JP4453136B2 - Matrix type image display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a display device using an electron emission source such as a cold cathode electron-emitting device or a matrix type image display device typified by an electroluminescence (hereinafter referred to as EL) display device, and in particular, driving of the image display device. It relates to the method.
[0002]
[Prior art]
Conventionally, as a matrix type flat display device, a display device using a cold cathode electron-emitting device and an EL display device are known.
[0003]
FIG. 7 shows an example of a conventional configuration of a matrix type image display apparatus. The display panel 10 is arranged in a matrix by, for example, a plurality (m) of row wirings connected to the scanning electrodes and a plurality of (n) column wirings connected to the data electrodes as shown in FIG. This is a display panel using the cold cathode electron-emitting device E.
[0004]
The video signal 100 input to the terminal 1 is written into the shift register 2. After one row of data is written in the shift register 2, the data is latched by the latch circuit 3 and sent to the PWM circuit 4. The PWM circuit 4 controls the switches Sd1 to Sdn with a pulse corresponding to the magnitude of the data. The switches Sd1 to Sdn are turned on when the pulse supplied from the PWM circuit 4 is High and sends a constant voltage + Vd to the data electrodes D1 to Dn of the display panel 10. On the other hand, on the scan electrode side of the display panel 10, the scan pulse Ts having one line width generated by the timing control circuit 6 based on the synchronization signal 200 input to the terminal 5 is sequentially transmitted from the first row via the shift register 7. The switch Ss1 to Ssm is controlled by this pulse. The switches Ss1 to Ssm are turned on when the scan pulse supplied from the shift register 7 is High, and send a constant voltage −Vs to the scan electrodes S1 to Sm of the display panel 10.
[0005]
Next, the operation principle will be described by taking as an example the case of driving a simple matrix type display device arranged in M rows and N columns. First, on the scan electrode side, drive voltages are sequentially applied to the scan electrodes S1 to Sm. Further, a rectangular voltage pulse-modulated (PWM) according to data corresponding to the selected line is applied to the data electrodes D1 to Dn. That is, for the data of i rows and j columns, a voltage is applied to the data electrode Dj during the period when the scan electrode Si is selected. The intensity of light emission (gradation) is expressed by applying a PWM-modulated signal to the data electrode and emitting light only during the period of the pulse width.
[0006]
FIG. 9 illustrates the display of column j as an example. Consider a case where the number of bits of a signal is represented as 8 bits, complete black is represented as 0, and complete white is represented as 255. In this case, one scanning period is composed of 255 unit times (hereinafter referred to as T), and gradation expression is performed by changing the pulse width applied to the data electrode from 0T to 255T (actually, one scanning period). May be configured with a unit time of 255 or more).
[0007]
Assume that the input signal is 0 for i row and j column, 128 for i + 1 row and j column, and 255 for i + 2 row and j column. In the i-th scanning period, -Vs is applied to the i-th scanning electrode Si, and the other scanning electrodes are zero. At this time, since the signal in the i row and the j column is “0”, the data electrode Dj in the j column is always at the 0 potential.
[0008]
When the i-th scanning period ends, the i + 1-th scanning period starts. In the scan period H1 of the i + 1th row, −Vs is applied to the scan electrode of the i + 1th row, and the other scan electrodes are zero. At this time, since the signal of i + 1 row and j column is “128”, + Vd is applied to the data electrode of j column for about a half period (128T) of the scanning period (255T) and then becomes 0.
[0009]
When the scanning period for the (i + 1) th row ends, the scanning period starts for the (i + 2) th row. In the scanning period of i + 2 row, −Vs is applied to the scanning electrode of i + 2 row, and the other scanning electrodes are 0. At this time, since the signal of i + 2 row and j column is “255”, + Vd is applied to the data electrode of j column in the entire scanning period (255T).
