JPH0950003A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the generation of ghost and to keep a high quality display when a scanning signal is made to be a positive or negative high voltage and a signal voltage is made to be in the neighborhood of an intermediate voltage between a positive selection voltage and a negative selection voltage in a simple matrix liquid crystal display device. SOLUTION: This device selects a positive or a negative voltage as a scanning voltage for one electrode group of liquid crystal cells 1 having orthogonal electrode groups perpendicular to each other, and is provided with a scanning circuit 2 supplying an approximately intermediate value between the positive selection voltage and the negative selection voltage during an unselective period, a signal circuit 3 selectively applying a signal voltage in the neighborhood of an intermediate value between the positive and the negative selection voltages on the other electrode group of the liquid crystal sells 1 in accordance with the picture signal, and a power source circuit 4 supplying specified voltages to the scanning circuit 2 and the signal circuit 3. The power source circuit 4 supplies a corrected intermediate voltage to the signal voltage. Alternatively, it outputs a different intermediate voltage value in accordance with an alternating signal selecting a positive or negative selection signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device suitable for so-called simple matrix driving, and more particularly to a liquid crystal display device using positive and negative selection voltages as a scanning circuit.

[0002]

2. Description of the Related Art Conventionally, in driving a liquid crystal cell having mutually orthogonal electrode groups, that is, so-called simple matrix driving, a voltage of a high voltage level is sequentially applied to the electrodes of one of the electrode groups to increase the voltage level. Line-sequential scanning is performed in which a voltage corresponding to an image signal is applied to the other electrode group while a voltage is being applied. Further, as no direct current is applied to the liquid crystal, as disclosed in Japanese Patent Publication No. 57-57718. Exchange,
That is, the polarity was reversed.

For example, taking AC driving by giving a polarity inversion signal M for inverting the polarity for each frame, for example, V0 is applied to the scanning electrode at the time of scanning of the first frame, and the other signal electrode is applied. When it is desired to display (selected pixel), V1 is applied, and in the next frame, V1 is applied to the scan electrode and V0 is applied to the signal electrode.

In such a method, a large capacitive load current caused by the liquid crystal flows at the time of switching the polarity inversion signal, and power consumption increases. In addition, the latest liquid crystal display device is 640x
It is about to develop from 480 pixels (VGA) to 1024 RGB × 768 pixels (color XGA) (the number of pixels on the signal side per line is 3072). For that purpose, the data transfer time and other operations are speeded up. I need it. However, for an integrated circuit, high speed and high withstand voltage are conflicting specifications, making it difficult to realize.

[0005]

Therefore, it has been considered to make the scanning signal a large positive and negative voltage and set the signal voltage to a voltage near the intermediate value between the positive selection voltage and the negative selection voltage. A ghost as described in the issue occurred. That is, in a dot matrix display having a large number of pixels, when a vertical or horizontal line segment or a frame having a certain width is displayed like a bar graph, a shadow appears in the non-lighted area on the extension of the line segment or the frame. Some light-colored streaks (sticks) are observed, which significantly deteriorates the display quality.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above points, and in a so-called simple matrix liquid crystal display device, one of the electrode groups of the liquid crystal cell has either a positive or negative selection voltage as a scanning voltage. And a scanning circuit that supplies an intermediate voltage that is approximately the intermediate value between the positive selection voltage and the negative selection voltage during the non-selection period, and the other electrode group of the liquid crystal cell near the intermediate value of the positive and negative selection voltages. And a power supply circuit that supplies at least the selection voltage, the signal voltage, and the intermediate voltage corrected with respect to the signal voltage.

According to the present invention, the scanning circuit selects either positive or negative selection voltage according to the alternating signal and supplies it as a scanning voltage, and the signal circuit selects a signal voltage in the vicinity of an intermediate value of the positive and negative selection voltages. In selectively applying the signal according to the signal, the scanning circuit applies to the electrode group on the scanning side an intermediate voltage having a different value according to the AC signal near the intermediate value between the positive selection voltage and the negative selection voltage in the non-selection period. It is configured to give.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a liquid crystal display device according to an embodiment of the present invention, and FIG. In FIG. 1, reference numeral 1 denotes a liquid crystal cell having mutually orthogonal electrode groups, for example, a field effect liquid crystal such as a super twist nematic liquid crystal display can be used, and the electrode of the liquid crystal cell 1 constitutes a so-called simple matrix, It does not have an active element such as a transistor at the pixel intersection.

