JPH04291389A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal display device, which is used in wide circumferential brightness environment from daytime to nighttime and holds the contrast of a liquid crystal panel surface above a constant value by using small-sized, inexpensive elements. CONSTITUTION:A switch panel 15 is added to the liquid crystal display device and a back light driving circuit 7 which switches the value of a resistance converting an external light detection current signal into a voltage and the address of a nonvolatile storage element 11 with the switch status signal from a switch panel 15 is improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a liquid crystal display device that detects the brightness of external light and controls the brightness of a liquid crystal panel in accordance with the brightness of external light.

0002

2. Description of the Related Art FIG. 4 shows an example of a schematic configuration of a conventional liquid crystal display device. In FIG. 4, reference numeral 1 denotes a timing generation circuit that generates a video timing signal, an X-direction display timing signal, and a Y-direction display timing signal; 2 is a display signal generation circuit that inputs a video timing signal and generates an X-direction video signal and a Y-direction video signal; 3 is an X-drive circuit that inputs an X-direction video signal and an X-direction display timing signal and converts it into an X-direction drive signal. , 4 is a Y drive circuit that inputs a Y direction video signal and a Y direction display timing signal and converts it into a Y direction drive signal, 5 is a liquid crystal panel that performs dot matrix display using an X direction drive signal and a Y direction drive signal, and 6 is an external device. 7 is a backlight drive circuit that inputs the DC power output value and the external light detection current signal and converts it into a backlight drive voltage; 8 is a liquid crystal panel; Backlight that illuminates 5 from the rear, SD, STX, STY, SV
X, SVY, Xd, Yd, IS, VDC, and Vd are respectively a video timing signal, an X-direction timing signal, a Y-direction display timing signal, an X-direction video signal, a Y-direction video signal, an X-direction drive signal, and a Y-direction drive signal. , an external light detection current signal, a DC power supply output value, and a backlight drive voltage. FIG. 5 is a diagram showing details of a backlight drive circuit 7 including an external light detector 6 of a conventional liquid crystal display device. In FIG. 5, 9 is a resistor RL for converting the output IS of the external light detector 6 into a voltage, and 10 is a resistor A for converting the analog signal converted into voltage into a digital signal by RL9.
11 is a nonvolatile memory element, 12 is a D/A converter that converts the digital signal output from the nonvolatile memory element 11 into an analog signal, 13 is an adder, and 14 is a booster circuit.

A conventional liquid crystal display device is constructed as described above, and the timing generation circuit 1 normally has an SD required by the display signal generation circuit 2 and an It generates STX and STY for address control in the direction (horizontal direction) and Y direction (vertical direction) and outputs them to the X drive circuit 3 and Y drive circuit 4. The display signal generation circuit 2 is
SVX and SV according to the input SD timing.
Y is generated and output to the X drive circuit 3 and the Y drive circuit 4, respectively, and in the X drive circuit 3, STX and S
The Y drive circuit 4 converts the drive load in the X direction of the liquid crystal panel 5 into the necessary Xd by VX, and converts it into the Yd necessary to drive the liquid crystal panel 5 in the Y direction by STY and SVY.
The liquid crystal panel 5 is controlled by Xd and Yd. On the other hand, the backlight drive circuit 7 inputs the output IS of the external light detector 6 which outputs a signal that changes depending on the brightness of external light, and after the IS is converted into a voltage by the RL9, the A/
It is converted into a digital signal by the D converter 10 and input to the nonvolatile memory element 11. The non-volatile memory element 11 stores appropriate data according to the brightness of external light, and the output signal from the A/D converter 10 is converted into appropriate data by the non-volatile memory element 11. ,D/
The signal is again converted into an analog signal by the A converter 12 and input to the adder 13 . Further, the adder 13 adds the output of the D/A converter 12 and VDC from the outside,
The boost circuit 14 boosts the voltage to a voltage suitable for driving the backlight 8, and outputs the voltage as Vd to the backlight 8.

FIG. 6 is a diagram showing the relationship between external light and the panel surface when the contrast on the panel surface of a conventional liquid crystal display device is kept constant. In the figure, the horizontal axis shows external light input in logarithmic form, and the vertical axis shows the luminance (LX) on the liquid crystal panel surface in logarithmic form. The external light input for conventional liquid crystal display devices is dark night (illuminance: approximately 0.1LX).
As shown in FIG. 5, the brightness on the liquid crystal panel surface is controlled while always maintaining the contrast above a certain value.

