JP3224424B2 - Liquid crystal display - Google Patents

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, and more particularly to a driving circuit capable of performing display without crosstalk.

[0002]

2. Description of the Related Art There are various theories regarding the causes of crosstalk in liquid crystal display devices, and various countermeasures have been taken in accordance with each theory. Representative explanations that have been published conventionally will be described in order. First, an equivalent circuit diagram of a liquid crystal display device is shown in FIG. 4 for explanation. As shown in FIG.
To 404 and the liquid crystal interposed between the signal electrodes 405 to 408 are represented as a capacitive load 409. FIG. 8 is a timing diagram for the first explanation of the cause of crosstalk. The scanning electrodes 401 to 404 are 1
Row drive selection pulses 801 to 804 whose polarity is inverted for each row
Are sequentially output, and all the pixels on the column 405 display only white (or black), the column driving voltage of the column 405 is inverted every time row scanning is performed, and the capacitive driving is performed every time the inversion is performed. Since the liquid crystal, which is a load, is charged and discharged, the drive voltage applied to both ends of an arbitrary pixel on the column 405 becomes blunt during the non-selection period, as shown at 805 in FIG. On the other hand, when the pixels on the column 406 are in a display state in which the display is inverted every row, the column drive voltage of the column 406 maintains a constant value, so that the liquid crystal is not charged or discharged during the non-selection period. The drive voltage applied to both ends of any one pixel is as shown by 806 in FIG. When comparing the non-selection periods of the two, the effective value of 805 is smaller than the effective value of 806, which is considered to be the cause of crosstalk.

[0003] As an improvement plan based on the above idea, there is a proposal as disclosed in Japanese Patent Publication No. 64-4197, for example, which has provided a certain effect. However, these prior arts do not improve the rounding of the waveform itself, but focus on making the number of times of charging and discharging causing the rounding of the waveform uniform, and the display data is binary (black and white). Therefore, it has been considered that an effective countermeasure is not provided when performing a gradation display such as a television image.

That is, when the display data is binary, the switching of the driving voltage coincides with the scanning switching timing of the row electrodes. Adjustment can be made so that the number of discharges is almost equal, and the effective value when each column is not selected is uniform regardless of the display pattern. The reason is that the number of times of charging / discharging cannot be adjusted even if the polarity of the row driving voltage is inverted because the timing does not always coincide with the switching timing of the electrodes.

[0005] The problem of the above model is that it focuses only on the column electrode as the resistance component, and also takes up only the output resistance of the transistor of the signal electrode drive circuit. Therefore, proposals have been made in consideration of various factors of crosstalk.

For example, a countermeasure for crosstalk in consideration of the resistance of the power supply line is described in “SID 90 DIgest 412”.
21.4: Crosstalk-Free Drivi
ng Methods for STN-LCDs "(hereinafter referred to as Reference 1). In Document 1, it is assumed that one cause of the crosstalk is a voltage effect due to the resistance of the power supply line, and in order to correct the effect of the voltage effect, a DC bias is added to the scanning electrode signal when it is not selected. At this time, the bias value is calculated from the difference between the number of ON pixels on the row electrode in the currently selected period and the number of ON pixels on the next selected row electrode. Since the DC bias mentioned here is based on the idea of canceling out the difference in the effective voltage during the non-selection period, the rounding of the waveform of the signal electrode does not change. This means that although the effective voltage can be made uniform during the non-selection period, the influence of the rounding of the waveform during the selection period is not greatly improved, and the cause of crosstalk is still left.

Further, paying attention to the parasitic resistance of the power supply system,
Japanese Unexamined Patent Application Publication No. Hei 10 (1999) -19764 attempts to solve the crosstalk by detecting a current that causes a voltage drop in these resistors and varying the voltage applied to the drive circuit in accordance with the amount of the current.
No. 184147. In the proposal, the influence of the resistance of each part (the output resistance of the power supply, the wiring resistance in the integrated circuit to be driven, the wiring resistance in the panel) causing the rounding of the waveform is caused by the current flowing through the resistance of each part. This current flows through the liquid crystal, which is a capacitive load, flows into and out of the row electrode circuit and the column electrode circuit, and causes a voltage drop when passing through the resistance of each part. It is noted that a voltage different from the applied voltage is applied to the liquid crystal.

