JPH09281462A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To relieve a pale display on the extension of continuously selected pixels efficiently compensating electric transmission loss, etc., in a simple matrix drive having an extremely large display capacity. SOLUTION: A scanning circuit 2 and a signal circuit 3 are connected to a liquid crystal cell 1 having electrode groups intersecting orthogonally with each other. The device is provided with a power source circuit 4 for supplying positive and negative selection voltages as a scanning voltage and the signal voltage near the intermediate values of the selection voltage. The power source circuit 4 outputs plural sets of signal voltages which consist of the positive and negative signal voltages meeting a voltage average impression method and the positive and negative correction signal voltages of the voltage values slightly different therefrom and vary in the absolute value. The signal circuit 3 selects the voltages from the positive and negative signal voltages meeting the voltage average impression method when the image signals are nearly the same as the contents of the previous display in accordance with the polarity signal and image signal. The signal circuit selects the voltages from the positive and negative correction signal voltages when the image signals vary form the contents of the previous display. The circuit outputs these voltages. Further, the impression voltages on the liquid crystal cell 1 are made approximately zero for a short time in the case of the response with the inversion of positive and negative polarities.

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 inverted based on the polarity signal.

For example, in a case where AC driving is performed by inverting the polarity for each frame, the polarity signal is inverted and provided for each frame. This polarity signal is also called an alternating signal, M. When V0 is applied to the scan electrode at the time of scanning in the first frame and V1 is applied to the other signal electrode (selected pixel), V1 is applied to the scan electrode and V0 is applied to the signal electrode in the next frame. give.

[0004] In such a method, a large capacitive load current due to the liquid crystal flows when the AC signal is switched, and the power consumption increases. A recent liquid crystal display device is 640 × 4
It is about to evolve from 80 pixels (VGA) to 1024 RGB × 768 pixels (color XGA) (the number of pixels per line on the signal side is 3072). For this purpose, the data transfer time and other operations become faster, so that a high-speed and high-voltage integrated circuit is required. It has become necessary. However, for an integrated circuit, high speed and high withstand voltage are conflicting specifications, making it difficult to realize.

[0005]

Therefore, it was studied to set the scanning voltage to a large positive and negative voltage and the signal voltage to a voltage in the vicinity of the intermediate value between the positive selection voltage and the negative selection voltage. The effect is high only on a large screen, and the capacitive load is large and the image signals are also large.Therefore, the influence of noise and transmission loss received from devices such as personal computers is large, and the periphery of the selected pixel, especially the continuous selected pixel A light display was observed on the extension, and the display quality was degraded. Further, in order to cope with the distortion of the voltage applied to the liquid crystal, it was considered to apply the correction voltage in a superimposed manner for a short time, for example, avoiding the influence of the distortion of the applied voltage waveform for only 1/3 of the central part of one scanning time. However, the burden on the high-speed switching circuit for superimposing such a correction voltage on the signal voltage is large, which is inconvenient.

[0006]

SUMMARY OF THE INVENTION The present invention efficiently compensates for transmission loss and the like in view of the above points, and scans a liquid crystal cell having mutually orthogonal electrode groups and one electrode group of the liquid crystal cell. A scanning circuit for applying a voltage, a signal circuit for applying a signal voltage to the other electrode group of the liquid crystal cell in accordance with an image signal, a positive / negative selection voltage as a scanning voltage to be applied to the scanning circuit, and an image signal for the signal circuit. A power supply circuit for supplying a signal voltage near the intermediate value between the positive selection voltage and the negative selection voltage of the scanning circuit and a drive voltage for each circuit is provided, and the power supply circuit is preferably a positive and negative signal voltage according to the voltage average addition. The signal circuit outputs a plurality of sets of signal voltages having different absolute values, which are positive and negative correction signal voltages whose voltage values are slightly different from the signal voltage according to the voltage average addition, and the signal circuit outputs a plurality of these voltage signals in accordance with the polarity signal and the image signal. Signal It is selected from among the above and is output to the liquid crystal cell. More preferably, when the image signal is almost the same as the content of the previous display, it is selected from the positive and negative signal voltages according to the voltage average addition and different from the content of the previous display. In this case, the voltage is selected from positive and negative correction signal voltages, and in the case of responding to the inversion of positive and negative polarities, the voltage applied to the liquid crystal cell is set to substantially zero for a short time.

