JPH04291395A - Information terminal device - Google Patents

Abstract

PURPOSE:To offer the low-cost, small-sized information terminal device which makes a gradational liquid crystal display. CONSTITUTION:The information terminal device divides one frame into plural fields, applies a specific voltage level selectively among plural different voltage levels, field by field, and makes the gradational display according to a mean effective voltage value. This device is equipped with a frame memory 4 which stores and holds gradational image data to be displayed in frame units, a data processing means 13 which outputs data based on the gradation levels of the image data stored and held in the frame memory 4 plural times in field units at the time-divided timing of a frame time, a data switching means 20 which switches and supplies the output data from the data processing means 20 selectively to a liquid crystal display means, an image signal output means which outputs the image data as one-frame image data consisting of plural fields.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an information terminal device,
Specifically, the present invention relates to an information terminal device that performs multi-gradation display using a liquid crystal display device, which is suitable for use in the field of information terminal devices such as small personal computers and word processors.

[0002] In recent years, information terminal devices such as personal computers and word processors have become smaller and more sophisticated.
User needs range from desk-top types called desktop types to lap-top types called laptop types.
Furthermore, there is a shift to information terminal devices such as notebook types and palmtop types, which are smaller than laptop types, and as a result, many small information terminal devices are on the market.

[0003] In these information terminal devices, the main body is small and
In order to reduce weight, it is desired that the display unit be lightweight and thin, and as such display devices, CRT (cathode ray), which is common in the desktop type mentioned above, is used.
liquid crystal display (LCD)
TN (twisted n
matic) and STN (super twist
Compared to simple matrix liquid crystal display devices such as ed nematic), it allows finer control of halftones,
In addition, TFT (thin film) can ensure a high contrast ratio and has a fast response speed.
transistor) and MIM (metal ins
Active matrix liquid crystal display devices such as ulator metal (lator metal) and the like are used.

[0004] However, the image signal output form of information terminal devices is generally adapted to CRT.
Displaying multi-gradation images on a liquid crystal display device based on an image signal for RT not only reduces efficiency due to an increase in the number of circuits for converting the image signal, but also increases the size and cost of the liquid crystal display device. invite.

[0005]Therefore, it is required to reduce the size of the liquid crystal display device by supplying image signals to the liquid crystal display device in an optimal form, thereby reducing the cost of the entire device.

[0006]

[Prior Art] Conventional information terminal devices of this type include:
For example, as shown in FIG. 7, there is an information terminal device such as a personal computer equipped with a liquid crystal display means.

[0007] This information terminal device is broadly divided into a personal computer 1 and a liquid crystal display means 2, which are information terminal devices.

[0008] The personal computer 1 has an MPU (micro pr
cessing unit) 3, frame memory 4
, a D/A converter 5, and the liquid crystal display means 2 includes a first field liquid crystal drive power supply 6, a second field liquid crystal drive power supply 7, a power supply switching circuit 8, a driver control section 9, a data driver 10, and a scan driver 11. , display panel 1
The driver control unit 9 includes a timing generation unit 13, an A/D converter 14, a first field frame memory 15, a second field frame memory 16, and a data switching circuit 17.

The power supply switching circuit 8 switches the liquid crystal drive power source for each field, and the scan driver 11 scans and drives an active matrix display panel 12 using TFTs.

[0010] Recently, for example, there has been a demand for multi-gradation display of information terminal devices such as computers, and in order to meet this demand, it is also possible to use an analog driver capable of outputting multi-gradation as a data driver. However, if an analog driver is used, it will significantly increase the cost of the liquid crystal display device in the information terminal device. Therefore, in order to reduce the cost of the information terminal device, the data driver 10 may be replaced with an expensive analog driver. An inexpensive STN driver is used.

In the above configuration, since the STN driver can output only two voltage levels at the same time, in the case of normal driving, the three primary colors R (red) and G (
When two gradation levels of each color (green) and B (blue) are displayed, the maximum number of displayed colors is eight.

