JP3499134B2 - Display device and display device driving method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device and a driving method thereof, and more particularly to a liquid crystal display device having a simple matrix type liquid crystal display panel which requires high speed response and a large capacity and a driving method thereof. Such a display device and its driving method are described in AV (Audio Vio).
equipment), OA (office automation)
ion) Used in equipment.

[0002]

2. Description of the Related Art In recent years, with the progress of advanced information society,
There is an increasing demand for a liquid crystal display device capable of displaying a moving image while achieving both high contrast and high-speed response.

The liquid crystal display panel provided in the liquid crystal display device is roughly classified into a simple matrix type liquid crystal display panel and an active matrix type liquid crystal display panel. Comparing the simple matrix type liquid crystal display panel and the active matrix type liquid crystal display panel, the simple matrix type liquid crystal display panel has a simpler panel structure, so that the manufacturing process is easier and the cost is lower. Is advantageous to

As a simple matrix type liquid crystal display panel capable of displaying a large capacity, STN (Super Twist)
Ted Nematic) liquid crystal display panels are often used.

The STN liquid crystal display panel has a pair of substrates. A plurality of scan electrodes that are parallel to each other are formed on one of the pair of substrates. The scan electrodes are covered with an alignment film. A plurality of data electrodes (signal electrodes) parallel to each other are formed on the other of the pair of substrates. The data electrode is covered with an alignment film. The pair of substrates are arranged so as to face each other such that the extending direction of the scanning electrodes and the extending direction of the data electrodes are orthogonal to each other. An STN liquid crystal is provided between the pair of substrates, and a deflection plate is arranged outside the pair of substrates.

The STN liquid crystal is obtained by twisting liquid crystal molecules from 180 degrees to 270 degrees and combining a deflector plate in order to realize high contrast.

A STN liquid crystal display panel further incorporating a phase compensating plate made of a liquid crystal or a polymer film has been commercialized. An STN liquid crystal display panel having a structure incorporating such a phase compensation plate is currently available.
It has become the mainstream of simple matrix type liquid crystal display panels.

The response speed of such an STN liquid crystal display panel is about 300 ms. As a driving method of the STN liquid crystal display panel, a line-sequential scanning driving method is used.

FIG. 1 shows the structure of a liquid crystal display panel 101,
The waveform of the selection pulse applied to each of the plurality of scan electrodes 102 according to the line-sequential scanning driving method is shown.

The liquid crystal display panel 101 has a plurality of scanning electrodes 102 and a plurality of data electrodes 103. Each of the plurality of scan electrodes 102 and the plurality of data electrodes 10
Pixels 104 are formed at intersections with the respective 3's.
A plurality of scan electrodes 10 are provided by a scan driver (not shown).
A selection pulse is applied to each of the data electrodes 2 and a data voltage is applied to each of the data electrodes 103 by a data driver (not shown). By applying the selection pulse and the data voltage to the pixel 104, ON display and OFF display of the pixel 104 are controlled.

As shown in FIG. 1, a plurality of scan electrodes 1
A selection pulse is sequentially output to each of 02. As a result, one of the plurality of scan electrodes 102 is sequentially selected. A data voltage is applied to the data electrode 103 in synchronization with the selection of the scan electrode 102.

On the other hand, in order to improve the response characteristics of the liquid crystal display panel, thinning of the liquid crystal layer and reduction of the viscosity of the liquid crystal material have been studied. As a result, liquid crystal display panels with a response speed of 150 ms or less that are capable of displaying moving images such as video images are being developed.

However, according to the conventional line-sequential scanning driving method,
When the fast response liquid crystal display panel is driven, a frame response phenomenon occurs. This is because the liquid crystal deviates from the original effective value response. Here, the frame response phenomenon is a phenomenon in which the transmittance changes in response to the applied voltage waveforms of the display pixel and the non-display pixel. When the frame response phenomenon occurs, the transmittance of non-display pixels increases and the transmittance of display pixels decreases. As a result, the contrast of the displayed image is lowered, and good display characteristics cannot be obtained.

As a driving method for suppressing the frame response phenomenon, a sequential addressing method (SAT) is used.
A driving method called a method) has been proposed. The sequence addressing method (SAT method) is described in, for example, T.W. N.
Ruckmongathan et al. , Japan
Display 92, Digest, p. 65, JP-A-6-4049.

FIG. 2 shows the structure of the liquid crystal display panel 101,
The waveform of the selection pulse applied to each of the plurality of scan electrodes 102 according to the sequential addressing method (SAT method) is shown.

The structure of the liquid crystal display panel 101 is the same as that of the liquid crystal display panel 101 shown in FIG.
The description is omitted here.