As described above, in the conventional device, brightness control is performed to maintain the contrast above a certain value according to the brightness of the outside environment, using Vd as a function of VDC and IS. Note that when external light in the range from 0.1LX to 10000LX is input, the backlight drive circuit 7
The accuracy required for the A/D converter 10 in the
÷0.1=100000 2N≧100000 ∴N≧17, and 17 bits or more are required. In addition, the nonvolatile memory element 11 in the backlight drive circuit 7 also has 217=1
A capacity of 31072 (128 KBIT) is required.

[0006]

[Problems to be Solved by the Invention] In the above-mentioned liquid crystal display device, external light input is difficult at night (illuminance: approximately 0.1L).
X) to direct sunlight during the day (illuminance: approx. 10,000 LX),
The conversion accuracy required for the converter 10 is 17 bits or more, and the non-volatile memory element 11 also requires a capacity of 128 KBIT or more, so there is a problem that a large and expensive element must be used. .

[0007] The present invention was made to solve this problem, and the IS
It is an object of the present invention to provide a liquid crystal display device that can use small and inexpensive elements by switching the value of RL that converts RL into a voltage and the address of a nonvolatile memory element.

[0008]

[Means for Solving the Problems] A liquid crystal display device according to the present invention is provided with a switch panel that converts IS into voltage by manual operation according to the magnitude of external light. The device is equipped with a means for switching between the two.

[0009] Furthermore, a level detector and an analog switch are provided in the backlight drive circuit to automatically control the I/O.
A means is provided for switching the value of RL for converting S into a voltage and the address of the nonvolatile memory element.

0010

[Operation] This invention has a function of switching the value of RL for converting IS into voltage and the address of the nonvolatile memory element according to the magnitude of external light input, so that the conversion accuracy required for the A/D converter is achieved. In addition, the capacity of the nonvolatile memory element can be reduced, and a liquid crystal display device equivalent to the conventional device can be realized by using a small and inexpensive element.

[0011]

[Example] Example 1 FIG. 1 is a schematic diagram showing an example of the present invention.
1-8, SD, STX, STX, SVX, SVY, Xd
, Yd, IS, VDC, and Vd are the same or equivalent parts as in the conventional device, and 15 is a switch panel, ST1, ST2
are switch status signal 1 and switch-status signal 2, respectively.

FIG. 2 is a diagram for explaining in detail the external light detector 6, backlight drive circuit 7, and switch panel 15 in FIG. 1, and 10 to 14 are the same or equivalent parts as in the conventional device. 16 is resistance RLA, 17 is resistance R
He is LB.

The liquid crystal display device according to the present description is constructed as shown in FIGS. 1 and 2, and emits 10,000 L of external light.
It is assumed that the brightness is controlled in the range from X to 0.1LX.

[0014] Now, assuming that the range from 10,000LX to 30LX is set to daytime mode and the range from 30LX to 0.1LX is set to nighttime mode, and the switching between daytime mode and nighttime mode is performed at 30LX by manual operation, the present invention will be explained. Explain the liquid crystal display device.

When external light from 10000LX to 30LX is input to the external light detector 6, the outputs ST1 and ST2 of the switch panel 15 are connected to GND by manual operation.
(LOW) level. At that time, the backlight drive circuit 7 inputs the output IS of the external light detector 6, and the IS is
After being converted to an appropriate voltage by the RLA 16, it is converted to a digital signal by the A/D converter 10 and input to the nonvolatile memory element 11.

The non-volatile memory element 11 stores appropriate data according to the brightness of external light, and the output signal from the A/D converter 10 and ST2 cause the non-volatile memory element 11 to store appropriate data. After being converted into an analog signal, the D/A converter 12 converts the signal into an analog signal again.
It is input to the adder 13. On the other hand, VDC is directly input to the adder 13. Adder 13 is D/A converter 1
The output of 2 and VDC are added, and the voltage is boosted by a booster circuit 14 and output as Vd.

However, the A/
The conversion accuracy required for the D converter 10 is 10000÷3
0=333 2N≧333 ∴N≧9, and 9 bits are required. Furthermore, the nonvolatile memory element 11 in the backlight drive circuit 7 also requires a capacity of 29=512 (512 BIT).

Next, when external light from 30LX to 0.1LX is input to the external light detector 6, the outputs ST1 and ST2 of the switch panel 15 are set to Vcc by manual operation.
(High) level. At that time, the backlight drive circuit 7 inputs the output IS of the external light detection circuit 6, and
S is converted into an appropriate voltage by the RLA 16 and RLB 17, then converted into a digital signal by the A/D converter 10, and input to the nonvolatile storage element 11.

