JP3338135B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dot matrix type liquid crystal device, and more particularly to a liquid crystal display device driven by a voltage averaging method.

[0002]

2. Description of the Related Art Conventionally, in a liquid crystal display device using a so-called simple matrix type liquid crystal cell, a scanning circuit and a driver circuit are connected to the liquid crystal cell, and a selection voltage and a non-selection voltage are supplied from a power supply circuit. Although the liquid crystal cell is driven by the voltage averaging method, an undesired display called a ghost appears as shown in JP-A-2-245726. The ghost, for example, when a bar graph or a frame is displayed, a display such as a thin shadow appears on the extension of the display pixel (selected pixel), and significantly degrades the display quality.

As a method of solving such a ghost, a bias voltage has been changed or a capacitor has been provided for a long time. For example, the above publication proposes to increase the scanning-side non-selection bias voltage. As another method, a method is known in which a capacitor is connected between a reference bias voltage line and another bias voltage line to absorb a change in each bias voltage. However, since these methods do not always realize sufficient voltage compensation, there is no problem in the case of a liquid crystal display device having a small number of display pixels,
In a liquid crystal display device having a large number of display pixels, it was not possible to suppress the appearance of ghosts. In addition, even when the number of display pixels is small, ghosts are remarkable when the ambient temperature fluctuates.

Here, a description will be given of how a ghost appears remarkably when the number of display pixels increases. Generally, the relationship between the liquid crystal applied voltage and the light transmittance is represented by the characteristics shown in FIG. The horizontal axis in FIG. 16 is the applied voltage applied to the liquid crystal cell,
The vertical axis indicates the light transmittance T. Reference numeral 61 denotes a light transmittance curve of the ON pixel, and reference numeral 62 denotes a light transmittance curve of the OFF pixel. Vop represents a normal operating voltage. If the number of scanning electrodes of the liquid crystal display device is small and the number N of time divisions is small, the ON curve and the OFF curve are sufficiently separated as shown in FIG.
The curves are 61a and 62a, 61b and 62b, 61c and 62
Even if it changes as c, no problem occurs because the working voltage Vop intersects the constant transmittance portion of those curves. However, when the number of scanning electrodes of the liquid crystal display device increases and the number N of time divisions also increases, the interval between the ON curve and the OFF curve decreases as shown in FIG. Therefore, the working voltage is calculated by using the curves 61a, 61b, 61c, 62a, 62b,
As shown in FIG. 18, if there is a voltage change, the change of the point Ton to be turned on and the point Toff to be turned off are △ Ton, △ Toff, and the contrast (Ton / Toff Ratio) becomes smaller and ghosts are more likely to appear.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device of good display quality with little ghosting irrespective of the number of display pixels and the change in ambient temperature.

[0006]

According to one aspect of the present invention, a liquid crystal display device is provided with the following. A liquid crystal cell; a first electrode group including a plurality of linear electrodes disposed on one surface of the liquid crystal cell; a first electrode group disposed on the other surface of the liquid crystal cell and intersecting the electrodes of the first electrode group with the liquid crystal cell interposed therebetween. A second electrode group consisting of a plurality of linear electrodes; a scanning circuit connected to the first electrode group; a driver circuit connected to the second electrode group; a selection voltage for driving the liquid crystal cell by a voltage averaging method. And a power supply circuit for providing a non-selection voltage to the scanning circuit and the driver circuit; a voltage compensation circuit provided in the power supply circuit, for compensating an output voltage of the power supply circuit according to the magnitude of an output current of the power supply circuit; Made of things. An operational amplifier having a first input terminal supplied with a predetermined voltage and a second input terminal connected to an output terminal thereof via a resistor; an impedance circuit connected between the output terminal of the operational amplifier and an output terminal of the power supply circuit; Feedback means for feeding back both the AC component and the DC component of the output of the impedance circuit to the second input terminal of the operational amplifier.

