JP2001175219A - Matrix type picture display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress degradation of light emission intensity and also to suppress the maximum clock frequency even though luminous characteristics of respective cold-cathode electron emitting elements are allowed to have inverse gamma characteristics. SOLUTION: Since this display device allows luminous characteristics of respective cold-cathode electron emitting elements to have inverse gamma characteristics by mixing the change of the frequency of a clock signal and the change of the driving voltage of the elements by constituting so that signals having pulse widths corresponding to magnitude of picture data are generated from a PWM circuit by using a clock signal which is generated by a clock generating circuit and whose frequency is changed in time and voltage or current waveforms which are generated by a waveform generating circuit 8 and which are changed in time are cut off with the pulse widths and the respective elements which are arranged and wired in a matrix shape in a display panel are driven by being applied with the cut off waveforms, the device can suppress the degradation of light emission intensity and can suppress the maximum clock frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a matrix type image display device typified by a display device using an electron emission source such as a cold cathode electron emission device or an electroluminescence (hereinafter, referred to as EL) display device. In particular, the present invention relates to a driving method of an image display device.

[0002]

2. Description of the Related Art Hitherto, as a matrix type flat display device, a display device using a cold cathode electron-emitting device and an EL display device have been known.

FIG. 7 shows an example of a conventional configuration of a matrix type image display device. The display panel 10 is arranged in a matrix by, for example, a plurality (m) of row wirings connected to scanning electrodes and a plurality (n) of column wirings connected to data electrodes as shown in FIG. This is a display panel using the cold cathode electron-emitting device E.

The video signal 100 input to the terminal 1 is written to 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. P
The WM 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 the 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 T of one line width generated by the timing control circuit 6 based on the synchronizing signal 200 input to the terminal 5.
s are sequentially output from the first row through the shift register 7, and the switches Ss1 to Ssm are 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 sends a constant voltage −Vs to the scan electrodes S1 to Sm of the display panel 10.

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, scan electrodes S1 to S
The drive voltage is sequentially applied up to m. Further, a rectangular voltage pulse-width modulated (PWM) is applied to the data electrodes D1 to Dn in accordance with data corresponding to the selected line. That is, a voltage is applied to the data electrode Dj for the data in the i-th row and the j-th column while the scanning electrode Si is selected. The intensity (gradation) of light emission is expressed by applying a PWM-modulated signal to the data electrode and emitting light only during the pulse width.

FIG. 9 illustrates the display of the j-th column as an example. Now, consider a case where the number of bits of the signal is 8 bits, perfect black is represented as 0, and perfect white is represented as 255. In this case, one scanning period is 255 unit time
T), and the gradation expression is performed by changing the pulse width applied to the data electrode from 0T to 255T (actually, one scanning period may be constituted by 255 or more unit times).

It is assumed that the input signals are 0 in the i-th row and j-th column, 128 in the i + 1-th row and the j-th column, and 255 in the i + 2 row and the j-th column. In the scanning period of the i-th row, −Vs is applied to the scanning electrode Si of the i-th row, and the other scanning electrodes are 0. At this time, since the signal in the i-th row and the j-th column is “0”, the data electrode Dj in the j-th column is always at the 0 potential.

When the scanning period of the i-th row is completed, the operation proceeds to the scanning period of the (i + 1) -th row. In the scanning period H1 of the (i + 1) th row, i
-Vs is applied to the scanning electrodes in the +1 row, and 0 is applied to the other scanning electrodes. At this time, the signal in the (i + 1) th row and the jth column is “12”.
8 ″, the data electrodes in the j-th column are applied to the scanning period (25
+ Vd is applied only for a period (128T) which is about half of (5T), and becomes 0 thereafter.

When the scanning period of the (i + 1) -th row is completed, the operation proceeds to the scanning period of the (i + 2) -th row. In the scanning period of the (i + 2) th row, i
+ Vs is applied to the scanning electrodes in the +2 rows, and the other scanning electrodes are 0. At this time, since the signal in the (i + 2) th row and the jth column is “255”, the data electrode in the jth column is applied to the entire scanning period (2
At 55T), + Vd is applied.

A display panel using the cold-cathode electron-emitting device E generally has a threshold for emitting electrons. The solid line in FIG. 10 shows the characteristic 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 emission current occurs. Voltage (absolute value) V applied to the scanning electrode during the scanning period
Both s and the voltage Vd applied to the data electrode may be 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, the voltage (V) of only one of the data electrode and the scan electrode is used.
Light emission does not occur when d or Vs) is applied, and light is emitted only when both are applied (Vd + Vs).

