JP2002040982A - Matrix type display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a matrix type display device having a light-emitting characteristic approximate to an inverse gamma-characteristic and having no decrease in brightness, by driving elements with a waveform combined by two PWM circuits. SOLUTION: A 1st PWM circuit 11, a waveform generation circuit 13, and switches Sd1-Sdn comprise a 1st driving means, and a 2nd PWM circuit 12, a constant voltage +Vd, and switches Sxd1-Sxdn comprise a 2nd driving means. The switches Sd1-Sdn are switched on only for a High period of a pulse supplied from the 1st PWM circuit 11, and supply an output signal of the waveform generation circuit 13 to data electrodes D1-Dn. The switches Sxd1-Sxdn are switched on only for a high period of a pulse supplied from the 2nd PWM circuit 12, and supply the constant voltage +Vd to data electrodes D1-Dn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a matrix type display device such as an FED display device or an electroluminescence display device using a cold cathode electron-emitting device.

[0002]

2. Description of the Related Art Conventionally, as an active matrix type flat display device, an FED display device using a cold cathode electron-emitting device and an electroluminescence (hereinafter, referred to as EL) display device have been known. FIG. 6 is a diagram showing a configuration of a conventional matrix type display device, and FIG. 7 is a diagram showing a wiring image of elements in a display panel. 6, the display panel 10 includes, for example, scan electrodes S1 to S1 shown in FIG.
A plurality of (m) row wirings connected to Sm and a plurality (n) column wirings connected to data electrodes D1 to Dn use cold cathode electron-emitting devices arranged in a matrix. It is a display panel.

An input video signal input from an input terminal 1 is supplied to a shift register 2. The shift register 2 writes data for one row of the input video signal. The latch circuit 3 latches an output signal (data) of the shift register 2 and supplies the output signal (data) to the PWM circuit 4. PWM circuit 4
Generates a pulse having a pulse width that increases according to the data value of the video signal, and supplies the pulse to the switches Sd1 to Sdn. The switches Sd1 to Sdn are turned on during a period when the pulse supplied from the PWM circuit 4 is High, and supplies the constant voltage + Vd to the data electrodes D1 to Dn of the display panel 10.

[0006] The synchronization signal input from the input terminal 5 is supplied to a timing control circuit 6. The timing control circuit 6 controls the latch circuit 3 and the shift register 7 at a timing based on the synchronization signal. The shift register 7 generates a scan pulse Ts of one line width sequentially from the first row under the control of the timing control circuit 6, and supplies the scan pulse Ts to the switches Ss1 to Ssm. The switches Ss1 to Ssm are turned on during a period when the scan pulse supplied from the shift register 7 is High, and supplies the 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. A pulse voltage having a pulse width modulated (PWM) in accordance with data corresponding to the selected line is applied to the data electrodes D1 to Dn. 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 P
It is expressed by applying a WM-modulated signal to the data electrode and emitting light only during the period of the pulse width.

FIG. 8 is a waveform chart for explaining the operation of FIG. For example, consider a case where the number of bits of a signal is expressed as 8 bits, complete black is represented as 0, and complete white is represented as 255. In this case, one scanning period is constituted by 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 composed of 255 or more unit times.) Assuming that the input signal is 0/255 in the i-th row and the j-th column and 1 in the (i + 1) -th row and the j-th column.
It is assumed that 28/255, (i + 2) row j column is 255/255. In the scanning period of the i-th row, as shown in FIG. 8A, −Vs is supplied to the scanning electrode Si of the i-th row, and the other scanning electrodes are 0. At this time, the signal in the i-th row and the j-th column is 0 /
8D, the data electrode Dj in the j-th column is at the zero potential during this period as shown in FIG.

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 of the (i + 1) row,
As shown in FIG. 8 (B), the scanning electrodes in the (i + 1) -th row have −Vs
Are supplied, and the other scan electrodes are zero. At this time,
Since the signal of (i + 1) row and j column is 128/255, as shown in FIG. 8D, + Vd is supplied to the data electrode Dj of j column only for a period (128T) which is about half of the scanning period (255T). And then becomes zero. When the scanning period of the (i + 1) -th row is completed, the process proceeds to the scanning period of the (i + 2) -th row. In the scanning period of the (i + 2) -th row, as shown in FIG. 8C, −Vs is supplied to the scanning electrodes of the (i + 2) -th row, and the other scanning electrodes are at zero. At this time, since the signal of (i + 2) row and j column is 255, as shown in FIG. 8D, + Vd is supplied to the data electrode Dj of j column during the entire scanning period (255T). .

