JPH08262404A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: To high speedily drive a simple matrix of a liquid crystal performing a high quality display with the large number of pixels at a low voltage and with a reduced load. CONSTITUTION: This device is provided with a liquid crystal cell 1 having electrode groups orthogonally intersecting with each other, a scan circuit 2 imparting a scan voltage, a signal circuit 3 imparting the voltage according to an image signal and a power source circuit 4 supplying a prescribed bias value voltage. The selection voltage of the scan circuit 2 is made the positive/ negative selection voltage, and the signal circuit 3 uses two kinds of signal voltages in the vicinity of the intermediate value of the selection voltage. The power source circuit 4 obtains the selection voltage and the source voltage of the scan circuit 2 from different power source lines, and supplies the voltage to the scan circuit 2 even after the selection voltage is short-circuited. Thus, the scan circuit 2 deals with the large selection voltage in a nearly normal operation state.

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. The polarity was reversed.

For example, taking AC driving by giving an AC signal M whose polarity is inverted every frame, as an example,
V0 is applied to the scan electrodes at the time of scanning of the first frame,
When displaying on the other signal electrode (selected pixel), V1
And V1 on the scan electrode in the next frame.
And V0 is applied to the signal electrode.

[0004]

In such a method, a large capacitance positive / negative current due to the liquid crystal flows when the alternating signal is switched, and the power consumption increases. In addition, recent liquid crystal display devices have 640 × 480 pixels (VGA) to 1024R.
The number of pixels is increasing to GB × 768 pixels (color XGA) (the number of pixels on the signal side is 3072), which requires a high-speed and high-voltage integrated circuit because the data transfer time and other operations are speeded up. However, for an integrated circuit, high speed and high breakdown voltage are contradictory specifications, which makes it difficult to realize.

Therefore, the scanning signal is set to a large positive and negative voltage,
The signal voltage is considered to be a voltage in the vicinity of the intermediate value between the positive selection voltage and the negative selection voltage. However, since the voltage levels are significantly different, the scanning circuit may become inoperative or damaged.

[0006]

The present invention has been made in consideration of the above points, and in a so-called simple matrix liquid crystal display device, either a positive or negative selection voltage is selected and a scanning voltage is applied to a predetermined electrode. Supply a scanning circuit, a signal circuit that selectively supplies a signal voltage in the vicinity of the intermediate value between the positive selection voltage and the negative selection voltage according to the image signal, and supply a voltage of a predetermined value to the scanning circuit and the signal circuit. And a power supply circuit for supplying a selection voltage and a driving voltage for the scanning circuit from different power supply lines.

Further, according to the present invention, as a power supply circuit, a short circuit of a selection voltage is provided, and a voltage is supplied to the scanning circuit even after the short circuit of the selection voltage.

[0008]

According to the present invention, as described above, the scanning circuit uses the selection voltage of large positive and negative values as the scanning voltage, and uses the signal voltage of the small value in the vicinity of the intermediate value of the selection voltage according to the image signal, and selects the large selection voltage. Since the voltage and the scanning circuit drive voltage are obtained from different power supply lines, the scanning circuit is in a substantially normal operating state when a large selection voltage is supplied to the scanning circuit, and the scanning circuit operates even when the selection voltage disappears. You can maintain a working state.

[0009]

1 is a block diagram of a liquid crystal display device according to an embodiment of the present invention, in which 1 is a liquid crystal cell having mutually orthogonal electrode groups, and for example, a field effect liquid crystal such as a super twist nematic liquid crystal display can be used. These liquid crystal cells 1
The electrodes of (1) form a so-called simple matrix and do not have active elements at pixel intersections.

Reference numeral 2 denotes a scanning circuit for applying a scanning voltage to one electrode group of the liquid crystal cell 1, which has positive and negative voltages -VL and + VH.
And intermediate voltage Vm are selected and supplied to a predetermined electrode, of which -VL and + VH are selection voltages. Reference numeral 3 is a signal circuit for applying a voltage according to an image signal to the other electrode group of the liquid crystal cell 1, and in particular, it is of two types in the vicinity of an intermediate value between the positive selection voltage + VH and the negative selection voltage -VL of the scanning circuit 2. The signal voltages -Vb and + Vb are selectively supplied to the electrodes according to the image signal.

Reference numeral 4 is a power supply circuit for supplying a voltage having a predetermined bias value to the scanning circuit 2 and the signal circuit 3, and the positive and negative selection voltages -VL and + VH and the signal voltage -Vb and + Vb and the intermediate voltage V.
m, the scanning circuit 2, the signal circuit 3, the signal transfer circuit 5, the drive voltages Vic and Vis of the buffer 44, and the like are supplied.
The power supply circuit 4 includes a voltage generation circuit 41, a switching circuit (SW circuit), a forced discharge circuit 42, and a resistance division circuit 4.
3 and the buffer 44, the select voltage and the drive voltage of the scanning circuit are provided from different power supply lines when generating the voltage, and the select voltage has a short circuit when the voltage is cut off. A drive voltage is supplied to the scanning circuit.