[0010]
A display panel using the cold cathode electron-emitting device E generally has a threshold value for emitting electrons. The solid line in FIG. 10 shows the characteristics of the emission current with respect to the voltage applied to the cold cathode electron-emitting device E. Vth in FIG. 10 is a threshold value at which an emission current is generated. In the scanning period, the voltage (absolute value) Vs applied to the scan electrode side and the voltage Vd applied to the data electrode are both set to Vth or less, and Vd + Vs may be set to be larger than Vth. Since the voltage applied to the cold cathode electron-emitting device E is the difference between the potential of the data electrode and the potential of the scan electrode, in this case, light emission occurs when only one of the data electrode and the scan electrode (Vd or Vs) is applied. Does not occur and emits light only when applied to both (Vd + Vs).
[0011]
In the example of FIG. 9, since the voltage applied to the element in i row and j column is always equal to or lower than Vth, no light emission occurs. Since the voltage applied to the element in the (i + 1) th row and jth column exceeds Vth only for the 128T period in the shaded area, light emission occurs only for the 128T period. Since the voltage applied to the element in i + 2 rows and j columns exceeds Vth only for the 255T period in the shaded area, light emission occurs during the 255T period.
[0012]
Here, only the display process from the i-th row to the i + 2-th row has been described, but actually, the scan pulse is sequentially applied from the first row to the M-th row, and the data electrodes from the first column to the N-th column are adapted to this scanning timing. A PWM modulated pulse is applied. In the case of display of 480 rows × 640 columns of effective pixels, there are 480 scan electrodes and 640 data electrodes, and in the case of color display with an RGB stripe structure, there are 1920 data electrodes.
[0013]
[Problems to be solved by the invention]
In such gradation expression by PWM modulation, it is possible to show a substantially linear light emission characteristic with respect to image data.
[0014]
However, actual image data has a gamma characteristic, and the display device desirably has an inverse gamma characteristic.
[0015]
We have already invented a display device in which the waveform applied to the element is changed to a ramp shape or a step shape as a method of giving an inverse gamma characteristic. Japanese Patent Laid-Open No. 8-137427 discloses a method for providing an inverse gamma characteristic by temporally changing the clock frequency applied to the PWM circuit.
[0016]
However, the former method has a problem that the light emission intensity when the pulse width in the PWM is maximized is smaller than that in the conventional method, and the latter method increases the frequency in a narrow pulse width region, and the PWM circuit. There is a problem that it exceeds the maximum operating frequency.
[0017]
The present invention has been made in order to solve the conventional problems as described above, and an object of the present invention is to provide a matrix capable of suppressing the deterioration of the light emission intensity and the maximum clock frequency even if the inverse gamma characteristic is provided. Type image display device.
[0018]
[Means for Solving the Problems]
In order to achieve the above object, a feature of the invention of claim 1 is that a matrix-type image display device includes a display panel having a plurality of elements arranged in a matrix with a plurality of row wirings and a plurality of column wirings, Within one scanning period of image data displayed on the display panel, the voltage value or current value increases stepwise in the first section from the start position of the one scanning period to a predetermined intermediate position, and ends from the intermediate position. Waveform generating means for generating a waveform in which a constant value equal to the voltage value or current value at the intermediate position continues in the second interval up to the position, and the cycle is constant in the first interval, a clock generating means for generating a clock signal period is stepwise increased in a section, for each scan period, the gradation magnitude of the image data by a clock signal, wherein the clock generating means generates Generates a pulse signal corresponding pulse width, the waveform in which the waveform generating means is cut based on a waveform generated in the pulse signal, to be provided with a driving means for emitting the device is applied to the element is there.
[0019]
A feature of the invention of claim 2 is that a matrix type image display device includes a display panel having a plurality of elements arranged in a matrix with a plurality of row wirings and a plurality of column wirings, and image data to be displayed on the display panel. Within one scanning period, the voltage value or the current value continuously increases in the first section from the start end position to the predetermined intermediate position in the one scanning period, and in the second section from the intermediate position to the end position. Waveform generating means for generating a waveform having a constant value that is the same value as the voltage value or current value at the intermediate position, and the cycle is constant in the first section, and the cycle is continuously long in the second section. a clock generating means for generating a clock signal comprising, for each scan period, a pulse signal having a pulse width said clock generating means in accordance with the magnitude of the gradation of the image data with a clock signal generated Was generated, a waveform the waveform generating means is cut based on a waveform generated in the pulse signal, is applied to the element is to comprise a driving means for emitting the element.