FIG. 9 is a characteristic diagram of a cold cathode electron-emitting device. A display panel using a cold cathode electron emission element generally has a threshold value for emitting electrons. In FIG. 9, the horizontal axis represents the applied voltage Va, the vertical axis represents the emission current ie, and the solid line represents the applied voltage Va of the cold cathode electron-emitting device.
3 shows the characteristics of the emission current with respect to. V in the figure
th is a threshold value at which emission current occurs. In the scanning period, the voltage (absolute value) Vs supplied to the scan electrode and the voltage Vd supplied to the data electrode are both set to Vth or less, and (Vd + Vs) may be set to be larger than Vth. Since the applied voltage of the cold cathode electron-emitting device is a difference between the potential of the data electrode and the potential of the scan electrode, in this case, the voltage (Vd) of only one of the data electrode and the scan electrode is used.
Or Vs) does not emit light, but emits light only when (Vd + Vs) is applied to both.

In the example shown in FIG. 8, no light emission occurs because the voltage applied to the element in the i-th row and the j-th column is always lower than Vth. As shown in FIG. 8 (F), the voltage applied to the element in the (i + 1) -th row and the j-th column exceeds Vth only for the shaded 128T period, so that light emission occurs only for the 128T period. As shown in FIG. 8 (G), the applied voltage to the element in the (i + 2) row and j column is 2
Since Vth is exceeded for only 55T, light emission occurs for 255T. Here, only the display process from the i-th row to the (i + 2) -th row has been described.
A scanning pulse is sequentially applied to the rows, and a PWM-modulated pulse is supplied to data electrodes in columns 1 to N in accordance with the scanning timing. In the case of display of 480 rows × 640 columns of effective pixels, there are 480 scanning electrodes and 640 data electrodes, and in the case of color display of an RGB stripe structure, there are 1920 data electrodes.

In such a gradation expression by PWM modulation, it is possible to exhibit a substantially linear light emission characteristic with respect to image data. However, in an actual video signal, the relationship between the image data amplitude and the image brightness is not linear,
It has gamma characteristics. Therefore, in a display device having a linear characteristic, it is necessary to perform inverse gamma correction on an image signal. In the image display by the CRT, there is no necessity because the light emission characteristic has the inverse gamma characteristic.

FIG. 10 is a diagram showing the structure of another conventional matrix type display device, and FIG. 11 is a waveform diagram for explaining the operation of FIG. 10, which will be described together. In FIG.
The same parts as those in FIG. 6 described above are denoted by the same reference numerals, and description thereof will be omitted. The main difference from FIG. 6 is that a waveform generator 8 is provided. This has a light emission characteristic similar to an inverse gamma characteristic like a CRT due to a method of modulating a drive voltage, and a waveform in which a voltage or a current changes with a certain gradient within one scanning period is represented by an image of each pixel. By supplying a waveform cut out with a pulse width corresponding to the data to the display element, the display device has a light emission characteristic similar to the inverse gamma characteristic.

In FIG. 10, a waveform generating circuit 8 generates an output signal having a ramp-shaped waveform in a scanning period cycle as shown in FIG. 11D under the control of a timing control circuit 6, and switches Sd1 to Sdn. To supply. PW
As described with reference to FIG. 6, the M circuit 4 has 0T to 255 corresponding to the data values 0 to 255 of the video signal (image data).
The pulse of T is output and supplied to the switches Sd1 to Sdn. During the High period of this pulse, the switches Sd1 to Sd
Turn on n. At this time, as shown in FIG. 11 (E), the voltage applied to the j-th column data electrode has a waveform obtained by cutting a ramp-shaped waveform by a pulse width. The applied voltage of the element in the i-th row and the j-th column is shown in FIG. 11 (F), the applied voltage of the element in the (i + 1) -th row and the j-th column is shown in FIG. The waveform shown in FIG. In these waveforms, light emission actually occurs in the shaded portions exceeding the threshold value Vth. That is, it is a portion where a voltage having a gradient is applied within the light emitting period.

The light emission characteristics when driven with such a waveform will be specifically described. In order to avoid complicated calculations, the applied voltage vs. emission current characteristics of the electron-emitting device shown in FIG. 9 are approximated not by the actual solid line but by the straight line indicated by the broken line. When this straight line is expressed by a mathematical formula, the following formula is obtained. Here, ie is the emission current, va is the applied voltage, and g is the slope (conductance) of the straight line.

