JPH02144592A - Drive circuit for liquid crystal panel - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a liquid crystal panel by providing a control circuit which sets the waveform of a selected level and that of a nonselected level to the same potential when operating clocks stop on the output side of an AC making circuit. CONSTITUTION:A control circuit 12 sets the waveform of a selected level and that of a nonselected level inputted from an AC making circuit 3 when operating clocks stop to voltages of the same potential and outputs the voltages to a column-side drive circuit 4 and row-side drive circuit 5. Since the waveforms of the selected and nonselected levels are set to the voltages of the same potential when the operating clocks stop in such way, the voltages of the same potential are uniformly applied across a liquid crystal panel 1 from the column- and row-side drive circuits. Therefore, no DC voltage is applied across the liquid crystal panel and deterioration of the panel by a DC pass can be prevented.

Description

[Detailed Description of the Invention] [Table of Contents] Overview Industrial Application Fields Prior Art (Fig. 5) Problems to be Solved by the Invention Embodiments of Means and Actions for Solving Problems to Be Solved by the Invention Explanation of the Principle of the Invention (Fig. 1) ) An embodiment of the present invention (Figures 2 to 4) Effects of the invention [Summary] Regarding the liquid crystal display panel drive circuit, a DC voltage that can be reliably applied to the liquid crystal display panel with an extremely simple configuration even when the operating clock stops. The purpose of the present invention is to provide a liquid crystal display panel drive circuit that can prevent the deterioration of the liquid crystal panel. An alternating circuit that converts a predetermined power supply voltage into a selected level waveform and a non-selected level waveform based on the alternating current signal is inputted, and the selected level waveform and the non-selected level waveform are inputted. , a drive circuit that generates a drive waveform for driving the liquid crystal display panel based on the selection and non-selection level waveforms, the drive circuit having the operation circuit on the output side of the AC converting circuit. A control circuit is provided to bring the selected level waveform and the non-selected level waveform to the same potential when the clock stops.

[Industrial application field]

The present invention relates to a drive circuit for a liquid crystal display panel.

Liquid crystals are being put into practical use as passive display elements in the field of small numeric displays. In particular, the use of liquid crystal displays in wristwatches is increasing due to their low voltage, low power consumption, and long lifespan. The method is DSM (dy
FEM (field eff
ect mode). Currently, there are two types of operating voltages for the FEM type in practical use: 3■ and 6■.
The shape is 7■ or more. In addition to 7-segment numeric displays, medium-sized and large-sized matrix dot displays are being developed. It is generally believed that liquid crystals have a slow response and are difficult to use in matrix displays due to crosstalk, but when a voltage with a pulse width within the liquid crystal's response time is repeatedly applied, the liquid crystal molecules gradually respond. Initially, there is a cumulative response effect in which the optical phenomenon reaches a saturation value when accumulated over a certain period of time, so scanning was performed at 30 to 60 Hz and 13 (
DSM) or 200m5 (FEM) that can display the entire screen are being made.

By the way, it is said that when a DC voltage is applied to a liquid crystal panel, the liquid crystal panel deteriorates in a short period of time. Therefore, the drive circuit for the liquid crystal panel needs to be a circuit that does not apply a DC voltage to the liquid crystal display panel.

[Conventional technology]

As a conventional liquid crystal display panel drive circuit of this type, there is one shown in FIG. 5, for example. In Figure 5, 1
2 is a liquid crystal display panel; 2 is a liquid crystal display panel drive circuit that drives the liquid crystal display panel 1; Consisting of 5. AC circuit 3
generates a selection level waveform and a non-selection level waveform, which are the source of the drive waveform of the liquid crystal display panel 1, based on the input power supply voltage divided to a predetermined voltage level and the alternating current signal,
The generated selection and non-selection signals are output to the column side drive circuit 4 and the row side drive circuit 5, respectively. The column side drive circuit 4 receives selection and non-selection signals as well as column side display data from an external circuit (not shown), and the column side drive circuit 4 inputs selection and non-selection signals and column side display data. Based on this, a column side drive waveform is generated and the column side of the liquid crystal display panel 1 is driven. In addition, selection and non-selection signals are input to the row side drive circuit 5, and
Low-side display data is input from an external circuit (not shown), and the row-side drive circuit 5 generates a low-side drive waveform based on the selection/non-selection signal and the low-side display data to drive the low side of the liquid crystal display panel 1. do. The liquid crystal display panel 1 displays the corresponding portion of the liquid crystal based on the drive waveforms on the column side and the row side, when the drive waveforms on both sides exceed a predetermined voltage level difference.

