JPH10104574A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that a voltage fluctuation is intensively generated on a specific bias potential or a waveform accent is generated in driving a simple matrix with a very large display capacity, by involvement in a power source circuit supplying a prescribed voltage (bias voltage). SOLUTION: This liquid crystal display device is provided with a liquid crystal cell 1 with groups of electrodes orthogonal to each other, scanning circuits 2 which select either of positive and negative selection voltages and supply it as a scanning voltage, signal circuits 3 which selectively supply a signal voltage near a median of the positive and negative selected voltages, a power source circuit 4 to supply a prescribed voltage value, and a data circuit 5 to supply necessary timing signal. The liquid crystal cell 1 is split into plural areas, and alternates an applied voltage with an alternating signal for each split area. The power source circuit 4 supplies a bias voltage through an operational amplifier circuit with a push-pull circuit at an output stage, and is provided with a capacitor connected across the outputs of the intermediate voltage and signal voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device suitable for so-called simple matrix driving.

[0002]

2. Description of the Related Art Conventionally, in driving a liquid crystal cell having electrode groups orthogonal to each other, that is, a so-called simple matrix drive, a voltage of a high voltage level is sequentially applied to the electrodes of one of the electrode groups, and the voltage of the high voltage level is increased. As shown in Japanese Patent Publication No. 57-57718, 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. However, the polarity is inverted for the purpose of converting the applied voltage with the AC signal.

For example, taking an example of AC driving by supplying an AC signal M whose polarity is inverted for each frame,
V0 is applied to the scan electrode at the time of the scan of the first frame,
When it is desired to display on the other signal electrode (selected pixel), V1
And in the next frame, V1
And V0 is applied to the signal electrode.

[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]

However, it has been found that when the display surface of the liquid crystal cell, which is a capacitive load, becomes large, a particular bias potential is concentrated depending on the display pattern. For example, the load on the bias circuit due to the inversion of the AC signal increases, especially when the screen is divided into a plurality of areas in order to secure the scanning duty ratio, as if the display patterns of the respective areas interfere with each other. Variation in applied voltage was observed. When a horizontal stripe pattern was drawn, a faint shade was displayed as an extension of the stripe pattern. When this state was observed with a bias potential, a clear waveform rounding was observed.

[0006]

SUMMARY OF THE INVENTION In view of the above, the present invention provides a power supply circuit for supplying a predetermined voltage (bias voltage) to a scanning circuit / signal circuit of a liquid crystal cell having mutually orthogonal electrode groups. It was made in connection with.

First, according to the present invention, the electrodes of one electrode group are sequentially scanned and supplied as a scanning voltage for each area of a liquid crystal cell which is divided into a plurality of areas and each of which has a group of electrodes orthogonal to each other. A power supply circuit for supplying a voltage of a predetermined value to the scanning circuit and a signal circuit for applying a signal voltage corresponding to an image signal to the other electrode group; a data circuit for supplying timing signals and the like necessary for the scanning circuit and the signal circuit; The data circuit outputs an AC signal for alternating the voltage applied to the liquid crystal cell, and the scanning circuit alternates the applied voltage with a different AC signal for each region. In the division, the timing of AC conversion differs for each area.

Further, according to the present invention, there is provided a scanning circuit for selecting one of the positive and negative selection voltages and supplying it as a scanning voltage, and a signal voltage near an intermediate value between the positive and negative selection voltages in accordance with the image signal. A signal circuit for selectively providing, a power supply circuit for supplying a voltage of a predetermined value to the scanning circuit and the signal circuit,
The power supply circuit supplies a bias voltage via an operational amplifier circuit having a push-pull circuit to an output stage at least for outputting a signal voltage.

Also, the present invention provides a scanning circuit for selecting any of the positive and negative selection voltages and supplying the selected voltage as a scanning voltage, and supplying an intermediate voltage having a substantially intermediate value between the positive and negative selection voltages to an electrode to which no scanning voltage is supplied. A signal circuit for selectively applying a signal voltage near an intermediate value between a positive selection voltage and a negative selection voltage of the scanning circuit to the other electrode group of the liquid crystal cell in accordance with an image signal; It has a power supply circuit for supplying a voltage of a value, and a capacitor is connected between the intermediate value voltage and the output of the signal voltage of the power supply circuit.

[0010]

FIG. 1 is a circuit diagram of a liquid crystal display device according to an embodiment of the present invention. In order to drive a liquid crystal cell having a large display capacity, FIG.
By setting the scanning signal to a large positive / negative voltage and setting the signal voltage to a voltage near an intermediate value between the positive selection voltage and the negative selection voltage, the scanning side uses a low voltage instead of using a large voltage, and the signal side uses a small voltage. A liquid crystal display device which can be driven at high speed by using the same will be described as an example.