[0007]

FIG. 1 is a circuit diagram of a liquid crystal display device according to an embodiment of the present invention, in which a liquid crystal cell 1 having electrode groups orthogonal to each other and a positive electrode and a negative electrode of a predetermined electrode of one electrode group of the liquid crystal cell 1 are formed. To the scanning circuit 2 which selects any one of the selection voltages and supplies it as a scanning voltage, and 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 1 according to the image signal. It has a signal circuit 3 selectively and selectively applied thereto, a power supply circuit 4 for supplying a voltage of a predetermined value to the scanning circuit 2 and the signal circuit 3, and a signal transfer circuit 5. This will be described more specifically.

The liquid crystal cell 1 is of a so-called simple matrix type, and a field effect liquid crystal such as a super twist nematic liquid crystal display can be used. The electrodes of the liquid crystal cell 1 are, for example, transparent electrodes arranged in stripes and have no active elements at pixel intersections.

The scanning circuit 2 applies a voltage with a high peak value to each scanning electrode during one frame in order to perform line-sequential scanning, and selects one of the positive and negative voltages -VL, + VH and the intermediate voltage Vm. Are supplied to predetermined electrodes, among which -VL and + VH are selection voltages. When the screen of the liquid crystal cell 1 is divided into upper and lower parts for driving, two sets of the scanning circuit 2 and the signal circuit 3 are required.

On the other hand, the signal circuit 3 considers the correction values for the two types of signal voltages -Vb and + Vb and the two types of signal voltages near the intermediate value between the positive selection voltage + VH and the negative selection voltage -VL. The correction signal voltages -Vc and + Vc of two types are selectively supplied to the electrodes of the liquid crystal cell 1 according to the polarity signal M and the image signal (data). The signal circuit 3 further includes positive and negative signal voltages -Vb, + V according to the voltage average addition when the image signal is almost the same as the content displayed last time.
If the selected content is different from the content displayed last time, it is selected from the positive and negative correction signal voltages −Vc and + Vc.
Further, when responding to the reversal of positive and negative polarities, the liquid crystal cell 1
The voltage applied to is made to be substantially zero for a short time.

The signal circuit 3 performs the above operation,
As shown in FIG. 2, a register 31 that receives the image signals D0 to D7, a latch 32 that receives the image signal of the register, a latch 33 that stores the image signal of the previous row, and a comparison circuit that compares the two image signals. 34, a level shifter 35, and a driver 36. The register 31 may be further combined with the register 37 that selects the transfer direction. The latches 32 and 33 store the image signals having the same number of bits, and the comparison circuit 34 compares these on a bit-by-bit basis for each latch. For example, if the number of bits exceeds 40%, the image signal changes. Output the flag. The degree (ratio) of the bit number fluctuation of 40% may be set for each model, or not only the fluctuation of the bit number is observed but only the image signal from off to on or gradation display. The bits of the dark pixels may be counted. Further, the driver 36 receives at least four kinds of signal voltages -Vb, + Vb, -Vc, + Vc from the power supply circuit 5, and each of the signal electrodes of the liquid crystal cell 1 has an analog for each bias voltage as shown in FIG. The controller 362 has an output stage having a switch 361 array, and the controller 362 selects either the positive or negative signal voltage −Vb, + Vb or the positive or negative correction signal voltage −Vc, + Vc according to the output of the comparison circuit 34. The polarity signal M and the image signal data are used to determine whether the signal is positive or negative depending on whether it is turned on or off, and selectively outputs one of the four signal voltages.

Referring again to FIG. 1, the power supply circuit 4 supplies voltages VDD and VEE supplied from, for example, a personal computer in which the display device is incorporated, to a voltage generation circuit (D).
C / DC converter) 41, and the positive and negative voltage -V
L, + VH are generated. The positive / negative here does not mean an absolute potential of some kind, for example, a potential regulated with respect to the power supply of the personal computer in which this display device is incorporated, but a potential with respect to the scanning voltage (intermediate voltage) Vm during non-scanning. expressing. The voltage generation circuit 41 more preferably buffers the drive voltage (voltage for integrated circuit) of the scanning circuit 2 and the signal circuit 3, and further signals corresponding to various timing signals and image signals supplied to the signal circuit 3. When it is transmitted via the power supply circuit, the drive transmission level is level-shifted to the supply power supply level as necessary, and the drive voltage of the signal transfer circuit or buffer circuit to which an initialization signal is added and generated is also generated and supplied.

Based on the positive and negative selection voltages generated by the voltage generating circuit 41 in this way, the voltage of a predetermined bias value in the resistance dividing circuit 42, that is, the signal voltage -Vb, + Vb, the correction signal voltage -Vc, + Vc. Then, the intermediate voltage Vm is obtained and is output through the buffer circuit 43. At this time, the voltage to be the signal voltage has different absolute values for each of positive and negative.
There are 4 sets in total.