As shown in FIG. 2, the frame period is equally divided into a plurality of periods, and the selection pulse is applied to the plurality of scan electrodes 102 simultaneously in each of the plurality of periods. In the example shown in FIG. 2, the selection pulse is simultaneously applied to the four scan electrodes 102. In this way, the four scan electrodes 102 are simultaneously selected. A data voltage G _j (t) is applied to the j-th column data electrode 103. The data voltage G _j (t) is obtained according to (Equation 1).

[0018]

[Equation 1] Here, k is a proportional constant, F _i (t) is a function value that determines the voltage applied to the i-th row scan electrode 102 at time t, and I
_ij indicates the display data in the i-th row and the j-th column, and L indicates the number of the scan electrodes 102 that are simultaneously selected.

Further, conventionally, in order to display a moving image such as a video image, it has been necessary to drive the liquid crystal display panel by using a driving method called a frame modulation method. According to the frame modulation method, O contained in a predetermined number of frames
A plurality of gradation levels are expressed by the number of N display pixels and the number of OFF display pixels.

However, in the conventional frame modulation method, the number of frames required for gradation display must be increased as the number of gradations increases. As a result, the flicker of the displayed image tends to increase as the number of gradations increases. Further, such image flicker becomes more remarkable in the case of a high-speed response liquid crystal display panel.

As a driving method for realizing the multi-gradation display without increasing the number of frames required for the gradation display, there is a driving method in which the amplitude of the selection pulse applied to the scan electrodes is changed every frame cycle. It has been proposed (for example, Japanese Patent Laid-Open No. 6-230752).

FIG. 3 shows the waveform of the selection pulse SEL ₁ applied to the scanning electrodes arranged in the first row of the liquid crystal display panel and the waveform of the selection pulse SEL ₁ arranged in the second row of the liquid crystal display panel in such a driving method. Select pulse SEL applied to scan electrodes
₂ waveforms are shown. In the example shown in FIG. 3, a selection pulse having an amplitude + V _R1 (or −V _R1 ) is applied to the scan electrodes in the frame period T ₁ , and an amplitude + V _R in the frame period T _2.
Selection pulse _R2 (-V _R2) is applied to the scanning electrodes. In this way, by changing the amplitude of the selection pulse applied to the scan electrodes for each frame period, it is possible to realize multi-gradation display without increasing the number of frames required for gradation display. As a result, image flicker is suppressed.

Further, a method of performing gradation display by controlling the pulse width of the data voltage applied to the data electrode has been proposed (for example, Japanese Patent Laid-Open No. 50-156396).

[0024]

FIG. 4 shows the configuration of the drive voltage generation circuit 107 required to generate selection pulses having different amplitudes as shown in FIG.

[0025] In the drive voltage generating circuit 107, a set of drive voltage (+ V _R1, -V _R1) and the driving voltage set of (+ V _R2, -
One of V _R2 ) is selected by the switches S _{1 to} S ₄ . The selected set of drive voltages is output to the scan driver (not shown). The scan driver generates a selection pulse based on the selected set of drive voltages. Switch S
₁ to S ₄ is turned on and off in response to the voltage switch signal SW.

Table 1 shows the voltage switching signal SW and the switch S.
The relationship between _{1 to} S ₄ and the potential of the selection pulse output to the scan electrode 102 is shown.

[0027]

[Table 1]

The number of ON display pixels 104 and the number of OFF display pixels 104 displayed on the same scan electrode 102.
There is a driving method in which the amplitude of the selection pulse is changed according to the ratio of the number of.

FIG. 5 shows the structure of the liquid crystal display panel 101,
The waveform of the selection pulse applied to each of the plurality of scan electrodes 102 according to this driving method is shown.

Since the structure of the liquid crystal display panel 101 is the same as that of the liquid crystal display panel 101 shown in FIG.
The description is omitted here.

As shown in FIG. 5, the same scan electrode 1
02 number of ON display pixels 104 and OFF
The amplitude of the selection pulse changes according to the ratio of the number of display pixels 104. This makes it possible to realize uniform display characteristics regardless of the ratio of the number of ON display pixels 104 and the number of OFF display pixels 104 displayed on the same scan electrode 102. In FIG. 5, the white pixel 10
4 indicates an ON display pixel, and a hatched pixel 104 is OFF
The display pixel is shown.

FIG. 6A shows that selection pulses having different amplitudes are generated, and the selection pulses are generated according to the ratio of the number of ON display pixels 104 and the number of OFF display pixels 104 displayed on the same scan electrode 102. The configuration of the drive voltage generation circuit 107a required to correct the potential of is shown.

