JPS61148492A - Method and apparatus for controlling liquid crystal display unit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Applications Liquid crystal displays are used in many devices to display information. However, the visibility of the display depends on the angle (hereinafter referred to as viewing angle) when observing this type of display device.
depends on. When viewed approximately perpendicular to the plane of the display, the contrast of the display is actually large when the field of view is small.

The larger the angle of deviation from the vertical, for example when the field of view is 5° to 60°, the contrast will depend on the direction in which the deviation is performed.

Problems to be Solved by the Invention This is particularly inconvenient if the liquid crystal display device is to be viewed from various directions, for example in a car radio.

It is therefore an object of the invention to reduce this directional dependence so that the contrast and therefore the visibility of the liquid crystal display device when viewed from various directions is as high as possible.

Means for Solving the Invention The above-mentioned problem is solved by the configuration described in the characterizing part of claim 1. The method according to the invention has the advantage that the visibility of the liquid crystal display from the widest possible viewing angles is guaranteed to a large extent independent of direction.

For example, a liquid crystal display device controlled by the present invention incorporated into a car radio can be read from either the driver's seat or the passenger's seat as long as the vehicle is in a normal seating position.

The device of the present invention is described in claims 6 and 7.

Embodiments Examples of the present invention will be explained in detail in the following description based on the drawings.

The polar coordinate diagram shown in FIG. 1 shows the contrast of a liquid crystal display device as radii in the direction in which it is viewed. The degree of viewing angle is selected as a parameter.

When the viewing angle is small, that is, when viewed almost vertically, the contrast is almost close to 100y, regardless of the viewing direction. It is depicted by curve 1.

When the viewing angle is 55 degrees, the contrast has a dip. There is one case in particular where the direction is 60 to 70 degrees. As can be seen from curve 2, the contrast in this case drops to about 40%, and the visibility of the display is no longer guaranteed, especially in unfavorable lighting conditions. However, this is precisely the angle from which the normal seating position 1 is observed from the passenger seat of a passenger car, if the car radio is installed in the center lower part of the instrument panel.

Curve 3 shows the change in contrast when using the method of the invention. In that case, the minimum contrast value is about 60%, which greatly contributes to the visibility of the display device.

FIG. 2 shows an apparatus for carrying out the inventive method. In this device, a triangular or sawtooth wave voltage is applied to the back electrode - also called the pack plane, and this voltage continuously changes between the extreme values of +6.5■ and -6.5■. It has a changing part. This voltage is generated by a function generator 4, which is known per se, and is supplied via a coupling capacitor 5 to a rear electrode 6 of a liquid crystal display 7, which is diagrammatically shown in cross section 1.

The segment electrode 8 is connected via a switch 9 to another output of the function generator. When the switch 9 is in the upper position, the same voltage as the voltage on the back electrode 6 is applied to the segment electrode 8 . In other words, the liquid crystal is not exposed to an electric field, and light can pass through the liquid crystal.

Next, when the switch 9, which is usually an electronic switch, is moved to the lower position, a ground potential is applied to the segment electrode 8.

In other words, a voltage exhibiting the illustrated change is applied between the back electrode 6 and the segment electrode 8. Liquid crystal molecules change their molecular arrangement and therefore no longer transmit light.

The liquid crystal follows changes in electric field strength, passing through good and poor viewing angle regions at the frequency of the change in electric field strength. This frequency should be higher than the flicker limit. Values of 35 to 50 Hz have proven advantageous in that case.

The upper limit of this frequency is determined by the inertia of the liquid crystal. At low temperatures, the inertia of the liquid crystal is such that a reduction in frequency may be advantageous. For this purpose, a temperature-dependent resistor 10 can be provided in the frequency determining circuit of the function generator 4.

A device similar to the device according to FIG. 2 is shown in FIG. However, the function generator 11 has at its disposal two outputs with opposite signals. The back electrode 6 is permanently connected to one output side, and the segment electrode 8 can be selectively connected via a switch 12 to the first or second output side.

In the upper switch position the electric field strength is zero. In other words, liquid crystals are transparent. When switch 12 is in the lower position, a negative sequence voltage is applied to the electrodes. The voltage applied to the liquid crystal exhibits the changes shown. The amplitude is twice as large as the one shown! be.

FIG. 4 shows the apparatus according to FIG. 2 in some detail. In the case of the device according to FIG. 4, instead of the switch 9, a resistor 17.
18.19 and field effect transistors 20, 21.
22 is provided.

Signals for controlling the liquid crystal display are supplied via inputs 23, 24, 25. Depending on the values of these signals, the field effect transistors 20, 21, 22 are controlled to be conductive or non-conductive. Segment electrode 1 connected to the field effect transistor 20.21.22
4.15.16 turns black when the field effect transistor is in a conductive state.

Other curved waveforms are also possible instead of the voltage changes shown in the figure. For example, a sinusoidal voltage can also be used.

Effects of the Invention According to the present invention, the directional dependence of the viewing angle of the liquid crystal display device can be reduced, the contrast of the liquid crystal display device can be increased, and the visibility can be increased.

[Brief explanation of drawings]

Fig. 1 is a polar coordinate diagram for illustrating the difference in the directional dependence of the contrast of a liquid crystal display device depending on whether the method of the present invention is used, and Fig. 2 is a route diagram of an example of a device in which the method of the present invention is implemented. , FIG. 3 is a route diagram of a variant embodiment implementing the method according to the invention, and FIG. 4 is a detailed circuit diagram of the apparatus according to FIG. 2. 4...Function generator, 6...Back electrode, 7...Liquid crystal display device, 8.14.1.5.16...Segment electrode

Claims (1)

[Claims] 1. A method for controlling a liquid crystal display device, characterized in that the voltage between the electrodes temporarily assumes not only two limit values but also a plurality of values between the limit values. 2. A method according to claim 1, in which a continuous voltage change is carried out between limit values. 3. A method according to claim 1, in which stepwise voltage changes are carried out between limit values. 4. The method according to claim 1, wherein the voltage change is performed periodically. 5. If the segment electrodes do not transmit light, a voltage of opposite phase to the segment electrodes is applied to the back electrode of the liquid crystal display device.
5. The method according to claim 4, wherein in-phase voltages are applied when the segment electrodes transmit light. 6. A function generator (4) is provided, the output side of which is connected to the back electrode (6) of the liquid crystal display (7), and a switch (9) is connected to each of the segment electrodes (8) of the liquid crystal display. A device for controlling a liquid crystal display device, characterized in that the switch selectively connects the segment electrode (8) to the output of the function generator (4) or to a point having a constant potential. 7. A function generator (11) is provided, the first output side of which is connected to the back electrode of the liquid crystal display (7);
A switch (
9) is provided, and the switch allows segment (8)
on the first output side of the function generator (11) or the function generator (
The function generator (11) is selectively connected to the second output of the function generator (11), so that the second output side of the function generator (11) is supplied with a signal having an opposite phase to the signal on the first output side. A device that controls a liquid crystal display device.