[0020]
A feature of the invention of claim 3 is that the element is a light emitting element or an electroluminescence element by a combination of an electron beam generation source and a phosphor that is irradiated with an electron beam output from the electron beam generation source. It is in.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an embodiment of a matrix type image display device of the present invention. However, the same parts as those in the conventional example will be described using the same reference numerals.
[0026]
The matrix type image display device holds a video signal 100 input terminal 1, a row of video signals 100 (data) shift register 2, and a row of video signals 100 written to the shift register 2. The latch circuit 3, the PWM circuit 4 that generates a pulse having a width corresponding to the magnitude of the data held in the latch circuit 3, the terminal 5 to which the synchronization signal 200 is input, and a scan pulse having a line width of 1 line based on the synchronization signal 200. A timing control circuit 6 for generating Ts, a shift register 7 in which scan pulses Ts for one column are written, a waveform generation circuit 8 for generating a step-like or ramp-like waveform signal at the period of the scan pulse Ts, and a scan pulse Ts. A clock generation circuit 9 for generating a PWM circuit driving clock whose period changes, and a cold cathode electron-emitting device (not shown) ) Arranged in a matrix, switches Sd1 to Sdn for turning on / off the waveform signal for driving the cold cathode electron-emitting devices, and switches for turning on / off the scan pulse Ts to the display panel 10 Ss1 to Ssm.
[0027]
Next, the operation of this embodiment will be described.
[0028]
Example 1
Circuits indispensable for the operation of this example to be different from the conventional example are the waveform generation circuit 8 and the clock generation circuit 9. The waveform generation circuit 8 outputs a signal that repeats, for example, a stepped waveform as shown by the waveform generation circuit output in FIG.
[0029]
Here, one cycle of the waveform applied to the cold cathode electron-emitting device as shown in FIGS. 2 (6) to (8) is shown in FIG. As shown in FIG. 3, the step-like waveform changes stepwise from vd1 to vd2 to vd3 . The period of the clock signal output from the clock generation circuit 9 changes stepwise from τ1 to τ2 to τ3 to τ4.
[0030]
Further, during the period when the output of the waveform generation circuit 8 is changing, the period of the clock signal output from the clock generation circuit 9 is constant (τ1) and the output of the waveform generation circuit 8 is constant (vd3). The clock signal cycle changes.
[0031]
In such a driving method, the voltage waveform applied to each cold cathode electron-emitting device is a waveform (shaded portion) obtained by cutting the waveform shown in FIG. 3 with a pulse width (for example, tp) corresponding to image data. The vertical lines indicating the clock waveform and the step of the pulse width in FIG. 3 indicate the image. When the image data has 256 gradations (8 bits), the number of clocks from 0 to t6 is 255. It becomes a cycle.
[0032]
The light emission characteristics (FIG. 4) when the cold cathode electron-emitting device of the display panel 10 is driven with such a waveform will be specifically described. First, when the image data is small, the clock cycle applied to the PWM circuit 4 is τ1, and the voltage applied to the PWM circuit 4 is vd1. That is, the pulse voltage applied to the cold cathode electron-emitting device is the smallest v1 (= vd1 + vs) as shown in FIG. 3, and the change in the pulse width per gradation of image data is also the smallest τ1. In this case, the amount of change in light emission per gradation of image data is the smallest, and the slope of the characteristics of the image data versus the amount of light emission is the smallest as shown in FIG. 4 (0 to t1 interval).
[0033]
When the image data becomes larger than t1, the voltage applied by the PWM circuit 4 is vd2, and the pulse voltage applied to the cold cathode electron-emitting device is also v2 (= vd2 + vs). A little larger (t1-t2 interval).