Reference numeral 2 denotes a scanning circuit for applying a scanning voltage to one electrode group of the liquid crystal cell 1, which selects one of the positive and negative voltages VH and VL and the intermediate voltage Vm and supplies it to a predetermined electrode. Of these, VH and VL are selection voltages. The intermediate voltage Vm is a voltage that is an approximately intermediate value between the positive selection voltage and the negative selection voltage applied to one of the electrode groups during the non-selection period, and is slightly deviated from the intermediate value VM of the positive and negative selection voltages as described later. Either the voltage Vm0 or Vm1 is selected. In this scanning circuit, either a positive or negative selection voltage is selected according to the alternating signal M and supplied to a predetermined electrode as a scanning voltage.

Reference numeral 3 is a signal circuit for applying a voltage corresponding to an image signal to the other electrode group of the liquid crystal cell 1, and in particular, 2 near the intermediate value between the positive selection voltage VH and the negative selection voltage VL of the scanning circuit 2.
Depending on the image signal D, the signal voltages −Vb and + Vb
The electrode is selectively supplied to the electrode.

A power supply circuit 4 supplies a voltage of a predetermined bias value to the scanning circuit 2 and the signal circuit 3, and at least positive and negative selection voltages VH and VL and signal voltages -Vb and + Vb.
It outputs the intermediate voltage Vm, and more preferably, the scanning circuit 2
It also supplies the drive voltage for the signal circuit 3, the buffer circuit, and other integrated circuits. However, here, the intermediate voltage Vm
Will be described as generating and outputting one of the two intermediate voltages Vm0 or Vm1 corrected with respect to the signal voltage, but the present invention is not limited to this.
It is also possible to internally generate two of 0 and Vm1 and select and output one of them, and output two intermediate voltages from the power supply circuit 4 and select one of them by the scanning circuit 2 or a separately provided selection circuit. It may be configured as follows. Further, the intermediate value VM of the positive and negative selection voltages may be output from the power supply circuit 4, and the intermediate voltages Vm0 and Vm1 may be generated by the scanning circuit 2 to give the intermediate voltage Vm according to the alternating signal.

The power supply circuit 4 includes a voltage generating circuit 41 including a DCDC converter and the like, a resistance dividing circuit 42,
Although the switching circuit 43 and the buffer circuits 44 and 45 are shown in the figure, it is preferable to have a switching circuit that controls the power supply sequence when the power is turned on, a forced discharge circuit 43 when the light is turned off, and the like.

In such a configuration, the voltage generating circuit 41
The signal voltages + Vb and -Vb are obtained by resistance-dividing the selection voltages VH and VL generated in the above and passing through a buffer. The intermediate voltage is originally obtained by mutually positioning the potentials of the selection voltages VH and VL and the signal voltages −Vb and + Vb, but a voltage substantially equal to the intermediate value VM of the positive and negative selection voltages is obtained by the resistor r, and this is converted into an alternating current. By selecting exclusively with the signal M, one of the two intermediate voltages Vm0 and Vm1 is obtained. In this configuration, only one of the resistors r in the resistor division circuit 41 is exclusively short-circuited by the switching circuit 43, and the size of the resistor r is the same as that of the other resistors R.
1 and R2 are smaller than the size of R2.
2 does not lead to output voltage fluctuation.

The magnitudes of the selection voltage and the signal voltage are obtained according to the voltage averaging method, for example, 1/24.
In the case of 0 duty driving, the optimum bias value is 1:16.
5 and the signal voltage is + for a selection voltage of 30 volts.
It is -1.8 volts. However, this voltage value merely represents the intermediate value VM of the positive and negative selection voltages as 0 volt, and the so-called DC level does not need to match the intermediate value VM of the positive and negative selection voltages at all, and in this sense The meanings of positive and negative described in the document are that the two selection voltages have different polarities with respect to the non-selection voltage. Due to such a voltage relationship, the voltage applied to the liquid crystal by scanning and driving with the voltage waveform as shown in FIG. 2a becomes as shown in FIG. In the figure, the scanning voltage is shown to select either positive or negative selection voltage VH or VL at a constant cycle, but the alternating signal M is not limited to one having a cycle of a frame unit. Further, the signal voltage output from the signal circuit 3 has two values + Vb and −V depending on the image signal and the alternating signal M.
Since which of the two b is selected changes, both of the two signal voltages are expressed in the abacus frame shape, and both signal voltages are selected as shown in the figure. The voltage waveform does not change gently.