Although the above-mentioned method has considerably reduced crosstalk, it is a correction that fluctuates the scanning line signal at the time of non-selection by detecting the amount of current of the power supply system. Done. Therefore, there is a pixel row that is over-corrected, and crosstalk still remains. In addition, a time delay occurs before the correction is fed back to the liquid crystal in order to detect the result of acting on the liquid crystal, which is a capacitive load called the amount of current, and apply the correction to the power supply. This also causes crosstalk. In order to reduce this delay, high-speed operation circuits are required for both the current detection circuit and the power supply control circuit, which complicates the circuit and increases the cost.

[0009]

The inventor of the present invention has studied in detail the cause of the crosstalk. In the conventional method, the rise of the potential of the signal electrode node due to capacitive coupling when the voltage of the selection pulse of the scan electrode changes is considered. Discovered that it was not. This increase in potential is observed as if the signal electrode were focused only on the signal electrode. This is because, when considering the behavior at the time of non-selection in the conventional example, the selection pulse performed by another scan electrode at that time was regarded as another phenomenon.

Actually, in a liquid crystal display device using an STN for displaying a large number of divisions, the peak value of the selection pulse is high, and the potential of the node on the signal electrode side is changed via the liquid crystal which is a capacitive load. Is enough.

Further, the reason why the crosstalk of the liquid crystal panel that performs inversion every several lines, which has been described in the past with attention paid to the waveform rounding, is small is that the selection pulse of the same polarity causes the rising and falling of the adjacent signal at the same time. Therefore, the explanation can be made by paying attention to the fact that the node on the signal electrode side does not change.

An object of the present invention is to reduce crosstalk by suppressing an increase in potential on the signal electrode side due to a selection pulse of a scanning electrode.

[0013]

In order to achieve the above object, the present invention provides a liquid crystal display element formed by a liquid crystal layer and scanning electrodes and signal electrodes provided on both sides of the liquid crystal layer. A signal electrode driving circuit for inputting and outputting a pulse signal having a time width corresponding to the display data to a signal electrode; a scanning electrode driving circuit for sequentially outputting a selection pulse to the scanning electrodes to scan each scanning electrode; In a liquid crystal display device comprising: a power supply that determines a signal potential of a pulse signal output from the signal electrode drive circuit, a differentiated pulse obtained by differentiating a pulse waveform of a peak value according to the peak value of the selection pulse, Differential pulse applying means for applying the pulse in accordance with the rising or falling timing of the selection pulse is provided.

[0014]

According to the present invention, the variation corresponding to the variation of the potential of the signal electrode generated by the selection pulse having a known peak value is corrected from the outside to correct the variation of the signal electrode caused by the selection pulse. Therefore, a high-speed detection circuit is not required, and further, since the change of the signal electrode node due to the selection pulse of the scanning electrode acts uniformly on all the signal electrodes, this correction is effective for all gradations. Extremely high-speed operation is not required because the correction is for the known energy. Therefore, crosstalk can be reduced by a relatively simple and inexpensive circuit configuration.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of the present invention, FIG. 2 is a circuit configuration diagram of the control circuit of the present invention, and FIG. 3 is a diagram showing potentials and timings of the control circuit of the present invention.

A video signal 101 to be displayed in FIG. 1 is input to a timing generation circuit 102, where synchronization separation and A
/ D conversion is performed to convert to digital data. Further, respective timings are generated by the signals separated in synchronization, and the scan electrode driving circuit 110 and the signal electrode driving circuit 111 are driven by the timing signals, and data is sequentially displayed on the liquid crystal display device 109. Here, the liquid crystal display device 109 is represented by an equivalent circuit shown in FIG. 4, and the scanning electrode driving circuit 110 and the column electrode 4
The signal electrode driving circuit 111 is connected to 05 to 408.

