JP2737209B2 - Driving method of display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of the Invention The present invention uses an active matrix having switching elements such as thin film transistors (hereinafter referred to as TFTs) and pixel electrodes in a matrix to form a liquid crystal or the like having an anisotropic dielectric constant. The present invention relates to a method of driving a display device that displays an image by AC-driving a display material (having properties), and aims at reducing driving power, improving display image quality, and improving driving reliability.

2. Description of the Related Art In recent years, the display quality of an active matrix liquid crystal display device has been greatly improved, and has reached a level comparable to that of a CRT. However, first of all, in terms of image quality, flicker, luminance change in the vertical direction of the screen, that is, luminance gradient, image memory phenomenon, gradation display performance, etc., which remain as if the image of the fixed image were burned immediately after displaying the fixed image, etc. Is still not inferior to CRT. Further, there has not yet been reported any technique for fundamentally solving the problem of the adverse effects of direct current (DC) voltage and crosstalk inevitably generated inside the display device through various parasitic capacitances inside the display device.

The following patents are known as measures against flicker. In other words, Japanese Patent Application Laid-Open Nos.
-256325 and 61-275823. Japanese Patent Application Laid-Open Nos. 60-3698, 60-156095 and 60-156095 disclose the polarity of the signal voltage for each scanning line of the display screen.
No. 61-275822. Japanese Patent Application Laid-Open No. 61-27 proposes a technique for performing inversion for each scanning line while performing field inversion.
There is 5824 publication. However, these methods do not compensate for the DC voltage inevitably generated due to the dielectric anisotropy of a display material such as a liquid crystal and the parasitic capacitance inside the display device described below. (2) Rather than causing flicker to occur, the overall reduction in apparent flicker.

Also, in a special active matrix configuration example, K.Oki
Others: Euro Display '87 P5
5 (1987) is known. In this example, the reference signal (other than the scanning signal) is added to the scanning signal wiring before applying the scanning signal, thereby reducing the amplitude of the image signal and thereby reducing the crosstalk. Other measures against crosstalk include WE Howard and others: IDRC (Inaternational Display Research Conferenc)
e)) '88 P230 (1988) is known. This method compensates for the crosstalk voltage after supplying the image signal. No consideration is given to compensating for a DC voltage due to the dielectric anisotropy of the liquid crystal described below.

An object directly aimed at the invention for improving the luminance gradient / gradation display performance of a display image has not been found within the scope of the present inventors' research.

Next, as a known document intended to compensate for a DC voltage unavoidably generated in a display device due to the dielectric anisotropy of liquid crystal, basically reduce flicker, and improve drive reliability, There are two cases. The first is T. Yanagisawa and others: Japan Display (JAPAN D)
ISPLAY) '86 P192 (1986). In this example, the DC voltage is compensated by changing the amplitude on the positive side and the negative side with respect to the amplitude center voltage (Vc) of the image signal voltage (Vsig). The second precedent is K. Suzuki: Euro Display '87 P107
(1987). In this example, a positive additional signal (Ve) is applied after the scanning signal to compensate.

Third, the scanning signal exerts an influence on the display electrode potential through the parasitic capacitance Cgd between the gate and the drain of the TFT, and generates a DC potential difference between the average potential of the image signal wiring and the average potential of the display electrode. When the liquid crystal is driven by AC, if the potential of each part of the display device is set so that the average DC potential difference between the display electrode and the counter electrode becomes zero, the DC potential difference inevitably appears between the image signal wiring and the counter electrode. This DC potential difference induces serious display defects such as an image memory. However, a method of compensating the DC potential difference to be essentially zero has not been reported yet.

Fourth, although a liquid crystal display device is characterized by a small driving power, a liquid crystal image display device handles analog signals and has a large number of signal output circuits. The power is large (several hundred mW). This is a power consumption that is not suitable for operating as a portable device using a dry battery power supply or the like. Therefore, development of a driving method with lower power consumption is demanded.

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems, that is, to improve the display image / drive reliability and further reduce the display device driving power.

