JP2590229B2 - Liquid crystal display - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device, and more particularly to a liquid crystal display device suitable for correcting a vertical luminance gradient.

[Conventional technology]

Conventionally, an active matrix type liquid crystal display device in which the power consumption is reduced by halving the dynamic lens of the horizontal scanning circuit (column drive circuit) by converting the counter common electrode into AC is disclosed in Japanese Patent Application Laid-Open No. 57-67993. Have been described.

[Problems to be solved by the invention]

In the above prior art, if there is an additional capacitor formed in parallel with each liquid crystal cell, when the common electrode potential changes, the pixel drive electrode potential also causes the same voltage change, and the voltage across each liquid crystal cell becomes constant. However, when the additional capacitance is not formed, the change in the potential of the common electrode is a voltage divided by the parasitic capacitance such as the gate-source capacitance of each pixel transistor and the capacitance of each liquid crystal cell. There is a problem that a luminance gradient in the vertical direction occurs due to a difference between a potential change and a timing of writing a signal to each pixel. Further, when the additional capacitance is formed, there are problems such as a decrease in the yield of the active matrix substrate and a decrease in the light transmittance of the liquid crystal panel.

It is an object of the present invention to provide a liquid crystal display device in which a vertical luminance gradient does not occur whether or not an additional capacitor is formed in parallel with each liquid crystal cell.

[Means for solving the problem]

In the active matrix type liquid crystal display device, the above object is to provide a binary potential for switching off the row scanning electrode in synchronization with the counter-common electrode potential alternating cycle, and a constant potential for the on potential of the row scanning electrode. Achieved by giving.

[Action]

When the potential of the opposing common electrode changes, the off-potential change of the row scanning electrode that changes at the same timing as the potential of the opposing common electrode,
The potential of each pixel drive electrode is changed, and by the effect of both, the amount of change in the potential of the common electrode and the potential of each pixel drive electrode can be made substantially equal. As a result, even if the potential of the common electrode changes, the voltage across the liquid crystal cell hardly changes.
No luminance gradient in the vertical direction of the screen occurs regardless of whether or not there is an additional capacitor formed in parallel with the liquid crystal cell.

〔Example〕

FIG. 1 shows an embodiment of the liquid crystal display device according to the present invention. 1 is an active matrix type liquid crystal panel, D is a column signal electrode, G is a row scanning electrode, C is a counter common electrode, S is a pixel drive electrode, M is a pixel transistor, C _GS is a gate-source capacitance, and LC is a liquid crystal cell. , Vi (i = 1, 2, 3,...) Are DC bias voltage sources, SC and SG ₁ , SG ₂ are changeover switches. FIG. 2 shows an operation waveform diagram of each part of the embodiment of FIG. 1, and shows a conventional liquid crystal display device in which the OFF potential of the row scanning electrode is fixed (corresponding to the case where V ₂ = V _{3 in} FIG. 1). ) Will be described in comparison with FIG. 3 which is an operation waveform diagram of each part. still,
In each part of the operation waveform diagram, the voltage generated by each DC bias voltage source Vi is represented using the same symbol Vi for the sake of simplicity.

Counter common electrode C is a switch SC, (the V _5> V ₄₎ potential V ₄ and V ₅ for each field is given alternately. The row scanning electrode G is switched to 1 by a switch SGi (i = 1, 2,...).
A potential V _{1 that} is sequentially selected once in the field and turns on the pixel transistor M when selected, and a potential V ₂ that turns off the pixel transistor M in synchronization with the timing of switching the potential applied to the common electrode C when not selected Or V ₃ (V ₂ > V ₃ )
Are given by switching. A signal corresponding to the selected pixel is applied to the column signal electrode D with the polarity inverted for each field in synchronization with the potential change timing of the counter common electrode C. For example, a normally-closed type liquid crystal panel that displays black when no voltage is applied to the liquid crystal cell LC is taken as an example. In the case of white display, as shown in FIG. 2, when the potential of the common electrode C is low (V ₄ ), the potential of the column signal electrode D is high (V ₆ ), and when the potential of the common electrode C is high. , The potential of the column signal electrode D becomes low (V ₇ ). Although not shown, the opposite is true for black display.

