JP4580063B2 - Liquid crystal display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device, and more particularly to temperature compensation of a liquid crystal panel.
[0002]
[Prior art]
Display devices for electronic devices used outdoors such as cellular phones are required to have a wide operating temperature range. In particular, in the case of a liquid crystal panel, the temperature is set to about −20 ° C. to 60 ° C., which is close to the entire temperature range in which the liquid crystal state can be maintained. There are many cases. For this reason, many parameters of liquid crystal panels often fluctuate greatly within this temperature range, and in particular, threshold characteristics relating to transmittance and voltage greatly fluctuate in the low temperature region immediately before solidification, as they have a large effect on the liquid crystal panel display. . However, many liquid crystal display devices change the drive voltage of the liquid crystal panel linearly with respect to temperature (hereinafter referred to as linear), and cope with sudden characteristic changes at low temperatures by using a brightness adjustment volume together. Is the current situation. On the other hand, if an attempt is made to make no adjustment, temperature compensation corresponding to a temperature characteristic that changes in a curve (hereinafter referred to as non-linearity) is required.
[0003]
A general method for performing non-linear temperature compensation in an open loop system is to first digitize the voltage output of the temperature sensor, which is an analog quantity (hereinafter referred to as A / D conversion), and to provide a digital circuit (hereinafter referred to as code conversion unit). Then, a compensation value (hereinafter referred to as a compensation code) is created from an A / D converter output (hereinafter referred to as a temperature code), and this compensation code is returned to an analog amount again (hereinafter referred to as a D / A conversion). It controls the driving voltage of the liquid crystal panel.
[0004]
A ROM (read only memory) is often used for the code conversion unit. A compensation code is written in advance in the ROM, and the compensation code is read out using the temperature code as an address signal. This is functionally equivalent to what is called a lookup table.
[0005]
[Problems to be solved by the invention]
When using a ROM as a code converter, the ROM must be rewritten every time the liquid crystal material or liquid crystal panel specifications change and the temperature characteristics change, and the application range that can be applied under one ROM condition is narrow There is. In order to avoid this, if a code indicating various conditions in addition to the temperature code is also adopted as the address signal of the ROM and the application range is expanded, there arises a problem that the ROM size increases. Accordingly, an object of the present invention is to provide a liquid crystal display device having a non-linear temperature compensation system having a wide application range for temperature compensation and a small circuit scale.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the liquid crystal display device of the present invention has the following features. It has a temperature sensor and an A / D converter that converts the output of the temperature sensor into a temperature code of a digital signal, and generates a driving voltage for the liquid crystal panel by calculation from the output value of the A / D converter, and the driving voltage for the temperature In a liquid crystal display device that automatically adjusts, the calculation is performed by dividing the operating temperature range of the liquid crystal display device into a plurality of temperature ranges, with a specific temperature as an initial value, a temperature code at the initial value as a reference temperature code, and an initial value The compensation code in the value is used as a reference compensation code, the temperature code output from the A / D converter is read, an approximate line segment specified by a multi-bit parameter is provided for each temperature range, and the read temperature code is If it corresponds to a temperature higher than the reference temperature code, or if the read temperature code corresponds to a temperature lower than the reference temperature code, respectively Quasi compensation code, by repetitively subtracting or adding the increment specified by register corresponding to the approximate line, and calculates a new compensation code, the calculated compensation code, the trimming circuit or electronic volume occurs A digital value is added, a value obtained by the addition is converted into an analog voltage, and the analog voltage is amplified to generate a drive voltage. In addition, a switching regulator is used to amplify the analog voltage. Further, the temperature range is divided into four temperature ranges. Further, the width of the temperature range is approximately 30 ° C., and the specific temperature is approximately 20 ° C.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a graph (A) showing a state of nonlinear temperature compensation according to an embodiment of the present invention and a block diagram (B) of a liquid crystal drive voltage generation circuit. In (A), the vertical axis is voltage and the horizontal axis is temperature. The temperature compensation range is −40 ° C. to 80 ° C., and is divided into four temperature ranges of −40 ° C. to −10 ° C., −10 ° C. to 20 ° C., 20 ° C. to 50 ° C., and 50 ° C. to 80 ° C. Line segments 1, 2, 3, and 4 indicated by solid lines in the respective temperature regions are temperature-compensated control voltages, and are continuous between the respective regions while decreasing. This control voltage has a similar tendency to the threshold voltage curve 100 (dotted line) relating to the transmittance and drive voltage of the liquid crystal panel, and is an approximate line segment for an ideal control voltage when complete temperature compensation is possible. ing. 20 ° C. is the central temperature, and an initial value is set for this temperature as will be described later.