Means for Solving the Problems A pixel electrode arranged in a matrix, a thin film transistor having a drain electrode connected to the pixel electrode, an image signal wiring connected to a source electrode, and a scanning signal wiring connected to a gate electrode And, via the pixel electrode and the capacitor,
A first wiring having a common potential at least in a row unit parallel to the scanning signal wiring, and a counter electrode facing the pixel electrode via a display material and having the same potential spatially over the entire display surface. In a display device that drives a display material by AC, an image signal voltage is transmitted to a pixel electrode during an on-period of the thin film transistor, and a first modulation signal whose polarity is inverted every scanning period is applied to the first wiring, A second modulation signal is also applied to the counter electrode in synchronization with the first modulation signal, and a third modulation signal is synchronized with the first modulation signal to the scanning signal line during an off period of the thin film transistor. The voltage is applied to the display material by changing the potential of the pixel electrode, or a pixel electrode arranged in a matrix and a drain electrode are connected to the pixel electrode. A thin film transistor having a source electrode connected to an image signal line, a gate electrode connected to a scan signal line, and the pixel electrode connected to an adjacent scan line via a capacitor, and a pixel electrode and a display material. And a counter electrode having the same potential over the entire display surface, and transmitting an image signal voltage to a pixel electrode during an ON period of the thin film transistor. A second modulation signal whose polarity is inverted for each scanning period is applied to the counter electrode to the image signal voltage, and a third modulation signal is applied to the scanning signal line during the off period of the thin film transistor by applying the second modulation signal. Synchronous application changes the potential of the pixel electrode to apply a voltage to the display material.

According to the above configuration, the first modulation signal is applied to the first wiring connected to the pixel electrode via the storage capacitor, the second modulation signal is applied to the counter electrode, and the first wiring is connected to the first wiring. By modulating the potential difference between the opposing electrodes, the capacitive coupling potential appearing at the pixel electrode through the associated capacitance can be used effectively. This compensates for the dielectric anisotropy of the liquid crystal and at least a part of the DC component induced by the scanning signal via the gate-drain capacitance, eliminates factors such as flicker and image memory, and provides high quality display. The driving reliability of the display device can be improved. Further, a part of the liquid crystal driving voltage is supplied from the capacitive coupling potential, so that the output amplitude of the image signal driver can be reduced and the driving power can be reduced.

EXAMPLES The theoretical background of the present invention will be described below.

FIG. 1 shows an electric drop circuit of a display element of a TFT active matrix drive LCD. Each display element has an intersection TFT3 of the scanning signal wiring 1 and the image signal wiring 2. The TFT has a gate-drain capacitance Cgd4, a source-drain capacitance Csd5, and a gate-source capacitance Cgs6 as parasitic capacitances. Further, as a capacitor formed intentionally, a liquid crystal capacitor Clc
* 7: There is a storage capacity Cs8.

A scanning signal Vg is applied to the scanning signal wiring 1, an image signal voltage Vsig is applied to the image signal wiring 2, and a second voltage is applied to the counter electrode of the liquid crystal capacitor Clc *.
And the first modulation signal Ve is applied to one electrode of the storage capacitor Cs. The influence of the driving voltage appears on the pixel electrode (point A in FIG. 1) through the above-described parasitic or various types of capacitors that are intentionally provided.

FIG. 2 (a) defined as a related voltage change component
When Vg, Ve, Vt and Vsig shown in FIG. 1 to (d) are respectively applied to the respective points in FIG.
* Is represented by the following general formula (1) (however, TFT
Is turned on, A by conduction from the image signal wiring
Excluding the potential change component of the point).

ΔV * = − (CgdVg + CsVe + CsdVsig + Clc * Vt) / Ct (1) Ct = Cs + Cgd + Csd + Clc * = Cp + Clc * Here, the first term of the equation (1) is that the scanning signal Vg is induced on the pixel electrode through the parasitic capacitance Cgd of the TFT. Potential change.
The second term represents the effect of the first modulation voltage. The third term indicates a potential change induced in the pixel electrode by the image signal voltage through the parasitic capacitance. The fourth term shows the effect of the second modulated signal. 4th
The term Clc * is the capacitance of the liquid crystal that changes under the influence of the dielectric anisotropy as the alignment state of the liquid crystal changes according to the magnitude of the signal voltage (Vsig). Therefore, Clc * and Δ
V * changes depending on the large (Clc (h)) and small (Cuc (l)) of the liquid crystal capacitance. (Cgs is the capacitance between the gate and signal electrodes, but the scanning signal wiring, image signal wiring, and image signal wiring are all driven by a low impedance power supply, and this coupling is ignored because it does not directly affect the display electrode potential.) .

As a condition for eliminating the effect of the capacitance change due to the liquid crystal alignment state, ΔV (l) -ΔV ( h) = 0 (2) Accordingly, CgdVg + CsVe + CsdVsig = CpVt (3) is derived.