Reference numeral 1 denotes a liquid crystal cell having electrode groups orthogonal to each other. For example, a field effect liquid crystal such as a super twisted nematic liquid crystal display can be used. The electrodes of these liquid crystal cells 1 constitute a so-called simple matrix, and have no active elements at pixel intersections. This liquid crystal cell 1
Is divided into a plurality of regions, and each of the divided regions has an electrode group orthogonal to each other. Specifically, for example, 1024R
If it is a display surface of GB × 768 pixels (color XGA),
It has pixels of 3072 (signal side) × 384 (scanning side) upper and lower two-screen configuration, and has 3072 signal electrodes separated at the center and 768 scanning electrodes intersecting with them.

Reference numeral 2 denotes a scanning circuit for applying a scanning voltage to one of the electrode groups for each area of the liquid crystal cell 1, which comprises two sets of circuits having 384 outputs in the above-described screen example. The scanning circuit 2 selects one of the positive and negative voltages -VL and + VH and the intermediate voltage Vm and supplies it to a predetermined electrode. Among them, -VL and + VH are selection voltages. Here, line-sequential driving is taken as an example. However, the present invention can be applied to a case where a plurality of electrodes are simultaneously scanned. In this case, the applied voltage is selected according to a function. The only difference is the number of electrodes provided.

Reference numeral 3 denotes a signal circuit for applying a voltage corresponding to an image signal to the other electrode group of the liquid crystal cell 1. In particular, a signal circuit 3 is provided near the intermediate value between the positive selection voltage + VH and the negative selection voltage -VL of the scanning circuit 2. Two kinds of signal voltages -Vb and + Vb are selectively supplied to the electrodes according to the image signal. These selection voltages + V
The magnitudes of H, -VL and the signal voltage ± Vb are obtained according to the voltage averaging method. For example, when the XGA screen is divided into two, the number of scanning lines is 384, and when driving at 1/384 duty, The optimum bias value is 1: 20.6. When the intermediate voltage Vm and the GND level are matched, the selection voltage ±
30 volts and the signal voltage ± Vb is ± 1.53 volts. In this case, as the scanning voltage, one of the positive and negative selection voltages is selected at a constant cycle, which is selected according to the AC signal M, and the signal voltage output from the signal circuit 3 is the image voltage. Which of the two values is selected changes with the signal and the polarity inversion. When a plurality of rows are simultaneously scanned, only the voltage value is calculated by a function, and there is no change in the application of the voltage averaging method.

Reference numeral 4 denotes a power supply circuit for supplying a voltage of a predetermined value to the scanning circuit 2 and the signal circuit 3, and supplies a bias voltage such as at least a positive / negative selection voltage -VL, + VH, a signal voltage -Vb, + Vb, and an intermediate voltage Vm. Output, more preferably,
The scanning circuit 2 and the signal circuit 3, as well as the driving voltage of the data circuit 5 and the buffer 45 are also supplied. This power supply circuit 4
Inputs, for example, a voltage VEE-VDD supplied from a personal computer in which the display device is incorporated to a voltage generation circuit (DC / DC converter) 41 to generate positive and negative voltages -VL and + VH. Here, “positive” or “negative” is not an absolute potential, for example, a potential specified for a power supply of a personal computer in which this display device is incorporated, but a scanning voltage (intermediate voltage) during non-scanning.
It is expressed by a potential with respect to Vm. Based on the selected voltage, a voltage having a predetermined bias value is obtained by a resistance dividing circuit 42, and the voltage is passed through a buffer circuit 43 to obtain signal voltages + Vb and -Vb and an intermediate voltage Vm. As a result, both the center of the signal voltage and the center of the selection voltage are substantially the intermediate voltage V
It is preferable to set m. The driving voltage of the scanning circuit 2 and the driving voltage of the signal circuit 3 are equal to the voltage V supplied from a personal computer in which the display device is incorporated.
EE-VDD may be used directly, or the voltage generation circuit (D
(C / DC converter) 41.

Reference numeral 5 denotes a data circuit for supplying timing signals and the like necessary for the scanning circuit 2, the signal circuit 3, and the power supply circuit 4. The data circuit 5 receives signals from a personal computer or the like in which the display device is incorporated, and It consists of a buffer, a timing gate, etc., which output various signals. The data circuit 5 generates a control signal obtained from a personal computer or the like via a buffer or by receiving the control signal and outputs an AC signal M for causing a voltage applied to the liquid crystal cell to be AC. An image signal is received and output via a buffer. This data circuit 5
When necessary, when a signal corresponding to various timing signals and image signals supplied to the signal circuit 3 is transmitted via a buffer, the drive transmission level is level-shifted to a supply power level as necessary, An operation such as adding a conversion signal is performed. When scanning a plurality of rows at the same time, the data circuit 5 performs an operation. The data circuit 5 may manage a memory.

