JPH0561060A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal display device in which a liquid crystal display element can be driven by a high voltage in substance by decreasing the effect of noise towards a logic circuit system. CONSTITUTION:This device is provided with the liquid crystal display element (liquid crystal panel) 20, a common driver IC 21, and a segment driver IC 22; the segment driver IC is constituted of at least plural data latch (160 bits data latch) 24, a voltage level shifter 25, and a high voltage driver 26; the first terminal of a resistive element 27 is respectively connected to respective wirings succeeding from the data latch to the voltage level shifter; the second terminal of the resistive element is connected in common; and the resistance common terminal connected in common is the terminal for external connecting of the segment driver IC; so that the aimed purpose can be attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multiplex drive liquid crystal display device.

[0002]

2. Description of the Related Art Generally, an XY matrix type liquid crystal display device is arranged so that a plurality of scanning lines Y and a plurality of signal lines X face each other in a matrix. To drive such a liquid crystal display element, first, only one scanning line is selected, and data corresponding to a desired display (white / black, etc.) is written on the scanning line from the signal electrodes. Then, this operation is sequentially performed for the number of scanning lines, and this is set as a minimum unit for obtaining one display, and normally, a display is performed by continuing a series of these operations (multiplex drive).
According to this driving method, it is known that the higher the number of scanning lines to be driven, the higher the voltage for driving the liquid crystal.

On the other hand, in recent years, the number of pixels (the number of scanning lines × the number of signal lines) required for a simple matrix type liquid crystal display device typified by a recent ST (super twist) type liquid crystal display device has remarkably increased. I'm doing it. Under such circumstances, a liquid crystal driving driver IC used in a liquid crystal display device is required to be usable at a high liquid crystal driving power supply voltage, that is, to have a high withstand voltage. For example, in a liquid crystal display device having 400 scanning lines (1/200 duty drive), the driving voltage was about 25 volts, but the number of scanning lines was 800.
In the liquid crystal display device of the present (1/400 duty drive), the drive voltage is about 30 volts or more.

[0004]

However, the driver IC which has been generally used in the past can tolerate a liquid crystal driving power source voltage of only up to about 28 V, and the number of scanning lines is 80.
It has been a problem to construct a liquid crystal display device having a large display capacity such as zero. In particular, since the signal waveform that drives the signal line has a large number of switching times, it is difficult to operate the driver-IC normally.

Conventionally, such a driver IC is constructed as shown in FIG. 7, and a logic circuit for data transfer and signal control such as a plurality of shift registers 11, a data latch 12 and the like, and a logic voltage for this logic circuit. Voltage level shifter 13 that converts the magnitude of voltage so that a high voltage can be controlled
And a high voltage driver 14 for controlling a high voltage by driving the final stage transistor with the voltage.

One cause of hindering the normal operation of the driver IC is that when a high liquid crystal drive voltage is handled by the final stage driver circuit of the IC, the noise generated during switching becomes larger than when a low liquid crystal drive voltage is handled. It is in. That is,
It is considered that the increase in the amount of noise flowing into the control logic circuit hinders the normal operation of the driver-IC.
Further, the liquid crystal display element can be regarded equivalently as a capacitor, and when it is driven, a large current is instantaneously supplied from the IC to the liquid crystal display device. It is considered that this current also increases as the liquid crystal drive voltage increases, which also contributes to the increase in noise. As described above, conventionally, it has been difficult to drive a simple matrix type liquid crystal display element with a high voltage.

The present invention has been made in view of the above circumstances, and reduces the influence of noise on the logic circuit system of a liquid crystal driving driver-IC, particularly a segment driver-IC,
An object of the present invention is to provide a liquid crystal display device that drives a liquid crystal display element with a substantially high voltage.

[0008]

According to the present invention, there is provided a liquid crystal display device having a plurality of scanning lines and a plurality of signal lines, a common driver-IC connected to the scanning lines, and a connection to the signal lines. In the liquid crystal display device in which the liquid crystal display element is multiplexed, the segment driver IC includes at least a plurality of data latches, a voltage level shifter, and a high voltage driver. A first terminal of the resistance element is connected to each wiring extending from the data latch to the voltage level shifter, a second terminal of the resistance element is commonly connected, and the common resistance terminal connected in common is the segment. The liquid crystal display device serves as an external connection terminal of the driver-IC.