The first point to note is that Clc * does not appear in equation (3). That is, if driven under the condition satisfying the expression (3), the influence of the dielectric anisotropy of the liquid crystal disappears, and the DC voltage due to Cuc * does not occur inside the display device. Or,
At the same time, under the driving condition satisfying the expression (3), the DC potential induced between the image signal wiring and the display electrode by the scanning signal Vg through the parasitic capacitance Cgd can be canceled to zero.

 Equation (3) can also be rewritten as:

Ve = {CpVt−CgdVg−CsdVsig} / Cs (4) When (4) is substituted into (1), ΔV * = ΔV (l) = ΔV (h) = Vt (5) Is the meaning of equation (5). That is, the potential ΔV * induced in the pixel electrode is always equal to the amplitude of the second modulation signal Vt. Therefore, the signal voltage applied between the pixel electrode and the counter electrode while the TFT is in the conductive state is maintained without being disturbed by the modulation signal. This is independent of the liquid crystal capacity. In this way, both positive and negative voltages are equally applied to the liquid crystal, and flicker is essentially reduced. (See FIG. 4 described later.) A third point to be noted is that the conditional expression (4) has two voltage parameters Vt and Ve that can be arbitrarily set on the display device side. Therefore, if Ve · Vt is controlled in accordance with the equation (4), the potential fluctuation ΔV * appearing on the pixel electrode can be set to an arbitrary value. On the other hand, Vg is a semi-fixed constant determined by driving conditions, but its effect can be corrected by Ve · Vt. On the other hand, Vsig is the display data itself and changes arbitrarily between the maximum value and the minimum value. Therefore, it is impossible with an actual device to always accurately and accurately satisfy the conditional expression (4) depending on the magnitude of CsdVsig. However,
In order to drive the display device with minimum deviation from the conditional expression (4), CsdVsig may be reduced. Csd is a device constant. To reduce CsdVsig, Vsig may be reduced by maximizing the effect of Vt · Ve. (It is important that there are two voltage parameters that can be arbitrarily set, Ve and Vt.) Further, reducing Vsig reduces the output amplitude of the image signal drive circuit that controls the analog signal. , The power consumption of the circuit is reduced in proportion to the square of the amplitude. In the case of color display, it also leads to power saving for chroma ICs that handle analog signals. On the other hand, Ve · Vt is a digital signal, and the IC is on / off controlled. Therefore, even if the first and second modulation signals Ve and Vt are applied, the overall extermination system constituted by the complementary MOSIC leads to power saving.

The approximate values of the capacitance and voltage parameters used in the device of the embodiment described below are listed.

Cs = 0.68 pF, Clc (h) = 0.226 pF, Clc (l) = 0.130 p
F, Cgd = 0.028 pF, Csd = 0.001 pF, Vg = 25 V, Ve = -3 to +4 V, Vt = ± 3.5 V, Vsig = ± 2.0
V.

Taking the above parameters into account, the third term of equation (4) can be substantially ignored and Ve = {CpVt-CgdVg} / Cs (4a).

Further, when there is no influence of a potential change Vg of the scanning signal described later, the equation (4a) becomes Ve = CpVt / Cs (4b).

FIGS. 2 (e) and 2 (f) show potential changes of pixel electrodes (point A in FIG. 1) when drive signals Vg and Vsig and modulation signals Ve and Vt are input to the respective electrodes of the display element in FIG. Is shown. For example, when Vsig is at Vs (h) as shown by the solid line in FIG. 4D in an odd field, when the scanning signal Vg is input at T = T1, the TFT conducts and A
The potential Va at the point is charged until it becomes equal to Vs (h). Next, when the scanning signal disappears at T = T2, this change in Vg appears as a potential change of ΔVg at point A through Cgd. Further, when Ve · Vt changes in the positive direction at T = T3 after the delay time τd, this effect appears as a positive displacement of the potential Va as shown in the figure. Then, at T = T4, Vsig is changed from Vs (h) to Vs.
When the state changes to (l), a potential change at the point A also appears.
This capacitive coupling component is indicated as ΔV * in the figure.