Therefore, when an image signal for display is output from the personal computer 1, first, the image signal for one frame from the frame memory 4 in the personal computer 1 is outputted by the MPU 3.
The analog RGB signal is output as an analog RGB signal via the /A converter 5, and the analog RGB signal is received from the personal computer 1 by the driver control unit 9 of the liquid crystal display means 2, which is called field voltage modulation to enable multi-gradation display. Processing takes place.

[0013] To explain this in detail, first, the computer 1
The analog RGB signal from is converted into a digital value by the A/D converter 14, and is sent to a first field frame memory 15 and a second field frame memory 16.
is stored in memory.

Based on the synchronization signal from the MPU 3, the timing generator 13 controls the operations of the power supply switching circuit 8, data driver 10, scan driver 11, and data switching circuit 17, and as shown in FIG. One frame of image data stored in the first field frame memory 15 and the second field frame memory 16 is divided into two fields and output at twice the speed, and a different voltage level is applied to each field. A gradation display is performed based on the average effective voltage value of the voltage level applied to each field in one frame by being output to the display panel 12.

That is, even with a two-gradation STN driver, the required effective voltage can be obtained by outputting different voltage levels for each of a plurality of fields, so the STN driver can perform four-gradation display.

In this case, as shown in Table 1, the two voltages V1 and V2 applied to the data driver 10 by the first field liquid crystal drive power supply 6 are 2V and 6V, and the second field liquid crystal drive power supply 7 applies the two voltages V1 and V2 to the data driver 10. applied to 2
If voltages V3 and V4 are 2V and 4V, average effective voltages VA, VB, VC, and VD corresponding to gradations 1 to 4 are 2V, 3V, 4V, and 5V, respectively.

[0017]

[Table 1]

[0018]

[Problem to be Solved by the Invention] However, in such conventional information terminal devices, the image signal output form of the personal computer 1 is adapted to the CRT, and the signal output form for the liquid crystal display device is Since it is not C.
When displaying a multi-gradation image using a liquid crystal display device based on an image signal for RT, there are problems as described below.

That is, in order to use the analog RGB signal, which is an image signal from the personal computer 1, in the liquid crystal display device, it is necessary to control the signal on the liquid crystal display means 2 side. In order to divide and output the first and second fields of time, it is necessary to store data in a frame memory or the like in order to output each field after receiving the image signal. , frame memory with capacity for one frame (
Two frame memories 15 for the first field and frame memories 16 for the second field are required.

[0020] Also, the first field frame memory 1
5, and an A/D converter 1 for signal processing the data stored in the second field frame memory 16.
In addition, a circuit (timing generation unit 13) that generates timing with twice the frequency of the synchronization signal is required.

[0021] As a result of the above, the circuit scale of the driver control section 9 is large and expensive, and the increase in the number of circuits for converting image signals causes problems such as an increase in the size of the liquid crystal display device and an increase in cost. Ta.

[Objective] Therefore, it is an object of the present invention to provide a low-cost, small-sized information terminal device that displays a multi-gradation liquid crystal display.

[0023]

[Means for Solving the Problems] In order to achieve the above object, a liquid crystal display device according to the present invention divides one frame into a plurality of fields, and selects a predetermined voltage level from among a plurality of different voltage levels for each field. An information terminal device having a liquid crystal display means for displaying gradations based on the average effective voltage value of the voltage level applied to each field in one frame, which is applied to each field in one frame, the information terminal device having a multi-gradation image to be displayed. Frame memory stores and retains data in frame units,
data processing means for outputting output data based on the gradation level of the image data stored in the frame memory a plurality of times at timings obtained by time-dividing the frame time in units of fields; The data switching means selectively switches the data to be applied to the liquid crystal display means, and the image signal outputting means outputs the image data as one frame of image data consisting of a plurality of fields. .

Preferably, the image signal output means has a gamma correction table based on the display characteristics of the liquid crystal display means.

[0025]

[Operation] In the present invention, the output data set based on the gradation level of the image data stored and held in the frame memory by the image signal output means is outputted multiple times at timings obtained by time-dividing the frame time in units of fields. Image data is output as one frame of image data consisting of a plurality of fields.

