JPH07295511A - Driving method for liquid crystal display device - Google Patents

Abstract

PURPOSE:To enable low-voltage driving and to reduce the size and cost of the device by supplying a signal voltage to one electrode of a capacitor as a storage means and then varying the voltage of the other electrode. CONSTITUTION:This device has the electrostatic capacitor as the signal storage means for one line, a control circuit which controls the potential of one electrode of the electric capacitor, and a switching transistor(TR) 16 which transfers a signal from the capacitor to a data line 17. A horizontal scanning circuit 12 makes a scan with pulses phiHn and a signal equipment to one line is stored in the capacitor as the storage means from a common signal line 14. When negative polarity is written, phi cap of the common electrode potential control means for the capacitor is turned ON in blanking periods of horizontal scanning to vary the potential Vcap of the common electrode of the capacitor from V1 to V2. When positive polarity is written, the signal is held in the capacity by the scanning of the horizontal scanning circuit 12 and then phiT is turned ON while the capacitor common electrode potential Vcap is still V1. Consequently, the signal held in the capacitor is transferred to a signal line as it is.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a liquid crystal display device, and more particularly to a method of driving an active matrix type liquid crystal display device in which a plurality of pixels are arranged in a matrix and a switching element is arranged in each pixel.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been put to practical use in many fields such as various displays such as word processors and personal computers, electronic viewfinders such as video cameras, projection televisions, and vehicle-mounted televisions. Further, there is a demand for further high-quality image display with a large screen and high definition.

FIG. 7 shows a schematic configuration diagram when such a liquid crystal display device is used as a television. 7, 71 is a vertical shift register, 72 is a horizontal shift register, 73 is a switching transistor, 74 is a common signal line, 30 is a signal inversion circuit, 40 is a clock oscillation circuit, 100 is a liquid crystal panel, V1, V2, ... Vm-1,
Vm are address signal lines, D1, D2, ..., Dm, respectively.
Reference numerals -1, Dn are vertical data signal lines, S is a signal having image information, and S'is an output signal having image information output from the signal inverting circuit 30.

The vertical data signal lines D1 to Dn are each connected to a signal line 74 via a horizontal transfer switch 73, and the gate of the horizontal transfer switch 73 receives the signal from the horizontal scanning circuit 72 as a signal from the clock oscillation circuit 40. A signal is supplied based on The signal from the clock oscillation circuit 40 is also supplied to the vertical scanning circuit 71, and in synchronization with the signal S, the address signal lines V1 to Vm are sequentially driven. Further, the signal from the clock oscillation circuit 40 is input to the signal inverting circuit 30, and the signal S is inverted in synchronization with the signal S. The clock oscillation circuit 40 is normally synchronized with the signal S by inputting a synchronization signal (not shown) generated by using the signal S having image information.

That is, the vertical scanning circuit 71, the horizontal scanning circuit 72, and the signal inverting circuit 30 perform desired television scanning by the pulse generated by the clock generator 40.

In the liquid crystal panel 100, a pixel column is selected by the address signal lines V1 to Vm from the vertical scanning circuit 71, and the horizontal transfer switch 73 is sequentially driven by the driving pulses H1 to Hm of the horizontal scanning circuit 72 to generate a vertical data signal. The lines D1 to Dn are selected, and the image signal is input to each pixel.

As described above, the input side of the horizontal transfer switch 73 is connected to the signal inverting circuit 30 via the common signal line 74. The signal inversion circuit 30 is a circuit for converting an input image signal into an AC drive signal in order to prevent deterioration of liquid crystal characteristics. Regarding AC driving of liquid crystal, frame inversion, field inversion, 1h (horizontal scanning period) inversion, bit (pixel by pixel) inversion and the like are known.

FIG. 8 is a timing chart for explaining an example of the output signal S'from the signal inverting circuit. In FIG. 8, the signal S having the input image information is inverted every 1h to be an output signal S '. In FIG. 8, V1c is the common electrode potential, Vd1 is the black level of the negative image signal, Vw1 is the white level of the negative image signal, and Vw is
dh is the black level of the positive polarity image signal, and Vwh is the white level of the positive polarity image signal.

Since the signal inversion generates a symmetrical image signal with reference to the common electrode potential V1c, the overall signal amplitude (Vd
1 to Vdh) is twice Vd1 to V1c, for example, Vd1 and Vd
If the potential difference from 1c is about 5V, about 10V is required.

