JPS6217735A - Static driving device for liquid crystal indicator - Google Patents

Abstract

PURPOSE:To easily display a half tone by applying the pulse train of the pule width of a half period portion to a common electrode, bringing plural pulses and the first pulse of a pulse signal train having the pulse width of two times of said pulse, to a pulse position modulation in accordance with a variable density detecting signal, and applying them to a segment electrode. CONSTITUTION:The pulse train of the pulse width of a half period portion from a pulse signal generator 1 is applied to the common electrode of a liquid crystal indicator 5. Also, the variable density gradation of an inputted image signal is detected by a gradation detector 2, and applied to a pulse position modulator 3. By this modulator 3, the pulse of the pulse width of a half period portion from the generator 1, and one pulse in a pulse train consisting of one pulse having the pulse width of two times of said pulse are brought to a pulse position modulation in accordance with the variable density gradation from the detector 2. Also, a pulse position modulating signal is applied to each segment electrode of the indicator 5 from an LCD driver 4, and the image of an intermediate gradation is displayed easily.

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, in static driving of a liquid crystal display, a pulse signal as shown in FIG. 7(a) is applied to the common electrode COH.
In-phase and π12 phase-shifted pulse signals as shown in b) and (c) were applied to the segment electrodes.

Therefore, 1. For example, if a pulse signal in phase with the common electrode COW is applied to the electrode St, the display element DEL
For example, when a pulse signal whose phase is shifted by π12 with respect to the common electrode COM is applied to the electrode S2, the display element DE2 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 therefore, the resulting images lack expressive power.

[Means for solving problems]

The present invention has been made by focusing on such conventional problems, and uses a pulse signal generating means.

Inputting a pulse having a pulse width of half a period to the common electrode, and a plurality of pulses having the pulse width;
Of the pulse train consisting of one pulse having twice the pulse width, the one pulse train is pulse-modulated according to the output from the gradation detecting means and is input to the segment electrode.

〔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. In FIGS. 1 and 2, reference numeral 1 denotes a pulse signal generator (pulse signal generating means) which generates a pulse having a pulse width t corresponding to a half period. 2 is a gradation detector (gradation detection means) that detects gradation from the image signal;
Reference numeral 3 denotes a pulse position modulator (pulse position modulating means) which modulates the position of the l pulse in a pulse train consisting of a plurality of pulses having the pulse width t and one pulse having the pulse width 2t. 4 is a liquid crystal display (L(:D) 5
This is an LCD driver that drives the .

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 common electrode GOH
Input the pulse signal shown in FIG. 3(a) (having a pulse width t for half a cycle) from the pulse signal generator l,
On the other hand, the pulse position modulator 3 modulates the pulse position of the signal from the pulse signal generator 1 according to the output from the gradation detector 2 and inputs the signal to the segment electrodes 51 to S4.

It is assumed that a pulse train whose pulse position is modulated as follows with respect to the pulse train input to the common electrode COx is input to the segment electrode 5l-S4.

That is, as shown in FIG. 3(b), the first pulse (pulse @2t) starts in the segment electrode S1 in synchronization with the falling edge of the first pulse of the pulse train, and then the pulse width changes. A pulse train consisting of two consecutive pulses of t is input. In addition, the segment electrode S2 has a structure shown in FIG. 3 (C
), in synchronization with the falling edge of the first pulse of the pulse train, a pulse @t, followed by a pulse 11@2t, and a pulse with a pulse width t are input in this order. Furthermore, as shown in FIG. 3(d), a pulse with a pulse width t is applied to the segment electrode S3 in synchronization with the falling edge of the first pulse of the pulse train, followed by a pulse with a pulse width t and a pulse width 2t. pulses are input in this order. Furthermore, the segment electrode S4 is provided with π for the pulse train.
A pulse train with a phase shift of 72 is input (Fig. 3(e)
reference).

Then, the common electrode C is connected to the segment electrode 5l-S4.
For ON, voltages having the waveforms shown in FIGS. 4(a) to 4(d) are inputted. From FIG. 4, display elements DEI, DE2. DE3. The voltage input to DE4 is
It can be seen that the effective value of the voltage increases in this order.

On the other hand, the relationship between LCD drive voltage and transmittance (contrast) is as shown in Figure 5, so the larger the effective value of the drive voltage, the whiter (in the case of monochrome display) one display element will be displayed. .

In this embodiment, the display element DE4 is white, and then the display elements DE3, I]E2, and DEI approach black in this order.

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

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 FIG.
) to (e) are waveform diagrams of pulse signals applied to the common electrode and segment electrode shown in Fig. 2, respectively, and Fig. 4 (a) to (d) are waveform diagrams of pulse signals applied to the common electrode and segment electrode, respectively. Voltage waveform diagram, Figure 5 is a diagram showing the relationship between the voltage applied to the liquid crystal display and transmittance, Figure 6 is a diagram showing a part of the display element in the liquid crystal display, and Figure 7 is the diagram showing the relationship between the voltage applied to the liquid crystal display and the transmittance. Figure 7(a) shows the pulse voltage waveform diagram applied to the common electrode, and Figures 7(b) and (c) show the pulse signals applied to the liquid crystal display shown in the figure. FIG. 3 is a diagram of voltage waveforms applied to electrodes. In the figure, COW is a common electrode, 5l-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 base. Figure 4

Claims (1)

[Claims] pulse signal generating means for inputting a pulse train having a pulse width equivalent to half a cycle into a common electrode; gradation detecting means for detecting gray scale from an image signal; a plurality of pulses having the pulse width and a pulse twice this pulse width; Static driving of a liquid crystal display device, comprising pulse position modulation means for modulating the pulse position of one pulse of a pulse train consisting of one pulse having a width according to the output from the gradation means and inputting it to the segment electrode. Device.