[0033] In the drive voltage generating circuit 107a, a set of drive voltage _{(+ V R1, + V RH1} , -V RH1, -V R1) set of the drive voltage _{(+ V R2, + V RH2} , -V RH2, -V R2) of one out is selected by the switch S ₁ to S _8. The selected set of drive voltages is output to the scan driver (not shown). The scan driver generates a selection pulse based on the selected set of drive voltages. The switches S _{1 to} S ₈ are turned on / off in response to the voltage switching signal SW.

Table 2 shows the voltage switching signal SW and the switch S.
The relationship between _{1 to} S ₈ and the potential of the selection pulse output to the scan electrode 102 is shown.

[0035]

[Table 2]

Comparing FIG. 4 and FIG. 6A, it can be seen that the drive voltage generation circuit 107a has a more complicated structure than the drive voltage generation circuit 107.

FIG. 6B shows a selection pulse S applied to the scan electrodes 102 arranged in the first row of the liquid crystal display panel 101.
The waveform of EL ₁ and the selection pulse SEL ₂ applied to the scan electrodes 102 arranged in the second row of the liquid crystal display panel 101.
And the waveform of. The selection pulse SEL ₁ and the selection pulse SEL ₂ are generated based on the drive voltage output from the drive voltage generation circuit 107a.

Further, the method of performing gradation display by controlling the pulse width of the data voltage applied to the data electrode is such that the amount of display data to be transferred within one horizontal period becomes several times, Since the frequency component of the data voltage applied to the electrode becomes high, there is a problem that the display quality is degraded due to the waveform distortion.

The present invention has been made in view of the above problems, and a display device capable of realizing multi-gradation display with a simple circuit configuration without increasing the number of frames required for gradation display. And a driving method thereof.

[0040]

A display device according to the present invention comprises a scan driver for applying a selection pulse to each of a plurality of scan electrodes, and a data driver for applying a data voltage to each of a plurality of data electrodes, A display device using a frame modulation method in which the selection pulse and the data voltage are applied to a pixel, and gradation display is performed by the number of ON displays and the number of OFF displays included in a predetermined number of frames,
The scan driver controls the pulse width of the selection pulse such that the pulse width of the selection pulse is different for each predetermined period, and the pulse of the selection pulse in a specific period which is one of the predetermined periods. The above-mentioned object is achieved by controlling the pulse width of the selection pulse so that the ratio of the width and the pulse width of the selection pulse in a predetermined period following the specific period becomes constant. The scan driver may control the ratio of the pulse widths of the selection pulses so that the gradation level changes substantially linearly with respect to the effective voltage value applied to the liquid crystal panel. The predetermined period may be a frame period. The predetermined period may be one or more horizontal periods. The plurality of scan electrodes are divided into a plurality of groups, a voltage according to a given orthogonal function is applied to the scan electrodes belonging to each of the plurality of groups, and display data and a display data are applied to each of the plurality of data electrodes. A voltage proportional to the sum of products of the orthogonal functions may be applied. The scan driver has a function of forcibly fixing the potential of the selection pulse to a non-selection level in response to a control signal, and control of the pulse width of the selection pulse is achieved by utilizing the function. May be done. A display device driving method according to the present invention includes a scan driver that applies a selection pulse to each of a plurality of scan electrodes, and a data driver that applies a data voltage to each of a plurality of data electrodes. A driving method using a frame modulation method in which a voltage is applied to a pixel and gradation display is performed by the number of ON displays and the number of OFF displays included in a predetermined number of frames, wherein the driving method is the selection. A step of controlling the pulse width of the selection pulse so that the pulse width of the pulse is different for each predetermined period, the pulse width of the selection pulse in a specific period being one of the predetermined periods, and Controlling the pulse width of the selection pulse so that the ratio to the pulse width of the selection pulse in a predetermined period following the specific period becomes constant. , Whereby the above-mentioned object can be achieved. The step of controlling the pulse width of the selection pulse further includes the step of controlling the ratio of the pulse width of the selection pulse so that the gradation level changes substantially linearly with respect to the effective voltage value applied to the liquid crystal panel. You may.

[0041]

[0042]

[0043]

[0044]

[0045]

[0046]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 7 shows a schematic configuration of a liquid crystal display device 100 according to Embodiment 1 of the present invention. The liquid crystal display device 100 includes a liquid crystal display panel 1. The liquid crystal display panel 1 is driven by the line-sequential scanning driving method.