[0009]

According to the present invention, the first terminals of the resistance elements are respectively connected to the respective wirings extending from the data latch to the voltage level shifter, and the second terminals of these resistance elements are commonly connected to each other. The connection terminal is taken out to the external connection terminal of the segment driver-IC, and this potential is set between the power supply voltages supplied to the driver-IC. As a result, the final stage driver that controls a high voltage
It is possible to reduce the sneak of noise generated in the circuit to the logic circuit, and it is possible to drive the liquid crystal display element with a high voltage.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Two embodiments of the present invention will be described in detail below with reference to the drawings. (Example 1)

The liquid crystal display device according to the first embodiment is a super device.
A twist type liquid crystal display element is used, and this super twist type liquid crystal display device is constructed as shown in FIGS. 1 and 2, and FIG. 2 shows a driving power supply circuit. As is apparent from FIG. 1, a liquid crystal display panel 20 including a liquid crystal display element having a plurality of scanning lines and a plurality of signal lines, a common driver-IC 21 connected to the scanning lines, and a signal line are provided. It is composed of a connected segment driver-IC 22.

The liquid crystal display panel 20 is of A4 size and comprises a 640.times.800 dot super twist type liquid crystal display element. The panel is composed of two glass plates with transparent electrodes made of ITO, and the liquid crystal is sealed between the electrodes with the electrodes facing each other. The number of transparent electrodes is 800 on the scanning electrode side and 640 on the signal electrode side.

Such a super twist type liquid crystal display device has a cell thickness of about 7 .mu.m and is provided with a rubbing alignment-treated polymide alignment layer.
° It has a twisted structure. In the first embodiment, in order to obtain a super twist liquid crystal display device for monochrome display, a liquid crystal cell for phase compensation is superposed on the driving cell.
The liquid crystal used is ZLI-2293 manufactured by Merck.

A liquid crystal driving common driver-IC 21 and a segment driver-IC 22 are connected to the liquid crystal display panel 20 as described above. Then, a control signal and a display data signal which can obtain a general multiplex drive waveform are applied to these driver ICs 21 and 22. Then, it is driven at a drive duty ratio of 1/400 and a frame frequency of 80 Hz.

Further, as shown in FIG. 2, the liquid crystal driving voltages V ₀ , V ₁ and V ₂ are obtained by dividing the resistors R ₁ and R ₂ , and a voltage follower of an operational amplifier is inserted for current amplification. .. V ₃ , V ₄ , and V ₅ are generated by an inverting amplifier circuit (differential amplification operation) while biasing the resistor R ₃ based on V ₀ , V ₁ , and V ₂ . The V ₀ , V ₁ , V ₂ , V ₃ , V ₄ , and V ₅ thus obtained are supplied to the liquid crystal driving voltage input terminals of the respective driver-ICs 21 and 22.

Regarding the common pulse voltage supplied to the scan electrodes, a selection potential V ₀ , a selection potential V ₅ at the time of polarity reversal,
The non-selection potential V ₄ , the non-selection potential V ₁ at the time of polarity reversal, and the segment pulse voltage supplied to the signal electrode are the selection potential V ₅ , the selection potential V ₀ at the time of polarity reversal, the non-selection potential V ₃ , the polarity reversal. The non-selection potential V ₂ at this time.

FIG. 8 shows an example of the common pulse voltage (a), the segment pulse voltage (b), and the composite waveform (c) actually applied to the liquid crystal pixel when the polarity is inverted every frame period. Shows the drive waveform for the ON pixel.

As described above, the common driver-IC 21 switches the voltages V ₀ , V ₁ , V ₄ and V ₅ and the segment driver-IC 22 switches the voltages V ₀ , V ₂ , V ₃ and V.
By switching _{5 the} drive voltage is supplied to the liquid crystal display panel 20. In FIG. 8C, V ₀ −V
The magnitude of ₅ is called the liquid crystal drive voltage.

In the driving power source of this embodiment, the bias ratio is R / (4 * R + 2 * R), where R ₁ = R ₂ = R
3), the bias ratio is 1/2 in the first embodiment.
It is set to 0. In the case of this circuit, since the gain for the non-inverting input is 2, the voltage input to the liquid crystal drive voltage input terminal is half the actual drive voltage. This set is a transmissive display device having a fluorescent light on the back.