As described above, since the driving method as described above requires a large driving voltage, the driving element of the liquid crystal display device is required to have a high withstand voltage, and the other wirings are also required to have a high withstand voltage design. This leads to a reduction in yield of the liquid crystal display device, an increase in cost, and an increase in power consumption.

Among these, there is a method of inverting the potential of the common electrode and driving at a low voltage (Japanese Patent Laid-Open No. 54-985).
25). However, since the pixel portion has a large electric capacity, the potential cannot be inverted well. For example, when a liquid crystal display device having 300,000 pixels is manufactured, the total capacity of the liquid crystal and the storage capacity is 100 fF per pixel. If this extends over 300,000 pixels of 600 horizontal × 500 vertical, 30n
It becomes a large capacity of F, and it is difficult to reverse this potential in an instant. Therefore, the change in the common potential cannot be properly pulsed. In addition, power consumption also increases.

Further, in the method described in Japanese Patent Application Laid-Open No. 1-138590, the common electrode of the liquid crystal and the common electrode of the storage capacitor are separated, and the reversal potential is applied only to the common electrode of the liquid crystal. In this case, since the capacitance of the liquid crystal is smaller than the storage capacitance, even if the common electrode potential of the liquid crystal is inverted, the image signal voltage applied to the liquid crystal does not change much. Therefore, the normal voltage is not applied to the pixel electrode. In order to prevent such a problem from occurring, it is necessary to make the storage capacity sufficiently smaller than the liquid crystal capacity, but in that case, the capacity of one pixel becomes small and it becomes difficult to hold the signal voltage, resulting in poor image display performance. Deteriorates.

[0013]

As described above, in the conventional driving method of the liquid crystal display device, since the AC signal which is positive / negative inversion with respect to the common potential is required, the signal amplitude becomes large and the signal processing IC, The liquid crystal display panel, other peripheral circuits, wiring, etc. need to be designed to have a high withstand voltage, which causes a problem that the liquid crystal display device becomes large in size and high in cost.

The present invention has been made in view of the above problems, and it is possible to realize a liquid crystal display device which can be driven at a lower voltage and which can be downsized and reduced in cost. The purpose is to propose a driving method.

[0015]

As a result of the inventors' earnest efforts to solve the above problems, the following inventions have been obtained in a method of driving a liquid crystal display device.

That is, according to the present invention, a liquid crystal having a plurality of pixels to which a signal that inverts at an arbitrary cycle is applied and an electric capacitance for each data line as a storage means capable of holding a signal for one line or more. In the driving method of the display device, after supplying a signal voltage to one electrode of the electric capacitance, the voltage of the other electrode of the capacitance is changed, which is a driving method of the liquid crystal display device.

As a result, low voltage driving becomes possible,
It is possible to reduce the size and cost of the device.

[0018]

EXAMPLES Examples of the present invention will be described below with reference to FIGS.
Will be explained.

(First Embodiment) FIG. 1 is an equivalent circuit diagram showing one embodiment of the present invention. In FIG. 1, it has an electric capacity as a signal storage means for one line, a control circuit for controlling one electrode potential of this electric capacity, and a switching transistor 16 as a means for transferring a signal from the capacity to the data line. The operation of this embodiment will be described below.
Here, it is assumed that the polarity of the signal is inverted line by line. In this embodiment, according to the timing shown in FIG.
First, the horizontal scanning circuit is scanned with a pulse of φHn, and a signal for one line is stored from the common signal line 14 in the capacitor as a storage unit. Then, in the case of writing the negative polarity, φcap of the common electrode potential control means of the capacitance is turned on in the blanking period of horizontal scanning, and the potential Vcap of the common electrode of the storage capacitance is changed from V1 to V2. Changes in the signal waveform applied to the pixel are shown in FIG. The waveform of FIG. 3A is set so that the signal processing circuit can be driven at a low voltage. In the present invention, the negative polarity side of the signal is shifted to change it to a desired signal amplitude (Vw1 'to Vdl' is shown in FIG.
(B) shift from Vwl to Vdl). After that, the signal transfer switch φT is turned on to transfer the signal to the signal line. When the positive polarity is written in the next horizontal scanning period, after the signal is held in the storage capacitor by the scanning of the horizontal scanning circuit in the same manner, the capacitance common electrode potential Vcap remains V1 as can be seen from the timing of FIG. , ΦT are turned on. As a result, the signal held in the storage capacity is directly transferred to the signal line. As described above, AC driving of the liquid crystal panel is possible even if the signal amplitude that can be transferred by the signal processing circuit is small.