In other words, since a driver control section for multi-gradation display by the liquid crystal display means is no longer necessary, the liquid crystal display means can be downsized, and the cost of the liquid crystal display means can be reduced, resulting in an inexpensive information terminal device. can get.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on the drawings. FIG. 1 is a diagram showing an embodiment of an information terminal device according to the present invention, and FIG. 1 is a block diagram showing the main configuration of the embodiment.

First, the configuration will be explained.

In FIG. 1, the same numbers as those given to the conventional example shown in FIG. 7 indicate the same parts. The personal computer 1 of this embodiment includes an MPU 3, a frame memory 4, a gamma correction ROM 18, a timing generator 19, and a data switching circuit 20. LCD drive power supply 7,
It is composed of a power supply switching circuit 8, a data driver 10, a scan driver 11, and a display panel 12, and the driver control section 9 that existed in the conventional example is eliminated.

The MPU 3 takes in the image data in the frame memory 4 and converts it into output data for the first field and the second field.
Reference numeral 9 generates a clock for double-speed scanning at twice the timing of the horizontal synchronization signal, based on a clock signal built into the personal computer 1.

The data switching circuit 20 switches the image data output from the MPU 3 based on the clock from the timing generation section 19, and switches the image data output from the power supply switching circuit 8 based on the clock from the timing generation section 19.
, and the first field and the second field by the data switching circuit.
The timing of the drive voltage applied to the data driver 10 is determined by switching for each field.

Next, the operation will be explained. FIG. 2 is a diagram showing the output state of the image signal in units of frames in this embodiment, and FIG. 3 is a diagram showing the output state of the image signals in units of dots in this embodiment.
FIG. 4 is a timing chart of the clock in this embodiment.

First, based on the clock timing from the timing generator 19, the image signal is time-compressed as shown in FIG. Twice during
It is output from the frame memory 4.

The MPU 3 outputs data for the first field and the second field based on the output data from the frame memory 4, and the data switching circuit 20 outputs different signals for each of the first and second fields to the liquid crystal display means 2. is output to.

Specifically, as shown in FIG. 3, for example,
To explain the case where the original image data is data with 24 gradations of 8 bits each for RGB, first, the data for one frame in the frame memory 4 is repeated twice in units of one dot, and the data for the first field is created. , and are output as data for the second field, and these 8 bits
Based on the data, the MPU 3 converts the data into the number of gradations that can be displayed by the liquid crystal display means 2, and outputs the converted data to the outside. That is, the image signal voltages for the first field and the second field are decoded from the image signal in the personal computer 1, and the voltage level for each field is obtained.

When outputting from the personal computer 1, the data switching circuit 20 outputs data converted in units of one dot for each of the first and second fields, and the timing of the first and second fields allows the data to be output from the personal computer 1. The data from the personal computer 1 and the liquid crystal driving power for the first and second fields are respectively switched, and the display panel 12 is driven with the liquid crystal driving voltage corresponding to the data from the personal computer 1.

That is, field voltage modulation is performed by a combination of different voltage levels of a plurality of fields on the liquid crystal display means 2 based on an image output signal from the personal computer 1, and a gradation display is performed based on the average effective voltage during one frame period. Ru.

Incidentally, the image signal data read out from the frame memory 4 in the personal computer 1, the first field,
It is easy to convert the data for the first and second fields from the identification timing of the second field, and it is also possible to obtain the clock timing twice the synchronization signal or the field identification timing. It can be easily generated using the reference clock in the personal computer 1, and the converted digital data can be outputted as is from the personal computer 1 to the liquid crystal display means 2.

That is, in this embodiment, since the output to the liquid crystal display means 2 may be digital data, the A/D converter 14, which is conventionally provided for converting the analog RGB signal from the personal computer into a digital signal, and the Frame memories 15 and 16 for 1st and 2nd fields for gradation display
There is no need to hold the driver control unit 9 shown in the conventional example.
That becomes unnecessary.