In the example shown in FIG. 9, since the voltage applied to the element in the i-th row and the j-th column is always lower than Vth, no light emission occurs. The voltage applied to the element in the (i + 1) -th row and the j-th column is 128
Since Vth is exceeded only for the T period, light emission occurs only for the 128T period. Since the voltage applied to the element in the (i + 2) -th row and the j-th column exceeds Vth only for the period of 255T in the shaded area,
Light emission occurs during the T period.

Here, only the display process from the i-th row to the (i + 2) -th row has been described. However, in actuality, scanning pulses are sequentially applied from the first row to the M-th row, and the first to N-th columns are synchronized with the scanning timing. Are applied with PWM-modulated pulses. Then, the effective pixels are 480 rows × 6
In the case of the display of 40 columns, there are 480 scanning electrodes and 640 data electrodes, and in the case of the color display of the RGB stripe structure, there are 1920 data electrodes.

[0013]

In such gradation expression by PWM modulation, it is possible to exhibit a substantially linear light emission characteristic with respect to image data.

However, the actual image data has a gamma characteristic, and the display device preferably has an inverse gamma characteristic.

We have already invented a display device in which the waveform applied to the element is changed to a ramp-like or step-like waveform as a method for providing the inverse gamma characteristic. (Hereinafter, refer to the prior application.) Also, in JP-A-8-137427, PWM
A method of giving a reverse gamma characteristic by changing a clock frequency given to a circuit with time is shown.

However, in the former method, there is a problem that the light emission intensity when the pulse width in the PWM is maximized is smaller than that in the conventional method. In the latter method, the frequency increases in a narrow pulse width region. , There is a problem that the maximum operating frequency of the PWM circuit is exceeded.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to suppress the deterioration of the light emission intensity and the maximum clock frequency even if the device has an inverse gamma characteristic. To provide a matrix-type image display device capable of performing the following.

[0018]

To achieve the above object, a feature of the present invention is a matrix type image display device in which a plurality of elements are arranged in a matrix by a plurality of row wirings and a plurality of column wirings. Means for generating a pulse signal having a width corresponding to the magnitude of image data with a clock signal having a frequency that changes with time, and a means for cutting and outputting a time-varying voltage or current waveform with the pulse width. To drive each element arranged and wired in a matrix.

According to the first aspect of the present invention, a pulse signal having a width corresponding to the magnitude of image data is generated by a clock signal whose frequency changes over time, and the pulse signal has a temporal (pulse width) width. A pseudo inverse gamma characteristic is created in the light emission characteristic of each element by cutting out a voltage or current waveform that changes in the above manner and supplying the same to each element arranged and wired in a matrix to drive each element.

According to a second aspect of the present invention, the clock signal is generated so that the pulse width has a substantially constant frequency when the pulse width is equal to or smaller than a predetermined width, and is stepwise or in a region where the pulse width is equal to or larger than the predetermined width. The frequency is set so as to be gradually lowered, and the voltage or current waveform is stepwise or stepwise, with the pulse width being the predetermined width or a little narrower or less than a wide width (period where the frequency is almost constant). It is set to change gradually.

According to the second aspect of the present invention, in the frequency region where the pulse width is equal to or less than the predetermined width and the clock signal is substantially constant, the voltage or current waveform supplied to each element is, for example, stepwise or It is set to be gradually higher, and in this region, a pseudo inverse gamma characteristic is created by the change in the voltage or current waveform.

According to a third aspect of the present invention, the clock signal is generated such that the pulse width has a substantially constant frequency when the pulse width is equal to or less than a predetermined width, and is stepwise or gradually in a region where the pulse width is equal to or more than the predetermined width. The frequency is set to be low, and the voltage or current waveform is stepwise or gradually with the pulse width being less than or equal to the predetermined width or a little narrower or wider width (a period in which the frequency is almost constant). The voltage or current waveform is set so as to be flat in a region where the pulse width is set to change and the pulse width is equal to or larger than the predetermined width or slightly smaller or wider than the predetermined width.

According to the third aspect of the present invention, in a region where the pulse width is equal to or greater than a predetermined width, the clock signal is set so that the frequency gradually or gradually decreases,
In a region where the pulse width is equal to or larger than the predetermined width, the voltage or current waveform is set to be flat. In a region where the voltage or current waveform is flat, the inverse gamma characteristic is changed due to the frequency change of the clock signal. Has been created.

According to the fourth aspect of the present invention, the elements arranged and wired in a matrix form are a light emitting element or a light emitting element formed by a combination of an electron beam generating source and a phosphor receiving irradiation of an electron beam output from the electron beam generating source. It is a luminescence element.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the matrix type image display device of the present invention. However, the same parts as in the conventional example will be described using the same reference numerals.