[0034]
Similarly, when the image data becomes larger than t2, the voltage applied by the PWM circuit 4 is vd3, and the pulse voltage applied to the cold cathode electron-emitting device is also v3 (= vd3 + vs). The inclination is further increased (t2 to t3 interval).
[0035]
Further, when the image data becomes larger than t3, the voltage applied by the PWM circuit 4 does not change with vd3, but the clock period becomes τ2, and the change of the pulse width per gradation of the image data becomes slightly larger. At this time, the gradient of the characteristics of the image data versus the light emission amount is further increased (section t3 to t4).
[0036]
Similarly, when the image data becomes larger than t4, the clock cycle becomes τ3, and the change of the pulse width per gradation of the image data becomes further larger. At this time, the inclination of the characteristics of the image data evening light emission amount further increases (t4 to t5 interval).
[0037]
Similarly, when the image data becomes larger than t5, the clock period becomes τ4, and the change of the pulse width per gradation of the image data becomes further larger. At this time, the gradient of the characteristics of the image data evening light emission amount is further increased (t5 to t6 interval).
[0038]
As shown in this figure, the image data versus light emission characteristic can be made similar to the inverse gamma characteristic although it is a polygonal line.
[0039]
If an attempt is made to obtain a small amount of change in light emission per gradation of image data, such as a period of 0 to t1, by simply setting the clock cycle, the clock cycle must be considerably reduced, and the PWM circuit 4 There is a risk that the operation guarantee speed of will be increased. Further, if the voltage applied to the PWM circuit 4 is changed over the entire period, the light emission amount when the image data is 100% becomes small.
[0040]
If driving is performed by changing both the clock cycle and the voltage as in this embodiment, the operation speed of the PWM circuit 4 can be suppressed, and a decrease in the light emission amount when the image data is 100% can be suppressed.
[0041]
Example 2
The voltage output from the waveform generation circuit 8 does not necessarily change stepwise, and the cycle of the clock signal generated from the clock generation circuit 9 does not necessarily change stepwise.
[0042]
5 differs from FIG. 4 of the first embodiment in that the voltage output from the waveform generation circuit 8 is stepped up (smoothly) in a ramp shape and the clock signal generated from the clock generation circuit 9 is also smooth. The clock cycle is made longer .
[0043]
In the second embodiment, the voltage changes from 0 to t1 and the clock cycle is constant, and the voltage is constant and the clock cycle changes from t1 to t2. In this case, the relationship between the light emission amount and the image data can be a smooth curve as shown in FIG.
[0044]
With such a configuration, an almost inverse gamma characteristic can be obtained, the operation speed of the PWM circuit 4 can be suppressed, and a decrease in light emission when the image data is 100% can be suppressed.
[0045]
According to the present embodiment, during one period of the waveform applied to the cold cathode electron-emitting devices in the display panel 10, the clock period of the PWM circuit 4 is initially constant, and during that period, the driver voltage (cold cathode electrons The applied voltage of the emission element) is changed stepwise or ramped, and then the clock cycle of the PWM circuit 4 is changed (increased stepwise) during a period in which the driver voltage is set to the maximum constant value, thereby causing cold cathode electron emission. By giving the light emission characteristic of the element an inverse gamma characteristic, the light emission intensity can be made larger than that in which the driver voltage is changed over the entire one period, and the light emission is compared with the conventional example in which the driver voltage is not changed. The strength can be recovered by about 80 to 90%.
[0046]
Furthermore, since the clock period of the PWM circuit 4 is not changed over the entire period of the waveform applied to the cold cathode electron-emitting device, the maximum clock frequency of the PWM circuit 4 is not increased so much. Since the reverse gamma characteristic can be provided, it is not necessary to use the PWM circuit 4 having an extremely high operating frequency, and the reverse gamma characteristic can be provided inexpensively and easily using a normal PWM circuit.
[0047]
In the waveform diagrams of FIGS. 3 and 5, the voltage for driving the cold cathode electron-emitting device, that is, the driver voltage, based on a predetermined pulse width where the clock frequency of the PWM circuit 4 is a boundary between the constant region and the variable region. Is divided into a region in which the driver voltage is constant and a region in which the driver voltage is changed stepwise or gradually. The driver voltage is not based on the predetermined pulse width just, but on the basis of a pulse width of a width slightly around this predetermined width. Similar effects can be obtained by dividing the voltage constant region into the driver voltage stepwise or gradually changing region.