[Problem to be solved by the invention]

However, such conventional liquid crystal display panel drive circuits do not have a reliable protection circuit against the voltage applied to the liquid crystal display panel when the operating clock stops. When the operating clock is stopped, such as when the panel is turned off, a DC voltage may be applied to the liquid crystal display panel, which may lead to further deterioration of the liquid crystal display panel.

Therefore, the present invention provides that even when the operating clock stops,
It is an object of the present invention to provide a liquid crystal display panel drive circuit that can reliably eliminate DC voltage applied to a liquid crystal display panel and prevent deterioration of the liquid crystal display panel with an extremely simple configuration.

[Means to solve the problem]

In order to achieve the above object, the liquid crystal display panel drive circuit according to the present invention inputs a liquid crystal display panel driven by a predetermined drive waveform and an alternating current signal generated based on a predetermined operation clock, and inputs an alternating current signal generated based on a predetermined operation clock. an alternating current converting circuit that converts a predetermined power supply voltage into a selected level waveform and a non-selected level waveform based on the selected level waveform and the non-selected level waveform; a drive circuit that generates a drive waveform for driving a display panel; and a drive circuit that generates a drive waveform for driving a display panel, the selection level waveform and the non-selection level being connected to the output side of the AC converting circuit when the operation clock stops. and a liquid crystal display panel drive circuit characterized by being provided with a control circuit that makes the waveform and the waveform have the same potential.

[Effect]

In the present invention, when the operating clock stops, the selected level waveform and the non-'J! A control circuit is provided that makes the i-select level waveform the same potential.

Therefore, when the operating clock is stopped, the selected level waveform and the non-selected level waveform have the same potential, and the same potential voltage is uniformly applied to the liquid crystal display panel 1 from all drive circuits. As a result, no DC voltage is applied to the liquid crystal panel (thus, deterioration due to the DC bus is prevented).

〔Example〕

Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 is a diagram for explaining the present invention in detail, and FIG.
Components that are the same as those of the conventional example shown in the drawings are given the same numbers and will not be described again. In FIG. 1, 11 is a liquid crystal display panel drive circuit that drives the liquid crystal display panel 1, and the liquid crystal display panel drive circuit 11 includes an alternating current converting circuit 3, a control circuit
2. It is composed of a column side drive circuit 4 and a row side drive circuit 5.

When the operating clock is stopped, the control circuit 12 converts the selected level waveform input from the AC conversion circuit 3 into a voltage having the same potential as the non-selected level waveform, and outputs it to the column side drive circuit 4 and the row side drive circuit 5.

Therefore, in the present invention, when the operating clock is stopped, the selected level waveform and the non-selected level waveform are made to have the same potential voltage, so that the same potential voltage is uniformly applied to the liquid crystal display panel from the column side and row side drive circuits. 1. As a result, no DC voltage is applied to the liquid crystal panel, and deterioration due to the DC path can be prevented.

Varnish 1 Next, a liquid crystal display panel drive circuit based on the above principle will be described as an example. 2 to 4 are diagrams showing one embodiment of the liquid crystal display panel drive circuit according to the present invention, FIG. 2 is a diagram of its overall configuration, and FIG. 3 is a diagram showing the selected level waveform and non-selected level waveform on the column side. FIG. 4 is a waveform diagram showing column side drive waveforms and row side drive waveforms. It should be noted that the same components as those in the principle explanatory diagram of FIG. 1 are designated by the same numbers.