The liquid crystal display panel 1 has a first substrate (not shown) and a second substrate (not shown). N scanning electrodes 2 are formed on the first substrate. An alignment film is formed on the scan electrodes 2. M data electrodes 3 are formed on the second substrate. An alignment film is formed on the data electrodes 3. The first substrate and the second substrate are arranged so as to face each other such that the N scanning electrodes 2 and the M data electrodes 3 intersect each other. A liquid crystal layer is sandwiched between the first substrate and the second substrate. Pixels 4 are formed at the intersections of the N scan electrodes 2 and the M data electrodes 3, respectively. Here, N and M represent arbitrary integers. The liquid crystal display device 100 further includes a scan driver 5 that sequentially applies a selection pulse as a scan voltage to each of the N scan electrodes 2, and a data driver 6 that applies a data voltage to each of the M data electrodes 3. .

The scan driver 5 produces a selection pulse based on the drive voltage produced by the drive voltage producing circuit 7. Scanning driver 5, the one scan electrode 2 that is selected from among the N number of scanning electrodes 2 four drive voltage of the selection level _{(+ V R, + V RH} , -V R, -V RH) selectively to Then, the drive voltage (V _M ) of the non-selection level is output to the non-selected scan electrode 2 of the N scan electrodes 2.

FIG. 8 shows the configuration of the drive voltage generating circuit 7.
You The drive voltage generation circuit 7 includes a resistor R₁~ R_Four, Operation
Operation amplifier OA₁~ OA₃, Capacitor C
₁~ C _Fiveincluding. Resistance R₁~ R_FourDepending on voltage + V_EE, -V
_EEIs divided. Drive voltage based on the divided voltage
(± V_R, ± V_RH, V_M) Is generated.

As can be understood by comparing FIG. 8 and FIG. 6A, the drive voltage generating circuit 7 shown in FIG.
The drive voltage generation circuit 107a shown in FIG. 6A has a simpler configuration. This is because the drive voltage generation circuit 7 does not need a switch, and the number of resistors, operation amplifiers, and capacitors can be smaller than that of the drive voltage generation circuit 107a. As described above, the configuration of the drive voltage generation circuit 7 can be simplified by generating selection pulses having different pulse widths instead of generating selection pulses having different amplitudes. This means that the liquid crystal display device 100
Helps reduce the circuit scale.

[0052] The scan driver 5, a control terminal for fixing the potential of the selection pulse to force non-selection level (V _M) (DI
SPOFF terminal) 5a. That is, the scan driver 5, a predetermined level to DISPOFF terminal 5a (e.g., low level) has a function to fix the potential of the selection pulse when the control signal CTL is applied to the non-selection level (V _M) There is. Such a function is realized by a known scan driver. The present invention intends to realize the function of “changing the pulse width of the selection pulse applied to the scan electrode 2” with a simple circuit configuration by positively utilizing this function. In addition,
The control signal CTL is generated by the control signal generation circuit 8.

FIG. 9 shows the waveform of the control signal CTL applied to the DISPOFF terminal 5a and the selection pulse SE applied to the scan electrodes 2 arranged in the first row of the liquid crystal display panel 1.
The waveform of L _{1 and} the waveform of the selection pulse SEL ₂ applied to the scan electrodes 2 arranged in the second row of the liquid crystal display panel 1 are shown.

[0054] In the first one horizontal period of a frame period T _1, the drive voltage _{(+ V R, + V RH} ) is applied to the scanning electrodes 2 of the first row. Further, in the next one horizontal period of a frame period T _1, the driving voltage (-V _{R, RH} -V) is applied in the second row to the scan electrode 2. DI during frame period T ₁
The control signal CTL applied to the SPOFF terminal 5a is maintained at the high level. As a result, in the frame cycle T ₁ , the pulse widths of the selection pulses SEL ₁ and SEL ₂ become substantially equal to the data voltage output period (1 horizontal period) in which the data voltage is output to the data electrode 3.

[0055] In the first one horizontal period of a frame period T _2, the drive voltage _{(+ V R, + V RH} ) is applied to the scanning electrodes 2 of the first row. Further, in the next one horizontal period of a frame period T _2, the driving voltage (-V _{R, RH} -V) is applied in the second row to the scan electrode 2. In the frame period T ₂ , the control signal CT applied to the DISPOFF terminal 5a during a predetermined period in the latter half of the data voltage output period (one horizontal period).
L becomes low level. In response to the control signal CTL changing from the high level to the low level, the selection pulse S
EL _1, functions to fix the potential of the SEL ₂ to the non-selection level (V _M) acts. As a result, in the frame period T ₂ ,
The pulse widths of the selection pulses SEL ₁ and SEL ₂ are shorter than the data voltage output period (1 horizontal period) by a period ΔT in which the control signal CTL is at the low level.