The magnitudes of the selection voltages + VH, -VL and the signal voltages -Vb, + Vb are determined in principle according to the voltage averaging method. For example, when the XGA screen is divided, the number of scanning lines is 384 ( The optimum bias value is 1: 20.6 at 1/384 duty driving), and the intermediate voltage Vm and G
When the ND levels are matched, the selection voltage ± 30.0 volts and the signal voltage ± Vb are ± 1.46 volts. When the ground level is shifted from 0 volt or the value of Vm is changed from the median value of the positive and negative selection voltages, the voltage value itself becomes different depending on whether the voltage is positive or negative, but the voltage level ratio applied to the liquid crystal is substantially maintained. Necessary for positive and negative. The correction signal voltages −Vc and + Vc may be extremely small because they are applied at all times of one scanning time. In the case of the positive / negative balance described above, ± 1.47 is displayed in the display of the size of 10 inches to 15 inches. It was ± 1.59 Volts from Volts. Rather than forming such a voltage of several tens to several hundreds of mV by the power supply circuit 4 and switching and supplying the voltage inside the power supply circuit, all of these bias voltages are supplied to the power supply circuit 4.
It is preferable to supply the power from the outside to the outside and to select inside the signal circuit 3 for each scanning period, because the power amount switched by switching is small, and the load on the power supply circuit 4 is small.
The load on the integrated circuit in the above is also dispersed and small, which is preferable.

On the other hand, an image signal which is data is given from the image controller or the microcomputer through the buffer circuit 51 of the signal transfer circuit 5, and the polarity signal M may be given from the image controller or the microcomputer. Alternatively, the signal transfer circuit 5 may generate the signal. And when the applied voltage switches from the positive voltage to the negative voltage and when the negative voltage switches to the positive voltage,
If the waveform is distorted unbalanced, the signal transfer circuit 5 is provided with a display control 53 to activate a flip-flop or a logical sum gate by a latch pulse and a display non-operation signal, including the period of the latch pulse. If the signal circuit 2 and the scanning circuit 2 output the intermediate voltage Vm once in a short period of time to make the applied voltage substantially zero and then output the predetermined signal voltage and scanning voltage, the liquid crystal The distortion of the voltage waveform applied to the cell is almost balanced, and the defective display is eliminated.

Due to this driving, the output stage of the integrated circuit of the scanning circuit 2 requires a withstand voltage approximately double that of the conventional one, but it is a low-speed process corresponding to the number of scanning lines and one of the three potentials at the output stage. Since one of them is selected, no large current is generated when switching the AC signal. On the other hand, the signal circuit 3 handles only a low voltage of 5 V or less in the above example, and is suitable not only for high-speed driving but also for waveform collapse. With respect to the unbalanced voltage that is still generated, the effective value is adjusted by applying or lowering the screen information to the liquid crystal cell for one scanning time by calculating or comparing the screen information. Smaller voltage can be smoothly switched compared to the case where voltage is superimposed only for time, there is little influence on other pixels, and high capacity display with high display quality is achieved without increasing the load on the integrated circuit for signal circuits. You can keep it.

[0017]

As described above, according to the present invention, the scanning circuit uses the positive and negative selection voltages as the scanning voltage, and the four kinds of signal voltages in the vicinity of the intermediate value of the selection voltage according to the image signal are used. It can be driven stably at a low voltage while correcting the effective value, and even if the display capacity increases and the image signal increases significantly, the signal circuit is less burdensome and can process at high speed, resulting in an image with good display quality. Can be displayed.

[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 block diagram of a signal circuit according to an embodiment of the present invention.

FIG. 3 is a circuit diagram of a driver of a signal 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 5 signal transfer circuit

Claims (1)

[Claims] 1. A liquid crystal cell having mutually orthogonal electrode groups, a scanning circuit for supplying one electrode group of the liquid crystal cell as a scanning voltage, and a signal voltage to the other electrode group of the liquid crystal cell according to an image signal. A liquid crystal display comprising: a signal circuit for giving a signal; and a power supply circuit for supplying a signal voltage near the intermediate value between the selection voltage given to the scanning circuit and the positive selection voltage and the negative selection voltage of the scanning circuit given to the signal circuit. In the device,
The power supply circuit outputs a plurality of sets of signal voltages having different absolute values, and the signal circuit selects from a plurality of signal voltages according to a polarity signal and an image signal and outputs the selected signal voltage to a liquid crystal cell. Liquid crystal display device.