Thereafter, when a scanning signal is input in an even field, the TFT charges the point A to the low level Vs (l) of Vsig. When the TFT is turned off, the capacitive coupling potential Δ
V * appears. When the TFT is turned on as above, Vsig
Is high, VeVt is low, or vice versa, Vsig is low, VeVt is high, and VeVt fluctuates after TFT is turned off.
On the other hand, the effective applied voltage Veff to the liquid crystal is almost
Vsigpp + 2ΔV *, and both overlap each other. In other words, the output amplitude of the image signal output IC can be reduced by 2ΔV *. (Hereinafter, the case where Ve · Vt and Vsig have a higher-order phase relationship is referred to as opposite phase.) On the other hand, when Vsig has a phase relationship as indicated by the dotted line in FIG. ), The effective applied voltage at point A is approximately 2ΔV * −Vsigpp, and ΔV *
And Vsig cancel each other out.

FIG. 3 shows the relationship between the applied voltage of the liquid crystal and the transmitted light intensity, and shows an example of a voltage range in which the transmitted light is controlled by ΔV * and Vsig. The voltage range where the transmitted light of the liquid crystal changes is Vt
h to Vmax. The required maximum signal amplitude voltage can be reduced to Vsigpp (Vmax-Vth) by setting the applied voltage based on ΔV * to VCT and controlling the amplitude and phase of the signal voltage.

FIG. 2 shows a case where the amplitudes of the first and second modulation signals in the positive and negative directions are the same. In this case, it is not possible to compensate for the effect that the scanning signal voltage induces a DC potential difference between the average potential of the pixel electrode and the average potential of the image signal wiring through coupling with the parasitic capacitance. However, as described above, one of the objects of the present invention has the effect of reducing the image signal amplitude.

FIG. 4 shows a driving method in which the waveform of FIG. 2 is further improved. The fundamental difference is that the amplitude of at least one of the modulation signals in the positive and negative directions is changed. That is, the fourth
(B) At T = T1 '(within the period when the TFT is on or before the TFT is turned off), as shown in the dotted circle in FIG.
e is changed once, and after the scanning by Vg is completed (after the TFT is turned off), at T = T3 ', the first modulation signal whose amplitude in the negative direction is reduced is applied. (According to equation (4),
It is also possible to change the amplitude of one or the other or both of the first and second modulation signals. When the potential change CsdVsig is small as in the TFT design conditions of the present inventors described above, the equation (4a) is ignored ignoring the third term of the equation (4). FIG. 5 shows the relationship between the first modulation signal Ve and the second modulation signal Vt in equations (4a) and (4b). << Note that under this condition, Vt = ΔV * >> Now, as shown in FIG. 3, when 3.4V is required as the effect of the modulation potential due to ΔV *, the amplitude Vt of the second modulation signal becomes positive.・ Set to 3.4V in both negative direction (see equation (5)). Next, when the first modulation signal is set, the amplitude of Ve from negative to positive at T = T3 is obtained from the straight line of equation (4a) in FIG.
4.58V, the amplitude from T to T3 'in the positive to negative direction is 2.50V
Should be set to. In Fig. 4, the voltage difference between the two is 2.08V.
During the ON period of Ve.

The effect of changing the amplitude of the modulation signal in the positive direction and the negative direction becomes apparent when comparing the schematic diagrams (e) and (f) showing the potential Va of the pixel electrode in FIGS. That is, in FIG. 2, the range of the amplitude of the pixel electrode potential is vertically asymmetric with respect to the range of the image signal amplitude. This is T = T2 and T = T
In 2 ′, the fluctuation of Vg in the negative direction through the parasitic capacitance Cgd
This is because the pixel electrode potential Va is constantly displaced in the negative direction. Therefore, the potential of the image signal wiring and the potential of the pixel electrode are on average Δ
Unlike Vg, this potential (ΔVg) exists as a DC component between both electrodes.

On the other hand, in FIG. 4, the fluctuation range of the pixel electrode potential is vertically symmetric with respect to the range of the image signal amplitude. This is T =
By changing the amplitude of the modulation signal in the positive direction at T3 and the amplitude of the modulation signal in the negative direction at T = T3 ', T = T2 and T = T2'
This is because Vg compensated for the potential change of the pixel electrode induced through the parasitic capacitance Cgd. Thus, the average potential of the pixel electrode can be made equal to the average potential of the image signal wiring. That is, the DC component between the two is also zero, which means that the DC component has been compensated. When driven in this manner, the image memory phenomenon becomes extremely small as described later.

FIG. 4 satisfies all of the objects of the present invention described above.

Next, an example of a circuit of a device which is a premise of the driving method of the present invention and a voltage waveform applied to the circuit will be described.

FIG. 6 is a first premise example showing an example of the circuit.
11 is a scanning drive circuit, 12 is a video signal drive circuit, 13 is a first modulation circuit, and 14 is a second modulation circuit. 15a, 15b, ...
15z is a scanning signal wiring, 16a, 16b,..., 16z is an image signal wiring, 17a, 17b,..., 17z is a common electrode of the storage capacitor Cs, 18a, 1
8b,..., 18z are counter electrodes of the liquid crystal. In the first premise example, as described above, the storage capacitor and the counter electrode are formed separately for each scanning signal wiring, and the first and second modulation signals are also applied corresponding to each scanning signal wiring. You. FIG. 7 shows a time chart of the scanning signal and the modulation signal. FIG. 7 shows a scanning signal and a modulation signal for the N-th scanning signal wiring and the (N + 1) -th scanning signal wiring. Modulation signal,
The relationship between the image signal and ΔV * · Vsig is essentially the same as in FIG. That is, the polarities of the video signal and the modulation signal are inverted every frame.

In the first assumption, the output amplitude of the signal voltage is only 2 Vpp
Thus, the entire region from black to white can be driven, and a display with good contrast can be performed. The brightness of the display image can be adjusted by changing the amplitude ΔV * of the modulation signal.

In the above-described first example, the first modulation signal Ve
A second example in which the displacement of (N) and Ve (N + 1) in the negative direction is changed in two stages as shown by the dotted line in FIG. 7 will be described.
That is, the Ve potential was once changed during the on-period of the TFT, and after the TFT was turned off, a modulation signal in the negative direction, the amplitude of which was smaller than the displacement in the positive direction, was applied.

In the second premise, in addition to the effects of the first premise, the flicker is reduced and the drive reliability is further increased.

An embodiment of the present invention will be described based on the above first and second premise.

Embodiment 1 FIG. 8 shows a circuit of an embodiment of the present invention, and FIG. 9 shows a voltage waveform applied to the circuit. In FIG. 8, 21a is the first
A scanning signal line, 21a 'is a storage capacitor common electrode line attached to the first scanning signal line, 21z is a final scanning signal line, and 21z' is a final storage capacitor common electrode line. In the present embodiment, the point that the common electrode of the storage capacitor Cs is formed by using the previous scanning signal wiring is on the circuit configuration, and the point that the modulation signal whose polarity is inverted every vertical scanning period is applied is on the applied voltage waveform. , Respectively. Therefore, the first modulation signal is applied to the preceding scanning signal wiring. As shown in FIG. 9, after the scanning to the (N + 1) th scanning signal line is completed (delay time τd), the first modulation signal applied to the Nth scanning signal line and the Nth scanning signal line The polarity of the second modulation signal Vt (N) applied to the opposing electrode attached to is inverted.

The polarity inversion of the modulation signal may be performed for the N-th and (N + 1) -th scanning signal wirings with respect to the call odd-even field, or may be performed only for the field. Potential change amount Ve of the first modulation signal in the positive direction
(+) And the potential change amount Ve (−) in the negative direction were independently variable. If the absolute values of the potential change amounts Ve (+) and Ve (-) are made equal, the effect equivalent to the first premise is that Ve (-) is relatively reduced as compared with Ve (+), and the equation (4) is used. When the start is matched, the same effect as in the second premise example can be obtained.

That is, in the configuration of the present embodiment, the first and second
The same effect as the premise example can be obtained.

Embodiment 2 FIG. 10 shows another driving circuit of the present invention, and FIG. 11 shows a voltage waveform applied in this embodiment.

In the present embodiment, the point that the first modulation signal is applied to the scanning signal wirings in a redundant manner is the same as in the first embodiment, but the counter electrode is not divided for each corresponding scanning signal wiring, The same potential throughout, and the pixel electrode
Embodiment 2 is different from Embodiment 1, the first and second premise examples in that the electric polarity between the opposing electrodes is changed every scanning period (1H). No.
In FIG. 10, 22 is a scanning drive circuit, 24 is a video signal drive circuit,
26 is a second modulation signal generation circuit. 25a, 25b,… 25z
Denotes an image signal wiring. In FIG. 11, Ch (N), Ch (N)
+1) indicates voltage waveforms applied to the N-th and N + 1-th scanning signal lines, respectively. Vt is the second modulated signal, Vs
ig indicates a video signal voltage waveform. The figure also shows the difference (polarity inversion) in the voltage waveform between the odd field and the even field for AC driving the liquid crystal.

A high waveform Vg in the waveforms Ch (N) and Ch (N + 1) in the figure is a running signal, and a rectangular wave connected before and after the running signal is a first modulation signal Ve.
It is. The amplitude of Ve was controlled with the same voltage and the amplitude constant over all the scanning signal lines. However, only the potentials Vge (+) and Vge (-) shown by thick solid lines in the figure immediately after the scanning signal were independently controlled. Therefore, as the first modulation signal immediately after the end of the scanning signal, the potential change in the positive direction is Vge
(−) − Ve (+), and the potential change in the negative direction is Vge
(+)-Ve (-). Further, the application time Ts of the scanning signal can be variably controlled within less than one scanning period. Thus, after the scanning of the next stage {Ch (N + 1)} is completed, the first and second modulation signals are applied after a delay time τd.

By the way, in the case of the present embodiment, Ve is commonly applied to all the scanning signal wirings in the same phase. Therefore, the second expression in the above-mentioned equation (1)
The term CsVe is (Cs + Cgd) Ve = CpVe. Accordingly, equation (3) becomes as follows.

CgdVg + CpVe + CsdVsig = CpVt When CsdVsig can be ignored, the conditional expression (4) is divided into the following two cases. (A) Immediately after the end of the scanning signal Vg, Ve = {CpVt−CgdVg} / Cp = Vt−VgCgd / Cp (4a ′) (2) In other cases, Ve = CpVt / Cp = Vt (4b ').

Ve after the scanning signal ends as in the first embodiment.
If the (−) and Ve (+) potentials are controlled independently of Ve, both conditions (4a ′) and (4b ′) can be satisfied.

Thus, in the case of this embodiment in which the polarity of the potential of the counter electrode and the potential of the pixel electrode is changed every scanning period, Ve
By adjusting (+) and Ve (-) independently, the effect of the dielectric anisotropy of the liquid crystal can be compensated and the DC potential difference generated between the image signal wiring and the pixel electrode can be reduced to zero (natural result). As a result, the average potential of the image signal applied to the image signal wiring is equal to the average potential of the pixel electrode.) In this way, the main causes of flicker and image memory were eliminated, driving reliability was improved, and driving power was further reduced.
In this case, the gradation controllability is also greatly improved.

Third Embodiment In the second embodiment, the potential Vge immediately after the end of the scanning signal is set.
(−) And Vge (+) were made equal to the potentials Ve (−) and Ve (+), respectively. In this case, driving is not performed in accordance with the conditional expression (4) during one scanning period immediately after the end of the scanning signal, but driving can be performed according to the basic conditional expression (4b) in other display periods.
For example, when the number of scanning lines is 240, the period according to (4b) is 238/240, which can be considered as almost the entire period. By doing so, the number of power supply outputs of the display device can be reduced by two compared to the second embodiment, and the configuration of the scan drive circuit can be simplified.

In this way, a display device with lower power consumption and lower price as compared with Example 2, but with little change in performance was obtained.

Embodiment 4 In the first and second premise examples, the common wiring 17 of the storage capacitor is used.
.. 17z are commonly connected, and common wirings 18a, 18b,... 18z of the counter electrodes are commonly connected. Driving similar to the above-described second embodiment in which the polarity was changed was performed. In this case, it is impossible to make the internal DC potential difference zero,
Good image display can be performed.

In the first to fourth embodiments, the opposing voltage is forcibly applied to the opposing electrode.
The effect of the driving method of the present invention can be obtained similarly.

For example, in the second embodiment, an example in which the potential of the second modulation signal generator 26 in FIG. 10 is floated will be described. That is, the electrode was driven in a state of floating potential without connecting the counter electrode anywhere. In that case, the first modulation signal Ve applied to all the scanning signal lines also appears on the counter electrode through the capacitance inside the display device. Inside the display device, there is an image signal wiring maintained at a potential irrelevant to Ve.
Is generally smaller than Ve, and does not accurately satisfy the conditional expression (4b ′). However, the second modulation signal generation source can be omitted, and the power saving effect is large. In addition, a good image can be displayed, and the object of the present invention can be almost satisfied.