In the example shown in FIG. 9, the scan electrode 2 is operated for a predetermined period in the latter half of the data voltage output period (one horizontal period).
Potential of the applied selective pulse is selectively fixed to the non-selection level (V _M) for each frame period. The predetermined period in the latter half is, for example, the data output period (1 horizontal period)
In the period from immediately before the end of the output of the data voltage to the end of the output of the data voltage. Alternatively, a predetermined period in the first half of the data voltage output period (1 horizontal period),
Potential of the selection pulse applied to the scan electrode 2 may be selectively fixed to the non-selection level (V _M) for each frame period. The predetermined period in the first half is, for example, a period from the start of the output of the data voltage to the immediately after the start of the output of the data voltage in the data output period (one horizontal period).

Further, the control signal CTL is low level.
The period ΔT may be variable for each frame cycle.
Yes. For example, the frame period T₁Then ΔT = 0, frame
Cycle T₂Then ΔT = ΔT₂, Frame period T₃Then ΔT =
ΔT₃May be In this case, the control signal CTL is
The level level period ΔT is 0, Δ for each frame period.
T ₂, ΔT₃repeat.

As described above, according to the scan driver 5, the pulse width of the selection pulse applied to the scan electrode 2 is controlled to be variable every predetermined period. The predetermined period is, for example, a frame period. By changing the pulse width of the selection pulse applied to the scan electrode 2 in units of frames, it is possible to realize multi-gradation display without increasing the number of frames required for gradation display. As a result, it becomes possible to suppress image flicker.

The selection pulse is generated based on the drive voltage generated by the drive voltage generation circuit 7. As described above, the drive voltage generation circuit 7 has a simplified configuration. As a result, the circuit scale of the liquid crystal display device 100 can be reduced.

Furthermore, it is not necessary to make the pulse width of the data voltage applied to the data electrode 3 variable by making the pulse width of the selection pulse applied to the scan electrode 2 variable. Therefore, the conventional problems (that is, increase in display data amount, deterioration in display quality due to waveform distortion, etc.) that have occurred by making the pulse width of the data voltage applied to the data electrode 3 variable may occur. There is no.

In the first embodiment, the drive voltage +
V _RH, the drive voltage using a _RH -V + V _R, a driving method for correcting the level of -V _R was taken as an example. It is obvious that the present invention can be applied to a line-sequential scanning driving method that does not perform such correction.

(Second Embodiment) FIG. 10 shows a schematic structure of a liquid crystal display device 200 according to a second embodiment of the present invention. The liquid crystal display device 200 includes a liquid crystal display panel 1. The liquid crystal display panel 1 has a sequential addressing method (SAT).
Method).

In FIG. 10, the same components as those of the liquid crystal display device 100 shown in FIG. 7 are designated by the same reference numerals, and the description thereof will be omitted.

The liquid crystal display device 200 includes the N scanning electrodes 2
Among them, a scan driver 15 that applies a selection pulse as a scan voltage to L scan electrodes 2 at the same time, and a data driver 1 that applies a data voltage to each of M data electrodes
6 and 6 are further included. Here, L represents an arbitrary integer smaller than N.

The scan driver 15 includes the drive voltage generation circuit 7
The selection pulse is generated based on the drive voltage generated by the above and the function data generated by the orthogonal function generating circuit 9. Scan driver 15, four drive voltage of the selection level to the scanning electrodes 2 of the L present being selected among N of scanning electrodes _{2 (+ V R, + V} RH, -V R, -V RH) selectively To the non-selected scan electrode 2 among the N scan electrodes 2.
The drive voltage (V _M ) of the non-selection level is output to.

[0066] The scan driver 15 includes a control terminal (D to fix the potential of the selection pulse to force non-selection level (V _M)
ISPOFF terminal) 15a. That is, the scan driver 15, a predetermined level to DISPOFF terminal 15a (e.g., low level) the non-selection level voltage of the selection pulse when the control signal CTL is applied (V _M)
It has the function of fixing to. Such a function is realized by a known scan driver. The present invention intends to realize the function of “changing the pulse width of the selection pulse applied to the scan electrode 2” with a simple circuit configuration by positively utilizing this function.
The control signal CTL is generated by the control signal generation circuit 8.

The display data is stored in the buffer memory 10 having at least a capacity of N × M bits. The arithmetic circuit 11 reads L-bit display data corresponding to the selected L scanning electrodes 2 from the buffer memory 10,
The L-bit function data is read from the orthogonal function generation circuit 9, and a signal proportional to the sum of the products of the L-bit display data and the L-bit function data is generated according to (Equation 1). The signal thus generated is output to the data driver 16.

The data driver 16 generates a data voltage according to the signal output from the arithmetic circuit 11, and outputs the data voltage to each of the M data electrodes 3.

[0069] Figure 11 is a waveform of the control signal CTL is applied to DISPOFF terminal 15a, are arranged in 1-4 line of the liquid crystal display panel 1 is applied to the scanning electrodes 2 of the selection pulse SEL ₁ to SEL ₄ And the waveform. In the example shown in FIG. 11, it is assumed that the number of the scan electrodes 2 selected at a time out of the N scan electrodes 2 is two. That is, it is assumed that L = 2.