Although various simple matrix driving methods have been added to the description, the output of the integrated circuit of the scanning circuit 2 is obtained by using a large positive and negative scanning voltage and setting the signal voltage to a small voltage value near an intermediate value. The stage requires a withstand voltage approximately double that of the conventional one, but is a low-speed process according to the number of scanning lines. Since one of three potentials is selected at the output stage, a large current when switching the AC signal is required. It does not occur, and it is extremely unlikely that the waveform collapse, which is the cause of the occurrence of crosstalk, which has often been seen in the past, will occur. On the other hand, the signal circuit 3 handles only a low voltage of less than 5 volts in the above-described example, and is suitable not only for high-speed driving but also for reducing the area of the integrated circuit. Drive elements with a narrow width are used even for cutting down on shortening
It is preferable because it can be arranged.

In such a configuration, first, the timing of AC conversion is made different for each drive area. Specifically, an inverter circuit is provided between the scanning circuits 2, and receives an inverted AC signal for each set of the scanning circuit 2 signal circuits 3. As a result, the scanning circuit alternates the applied voltage with an alternating signal different for each region. This is based on the result of the study that it is presumed that the image signals in the respective regions interfere with each other at the time of switching of the alternating current and fluctuate the bias potential. FIG. 2 is a diagram in which a clock, a scanning circuit output, and a signal circuit output are monitored one by one when a horizontal stripe pattern is displayed. FIG. 2A is a waveform diagram when the same alternating signal is used for both the upper and lower screen areas. The output of the scanning circuit is inverted, but at the time of the switching, a sharp beard-like potential change appears in addition to the waveform rounding. The signal circuit output, which should be, is greatly kicked in accordance with the potential change. When observing the screen, pale shades are relatively clearly observed near the stripes. On the other hand, FIG. 2B is a waveform diagram when an alternating signal inverted in the upper and lower screen areas is used. When the output of the scanning circuit is inverted, although the waveform is rounded, a sharp mustache-like potential change disappears and is a straight line. The kick at the output of the power signal circuit is small. When observing the screen, the pale shade near the stripes is almost inconspicuous.

Next, in the buffer circuit 43 of the power supply circuit 4 described above, at least the output of the signal voltage
A bias is supplied to the output stage via an operational amplifier circuit having a push-pull circuit, and capacitors are connected to each other between the output of the intermediate voltage and the output of the signal voltage. To explain this in more detail, while considering measures for observing pale display in detail, for example, in a horizontal stripe pattern, the extension of the stripe is observed to be lightly colored, In both cases, it was found that there was a waveform rounding in both cases. The bias voltage output was intended to provide sufficient power supply capability through an operational amplifier, but its transient characteristics and instantaneous response characteristics have not been sufficiently elucidated.

Therefore, waveform rounding was examined by using several power boost circuits as shown in FIGS. 3 and 4, and by using a push-pull circuit, light shades could be made inconspicuous. This will be described with reference to FIG. 5. For example, when a horizontal stripe pattern is displayed, as shown in FIG. 5A, the output supposed to be rectangular changes gradually and the effective value of the area of a substantially triangular shape is obtained. Will be missing. This magnitude is, for example, −− on the signal side (+ Vb) in the above display device.
0.6 to -0.8 volt, +0.3 to scanning side (Vm)
+0.5 volt change. Therefore, when the resistance value is variously changed by providing a push-pull or a color as shown in FIG. 3, the voltage change on the signal side is particularly reduced from １ ／ to １ ／,
The voltage change on the scanning side also tended to decrease. Further, in the case of a push-pull circuit in which power can be supplied directly from the power supply as shown in FIG. 4, -0.00 to-on the signal side (+ Vb).
0.03 volts, -0.04 to +0.05 on the scanning side (Vm).
The change amount was remarkably reduced to 01 volt, and no pale color was observed when the display was observed.