The common driver-IC 21 has 10 outputs.
No. 0 is Toshiba T9822, and eight of them are used.
The segment driver-IC 22 shown in FIG.
8 is used, and eight of them are used. The segment driver-IC 22 is configured as shown in FIG.
Bit × 20 shift register-23, 160-bit data latch 24, 160 voltage level shifters
25 and 160 sets of high voltage drivers-26. The high voltage driver 26 selects one of the voltages V ₀ , V ₂ , V ₃ and V ₅ based on the data stored in the data latch 24. Here, the wiring connecting between the data latch 24 composed of 160 flip-flops and the 160 voltage level shifter 25 is
A resistance element 27 is connected to each. The first terminal of the resistance element 27 is connected to the data latch 24 and the voltage level shifter 25.
These resistance elements 27 are connected to the wiring connecting between
A circuit in which the second terminals of are commonly connected.

This commonly connected resistor common terminal is provided as an external connection terminal of the segment driver-IC 22. In the liquid crystal display device according to the first embodiment, the common resistance terminals are connected between the eight segment driver ICs and the ground potential (0 volt potential of the logic power supply).

The potential of the resistor common terminal is preferably the ground potential, but this voltage does not necessarily have to be the ground potential, and the logic system of the driver-IC is affected by noise from the high-voltage driver-section. Instead, a voltage that operates stably can be selected. The shift register circuit is provided with an enable input / output terminal in order to transfer data to the next IC when this IC is connected in multiple stages. The liquid crystal display device configured as described above operates stably even when the liquid crystal drive voltage is 35 V, and a good display screen can be obtained.

Next, a comparative example will be described. The structure of the liquid crystal display device is the same as that of the above-described first embodiment, and only the segment driver-IC has the conventional structure. That is, the IC having the configuration shown in FIG. 7 is used in which all the resistance elements connected to the wiring connecting between the data latch 24 and the voltage level shifter 25 of the segment driver-IC 22 used in the first embodiment are removed.

In the liquid crystal display device having this structure, when the liquid crystal drive voltage exceeds 29 V, the logic system of the driver-IC is affected by noise from the high-voltage driver section, and the operation becomes unstable. It was impossible to display the screen. Incidentally, FIG. 4 shows a driver IC according to the present invention.
4 is a block diagram showing the same as that of FIG. (Example 2)

The liquid crystal display device of the second embodiment is constructed as shown in FIGS. 5 and 6, and FIG. 6 shows a driving power supply circuit. As is apparent from FIG. 5, the basic configuration is the same as that of the first embodiment, and here, a part of the liquid crystal drive voltage can be changed according to the display content by using the common resistor terminal. A new voltage control circuit (right half of FIG. 6) is added.

Similar to the first embodiment, the resistance common terminal is connected between each of the eight ICs, and in the second embodiment, it is further connected to the inverting input terminals of the operational amplifier circuits 28 and 29.
In order to bring this inverting input terminal to the ground potential, the non-inverting input terminal of the operational amplifier is connected to the ground potential. This is substantially the same as the configuration of the first embodiment. On the other hand, the liquid crystal display element is driven by a square wave multiplex drive waveform, but the rising and falling of the waveform are dull due to the capacitance of the connected liquid crystal. For example,
The size of the waveform rounding appearing in the selected portion of the scanning line drive waveform is greatly different depending on the number of ON pixels and OFF pixels on the display electrode. This state is shown in FIG. This is because the driving capacity of the driver is constant and the electrostatic capacity of the liquid crystal is different depending on whether it is in the on state or the off state due to the dielectric anisotropy of the liquid crystal. It happens. Specifically, the size of the waveform rounding appearing on the scan electrode increases as the number of ON pixels displayed on the scan electrode increases, and the effective value of the voltage waveform applied to the liquid crystal on this scan line decreases. To do. As described above, the waveform rounding causes a decrease or increase in the effective value voltage of the voltage waveform applied to the liquid crystal layer, which is observed as a difference in light transmittance. As a result, display unevenness depending on the display content, that is, a so-called crosstalk appears in the scanning line direction, and the display quality is deteriorated.

In the liquid crystal display device of the present invention, the withstand voltage of the driver IC can be substantially increased as described above, and as described below, it can be easily applied to a circuit for reducing crosstalk. You can do it.