[0070] In the first one horizontal period of a frame period T _1, the drive voltage _{(+ V R, + V RH} ) is applied to the scanning electrodes 2 of the first row, driving voltage (-V _R, -V _RH) two lines It is applied to the scan electrode 2 of the eye. In the next one horizontal period of a frame period T _1, the drive voltage _{(+ V R, + V RH} ) is applied in the third row to the scanning electrodes 2, the driving voltage (-V _R, -V _RH)
Is applied to the scan electrode 2 in the fourth row. Frame period T ₁
During this period, the control signal CTL applied to the DISPOFF terminal 15a is maintained at the high level. As a result, in the frame cycle T ₁ , the pulse widths of the selection pulses SEL _{1 to} SEL ₄ become substantially equal to the data voltage output period (1 horizontal period) in which the data voltage is output to the data electrode 3.

[0071] In the first one horizontal period of a frame period T _2, the drive voltage _{(+ V R, + V RH} ) is applied to the scanning electrodes 2 of the first row, driving voltage (-V _R, -V _RH) two lines It is applied to the scan electrode 2 of the eye. In the next one horizontal period of a frame period T _2, the drive voltage _{(+ V R, + V RH} ) is applied in the third row to the scanning electrodes 2, the driving voltage (-V _R, -V _RH)
Is applied to the scan electrode 2 in the fourth row. Frame period T ₂
Then, the control signal CTL applied to the DISPOFF terminal 15a is at a low level for a predetermined period in the latter half of the data voltage output period (one horizontal period). In response to the control signal CTL is changed from a high level to a low level, it acts function to fix the potential of the selection pulse SEL ₁ to SEL ₄ to the non-selection level (V _M). As a result, in the frame cycle T ₂ , the pulse widths of the selection pulses SEL _{1 to} SEL ₄ are shorter than the data voltage output period (one horizontal period) by the period ΔT in which the control signal CTL is at the low level.

In the example shown in FIG. 11, the potential of the selection pulse applied to the scan electrode 2 is selectively at the non-selection level for each frame period during a predetermined period in the latter half of the data voltage output period (one horizontal period). It is fixed at (V _M ). The predetermined period in the latter half is, for example, a period from immediately before the output of the data voltage ends to the output of the data voltage in the data output period (one horizontal period). Alternatively, the predetermined period of the first half of the data voltage output period (one horizontal period), the potential of the selection pulse applied to the scan electrode 2 is selectively fixed to the non-selection level (V _M) for each frame period Good. The predetermined period in the first half is, for example, a period from the start of the output of the data voltage to the immediately after the start of the output of the data voltage in the data output period (one horizontal period).

Further, the control signal CTL is low level.
The period ΔT may be variable for each frame cycle.
Yes. For example, the frame period T₁Then ΔT = 0, frame
Cycle T₂Then ΔT = ΔT₂, Frame period T₃Then ΔT =
ΔT₃May be In this case, the control signal CTL is
The level level period ΔT is 0, Δ for each frame period.
T ₂, ΔT₃repeat.

Thus, according to the scan driver 15,
The pulse width of the selection pulse applied to the scan electrode 2 is controlled to be variable every predetermined period. The predetermined period is, for example, a frame period. By changing the pulse width of the selection pulse applied to the scan electrode 2 in units of frames, it is possible to realize multi-gradation display without increasing the number of frames required for gradation display. As a result, it becomes possible to suppress image flicker.

In the second embodiment, the drive voltage +
V _RH, the drive voltage using a _RH -V + V _R, a driving method for correcting the level of -V _R was taken as an example. Sequential addressing method (SAT method) without such correction
It is obvious that the present invention can be applied to

Table 3 shows the relationship between the display data of each frame and the gradation level when the liquid crystal display panel 1 is driven using the conventional frame modulation method (the pulse width of the selection pulse is constant). A data voltage corresponding to display data is applied to the data electrode 3 in each frame.

[0077]

[Table 3]

In Table 3, white circles indicate that the display data is pixel 4
Indicates that the display data is data corresponding to ON display, and the black circle indicates that the display data is data corresponding to OFF display of the pixel 4. In addition, the numbers in parentheses in Table 3 are
The ratio of the pulse width of the selection pulse is shown.

In the example shown in Table 3, there are five gradation levels (gradation level 1 to gradation level 5) depending on the number of ON display pixels 4 and the number of OFF display pixels 4 included in 4 frames. It is expressed.