In the second embodiment, the second modulation signal generator 26 is formed by a capacitor. That is, one electrode of the capacitor was connected to the counter electrode, and the other electrode was connected to the first modulation signal generator. However, the capacitance of the capacitor may be sufficiently larger than the capacitance between the counter electrode of the display device and all the image signal wirings, and may not be as large as the capacitance between the counter electrode and all the electrodes on the other substrate. According to this configuration, driving satisfying the conditional expression (4b ′) of Ve = Vt can be performed. Further, there is no need to provide a special second modulation signal generator, and the power saving effect is great.

A counter electrode connected to one electrode of the above-mentioned capacitor was further connected to one electrode of a resistor in parallel with the capacitor, and the other electrode of the resistor was connected to the electrode while being kept at a specific potential. The resistance value R of the resistor may be such that the time constant CR is sufficiently larger than the period (1 / H) of the modulation signal.

As apparent from the above description, the present invention has the following remarkable effects.

First, the output signal voltage of the signal drive circuit of the active matrix display device can be greatly reduced, and thus the power consumption of the drive circuit that handles analog signals can be reduced. Further, when the present invention is used for color display, the output amplitude of the chroma IC was reduced, and the power saving of the circuit was also achieved. Thus, the driving power of the entire display device can be reduced. On the other hand, the amplitude of the output signal voltage is reduced,
In order to increase the density of the display and to increase the frequency of the signal drive circuit, it is easier to manufacture the circuit, and furthermore, it is possible to use a linear region of the signal amplifier. It also has a secondary advantage that it leads to an improvement in display quality.

Second, the display quality was improved. Even in the AC drive for each field as in the second and third embodiments, it was possible to eliminate the cause of the flicker. In addition, in Example 4, in addition to the above, uniformity of display luminance and remarkable improvement of gradation display performance were observed.

Third, the reliability of the display device has been improved. This is because the DC voltage which has conventionally been inevitably generated in the display device is removed due to the anisotropy of the liquid crystal and the capacitive coupling of the scanning signal through Cgd. These DC voltage components caused various display defects. By removing the DC voltage, the image burning phenomenon that occurs immediately after displaying the fixed image has been significantly improved. Further, the driving condition according to the equation (4) is not affected by the dielectric anisotropy of the liquid crystal. This means that when the display device is used in a wide temperature range, even if the dielectric constant itself changes, the effect does not appear and stable driving can be performed.

In the above, the present invention has been described using a liquid crystal display device as an example.
The idea of the present invention can be applied to driving of other flat panel display devices.

According to the present invention, reduction in power consumption, improvement in image quality, and improvement in reliability of a display device can be achieved at the same time, and the industrial effect is great.

[Brief description of the drawings]

FIG. 1 is a diagram showing an element configuration for explaining the principle of the present invention, FIGS. 2 and 4 are diagrams showing voltage waveforms applied to the basic configuration of FIG. 1, and FIG. FIG. 5 is a diagram showing the relationship between the intensity and the applied voltage and the effect of the voltage according to the present invention; FIG. 5 is a diagram showing the relationship between the first and second modulation signal amplitudes and the potential change ΔV * of the pixel electrode due to capacitive coupling; FIG. 7 is a diagram showing a basic configuration of a device similar to the fourth embodiment of the present invention and a basic configuration of a device of an example which is a premise of the present invention, and FIG. 7 is a diagram showing an applied voltage waveform of an example which is a premise of the present invention. FIG. 8, FIG. 8 is a diagram showing a basic configuration of the device of the first embodiment of the present invention, FIG. 9 is a diagram showing an applied voltage waveform of the first embodiment, and FIG. FIG. 6 is a diagram showing a basic configuration of the device according to the third embodiment,
FIG. 11 is a diagram showing an applied voltage waveform of the second and third embodiments. 1 ... Scan signal wiring, 2 ... Image signal wiring, 3 ... TF
T, 4: Gate-drain capacitance, 5: Source-drain capacitance, 6: Gate-source capacitance, 7: Liquid crystal capacitance Clc *, 8: Storage capacitance Cs, Vs (h) · Vs (L)
High / low potential of signal voltage, ΔV *: potential change of pixel electrode due to capacitive coupling, ΔVg: potential change appearing at pixel electrode due to capacitive coupling of scanning signal, Ve: first modulation signal, Vt
… Second modulation signal, Vsig… signal potential, Va… pixel electrode potential, Vth… liquid crystal light transmission start voltage, Vmax… liquid crystal light transmission saturation voltage, 11, 20, 22… scanning Drive circuit, 12
24 video signal drive circuit 13 first modulation signal generator 14 26 second modulation signal generator 15a / 15b
15z ・ 21a ・ 21b ・ ・ ・ 21z ・ ・ ・ ・ ・ ・ Scan signal wiring, 16a ・ 6b ・
・ ・ 16z ・ 25a ・ 25b ... 25z ......... Image signal wiring, 17a ・ 17b
·············· 17z …… Common wiring of storage capacitors, 18a ··· 18b ······· 18z…
Common wiring of counter electrode, Ts: scanning signal duration, τd ...
The delay time until the modulation signal is input after the end of the scanning signal,
Vge (+) · Vge (−)... Potential of the first modulation signal immediately after the end of the scanning signal, Ve (+) · Ve (−): potential of the first modulation signal.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroshi Minamino 1006 Kazuma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-60-39620 (JP, A) JP-A-64- 91185 (JP, A)