The pixel drive electrode S is connected to the row scan electrode G in the first field.
There during a period when the ON potential V _1, changes to the potential V ₆ that is applied to the column signal electrodes D. When the row scanning electrode G is changed to OFF potential V _3, the gate-source capacitance C _GS, the potential of the pixel driving electrode S voltage [Delta] V ₁₃ drops, (V ₆ -ΔV _13), and the the potential first Hold for the rest of the field. At the beginning of the second field, the V ₅ potential of the counter common electrode C from V _4, line when the potential of the scan electrode G changes from V ₃ to V _2, capacity of the gate-source capacitance of each liquid crystal cell LC Due to C _GS , the potential of the pixel drive electrode S becomes the voltage Δ
V ₂₃ and ΔV ₄₅ rise to become (V ₆ −ΔV ₁₃ + ΔV ₂₃ + ΔV ₄₅ ). Subsequently, when the row scanning electrodes G becomes ON potential V _1, the potential of the pixel driving electrode S toward the column signal electrode potential V _7. Again, when the row scanning electrode G is changed to OFF potential V _2, the gate-source capacitance C _GS, the potential of the pixel driving electrode S voltage [Delta] V ₁₂ drops, (V ₇ -ΔV _12), and the this potential Hold for the rest of the second field. The next field, the operation is the same as the first field of the first, at the beginning, to V ₄ potential of the counter common electrode C from V _5, the potential of the row scanning electrode G changes from V ₂ to V _3, respectively Due to the capacitance of the liquid crystal cell LC and the gate-source capacitance C _GS , the potential of the pixel drive electrode S drops by the voltage ΔV ₂₃ and ΔV ₄₅ to (V ₇ −ΔV ₁₂ −ΔV ₂₃ −
ΔV ₄₅ ). Subsequently, when the row scanning electrodes G becomes ON potential V _1, the potential of the pixel driving electrode S toward the column signal electrode potential V _6. Hereinafter, the same operation is repeated, and the signal potential of which the polarity is inverted for each field is applied to the pixel drive electrode S.

The voltage between both terminals related to the display luminance of the liquid crystal cell LC is obtained by subtracting the potential of the common electrode C from the potential of the pixel drive electrode S, and the relationship of (V ₅ −V ₄ = ΔV ₂₃ + ΔV ₄₅ ) Holds, a waveform having no voltage change at the boundary between fields can be obtained as in the operation waveform example indicated by LC in FIG. This is to the voltage waveform applied to the liquid crystal cell LC of the top of the screen, the voltage waveform row drive electrode G is applied to the liquid crystal cell LC 'of the bottom of the screen delayed timing to be ON potential V ₁ is,
As shown in FIG. 2, since the waveform is the same except that the phase can be sent, it means that there is no vertical luminance gradient.

Next, assuming that each capacitor has no voltage dependency,
When the condition _{(V 5 -V 4 = ΔV 23} + ΔV 45) is satisfied,
The relationship between the off-potentials V ₂ and V ₃ of the row scanning electrodes G is determined in advance. If the gate-source capacitance C _GS and the equivalent capacitance C _LC of the liquid crystal cell LC are Therefore, substituting into the above conditions gives V ₂ −V ₃ = V ₅ −V ₄ .

In the conventional liquid crystal display device, the off-potential of the row scanning electrode G is constant, which corresponds to the case where V ₂ = V _{3 in} FIG. 1, and the operation waveform explanatory diagram in FIG. FIG. 4 is an explanatory diagram of operation waveforms. In this case, the voltage between both terminals of the liquid crystal cell LC becomes (V ₅ −V ₄ ) − at the boundary between the fields.
A voltage difference of ΔV ₄₅ is generated. This means that the voltage waveform between the terminals of the liquid crystal cell LC 'at the top of the screen is not only out of phase but also hatched, as is clear from FIG. The effective voltage applied to the liquid crystal decreases because the voltage is reduced by the voltage indicated by. That is, a luminance gradient in the vertical direction occurs.