Reference numeral 5 denotes a signal transmission / reception circuit, which can directly transmit signals corresponding to various timing signals and image signals supplied to the signal circuit 3 through a buffer, but to the scanning circuit 2 a drive transmission level ( Since Vic to VL is different from the power supply level (VDD to VEE), it is necessary to perform level shift or add an initialization signal to give it, so this is a circuit for performing these processes.

Such a structure will be described in more detail. First, the voltage relationship in the present invention is shown in the central portion of FIG. FIG. 2 shows a case where each voltage value is generated based on the supply voltage VEE-VDD of 0-5 volts, and the selection voltage + V
H and -VL are generated from the supply voltage VEE (power line of low level) by the voltage generation circuit 41 including a DC / DC converter, and the signal voltage ± Vb and the intermediate voltage Vm are the selection voltage + V.
The buffer 44 is generated by the resistance division circuit 43 from H and -VL.
It is supplied by way of. On the other hand, the drive voltage Vic of the scanning circuit 2 is generated by the voltage generation circuit 41 from the supply voltage VDD (high level power supply line). As described above, even when only one voltage of 0-5 VEE-VDD is applied, the potential difference is used to select voltage -V.
Since L and the driving voltage Vic are generated respectively, a large selection voltage is applied to the scanning circuit 2, but a driving voltage having a constant potential difference is supplied earlier than that, and when the selection voltage is applied, integration is performed. It does not mean that the circuit does not work. As a result, the scanning circuit 2 is damaged or locked,
Alternatively, there is no inconvenience that a DC voltage is applied to the liquid crystal cell. The voltage difference (Vi) between the selection voltage −VL and the scanning circuit drive voltage may be applied to the power supply circuit 4, if necessary.
The switch circuit may be configured to detect that c) has become a constant voltage (for example, 3 V or more) and raise another selection voltage + VH. This is designed so that various signals and liquid crystal drive voltages (bias voltages such as a selection voltage) are applied after the scanning circuit 2 enters the operating voltage region where it normally operates.

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, the signal voltage for the supply voltage 0 volt level is 4.3 volt and 0.7 volt for the selected voltage 30 volt. Due to this driving, the output stage of the integrated circuit of the scanning circuit 2 requires a withstand voltage that is approximately double that of the conventional one, but this is low-speed processing according to the number of scanning lines, and one of three potentials is selected at the output stage. As a result, a large current does not occur when switching the alternating signal, and the waveform collapse that is the basis of crosstalk, which was often seen in the past, is extremely unlikely to occur. On the other hand, the signal circuit 3 is driven by a low voltage of only 5 V in the above-mentioned example, which is suitable for high-speed driving, and the area of the integrated circuit can be reduced.

When the power supply is cut off, the forced discharge circuit 42 detects that the supply voltage VDD has dropped below a certain level and short-circuits the selected voltages + VH and -VL via a short-circuit resistor, resulting in an unbalanced voltage. The liquid crystal is prevented from deteriorating due to the residual. In this case, the driving voltage to the integrated circuit also drops. However, in the present invention, since the driving voltage Vic of the scanning circuit 2 is obtained from the higher supply voltage VDD, even if the voltage generating circuit 41 does not work, the magnitude of the supply voltage is as shown in the right side of FIG. Is secured. Thus, for example, the supply voltage VEE-VD
If the forced discharge circuit 42 short-circuits the selection voltage and the voltage becomes sufficiently small before the voltage between D drops to 3 V, the liquid crystal cell may be given undesired power due to runaway of the scanning circuit 2. Absent.

[0016]

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 becomes larger. The large selection voltage is applied after the drive voltage, and before the drive voltage drops. Since the selection voltage disappears, the scanning circuit does not malfunction or run away, and the DC voltage does not remain applied to the liquid crystal.

[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 time chart of voltage according to the present invention.

[Explanation of symbols]

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

Claims (2)

[Claims] 1. A liquid crystal cell having electrode groups orthogonal to each other, a scanning circuit for selecting one of positive and negative selection voltages for one electrode group of the liquid crystal cell and supplying the selected electrode with a scanning voltage as a scanning voltage, A signal circuit for selectively applying to the other electrode group of the liquid crystal cell a signal voltage in the vicinity of an intermediate value between the positive selection voltage and the negative selection voltage of the scanning circuit according to an image signal, and the scanning circuit and the signal circuit. A liquid crystal display device comprising a power supply circuit supplying a voltage of a predetermined value, wherein the power supply circuit provides the selection voltage and the driving voltage of the scanning circuit from different power supply lines. 2. A liquid crystal cell having mutually orthogonal electrode groups, a scanning circuit for selecting one of positive and negative selection voltages for one electrode group of the liquid crystal cell and applying it as a scanning voltage to a predetermined electrode, and the liquid crystal. A signal circuit that applies a signal voltage in the vicinity of an intermediate value between the positive selection voltage and the negative selection voltage of the scanning circuit to the other electrode group of the cell according to the image signal, and a predetermined bias value for the scanning circuit and the signal circuit. In a liquid crystal display device comprising a power supply circuit for supplying a voltage of 1 and a drive voltage for each circuit, the power supply circuit has a short circuit for the selected voltage,
A liquid crystal display device characterized in that a driving voltage is supplied to a scanning circuit even after a selection voltage is short-circuited.