The matrix type image display device has a video signal 1
00, a shift register 2 in which the video signal 100 (data) for one row is written, a latch circuit 3 for holding the video signal 100 for one row written in the shift register 2, and a latch circuit 3. A PWM circuit 4 for generating a pulse having a width corresponding to the magnitude of the held data, a terminal 5 to which a synchronization signal 200 is input, a timing control circuit 6 for generating a scan pulse Ts having one line width based on the synchronization signal 200, A shift register 7 into which a scan pulse Ts for one column is written, a waveform generation circuit 8 that generates a step-like or ramp-like waveform signal at the cycle of the scan pulse Ts, and a P whose cycle changes based on the scan pulse Ts.
A clock generation circuit 9 for generating a clock for driving the WM circuit, a display panel 10 in which cold cathode electron-emitting devices (not shown) are arranged in a matrix, and a waveform signal for driving the cold cathode electron-emitting devices input to the display panel 10. Switch S for turning off
Switches Ss1 to Ssm for turning on and off the display panel 10 with d1 to Sdn and the scan pulse Ts are provided.

Next, the operation of this embodiment will be described.

Embodiment 1 Circuits indispensable for the present embodiment to perform operations different from those of the conventional example are a waveform generating circuit 8 and a clock generating circuit 9. The waveform generating circuit 8 outputs a signal that repeats a step-like waveform in the scanning period, for example, as shown by the waveform generating circuit output in FIG.

Here, FIG. 3 shows one cycle of the waveform applied to the cold cathode electron-emitting device as shown in FIGS. 2 (6) to (8). As shown in FIG. 3, the step-like waveform changes stepwise from vd1 to vd2 to vd3. The cycle of the clock signal output from the clock generation circuit 9 changes stepwise from τ1 to τ2 to τ3 to τ4.

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). During this period, the cycle of the clock signal changes.

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. Become. Note that the vertical line indicating the clock waveform and the pulse width in FIG. 3 shows the image. When the image data has 256 gradations (8 bits), the number of clocks from 0 to t6 is 255. Cycle.

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 as shown in FIG.
(= Vd1 + vs), and the change in pulse width per one gradation of image data is τ1 which is the smallest. In this case, the amount of change in light emission per one gradation of the image data is the smallest, and as shown in FIG. 4, the slope of the characteristic of the image data versus the amount of light emission is the smallest (0 to t1 section).

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).
Therefore, the slope of the characteristic of the image data versus the light emission amount becomes slightly large (the interval from t1 to t2).

Similarly, when the image data becomes larger than t2, the voltage applied by the PWM circuit 4 becomes vd3, and the pulse voltage applied to the cold cathode electron-emitting device is also v3 (= vd3 +
vs), the inclination of the characteristic of the image data versus the light emission amount is further increased (t2 to t3 section).

Further, when the image data becomes larger than t3, the voltage applied by the PWM circuit 4 does not change at vd3, but the clock cycle becomes τ2, and the change of the pulse width per one gradation of the image data is small. growing. At this time, the slope of the characteristic of the image data versus the amount of light emission becomes even larger (section from t3 to t4).

Similarly, when the image data becomes larger than t4, the clock cycle becomes τ3, and the change of the pulse width per one gradation of the image data further increases. At this time, the inclination of the characteristics of the image data and the amount of light emission becomes even larger (section from t4 to t5).

Similarly, when the image data becomes larger than t5, the clock cycle becomes τ4, and the change of the pulse width per one gradation of the image data further increases. At this time, the inclination of the characteristic of the image data and the amount of light emission becomes even greater (section from t5 to t6).

As shown in this figure, the characteristic of the image data versus the amount of light emission can be similar to the inverse gamma characteristic although it is a polygonal line.

If only the clock cycle is set, 0 to t1
If an attempt is made to obtain an image data in which the amount of change in light emission per gradation of image data is small as in a period, the clock cycle must be considerably reduced, and the operation assurance speed of the PWM circuit 4 may be increased. is there. Further, when 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.

When the 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 the decrease in the light emission amount when the image data is 100% can be suppressed.

Embodiment 2 The voltage output from the waveform generating circuit 8 does not necessarily need to change stepwise, and the cycle of the clock signal generated from the clock generating circuit 9 does not necessarily need to change stepwise.

FIG. 5 differs from FIG. 4 of the first embodiment in that the voltage output from the waveform generation circuit 8 is stepped up (smoothly) like a ramp and the clock signal generated from the clock generation circuit 9 is generated. Is also designed to smoothly shorten the clock cycle.

In the second embodiment, the voltage changes from 0 to t1 and the clock cycle is constant, and from t1 to t2, the voltage is constant and the clock cycle changes. In this case, the relationship between the light emission amount and the image data can be a smooth curve as shown in FIG.