The selection pulse generated by the scan electrode drive circuit 110 is applied to a signal electrode 405 via a liquid crystal 409 which is a capacitive load.
４０ 408 is varied. The charge corresponding to the variation is supplied to the signal electrode via the signal electrode driving circuit 111. However, since the output circuit of the signal electrode driving circuit 111 has an output resistance, it takes time until the potential of the signal electrode is stabilized. As a result, the potential of the signal electrode fluctuates as shown by 505 in FIG. 5 to be described later, and a whisker pulse is generated in all the electrodes in the same direction, which causes crosstalk.

Since the peak value of the selection pulse, which is the source of the fluctuation of the potential of the signal electrode, is a value set in advance by the power generation circuit, the capacitance ratio of the liquid crystal of the transition portion of the selection signal to the liquid crystal of the non-selection portion and the signal From the output resistance of the output part of the electrode drive circuit 111, the peak value and pulse width of the beard pulse can be predicted,
This expected waveform can be canceled by changing the power supply voltage of the signal electrode drive circuit 111 in the direction opposite to the direction of the beard pulse. The control circuit 1 controls the fluctuation of the power supply of the signal electrode drive circuit for canceling the beard pulse.
In step 03, the control is applied to the signal electrode drive circuit 111 to cancel the fluctuation of the signal electrode generated when the voltage of the selection pulse changes. Details will be described below with reference to FIGS.

The control circuit 103 shown in FIG. 1 comprises a differentiating circuit comprising a resistor 202 and a capacitor 203 and an operational amplifier 201 for impedance conversion in FIG. The potential of the pulse output from the signal electrode drive circuit 111 to the signal electrode of the liquid crystal display device 109 is determined by the potentials V1 and V2 input from the power supply generation circuit 112 to the control circuit 103. The peak value of the control signal P1 is
The control is performed in accordance with the peak value of the selection pulse of the scanning electrode generated by the scanning (the control circuit is not shown), and is input to the control circuit 103. The input control signal P1 includes a resistor 202 and a capacitor 2
A whisker-like pulse is generated by a differentiating circuit constituted by the circuit 03 and added to the potentials V1 and V2. The correction potential thus obtained is impedance-converted by, for example, an operational amplifier 201 and is hardly affected by a load, and is applied to signal electrodes of a liquid crystal panel as potentials V3 and V4. Here, 201 may be a circuit including a transistor, an FET, a MOS, and the like.

FIG. 3 is a diagram showing each potential and timing in FIG. The beard pulse corrected by the control signal P1 is added to V1 and V2 and fluctuates in the same direction as indicated by V3 and V4. The operation will be described in detail with reference to an equivalent circuit shown in FIG. 4 and a timing chart shown in FIG.

The timings of the scanning electrodes 401 to 403 shown in FIG. 4 are shown in FIG. 5 at 501 to 503, respectively, and the timings of the data applied to the signal electrodes are shown at 504 in FIG. The selection pulses output to the adjacent scanning electrodes 401 to 403 change in polarity every row, and the end timing of the first selection pulse 501 and the start timing of the second selection pulse 502 are performed at the same timing. . Now the polarity is 1
Since each row is inverted, the first selection pulse 50
The direction of the change in the potential at the end of 1 and the direction of the change in the potential at the beginning of the second selection pulse 502 become the same, and the signal is transmitted to the signal electrode via the liquid crystal which is a capacitive load. When the correction is not performed, the data 504 output from the signal electrode becomes a waveform 505 of the signal electrode including a whisker-like pulse in which noise of switching the selection pulse appears through the capacitive load.

