN corresponding to each line.
By connecting to the collector of the transistor and increasing the voltage of the DC power supply, each LED is compared with the case where each LED is connected between the high potential side of the DC power supply and the collector of the NPN transistor corresponding to each line. , NPN transistor can be reduced.

Next, the counter is a circuit for dividing the horizontal synchronizing signal supplied to the LCD and outputting a count value. The division ratio is obtained by dividing the total number of LCD lines by the number of LED lines. Is set to a value. For example, when the total number of lines of the LCD is 64 and the number of lines of the LED is 8, the frequency division ratio is 8, so that every time eight horizontal synchronization signals are counted, the output count value is counted by one. Will be up.

The decoder decodes the count value output from the counter and outputs a High signal only to an output terminal corresponding to the count value. For example, a decoder having eight output terminals is connected to a counter that counts values from 0 to 7, and the eight outputs of the decoder are sequentially H in accordance with the count values 0 to 7.
It is configured to be in the high state.

The display shown in FIG. 1 uses the horizontal synchronizing signal to
It is determined which line of the LCD is currently being displayed, and the L corresponding to the currently displayed line of the LCD is determined.
Only one line of the ED is turned on. For example, if the total number of LCD lines is 64 and LE
When the number of lines of D is eight, the count value output from the counter is incremented by one each time eight horizontal synchronizing signals are counted, and the eight output terminals of the decoder correspond to the count-up. Are sequentially turned to the high state, so that each line of the LED of the backlight is turned on one line at a time from the top using signals output from the eight output terminals of the decoder. , One line of the LED corresponding to the eight lines of the LCD can be turned on. That is, the LEDs arranged behind the lines of the LCD on which the display is being performed can always be turned on, so that the entire screen can be uniformly displayed with the same luminance. Further, the duty ratio of the signal for driving the LED can be increased, and the ratio of the lighting time can be reduced, so that the heat generation of the LED can be significantly reduced.

Next, a specific configuration of the display device of the present invention will be described with reference to FIGS. FIG. 2 is a circuit diagram showing a configuration other than the CPU, FIG. 3 is a diagram showing a relationship between signals, and FIG. 4 is a display screen.

The LCD comprises 64 vertical dots (64 lines) × 160 horizontal dots, and the backlight comprises 8 vertical (8 lines) × 15 horizontal LEDs arranged in a matrix. HD61202 and HD61203 are elements for driving the LCD. IC1 is the counter shown in FIG. 1, IC2 is the decoder shown in FIG. 1, and IC3 is a one-shot multivibrator for generating a signal for clearing the counter from the vertical synchronizing signal. Q1-Q
Reference numeral 8 denotes a drive circuit for driving the first to eighth rows of the LED matrix, respectively. Further, FRM is a terminal for outputting a vertical synchronization signal, and CL2 is a terminal for outputting a horizontal synchronization signal. LE1 to LE8 are respectively
LEs arranged in each row (each line) of the LED matrix
Group D.

First, the falling edge of the vertical synchronizing signal output from the FRM is captured, and the counter IC 1
Is generated and the counter IC1 is cleared. As a result, the outputs of the counter IC1 are all in the Low state, and the output of the decoder IC2 that receives the signals output from the output terminals 2QA to 2QC of the counter IC1 is
Only the signal output from the output terminal Y0 is in a low state (enable state).

Next, the horizontal synchronizing signal output from CL2 is inverted, input to the clock input terminal 1CK of the counter, and counted. The counter IC1 is an IC containing two 4-bit counters, divides the horizontal synchronizing signal by 8 using one counter, counts the frequency-divided signal by another set of counters, and outputs the output terminals 2Qa to 2Qc. Outputs the count value.

Output terminals 2Qa to 2Qc of counter IC1
Are connected to the input terminals A to C of the decoder IC2, respectively, and the output terminals Y0 to Y7 of the decoder IC2 are sequentially turned to the Low state in response to the count-up. Decoder IC
2 are connected to the bases of the PNP transistors of the driving circuits Q1 to Q8 via the base resistors, respectively, so that the output terminal Y0 of the decoder IC2 is
To Y7 are sequentially turned to the Low state, the PNP transistors of the driving circuits Q1 to Q8 are sequentially turned on, and the LEDs arranged in the first to eighth rows of the backlight
The groups LE1 to LE8 are sequentially turned on.

