JPS6151774B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a driving device for a liquid crystal display device, and more particularly to a circuit for reducing waveform distortion of a driving voltage.

Conventionally, it has been known to AC drive a liquid crystal matrix panel using a line sequential scanning method and a voltage averaging method. Previously, we proposed the system shown in FIG. 1 as a circuit that specifically implements this type of drive system. (Japanese Patent Application No. 51-112994) In FIG. 1, scanning voltages and signal voltages are applied to scanning electrodes 2 and signal electrodes 3 of liquid crystal panel 1 from electronic switch circuits 5a and 5b. The electronic switches 6a, 6b and 7a, 7b of the electronic switch circuits 5a, 5b output selection voltages V _S1 , V _S2 and non-selection voltages V _NS1 , V _NS2 by opening and closing the switches. On the other hand, signals for opening and closing the electronic switch are obtained by the scanning circuit 4, the serial/parallel conversion circuit 10, and the line memory 9. Here, the selection voltage V _S1 and the non-selection voltage V S1 applied to the electronic switches 6a and 6b on the scanning side are
The selection voltage V _S2 and non-selection voltage V _NS2 to be applied to _NS1 and the signal side electronic switches 7a and 7b are generated by a drive voltage generation circuit 11. We have proposed the drive voltage generation circuit shown in Fig. 2 (Patent Application No. 52-
No. 67044) The circuit shown in FIG. 2 is composed of a resistive voltage divider circuit 12a and an electronic switch circuit 14a. The resistor voltage divider circuit 12a has V0 to V4 necessary for matrix drive.
Generates a voltage of These voltages are applied to electronic switch circuits 14b and 14c. Further, by applying a selection signal CP to the selection signal input terminal 13 and alternately opening and closing the electronic switch, selection voltages V _S1 , V _S2 and non-selection voltages V _NS1 , V _NS2 are generated. In Figure 3,
Selection signal CP and selection switch output terminal 14d~1
The relationship between the voltages appearing at 4g is shown.

By the way, the voltage V0 to V of the resistive voltage divider circuit 12a
4 fluctuates during the transition between the rise and fall of the selection signal CP, as shown in FIG. This is the stray capacitance C _O in the selection switch, and the capacitance C _C of the liquid crystal.
This is due to the charge/discharge circuit formed by the resistance of the resistor voltage divider circuit. As a result of this voltage variation, the voltage applied to the liquid crystal becomes as shown in FIG. The figure is 1
As an example, the voltage applied to a non-lit pixel is shown. The voltage waveform distortion shown here changes depending on the number and type of characters displayed on the liquid crystal panel. this is,
This causes crosstalk, contrast fluctuations, and asymmetric voltage waveforms that increase the DC component, causing deterioration of the liquid crystal panel. On the other hand, in order to reduce this waveform distortion, it is necessary to lower the resistance of the resistive voltage divider circuit. However, this increases the power consumption of the device, which is undesirable.

An object of the present invention is to solve the conventional problems and provide a liquid crystal display device with low power consumption.

To summarize the features of the present invention, during a transient period when the potentials of the selection voltage and the non-selection voltage change,
It changes the resistance value of the resistor voltage divider circuit during steady state. This is equipped with a resistance voltage divider circuit made of high resistance and a resistance voltage divider circuit made of low resistance, and voltages of the same potential are applied from each resistance voltage divider circuit to two pairs of electronic switches. Then, during a transient period, a low resistance measurement is selected, and during a steady state, a high resistance measurement is selected. Furthermore, the time for selecting the low resistance measurement is set so that at least the waveform distortion is sufficiently small.

Examples of the present invention will be described below.

FIG. 6 shows a concrete embodiment of the present invention. Between the power supply terminal 15 and GND, there is a variable resistor 17a and a resistive voltage divider circuit connected to it.
There is (1) 17 and a resistor voltage divider circuit (2) 18. The resistor voltage divider circuit (1) 17 is composed of resistors 17b to 17f, and the ratio of each resistor is set to 1:1:(a-
4): Set to 1:1. On the other hand, resistor voltage divider circuit (2)
18 is composed of resistors 18a to 18e,
Voltage is supplied via an electronic switch 19. This electronic switch 19 is opened and closed by a cutoff signal CP1 supplied to the cutoff signal input terminal 16. In addition,
The ratio of each resistor is the same as that of the resistor voltage divider circuit (1) 17. Here, the resistance R _a of the resistance voltage divider circuit (1) 17 is set higher than the resistance R _b of the resistance voltage divider circuit (2) 18. In addition, two electronic switches can be used to create two pairs of electronic switches.
Configure 2i. From the above, if the highest voltage of the resistive voltage divider circuit is the voltage V ₀ , the voltage at each point is (1-1/a)·V ₀ , (1-1/a) required for matrix drive.
2/a)・V ₀ , 2/a・V ₀ , 1/a・V ₀ .

