JPS6231349B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a driving device for a liquid crystal display device that drives a liquid crystal panel using a line sequential scanning method.

In order to drive a matrix type liquid crystal panel and display arbitrary characters, line drawings, etc., a scanning method called a line sequential scanning method is generally used. FIG. 1 shows the structure of a conventional driving device for such a liquid crystal display device, and the following description will be made with reference to this drawing.
Reference numeral 1 in FIG. 1 is a liquid crystal matrix panel, which has a group of orthogonal electrodes, one of which is used as a scanning electrode and the other as a signal electrode. 2 is a drive circuit array for scanning electrodes, and 3 is a drive circuit array for signal electrodes. 4
is a scanning circuit, which sequentially issues a scanning output at a constant period to a drive circuit for each scanning electrode. Further, 5 is a line memory, 6 is a serial/parallel conversion circuit, and 7 is an image signal input terminal. The image signal input in the form of a serial signal to the image signal input terminal is converted into serial/parallel data and given to the line memory 5, and the contents of each memory bit of the line memory 5 are stored in the drive circuit array 3 for the signal electrode. It is output to each constituent drive circuit.

Here, each drive circuit constituting the scan electrode drive circuit array 2 outputs a selection voltage when receiving a scan output from the scan circuit 4, and at other times outputs a non-selection voltage in a predetermined waveform. Further, each of the drive circuits constituting the drive circuit 3 outputs either a selection voltage or a non-selection voltage with a waveform determined according to the contents of each memory bit of the line memory 5. On the other hand, the liquid crystal located at each intersection point (generally called a picture element) of the matrix of a liquid crystal matrix panel has a selection voltage applied to the corresponding signal electrode every cycle when a selection voltage is applied to the corresponding scanning electrode (in this state (referred to as a selected state) is excited, thereby selectively displaying a plurality of picture elements.

However, it is preferable to drive the liquid crystal matrix panel as described above using the voltage averaging method, which will be explained later. The circuit has a relatively complex configuration.

Furthermore, circuit constants vary depending on the specifications of the liquid crystal display device, making standardization relatively difficult.

The present invention connects an electronic switch to each electrode,
The drive signal is generated by a small number of drive circuits, and the drive signal is selected by selecting an electronic switch, and the electronic switch connected to each electrode simplifies and standardizes the drive circuit of the liquid crystal display device. It tries to make it easier.

A feature of the present invention is that two parallel electronic switches are connected to each of the scanning electrode and the signal electrode, and only one of them is always closed and the other is open, and the control is performed by the scanning circuit and line memory. This is done by the output of the electronic switch, and the input of the electronic switch is
A selection voltage is applied to one side and a non-selection voltage is applied to the other side, and the selection voltage and the non-selection voltage are generated by a common drive circuit. Therefore, each electrode is connected to an electronic switch with the same circuit configuration, and only a small number of drive circuits need to be configured according to the specifications, which simplifies the drive circuit of the liquid crystal display device and facilitates standardization. .

Another feature is that in the above drive circuit, the selection voltage of the scanning electrode is V ₁₁ +V ₀ or
V ₁₁ ′−V ₀ , V ₁₁ +1/aV ₀ or V ₁₁ ′1/aV ₀ as the non-selection voltage of the scanning electrode, V ₁₁ or V ₁₁ ′ as the selection voltage of the signal electrode, V as the non-selection voltage of the signal electrode ₁₁ +2/aV ₀ or V ₁₁ '-2/aV ₀ . Here, V ₀ is the amplitude of the AC voltage applied to the picture element in the selected state, V ₁₁ is an arbitrary voltage, a is an arbitrary constant, and when the duty ratio is 1/N, the constant a is √
It is desirable to set it near +1.

FIG. 2 explains the principle of the drive circuit according to the present invention. Two electronic switches 12 and 13 are connected in parallel to the scanning electrodes of the liquid crystal matrix panel 11, one of which is always closed and the other open. The drive circuit 14 connected to SX ₁₁ , SX ₂₁ , ... applies a selection voltage to the scan electrode, and the drive circuit 15 connected to SX ₁₂ , SX ₂₂ , ... applies a non-selection voltage to the scan electrode. If added, the electronic switches SX ₁₁ , SX ₂₁ , . . . are sequentially closed by the signals of the scanning circuit according to the line-sequential scanning method. In addition, the signal electronic switch 1
A selection voltage is applied to the signal electrode by a drive circuit 18 connected to SY ₁₁ , SY _{21 ,} . _. . Assuming that a non-selection voltage is applied to the electrodes, one of the electronic switches SY ₁₁ , SY ₁₂ or SY ₂₁ , SY ₂₂ is closed in accordance with the image signal to apply the driving voltage.

Here, the waveforms of each selection voltage and non-selection voltage will be explained. In order to prevent unevenness in the excited state of the liquid crystal due to the display pattern, driving using a voltage averaging method is necessary. Figure 3 is a state diagram for explaining the general conditions of the voltage averaging method, where V _X is the voltage applied to the scanning electrode, V _Y is the voltage applied to the signal electrode, and V _X - V _Y is the voltage applied to the scanning electrode. , indicates the voltage applied to the liquid crystal, A is the selected state, B and C are the half-selected state, D
indicates a non-selected state. Now, in order to drive by the voltage averaging method, the selection voltage V ₁₁ and non-selection voltage V ₁₂ of the signal electrode, and the selection voltage V ₂₁ and non-selection voltage V ₂₂ of the scanning electrode, shown in FIG. It is known that the relationship expressed by equation (1) can be used.