[0008]
In FIG. 1B, a code conversion unit 126 includes registers 101, 102, 103, and 104 that store approximate line segment numbers corresponding to respective temperature regions, and a comparison operation unit 105, and a 6-bit temperature code 106 is input. Then, a 7-bit compensation code 109 is output. Since an arbitrary approximate line segment can be selected by designating a number from a group of approximate line segments with eight inclination values set in advance, each register 101, 102, 103, 104 has 3 bits. is there. The output of the temperature sensor 108 is converted into a 6-bit temperature code 106 by an A / D converter 107. In addition to the 7-bit compensation code 109, the 8-bit adder 110 includes an 8-bit line set by the limiter 111, a 6-bit line set by the trimming circuit 116, and a 6-bit set by the electronic volume circuit 113. A line enters. The output of the adder 110 is converted into an analog voltage by the D / A converter 114 and becomes the control voltage 125. The control voltage 125 corresponds to the temperature-compensated control voltage of (A), and is input to the comparison reference terminal (+ side) of the comparator 115.
[0009]
The comparator 115 that compares the voltage with the control voltage 125, the oscillator 116 that oscillates when the output of the comparator 115 is at a high level, and the on-state of the current flowing from the battery 118 to the ground via the coil 119 by the output of the oscillator 116 A switching regulator is configured by the transistor 117 that performs the off control, the rectifying and smoothing diode 120 and the capacitor 121, and the resistors 123 and 124 that divide the obtained high voltage 122 and feed back the divided voltage to the comparator 115. ing. Since the high voltage 122 is divided to create various drive voltages for the liquid crystal panel, the drive voltage is linked with temperature compensation of the control voltage 125.
[0010]
In FIG. 1B, the D / A converter 114 is set so that the 1-bit change of the adder 110 corresponds to the 10 mV change of the control voltage 125. The limiter 111 determines the upper limit of the addition value of the adder 110 so as not to generate an excessively high voltage, and the adder 110 outputs this upper limit value when the addition value exceeds the upper limit value.
The trimming 112 adjusts variations in the threshold voltage of the liquid crystal panel, the offset voltage of the temperature sensor 108, the A / D converter 107 and the D / A converter 114, and the values of the resistors 123 and 124. The electronic volume 113 controls the contrast (or brightness) of the liquid crystal panel with a digital signal.
[0011]
FIG. 2 is a block diagram of the comparison operation unit 105 of the code conversion unit 126 according to the embodiment. Since it is a synchronous circuit, the clock signal is omitted. As the temperature rises, the temperature code 106 also increases. The temperature code 106 is input to the data terminal D of the T register 201. A signal 200 indicating the start of code conversion is input to the enable terminal E of the T register 201 and the control terminals of the selectors 207 and 214. The output Q of the T register 201 is input to the comparator 202. The output of the comparator 202 is input to the control terminals of the selectors 205 and 210 and the enable terminal E of the U register 208. The output Q of the S register 206 is input to an adder (+1) 203 adding the comparators 202 and 1, a subtracter (−1) 204 subtracting 1 and a selector 205. The outputs of the adder (+1) 203 adding 1 and the subtracter (−1) 204 subtracting 1 are input to the selector 205. The output of the selector 205 is input to the selector 207, and a temperature code corresponding to 20 ° C. is input to the other terminal of the selector 207. The output of the selector 207 is input to the data terminal D of the S register 206. The output Q of the R register is input to the data terminal D of the U register, the adder (+ δ) 211, the subtracter (−δ) 212, and the selector 210.
The outputs of the adder (+ δ) 211 and the subtracter (−δ) 212 are input to the selector 210. The output of the selector 210 is input to the selector 214, and a compensation code (1000000) of 20 ° C. is input to the other terminal of the selector 214. The output of the selector 214 is input to the data terminal of the R register 213. The output Q of the U register is a compensation code 109.
[0012]
In FIG. 2, when a signal 200 indicating the start of code conversion is input, the T register 201 reads the temperature code 106, and at the same time, the selector 207 selects a temperature code corresponding to 20 ° C., and the S register 206 reads this. The selector 214 selects a compensation code corresponding to 20 ° C., and the R register 213 reads it.
Subsequently, the comparator 202 compares the output Q of the T register 201 with the temperature code of 20 ° C., which is the output Q of the S register 206, and determines whether T> 20 ° C., T <20 ° C., or T = 20 ° C. . When T = 20 ° C., the U register 208 reads the output Q of the R register at the next clock and outputs it as the compensation code 109. Thereafter, this state is maintained until a signal 200 indicating the start of code conversion is input again.