[0014]

(Equation 1)

FIG. 12 is a waveform chart for explaining the applied voltage of the element. The voltage va applied to each element is shown in FIG.
As shown in the figure, the voltage at t = 0 is v0 and the voltage at t = tw is v1.
Assuming that it increases linearly as follows, it can be expressed as a function of time t as in the following equation.

[0016]

(Equation 2)

From these equations, the amount of electrons q emitted from each element in the pulse width from time 0 to time tp is obtained.
Is derived, the following equation is obtained, and it can be seen that the emitted electron quantity q with respect to the pulse width tp shows a quadratic function.

[0018]

(Equation 3)

FIG. 13 is a diagram showing the light emission characteristics of the device.
Since light emission is caused by the irradiation of electrons from the electron-emitting device, the light emission amount with respect to the image data (the number of pulses) becomes an inverse gamma curve approximated to a quadratic function as shown in FIG. In practice, a complete quadratic function may be generated due to an error caused by approximating the applied voltage vs. emission current characteristic shown in FIG. 9 with a straight line or a saturation phenomenon of a phosphor that emits light upon irradiation with electrons. No. Also, here, as shown in FIG.
Although the case where the end voltage is higher than the start voltage of the ramp waveform has been described, the pulse generated from the PWM circuit cuts off the end side of the ramp waveform so that the end voltage is lower than the start voltage. It is needless to say that the same effect can be obtained even if the control is performed in the above manner.

[0020]

In such gradation expression by PWM modulation, it is possible to exhibit a substantially linear light emission characteristic with respect to image data. In the conventional example described with reference to FIG. 10, an inverse gamma characteristic can be obtained by changing the waveform applied to the element to a ramp-like or step-like waveform. However, in this method, there is a problem that the luminance is reduced due to the inverse gamma correction.

FIG. 14 is a characteristic diagram for explaining a decrease in luminance. Since the maximum voltage v2 to be applied is determined, the peak value of the ramp waveform must be adjusted to a conventional constant voltage as shown in FIG. Since the obtained luminance (light emission amount) is determined by the total amount of injected electrons, when driven by a ramp-shaped waveform, the charge amount corresponding to the hatched portion in FIG. 14B decreases, and as a result, FIG. As shown in (1), when inverse gamma correction is performed, there is a problem that the luminance (light emission amount) is lower than when the inverse gamma correction is not performed. Experiments under certain conditions have shown that the brightness is reduced by half when the gradient is applied. The present invention has been made to solve the above-mentioned problem, and has a light emission characteristic approximate to an inverse gamma characteristic by driving an element with a waveform obtained by combining two PWM circuits, and furthermore, there is no reduction in luminance. It is an object to provide a matrix display device.

[0022]

In order to achieve the above object, a plurality of row wirings connected to a plurality of scanning electrodes of a plurality of elements and a plurality of column wirings connected to a plurality of data electrodes are provided. In a matrix type display device having a display panel with a matrix wiring, a pulse width which increases in accordance with a data value of an input video signal is synchronized with a portion where the data value of the input video signal is equal to or less than a predetermined value. A first driving unit that outputs a pulse voltage having a constant peak value in a portion where the peak value changes with time and the data value is equal to or higher than a predetermined value; and when the data value is equal to or lower than a predetermined value, A second drive that does not output a pulse voltage and outputs a pulse voltage having a pulse width that increases according to the data value of the input video signal and has a constant peak value when the data value is equal to or greater than a predetermined value; Means A matrix type display device comprising: superimposing means for superimposing an output pulse of the first driving means and an output pulse of the second driving means and supplying the superposed output pulses to the plurality of data electrodes. Things.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 to 4 are waveform diagrams for explaining FIG. 1, and FIG. And
Also described. In FIG. 1, FIG. 6 and FIG.
The same reference numerals are given to the same parts as in FIG.
The main difference in configuration from FIG. 10 is that the PWM circuit
The point that the WM circuit 11 and the second PWM circuit 12 are in a parallel configuration and that the switches Sxd1 to Sxdn are added will be described in detail below.