Furthermore, as shown in FIG. 6, the transmittance of the liquid crystal -
The voltage characteristic (TV characteristic) is non-linear, and in this embodiment, gamma correction is performed to correct this characteristic to a linear one.

That is, a gamma correction ROM in which conversion table data is written in the personal computer 1 for gamma correction.
ROM 1 for gamma correction with image signal data.
Since gamma-corrected voltage data can be obtained by addressing 8, gamma correction can be performed at the same time when the MPU 3 reads the image data in the frame memory 4.

As described above, in this embodiment, the driver control section 9 controls the frame memories 15 and 16 for the first and second fields.
In addition, the D/A converter in the personal computer 1 and the A/D converter 1 in the driver control unit 9 are no longer required.
4 becomes unnecessary.

Furthermore, the image output signal for driving the liquid crystal display means 2 can be optimized, and the signal processing speed of the liquid crystal display means 2 can remain the same as the synchronization signal, that is, half of that of the conventional example. 2. Clock control becomes easy.

Therefore, since an A/D converter for multi-gradation display, a frame memory, etc. are not required, the driver control unit 9 is not required, and the liquid crystal display means can be downsized. By suppressing the cost of the liquid crystal display means, the device can be The cost of the main unit can be reduced.

Note that in the above embodiment, the data driver is ST
Although the explanation has been given by taking as an example the case where four-gradation display is performed as an N driver, the present invention is not limited to this, and the number of field divisions may be arbitrary, so that further multi-gradation display may be performed.

[0046]

[Effects of the Invention] According to the present invention, the output data set based on the gradation level of the image data stored in the frame memory can be output multiple times by the image signal output means at the time-divided timing of the frame time for each field. ,
Image data can be output as one frame of image data consisting of a plurality of fields, and the image output signal for driving the liquid crystal display means can be optimized.

[0047] Therefore, since an A/D converter for multi-gradation display, a frame memory, etc. are not required, the liquid crystal display means can be downsized, and by reducing the cost of the liquid crystal display means, the cost of the main body of the device can be reduced. can.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main part configuration of an information terminal device according to an embodiment of the present invention.

FIG. 2 is a diagram showing the output state of image signals in units of frames according to an embodiment of the present invention.

FIG. 3 is a diagram showing an output state of an image signal in units of dots according to an embodiment of the present invention.

FIG. 4 is a timing chart of a clock according to an embodiment of the present invention.

FIG. 5 is a diagram showing an output state of image data according to an embodiment of the present invention.

FIG. 6 is a diagram showing TV characteristics of liquid crystal.

FIG. 7 is a block diagram showing the main part configuration of a conventional information terminal device.

FIG. 8 is a diagram showing the output state of image data in a conventional example.

[Explanation of symbols]

1 Personal computer (information terminal device) 2 Liquid crystal display means 3 MPU 4 Frame memory 5 D/A converter 6 1st field liquid crystal drive power supply 7 2nd field liquid crystal drive power supply 8 Power supply switching circuit 9 Driver control unit 10 Data driver 11 Scan Driver 12 Display panel 13 Timing generator 14 A/D converter 15 First field frame memory 16
Second field frame memory 17 Data switching circuit 18 Gamma correction ROM 19 Timing generator 20 Data switching circuit

Claims (2)

[Claims] 1. A voltage level applied to each field in one frame, in which one frame is divided into a plurality of fields, and a predetermined voltage level is selectively applied from among a plurality of different voltage levels to each field. An information terminal device having a liquid crystal display means for displaying gradations based on the average effective voltage value of the information terminal device, the information terminal device having a frame memory for storing and holding multi-gradation image data to be displayed in units of frames, and storing data in the frame memory. data processing means for outputting output data based on the gradation level of the retained image data a plurality of times at timings in which the frame time is time-divided for each field, and selectively switching the output data from the data processing means. , data switching means for supplying the data to the liquid crystal display means, and image signal output means for outputting the image data as one frame of image data composed of a plurality of fields. 2. The information terminal device according to claim 1, wherein said image signal output means has a gamma correction table based on display characteristics of said liquid crystal display means.