[0048]
【The invention's effect】
As described above in detail, according to the matrix type image display device of the present invention, the maximum emission intensity can be obtained with a simple circuit configuration in a display device in which cold cathode electron-emitting devices and EL devices are arranged in a matrix. There is an advantage that the gradation characteristic of the low luminance part can be improved without lowering, and the light emission characteristic with respect to the image data can have an inverse gamma characteristic. In addition, the maximum operating frequency of the PWM circuit can be lowered as compared with a method of simply switching the pulse width modulation clock signal.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment of a matrix type image display device of the present invention.
FIG. 2 is a waveform diagram (Example 1) for explaining the operation of the apparatus shown in FIG. 1;
3 is a waveform diagram (Example 1) for explaining an operation example of the cold cathode electron-emitting device in the display panel shown in FIG.
4 is a characteristic diagram (Example 1) showing light emission characteristics of the cold cathode electron-emitting devices in the display panel shown in FIG. 1. FIG.
5 is a waveform diagram (Example 2) for explaining another operation example of the cold cathode electron-emitting device in the display panel shown in FIG. 1. FIG.
6 is a characteristic diagram (Example 2) showing another light emission characteristic of the cold cathode electron-emitting device in the display panel shown in FIG. 1. FIG.
FIG. 7 is a block diagram illustrating a configuration example of a conventional matrix type image display device.
FIG. 8 is a diagram showing a wiring image of elements in a conventional display panel.
9 is a waveform diagram for explaining the operation of the conventional apparatus shown in FIG. 7;
FIG. 10 is a characteristic diagram showing a characteristic of an emission current with respect to a voltage applied to a conventional cold cathode electron-emitting device.
[Explanation of symbols]
1, 5 Terminals 2, 7 Shift register 3 Latch circuit 4 PWM circuit 6 Timing control 8 Waveform generation circuit 9 Clock generation circuit 10 Display panel Sd1 to Sdn, Ss1 to Ssm switch

Claims (3)

A display panel having a plurality of elements arranged in a matrix with a plurality of row wirings and a plurality of column wirings;
Within one scanning period of the image data displayed on the display panel, the voltage value or current value increases stepwise in the first section from the start position of the one scanning period to a predetermined intermediate position. Waveform generating means for generating a waveform in which a constant value of the same value as the voltage value or current value at the intermediate position continues in the second section to the end position;
Clock generating means for generating a clock signal having a constant period in the first interval and a stepwise increase in the period in the second interval;
In each scanning period, a pulse signal having a pulse width corresponding to the gradation level of the image data is generated by the clock signal generated by the clock generation unit, and the waveform generated by the waveform generation unit is converted into the pulse signal. waveforms taken based, driving means for emitting the device is applied to the element,
A matrix-type image display device comprising: A display panel having a plurality of elements arranged in a matrix with a plurality of row wirings and a plurality of column wirings;
Within one scanning period of image data to be displayed on the display panel, the voltage value or current value continuously increases in the first section from the start position of the one scanning period to a predetermined intermediate position. Waveform generating means for generating a waveform in which a constant value of the same value as the voltage value or current value at the intermediate position continues in the second section to the end position;
A clock generating means for generating a clock signal having a constant period in the first section and a period continuously increasing in the second section;
In each scanning period, a pulse signal having a pulse width corresponding to the gradation level of the image data is generated by the clock signal generated by the clock generation unit, and the waveform generated by the waveform generation unit is converted into the pulse signal. Driving means for applying a waveform cut out based on the element to cause the element to emit light ;
A matrix-type image display device comprising:   The element is a light emitting element or an electroluminescence element by a combination of an electron beam generation source and a phosphor that is irradiated with an electron beam output from the electron beam generation source. The matrix type image display device described in 1.

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