In FIG. 1, the output signal of the latch circuit 3 is supplied to a first PWM circuit 11 and a second PWM circuit 12. The first PWM circuit 11, the waveform generation circuit 13, and the switches Sd1 to Sdn constitute first driving means,
Second PWM circuit 12, constant voltage + Vd and switch Sxd
1 to Sxdn constitute a second driving unit. First,
In the first driving means, the output signal of the waveform generating circuit 13 is supplied to the switches Sd1 to Sdn. The switches Sd1 to Sdn are turned on only during the High period of the pulse supplied from the first PWM circuit 11, and supply the output signal of the waveform generating circuit 13 to the data electrodes D1 to Dn of the display panel 10 during this period.

Next, in the second driving means, the switches Sxd1 to Sxdn are turned on only during the High period of the pulse supplied from the second PWM circuit 12, and during this period, the constant voltage + Vd is applied to the data electrode of the display panel 10. D1
Dn. Therefore, the output signals of the first driving unit and the output signals of the second driving unit are supplied to the data electrodes D1 to Dn of the display panel 10 in a superimposed manner. Hereinafter, the detailed operation will be described.

The first PWM circuit 11 is the same as the conventional PWM circuit.
Similarly to the WM circuit 4, a pulse having a pulse width that increases according to the data value of the video signal is generated and output.
The output signal of the waveform generation circuit 13 is different from the output signal of the conventional waveform generation circuit 8 and, for example, as shown in FIG.
In the portion up to 8), the peak value changes with a time gradient in synchronization with the input video signal, and the data value becomes a predetermined value of 128.
In the above part, the peak value is the constant voltage Vd2. FIG. 2A shows a signal that is cut out in accordance with the image data by the switches Sd1 to Sdn and supplied to the switches Sxd1 to Sxdn in response to the output pulse of the first PWM circuit 11. The pulse width starts from the position of the image data value 128 of the first PWM circuit 11 and increases in the forward direction (rightward from tp in FIG. 2A). On the other hand, FIG. 2B shows an output pulse of the second PWM circuit 12, where the data value is a predetermined value 12
When the data value is equal to or less than 8, the pulse voltage is not output. When the data value is equal to or more than the predetermined value 128, a pulse voltage having a constant peak value is output, and the pulse width increases according to the data value of the input video signal. The output pulse of the first PWM circuit 11 increases in the opposite direction (to the left from tp in FIG. 2B).

Next, the voltage applied to the element when the image data value is a specific value will be described. FIG. 2C shows the applied voltage of the element when the image data value is 64 (that is, the predetermined value is 128 or less), and depends only on the pulse related to the first PWM circuit 11 shown in FIG. You can see that there is. FIG. 2 (D)
A pulse waveform obtained by combining the pulse shown in FIG. 2A and the pulse shown in FIG. 2B when the image data value is 192 (that is, the predetermined value is 128 or more). It turns out that it becomes.

At this time, as shown in FIG. 3E, the voltage applied to the j-th column data electrode is such that the waveform shown in FIG. 3D has a ramp shape when the pixel data value is in the range of 0 to 127. It becomes a waveform cut by the pulse width having. When the image data value is 128 to 255, the waveform is applied to the element with a constant voltage pulse width increased in both the left and right directions in accordance with the image data. Then, the applied voltage of the element in the i-th row and the j-th column is shown in FIG.
FIG. 3 (G), (i + 2)
The applied voltage to the element in the row j column has a waveform shown in FIG.
In these waveforms, light emission actually occurs when the threshold value V
This is a portion indicated by oblique lines exceeding th. In the i-th row and the j-th column, Vth does not exceed since the image data is 0. (i + 1)
In the row j column, since the image data is 127, the ramp waveform in the 127T period exceeds Vth. Further, since the image data of the (i + 2) row and the j th column is 224, the constant voltage
(Vd + Vs) is supplied to the element.

The light emission characteristics when driven with such a waveform will be specifically described. When a ramp-shaped waveform is applied, the principle of obtaining an inverse gamma characteristic (quadratic function) has been described with reference to FIG. Here, when the image data value is equal to or more than the predetermined value 128, the voltage applied to the light emitting element increases left and right at a constant voltage Vd more than half of the scanning period as shown in FIG. . When this is considered as an increase in the voltage applied to the element, it is considered that the waveform becomes similar to a waveform that increases like a ramp as shown in FIG. In addition, when the image data value is 255, as shown in FIG. 4 (C), it is the same as when a constant voltage is applied without using a ramp waveform. That is, since the amount of electrons is an integral value, it is determined by the area of the applied voltage, so that the brightness does not decrease.

FIG. 5 is a diagram showing the light emission characteristics of the device in this embodiment. As shown by the solid line in FIG. 5, in the image data value 255, it is possible to obtain the same luminance (light emission output) as when driving with a constant voltage instead of the conventional lamp shape. Note that the broken line in FIG. 5 is the light emission characteristic in the conventional example described with reference to FIG.

As described above, in the matrix type display device of the present invention, the first driving means has a pulse width which increases in accordance with the data value of the input video signal, and the data value of the input video signal is a predetermined value. In the portion below the value, the peak value changes with time in synchronization with the input video signal, and in the portion where the data value is more than the predetermined value, a pulse voltage having a constant peak value is output.
The second driving means does not output the pulse voltage when the data value of the input video signal is equal to or less than a predetermined value, and increases according to the data value of the input video signal when the data value is equal to or more than the predetermined value. And outputs a pulse voltage having a constant peak value. The output pulse of the first driver and the output pulse of the second driver are superimposed and supplied to the data electrodes of the display panel. As a result, the light emission characteristic approximates to the inverse gamma characteristic, and the luminance does not decrease.

In the embodiment, the first PWM and the second PWM are set at a half of the horizontal period (the predetermined value is 128 of the half of the image data value).
Although the operating points of the PWM are divided, it is needless to say that the operating points may be divided in an arbitrary period. In addition, in FIGS. 2 to 4, the case of the ramp waveform increasing linearly has been described, but it is needless to say that an arbitrary waveform may be used. Further, the present invention can be applied to a general display device in which self-luminous elements, such as EL elements, which can express a gradation by a pulse width are arranged in a matrix even if they do not necessarily use cold cathode electron-emitting elements. According to the present invention, in a display device in which cold-cathode electron-emitting devices, EL devices, and the like are arranged in a matrix, without decreasing the absolute luminance,
The light emission characteristic for the image data may have an inverse gamma characteristic. Although not shown, when the end voltage has a higher absolute value than the start voltage of the ramp waveform, there is also an effect that ringing (overshoot) is unlikely to occur.

[0033]

According to the matrix type display device of the present invention, by driving the elements with a waveform obtained by combining two PWM circuits, the matrix type display device has an excellent light emission characteristic close to the inverse gamma characteristic and no luminance reduction. Has an effect.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a waveform chart for explaining the operation of FIG.

FIG. 3 is a waveform chart for explaining the operation of FIG. 1;

FIG. 4 is a waveform chart for explaining the operation of FIG. 1;

FIG. 5 is a diagram showing the light emission characteristics of the device in this example.

FIG. 6 is a diagram showing a configuration of a conventional matrix type display device.

FIG. 7 is a diagram showing a wiring image of elements in a display panel.

FIG. 8 is a waveform chart for explaining the operation of FIG.

FIG. 9 is a characteristic diagram of the cold cathode electron-emitting device.

FIG. 10 is a diagram showing a configuration of another conventional matrix type display device.

FIG. 11 is a waveform chart for explaining the operation of FIG.

FIG. 12 is a waveform chart for explaining an applied voltage of an element.

FIG. 13 is a graph showing light emission characteristics of the device.

FIG. 14 is a characteristic diagram for explaining a decrease in luminance.

[Explanation of symbols]

 1,5 input terminal 2,7 shift register 3 latch circuit 4 PWM circuit 6 timing control circuit 8,13 waveform generation circuit 10 display panel 11 first PWM circuit 12 second PWM circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) G09G 3/30 G09G 3/30 K

Claims (1)

[Claims] A matrix-type display device having a display panel in which a plurality of row wirings connected to a plurality of scanning electrodes of a plurality of elements and a plurality of column wirings connected to a plurality of data electrodes are arranged in a matrix. A pulse width that increases in accordance with the data value of the input video signal, and where the data value of the input video signal is less than or equal to a predetermined value, the peak value changes with time in synchronization with the input video signal; First driving means for outputting a pulse voltage having a constant peak value in a portion where the value is equal to or more than a predetermined value; and outputting no pulse voltage when the data value is equal to or less than the predetermined value; In the above case, a second driving unit that has a pulse width that increases in accordance with the data value of the input video signal and outputs a pulse voltage having a constant peak value, and an output pulse of the first driving unit, The second Matrix display device characterized by by superimposing the output pulse of the driving means and a superimposition means for supplying to said plurality of data electrodes.