According to the present invention, the signal electrode drive circuit 111
The signal 506 from the power supply for determining the output potential of the signal electrode 506 is applied so as to cancel the beard pulse at a timing corresponding to the beard pulse of the signal electrode waveform 505 including the beard pulse, such as V3 and V4 shown in FIG. Therefore, the voltage 507 applied to the liquid crystal is a signal without a whisker-like pulse that causes crosstalk.

FIG. 6 shows the selection pulses 601 to 604 and the correction signal 605 when the polarity of the selection pulse is inverted every two rows. In the figure, the timing 606 at which the polarity is inverted,
At 608, the control signal is switched, and at the timing 607 when the polarity is not inverted, the control signal is not switched.

FIG. 7 shows a correction signal when switching between adjacent selection pulses is performed at different timings. In the figure, the switching edges of the selection pulses 701 to 703 are performed at different timings, and the polarity of the correction signal in this case is inverted at the switching edge of each selection pulse. Accordingly, a differentiated waveform such as 705 obtained by differentiating the pulse 704 is applied.

[0025]

As is apparent from the above description, according to the present invention, it is possible to cancel the potential fluctuation of the signal electrode due to the selection pulse of the scanning electrode. Because it is caused by the capacitance, it does not depend on the video data and has a predictable value in advance.Therefore, a high-speed current detection circuit is not required, and the energy can be corrected in accordance with the potential fluctuation due to the capacitive coupling. An extremely high-speed control circuit is not required. Therefore, the circuit configuration is relatively simple, the number of components can be reduced, and a good crosstalk correction circuit can be provided with inexpensive circuit components.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a configuration of a control circuit.

FIG. 3 is a timing chart of signals of various parts of the control circuit.

FIG. 4 is an equivalent circuit diagram of the liquid crystal display device.

FIG. 5 is a diagram showing the operation of the present invention.

FIG. 6 is a diagram illustrating the operation of one embodiment of the present invention.

FIG. 7 is a diagram illustrating the operation of one embodiment of the present invention.

FIG. 8 is a diagram showing a cause of crosstalk conventionally considered.

[Explanation of symbols]

 Reference Signs List 101 video signal 102 timing generation circuit 103 control circuit 109 liquid crystal display device 110 scan electrode drive circuit 111 signal electrode drive circuit 112 power supply circuit 201 operational amplifier 202 resistor 203 capacitance 401 to 404 scan electrode 405 to 408 signal electrode 409 capacitance load (liquid crystal) 501-503 selection pulse 504 data signal 505 signal electrode potential before correction 506 cancellation signal 507 signal electrode potential after correction 601-604 selection pulse 605 correction signal 701-703 selection pulse 704 correction signal 705 cancellation signal 801-804 selection pulse 805 All white (black) data signal 806 Data signal that is black and white inverted for each row

Claims (3)

(57) [Claims] 1. A liquid crystal display element formed by a liquid crystal layer and a scanning electrode and a signal electrode provided on both sides of the liquid crystal layer, a display signal being input, and a pulse signal having a time width corresponding to the display data. And a scanning electrode driving circuit that sequentially outputs a selection pulse to the scanning electrodes and scans each scanning electrode, in the liquid crystal display device, which is output from the signal electrode driving circuit. A differential pulse obtained by differentiating a correction pulse having a peak value corresponding to the peak value of the selection pulse to a power supply for determining a signal potential of the pulse signal to be applied, in accordance with the rising or falling timing of the selection pulse. A liquid crystal display device comprising an application unit. 2. When the end of the selection period of the selected scanning electrode is different from the start of the next selection period, the differential pulse applying means applies the differential pulse at each rising and falling of each selection pulse. The liquid crystal display device according to claim 1, wherein: 3. When the end of the selection period of the selected scanning electrode is the same as the start of the next selection period, the differential pulse applying means is configured to select the selection pulse of the selected scanning electrode and the next scanning electrode. 2. The liquid crystal display device according to claim 1, wherein the differential pulse is applied only when the selection polarity of the selection pulse is different.