[0007]

The bias power is stably supplied by such a feedback means, and the waveform collapse causing ghost is significantly reduced.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 shows the layout of the overall circuit configuration of the liquid crystal display device of the present invention. In FIG. 1, reference numeral 1 denotes a plurality of electrodes intersecting each other across a liquid crystal layer, that is, a scanning electrode group 5 and a signal electrode group 6.
A liquid crystal cell having, for example, 180 to 260
It consists of a super-twisted field-effect liquid crystal cell that is twisted to a degree. Reference numeral 2 denotes a scanning circuit connected to a scanning electrode group 5, which is one group of electrodes of the liquid crystal cell 1. Reference numeral 3 denotes a driver circuit connected to a signal electrode group 6 which is the other group of electrodes of the liquid crystal cell 1. A clock signal, a timing signal, a data signal, and the like are supplied to both of these circuits, and the liquid crystal cells are driven based on a voltage averaging method. FIG. 2 shows the scanning electrode group 5 and the signal electrode group 6. Terminals X ₁ , X ₂ ,
X _3, and a plurality of scanning electrodes a scanning signal is supplied via a · · · X _N, the terminal _{Y 1, Y 2, Y 3} , a plurality of signal electrodes is given display signal via · · · Y _N Run in the horizontal and vertical directions, respectively, and cross each other across a liquid crystal layer (not shown). Each intersection corresponds to a pixel.

Returning to FIG. 1, reference numeral 4 denotes a control circuit for providing a control signal to the scanning circuit 2 and the driver circuit 3. For example, when a television video signal is displayed on a liquid crystal display device, a control signal based on the video signal is used. Is output. Reference numeral 7 denotes a power supply circuit that supplies a selection voltage and a non-selection voltage obtained by resistance division to the scanning circuit 2 and the driver circuit 3. The power supply circuit 7 is provided with a resistor voltage dividing circuit 10 including resistors R ₁₁ , R ₁₂ , R ₁₃ , R ₁₄ , R ₁₅ for dividing a DC voltage applied between the terminals 8 and 9 and a transistor TR. Partial pressure point a,
From b, c, d, e, f, the respective voltages V _H , V _SH , V _DH ,
V _DL , V _SL , and V _L occur. V _H is common high selection voltage to the scanning circuit 2 and the driver circuit 3, V _SH is high non-selection voltage of the scanning circuit, V _DH high unselect voltage for the driver circuit, V _DL
Is a low non-selection voltage for the driver circuit, V _SL is a low non-selection voltage for the scanning circuit, and _VL is a low selection voltage common to the scanning circuit and the driver circuit. 11 is a high non-selection voltage V for the scanning circuit
This is a voltage compensation circuit inserted in the line of _SH and the low non-selection voltage _VSL . This voltage compensation circuit 11 performs voltage compensation according to the magnitude of the output current. It may be provided a similar voltage compensation circuit 11 to a high non-selection voltage V _DH and low non-selection voltage V _SL of the line of the driver circuit as necessary. Such a voltage compensating circuit 11 is introduced by presuming that the cause of the ghost is waveform distortion or voltage drop. In other words, a ghost should reduce the voltage applied to the liquid crystal by the non-selection voltage applied to one electrode when the selection voltage is applied to one electrode, but the application timing of both electrodes is due to waveform distortion. This is considered to be caused by the fact that it is not sufficient to reduce the liquid crystal voltage due to the shift to the non-selection voltage or the lower non-selection voltage. Therefore, based on this idea, it is only necessary to respond quickly to voltage fluctuations and perform voltage compensation for voltage drops. The present invention focuses on increasing the equivalent wiring resistance of the liquid crystal cell and each circuit with the increase in the screen size and capacity of the liquid crystal display device and the high-speed driving by high time-division driving. Is monitored to perform voltage compensation.

FIGS. 3 to 12 show examples of the configuration of the voltage compensating circuit 11. FIG.
It is shown in 3, an operational amplifier 12 has a non-inverting input terminal supplied with a non-selection voltage _VA from the resistance voltage dividing circuit 10 (FIG. 1). Here, the non-selection voltage _VA is assumed to represent any one of the above-described non-selection voltages V _SH , V _DH , V _DL , and V _SL . The inverting input terminal of the operational amplifier 12 is connected to its output terminal via a resistor. Reference numeral 13 denotes an operational amplifier functioning as a buffer (hereinafter, referred to as a "buffer"). The output of the operational amplifier 12 is applied to a non-inverting input terminal, and the inverting input terminal and the output terminal are directly connected. The amplification degree of the buffer 13 is set to 1. A resistor R2 is inserted between the output terminal of the buffer 13 and the output terminal 14 of the power supply circuit 7. The output side of the resistor R2 is connected to the inverting terminal of the operational amplifier 12 via the resistor R3. This allows output terminal 1
4 is fed back to the inverting terminal of the operational amplifier 12 via the resistor R3. The resistor R2 forms an impedance circuit that monitors the output current.