With such a configuration, substantially inverse gamma characteristics can be obtained, the operating 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.

According to the present embodiment, the clock cycle of the PWM circuit 4 is initially set to be constant during one cycle of the waveform applied to the cold cathode electron-emitting devices in the display panel 10.
In the meantime, the driver voltage (applied voltage of the cold cathode electron-emitting device) is changed in a step-like or ramp-like manner.
(E.g., by gradually increasing the clock period) to give the light emitting characteristics of the cold cathode electron-emitting device an inverse gamma characteristic, thereby changing the driver intensity over the entire one period of the light emitting intensity. The light emission intensity can be recovered by about 80 to 90% as compared with the conventional example in which the driver voltage is not changed.

In addition, since the clock cycle of the PWM circuit 4 is not changed over the entire cycle of the waveform applied to the cold cathode electron-emitting device, the maximum clock frequency of the PWM circuit 4 is increased. Therefore, the inverse gamma characteristic can be provided without using the PWM circuit 4 having an extremely high operating frequency, and the inverse gamma characteristic can be easily and inexpensively provided using a normal PWM circuit.

In the waveform diagrams of FIGS. 3 and 5, PW
Based on a predetermined pulse width at which the clock frequency of the M circuit 4 becomes a boundary between the constant region and the variable region, a voltage for driving the cold cathode electron-emitting device, that is, a region where the driver voltage is constant, and a stepwise or Although it is divided into a region that changes gradually, it is not the above-mentioned predetermined pulse width just,
Based on a pulse width slightly before and after this predetermined width,
A similar effect can be obtained by dividing the region into a region where the driver voltage is constant and a region where the driver voltage is gradually or gradually changed.

[0048]

As described above in detail, according to the matrix type image display device of the present invention, in a display device in which cold cathode electron-emitting devices and EL devices are arranged in a matrix, a simple circuit configuration is used. In addition, there is an advantage that the gradation characteristics of the low luminance portion can be improved without lowering the maximum light emission intensity, and further, the light emission characteristics for image data can have an inverse gamma characteristic. In addition, the maximum operating frequency of the PWM circuit can be reduced as compared with the 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 chart (Example 1) for explaining the operation of the device shown in FIG. 1;

FIG. 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. 1;

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 chart (Example 2) for explaining another operation example of the cold cathode electron-emitting device in the display panel shown in FIG.

FIG. 6 is a characteristic diagram (Example 2) showing another emission characteristic of the cold cathode electron-emitting device in the display panel shown in FIG. 1;

FIG. 7 is a block diagram showing 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.

FIG. 9 is a waveform chart for explaining the operation of the conventional device shown in FIG. 7;

FIG. 10 is a characteristic diagram showing characteristics of an emission current with respect to a voltage applied to a conventional cold cathode electron-emitting device.

[Explanation of symbols]

 1, 5 terminal 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-Sdn, Ss1-Ssm switch

Claims (4)

[Claims] 1. A matrix-type image display device in which a plurality of elements are arranged in a matrix by a plurality of row wirings and a plurality of column wirings, wherein the width of the clock data changes in time with respect to the size of image data. A matrix-type image, wherein each of the elements arranged and wired in a matrix is driven by means for generating a pulse signal of the following and means for cutting out and outputting a time-varying voltage or current waveform with the pulse width. Display device 2. The clock signal is generated such that the pulse width has a substantially constant frequency when the pulse width is equal to or less than a predetermined width, and in a region where the pulse width is equal to or greater than the predetermined width, the frequency is gradually or gradually increased. The voltage or current waveform changes stepwise or gradually when the pulse width is less than or equal to the predetermined width or slightly smaller or wider than the predetermined width (period in which the frequency is substantially constant). 2. The matrix type image display device according to claim 1, wherein: 3. The clock signal is generated such that the pulse width has a substantially constant frequency when the pulse width is equal to or less than a predetermined width, and the frequency is gradually or gradually increased in a region where the pulse width is equal to or more than the predetermined width. The voltage or current waveform is set so as to be lower, and the pulse width changes stepwise or gradually when the pulse width is equal to or smaller than the predetermined width or slightly smaller or wider than the predetermined width (period in which the frequency is substantially constant). The voltage or current waveform is set to be flat in an area where the pulse width is set to the predetermined width or a width slightly smaller or wider than the predetermined width. Matrix image display device. 4. The elements arranged and wired in a matrix,
A light-emitting element comprising a combination of an electron beam source and a phosphor receiving irradiation of an electron beam output from the electron beam source,
4. The matrix type image display device according to claim 1, wherein the matrix type image display device is an electroluminescence element.