Here, the output of the operational amplifier is applied to a power supply circuit for generating a liquid crystal drive voltage. The circuit of FIG. 5 has a configuration in which the magnitude of the voltage of the selection waveform applied to the scan electrodes is changed according to the display content.
Here, the operational amplifier circuits 28 and 29 function as adders and output a voltage proportional to the display content for each scanning line.
Then, this output passes through the voltage level conversion circuit, and the selected potential of the common driver-IC 21 (V ₀ ′ in the figure,
V ₅ ′ and V ₀ ″, V ₅ ″). In particular,
When the number of ON pixels displayed on the scanning line of interest is small, the magnitude of the voltage of the selection waveform applied to the scanning electrodes is V ₀ ′ −V ₅ ′, V ₀ ″ −V ₅ ″. Is increased by increasing. This state is shown in FIG.
Shown in. (A) is a common pulse voltage, (b) is a segment pulse voltage, and (c) is a liquid crystal applied voltage.

Since the display area of the liquid crystal display panel used is divided into the upper half and the lower half as shown in FIG. 5, the upper half four segment driver ICs 22 have a common resistance terminal and the lower half four. Segment driver-I
The common resistance terminals for C22 are connected to different operational amplifier circuits 28 and 29, respectively, and are passed through the individual voltage level conversion circuits 30 and 31 shown in FIG. 6 to obtain the selection potentials V ₀ ′ and V ₅ ′ of the liquid crystal drive voltage. Converted to V ₀ ″ and V ₅ ″, common driver ICs for upper half and lower half respectively
Of the selected potential.

The liquid crystal display device having such a structure operates stably even when the liquid crystal drive voltage is 35 volts.
Further, it is possible to obtain a uniform display screen without display unevenness (crosstalk) occurring in the scanning line direction. This Example 2
If a segment driver IC such as the one described above is used, the liquid crystal can be driven at a high drive voltage, and the increase in capacitance when the number of ON pixels is large can be changed to a selected waveform by simply adding a simple circuit. The given waveform rounding can be offset.

In the liquid crystal display device of the present invention, the ST
Not only (super twist) type liquid crystal display element but also TN
(Twisted nematic) type liquid crystal display device, GH
It goes without saying that a (guest host) type liquid crystal display device, a polymer dispersed liquid crystal display device (PDLCD), etc. can be used. Further, the present invention can be applied to an active matrix type liquid crystal display device.

[0032]

As described above, according to the present invention, since the segment driver-IC in which the resistance element is added to the inside of the segment driver-IC which has been conventionally used is used, the liquid crystal display is operated at a higher voltage than the conventional one. Not only can the element be driven and good display can be obtained, but a simple circuit can be added to this display device to greatly reduce the crosstalk and achieve uniform display. I can.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a driving power supply circuit of the same.

FIG. 3 is a block diagram showing a segment driver-IC in the liquid crystal display device according to the first embodiment.

FIG. 4 is a block diagram showing a general driver-IC according to the present invention.

FIG. 5 is a block diagram showing a liquid crystal display device according to a second embodiment of the present invention.

FIG. 6 is a block diagram showing a driving power supply circuit of the same.

FIG. 7 is a block diagram showing a general driver-IC in a conventional liquid crystal display device.

FIG. 8 is a waveform diagram showing a general liquid crystal drive waveform.

FIG. 9 is a waveform diagram showing rounding of a scanning line drive waveform.

FIG. 10 is a waveform diagram showing drive waveforms of the liquid crystal display device according to the second embodiment of the present invention.

[Explanation of symbols]

20 ... Liquid crystal display panel (liquid crystal display element), 21 ... Common driver-IC, 22 ... Segment driver-IC, 2
3 ... Shift register, 24 ... Data latch, 25 ... Voltage level shifter, 26 ... High-voltage driver, 27 ... Resistor element.

Claims (1)

[Claims] 1. A liquid crystal display device having a plurality of scanning lines and a plurality of signal lines, a common driver-IC connected to the scanning lines, and a segment driver-IC connected to the signal lines. In the liquid crystal display device, in which the liquid crystal display element is driven in multiplex, the segment driver-IC includes at least a plurality of data.
A data latch, a voltage level shifter, and a high-voltage driver. The first terminals of the resistance elements are connected to the respective wirings extending from the data latch to the voltage level shifter, and the second terminals of the resistance elements are commonly connected. The commonly connected resistor common terminal serves as an external connection terminal of the segment driver-IC.