JP2001282172A - Gradation display method, multilevel voltage generating device and picture display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gradation display method, a multilevel voltage generating device and a picture display device in which flicker is reduced and display quality is not changed by gradation at the time of displaying a halftone while generating an effective halftone voltage by changing over a reference voltage corresponding to a certain gradation and a reference voltage corresponding to a gradation higher by one step. SOLUTION: A first fluctuation reference voltage vn corresponding to a first gradation level and a second fluctuation reference voltage vn+1 corresponding to a second gradation level whose fluctuation amplitudes are made to be smaller than ΔV being the difference between the reference voltage Vn and the reference voltage Vn+1. Then, an intermediate fluctuation voltage vm is generated by selectively changing over both reference voltages Vn, Vn+1 in accordance with a fluctuation frequency. Thus, since the amplitude of the intermediate fluctuation voltage vm is made to be smaller than ΔV and, also, fluctuation frequencies are made to be even among respective voltages vn, vn+1, vm, the purpose can be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gray scale display method and a gray scale of an image display device such as a liquid crystal display device having a plurality of display pixels capable of changing the luminance by controlling the magnitude of a driving voltage. Regarding the voltage generator, in particular, in order to obtain the number of gradations equal to or more than the number of gradations of the image display device, a frame rate control method (FRC).
As shown in d), by switching drive voltages of different magnitudes in predetermined time units and applying them to display pixels, an effective voltage having a magnitude between the respective drive voltages when averaged or smoothed over a certain period is obtained. The present invention relates to a gray scale display method and a gray scale voltage generator capable of improving display quality in an image display apparatus of a type capable of displaying a halftone between gray scale levels corresponding to respective drive voltages. It is.

[0002]

2. Description of the Related Art An active matrix liquid crystal display device comprises:
This is an example of an image display device including display pixels whose luminance can be changed by controlling the magnitude of a driving voltage. For example, in the case of a TFT active matrix liquid crystal display device shown in FIG.
In, the liquid crystal layer is sandwiched between two transparent substrates,
A common electrode is provided on one transparent substrate, and a plurality of signal lines 51 and scanning lines 52 are arranged in a grid on the other transparent substrate, and a pixel surrounded by the signal lines 51 and the scanning lines 52 is provided. A pixel electrode 53 and a TFT (Thin Film Transistor) 54 as a switching element are provided independently for each region.

[0003] A predetermined voltage signal (G
1, G2, etc.), the TFT 54 is turned on, and the image signal (S1, S2, etc.) inputted to the signal line 51 is written to each pixel electrode 53. As a switching element for selectively driving the pixel electrode 53, in addition to a three-terminal TFT, a two-terminal MIM (metal-insulating-film-metal) element or the like is generally known.

Since the liquid crystal has a property that the light transmittance changes continuously according to the magnitude of the applied voltage, the voltage corresponding to each of the white level and the black level is divided into n stages. When the voltage applied to the liquid crystal is changed in n stages, the brightness of a display pixel formed by the liquid crystal can be changed in n stages. That is, n gradation display is possible.

The control of the applied voltage according to the image signal is performed by a driver constituted by an LSI (Large Scale Integrated circuit) or the like. In other words, the applied voltage in n stages can be obtained by changing the amplification factor of an amplifier circuit for amplifying a predetermined constant voltage in multiple stages, or by dividing two high and low constant voltages into n stages by a resistor, and applying one of n applied voltages. It is generated by a method of selecting one or the like.

However, these systems require n-stage applied voltages for n-gradation display, and therefore increase the number of gradations to cope with higher definition and larger screen of the liquid crystal display screen. This involves the following difficulties.

That is, when the applied voltage of the n stages is obtained by varying the amplification factor of the amplifier circuit, the minimum variable width of the amplification factor depends on the characteristics of the amplifier circuit, so that there is a limit to the number of gradations that can be obtained. When an n-stage applied voltage is obtained by dividing two constant voltages, the number of voltage dividing resistors and the number of switching elements for selecting one of the n-stage applied voltages are proportional to the number of gradations. As a result, the circuit scale of the driver increases.

[0008] In view of the above, a technique for realizing multi-gradation display with a number of gradations larger than n gradations by using an n-stage applied voltage has been actively studied in recent years.

One of the methods is a frame rate system.
The FRC (Frame Rate Control method)
You. The frame rate control gradation method uses two types of reference voltages, high and low.
Pressure V_{n + 1}And V_nCan be switched in display frame units.
And the effective electric current when the reference voltage is smoothed for a certain period
Reference voltage V_{n + 1}And V_nGet an intermediate voltage between
It is a technique that

[0010] Here, the display frame means that N scanning lines included in one screen are scanned from the first to the Nth, and
It means the time it takes to display the screen, usually 1
/ 60 seconds ($ 16.7 ms). Less than,
The display frame is simply called a frame.

A conventional frame rate control gradation method will be described below.
Will be described more specifically with reference to FIG. Figure 9 shows two types
Reference voltage V_{n + 1}And V_n, Three types of intermediate control
Pressure V _n(1), V_n(2), V_n(3) can be newly obtained
9 shows a frame rate control gradation method. Shown in FIG.
Numbers 1 to 4 corresponding to F mean frame numbers
I have.

Therefore, two kinds of reference voltages V_{n + 1}And
And V_nBy switching the frame by frame, the reference
Pressure V_{n + 1}And V_nCombination in 4 frame periods
When sliding, the reference voltage V_{n + 1}And V_nHow to switch
The corresponding halftone voltage V_n(1), V _n(2), V_n(3) gain
Can be.

[0013] That is, as shown in (i) of FIG. 9, if all the frames F1~F4 reference voltage V _n, the effective voltage of 4 frame periods equal to the V _n, corresponding to the reference voltage V _n The display of the reference gradation becomes possible.

Further, as shown in FIG. 9 (ii), after the frame F1 is set to the reference voltage V _{n + 1} and the frames F2 to F4 are switched to the reference voltage V _n , the halftone voltage V as the effective voltage is changed. _n (1) is, V _n (1) = a _{(3V n + V n + 1} ) / 4. Thus, when the difference between the reference voltage V _{n + 1} and V _n and [Delta] V, V _n (1) = Since the _{{3V n + (V n +} ΔV)} / 4 = V n + ΔV / 4, ΔV / 4 Can be displayed at ΔV / 4 gradation corresponding to

Further, as shown in FIG. 9 (iii), when the reference voltages V _{n + 1} and V _n are alternately switched in frame units, the halftone voltage V _n (2) as the effective voltage becomes V _n (2) = a _{(V n + 1 + V n} ) / 2 = V n + ΔV / 2. As a result, display of ΔV / 2 gradation corresponding to ΔV / 2 can be performed.

Further, as shown in FIG. 9 (iv), after setting the frames F1 to F3 to the reference voltage Vn _{+ 1} , the frame F4
Switching the reference voltage V _n, halftone voltage V _n as the effective voltage (3), V _n (3) = a _{(V n + 3V n + 1} ) / 4 = V n + 3ΔV / 4. Thereby, 3ΔV / 4 corresponding to 3ΔV / 4
It is possible to display gradation.

Here, a system configuration for implementing the above-mentioned frame rate control gradation method will be described with reference to FIG. A source driver 55 is connected to each signal line 51 of the liquid crystal panel 50, and a gate driver 56 is connected to each scanning line 52.

The source driver 55 includes a drive circuit for displaying 64 gradations, and according to a 6-bit data signal a ₁ supplied from an FRC circuit 57 described later, a reference voltage V _i (i = 0 to i = 0) in 64 steps is provided. 63), and sequentially select signal lines 5
Distribute to 1. Reference voltage V _i of the 64 stages, a fixed voltage V0~V7 8-step supplied from the voltage generating unit 58 to the source driver 55, as shown in FIG. 10, is divided by the internal resistance r of the source driver 55 Is to be generated.

On the other hand, the gate driver 56 sequentially selects and activates the scanning lines 52 in a line-sequential driving method according to the scanning driving signal a ₂ supplied from the timing circuit 59. Thus, each T connected to one scanning line 52
The FTs 54 are simultaneously turned on. Source drive signal a ₃ which is synchronized with the activation of the scanning line 52, is input from the timing circuit 59 to the source driver 55, the reference voltage V _i which has been held in the source driver 55, simultaneously to the signal line 51 The output is applied to the liquid crystal of each pixel via the TFT 54 in a conductive state.

As described above with reference to FIG. 9, the data signal a ₁ is supplied from the FRC circuit 57 to the reference voltage V _n which is one of the 64 levels of reference voltages V _i and the reference voltage V _n . 6 for switching the reference voltage V _{n + 1} , which is one level higher, at a period of four frames per pixel
A bit signal is generated from the data signals a ₅ to 8 bits supplied from the display data processing unit 60. Also, F
The RC circuit 57, the frame designation signal a ₄ for timing to switch every 4 frames and the reference voltage V _n and the reference voltage V _{n + 1,} as described above, the timing circuit 5
9 is input.

The 8-bit data signal a ₅ is generated by converting the image data a ₆ input from the external CPU via the interface 61 in the display data processing unit 60, and generates the reference voltage V _i in 64 steps. Upper 6-bit data to be specified, and the above-described ΔV / 4 gradation to 3ΔV /
4 and halftone gradation, constituted by the lower 2-bit data for designating any one of reference gray corresponding to the reference voltage V _n. It should be noted that the lower 2-bit data designating either the above-mentioned intermediate gradation or the reference gradation is represented by D _{0 to} D in FIG.
Represented by ₃ . Hereinafter, D _j (j = 0 to 3) is referred to as intermediate gradation designation data.

Incidentally, the scanning drive signal a ₂ , the source drive signal a ₃ and the frame designation signal a ₄ are converted into a horizontal synchronizing signal, a vertical synchronizing signal and the like inputted from the external CPU via the interface 61 in the timing circuit 59. Generated based on

Next, the reference voltage V _n and the reference voltage V _{n + 1} relates to a circuit configuration for switching every 4 frames will be described with reference to FIG.

First, the source driver 55 inputs a 6-bit data signal a ₁ specifying a reference voltage V _i (i = 0 to 63) in 64 steps, and outputs a reference voltage V _i corresponding to the data signal a _1. A multiplexer (MUX) 62 for selecting
Eight-stage fixed voltages V0 to V0 supplied from the voltage generator 58
V7 is divided into 64 reference voltages V _i by an internal resistor r.
And

On the other hand, the FRC circuit 57 has a ROM 63 and an increment circuit (INC) 64.
ROM63 inputs the frame designation signal a ₄ and the gradation designating data D _j, both a certain reference voltage V _n, a reference voltage V _{n + 1} is the level up one than the reference voltage V _n of The data that determines whether to select is stored.
Then, ROM 63 is in the case of selecting the reference voltage V _n lower-level and outputs a select signal 0, when selecting the reference voltage V _{n + 1} levels above outputs a select signal 1.

The increment circuit 64 includes a ROM
When the select signal 0 is input from the display data processing unit 63, the 8-bit data signal a ₅ input from the display data processing unit 60 is output.
Is output to the source driver 55 as it is. On the other hand, the increment circuit 64
3 If you enter a select signal 1 from, increase the value of the upper 6-bit data of the data signals a ₅ to 8-bit input from the display data processing unit 60 by one, the level of upper reference voltage V _{n + The} data is converted into 6-bit data designating ₁ and output to the source driver 55.

With the above configuration, for example, the FRC operation shown in FIG. 9 (ii) is performed as follows. In ROM63,
When the frame designation signal a ₄ is input to designate the first frame of a cycle of four frames (F1), is the reference voltage V
8 for designating ΔV / 4 gradation between _n and reference voltage V _{n + 1}
When the data signal a ₅ bit, the input from the display data processing unit 60 to the FRC circuit 57, the ROM 63,
It receives the intermediate gradation designation data D ₁ , which is the lower two bits of the data signal a ₅ , and outputs the select signal 1 to the increment circuit 64. Thus, the increment circuit 64, the value of the upper 6-bit data for designating a reference voltage V _n of the data signal a ₅ is increased by 1, and outputs to the source driver 55.

Then, since the source driver 55 receives the 6-bit data designating the reference voltage V _{n + 1} , the source driver 55 sets the reference voltage V _n as the reference voltage of the first frame.
_{n + 1} is output from the multiplexer 62.

[0029] Then, ROM 63, based on the frame designation signal a ₄ to specify a second frame of a cycle of four frames (F2) and the intermediate gradation designating data D _1, and outputs a select signal 0 to the increment circuit 64 . Thus, the increment circuit 64 outputs intact source driver 55 the upper 6-bit data for designating a reference voltage V _n of the data signal a _5.

[0030] Then, the source driver 55, it means that receives a 6-bit data for designating a reference voltage V _n, as the reference voltage of the second frame, to output the reference voltage V _n from the multiplexer 62.

Thereafter, the third frame (F
The same operation as in the second frame (F2) is repeated for the third frame (F4) and the fourth frame (F4). As a result, the switching of the reference voltage shown in (ii) of FIG. 9 is performed, and when the reference voltage applied to the liquid crystal is smoothed in four frame periods, the reference voltage of V _n + ΔV / 4 is effectively applied. since the can display the [Delta] V / 4 gradations between the reference voltage V _n and the reference voltage V _{n + 1.}

[0032] Thus, for 64 steps the reference voltage V _i each reference gray corresponding 64 stages, more can be added three halftone allows multi-gradation display of generally 256 gradations .

[0033]

However, the conventional frame rate control gradation method has the following problems: (1) the first problem that display quality may be impaired; and (2) the display quality varies depending on the gradation. This is the second problem.

[0034] (1) For example for the first problem, as (ii) (iv) of FIG. 9, when switching the reference voltage V _n and the reference voltage V _{n + 1,} of once per 4 Frame Switching has been done. The display frequency (reciprocal of one frame period) of the image display device is usually 60 Hz, that is, 60 frames / second. Therefore, when the reference voltage is switched once every four frames, the switching cycle is 15 Hz. become. For the FIG. 9 (ii) (iv), the effective voltage Nevertheless becomes V _n + 3ΔV / 4 or V _n + ΔV / 4, the actual reference voltage of the waveform, 15H
A z wave appears.

As shown in FIG. 9 (iii), the reference voltage V
The switching cycle when _n and the reference voltage V _{n + 1} are alternately switched is 30 Hz.

By the way, at a frequency lower than 15 Hz, human visual perception can recognize a change in gradation as flicker. Therefore, the gradation fluctuation of 15 Hz as shown in (ii) and (iv) of FIG. 9 corresponds to the limit of whether or not human eyes can see flicker. Further, even with the same gradation variation of 15 Hz, the larger the difference ΔV between the switched reference voltages V _n and V _{n + 1} , the more easily human eyes can perceive flicker.

As described above, the frame rate control gradation method is accompanied by the problem of the occurrence of flicker, which lowers the display quality. To suppress flicker, (a) reduce ΔV, (b) increase the switching frequency to 15 Hz or more, take at least one of the measures (a) and (b) to reduce the low-frequency component that human eyes can perceive. It is necessary to take measures to reduce energy.

[0038] The above ΔV, since the number of reference voltage V _i becomes inevitably large if small, the frame rate control gradation method shown in Figure 9, increasing the number of reference voltage V _i, a smaller ΔV It can be said that this method cannot be used without it.

(2) Regarding the Second Problem As is apparent from comparison of the waveforms shown in FIGS. 9 (i) to 9 (iv), the frequency components included in the waveform differ depending on the gradation. That is, in the case of (i), the switching frequency is 0, and the observer is viewing the image at the display frequency of 60 Hz. However, in the cases (ii) and (iv), the switching frequency is 15 Hz, as described above, so that the observer sees an image in which the switching frequency of 15 Hz is superimposed on the display frequency of 60 Hz. Further, in the case of (iii), the observer sees an image in which the above-mentioned switching frequency of 30 Hz is superimposed on the display frequency of 60 Hz.

For this reason, the display quality looks different depending on the gradation, and it is not possible to meet the needs of high image quality.

The present invention has been made to solve the above problems, and an object regardless of the set number of reference voltage V _i, the reference voltage level below the reference level up one By switching the voltage with an amplitude smaller than the difference ΔV from the voltage, an effective halftone voltage can be obtained, and furthermore, a gradation display method in which the display quality does not change depending on the gradation, and a method for implementing the method. It is an object of the present invention to provide an adjustment voltage generator and an image display device provided with the gradation voltage generator.

[0042]

According to the present invention, there is provided a gradation display method comprising: (1) a first gradation level corresponding to a first gradation level of an image displayed on an image display device; The first grayscale voltage and the second grayscale voltage corresponding to the second grayscale level are each obtained as an average value obtained by periodically changing the voltage value to a plurality of values, and The amplitude of
The difference between the first gradation voltage and the second gradation voltage should be smaller than ΔV. (2) Further, a plurality of voltage values for generating the first gradation voltage and the second gradation voltage When generating a halftone voltage between the first grayscale voltage and the second grayscale voltage by selectively combining a plurality of voltage values for generating a voltage, the halftone voltage also has a voltage value. It is characterized in that it is obtained as an average value periodically changed to a plurality of values and the amplitude of the change is smaller than the above-mentioned ΔV.

In the above-described method, the prior art employs a method in which the voltage values of the first grayscale voltage and the second grayscale voltage themselves from which the halftone voltage is effectively generated are periodically changed. There is a big feature that has not been done. The halftone voltage includes a plurality of voltage values for generating the first grayscale voltage and a second
Are generated by selectively combining a plurality of voltage values for generating the gray scale voltage.

The first gradation voltage, the second gradation voltage, and the halftone voltage all have a fluctuation amplitude ΔV which is a difference between the first gradation voltage and the second gradation voltage. Generated to be smaller. On the other hand, in the conventional frame rate control gradation method, the amplitude of the fluctuation of the halftone voltage is ΔV.

As described above, the amplitude of the fluctuation of the halftone voltage is Δ
As a result, according to the gradation display method of the present invention, the energy of the low-frequency component, which is a cause of flicker that can be perceived by the human eye, is reduced in the halftone display compared to the conventional frame rate control gradation method. be able to.

It should be noted that the amplitude of the halftone voltage can be generated as long as the amplitudes of the first and second grayscale voltages are made smaller than ΔV by intentional setting. The voltage can be made smaller than ΔV by a selective combination of a plurality of voltage values to be made. The reason will be described below.

First, a plurality of voltage values for generating the first gradation voltage as an average value of fluctuation are dispersed in the + and-directions with respect to the first gradation voltage. Similarly, the second
Are also distributed in the + and-directions with respect to the second gradation voltage. Then, needless to say, the voltage value dispersed in the + direction with respect to the first gray scale voltage has a magnitude between the first gray scale voltage and the second gray scale voltage. The voltage value dispersed in the negative direction with respect to the second gradation voltage has a magnitude between the first gradation voltage and the second gradation voltage.

Therefore, a voltage value having a magnitude between the first gradation voltage and the second gradation voltage and different values from each other is selected, and the selected plural voltage values are set in a certain period unit ( For example, if switching is performed every frame), the amplitude of the fluctuation always falls between the first gradation voltage and the second gradation voltage. Moreover, thereby, it is possible to generate a halftone voltage having an average value of fluctuation between the first grayscale voltage and the second grayscale voltage.

Further, by using a voltage value dispersed between the first gradation voltage and the second gradation voltage and a voltage value dispersed in the negative direction with respect to the first gradation voltage, It is possible to generate a new halftone voltage having a value obtained by leveling down the halftone voltage generated from only the voltage value dispersed between the first grayscale voltage and the second grayscale voltage in the negative direction. Moreover, the selection of the voltage value may be performed on condition that the amplitude of the fluctuation is always smaller than ΔV.

Similarly, by using a voltage value dispersed between the first gradation voltage and the second gradation voltage and a voltage value dispersed in the + direction based on the second gradation voltage, It is possible to generate a new halftone voltage having a value obtained by leveling up the halftone voltage generated in the + direction from only the voltage value dispersed between the first grayscale voltage and the second grayscale voltage. Also in this case, the selection of the voltage value may be performed on condition that the amplitude of the fluctuation is always smaller than ΔV.

Needless to say, the types of the gradation voltages are not limited to the two types of the first gradation voltage and the second gradation voltage. That is, the type of the gradation voltage is 64
By setting the type and applying the above method to each combination of a certain gradation voltage and the gradation voltage of the next higher level, three types of halftone voltages can be set between adjacent gradation voltages. If it is generated, a multi-gradation display with a total of 256 gradations can be realized. This applies to any of the claims of the present application.

According to another gradation display method according to the present invention, in order to solve the above-mentioned problems, (1) a first gradation corresponding to a first gradation level of an image displayed on an image display device. Voltage and
Each of the second grayscale voltage corresponding to the second grayscale level is obtained as an average value obtained by periodically changing the voltage value to a plurality of values, and the amplitude of the change is equal to the first grayscale voltage. Generating a first variation reference voltage and a second variation reference voltage, each of which is smaller than ΔV, which is a difference between the gradation voltage and the second gradation voltage, and (2-1) the first variation Reference voltage and second
(2-2) The first gray scale is used to generate a halftone voltage between the first gray scale voltage and the second gray scale voltage by selectively switching the fluctuation reference voltage of the first gray scale voltage in a certain period unit. A plurality of voltage values for generating a voltage and a plurality of voltage values for generating a second gradation voltage are selectively combined, and the halftone voltage is also an average obtained by periodically changing the voltage value to a plurality of values. It is characterized in that it is obtained as a value and the amplitude of the fluctuation is smaller than the above-mentioned ΔV.

The difference between this gradation display method and the above-mentioned gradation display method is that in generating a halftone voltage, a first fluctuation reference voltage and a second fluctuation reference voltage are generated, and both are generated for a certain period. The point is that it is selectively switched in units.

Since the first variation reference voltage and the second variation reference voltage each include a plurality of voltage values having exactly the same contents as those of the above-mentioned gradation display method, the present gradation display method also has For the same reason, it is possible to reduce the energy of the low-frequency component, which is a cause of flicker that can be sensed by the human eye, in the halftone as compared with the conventional frame rate control gradation method.

In another gradation display method according to the present invention, in order to obtain the first gradation voltage, the second gradation voltage, and the halftone voltage, the period in which each voltage value is varied is set to the same length. (For example, four frame periods).

As a result, there is no difference in the fluctuation period of the voltage value among the first gradation voltage, the second gradation voltage, and the halftone voltage. The frequency components included in the grayscale voltage and the halftone voltage become equal. As a result, the display quality does not change depending on the gradation, and higher-quality gradation display can be realized.

Note that the fluctuation cycle is such that the frequency of the fluctuation is 1
What is necessary is just to set it based on a display frequency so that it may be set to 5 Hz or more. This is because the lower limit of the frequency at which flicker is not detected by the human eye is 15 Hz, as described above.

Further, the above-mentioned changing cycle is, for example, 1
Assuming a frame, the fluctuating frequency matches the display frequency. In this case, in any gradation display, a frequency component lower than the display frequency is not superimposed on the display frequency, so that a higher-quality gradation display can be realized.

In the gradation display method according to the present invention, the first gradation voltage and the second gradation voltage may be changed in the same phase.

This makes it possible to unify information signals for varying each gradation voltage into one type and vary each gradation voltage based on the same information signal. The circuit configuration for generating each gradation voltage can be simplified.

In order to solve the above-mentioned problems, the present invention provides the following: (1) a first gradation voltage corresponding to a first gradation level of an image displayed on an image display device; When,
Each of the second grayscale voltage corresponding to the second grayscale level is obtained as an average value obtained by periodically changing the voltage value to a plurality of values, and the amplitude of the change is equal to the first grayscale voltage. A first fluctuation reference voltage having an average value of the first gradation voltage and a second fluctuation voltage, wherein the first fluctuation voltage is smaller than ΔV which is a difference between the gradation voltage and the second gradation voltage; (2) a plurality of voltage values included in the first variable reference voltage, and a plurality of voltage values included in the second variable reference voltage. When a halftone voltage between the first grayscale voltage and the second grayscale voltage is generated by selectively combining the voltage values, the halftone voltage also periodically changes the voltage value to a plurality of values. In order to obtain an average value fluctuated in the above manner, and to make the amplitude of the fluctuation smaller than the above ΔV. One of the variation reference voltage and the second variation reference voltage, is characterized in that by selecting the voltage value of the halftone voltage for each vary and a variation reference voltage selecting unit for outputting.

According to the above configuration, the fluctuation reference voltage generating means periodically changes the voltage value to a plurality of values so that the first gradation voltage becomes the average value, and the amplitude of the fluctuation is ΔV A first fluctuating reference voltage that is smaller and a second fluctuating reference voltage similar thereto are generated. Therefore, the first
Between the grayscale voltage and the second grayscale voltage, a plurality of levels of the voltage value forming the first grayscale voltage and the voltage value configuring the second grayscale voltage are formed.

Therefore, the variation reference voltage selecting means sets one of the first variation reference voltage and the second variation reference voltage as
When appropriately selected every time the voltage value of the halftone voltage is changed,
It is possible to generate a halftone voltage fluctuated by combining a voltage value for generating the first gray scale voltage and a voltage value for generating the second gray scale voltage.

At this time, if the halftone voltage is generated by combining only the voltage values falling between the first grayscale voltage and the second grayscale voltage, the amplitude of the halftone voltage necessarily becomes smaller than ΔV. Is clear. Further, since the plurality of voltage values fluctuate in the + direction and the − direction with respect to each gradation voltage so that each gradation voltage itself has an average value of each gradation voltage, the first gradation voltage and By using a voltage value that does not fall within the range between the second gradation voltage and the second gradation voltage, for example, a halftone voltage larger by ΔV / 4 than the first gradation voltage or 3 V from the second gradation voltage is used.
A halftone voltage smaller by ΔV / 4 can be easily generated with an amplitude smaller than ΔV.

As a result, the energy of the low-frequency component, which is a cause of flicker that can be sensed by the human eyes, can be reduced in the halftone as compared with the conventional frame rate control gradation method.

In the grayscale voltage generator according to the present invention, in order to obtain the first grayscale voltage, the second grayscale voltage, and the halftone voltage, the period in which each voltage value is changed is set to the same length. It may be unified.

As a result, there is no difference in the fluctuation period of the voltage value among the first gradation voltage, the second gradation voltage, and the halftone voltage. The frequency components included in the grayscale voltage and the halftone voltage become equal. As a result, the display quality does not change depending on the gradation, and higher-quality gradation display can be realized.

In the gradation voltage generating device according to the present invention, the variable reference voltage generating means includes the first variable reference voltage and the second variable reference voltage.
May be provided with fluctuation information generating means for generating fluctuation information for causing the fluctuation reference voltage to fluctuate in phase.

According to the above configuration, the first fluctuation reference voltage and the second fluctuation reference voltage are changed in the same phase, whereby
The fluctuation information is shared by both the fluctuation reference voltages, and the waveforms of both the fluctuation reference voltages become equal. Therefore, since the fluctuation information generating means only needs to generate one type of fluctuation information, the circuit configuration can be simplified. Further, since the same type of configuration can be employed for the circuits that generate the respective variable reference voltages, the configuration of the variable reference voltage generating means can be simplified.

In order to solve the above-mentioned problems, an image display device according to the present invention uses the above-mentioned gradation voltage generator, the first fluctuation reference voltage, the second fluctuation reference voltage and the halftone voltage. And display means having a plurality of display pixels which are driven and perform gradation display.

As a result, a halftone voltage that fluctuates periodically with an amplitude smaller than the difference ΔV between the first gradation voltage and the second gradation voltage can be obtained for the same reason as described above. In addition, it is possible to provide an image display device that realizes high-quality multi-gradation display, in which the energy of low-frequency components, which is a cause of flicker that can be sensed by the human eye, is reduced compared to the conventional frame rate control gradation method. .

Furthermore, if the first gradation voltage and the second gradation voltage themselves are periodically changed and the halftone voltage is generated based on both of the fluctuating gradation voltages, the first gradation voltage can be obtained. Voltage, second
Since the fluctuation frequency of the gray scale voltage and the halftone voltage can be made equal, it is possible to provide an image display device which realizes higher quality multi-gray scale display in which the display quality does not change depending on the gray scale.

[0073]

[Embodiment 1] An embodiment of a gradation display method according to the present invention will be described below with reference to FIG.

In this embodiment, first, the following (a) to
A specific example of the first gradation display method comprising (d) will be described. (a) Each of a first gradation voltage corresponding to a first gradation level and a second gradation voltage corresponding to a second gradation level of an image displayed on an image display device has a voltage value Is obtained as an average value periodically changed to a plurality of values. (b) The amplitude of the fluctuation is set to be smaller than ΔV which is a difference between the first gradation voltage and the second gradation voltage. (c) a plurality of voltage values for generating a first gray scale voltage;
And a plurality of voltage values for generating the gray scale voltage are selectively combined to generate a halftone voltage between the first gray scale voltage and the second gray scale voltage. (d) The halftone voltage is also obtained as an average value in which the voltage value is periodically changed to a plurality of values, and the amplitude of the change is smaller than the above ΔV.

[0075] Figure 3 shows the reference voltage V _n and the reference voltage V _{n + 1} as a first gradation voltage and a second gray voltage. Reference voltage V _n, for example 64 steps of the reference voltage V
_i (i = 0 to 63), and the reference voltage V _{n + 1} corresponds to a reference voltage one step higher than the reference voltage V _n .

Then, the reference voltage V_nIs the reference voltage V_nWhen
Reference voltage V_{n + 1}2 frames based on the voltage difference ΔV
In the cycle, V_n+ ΔV / 4 and V_n-ΔV / 4
Voltage value, and the average value of the change, that is, 2
It is equal to the average of the voltage values during the frame period. Ma
The reference voltage V_{n + 1}Similarly, in a two-frame cycle, V
_{n + 1}+ ΔV / 4 and V_{n + 1}-Two voltage values of ΔV / 4
And the average of the fluctuations, ie, 2 frames
It is equal to the average value of the program period ((a) above).

The amplitude of the fluctuation of each of the reference voltages V _n and V _{n + 1} is
Since each of them is ΔV / 2, each is set to be smaller than ΔV ((b) above).

Next, two voltage values to generate a reference voltage _{V n (V n + ΔV /} 4 and V _n -ΔV / 4) and two voltage values to generate a reference voltage _{V n + 1 (V n +} 1 + ΔV / 4
And V _{n + 1} −ΔV / 4),
Each reference voltages V _n, V is a halftone voltage between V _{n + 1} n ₊
Generate ΔV / 2. In this case, the halftone voltage V _n + ΔV
/ 2 is obtained as an average value in which the voltage value is changed to a plurality of values in the same two-frame period as described above, and the amplitude of the change is set to be smaller than ΔV (see
(c) (d)).

For this purpose, as shown by a circle in FIG. 3, V _n + ΔV / 4 is selected in the first frame F1, and V _{n + 1} −ΔV / 4 is selected in the second frame F2. combine. Thus, it is possible to obtain the halftone voltage V _n + ΔV / 2 the amplitude was [Delta] V is smaller than [Delta] V / 2. Moreover, the reference voltage V _n, V _{n + 1} and the halftone voltage V _n + [Delta] V
The cycle of the fluctuation of / 2 can be unified to all two frames. As the number of gradations, the reference gray corresponding to the reference voltage V _n, since a halftone corresponding to the halftone voltage V _n + ΔV / 2 can be one step additional, reference voltage number (in this example 64), which is twice as many as the number of gradations.

As described above, the halftone voltage V _n + ΔV / 2
A reference voltage V _n, since it is generated by selectively combining a plurality of voltage values having a magnitude between V n _{+ 1,} the amplitude of the fluctuations, the reference voltage V _n, V _{n + 1} of the voltage It is always smaller than the difference ΔV. Therefore, it is possible to perform halftone display in which the energy of the low-frequency component, which is a cause of flicker that can be sensed by human eyes, is reduced as compared with the conventional frame rate control gradation method.

In addition, since each of the reference voltages V _n and V _{n + 1} and the halftone voltage V _n + ΔV / 2 have the same frequency of fluctuation, the frequency components included in each voltage are equal.
As a result, the display quality does not change depending on the gradation, and a high-quality gradation display can be realized.

Next, a second (e) to (g) described below will be described.
Will be described. (e) The first gradation voltage corresponding to the first gradation level and the second gradation voltage corresponding to the second gradation level of the image displayed on the image display device have voltage values Is obtained as an average value periodically changed to a plurality of values, and the amplitude of the change is set to be smaller than ΔV which is a difference between the first gradation voltage and the second gradation voltage. A first variable reference voltage and a second variable reference voltage are generated. (f) generating a halftone voltage between the first gradation voltage and the second gradation voltage by selectively switching the first fluctuation reference voltage and the second fluctuation reference voltage in a certain period unit; . (g) a plurality of voltage values for generating the first gradation voltage, and
And a plurality of voltage values for generating the gray scale voltage are selectively combined so that the halftone voltage is also obtained as an average value in which the voltage value is periodically changed to a plurality of values, and the amplitude of the change is , ΔV.

In the second gradation display method, as shown in FIG. 3, the voltage value is set to V _n + ΔV / 4 in two frame cycles.
And V _n - [Delta] V / 4 first and variation reference voltage v _n of varying, the voltage value at two frame _{periods, V n + 1 + ΔV /} 4
And V _{n + 1} to generate the second and variation reference voltage v _{n + 1} of varying the - [Delta] V / 4, the first frame F1, selecting a first variation reference voltage v _n, the second frame F2 Then, the second
So as to select the variation reference voltage v _{n + 1} of the switches each variation reference voltage v _n, v n _{+ 1} of the frame by frame.

[0084] Thus, the same result as the first gray level display method, it is possible to generate the intermediate variable voltage v _m the effects of the present invention.

[0085] Incidentally, each of the voltage _{v n, v n + 1,} v to less than sure ΔV amplitude of _m, each voltage v _n,
v n _{+ 1,} v half the amplitude of _m should be less than [Delta] V / 2.

In the example shown in FIG._n+ ΔV / 4
And V_nBy switching between −ΔV / 4, the amplitude ΔV / 2
Reference voltage v_nAnd a voltage value V_{n + 1}+ ΔV / 4
And V _{n + 1}By switching between −ΔV / 4, the amplitude ΔV /
2 fluctuating reference voltage v_{n + 1}Is generated, and the fluctuation reference voltage v_nTo
Generated voltage value V_n+ ΔV / 4 and the fluctuation reference voltage v_{n + 1}
To generate a voltage value V_{n + 1}-ΔV / 4 is selectively combined
The intermediate fluctuation voltage v having the amplitude ΔV / 2_mGenerate a
did.

[0087] The amplitude of the voltage _{v n, v n + 1,} v m are both the reference voltage V _n, a V n _{+ 1} of a difference [Delta] V, the number of frames is the period of variation, i.e. divided by 2 , ΔV to Δ
It is a value obtained by subtracting one V / 2.

[0088] Therefore, the formula representing the amplitude of each voltage _{v n, v n + 1,} v m, the number of frames is the period of variation as N, the reference voltage V _n, corresponding to V n _{+ 1} 2 When increasing from gradation to N gradation using N frames, Δ
V is a value obtained by subtracting one of ΔV / N, that is, ΔV−ΔV / N = ΔV (1-1 / N) = ΔV (N−1) / N... voltage v _n, the amplitude of v n _{+ 1,} v _m may be less than [Delta] v.

[Embodiment 2] Another embodiment of the gradation display method according to the present invention will be described below with reference to FIG.

In this embodiment, the reference voltages V _n , V
_{n + 1} of the voltage difference [Delta] V 3 equal parts, the reference voltage V _n, as two new halftone voltage between V n _{+ 1,} to generate and V _n + ΔV / 3 and V _n + 2ΔV / 3, Regarding the gradation display method that can triple the number of gradations, the first gradation display methods (a) to (d) and the second gradation display methods (e) to
This will be specifically described with reference to (g).

The reference voltage V _n is calculated based on the voltage difference ΔV between the reference voltage V _n and the reference voltage V _{n + 1} in three frame cycles,
V _n + ΔV / 3, V _n −ΔV / 3, and V _n are repeatedly changed, and are equal to the average value of the changes, that is, the average value of three frame periods (F1 to F3). Has become. In addition, the reference voltage V _{n + 1} repeatedly changes in three frame periods into three voltage values of V _{n + 1} + ΔV / 3, V _{n + 1} −ΔV / 3, and V _{n + 1.} , The average value of the variation, that is, three frame periods (F
1 to F3) (the above (a)).

The amplitude of the fluctuation of each of the reference voltages V _n and V _{n + 1} is
Since each is 2ΔV / 3, each is set to be smaller than ΔV ((b) above).

Next, the three voltage values for generating the reference voltage V _n and the three voltage values for generating the reference voltage V _{n + 1} are selectively combined to form each of the reference voltages V _n and V _{n + 1.} a halftone voltage between V _n + ΔV / 3 and V _n + 2.DELTA.V /
3 is generated. In this case, the halftone voltages V _n + ΔV / 3 and V _n + 2ΔV / 3 are obtained as an average value in which the voltage value is changed to a plurality of values in the same three-frame cycle as described above, and the amplitude of the change is It is set to be smaller than the above ΔV (the above (c) and (d)).

For this purpose, as shown by a circle in FIG. 5, V _n + ΔV / 3 is selected in the first frame F1, and V _{n + 1} −ΔV / 3 is selected in the second frame F2. In the third frame F3, V _n is selected and combined. Thus, the frequency of the fluctuation is equal to the frequency of the fluctuation of each of the reference voltages V _n and V _{n + 1} and the amplitude is 2ΔV / 3 smaller than ΔV.
It can be obtained halftone voltage V _n + ΔV / 3, which was.

Further, as shown by the crosses in FIG. 5, by selecting a voltage value for each of the frames F1 to F3, a halftone voltage V _n + 2ΔV having an amplitude of 2ΔV / 3 is similarly obtained.
/ 3 can be obtained.

Further, in accordance with the same concept as in the first embodiment, the first gradation display methods (a) to (d) are replaced by the second gradation display methods (e) to (g), Reference voltage v _n
And a second fluctuation reference voltage v _{n + 1,} and by selecting and switching them for each frame, as shown by a circle or a cross in FIG. 5, the intermediate fluctuation voltage v _m (1 / 3) and the intermediate fluctuation voltage v _m (2/3) can be generated.

[0097] Incidentally, in the case of the present embodiment also, the amplitude of each voltage _{v n, v n + 1,} v m is smaller than ΔV according to the general formula (1) above.

[0098] That is, the amplitude of the voltage _{v n, v n + 1,} v m is the reference voltage V _n, the number of frames of the difference [Delta] V the fluctuation cycle of V _{n + 1,} ie is divided by 3, the [Delta] V [Delta] V / 3 is obtained by subtracting one of the three.

Therefore, from the general formula (1), each voltage v
_n, the amplitude of v _{n +} 1, v _m, since the 2.DELTA.V / 3, delta
V.

[Embodiment 3] Still another embodiment of the gradation display method according to the present invention will be described below with reference to FIGS.

In this embodiment, the reference voltages V _n , V
The voltage difference ΔV of _{n + 1} is divided into four equal parts, and three new halftone voltages between the reference voltages V _n and V _{n + 1} are obtained as V _n + ΔV / 4,
_{V n + ΔV / 2, V} n + 3ΔV / 4 to generate the gray scale display method capable of a number of gradations to four times, the first gray-scale display method (a) ~ (d) and the first 2 gradation display method
This will be specifically described with reference to (e) to (g).

Reference voltage V_nIs the reference voltage V_nAnd reference voltage
V_{n + 1}And a four-frame cycle based on the voltage difference ΔV
V_n-3ΔV / 8, V_n−ΔV / 8, V_n+ 3ΔV /
8, V _n+ ΔV / 8
The average value of the change, that is, 4 frames
It is equal to the average value of the periods (F1 to F4).

The reference voltage V _{n + 1} is V _{n + 1} −3ΔV / 8, V _{n + 1} −ΔV / 8, V _{n + 1} +
It repeatedly changes to four voltage values of 3ΔV / 8, V _{n + 1} + ΔV / 8, and is equal to the average value of the changes, that is, the average value of four frame periods (F1 to F4) (the above-described value). (a)).

The amplitude of the fluctuation of each of the reference voltages V _n and V _{n + 1} is
Since each is 3ΔV / 4, each is set to be smaller than ΔV ((b) above).

[0105] Next, the four voltage values to generate a reference voltage V _n, and four voltage values to generate a reference voltage V _{n + 1} in combination selectively, the reference voltages V _n, V _{n + 1} a halftone voltage between _{V n + ΔV / 4, V} n + ΔV / 2, V
Generate _n + 3ΔV / 4. In this case, the halftone voltage V _n
+ ΔV / 4, V _n + ΔV / 2, V _n + 3ΔV / 4 are obtained as an average value in which the voltage value is changed to a plurality of values in the same four frame period as described above, and the amplitude of the change is
It is set to be smaller than the above ΔV (the above (c) and (d)).

For this purpose, as shown by a circle in FIG. 1, V _{n + 1} -3ΔV / 8 is selected in the first frame F1, and V _n -ΔV / 8 is selected in the second frame F2. In the third frame F3, V _n + 3ΔV / 8 is selected, and in the fourth frame F4, V _n + ΔV / 8V _n is selected and combined. As a result, the frequency of the fluctuation is changed to each reference voltage V _n ,
Equal to the frequency of the variation of V n _{+ 1,} it is possible to obtain a halftone voltage V _n + ΔV / 4 the amplitude was [Delta] V smaller 3ΔV / 4.

As shown by the crosses in FIG. 1, by selecting a voltage value for each of the frames F1 to F4, a halftone voltage V _n + ΔV / 2 having an amplitude of 3ΔV / 4 is similarly obtained.
Can be obtained.

Further, as shown by the squares in FIG. 1, by selecting a voltage value for each of the frames F1 to F4, a halftone voltage V _n + 3ΔV having an amplitude of 3ΔV / 4 is similarly obtained.
/ 4 can be obtained.

Further, the concept is completely the same as that of the first embodiment.
Therefore, the first gradation display methods (a) to (d) are
(E) to (g), the first variable reference voltage v_n
And the second variable reference voltage v_{n + 1}Is generated, and as shown in FIG.
Each frame according to the order of mark, x mark, or □ mark
By switching between the two, the intermediate fluctuation voltage v _m
(1/4), v_m(1/2) and v_mCan produce (3/4)
it can.

[0110] In the case of performing gradation display corresponding to the reference voltage V _n, as shown in FIG. 1, as in the first variation reference voltage v _n itself is used, the variation of each frame F1~F4 It goes without saying that the reference voltage is selected.

That is, as shown in FIG. 1, when the reference voltage V _n is generated, the selective switching of the fluctuation reference voltage for each of the frames F 1 to F 4 is performed as follows: v _n / v _n / v _n / v
It becomes _n . Halftone voltage _{V n + ΔV / 4, V} n + ΔV / 2
And V _n + 3ΔV / 4, v
_{n + 1 / v n / v} n / v n, v n + 1 / v n + 1 / v n /
v _n, and v a _{n + 1 / v n + 1} / v n / v n + 1.

[0112] Incidentally, in the case of the present embodiment also, the amplitude of each voltage _{v n, v n + 1,} v m is set to follow the general formula (1) above.

[0113] That is, according to the concept of the general formula (1), the amplitude of each voltage _{v n, v n + 1,} v m is the reference voltage V _n, the difference ΔV of V _{n + 1} 4 divided, each Voltage v _n ,
The amplitudes of v _{n + 1} and v _m are (ΔV−ΔV / 4), that is, 3
It can be said that different combinations of voltage values are set so as to be ΔV / 4.

Next, a modification of the embodiment shown in FIG. 1 is shown in FIG.

The modification of FIG. 2 is different from the reference voltages V _n , V
The voltage difference ΔV of _{n + 1} is divided into four equal parts, and three new halftone voltages between the reference voltages V _n and V _{n + 1} are obtained as V _n + ΔV / 4,
_{V n + ΔV / 2, V} n + 3ΔV / 4 to generate, in terms of the number of gradations to four times, but the same as the embodiment shown in FIG. 1, the reference voltage V _n and V _{n + 1,} Fig. 1 The point is different from the specific example shown in FIG. 1 in that it is generated by changing using a voltage value different from the case of FIG.

That is, the reference voltage V _n is _equal to the reference voltage V _n
And based on the voltage difference [Delta] V between the reference voltage V _{n + 1,} every 4 _{frames, V n + ΔV / 6,} V n -2ΔV / 6, V n -
_{ΔV / 6, V n + 2ΔV} / 6 and repeats the varying four voltage values, the average value of the variation, i.e. 4
It is equal to the average value of the frame period (F1 to F4).

The reference voltage V _{n + 1} is V _{n + 1} + ΔV / 6, V _{n + 1} -2ΔV / 6, V _{n + 1} − in a 4-frame cycle.
It repeatedly changes to four voltage values of ΔV / 6 and V _{n + 1} + 2ΔV / 6, and is equal to the average value of the changes, that is, the average value of four frame periods (F1 to F4).

As in the specific example shown in FIG. 1, when generating the reference voltage V _n , the first variable reference voltage v _n
Outputs itself, halftone voltage _{V n + ΔV / 4, V} n +
When generating _{ΔV / 2, V n + 3ΔV} / 4 , as shown in FIG. 2
When the respective voltage values are selectively combined in accordance with the circles, crosses, and squares shown in, the intermediate fluctuation voltages v _m (1/4), v _m (1/2), and v _m whose amplitude is smaller than ΔV (3/4) can be generated.

[0119] Alternatively, when performing selective switching of the variation reference voltage for each frame F1~F4 generates a reference voltage V _n is the selective switching, as shown in FIG. 2, v _n / V _n / v _n / v _n and the halftone voltage V _n
+ ΔV / 4, V _n + to generate a [Delta] V / 2 and V _n + 3ΔV / 4, respectively _{v n / v n + 1 /} v n / v n, v
_{n / v n + 1 / v} n + 1 / v n, and _{v n + 1 / v n +} 1 / v
_{n + 1} / v may be set to _n.

Also in this case, the voltages v _n , v _{n + 1} , v _m
And the amplitude can be made smaller than ΔV.

[Fourth Embodiment] According to the gradation display method described in the third embodiment, the first variation reference voltage v _n , the second
Reference voltage v _{n + 1} and intermediate fluctuation voltage v _m (1/4),
An embodiment of a gradation voltage generating device for generating v _m (1/2) and v _m (3/4) and an image display device including the gradation voltage generating device will be described with reference to FIGS. 6 and 7. This will be described below.

FIG. 6 shows a TFT type active matrix liquid crystal display device as an example of the configuration of the image display device according to the present invention. In the liquid crystal panel 1 serving as a display unit,
A liquid crystal layer is sandwiched between two transparent substrates. A common electrode is provided on one transparent substrate, and a plurality of signal lines 2 and scanning lines 3 are arranged in a grid on the other transparent substrate. Further, in a pixel region surrounded by the signal line 2 and the scanning line 3, a pixel electrode 4 and a TFT (Thin Film Transistor) 5 serving as a switching element are provided for each pixel.

A predetermined voltage signal (G1, G2) is applied to the scanning line 3.
), The TFT 5 is turned on, and the image signals (S1, S2, etc.) input to the signal line 2 are written to each pixel electrode 4. As a switching element for selectively driving the pixel electrode 4, a two-terminal MIM (metal-insulating-film-metal) element may be used in addition to the three-terminal TFT 5.

Each signal line 2 of the liquid crystal panel 1 is connected to a source driver 6, and each scanning line 3 is connected to a gate driver 7. The source driver 6 has 64
A drive circuit for gradation display is provided, and 64 bits are provided according to a 6-bit data signal b ₁ supplied from an FRC circuit 8 described later.
The stepwise reference voltages v _i (i = 0 to 63) are selected and sequentially distributed to the signal line 2. Variation reference voltage v _i of the 64 stage, a variable voltage V _r 0 to V _r 7 of 8 steps supplied from the variable voltage generator 9 to the source driver 6, as shown in FIG. 7, the interior of the source driver 6 It is generated by dividing by a resistor R.

[0125] Incidentally, the average value of the variation in the variable voltage V _r 0 to V _r 7 are shown in FIGS. 8 and 10 as a conventional example, is equal to the voltage V0~V7 each fixed to a constant value.

On the other hand, the gate driver 7 controls the gate driver control signal b supplied from the control circuit 10.
_{According to 2} , scanning lines 3 are sequentially selected and activated by a line sequential driving method. Thereby, the TFTs 5 connected to one scanning line 3 are simultaneously turned on. A source driver control signal b ₃ to synchronize the activation of the scanning line 3, is input from the control circuit 10 to the source driver 6, variation reference voltage v _i which has been held in the source driver 6, the signal line 2 TF output simultaneously and conducting
The voltage is applied to the liquid crystal of each pixel via T5.

[0127] The data signal b ₁ as described for switching between a first variation reference voltage v _n and the second variation reference voltage v _{n + 1} on the basis of FIG. 1, the FRC circuit 8, first and variation reference voltage v _n is any of the 64 stages of the variation reference voltage v _i, the first variation reference voltage v
_The source driver switches the second variation reference voltage vn _{+ 1} corresponding to the gray level one level higher than _{n in} units of one frame per pixel, and repeats the switching in one unit in a cycle of four frames. a 6-bit signal for instructing 6, is generated from the data signal b ₅ of 8 bits supplied from the display data processing unit 11 to be described later.

The FRC circuit 8 stores the frame number F
1~F4 frame designation signal b ₄ as 2-bit data for designating a is input from the control circuit 10 in synchronism with the frame period. This frame designation signal b ₄ is
The timing for switching in accordance with a first variation reference voltage v _n and the second and the variation reference voltage v _{n + 1} to the frame number F1~F4 as described above and gives the FRC circuit 8.

On the other hand, as will be described later in detail, the frame designating signal b ₄ is generated by the fluctuating voltage V _r 0 in the fluctuating voltage generator 9.
ＶV _r 7 is also used. In other words, variable voltage generator 9, by inputting a frame designation signal b ₄ from the control circuit 10 may take the timing of varying the voltage value for each frame.

Note that F [1: 0] entered in FIG.
Is among eight bus lines corresponding to 8-bit data,
This indicates that the first and zeroth bus lines corresponding to the lower two-bit data are used for signal transmission, and the frame designating signal b ₄ is transmitted from the control circuit 10 through the zeroth and first bus lines. This means that the signal is transmitted to and received from the FRC circuit 8 and the variable voltage generator 9.

The 8-bit data signal b ₅ is converted into 8-bit display data b ₆ inputted from an external CPU via the interface 12 in the display data processing section 11.
Is generated by converting the data into upper 6-bit data and lower 2-bit data. Upper 6-bit data is data for specifying either the variation reference voltage v _i of 64 stages described above. On the other hand, the lower 2-bit data is the first 2-bit data specified by the upper 6-bit data.
The variation reference voltage v _n and the intermediate variable voltage described above to generate a halftone between the gradation on one than v _m (1/4), v _m
(1/2) and v _m (3/4), which are hereinafter referred to as intermediate gradation specifying data as necessary.

[0132] Incidentally, In FIG. 7, the 8-bit display data b ₅ to D [7: 0] gives the sign of the upper 6-bit data and lower 2-bit data, respectively D [7: 2]
And D [1: 0]. That is, the display data b _5, through the bus line No. 0 to 7 th, when it is output to the FRC circuit 8 from the display data processing unit 11, the upper 6-bit data, the number 2 to 7 bus number Lines are used, and the lower two-bit data uses the 0th and 1st bus lines.

Incidentally, the gate driver control signal b ₂ , the source driver control signal b ₃ and the frame designation signal b ₄ are used in the control circuit 10 by various timing signals (horizontal synchronization signal) input from the external CPU via the interface 12. (H), vertical synchronizing signal (V) and clock signal (CLK)).

Next, a first fluctuation reference voltage v _n and a second fluctuation reference voltage v _{n + 1} are generated, and both fluctuation reference voltages v _n and v _{n + 1} are generated in a fixed period unit, that is, in a frame unit. The circuit configuration of the gray scale voltage generator for switching will be described with reference to FIG. The grayscale voltage generator according to the present invention includes an FRC circuit 8 as a fluctuation reference voltage selection unit and a fluctuation voltage generation unit 9 as a fluctuation reference voltage generation unit.

First, 64 steps of the fluctuation reference voltage v _i (i
= 0 to 63) will be described. The fluctuating voltage generating unit 9 includes a ROM 2 as fluctuating information generating means.
1, is connected to the output of the ROM 21, the variable voltage V _r 0 to
D / A converters 220 to 227 that output V _r 7 are provided. ROM21, as the first variation reference voltage v _n and the second variation reference voltage v _{n + 1} shown in FIG. 1, the variable voltage V which varies the voltage value according to the frame number F1~F4
The _r 0 to V _r 7, and stores the voltage value specified data to be output to the D / A converter 220-227.

Therefore, when the ROM 21 receives the frame designation signal b ₄ from the control circuit 10,
Voltage value specifying data specifying voltage values corresponding to each of the input frame numbers F1 to F4 is input to each D / A converter 2.
20 to 227. Thus, the D / A converter 220 to 227 outputs a variable voltage V _r 0 to V _r 7 the average value of the voltage values are different in 8 stages varies.

Note that the address of the voltage value designation data stored in ROM 21 is stored in D / A converters 220 to 2.
27 and the frame numbers F1-
F4, and the ROM 21 and each D /
A register may be provided between each of the A / A converters 220 to 227 to switch required voltage value designation data in time series and supply the data to each of the D / A converters 220 to 227.

Alternatively, when the voltage value designation data is composed of 6-bit data, 48 output buses of the ROM 21 are prepared, and the D / A converters 220 to 22 are provided.
7 are assigned 6 output buses each, and the frame designation signal b
_{If the} ROM 21 outputs 48-bit data to ₄ , the voltage value designation data required for each of the D / A converters 220 to 227 can be allocated by 6 bits.

[0139] Then, the source driver 6, a variable voltage V _r 0 to V _r 7 supplied from the variable voltage generator 9, 64
And the internal resistance R for dividing the phase variation reference voltage v _{i (i} = 0~63), a data signal b ₁ of 6 bits specifying one of the variation reference voltage v _i, and input from the FRC circuit 8, and a multiplexer (MUX) 31 for selecting the variation reference voltage v _i corresponding to the data signal b _1. MU
X31, together with the FRC circuit 8, also constitutes the fluctuation reference voltage selection means.

On the other hand, the FRC circuit 8 includes a ROM 32 and an increment circuit (INC) 33.
ROM32 is the frame designation signal b ₄ and the intermediate gradation designating data (D [1: 0]) to input first and variation reference voltage v _n with 1 than the first variation reference voltage v _n Data for determining which one of the second fluctuation reference voltage vn _{+ 1} , which is the next higher level, is selected is stored. Then, the ROM 32 stores the lower-level first fluctuation reference voltage v
_{When n} is selected, a select signal 0 is output, and when an upper level second variation reference voltage vn _{+ 1} is selected, a select signal 1 is output.

The increment circuit 33 has a ROM
When the select signal 0 is input from the display data processing unit 32, the 8-bit data signal b ₅ input from the display data processing unit 11 is input.
Is output to the source driver 6 as it is. On the other hand, the increment circuit 33
If you enter a select signal 1 from, increase the value of the upper 6-bit data of the data signal b ₅ of 8 bits input from the display data processing unit 11 by one, the second variation of one level The reference voltage vn _{+ 1} is converted into 6-bit data for designating, and output to the source driver 6.

With the above configuration, for example, the generation of the intermediate fluctuation voltage v _m (1/4) shown in FIG. 1 is performed as follows. R
To OM32, when the frame designation signal b ₄ to specify the first frame (F1) is input, specifies the halftone voltage V _n + [Delta] V / 4 between the certain reference voltage V _n and the reference voltage V _{n + 1} 8-bit data signal b ₅ to the, if the input from the display data processing unit 11 to the FRC circuit 8, ROM 3
2 receives the intermediate gradation designation data, which is the lower 2 bits of the data signal b ₅ , and outputs the second fluctuation reference voltage v
A select signal 1 designating _{n + 1} is output to the increment circuit 33. Thereby, the increment circuit 33
The value of the upper 6-bit data for designating a first variation reference voltage v _n of the data signal b ₅ is increased by 1, and outputs to the source driver 6.

Then, the source driver 6 receives the 6-bit data designating the second fluctuation reference voltage v _{n + 1} , so that the intermediate fluctuation voltage v _m (1/4) of the first frame (F1) is received. ), The second variable reference voltage vn _{+ 1} is MUX
31 is output. At this time, R
Since OM21 frame designation signal b ₄ to specify the first frame (F1) simultaneously to have been input, variation reference voltage v _{n + 1} of the second source driver 6 outputs the first frame shown in FIG. 1 The voltage value corresponds to (F1).

Next, the ROM 32 stores the second frame (F
2) Based on the frame designation signal b ₄ to specify the intermediate gradation designating data, and outputs a select signal 0 that specifies the first variation reference voltage v _n to the increment circuit 33.
Thus, the increment circuit 33 outputs the upper 6-bit data of the data signal b ₅ as it is to the source driver 6.

Then, the source driver 6 receives the 6-bit data designating the first fluctuation reference voltage v _n , so that the intermediate fluctuation voltage v in the second frame (F2) is received.
As _m (1/4), to output the first variation reference voltage v _n from the multiplexer 62. At this time, the fluctuation voltage generator 9
Since the frame designation signal b ₄ to specify a second frame (F2) at the same time in ROM21 of is inputted, the first variation reference voltage v _n of the source driver 6 outputs, as shown in FIG. 1
The voltage value corresponds to the second frame (F2) shown in FIG.

Thereafter, the same operation as that of the second frame (F2) is repeated for the third frame (F3) and the fourth frame (F4). Thus, a first variation reference voltage v _n and the second variation reference voltage v switching of _{n + 1} is performed, the intermediate variable voltage v _m (1 to be applied to the liquid crystal /
If 4) is smoothed in four frame periods, the halftone voltage of V _n + ΔV / 4 is effectively applied.
It is possible to display a gray level corresponding to the variation reference voltage v _n, the [Delta] V / 4 gradations between gradation corresponding to the reference voltage v _{n + 1} second variation of.

The above description is based on another intermediate fluctuation voltage v _m (1 /
2) and the generation of the intermediate fluctuation voltage v _m (3/4), the detailed description is omitted. When the data signal b ₅ input from the display data processing unit 11 to the FRC circuit 8 specifies the reference voltage V _n , RO
M32, for each to enter the frame number F1~F4 by the frame designation signal b _4, since repeated output of the select signal 0 that specifies the first variation reference voltage v _n, a first variation reference voltage v _n is as Output to the source driver 6.

[0148] Thus, during the gradation corresponding to the reference voltage V _n and the reference voltage V _{n + 1,} since it is possible to display the three halftone, 64 steps of variation reference voltage v
It is possible to realize multi-gradation display of 256 gradations, which is four times as large as _i .

[0149] In the above description, the first and the variation reference voltage v _n second and variation reference voltage v _{n + 1,} are different only the average value of the voltage fluctuation, amplitude and phase variations from each other Are equal. Therefore, each variation in voltage V _r 0~
The amplitude and phase of the fluctuation of V _r 7 can be unified into one type. Thereby, each D / A converter 220-2
In order to output the variable voltage V _r 0 to V _r 7 to 27, as a means for generating variation information given to each D / A converter 220 to 227, the voltage value required for the input of the same frame designation signal b ₄ Only one ROM 21 for outputting the designated data is required. Therefore, the circuit configuration of the fluctuating voltage generator 9 is simplified.

Further, only one D / A converter 227 is provided, and the output of D / A converter 227 is
If four variation reference voltage v _i so that the partial pressure, it is possible to further simplify the structure of the variable voltage generator 9.

The cycle of changing the voltage value may be set so that the changing frequency is 15 Hz or more in consideration of the display frequency. For example, if the display frequency is 60H
In the case of z, in order for the fluctuation frequency to be 15 Hz or more,
The cycle of changing the voltage value is preferably set to four frames or less.

Further, as shown in FIG.
_In generating _i , the voltage value may be changed every フ_レー ム frame, and the cycle of the change may be set to one frame. FIG.
Switching manner, 1/2-frame basis varies the voltage value to be the variation reference voltage v _n, when generating a v n _{+ 1,} the variation reference voltage v _n, v n _{+ 1} of every half frame It was capable of generating an intermediate variable voltage v _m.

[0153] In this case, the variation frequency of the voltage _{v n, v n + 1,} v m is equal to 1 frame, matching the display frequency. Accordingly, in any gradation display, a frequency component lower than the display frequency is not superimposed on the display frequency, so that higher-quality gradation display can be realized.

[0154]

As described above, the gradation display method according to the present invention comprises: (1) a first gradation voltage corresponding to a first gradation level of an image displayed on an image display device; The second gradation voltage corresponding to the second gradation level is obtained as an average value obtained by periodically varying the voltage value to a plurality of values, and the amplitude of the variation is set to the first gradation level. (2) a plurality of voltage values for generating the first gradation voltage and a second voltage value for generating the first gradation voltage;
In generating a halftone voltage between the first grayscale voltage and the second grayscale voltage by selectively combining a plurality of voltage values for generating the grayscale voltage, the halftone voltage is also In this configuration, the voltage value is obtained as an average value that is periodically changed to a plurality of values, and the amplitude of the change is smaller than ΔV.

Therefore, the first gray scale voltage, the second gray scale voltage, and the second gray scale voltage generated by selectively combining a plurality of voltage values.
The grayscale voltage and the halftone voltage have the fluctuation amplitude ΔV that is the difference between the first grayscale voltage and the second grayscale voltage.
Since it is set smaller, it is possible to achieve an effect that the energy of the low-frequency component, which is a factor of flicker that can be sensed by human eyes, can be reduced in the halftone as compared with the conventional frame rate control gradation method.

Needless to say, the types of the gradation voltages are not limited to the two types of the first gradation voltage and the second gradation voltage. That is, the type of the gradation voltage is 64
By setting the type and applying the above method to each combination of a certain gradation voltage and the gradation voltage of the next higher level, three types of halftone voltages can be set between adjacent gradation voltages. If it is generated, a multi-gradation display with a total of 256 gradations can be realized. This applies to any of the claims of the present application.

As described above, the other gradation display method according to the present invention comprises: (1) a first gradation voltage corresponding to a first gradation level of an image displayed on an image display device; The second gradation voltage corresponding to the second gradation level is obtained as an average value obtained by periodically varying the voltage value to a plurality of values, and the amplitude of the variation is set to the first gradation level. Generating a first variation reference voltage and a second variation reference voltage that are smaller than ΔV, which is a difference between the adjustment voltage and the second gradation voltage, respectively, and (2-1) the first variation reference By selectively switching the voltage and the second fluctuation reference voltage in units of a certain period, the first
(2-2) When generating a halftone voltage between the grayscale voltage and the second grayscale voltage, (2-2) a plurality of voltage values for generating the first grayscale voltage and the second grayscale voltage A plurality of voltage values to be generated are selectively combined, so that the halftone voltage is also obtained as an average value in which the voltage value is periodically changed to a plurality of values, and the amplitude of the change is smaller than ΔV. This is a configuration in which

The difference between this gradation display method and the above-mentioned gradation display method is that in generating a halftone voltage, a first fluctuation reference voltage and a second fluctuation reference voltage are generated, and both are generated for a certain period. Since this is a point of selective switching in units, the grayscale display method uses the energy of the low-frequency component, which is the cause of flicker that can be perceived by the human eye, as the conventional frame rate control level for the halftone for exactly the same reason. This has the effect of being able to be reduced compared to the toning method.

In another gradation display method according to the present invention, in order to obtain the first gradation voltage, the second gradation voltage, and the halftone voltage, the period in which each voltage value is changed is set to the same length. May be unified.