Therefore, as shown in the embodiment of FIG. 1, the off-potential of the row scanning electrode G is switched at the same timing as that of the common electrode C, so that the off-potential of the row scanning electrode G can be changed as compared with the conventional off-potential fixing method of the row scanning electrode G. In addition, the vertical luminance inclination can be reduced. Unless other parasitic capacitance, voltage dependency, etc. are considered, the off-potential change amplitude (V ₂ −V ₃ ) of the row scan electrode G is substantially equal to the potential change amplitude (V ₅ −V ₄ ) of the common electrode C. By doing so, the vertical luminance gradient is almost eliminated.

As described above, by using the present invention, even if there is no additional capacitance connected in parallel with the liquid crystal cell, the vertical luminance gradient does not occur. A low-cost, bright liquid crystal display device without deterioration in transmittance can be obtained.

FIG. 4 shows a liquid crystal display according to another embodiment of the present invention. In the embodiment shown in FIG. 1, the potential given to the row scanning electrode G is
In the embodiment shown in FIG. 2, the vertical scanning circuit 2 uses a conventional off-potential fixing method.
The off-potential is switched by a common switch using a shift register 3 that sequentially selects and outputs one time in one field and controls a changeover switch of each two contacts to sequentially output a binary potential. The operation itself of the liquid crystal panel 1 is the first
This is the same as the embodiment shown in FIG. According to the embodiment shown in FIG. 2, there is an advantage that a conventional vertical scanning IC is not required for implementing the present invention, and a conventional vertical scanning IC can be used.

FIG. 5 shows another embodiment of the present invention. The difference from the embodiment of FIG. 4 is that the liquid crystal panel 1 is replaced with the pixel driving electrode S
When a point of using a liquid crystal panel 4 provided an additional capacitor C _S during the row scanning electrodes G adjacent to the pixel. Liquid crystal cell LC
Is connected in parallel (between the pixel driving electrode S and the opposing common electrode C). The conventional additional capacitance requires an extra electrode wiring in the active matrix substrate which has the same potential as the opposing common electrode C, so that the wiring is disconnected. This leads to a decrease in yield due to a short circuit and a decrease in aperture ratio. However, if the additional capacitance is formed between the pixel driving electrode S and the row scanning electrode G as shown in the embodiment of FIG. 5, the above problem is reduced. By forming the additional capacitance C _S, the liquid crystal cell LC and the pixel transistor M
Pixel display can be performed stably even if there is a leak in The operation according to the embodiment of FIG. 5 is almost the same as that of the embodiment of FIG. 4, and the detailed description is omitted.

FIG. 6 shows another embodiment of the present invention, and FIG. 7 is an operation waveform diagram of each portion. FIG. 7 is an operation waveform diagram of each portion of a conventional liquid crystal display device in which the OFF potential is fixed (V ₂ = V ₃ ). This will be described below in comparison with FIG. The difference from the embodiment of FIG. 6 is a fourth view of an embodiment, given a counter common electrode C at a constant potential V _8, the source-drain capacitance C of the pixel transistors M
_{This is because DS} is taken into account.

Since the opposite common electrode C is given constant potential V _8, to perform the AC driving which inverts the polarity of the liquid crystal panel for each field, as shown in operation waveform diagram of FIG. 7, the counter common electrode C It is necessary to apply a signal having approximately twice the amplitude to the column signal electrode D as compared with the embodiment of FIG.
The same waveform as in the embodiment of FIG. 4 is applied to the row scanning electrodes G.

The pixel drive electrode S is connected to the row scan electrode G in the first field.
There during a period when the ON potential V _1, changes to the potential V ₉ being applied to the column signal electrodes D. When subsequently the row scanning electrodes G is changed to OFF potential V _3, the gate-source capacitance C _GS,
The potential of the pixel driving electrode S decreases by the voltage ΔV ₁₃ and (V ₉ −Δ
V ₁₃ ), and this potential is maintained for the rest of the first field. At the beginning of the second field, V from the potential V ₃ of the row scanning electrodes G to V ₁₀ the potential of the column signal electrodes from V _{9 2}
When changes to, the drains lease capacitance C _DS and the gate-source capacitance C _GS, and potential voltage [Delta] V ₉₀ drops of the pixel driving electrode S, the voltage [Delta] V ₂₃ rises, (V ₉ - [Delta] V ₂₃
−ΔV ₉₀ + V ₂₃ ). In FIG. 7, assuming that ΔV ₉₀ = ΔV ₂₃ , the potential of the pixel drive electrode S does not change. This condition Therefore, it is given by (V ₉ −V ₁₀ ) × C _DS = (V ₂ −V ₃ ) × C _GS .

Subsequently, when the row scanning electrodes G becomes ON potential V _1, the potential of the pixel driving electrode S toward the column signal electrode potential V _10. When the row scanning electrode G is changed to OFF potential V ₂ again, the gate-source capacitance C _GS, the potential of the pixel driving electrode S voltage [Delta] V ₁₂ drops, (V ₁₀ -ΔV _12), and the the potential first Hold for the rest of the two fields. V The next field operation is the same as the first field in the head, the potential of the column signal electrodes D to V ₉ from V _10, the potential of the row scanning electrode G from the V ₂
When changes to _3, the respective drain-source capacitance C _DS and the gate-source capacitance C _GS, the potential of the pixel driving electrode S voltage [Delta] V ₂₃ descends, [Delta] V ₉₀ rises, (V ₁₀ -ΔV ₁₂ -Δ
V ₂₃ + ΔV ₉₀ ). Here, similarly to the description at the head of the second field, by giving the condition of ΔV ₂₃ = ΔV _90, the potential change of the pixel driving electrode S at the head of each field is eliminated.

Voltage between the two terminals of the liquid crystal cell LC, the potential of the pixel driving electrode S, and minus the potential V ₈ of the opposing common electrode C, a voltage waveform as shown by LC of Figure 7. This means that the voltage waveform applied to the liquid crystal cell LC 'at the lower part of the screen is delayed from the voltage waveform applied to the liquid crystal cell LC at the upper part of the screen. As shown, since the waveforms are the same except that the phase is delayed, it means that there is no vertical luminance gradient.

In the conventional liquid crystal display device, since the off-potential of the row scanning electrode G is constant, it corresponds to the case where V ₂ = V _{3 in} FIG. 6, and the operation waveform explanatory diagram of FIG. FIG. 8 is an explanatory diagram of operation waveforms. In this case, the voltage between the two terminals of the liquid crystal cell LC, at the boundary between fields, resulting in voltage change [Delta] V _90. This means that the voltage waveform between the terminals of the liquid crystal cell LC 'at the bottom of the screen is not only out of phase but also smaller by the voltage indicated by hatching, compared to the voltage wave between the terminals of the liquid crystal cell LC at the top of the screen. As a result, the effective voltage applied to the liquid crystal decreases. That is, a vertical luminance gradient has occurred.

Therefore, as shown in the embodiment of FIG. 6, by switching the off-potential of the row scanning electrode G at the timing of inverting the polarity of the column signal electrode D, the off-potential of the row scanning electrode G is more vertical than the conventional off-potential fixing method of the row scanning electrode G. The luminance gradient can be reduced. Also in the embodiment of FIG. 6, even when adding the row scanning electrodes G capacitance C _S adjacent to the pixel driving electrode S was added in the embodiment of FIG. 5, there is a similar effect is obviously It is.

As described above, by using the present invention, even in the case of the driving method in which the potential of the common electrode is set to a constant range without changing to the alternating current, the effect of compensating the vertical luminance gradient due to the drain-source capacitance and the like can be obtained. is there.

〔The invention's effect〕

According to the present invention, the additional capacitance connected in parallel with the liquid crystal cell is omitted, the signal voltage amplitude applied to the column signal electrode is reduced by half by converting the potential of the common electrode to AC, and the power consumption is reduced even in the vertical direction. A liquid crystal display device having almost no luminance gradient can be obtained. By omitting the additional capacitance connected in parallel with the liquid crystal cell, it is not necessary to wire the common electrode on the active matrix substrate even when an additional capacitance is formed between each pixel driving electrode and the row scanning electrode. By improving the yield of the active matrix substrate and improving the aperture ratio, a liquid crystal display device having a high light transmittance can be obtained.