In FIG. 3, R _D is the equivalent resistance of the scanning circuit 2 or the driver circuit 3, and R _E is the equivalent resistance of the electrodes of the liquid crystal cell 1. When the circuit of FIG. 3 is used for V _DH or V _DL , R _D is an equivalent resistance of the driver circuit 3, for example, an internal resistance and a wiring resistance of the driver circuit 3, and is approximately 0.5 to 2 KΩ. _RE is the equivalent resistance of the electrode of the liquid crystal cell 1. For example, when an anisotropic conductive film is used for connection to the driver circuit 3 and the signal electrode group 6 is indium-based ITO having a width of 100 μm, it depends on the position of the pixel. But, generally 1-2
0 KΩ. LC indicates the liquid crystal in the pixel, and the counter electrode and the scanning circuit 2 are omitted.

In FIG. 3, the voltage _VA is applied to the output terminal 14 via the buffer 13 only, as in the prior art.
Is supplied to the pixel LC.
When the current is supplied to the pixel, the voltage decreases as shown by the dotted line B, and the voltage applied to the pixel decreases significantly. The magnitude of this voltage drop is about 60 to 180 mV. This means that a ghost occurs for the reason described above. However, the voltage compensation circuit shown in FIG. 3 has the voltage characteristics as shown by the solid line A, and the voltage applied to the pixel can be sufficiently suppressed from decreasing. In FIG. 3, a vertical dotted line 15 is written to make the voltage at each point of the circuit correspond to the characteristic A.

FIG. 4 and FIG. 5 are modifications of FIG. FIG. 4 is obtained by removing the buffer 13 from FIG. 3, and FIG. 5 is obtained by removing the resistor R2 from FIG. When the buffer 13 has an amplification degree of 1, the buffer 13 is not always necessary, and therefore the buffer 13 may be deleted as shown in FIG. Buffer 13
Has a resistor on the output side, the buffer 13 has the role of the resistor R2, so that R2 may be eliminated as shown in FIG. In FIG. 3, the buffer 13 may have a resistor on the output side. In that case, the resistor and the resistor R2 function as an output monitoring impedance circuit. 3 to 5
The output voltage (the voltage of the output terminal 14) in the voltage compensation circuit of (1) is constant as shown in FIG. 13A. At this time, the output voltage of the scanning circuit 2 or the driver circuit 3 receiving the voltage from the voltage compensating circuit 11 has the solid line waveform of FIG.
The voltage applied to C has a solid waveform in FIG. 13C. FIG.
B, in FIG. 13C, the dotted waveform shows an ideal voltage waveform.

The voltage compensating circuits shown in FIGS. 6, 7 and 8 are designed to feed back the AC component of the voltage at the output terminal 14 to the operational amplifier 12.
And a capacitor C between the inverting input terminal of the operational amplifier 12
1 are connected. Other configurations are the same as those in FIGS. 3, 4, and 5, respectively. In each of the embodiments shown in FIGS. 6 to 8, the voltage of the output terminal 14 is as shown in FIG.
Alternatively, the output voltage of the driver circuit 3 has a voltage waveform indicated by a solid line in FIG. 14B. The voltage waveform applied to the pixel LC at that time is as shown by the solid line in FIG. 14C.

In the embodiments of FIGS. 9, 10 and 11, both the DC component and the AC component of the voltage at the output terminal 14 are applied to the operational amplifier 1.
The resistor R3 and the capacitor C1 are connected between the output terminal 14 and the inverting input terminal of the operational amplifier 12 for that purpose.
The capacitor C1 feeds back the AC component, and the resistor R3 feeds back the DC component. Other parts are the same as those in FIGS. 3, 4, and 5, respectively.