(Second Embodiment) FIG. 4 is an equivalent circuit diagram showing a second embodiment according to the present invention. In this embodiment,
As a signal transfer means to the signal line, a signal transfer circuit that can shift the signal amplitude that can be transferred by the reference potential Vref is used. Here, as in the example of FIG. 1, the potential control circuit shifts the signal level and simultaneously changes the reference potential of the signal transfer circuit to control the transferable signal amplitude. Conceptually, the transferable signal amplitude is shifted symmetrically around the common potential V _LC as shown in FIG. As a result, even if the transferable signal amplitude of the signal transfer circuit is small, it becomes possible to effectively cope with AC driving of the liquid crystal, which is very advantageous in terms of design such as breakdown voltage.

(Third Embodiment) FIG. 6 shows a third embodiment of the present invention.
It is the equivalent circuit schematic which showed the Example. In this embodiment, FIG.
In the above example, a means for controlling the voltage of the data line is added. In general, a signal line has a certain capacitance value, and thus holds a signal even after the signal is written to a pixel. At this time, when the transferable signal amplitude of the signal transfer circuit changes in the next horizontal scanning, a potential difference occurs between the input end and the output end. This may cause damage or malfunction of the signal transfer circuit. In order to prevent this, this embodiment is provided with a control means capable of setting the potential of the signal line to an arbitrary value. With this control means, the potential of the signal line can be temporarily fixed to a level at which the signal transfer circuit is not destroyed or malfunction, and the reliability can be improved.

[0022]

As described above, according to the driving method of the present invention, the amplitude of the input image signal can be reduced by controlling the electrode potential of one of the capacitors as the signal storage means, and the peripheral processing IC It becomes possible to reduce the size and cost of the device by designing the above as a low voltage.

Further, unlike the one in which the potential of the common electrode is inverted, each pixel has an electric capacity of about 10 pF. However, since the electric charge accumulated in this electric capacity is rewritten every scanning of one line. The capacity is required only for one line. That is, even in a liquid crystal display device of 600 × 500 × 300,000 pixels, it suffices to invert the potential of a small electric capacitance of 10 pF × 600 = 6 nF, the potential can be successfully changed in a pulse shape, and the voltage drop can be achieved. small. Therefore, power consumption is small.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram according to a first embodiment of the present invention.

FIG. 2 is a timing diagram for explaining the operation of the present invention.

FIG. 3 is a conceptual signal waveform diagram for explaining an image signal waveform of the present invention.

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

FIG. 5 is a conceptual signal waveform diagram for explaining the operation of the second embodiment of the present invention.

FIG. 6 is an equivalent circuit diagram according to a third embodiment of the present invention.

FIG. 7 is a schematic configuration diagram of a conventional liquid crystal display device.

FIG. 8 is a signal waveform diagram for explaining an image signal waveform of a conventional liquid crystal display device.

[Description of Reference Signs] 11, 41, 61, 71 Vertical scanning circuit 12, 42, 62, 72 Horizontal scanning circuit 13, 43, 63, 73 Signal transfer switching transistor 14, 44, 64 Common signal line 15, 45, 65 Electric capacitance 16 Switching transistor 17, 47, 67 Data line 18, 48, 68 Horizontal scanning line 19, 49, 69 Pixel electrode 46 Signal transfer circuit

Claims (3)

[Claims] 1. A liquid crystal display device having a plurality of pixels to which a signal that inverts at an arbitrary cycle is applied, and an electric capacitance for each data line as a storage means capable of holding a signal for one line or more. In the driving method, after supplying a signal voltage to one electrode of the capacitance, the voltage of the other electrode of the capacitance is changed. 2. The method of driving a liquid crystal display device according to claim 1, wherein the transferable signal amplitude of the signal transfer circuit from the storage unit is changed at the same time that the voltage of the other electrode of the electric capacitance is changed. 3. The method for driving a liquid crystal display device according to claim 2, further comprising means for fixing the potential of the signal line to an arbitrary voltage.