Claims (14)

(57) [Claims] A pixel electrode arranged in a matrix, a drain electrode connected to the pixel electrode, an image signal wiring connected to a source electrode, and a thin film transistor connected to a scanning signal wiring to a gate electrode; A first wiring having a common potential at least in a row unit parallel to the scanning signal wiring via the pixel electrode and the capacitor; and a first wiring facing the pixel electrode via a display material, and spatially over the entire display surface. In a display device having an opposite electrode having the same potential and driving a display material by AC, an image signal voltage is transmitted to a pixel electrode during an ON period of the thin film transistor, and the polarity is inverted to the first wiring every scanning period. A first modulation signal is applied, and a second modulation signal is also applied to the counter electrode in synchronization with the first modulation signal. A method of driving a display device, wherein a voltage is applied to the display material by changing a potential of the pixel electrode by applying a third modulation signal in synchronization with the first modulation signal during a period. . 2. The method according to claim 1, wherein the first, second and third modulation signals have the same amplitude. 3. The method according to claim 1, wherein the first, second and third modulation signals have the same polarity. 4. The method according to claim 1, wherein the polarity of the first, second and third modulation signals is inverted at a constant period. 5. The modulation signal according to claim 4, wherein the fixed period is one horizontal period or a plurality of horizontal periods.
4. The method for driving a display device according to claim 1. 6. When the thin film transistor has N channels,
When the amplitude of the first modulation signal is larger in the positive direction than in the other periods only in a specific period after the application of the scanning signal compared to other periods, and the thin film transistor is a P-channel,
2. The display device according to claim 1, wherein the amplitude of the first modulation signal is smaller in amplitude in the positive direction than in other periods only in a specific period after the application of the scanning signal. Drive method. 7. The method according to claim 1, wherein the potential of the third modulation signal is equal to or lower than a gate potential at which the thin film transistor is turned off. 8. A pixel electrode arranged in a matrix, a thin film transistor having a drain electrode connected to the pixel electrode, an image signal wiring connected to a source electrode, and a scanning signal wiring connected to a gate electrode. The pixel electrode is connected to the adjacent scanning wiring via a capacitor, is opposed to the pixel electrode via a display material, and has a counter electrode having the same potential over the entire display surface. In the display device to be driven, an image signal voltage is transmitted to a pixel electrode during an on-period of the thin film transistor, and a second modulation signal whose polarity is inverted for each scanning period is applied to the counter electrode to the image signal voltage, and By applying a third modulation signal to a scanning signal line in synchronization with the second modulation signal during an off period of the thin film transistor, the pixel voltage is reduced. The driving method of a display device and applying a voltage to the display material by changing the potential. 9. The method according to claim 8, wherein the second and third modulation signals have the same amplitude. 10. The method according to claim 8, wherein the second and third modulation signals have the same polarity. 11. The method according to claim 8, wherein the polarity of the second and third modulation signals is inverted at a constant period. 12. The modulation signal according to claim 1, wherein the fixed period is one horizontal period or a plurality of horizontal periods.
12. The method for driving a display device according to item 11. 13. When the thin film transistor has N channels, the amplitude of the third modulation signal is larger in the positive direction than in the other periods only in a specific period after the application of the scanning signal compared to the other periods, and 9. If P is a P-channel, the amplitude of the third modulation signal is smaller in amplitude in the positive direction than in the other period only in a specific period after the application of the scanning signal. 4. The method for driving a display device according to claim 1. 14. The method according to claim 8, wherein the potential of the third modulation signal is equal to or lower than a gate potential at which the thin film transistor is turned off.