Table 4 shows the relationship between the display data of each frame and the gradation level when the liquid crystal display panel 1 is driven by using the frame modulation method by changing the pulse width of the selection pulse for each frame period. Show. A data voltage corresponding to display data is applied to the data electrode 3 in each frame.

[0081]

[Table 4]

In Table 4, white circles indicate that display data is pixel 4
Indicates that the display data is data corresponding to ON display, and the black circle indicates that the display data is data corresponding to OFF display of the pixel 4. The numbers in parentheses in Table 4 are
The ratio of the pulse width of the selection pulse is shown.

In the example shown in Table 4, the first frame and the second frame
The ratio of the pulse widths of the selection pulses of the third frame or the fourth frame is set to 1: 0.67.
Thus, nine gradation levels (gray level 1 to gradation level 9) can be expressed by changing the number of ON display pixels 4 and the number of OFF display pixels 4 included in four frames. It will be possible. This is because a plurality of gradation levels can correspond to one combination of the number of ON display pixels 4 and the number of OFF display pixels 4 included in four frames. For example, the number of ON display pixels 4 = 3, OF
The gradation levels 2 and 3 correspond to the number of pixels 4 of F display = 1. The gradation levels 4, 5 and 6 correspond to the number of ON display pixels 4 = 2 and the number of OFF display pixels 4 = 2.
Number of ON display pixel 4 = 1, Number of OFF display pixel 4 =
The gradation levels 7 and 8 correspond to 3.

FIG. 12 shows gradation levels 1 to 1 shown in Table 4.
The relationship between the gradation level 9 and the effective voltage value applied to the liquid crystal display panel 1 is shown. As shown in FIG. 12, the effective voltage value can be changed substantially linearly with respect to the gradation levels 2 to 8.

The characteristics of the effective voltage value are non-linear at gradation levels 1 and 9. This is to match the characteristics of the effective voltage value with the transmittance characteristics of the liquid crystal display panel 1.

When the driving method shown in FIG. 11 is applied to a liquid crystal display panel having a high-speed response, the frame response phenomenon becomes conspicuous and the contrast may deteriorate. This is because the value of the effective voltage applied to the scan electrode 2 largely changes for each frame period.

Such a problem is solved by making the pulse width of the selection pulse applied to the scan electrode 2 variable in a cycle shorter than the frame cycle. For example, the pulse width of the selection pulse may be controlled to be variable for each horizontal period or for each of a plurality of horizontal periods.

FIG. 13 shows a control signal C in the case where the pulse width of the selection pulse is variable for every one horizontal period.
The TL waveform and the waveforms of the selection pulses SEL _{1 to} SEL ₄ are shown. In the example shown in FIG. 13, it is assumed that the number of scan electrodes 2 selected at a time out of the N scan electrodes 2 is two. That is, it is assumed that L = 2. According to the driving method shown in FIG. 13, the difference between the effective voltage values applied to the scan electrodes 2 in each frame becomes small. As a result, the frame response phenomenon is suppressed and the deterioration of contrast is prevented.

Table 5 shows that when the liquid crystal display panel 1 is driven by using the frame modulation method, the pulse width of the selection pulse is made variable every plural horizontal periods as shown in FIG. The relationship between display data and gradation levels is shown.

[0090]

[Table 5]

Table 6 is presented for comparison with Table 5. Table 6 shows a case where the pulse width of the selection pulse is made variable for each frame period as shown in FIG. 11 and the liquid crystal display panel 1 is driven by using the frame modulation method.
The relationship between the display data of each frame and the gradation level is shown.

[0092]

[Table 6]

The waveform of the selection pulse shown in FIG. 13 is obtained by exchanging the second selection pulse of the i-th frame and the first selection pulse of the (i + 1) th frame shown in FIG. Corresponding to such replacement of the selection pulses, the patterns of the display data shown in Table 5 are the display data corresponding to the first selection of the i frame shown in Table 6 and the first selection of the (i + 1) th frame. It is obtained by replacing the display data corresponding to.
Here, i is an arbitrary integer. In addition, Table 5 and Table 6
In, the white circle indicates that the display data corresponds to the ON display of the pixel, and the black circle indicates that the display data corresponds to the OFF display of the pixel. Also,
The numbers in parentheses in Tables 5 and 6 indicate the pulse width ratios of the selection pulses.

[0094]

According to the present invention, the pulse width of the selection pulse applied to the scan electrodes is controlled so that the pulse width of the selection pulse can be changed in every predetermined period. This allows
With a simple circuit configuration, it is possible to realize multi-gradation display without increasing the number of frames required for gradation display. As a result, it becomes possible to suppress image flicker.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a conventional line-sequential scanning driving method.

FIG. 2 A conventional sequential addressing method (SAT
FIG.