As a result, there is no difference in the fluctuation period of the voltage value among the first gradation voltage, the second gradation voltage, and the halftone voltage. Since the frequency components included in the gradation voltage and the halftone voltage are equal, the display quality does not change depending on the gradation.
There is an effect that higher-quality gradation display can be realized.

In the gradation display method according to the present invention, the first gradation voltage and the second gradation voltage may be changed in phase.

As a result, the information signal for changing each gradation voltage can be unified into one type, and each gradation voltage can be changed based on the same information signal. Therefore, a circuit configuration for generating the information signal, There is an effect that the circuit configuration for generating each gradation voltage can be simplified.

As described above, the grayscale voltage generator according to the present invention provides (1) a first grayscale voltage corresponding to a first grayscale level of an image displayed on an image display device, and a second And the second gradation voltage corresponding to the first gradation level is obtained as an average value obtained by periodically changing the voltage value to a plurality of values, and the amplitude of the fluctuation is the first gradation voltage. A first variation reference voltage having an average value of the first gradation voltage and an average of the second gradation voltage, which are set to be smaller than ΔV which is a difference between the voltage and the second gradation voltage. A variable reference voltage generating means for generating a second variable reference voltage as a value; (2) a plurality of voltage values included in the first variable reference voltage and a plurality of voltage values included in the second variable reference voltage Are selectively combined to generate a halftone voltage between the first grayscale voltage and the second grayscale voltage. The first variation reference voltage and the halftone voltage are also determined so that the halftone voltage is obtained as an average value obtained by periodically varying the voltage value to a plurality of values, and the amplitude of the variation is smaller than ΔV. A fluctuation reference voltage selecting means for selecting and outputting one of the second fluctuation reference voltages every time the voltage value of the halftone voltage is changed.

Therefore, between the first gradation voltage and the second gradation voltage, a voltage value forming the first gradation voltage and a voltage value forming the second gradation voltage are set to a plurality of levels. A variable reference voltage generating means to be formed; and a variable reference voltage selecting means for appropriately selecting one of the first and second variable reference voltages every time the voltage value of the halftone voltage is changed. Thus, it is possible to provide a grayscale voltage generation device that realizes a grayscale display method having the effects described above.

In the grayscale voltage generating device according to the present invention, in order to obtain the first grayscale voltage, the second grayscale voltage, and the halftone voltage, the period of changing each voltage value is set to the same length. It may be unified.

As a result, there is no difference in the voltage value fluctuation cycle between the first gradation voltage, the second gradation voltage, and the halftone voltage. Since the frequency components included in the gradation voltage and the halftone voltage are equal, the display quality does not change depending on the gradation.
There is an effect that higher-quality gradation display can be realized.

The variable reference voltage generating means of the gradation voltage generating device according to the present invention comprises the first variable reference voltage and the second variable reference voltage.
May be provided with fluctuation information generating means for generating fluctuation information for causing the fluctuation reference voltage to fluctuate in phase.

Therefore, by causing the first fluctuation reference voltage and the second fluctuation reference voltage to fluctuate in the same phase, the fluctuation information is shared by both the fluctuation reference voltages, and one type of fluctuation information generating means is provided. Since it is only necessary to generate the variation information, the circuit configuration can be simplified. Further, since the same type of configuration can be employed for the circuits that generate the respective variable reference voltages, there is an effect that the configuration of the variable reference voltage generating means can be simplified.

As described above, the image display device according to the present invention is driven by the gradation voltage generator, the first fluctuation reference voltage, the second fluctuation reference voltage, and the halftone voltage, and And a display unit having a plurality of display pixels for performing tonal display.

Therefore, for the same reason as described above, the energy of the low-frequency component, which is a cause of flicker that can be sensed by the human eye, is reduced by the conventional frame rate control gray scale method, and displayed by gray scale. There is an effect that it is possible to provide an image display device that realizes high-quality multi-gradation display without changing the quality.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one embodiment of a gradation display method according to the present invention, and is an explanatory diagram showing an example of a method of generating a fluctuation reference voltage and a halftone voltage.

FIG. 2 is an explanatory diagram showing a modification of the method of generating the fluctuation reference voltage and the halftone voltage.

FIG. 3 is an explanatory diagram showing another embodiment of the gradation display method according to the present invention, and is an explanatory diagram showing an example of a method of generating a fluctuation reference voltage and a halftone voltage.

FIG. 4 is an explanatory diagram showing a modification of the method of generating the fluctuation reference voltage and the halftone voltage shown in FIG.

FIG. 5 is an explanatory view showing still another embodiment of the gradation display method according to the present invention, and is an explanatory view showing an example of a method of generating a fluctuation reference voltage and a halftone voltage.

FIG. 6 is a block diagram illustrating a configuration example of an image display device including a grayscale voltage generator according to the present invention.

FIG. 7 is a block diagram illustrating a configuration example of a grayscale voltage generator according to the present invention.

FIG. 8 is a block diagram illustrating a configuration of an image display device that performs gradation display by a conventional frame rate control gradation method.

FIG. 9 is an explanatory diagram showing a method of generating a halftone voltage from a reference voltage by a conventional frame rate control gradation method.

FIG. 10 is a block diagram showing a configuration of a conventional grayscale voltage generator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Liquid crystal panel (display means) 6 Source driver (fluctuation reference voltage generation means) 8 FRC circuit (fluctuation reference voltage selection means) 9 Fluctuating voltage generation part (fluctuation reference voltage generation means) 21 ROM (fluctuation information generation means) 31 MUX ( V _n reference voltage (first gradation voltage) V _{n + 1} reference voltage (second gradation voltage) v _n first fluctuation reference voltage v _{n + 1} second fluctuation reference voltage v _m Intermediate fluctuation voltage

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09G 3/36 G09G 3/36

Claims (8)

[Claims] A first gradation voltage corresponding to a first gradation level and a second gradation voltage corresponding to a second gradation level of an image displayed on the image display device, The voltage value is changed so as to be obtained as an average value that is periodically changed to a plurality of values, and the amplitude of the change is smaller than ΔV, which is the difference between the first gradation voltage and the second gradation voltage. And a plurality of voltage values for generating the first gradation voltage;
In generating a halftone voltage between the first grayscale voltage and the second grayscale voltage by selectively combining a plurality of voltage values for generating the second grayscale voltage, A voltage value that is periodically varied to a plurality of values, and an amplitude of the variation is smaller than ΔV. 2. A first gradation voltage corresponding to a first gradation level and a second gradation voltage corresponding to a second gradation level of an image to be displayed on an image display device, respectively. The voltage value is changed so as to be obtained as an average value that is periodically changed to a plurality of values, and the amplitude of the change is smaller than ΔV that is the difference between the first gradation voltage and the second gradation voltage. A first variation reference voltage and a second variation reference voltage, respectively, and selectively switching between the first variation reference voltage and the second variation reference voltage in a certain period unit to thereby obtain a first gradation. When generating a halftone voltage between the voltage and the second grayscale voltage, a plurality of voltage values for generating the first grayscale voltage;
A plurality of voltage values for generating the second gradation voltage are selectively combined, and the halftone voltage is also obtained so as to be obtained as an average value in which the voltage value is periodically changed to a plurality of values, and A gradation display method, wherein the amplitude is made smaller than the above ΔV. 3. The method according to claim 1, wherein the first and second gradation voltages and the halftone voltage are obtained by unifying the cycle of changing each voltage value to the same length. Or the gradation display method according to 2. 4. The gradation display method according to claim 2, wherein the first gradation voltage and the second gradation voltage are changed in the same phase. 5. A first gradation voltage corresponding to a first gradation level and a second gradation voltage corresponding to a second gradation level of an image displayed on an image display device, respectively. The voltage value is changed so as to be obtained as an average value that is periodically changed to a plurality of values, and the amplitude of the change is smaller than ΔV, which is the difference between the first gradation voltage and the second gradation voltage. A variable reference voltage generating means for generating a first variable reference voltage having the first grayscale voltage as an average value and a second variable reference voltage having the second grayscale voltage as an average value; A plurality of voltage values included in the first variation reference voltage and a plurality of voltage values included in the second variation reference voltage are selectively combined to form a first gradation voltage and a second gradation voltage; In generating the halftone voltage between the halftone voltage and the halftone voltage, the halftone voltage also periodically fluctuates to a plurality of values. One of the first fluctuation reference voltage and the second fluctuation reference voltage is changed every time the voltage value of the halftone voltage is changed so that the average value is obtained and the amplitude of the change is smaller than the above ΔV. And a fluctuation reference voltage selection means for selecting and outputting the selected reference voltage. 6. A cycle in which each voltage value is varied to have the same length in order to obtain the first gradation voltage, the second gradation voltage, and the halftone voltage. 4. The grayscale voltage generator according to claim 1. 7. The fluctuation reference voltage generation means includes fluctuation information generation means for generating fluctuation information for causing the first fluctuation reference voltage and the second fluctuation reference voltage to fluctuate in the same phase. The gray-scale voltage generator according to claim 5 or 6, wherein 8. A grayscale voltage generator according to claim 5, wherein said grayscale voltage generator is driven by said first variable reference voltage, said second variable reference voltage, and said halftone voltage. An image display device comprising: a display unit having a plurality of display pixels for performing display.