First, the configuration will be explained. The liquid crystal display panel drive circuit 11 is converted to AC (no. 8 and four types of power supply voltages V3, ■2, vl
, an AC conversion circuit 3 that generates a selected level waveform and a non-selected novel waveform from VO, and a control circuit 12 that makes the selected and non-selected level waveforms have the same potential when the operating clock stops.
A column-side drive circuit 4 and a row-side drive circuit 5 that generate column-side and row-side drive waveforms based on selection and non-selection signals,
The alternating current converting circuit 3 is configured with an alternating current converting signal (M
a selection level waveform generation circuit 13 that generates a selection level waveform based on the signal) and power supply voltages v3 and vO, and a non-selection level waveform generation circuit 13 that generates a non-selection level waveform based on the alternating current signal (M signal) and ■2 and ■1. and a level waveform generation circuit 14. As mentioned above, there are two types of drive waveform generation circuits in the liquid crystal display panel drive circuit 11: column (row) and row (column). By applying a voltage to the liquid crystal display panel 1, the liquid crystal display panel 1 is driven. Therefore, as shown in Fig. 3, the selected/unselected waveform on the column side is set to the selected level. waveform, and when the M signal is I(", the voltage is 1, "
If the waveform in which the voltage becomes 2 when the voltage is L is the non-selected waveform, then
The selection/non-selection waveform on the low side is a selection level waveform in which the voltage is 0 when the M signal is “H” and voltage 3 when it is “L”, and the voltage V2 and 3 when the M signal is “H”. When the voltage is
1, resulting in a non-selected level waveform.

The column-side drive circuit 4 includes column-side drive waveform generation circuits 15 to 17 that generate column-side drive waveforms for driving each column of the liquid crystal display panel 1 based on column-side display data and selected and non-selected level waveforms. Similarly, the row-side drive circuit 5 includes row-side drive waveform generation circuits 18 to 18 that generate row-side drive waveforms for driving each row of the liquid crystal display panel 1 based on the row-side display data and selected and non-selected level waveforms. 20. The column side drive circuit 4 and the row side drive circuit 5 generate drive waveforms as shown in FIGS. 4(b), (d) (f>(h)) based on their respective liquid crystal display data to generate liquid crystal display pulses. 1 directly, and generates a drive waveform by selecting a selection level waveform when the display data is "H" and selecting a non-selection level waveform when the display data is "L".For example, The column side drive waveform generation circuit 15 has a fourth
When the column side display data as shown in FIGS. ” only when the column-side display data is “S”, a drive waveform with a large amplitude (“L”=Vs, “L”=Vo) is generated as shown in FIG. 4(b) and (d). 4(b) (
A drive waveform with a small amplitude is generated as shown in d), and the drive waveform is applied to the corresponding column of the liquid crystal display panel 1. Similarly, on the 1st day of the low-side drive waveform generation circuit, FIG.
) When the low-side display data as shown in (g) is input, the low-side drive waveform generation circuit 18 outputs the low-side display data as “
4(f) and (h), and this driving waveform is applied to the corresponding row of the liquid crystal display panel 1. Therefore, the liquid crystal display panel 1 The drive waveform on the column side is “I(”=Vs,
And when the low side drive waveform is "L'=Vo" (for example,
In cases (a) shown in FIG. 4(b), (b) shown in FIG. It turns out.

On the other hand, a control circuit 12 is interposed between the AC converting circuit 3, the column side drive circuit 4, and the row side drive circuit 5.
The control circuit 12 is composed of N-type transistors 21 and 22. The drain of the N-type transistor 21 is connected to the selection level waveform line 23, the source is grounded, and the gate receives a signal that becomes "H" when the operating clock is stopped ("H" active signal). . The drain of the N-type transistor 22 is connected to the non-selection level waveform line 24, the source thereof is grounded, and the gate has a signal (
"H" active signal) is input.

Next, the effect will be explained.

4) The column side drive circuit 4 and the row side drive circuit 5 control the column side and row side display data according to the column side display data shown in FIGS. When the side drive waveform is generated, (b), (d,)Cr
) (h)), as mentioned above, the drive waveform on the column side is “H” = Vs, and the drive waveform on the row side is “L” = Vo.
At this time, the potential difference in the corresponding predetermined area portion of the liquid crystal display panel 1 becomes equal to or greater than the predetermined value, and the corresponding portion is driven.

5. When the operating clock stops, in the conventional circuit shown in Fig. 5, the waveform immediately before the operating clock stops is applied to the liquid crystal display panel 1 as it is, so it becomes a DC voltage. ,
This causes the deterioration of the liquid crystal display panel 1 to progress. In this embodiment, a control circuit 12 consisting of N-type transistors 21 and 22 is installed between the AC converter circuit 3, the column side drive circuit 4, and the row side drive circuit 5 in the selected level waveform line 23 and the non-selected level waveform line 24. , the signal accompanying the stop of the operating clock (“H” active) is transmitted to both transistors 21.
．． By adopting the configuration with 22 gate inputs, when the operating clock stops, both the selected level waveform and the non-selected level waveform are pulled to "L" level, and the column side drive circuit 4 and the row side drive circuit All the drive waveforms applied from 5 to the liquid crystal display panel 1 also become "L". Therefore, no DC voltage is applied to the liquid crystal display panel 1.

Here, selected and non-selected level waveforms are input from the AC circuit 3 to the drivers of the column side drive circuit 4 and row side drive circuit 5 to create drive waveforms. It is actually very difficult to achieve the same level for both. In this embodiment, the selection and non-selection level waveforms, which are the source of generating the drive waveforms, are set to the same level at the time they are input to the column side drive circuit 4 and the row side drive circuit 5. With a simple circuit configuration, the drive waveforms on the row side and column side can all be at the same level. In addition, when setting the same level, in addition to using an N-type transistor to set the level to "L" as in this embodiment, it is also possible to use a P-type transistor to set the level to "H". Due to the characteristics of the transistor, it is faster to pull the signal to the 'L' level using an N-type transistor, and if GND is selected as the 'L' level, the circuit configuration can be simplified.

〔Effect of the invention〕.

According to the present invention, it is possible to reliably prevent DC voltage from being applied to a liquid crystal display panel with an extremely simple circuit configuration, and it is possible to appropriately prevent deterioration of the liquid crystal display panel.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the principle of a liquid crystal display panel drive circuit according to the present invention, FIGS. 2 to 4 are diagrams showing an embodiment of the liquid crystal display panel drive circuit according to the present invention, and FIG. 2 is an overall configuration thereof. Figure 3 is a waveform diagram showing the selected level waveform and non-selected level waveform on the column side, Figure 4 is a waveform diagram showing the column side driving waveform and row side driving waveform, and Figure 5 is a conventional liquid crystal display. FIG. 1 is an overall configuration diagram showing a panel drive circuit. 11...Liquid crystal display panel drive circuit, 12...
...control circuit, 13...selection level waveform generation circuit, 14...
...Non-selected level waveform generation circuit, 15 to 17...
...Column side drive waveform generation circuit, 18-20...
- Low side drive waveform generation circuit, 2122... N-type transistor, 23... Selected level waveform line, 24... Non-selected level waveform line. Engineering: Liquid crystal display panel, 3: AC circuit, 4: Column side drive circuit, 5: Row side drive circuit,

Claims (1)

[Claims] A liquid crystal display panel driven by a predetermined drive waveform, an alternating current signal generated based on a predetermined operating clock, and a predetermined power supply voltage selected based on the alternating signal. an alternating circuit that converts the waveform and the non-selected level waveform into alternating current; the selected level waveform and the non-selected level waveform are input;
a drive circuit that generates a drive waveform for driving the liquid crystal display panel based on the selection and non-selection level waveforms, the operation clock being connected to the output side of the AC converting circuit; 1. A liquid crystal display panel drive circuit comprising: a control circuit that brings the selected level waveform and the non-selected level waveform to the same potential when the selected level waveform stops.