JPH0429049B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a static drive device for a liquid crystal display that displays halftones.

[Conventional technology]

Conventionally, static driving of a liquid crystal display involves applying a pulse signal as shown in Figure 7a to the common electrode COM.
In-phase and π/2 as shown in Figure 7b and c
This was done by applying phase-shifted pulse signals to the segment electrodes.

Therefore, for example, the common electrode is connected to the electrode S1.
When applying an in-phase pulse signal to COM,
The display element DE1 displays an OFF display, and, for example, the electrode S2 has a phase of π// with respect to the common electrode COM.
When a pulse signal shifted by 2 is applied, the display element DE
2 is displayed as ON.

[Problem that the invention seeks to solve]

Conventional static drive devices for liquid crystal displays are unable to obtain the required number of gray levels, and the resulting images therefore lack expressive power.

[Means for solving problems]

This invention was made by focusing on such conventional problems, and aims to express the necessary number of gray scales. A pulse train is generated periodically at intervals equal to the width of this pulse train and inputted to the common electrode, and the pulse position modulation means changes the pulse position of the entire group of pulse trains according to the output from the gradation detection means. The pulses are modulated and input to the segment electrodes, and gradation display is performed by the number of pulses applied to the pixels.

〔Example〕

An embodiment of the present invention will be explained based on FIGS. 1 to 5. Note that the same or equivalent parts as in the conventional example are given the same reference numerals and the description thereof will be omitted. 1st
In FIGS. 1 and 2, reference numeral 1 denotes a pulse signal generating circuit (pulse train generating means) which periodically generates a plurality of pulse trains corresponding to the required number of gradations at intervals equal to the width of the pulse train. 2 is a gradation detector (gradation detection means) that detects gradation from an image signal; 3;
is a pulse position modulator (pulse position modulation means),
A group of pulse trains from the pulse signal generator 1 is pulse position modulated. 4 is liquid crystal display (LCD)
5, the LCD driver drives the LCD display 5.
In this method, a plurality of pixels are formed by interposing a liquid crystal at the intersection of one common electrode and a plurality of segment electrodes. DEn (n=1, 2, . . . , m) is a display element constituting the liquid crystal display 5, and FIGS. 1 and 2 show display elements DE1 to DE4.

Next, the operation will be explained based on the timing chart shown in FIG.

Now, in order to express four gradations of light and shade, the pulse signal shown in FIG. 3a is input from the pulse signal generator 1 to the common electrode COM, while the pulse signal shown in FIG. It is assumed that the signal from the generator 1 is pulse position modulated by the pulse position modulator 3 according to the output from the gradation detector 2 and then inputted. Note that the pulse signal generator 1
To simplify the explanation, it is assumed that the pulse signal outputted from the pulse train, that is, the pulse train, consists of four pulses, as shown in FIG.

Segment electrodes S1 to S4 include common electrodes.
Assume that a pulse train whose pulse position is modulated is input to a group of pulse trains input to the COM as follows. That is, in the segment electrode S4, in synchronization with the second pulse of the pulse train,
A pulse train starting from the first pulse is input (see Figure 3e). Furthermore, in the segment electrode S3, in synchronization with the third pulse of the pulse train,
Furthermore, a pulse train in which the first pulse starts in synchronization with the fourth pulse train of the pulse train is inputted to the segment electrode S2 (see FIGS. 3c and d). Moreover, in the segment electrode S1,
1 from the 4th pulse of this pulse train for a group of pulse trains input to the common electrode COM.
A pulse train is input in which the first pulse begins with a delay of one pulse (see FIG. 3b).

Then, voltages having waveforms shown in FIGS. 4a to 4d, respectively, are inputted to the common electrode COM to the segment electrodes S1 to S4. Figure 3,
From Figure 4, display elements DE1, DE2, DE3, DE4
It can be seen that the effective value of the voltage input to the voltage decreases in this order.

On the other hand, the relationship between LCD driving voltage and transmittance (contrast) is as shown in Figure 5.
As the effective value of the drive voltage increases, the display element displays whiter (in the case of black and white display).

In this embodiment, the display element DE1 is white, and then the display elements DE2, DE3, and DE4 approach black in this order. In this way, the pulse position of the output pulse train of the pulse signal generator 1 is modulated according to the density of the image and input to the segment electrodes, and gradation is displayed by the number of pulses applied to the pixel. It is possible to display halftones.

The device of the present invention can be applied to all field effect type liquid crystal elements such as TN type or CH type liquid crystal elements.

〔Effect of the invention〕

Since the present invention has the above configuration, it has the effect of being able to display halftones.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram schematically showing a part of the liquid crystal display shown in FIG. 1, and FIGS. Waveform diagrams of the pulse signals applied to the electrodes and segment electrodes; Figures 4a to d are waveform diagrams of the voltages applied to the liquid crystal between the common electrode and the segment electrodes; Figure 5 is the waveform diagram of the voltage applied to the liquid crystal display. A diagram showing the relationship between voltage and transmittance, FIG. 6 is a diagram showing a part of a display element in a liquid crystal display, and FIG. 7 is a diagram showing a pulse signal applied to the liquid crystal display shown in FIG.
FIG. 7a is a pulse voltage waveform diagram applied to the common electrode, and FIGS. 7b and 7c are voltage waveform diagrams applied to the segment electrodes in the conventional example. In the figure, COM is a common electrode, S1 to S4
are segment electrodes, 1 is a pulse signal generator, 2 is a gradation detector, 3 is a pulse position modulator, and 5
is a liquid crystal display.

Claims (1)

[Claims] 1. In a static drive device for a liquid crystal display in which a plurality of pixels are formed by interposing a liquid crystal at the intersection of one common electrode and a plurality of segment electrodes, and gradation display is performed by the potential difference between the common electrode and the segment electrodes. , a pulse train generating means that periodically generates a plurality of pulse trains corresponding to the required number of gradations at intervals equal to the width of the pulse train and inputs them to a common electrode; and a gradation system that detects gray scales from the image signal. It is equipped with a tone detecting means and a pulse position modulating means for displaying a tone by modulating the pulse position of the entire pulse train according to the future output and inputting it to the segment electrode. 1. A static drive device for a liquid crystal display, which is characterized by displaying an adjustable display.