In the embodiment shown in FIG. 12, a DC component and an AC component are fed back similarly to FIGS. 9 to 11, but a resistor R4 is inserted in series in an AC feedback path having a capacitor C1. I have. A capacitor C2 connected in parallel with the resistor R1 is connected between the output terminal and the inverting input terminal of the operational amplifier 12.
Is inserted. Other configurations are the same as those in FIG. The circuit of FIG. 12 relates to the buffer 13 and the resistor R2, and FIG.
It may be changed as shown in FIG. 10 to 1
The output voltage of the voltage compensating circuit No. 2 is as shown in FIG. 15A, and the DC voltage rises with respect to the level of the input voltage _VA . In the generation period of the pulse voltage from the scanning circuit 2 or the driver circuit 3, the overshoot OP occurs at the rising portion and the undershoot DP occurs at the falling portion in the case of FIGS. Is the same as FIG. 1 shows an output voltage waveform of the driver circuit, and FIG.
The solid line waveform of 5C indicates the voltage applied to the pixel LC.

The voltage compensating circuit shown in FIG. 3 is incorporated in the line of the data circuit non-selection voltages V _DH and V _DL of the power supply circuit 7.
100 × on a 400 × 560 dot matrix display
When drawing straight lines of 10 and 10 x 200, no ghost appears at room temperature on any straight line extension of the power supply circuit, and when using this liquid crystal display device in a word processor for one week, the ghost is observed However, the ghost could be eliminated only by adjusting the display brightness. Further, when the voltage compensating circuit of FIG. 3 is used for a non-selection voltage on the scanning side and a non-selection voltage on the data side in a liquid crystal cell having an effective display area equivalent to the B4 size having a non-linear element for each pixel,
Ghost did not occur even in 1/350 duty driving.

In the voltage compensation circuit shown in FIG.
= 1KΩ, R3 = 330-830Ω, C1 = 10000
PF and this circuit is V_SHAnd V_SLV line_DH
And V _DLThe railroad tracks consist of simple voltage
1/400 duty, 1024
Display drive for liquid crystal cell with 2,000 pixels
Of course, a black frame is displayed on a white background where ghosts are most likely to occur.
Or a white frame on a black background, or a bar with a different width
Ghosts are observed at all times when rough display is performed.
Change the contrast (display density) in that state.
The ghost was inconspicuous even after the conversion.

It is necessary to drive the liquid crystal cell by the voltage averaging method.
Required voltage V_H, V_L, V_DH, V_DL, V _SH, V_SLOut of
The above voltage compensation circuit may be provided for the deviation,
A compensation circuit may be provided. The standard of the driving voltage of the liquid crystal cell is
Non-selection voltage V on scanning circuit side_SH, V_SLAre these voltages
Is the time ratio of (N-1) / N, where N is the number of time divisions.
As N becomes large because it is used, it is used almost all the time.
And only scanning time V_H, V_LUse Therefore at least
Also V_SH, V_SLIt is desirable to provide a voltage correction circuit for
Good.

[0020]

As described above, according to the present invention, since the bias voltage can be compensated efficiently, it is possible to perform a display with good display quality without ghost, which is the biggest drawback of the simple matrix.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of a liquid crystal display device of the present invention.

FIG. 2 is a plan view showing a scanning electrode and a signal electrode of a liquid crystal cell.

FIG. 3 is a diagram showing a voltage compensation circuit and a load-side portion thereof according to the first embodiment of the present invention.

FIG. 4 is a circuit diagram of a voltage compensation circuit according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram of a voltage compensation circuit according to a third embodiment of the present invention.

FIG. 6 is a circuit diagram of a voltage compensation circuit according to a fourth embodiment of the present invention.

FIG. 7 is a circuit diagram of a voltage compensation circuit according to a fifth embodiment of the present invention.

FIG. 8 is a circuit diagram of a voltage compensation circuit according to a sixth embodiment of the present invention.

FIG. 9 is a circuit diagram of a voltage compensation circuit according to a seventh embodiment of the present invention.

FIG. 10 is a circuit diagram of a voltage compensation circuit according to an eighth embodiment of the present invention.

FIG. 11 is a circuit diagram of a voltage compensation circuit according to a ninth embodiment of the present invention.

FIG. 12 is a circuit diagram of a voltage compensation circuit according to a tenth embodiment of the present invention.

FIG. 13 is a diagram illustrating operating voltage waveforms of the first to third embodiments.