The non-volatile memory element 11 stores appropriate data according to the brightness of external light, and the output signal from the A/D converter 10 and ST2 cause the non-volatile memory element 11 to store appropriate data. After being converted into an analog signal, it is converted again into an analog signal by the D/A converter 12,
It is input to the adder 13. On the other hand, VDC is input to the adder 13 immediately after. Adder 13 is D/A converter 1
The output of 2 and VDC are added, and the result is boosted by a booster circuit 14 and output as Vd.

However, the A/
The conversion accuracy required for the D converter 10 is 30÷0.1=
300 2N≧300 ∴N≧9, and 9 bits are required. Furthermore, the nonvolatile memory element 11 in the backlight drive circuit 7 also requires a capacity of 29=512 (512 BIT).

In the above explanation, RLA16 and RLB1
The relationship between 7 is daytime mode: nighttime mode = RLA: RLA + RLB1:
It goes without saying that 333=RLA:RLA+RLB ∴RLB=332RLA.

From the above explanation, by manually switching between the day mode and the night mode, the A/D
The conversion accuracy required for the converter 10 is 17b of the conventional device.
In addition, the capacity of the non-volatile memory element can be reduced from 128KBIT of the conventional device to 1Kbit.
It can be made into BIT.

Example 2. In the first embodiment described above, a switch panel 15 is provided and the value of RL and the address of the non-volatile memory element 11 are switched by manual operation, but in this embodiment, the switch panel 15 is replaced with a switch panel 15 as shown in FIG. , a level detector 18 and an analog switch 19 are provided in the backlight drive circuit 7, the level detector 18 automatically detects the magnitude of IS, and the analog switch 19 stores the value of RL in a non-volatile memory element. A similar operation can be expected by switching the address of No. 11.

[0024]

Effects of the Invention: As explained above, the present invention provides an interface that can be operated manually or automatically depending on the magnitude of external light input.
By providing a switch panel that switches the resistance value that converts S into voltage and the address of the nonvolatile memory element, A
The conversion accuracy required for the /D converter can be reduced, and
This has the effect of reducing the capacity of the nonvolatile memory element.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of Example 1 according to the present invention.

FIG. 2 is a detailed explanatory diagram of an external light detector, a backlight drive circuit, and a switch panel of Example 1 according to the present invention.

FIG. 3 is a detailed explanatory diagram of an external light detector and a backlight drive circuit according to a second embodiment of the present invention.

FIG. 4 is a schematic configuration diagram of a conventional liquid crystal display device.

FIG. 5 is a detailed explanatory diagram of a backlight drive circuit including an external light detector of a conventional device.

FIG. 6 is a diagram showing the relationship between external light panel surfaces when the contrast light on the panel surface of the liquid crystal display device is kept constant.

[Explanation of symbols]

1 Timing generation circuit 2 Display signal generation circuit 3.X drive circuit 4 Y drive circuit 5. LCD panel 6. Ambient light detector 7 Backlight drive circuit 8 Backlight 9 RL 10 A/D converter 11 Nonvolatile memory element 12 D/A converter 13 Adder 14 Boost circuit 15 Switch panel 16 RLA 17 RLB 18 Level detector 19 Analog switch

Claims (2)

[Claims] 1. A timing generation circuit that generates a video timing signal, an X-direction display timing signal, and a Y-direction display timing signal, and a display generation circuit that receives the video timing signal and generates an X-direction video signal and a Y-direction video signal. an X drive circuit which inputs the X-direction video signal and the X-direction display timing signal and converts them into an X-direction drive signal; and an X-drive circuit which inputs the Y-direction video signal and the Y-direction display timing signal and converts them into a Y-direction drive signal. a Y drive circuit that inputs the above Y-direction drive signal and displays a dot matrix, an external light detector that outputs an external light detection current signal proportional to external brightness, and a switch status signal 1 that is manually operated. and a switch panel that outputs the switch status signal 2, a resistor that converts the external light detection current signal into a voltage appropriate for the switch status signal 1, and A that converts the analog signal converted into voltage by the resistor into a digital signal. /D converter, a nonvolatile memory element that outputs appropriate data according to external brightness based on the output of the A/D converter and the switch status signal 2, and converts the output from the nonvolatile memory element into an analog signal. A backlight drive circuit including a D/A converter, an adder that adds the output of the D/A converter and a DC power output value, and a boost circuit that boosts the output signal of the adder, and the backlight drive. A liquid crystal display device comprising: a backlight that illuminates the liquid crystal panel from the rear using an output from a circuit. 2. The liquid crystal display device according to claim 1, further comprising a level detector and an analog switch provided in the backlight drive circuit.