The fact that the intermediate voltage Vm is deviated from the intermediate value VM of the positive and negative selection voltages and the two intermediate voltages are selectively used in this way is nothing but the experimental result that a ghost does not appear. The reason for this is not clear, but it is speculated as follows.

By increasing the scanning voltage and lowering the signal voltage, the output stage of the integrated circuit of the scanning circuit 2 needs to have a withstand voltage that is approximately double that of the conventional one, but it is a low-speed process corresponding to the number of scanning lines.
Since one of the three potentials is selected in the output stage, a large current does not occur when switching the AC signal, and the waveform collapse that is the basis of crosstalk, which has been often seen in the past, is extremely unlikely to occur. On the other hand, the signal circuit 3 is only 5 in the above example.
It is driven by a low voltage of volt, and high-speed driving can be done without difficulty. Therefore, ghosts should be inherently less likely to occur as compared with the conventional driving in which the voltages of scanning and signals are exchanged.

However, when the liquid crystal cell 1 becomes large or the image signal draws a specific pattern, not a remarkable display deterioration such as a decrease in contrast but a partial display defect such as the above-mentioned ghost was observed. Therefore, assuming that a large change occurs in the current supplied by the pixel or the scanning line and the power supply of the power supply unit cannot respond, a feedback circuit is provided as the buffers 44 and 45 to strengthen the supply of the bias current. It is composed of the operational amplifier circuit. In the present invention in which positive and negative high voltages are used as the scanning voltage, the effect of the non-selection voltage (VM) buffer 45 was small, but the buffer 44 for the signal voltage is provided with a feedback circuit including a differential circuit for current consumption compensation. It was effective to provide it, and it was confirmed that the shade extending to the left and right around the black bar display changed depending on the degree of return.

However, there are cases where crosstalk appears in a bar display having a different place and a different thickness or in a drawing other than the bar display. Therefore, this time, when the liquid crystal cell 1 exhibits a characteristic that is not symmetrical with respect to positive and negative voltages, for example, the liquid crystal cell 1 has a color filter only on one electrode in order to perform color display, and the capacitance with electrodes is different. Moreover, as a result of examining the positive / negative balance between the period of the alternating signal and the applied voltage, assuming the change in the dielectric constant distribution due to the arrangement of the liquid crystal cell molecules, the present invention has been achieved in which the intermediate voltage is slightly shifted. As a result, the ghost that appears on the screen is
It was confirmed that the white ghost changed to a black ghost depending on the amount of deviation from the white ghost.

Further, in the present invention, in the relation between the intermediate voltage Vm and the intermediate value VM of the positive and negative selection voltages, this value is 0.17 V in the case of 450 × 1440 dots,
In the case of 480 x 1860 dots, it was 0.09 volt, which was extremely low, but the expression of ghost was extremely large.
It has been found that it is more desirable that the relationship between the two intermediate voltages Vm0 and Vm1 and the intermediate value VM of the positive and negative selection voltages be symmetrical in relation to the erasing. This means that the resistors r in FIG. 1 have the same value, but it is more preferable that the resistors r can be finely adjusted for each display device.

FIG. 3 is a main part circuit diagram of a power supply circuit therefor. The operational amplifiers 51 and 52 are for generating a signal voltage + -Vb, and one signal generated by resistance division or the like from a predetermined voltage. Voltage + Vb and an intermediate value VM of positive and negative selection voltages (absolute voltage in the case of FIG. 3 is TTL / 2 =
2.5 V) as the center to generate the other signal voltage -Vb. In the other signal voltage generation, the buffer 53 at the input of the operational amplifier 52 is designed so as not to be affected by the voltage fluctuation.