Further, even in a method in which the potential of the common electrode is fixed,
At the time of polarity inversion for each field, there is an effect that a vertical luminance gradient due to the capacitance between the drain and the source of the pixel transistor can be reduced.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram showing a liquid crystal display device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of operation waveforms of the embodiment of FIG. 1, and FIG.
FIG. 4 is a diagram for explaining a conventional operation waveform in comparison with FIG. 2, and FIGS. 4, 5 and 6 are second, third and fourth embodiments of the present invention, respectively.
7 is an equivalent circuit diagram showing the liquid crystal display device of the embodiment shown in FIG. 7, FIG. 7 is an explanatory diagram of operation waveforms of the embodiment of FIG. 6, and FIG. 8 is an explanatory diagram of conventional operation waveforms in comparison with FIG. 1,4,5 …… Active matrix type liquid crystal panel, 2…
… Vertical scanning circuit, 3… shift register, M… pixel transistor, LC… liquid crystal cell, C _GS … gate-source capacitance, C _s … additional capacitance, _CDS … drain-source capacitance, D: column signal electrode, G: row scanning electrode, S: pixel driving electrode.

Claims (5)

(57) [Claims] A plurality of gate buses (G) are connected to one inner surface of a liquid crystal panel, and a plurality of gates are connected to the gate buses, and a plurality of gate buses are selectively turned on / off according to the potential of the gate buses. A pixel transistor (M) and a pixel drive electrode (S) connected to the source of the pixel transistor are formed, and an alternating voltage (V ₄ ) is applied to a counter common electrode (C) formed on the other inner surface of the liquid crystal panel. , V ₅ ), the display control is performed by applying a different binary potential (V) as the potential applied to the gate of the pixel transistor during the off period in synchronization with the alternating timing of the alternating voltage. ₂ , V ₃ ), and the potential applied to the gate during the ON period is a constant potential (V ₁ ). 2. A plurality of gate buses (G) on one inner surface of the liquid crystal panel, and a plurality of gates connected to the gate buses, the plurality of gates being selectively turned on / off according to the potential of the gate buses. A pixel transistor (M) and a pixel drive electrode (S) connected to the source of the pixel transistor are formed, and an alternating voltage (V ₄ ) is applied to a counter common electrode (C) formed on the other inner surface of the liquid crystal panel. , V ₅ ) for controlling display by applying a voltage (Cs) between the pixel driving electrode and an adjacent gate bus to which the gate of the pixel transistor connected to the pixel driving electrode is not connected. forming a, and a potential at which the pixel transistor is applied to the gate in the oFF period, the synchronization with the alternating timing of the alternating voltage, two different values of the potential (V _2, V ₃₎ applied child switches the The liquid crystal display device according to claim. 3. The liquid crystal display device according to claim 1, wherein different binary potentials (V ₂ , V ₃ ) are switched and applied in synchronization with the alternating timing of the alternating voltage. The liquid crystal display device according to claim 1, wherein a potential difference between the values is substantially equal to an amplitude of an alternating voltage applied to the common electrode. 4. A plurality of gate buses (G) on one inner surface of the liquid crystal panel, and a plurality of gates connected to the gate buses, the plurality of gates being selectively turned on / off according to the potential of the gate buses. A pixel transistor (M) and a pixel drive electrode (S) connected to the source of the pixel transistor are formed, and an alternating voltage (V ₄ ) is applied to a counter common electrode (C) formed on the other inner surface of the liquid crystal panel. , V ₅ ) to perform display control, and as a potential applied to the gate of the pixel transistor during the off period, in synchronism with the alternating transistor of the alternating voltage, different binary potentials (V ₂ , V ₃ ) a liquid crystal display device that switches and applies: an off potential applied to the gate of the pixel transistor during an off period, an on potential applied to the gate of the pixel transistor during an on period, Switch means (SG ₁ , SG ₂ ,...) For supplying to the gate of the pixel transistor
And when the first switch means supplies an off-potential to the gate of the pixel transistor, a different binary potential (V ₂ , V ₃ ) is used as the off-potential in synchronization with the alternating timing of the alternating voltage. And a second switch means (SG ₀ ) enabling switching supply. 5. The liquid crystal display device according to claim 4,
The first switch means is formed in a vertical scanning IC provided for sequentially scanning the gate bus, and the second switch means is provided outside the vertical scanning IC. Liquid crystal display.