Of the voltages obtained by the resistance voltage divider circuit, the voltages with the same potential are applied to the electronic switch 2 of the electronic switch circuit 22.
Add to 2a-22f. Voltage (1-1/a)・V ₀
are electronic switches 22a and 22b, (1-2/
a)・V ₀ is electronic switch 22c and 22d, 2/
a・V ₀ are electronic switches 22e and 22f, 1/
a·V ₀ is supplied to 22g and 22f, respectively.

Each electronic switch has two voltage selection signal input terminals.
0 voltage selection signal CP2 and inverter 2
It is opened and closed by CP2 after passing through 1. As a result, the voltages appearing at the voltage output terminals 23a to 23d of the electronic switch always have the same potential.

The voltage obtained by the above operation is supplied to the electronic switch circuit 14a shown in FIG. On the other hand, Fig. 7 shows the control signals CP1 and CP necessary for Fig. 6.
2 and a time chart of the selection signal CP shown in FIG. Fluctuations in each voltage of the resistor voltage divider circuit occur during transitions at the rise and fall of the selection signal CP. In other steady states, the voltage is divided by the resistors. In order to shorten this voltage fluctuation time and reduce drive waveform distortion, the electronic switch 1 shown in FIG.
Close 9. Furthermore, among the electronic switches of the electronic switch circuit 22, 22a, 22c, 22e, 22
Close g and open the other switch. This is controlled by voltage selection signal CP2. As a result, the resistance value of the resistance voltage divider circuit as seen from the selection switch circuit 22 becomes low only during the time ΔT. As a result, the charging and discharging time due to the capacitances C _O and C _C and the resistance of the resistance voltage divider circuit is shortened, and the voltage fluctuation resistance can be shortened.

On the other hand, during a steady state other than the time ΔT, the electronic switch 19 is opened to reduce the power consumption in the resistance voltage divider circuit. Note that in order to satisfy the optimum conditions for driving the liquid crystal matrix, adjustment is performed using the resistor 17d and resistor 18c, and brightness adjustment is performed using the resistor 17a.

FIG. 8 shows a modification of the present invention. Among the voltages obtained by the resistance voltage divider circuit, the voltage fluctuations of (1-2/a)·V ₀ and 2/a·V ₀ are the most remarkable. This is because the resistance of the resistance voltage divider circuit as seen from the selection switch circuit is larger than other circuits, and the charging/discharging time becomes longer. Therefore, the voltage necessary for matrix driving is obtained by the resistive voltage divider circuit (2) 25 and the resistive voltage divider circuit (1) 24 that obtain both of the voltages described above. Further, switching of the voltage is performed by the selection switch circuit 26. In addition, the time chart of signals CP1 and CP2 is the 7th
It is similar to the figure. As a result, the circuit can be simplified,
Drive waveform distortion can be reduced.

According to the present invention, distortion of the drive waveform can be reduced without impairing the characteristics of the resistive voltage divider circuit conventionally used to obtain the voltage necessary for driving the liquid crystal matrix. Furthermore, the power consumption of the resistive voltage divider circuit can be reduced. This makes it possible to prevent the occurrence of crosstalk and to eliminate variations in contrast. Furthermore, the DC voltage component can be lowered and deterioration of the liquid crystal panel can be prevented. Furthermore, power consumption of the drive device can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a liquid crystal matrix panel driving device according to the prior art, FIG. 2 is a circuit diagram of a driving voltage generation circuit according to the prior art, and FIG. 3 is a voltage waveform obtained by the circuit shown in FIG. 2. , Figure 4 is
The voltage waveform at each point of the resistor voltage divider circuit shown in Figure 2,
FIG. 5 is an example of a voltage waveform applied to a liquid crystal, FIG. 6 is an embodiment of the present invention, FIG. 7 is a time chart of the signal shown in FIG. 6, and FIG. 8 is a diagram of an embodiment of the present invention. This is a modified example. 17a to 17f...Resistance, 18a to 18e...
Resistor, 19...electronic switch, 21...inverter, 22 (22a to 22h)...electronic switch circuit.

Claims (1)

[Claims] 1. In a liquid crystal display device having a liquid crystal panel and a driving device for driving the liquid crystal panel, a voltage generating circuit included in the driving device is constituted by two resistor groups each having a plurality of resistors connected in series. , are connected in parallel between a pair of potential terminals, and two voltages of the same potential between the potential terminal and the resistor connection are input to a two-pair electronic switch, and the voltage required for matrix drive is generated by opening and closing the two-pair electronic switch. A liquid crystal display device characterized by generating. 2. In the liquid crystal display device according to claim 1, at least one electronic switch is provided in series with the resistor in at least one of the resistor groups, and the electronic switch is activated in synchronization with opening and closing of the two-pair electronic switch. A liquid crystal display device characterized by opening and closing. 3. A liquid crystal display device according to claim 1, wherein one of the resistor groups has a high resistance and the other resistor group has a low resistance. 4. In the liquid crystal display device according to claim 1, the two-pair electronic switch switches one of the resistance groups for a certain period of time ΔT during a transition in which the selection voltage and non-selection voltage potentials generated in the drive device change. The low resistance side is selected, and at other times, the two-pair electronic switch selects the high resistance side of the resistance group and disconnects the low resistance side of the resistance group from the potential terminal. LCD display device.