The operational amplifiers 54 and 55 have an intermediate value voltage Vm.
0, Vm1 is generated, and one of the intermediate voltages Vm0 is generated by the variable resistor 56 provided between the signal voltages + -Vb or the correction signal INT supplied based on the correction voltage calculated according to the image signal. Is generated and is made symmetrical with the intermediate value VM of the positive and negative selection voltages to obtain the other intermediate voltage Vm1. Although it is described that the intermediate voltage Vm can take an arbitrary value between the signal voltages by the variable resistor 56, in reality, the display itself cannot be performed if any of the signal voltages is approached. Centered within 10% of signal voltage, more practically 0.1-5
Effective within%. The switch 57 is an analog switch that exclusively selects the intermediate voltages Vm0 and Vm1, and the selection switching signal uses the alternating signal M as in the previous example. With such a configuration, the variable resistor 56 can obtain the intermediate voltage Vm suitable for each symmetrical liquid crystal module in the vicinity of the intermediate value VM of the positive and negative selection voltages.

[0022]

As described above, according to the present invention, since the scanning circuit uses the positive and negative selection voltages as the scanning voltage and the two kinds of signal voltages near the intermediate value of the selection voltage according to the image signal, the image signal is Even if the number is significantly increased, the signal circuit is low in voltage, has a small burden, and can process at high speed. In this way, the scanning circuit and the signal circuit handle different voltage ranges, and the selection voltage is further increased. The large selection voltage is sequentially generated and applied in a substantially fixed sequence or time difference. Therefore, the integrated circuit does not malfunction or run out of control, and the DC voltage does not remain applied to the liquid crystal.

Thus, even when the scanning circuit and the signal circuit handle different voltage ranges, the ghost peculiar to the simple matrix can be suppressed very efficiently, and the display quality can be maintained high.

[Brief description of drawings]

FIG. 1 is a block diagram of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a drive waveform diagram according to an embodiment of the present invention, in which a is an output voltage of a scanning circuit and a signal circuit, b is an alternating signal, and c is a voltage applied to a liquid crystal.

FIG. 3 is a circuit diagram of a main part of a power supply circuit according to an embodiment of the present invention.

[Explanation of symbols]

 1 liquid crystal cell 2 scanning circuit 3 signal circuit 4 power supply circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Koushi Maeda 3 201 Minamiyoshikata, Tottori City, Tottori Prefecture Santoyo Electric Co., Ltd. (72) Norimitsu Kobayashi 3 201 Minamiyoshikata, Tottori City, Tottori Prefecture Sanyo Tottori Electric Co., Ltd. (72) Inventor Shoji Iwasaki 3 201 Minamiyoshikata, Tottori City, Tottori Prefecture Tottori Sanyo Electric Co., Ltd.

Claims (2)

[Claims] 1. A liquid crystal cell having mutually orthogonal electrode groups, and either a positive or negative selection voltage is selected as a scanning voltage for one electrode group of the liquid crystal cell, and a positive selection voltage or a negative selection voltage is selected in a non-selection period. And a scanning circuit for supplying an intermediate voltage which is approximately the intermediate value of the selection voltage, and a signal voltage near the intermediate value between the positive selection voltage and the negative selection voltage of the scanning circuit to the other electrode group of the liquid crystal cell as an image signal. A liquid crystal display device comprising: a signal circuit for selectively applying the signal; and a power supply circuit for supplying the scanning circuit and the signal circuit with at least a selection voltage, a signal voltage, and an intermediate voltage corrected with respect to the signal voltage. 2. A liquid crystal cell having mutually orthogonal electrode groups, and one of the electrode groups of the liquid crystal cell is selected from positive and negative selection voltages according to an alternating signal and is supplied to a predetermined electrode as a scanning voltage. And a signal circuit that selectively applies a signal voltage near the intermediate value between the positive selection voltage and the negative selection voltage to the other electrode group of the liquid crystal cell according to an image signal. In the above liquid crystal display, the scanning circuit provides the one electrode group with an intermediate voltage having a different value in accordance with an alternating signal having a substantially intermediate value between the positive selection voltage and the negative selection voltage in the non-selection period. apparatus.