The operation will be further described with reference to FIG. When the first horizontal synchronization signal is input to the clock input terminal 1CK of the counter IC1, the LCD is driving (displaying) the first line. Since the counter IC1 divides the horizontal synchronization signal by 8, the output signal of the counter IC1 does not change even if the second to eighth horizontal synchronization signals are input, and the 1 to 8 lines of the LCD are changed. While driving, a plurality of LEDs belonging to the LED group LE1
The ED is turned on. FIG. 4A is a diagram showing the contents displayed on one screen of the LCD. While driving lines 1 to 8 of the LCD, a plurality of LEDs belonging to the LED group LE1 are turned on, and a state is displayed as shown in FIG. 8B.

Next, when the ninth horizontal synchronization signal is input, the outputs 2QA to 2QC of the counter IC1 become "LLH".
, And only the output terminal Y1 of the output of the decoder IC2 is switched to the enable state (Low state). As a result, in the backlight, the LEDs arranged in a horizontal row as the second-stage LED group LE2 from the top are turned on, and the screen display is in the state shown in FIG. 8C.

Similarly, the LED group LE3 corresponds to the 17th to 24th horizontal synchronization signals, the LED group LE4 corresponds to the 25th to 32nd horizontal synchronization signals, and the 33rd to 40th horizontal synchronization signals. LED group LE5, LED group LE6 corresponding to the 41-48th horizontal synchronization signal, and LED group LE7, 57-64 corresponding to the 49-56th horizontal synchronization signal.
Since the LED group LE8 is turned on in response to the second horizontal synchronization signal, the screen display is shown in FIGS.
The state shown in FIG.

Next, different examples of the specific structure of the display device of the present invention will be described with reference to FIGS. FIG.
Is a circuit diagram showing a configuration other than the CPU, FIG. 6 is a diagram showing a relationship between signals, and FIG. 7 is a display screen.

The LCD has a feature that, even if a voltage is applied to a line to be displayed, the reaction takes a long time, and if the period is too fast, the contrast is deteriorated. On the other hand, if the frame period of the LCD is slow, the afterimage effect of the eyes cannot be obtained, and flickering occurs where the light emitting portion of the backlight flows from above. The display shown in FIGS. 5 to 7 has a more effective configuration when such a frame period of the LCD is slow.

The display shown in FIG. 5 synchronizes the LEDs of the LED group in the off state with the horizontal synchronizing signal,
It is characterized by blinking for each line of a CD. By blinking at a high speed in this manner,
The afterimage effect can be obtained, and flicker does not occur even if the lighting state and the bright state come around at a slow cycle. Further, the difference in brightness between a bright portion in a lighted state and a blinking portion is reduced, and a more legible display can be realized.

The circuit shown in FIG. 5 is different from the circuit shown in FIG. 2 in that a two-input AND circuit is newly provided, and the other configuration is the same as the configuration shown in FIG. Eight two
The input AND circuit IC4 is provided between the decoder IC2 and the drive circuit.
Output signals of output terminals Y0 to Y7 of the decoder IC2 are supplied, a signal obtained by inverting the horizontal synchronizing signal is supplied to the other input, and each output signal of the two-input AND circuit IC4 is connected to a base resistor. Is supplied to the base of the PNP transistor via the. Since only one output of the decoder IC2 corresponding to the LED group to be turned on is in a low state (enable state), and during that time, the outputs of the other decoder IC2 are in a high state. IC2
The output of the two-input AND circuit IC4 corresponding to the output of (1) and (2) repeats the High state and the Low state in synchronization with the signal obtained by inverting the horizontal synchronization signal. Flashes.