In the buffer circuit 43 of the power supply circuit 4, a capacitor is usually connected between the ground and each bias output terminal as shown on the left side of FIG. 6A. FIG.
The right side of FIG. 6 shows a state in which a pixel is selected in the liquid crystal cell, and FIG. 6B is an equivalent circuit thereof. As in this example, by setting the scanning signal to a large positive / negative voltage and setting the signal voltage to a voltage near an intermediate value between the positive selection voltage and the negative selection voltage, a large current is generated when the AC signal is switched. It also has the advantage that the waveform collapse that is the basis of the occurrence of crosstalk, which is often seen in the past, is unlikely to occur.However, such connection of the capacitor is merely a perspective on the power supply circuit side, Seems to increase the capacity of the capacitive load. Therefore, as shown in FIG. 7A, capacitors are connected to each other between the output of the intermediate voltage and the output of the signal voltage.
FIG. 7 also shows an equivalent circuit as in FIG. With such a connection, waveform rounding was improved.

As described above, although the waveform rounding is reduced even when each of them is used alone, the use of an operational amplifier circuit having a push-pull circuit at the output stage and the connection of capacitors between the output of the intermediate value voltage and the output of the signal voltage allows a checkerboard pattern to be formed. Light display on horizontal stripes and color bars was hardly visually observed.

[0022]

As described above, according to the present invention, the burden on the bias voltage is reduced or the responsiveness is enhanced, so that the display quality can be maintained high even when the display surface of the liquid crystal cell becomes large.

Further, the scanning circuit uses positive and negative selection voltages as scanning voltages, and can reduce waveform distortion when two kinds of signal voltages near an intermediate value of the selection voltages are used in accordance with an image signal. It was possible to prevent the light shade on the elongation from causing discomfort to the observer.

[Brief description of the 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 waveform diagram a of a conventional driving circuit and a waveform diagram b of a driving circuit in an embodiment of the present invention.

FIG. 3 is a circuit diagram of a buffer circuit according to an embodiment of the present invention.

FIG. 4 is a circuit diagram of a buffer circuit according to an embodiment of the present invention.

FIG. 5 is a waveform diagram a of the conventional driving circuit and a waveform diagram b of the driving circuit in the embodiment of the present invention.

FIG. 6 shows a capacitor connection diagram a of a conventional buffer circuit and an equivalent circuit diagram b thereof.

FIG. 7 shows a capacitor connection diagram a of the buffer circuit of the embodiment of the present invention and an equivalent circuit diagram b thereof.

[Explanation of symbols]

 Reference Signs List 1 liquid crystal cell 2 scanning circuit 3 signal circuit 4 power supply circuit 5 data circuit

Claims (3)

[Claims] 1. A liquid crystal cell which is divided into a plurality of regions and has electrode groups orthogonal to each other in each of the divided regions, and sequentially scans electrodes of one of the electrode groups for each region of the liquid crystal cell to generate a scanning voltage. A scanning circuit for supplying, a signal circuit for applying a signal voltage corresponding to an image signal to the other electrode group, a power supply circuit for supplying a voltage of a predetermined value to the scanning circuit and the signal circuit,
In a liquid crystal display device having a data circuit that supplies a timing signal and the like necessary for the scanning circuit and the signal circuit, the data circuit outputs an alternating signal that causes an alternating voltage to be applied to a liquid crystal cell, 2. The liquid crystal display device according to claim 1, wherein the scanning circuit converts an applied voltage into an alternating voltage using a different alternating signal for each of the regions. 2. A liquid crystal cell having electrode groups orthogonal to each other, a scanning circuit for selecting one of positive and negative selection voltages to a predetermined electrode of one electrode group of the liquid crystal cell and supplying the selected voltage as a scanning voltage, A signal circuit that selectively supplies a signal voltage near an intermediate value between a positive selection voltage and a negative selection voltage of the scanning circuit to the other electrode group of the liquid crystal cell in accordance with an image signal; and the scanning circuit and the signal circuit. A power supply circuit for supplying a voltage of a predetermined value, wherein the power supply circuit supplies a bias via an operational amplifier circuit having a push-pull circuit at an output stage at least for outputting a signal voltage. A liquid crystal display device comprising: 3. A liquid crystal cell having an electrode group orthogonal to each other, and a positive or negative selection voltage is selected and supplied as a scanning voltage to a predetermined electrode of one of the electrode groups of the liquid crystal cell, and the scanning voltage is supplied. A scanning circuit that supplies an intermediate voltage having a substantially intermediate value between the positive and negative selection voltages to the non-electrodes, and a scanning circuit that supplies the other electrode group of the liquid crystal cell with a voltage near the intermediate value between the positive selection voltage and the negative selection voltage of the scanning circuit. A liquid crystal display device comprising: a signal circuit for selectively applying a signal voltage according to an image signal; and a power supply circuit for supplying a voltage of a predetermined value to the scanning circuit and the signal circuit. A liquid crystal display device comprising a capacitor connected between a voltage and a signal voltage output.