Furthermore, in order to drive the liquid crystal with AC,
The selection voltage and non-selection voltage of the signal electrode and scanning electrode are as follows.
The values shown in V ₁₁ , V ₁₂ , V ₂₁ , and V ₂₂ in Equation (1) are alternately changed to the values shown in Equation (2) as V ₁₁ ′, V ₁₂ ′, V ₂₁ ′, and V ₂₂ ′, respectively. All you have to do is switch. (However, V ₁₁ ′−V ₁₁ = V ₀ ) In equation (1), V ₁₁ =0, and in equation (2),
If V ₁₁ ′=V ₀ , the result will be as shown in Figure 4. Also, (1)
In the equation, V ₁₁ = -1/aV ₀ , in equation (2), V ₁₁ '=
If it is 1/a V ₀ , it will be as shown in Figure 5. Here, to explain Figures 4 and 5, A is a fully selected state, B is a half-selected state where a selection voltage is applied only to the scanning electrode, and C is a state where a selection voltage is applied only to the signal voltage. A half-selected state D indicates a non-selected state.

When the drive waveform shown in FIG. 4 is adopted, the drive circuit 14 shown in FIG. 2 emits a repetitive waveform of voltages V ₀ and O shown in states A and B on the waveform V _X shown in FIG. The drive circuit 15 is also in states C and D.
The driving circuit ₁₈ has a repetitive waveform of voltages 1/aV ₀ and (1-1/a)V ₀ shown in _FIG . It is assumed that repetitive waveforms of voltages 2/aV ₀ and (1-2/a)V ₀ shown in states B and C are generated, respectively.

Even when the drive waveform shown in FIG. 5 is adopted, if the same steps as in the case of _FIG . Since the drive circuit 15 only needs to generate a ground level, this terminal is grounded. It is assumed that the drive circuits 17 and 18 generate alternating current waveforms of ±1/aV ₀ with mutually opposite phases. These can be easily constructed using existing circuits.

FIG. 6 shows an embodiment of the invention. An electronic switch 2 is connected to each electrode of the liquid crystal matrix panel 21.
2, 23, 26, 27 are connected, and the drive circuit 24,
Drive waveforms are generated by 25, 28, and 29. These electronic switches are controlled by line-sequential scanning by a scanning circuit 30, converting the image signal input 33 into parallel for one line by a serial/parallel conversion circuit 32, storing it in a line memory 31, and then The output signal opens and closes an electronic switch. As the electronic switch, a C-MOS circuit as shown in FIG. 7 can be used.

According to the present invention, by using an electronic switch in the driving circuit of a liquid crystal display device, driving waveforms can be obtained with a small number of driving circuits, so that the driving circuit can be simplified and standardized. Therefore, since it is only necessary to change the circuit configuration of a small number of drive circuits according to the specifications, it is possible to easily integrate the drive circuits and easily obtain a drive circuit that meets the specifications.

[Brief explanation of the drawing]

FIG. 1 shows the configuration of a drive circuit for a conventional liquid crystal display device. Figure 2 shows the configuration that is the principle of the present invention, Figure 3 shows general drive waveforms for the voltage averaging method, Figures 4 and 5 show specific examples of drive waveforms, and Figure 6. 7 shows an embodiment of the present invention. FIG. 7 is a diagram showing an example of an electronic switch used in the present invention. Explanation of symbols, 11, 21...Liquid crystal matrix panel, 12, 13...Electronic switch, 16, 1
7...Electronic switch, 14, 15... Drive circuit, 18, 19... Drive circuit.

Claims (1)

[Claims] 1. Each electrode of a liquid crystal panel has a plurality of picture elements formed by a plurality of scanning electrodes, a plurality of signal electrodes facing each other, and a liquid crystal located between them. In a device that selectively displays the picture element by voltage averaging method by driving with either a constant selection voltage waveform or a non-selection voltage waveform, the selection voltage (V ₁₁
+V ₀ or V ₁₁ ′−V ₀ , where V ₁₁ and V ₁₁ ′ are arbitrary voltages, and V ₀ is the amplitude of the AC voltage applied to the picture element in the selected state). a second drive circuit that supplies only a non-selection voltage (V ₁₁ +1/aV ₀ or V ₁₁ '-1/aV ₀ , where a is an arbitrary constant) for the scanning electrode; a first switch group consisting of electronic switches connected to selectively apply the output of one of the first and second drive circuits to each scanning electrode;
a third drive circuit that supplies only the selection voltage (V ₁₁ or V ₁₁ ') for the signal electrode; and a non-selection voltage (V ₁₁ +2/aV ₀ or V ₁₁ '-2/aV) for the signal electrode; ₀ ), and an electronic circuit connected to select and apply one of the outputs of the third and fourth drive circuits to each signal electrode. A second switch group consisting of switches is provided, and the first switch group is sequentially switched at a constant cycle, and the second switch group is selected according to the display pattern in synchronization with the switching of the first switch group. 1. A driving device for a liquid crystal display device, which is characterized by switching automatically. 2. In claim 1, the first switch group includes a first electronic switch connected to the first drive circuit and a second electronic switch connected to the second drive circuit. 1. A driving device for a liquid crystal display device, characterized in that the first electronic switch is sequentially selected at a constant period.