FIG. 14 is a diagram illustrating operating voltage waveforms of the fourth to sixth embodiments.

FIG. 15 is a diagram illustrating operating voltage waveforms of the seventh to tenth embodiments.

FIG. 16 is a characteristic diagram of voltage versus light transmittance of a liquid crystal cell.

FIG. 17 is a characteristic diagram of voltage versus light transmittance of a liquid crystal cell when the number N of time divisions is small.

FIG. 18 is a characteristic diagram of voltage versus light transmittance of a liquid crystal cell when the number N of time divisions is large.

[Explanation of symbols]

 Reference Signs List 1 liquid crystal cell 2 scanning circuit 3 driver circuit 7 power supply circuit

Continuation of the front page (72) Inventor Shoji Iwasaki 3-201 Minamiyoshikata, Tottori City, Tottori Prefecture Tottori Sanyo Electric Co., Ltd. (56) References JP-A-5-19232 (JP, A) JP-A-61- 184004 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G09G 3/36 G02F 1/133 520 G02F 1/133 545

Claims (3)

(57) [Claims] 1. A liquid crystal cell, a first electrode group consisting of a plurality of linear electrodes disposed on one surface of the liquid crystal cell, and a first electrode disposed on the other surface of the liquid crystal cell with the liquid crystal cell interposed therebetween. A second electrode group consisting of a plurality of linear electrodes intersecting the group electrodes; a scanning circuit connected to the first electrode group; a driver circuit connected to the second electrode group; A power supply circuit for applying a selection voltage and a non-selection voltage to the scanning circuit and the driver circuit so as to be driven by the driving method, and a voltage provided in the power supply circuit for compensating the output voltage of the power supply circuit according to the magnitude of the output current of the power supply circuit. An operational amplifier having a first input terminal to which a predetermined voltage is applied and a second input terminal connected to an output terminal thereof via a first resistor;
A liquid crystal display device comprising: an impedance circuit connected between an output terminal of an operational amplifier and an output terminal of a power supply circuit; and a second resistor that feeds back the output of the impedance circuit to a second input terminal of the operational amplifier. 2. A liquid crystal cell, a first electrode group consisting of a plurality of linear electrodes disposed on one surface of the liquid crystal cell, and a first electrode disposed on the other surface of the liquid crystal cell with the liquid crystal cell interposed therebetween. A second electrode group consisting of a plurality of linear electrodes intersecting the group electrodes; a scanning circuit connected to the first electrode group; a driver circuit connected to the second electrode group; A power supply circuit for applying a selection voltage and a non-selection voltage to the scanning circuit and the driver circuit so as to be driven by the driving method, and a voltage provided in the power supply circuit for compensating the output voltage of the power supply circuit according to the magnitude of the output current of the power supply circuit. A compensation circuit, wherein the voltage compensation circuit has a first input terminal supplied with a predetermined voltage, a second input terminal connected to an output terminal thereof via a resistor, and an operational amplifier. Connected between the output terminal of the amplifier and the output terminal of the power supply circuit A liquid crystal display device comprising: an impedance circuit; and feedback means for feeding back both an AC component and a DC component of the output of the impedance circuit to a second input terminal of the operational amplifier. 3. A liquid crystal cell, a first electrode group including a plurality of linear electrodes disposed on one surface of the liquid crystal cell, and a first electrode disposed on the other surface of the liquid crystal cell with the liquid crystal cell interposed therebetween. A second electrode group consisting of a plurality of linear electrodes intersecting the group electrodes; a scanning circuit connected to the first electrode group; a driver circuit connected to the second electrode group; And a power supply circuit for applying a selection voltage and a non-selection voltage to the scanning circuit and the driver circuit so as to be driven by the driving circuit, and compensating for the output voltage of the power supply circuit according to the magnitude of the output current of the power supply circuit. A liquid crystal display device having a voltage compensating circuit, wherein the voltage compensating circuit has a first input terminal supplied with a predetermined voltage, and a second input terminal connected to an output terminal of the operational amplifier via a resistor; Connected between the output terminal of the operational amplifier and the output terminal of the power supply circuit And the AC component of the output of the impedance circuit to the second
A liquid crystal display device comprising: a capacitor that feeds back to an input terminal.