FIG. 3 is a diagram for explaining a conventional driving method in which the amplitude of a selection pulse applied to a scan electrode is changed.

FIG. 4 is a diagram showing a configuration example of a drive voltage generation circuit for a conventional drive method.

FIG. 5 is a diagram for explaining a conventional driving method for correcting the waveform of a selection pulse applied to a scan voltage according to the display state of pixels on the same scan electrode.

FIG. 6A is a combination of a conventional driving method that changes the amplitude of a selection pulse and a conventional driving method that corrects the waveform of a selection pulse applied to a scanning voltage according to the display state of pixels on the same scan electrode. It is a figure which shows the structural example of a drive voltage generation circuit in a case.

6B is a diagram showing a waveform of a selection pulse generated based on the drive voltage output from the drive voltage generation circuit of FIG. 6A.

FIG. 7 is a block diagram showing a schematic configuration of the liquid crystal display device 100 according to the first embodiment of the present invention.

8 is a diagram showing a configuration of a drive voltage generation circuit 7 included in the liquid crystal display device 100. FIG.

FIG. 9 is a waveform of a control signal CTL and a selection pulse SE
L _1, is a diagram showing the SEL ₂ waveforms.

FIG. 10 is a liquid crystal display device 200 according to a second embodiment of the present invention.
3 is a block diagram showing a schematic configuration of FIG.

FIG. 11 is a waveform of a control signal CTL and a selection pulse SEL.
Is a diagram showing the waveform of ₁ to SEL _4.

FIG. 12 is a diagram showing characteristics of effective voltage values with respect to gradation levels.

FIG. 13 is a waveform of a control signal CTL and a selection pulse SEL
Is a diagram showing the waveform of ₁ to SEL _4.

[Explanation of symbols]

1 Liquid crystal display panel 2 scanning electrodes 3 data electrodes 4 pixels 5 Scan driver 5a DISPOFF terminal 6 Data driver 7 Drive voltage generation circuit 8 Control signal generation circuit 9 Orthogonal function generator 10 buffer memory 11 arithmetic circuit 15 Scan driver 15a DISPOFF terminal 16 Data driver 100 liquid crystal display 200 LCD

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02F 1/133 575 G02F 1/133 545 G09G 3/36

Claims (8)

(57) [Claims] 1. A scan driver for applying a selection pulse to each of a plurality of scan electrodes, and a data driver for applying a data voltage to each of a plurality of data electrodes, the selection pulse and the data voltage being applied to a pixel. A display device using a frame modulation method for performing gradation display according to the number of ON displays and the number of OFF displays included in a predetermined number of frames applied, wherein the scan driver has a pulse width of the selection pulse. The pulse width of the selection pulse is controlled to be different for each predetermined period, and the pulse width of the selection pulse in a specific period that is one of the predetermined periods and a predetermined period that follows the specific period The display device is characterized in that the pulse width of the selection pulse is controlled so that the ratio to the pulse width of the selection pulse becomes constant. 2. The scan driver controls the ratio of the pulse width of the selection pulse so that the gradation level changes substantially linearly with respect to the effective voltage value applied to the liquid crystal panel. Display device. 3. The display device according to claim 1, wherein the predetermined period is a frame period. 4. The display device according to claim 1, wherein the predetermined period is one or more horizontal periods. 5. The plurality of scan electrodes are divided into a plurality of groups, and a voltage according to a given orthogonal function is applied to the scan electrodes belonging to each of the plurality of groups,
The display device according to claim 1, wherein a voltage proportional to a sum of products of display data and the orthogonal function is applied to each of the plurality of data electrodes. 6. The scan driver has a function of forcibly fixing the potential of the selection pulse to a non-selection level in response to a control signal, and controlling the pulse width of the selection pulse is performed by the function. The display device according to claim 1, which is achieved by utilizing. 7. A scan driver for applying a selection pulse to each of the plurality of scan electrodes, and a data driver for applying a data voltage to each of the plurality of data electrodes,
A driving method using a frame modulation method, in which the selection pulse and the data voltage are applied to a pixel, and gradation display is performed by the number of ON displays and the number of OFF displays included in a predetermined number of frames, The driving method is a step of controlling the pulse width of the selection pulse so that the pulse width of the selection pulse is different for each predetermined period, the selection in a specific period being one of the predetermined periods. A method of driving a display device, comprising the step of controlling the pulse width of the selection pulse so that the ratio of the pulse width of the pulse and the pulse width of the selection pulse in a predetermined period following the specific period is constant. . 8. The step of controlling the pulse width of the selection pulse controls the ratio of the pulse width of the selection pulse so that the gradation level changes substantially linearly with respect to the effective voltage value applied to the liquid crystal panel. The method for driving a display device according to claim 7, further comprising: