JPH10319367A - Liquid crystal display module and portable terminal using the module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate data correction of a pen position by suppressing a noise level occurring from itself when an alternating signal is switched in a liquid crystal display module. SOLUTION: Since thins module is provided with a display off generation circuit 21 making a display off signal active when the alternating signal is switched and outputting it to a COM driver 4 of a liquid crystal panel 2, and since the display off signal is made active when the alternating signal is switched when the noise level occurring from the liquid crystal module 1 itself becomes maximum, a drive voltage applied to the liquid crystal display panel 2 becomes a non-selection level, and becomes a voltage level lower than a regular selection level, and the noise level occurring from the liquid crystal display module 1 itself is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display module used as a display device and a portable terminal using the liquid crystal display module.

[0002]

2. Description of the Related Art In recent years, there has been a demand for a portable terminal (PDA) to smoothly and easily input and output more data. In such a portable device, the liquid crystal display module and the transparent touch panel are indispensable as a display device and an input device.

In the liquid crystal display module as the display device, as the demand for lower power consumption and higher image quality is increasing, the problem of power consumption is given top priority. Type is often used. In addition, a transparent touch panel as an input device is often arranged on the upper surface of a liquid crystal display module. By touching the surface, it is possible to easily input data and operate a PDA without providing a keyboard. ing.

In a liquid crystal display module of a PDA having such a configuration, an alternating signal is generally required. The reason for this is that the liquid crystal display module controls the molecular alignment by applying an electric field to the liquid crystal molecules, and turns on and off the input light by the change in the alignment to enable display. Is applied, the molecules themselves are electrolyzed and, at the same time, have a bad influence on the molecular arrangement structure. Therefore, an alternating signal for canceling the applied electric field is required. However, since a demand for displaying a large amount of data simultaneously on the PDA has arisen, it is necessary to increase the display capacity and enlarge the screen, that is, the display area of the liquid crystal display panel. The liquid crystal display panel can be regarded as a capacitive element (capacitor) electrically, but increasing the display area is equivalent to increasing the capacitance value. As a result, in a large-screen PDA, when a large-capacity capacitor is driven by alternating current, a large charge / discharge current flows instantaneously, so that the rising of the alternating signal frequency
At the time of falling, a large noise is generated and a fluctuation of the power supply voltage is generated. On the other hand, the reading of the pen position on the transparent touch panel is generally controlled by an AD converter, but if there is a lot of noise from the liquid crystal display module and fluctuations in the power supply voltage, there will be many errors in the reading position as a digital value. Because of the inclusion, the pen position greatly deviates from the actual value. For this reason,
A configuration in which a function of correcting a deviation amount from an actual value by software is provided is employed. Furthermore, limiting the pen position reading timing to a timing other than the switching timing of the AC signal input to the liquid crystal display module is also adopted as an effective method for reducing the pen position reading error due to the influence of noise and power supply fluctuation.

[0005] The configuration of a main portion of a conventional portable terminal combining a liquid crystal display module having a function of correcting the amount of deviation of the pen position from an actual value by software and a transparent touch panel will be described below with reference to FIG. .

In FIG. 3, reference numeral 1 denotes a liquid crystal display module.
A plurality of SEG drivers 3 for applying a drive voltage to the segment electrodes of the liquid crystal display panel 2, a plurality of COM drivers 4 for applying a drive voltage to the common electrode of the liquid crystal display panel 2, and generating the above-described AC signal An AC signal generating circuit 5 for outputting the signal to the SEG driver 3 or the COM driver 4 and a power supply circuit 6 for supplying power to the SEG driver 3, the COM driver 4 and the AC signal generating circuit 5 are provided. The AC signal generated by the AC signal generating circuit 5 is input to an AC signal switching timing confirmation circuit 7, which detects the switching timing of the AC signal and detects a pen position described later. The data is input to the data processing circuit 14 for data correction.

In FIG. 3, reference numeral 11 denotes a transparent touch panel. The pen 12 position of the transparent touch panel 11 is read as a digital value by a pen position reading circuit 13 of the transparent touch panel 11 and is input to a data processing circuit 14 for pen position data correction. Is done. The data processing circuit 14 corrects the above-described deviation amount of the pen position from the actual value by the software based on the input pen position data and the switching timing detection signal of the AC signal, and outputs the main CPU (MCP
U) Output the corrected pen position to 15.

The MCPU 15 outputs display data to a controller (LCD controller) 16 of the liquid crystal display module 1 in accordance with the input pen position data, and the LCD controller 16 controls the SEG driver 3 and the COM driver in accordance with the display data. 4 and a control signal is output to the AC signal generation circuit 5 to cause the liquid crystal display panel 2 to display a screen corresponding to the pen position. Reference numeral 17 denotes a video RAM (VRAM), which constitutes a memory of the MPU 15.

The operation of reading the pen position in the combination of the liquid crystal display module and the transparent touch panel configured as described above will be described below. After any data is displayed on the liquid crystal display module 1, the pen
When a data position on the transparent touch panel 11 is pointed out from the position 12, the pen position reading circuit 13 obtains the position as a digital value. Since the position data includes an error as described above, the data processing circuit 14 performs data processing by software to correct the amount of deviation from the actual position. In this software processing, a type in which a data value is simply replaced using a table written in a ROM, a type in which a shift amount is calculated by an MPU and added as a correction value, and the like have been put to practical use. Also, when the AC signal switching timing confirmation circuit 7 outputs an enable output, that is, only the pen position reading data at a time other than the AC signal switching timing is valid, so that the deviation correction by software processing can be reduced. ing.

[0010]

In the pen position data correction data processing circuit 14, however, the conventional method of correcting the deviation from the actual value at the time of reading the pen position requires the use of software to process the deviation. It takes a long time to read the pen position and it is very difficult to create software.In addition, the method of invalidating data when the AC signal is switched takes more time to obtain valid data than the software correction method alone Each has the problem that

[0011] It is an object of the present invention to provide a liquid crystal display module in which the noise level generated by itself when the AC signal is switched can be kept low, and the pen position data correction can be made unnecessary.

[0012]

According to the present invention, there is provided a liquid crystal display module comprising a display off generating circuit for activating a display off signal when an alternating signal is switched and outputting the signal to a driver of a liquid crystal panel. .

According to the present invention, it is possible to obtain a liquid crystal display module capable of suppressing the noise level generated by itself at the time of switching of the AC signal, and eliminating the need for correcting the pen position data.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention provides a liquid crystal panel, an alternating signal generating circuit for outputting an alternating signal to a driver of the liquid crystal panel, and a display when the alternating signal is switched. A display-off generating circuit for activating an off signal and outputting the signal to a driver of the liquid crystal panel, wherein a noise level generated from the liquid crystal display module itself is switched to an alternating signal at which the noise level is maximized. The drive voltage applied to the liquid crystal display panel becomes the non-selection level in order to activate the display-off signal, and the voltage level is lower than the normal selection level, thereby reducing the noise level generated from the liquid crystal display module itself. It becomes possible.

The invention according to claim 2 is characterized in that the function of the display-off generating circuit is incorporated in the AC signal generating circuit in a hardware manner, and the display-OFF is automatically switched when the AC signal is switched. It can be set by hardware to activate the signal.

According to a third aspect of the present invention, there is provided the liquid crystal display module according to the first or second aspect, further comprising a transparent touch panel. Since the noise level can be reduced, effective data can be obtained at any timing when the pen position data is taken in, so that the pen position can be read at high speed against noise.

Hereinafter, a main configuration of a portable terminal in which a liquid crystal display module and a transparent touch panel according to an embodiment of the present invention are combined will be described with reference to FIG. In addition,
The same components as those of the conventional configuration shown in FIG. 3 are denoted by the same reference numerals, and description thereof is omitted.

In FIG. 1, reference numeral 21 denotes an automatic display-off generating circuit for automatically activating a display-off signal when an AC signal is switched (details will be described later).
And the display-off signal is output to the COM driver 4. Further, the conventional AC signal switching timing confirmation circuit 7 and the pen position data correction data processing circuit 14 are deleted, and the pen position data read as digital values by the pen position reading circuit 13 is directly sent to the MPU.
15 has been entered.

The combination of the 320 × 240 dot liquid crystal display module 1 and the transparent touch panel 11 will be specifically described. In the liquid crystal display module 1, the noise level generated from the liquid crystal display module 1 becomes the largest when the alternating signal is switched by examining the noise generation frequency with a spectrum analyzer. In the liquid crystal display module 1 of 320 × 240 dots, the alternating signal is transmitted at the frame frequency (normally
(About 100 Hz)
As shown in the figure, it is common to use a frequency which is an odd multiple (often 11 or 13 times) of the data latch signal which is a control signal of the SEG driver 3. The noise level peaks. The noise level depends on the pattern displayed on the liquid crystal display module 1.
In the case of monochrome positive reflection display type like DA,
The more the black display, that is, the more the display portion, the higher the noise level. From this, it can be seen that the noise can be reduced by reducing the lighting area or lowering the driving voltage for lighting. Since it is not possible to actually reduce the lighting area, it is required to lower the drive voltage as very important from the viewpoint of lowering the voltage. Therefore, lowering the drive voltage only when the AC signal is switched is effective for substantially reducing the noise level. That is, an automatic display-off generation circuit
At 21, as shown in FIG. 2, in synchronization with the rise of the data latch signal, an odd multiple of the data latch signal (11
If the display off signal is activated in order to lower the liquid crystal driving voltage at the time of switching of the alternating signal of the frequency of which the frequency is doubled or 13 times, the non-selection level is applied to the liquid crystal display panel 2. The drive voltage value can be reduced as compared with the case where the selection level at the time of display is applied, and the noise level can be substantially reduced. As shown in FIG. 2, the period during which the display-off signal is active is defined from the rising of the display data latch signal immediately before the switching of the AC signal to the rising of the data latch signal immediately after the switching of the AC signal. Sometimes screen flicker does not occur. In the liquid crystal display module 1 of 320 × 240 dots, the driving voltage is about 26 to 29 V under the driving conditions of 1/240 duty and 1/16 bias, and the selection level of the common driver 4 is 29 V and the non-selection level is 25 V. Therefore, the noise voltage level can be reduced.

As described above, the noise level of the liquid crystal display module 1 at the time of switching of the alternating signal can be reduced. Therefore, when the position data is taken in by the pen position reading circuit 13, valid data is always taken at any timing. Can be. As a result, it is possible to process the pen position reading at a higher speed than the method of correcting the shift amount by software.

In the AC signal generating circuit 5, the AC signal is often supplied from a gate array that generates a data latch signal. Therefore, as shown in FIG.
It is possible to easily implement the function of activating the display-off signal when the AC signal is switched this time into the AC signal generating circuit 5.

Further, in the conventional example, since the pen position reading circuit side of the transparent touch panel 11 needs to know the switching timing of the AC signal, the AC signal is supplied from the liquid crystal display module 1 side to the outside (the transparent touch panel side). However, in the case of the present invention, it is possible to reduce the number of transmission lines because it is not necessary,
This can also lead to cost reduction.

[0023]

As described above, the present invention is advantageous in that the noise level generated by itself can be suppressed by providing a circuit for automatically activating the display-off signal when the AC signal is switched. The effect is obtained.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram of a mobile terminal including a liquid crystal display module and a transparent touch panel according to an embodiment of the present invention.

FIG. 2 is a signal characteristic diagram of an automatic display-off generation circuit of the liquid crystal display module.

FIG. 3 is a main part configuration diagram of a conventional mobile terminal including a liquid crystal display module and a transparent touch panel.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal display module 2 Liquid crystal display panel 5 AC generation circuit 11 Transparent touch panel 13 Transparent touch panel pen position reading circuit 15 MPU 16 LCD controller 21 Automatic display off generation circuit

Claims (3)

[Claims] A liquid crystal panel; an alternating signal generating circuit for outputting an alternating signal to a driver of the liquid crystal panel; and a display-off signal being activated when the alternating signal is switched, and outputting the signal to the driver of the liquid crystal panel. A liquid crystal display module comprising a display off generation circuit. 2. The liquid crystal display module according to claim 1, wherein the function of the display-off generating circuit is incorporated in the AC signal generating circuit in a hardware manner. 3. A mobile terminal comprising the liquid crystal display module according to claim 1 and a transparent touch panel.