For example, in FIG. 6, while the LED group LE1 corresponding to the output terminal Y0 of the decoder IC2 in the low state is in the lighting state, the output terminal Y1 of the decoder IC2 is in the lighting state.
The output signals to Y7 repeat a High state and a Low state in synchronization with a signal obtained by inverting the horizontal synchronization signal output from CL2 (signal input to 1CK of the counter IC1). Thereby, the output terminals Y1 to Y1 of the decoder IC2
Since the LED groups LE2 to LE8 corresponding to Y7 are in a blinking state, as shown in FIG.
The area illuminated by the group LE1 is bright and the LED groups LE2
The area illuminated by LE8 is in a slightly dark state.

The number of dots of the display, the number of lines of the LED, and the like are not limited to the embodiment.

[0038]

According to the display device of the present invention, the backlight for illuminating the line being displayed is turned on in synchronization with the line display timing of the LCD.
When the largest contrast ratio is displayed on the LCD, the corresponding backlight can be turned on, and a display with high heat generation efficiency and high luminance can be realized.

In the display device according to the present invention, the portion of the backlight which is not lit is blinked for each line of the LCD in synchronization with the horizontal synchronizing signal. Can be obtained, and flicker does not occur even if the light-on state and the bright state come around at a slow cycle. Further, the difference in brightness between a bright portion in a lighted state and a blinking portion is reduced, and a more legible display can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a display device of the present invention.

FIG. 2 is a circuit diagram showing a specific configuration of a display device of the present invention.

FIG. 3 is a diagram showing a relationship between signals of the display device of the present invention.

FIG. 4 is a display screen of the display device of the present invention.

FIG. 5 is a circuit diagram showing a specific configuration of another embodiment of the display device of the present invention.

FIG. 6 is a diagram showing a relationship between signals of different embodiments of the display device of the present invention.

FIG. 7 is a display screen of another embodiment of the display device of the present invention.

FIG. 8 is a perspective view showing a configuration of a display device provided with a backlight made up of LEDs.

FIG. 9 is a circuit diagram showing an example of a conventional display circuit.

FIG. 10 is a circuit diagram showing another example of the circuit of the conventional display.

FIG. 11 is an explanatory diagram showing an example of a synchronous blinking method of a display.

[Explanation of symbols]

 LCD Transmissive liquid crystal LE1 to LE8 LED group IC1 Counter IC2 Decoder

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09G 3/20 611 G09G 3/20 611D F term (Reference) 2H093 NC27 NC44 NC49 NC50 NC59 ND08 ND09 ND10 5C006 AF42 AF44 BF22 BF23 BF26 BF31 EA01 FA22 FA23 FA54 5C080 AA10 BB05 DD05 DD06 EE28 JJ01 JJ02 JJ04 5C094 AA03 AA07 AA55 BA43 CA19 GA10 5G435 AA01 AA03 BB12 BB15 CC09 EE27 EE30 GG26

Claims (2)

[Claims] 1. A transmissive liquid crystal which performs display on a line-by-line basis in accordance with a horizontal synchronizing signal, and a group of LEDs arranged on a back side of the transmissive liquid crystal and constituted by a plurality of LEDs arranged in a horizontal direction. And a counter configured to divide the horizontal synchronization signal supplied to the transmissive liquid crystal and output a count value of the frequency-divided signal, and a counter value output from the counter. A decoder that outputs a signal so that only the corresponding LED group is turned on, wherein only the LED group located on the back side of the transmission type liquid crystal line on which display is being performed is turned on. Indicator to do. 2. A transmission type liquid crystal which performs display on a line-by-line basis in accordance with a horizontal synchronizing signal, and an LED group which is arranged on the back side of the transmission type liquid crystal and is composed of a plurality of LEDs arranged in a horizontal direction. And a counter configured to divide the horizontal synchronization signal supplied to the transmissive liquid crystal and output a count value of the frequency-divided signal, and a counter value output from the counter. A decoder for outputting a signal so that only the corresponding LED group is turned on, and only the LED group located on the back side of the transmission type liquid crystal line on which display is being performed is turned on, and the other LEDs are turned on. An indicator, wherein the group is in a blinking state.