[0013]
When T <20 ° C., the selector 205 selects the output of the subtracter (−1) 204 which subtracts 1, and the selector 207 selects the output of the selector 205 (hereinafter, the selector 207 selects the selector 205 until the signal 200 is input). The S register 206 reads the value obtained by subtracting 1 from its output Q and switches the output Q at the next clock. Similarly, the selector 210 selects the output of the adder (+ δ) 211 and the selector 214 selects the output of the selector 210 (hereinafter, the selector 214 continues to select the output of the selector 210 until the signal 200 is input. The R register 213 reads a value obtained by adding the increment δ to its own output Q and switches the output Q at the next clock. Subsequently, the comparator 202 compares the output Q of the T register 201 with the updated output Q of the S register 206 and determines whether or not they match. If they match, the U register 208 reads the output Q of the R register and outputs it as the compensation code 109 at the next clock. If they do not match, 1 is again subtracted from the S register 206, and an increment δ is added to the R register 213, and it is compared again whether they match. This is repeated until the output Q of the T register 201 and the output Q of the S register 206 match, and when they match, the U register 208 reads the output Q of the R register 213 and outputs it as the compensation code 109. If they match, this state is maintained until the signal 200 indicating the start of code conversion is input again.
[0014]
When T> 20 ° C., the selector 205 selects the output of the adder (+1) 204 to which 1 is added, and at the next clock, the S register 206 reads a value obtained by adding 1 to its own output Q and switches the output Q. . Similarly, the selector 210 selects the output of the subtracter (−δ) 212, and at the next clock, the R register 213 reads a value obtained by subtracting the increment δ from its own output Q and switches the output Q. Subsequently, the comparator 202 compares the output Q of the T register 201 with the updated output Q of the S register 206 and determines whether or not they match. If they match, the U register 208 reads the output Q of the R register and outputs it as the compensation code 109 at the next clock. If they do not match, 1 is again added to the S register 206, the increment δ is subtracted from the R register 213, and it is compared again whether they match. This is repeated until the output Q of the T register 201 and the output Q of the S register 206 match, and when they match, the U register 208 reads the output Q of the R register 213 and outputs it as the compensation code 109. If they match, this state is maintained until the signal 200 indicating the start of code conversion is input again.
[0015]
Here, the increment δ is determined by two conditions such as which approximate line segment is used and what the lower 2 bits of the output Q of the S register 206 are. The line segment is switched between −10 ° C. and 50 ° C., and in the temperature range from −40 ° C. to −10 ° C., an approximate line segment (in other words, an incremental table) designated by the register 101 in FIG. 1B is used. Similarly, in the temperature ranges of −10 ° C. to 20 ° C., 20 ° C. to 50 ° C., and 50 ° C. to 80 ° C., the approximate line segments specified by the registers 102, 103, and 104 are used. A table for determining the increment δ is shown in FIG. As shown in FIG. 3, in the embodiment of the present invention, eight kinds of inclination values (Vr inclination mV / bit) approximate line segments are formed. Each approximate line segment is designated by the values of 3-bit parameters P1, P2, and P3. Since the increment is a decimal value of 0, 1, 2, or 3, the binary number is indicated by 2 bits. When the approximate line segment and the lower 2 bits of the S register 206 output Q are designated, the increment is determined. For example, if the approximate line segment is (011), the lower 2 bits are (00), (01), (10), (11) and the increment is 1 (01), 2 (10), 1 (01) 2 (10). When the compensation code changes by 1 bit, the output of the D / A converter (hereinafter referred to as control voltage Vr) changes by 10 mV. Therefore, when the compensation code changes by 4 bits, the control voltage Vr changes by 60 mV ((1 + 2 + 1 + 2) × 10 mV). From this, the slope of the control voltage Vr becomes 15 mV / bit.
Further, since the entire temperature compensation range is 120 ° C. (−40 ° C. to 80 ° C.) and the temperature code is 6 bits, the temperature step width is 1.875 ° C./bit.
[0016]
In the embodiment, the temperature at the center of the temperature compensation range is selected as the initial value, but any temperature can be realized. In particular, if the initial value is set to the lowest temperature or the highest temperature in the temperature compensation range, it is possible to add or subtract calculations. In addition, it is possible to increase the number of registers in the comparison operation unit and adopt the previous measurement temperature as the initial value, thereby reducing the number of operations.
[0017]
【The invention's effect】
The temperature compensation of the liquid crystal panel has a favorable condition that the control speed can be slow while there are circumstances that are allowed even with relatively rough accuracy because there are other parameters that deteriorate the performance such as response speed in the low temperature region. It must have strong nonlinearity. As apparent from the above description, the configuration of the present invention to perform temperature compensation of dividing the temperature compensation range to a plurality of temperature ranges in the temperature regions in the approximate line segments, the temperature characteristics lying beside related threshold of the liquid crystal panel well it reflects the property of decreasing the S-shape was. In addition, the main calculation also generates a digital value (compensation code in the embodiment) corresponding to the temperature-compensated driving voltage at the temperature detected from the increment (or slope value) of the approximate line segment and the initial value. Since a simple calculation (or conversion table) is sufficient, a plurality of types of line segments can be easily created in the circuit in advance, so that it is possible to cope with a wide range of changes in the number of divisions and liquid crystal substances. In addition, since the code conversion unit of this system can use repetitive calculation under the condition that the temperature compensation is low, it can be composed of a small number of registers, a comparison circuit, and a small value addition / subtraction circuit, so the circuit scale is small.
[0018]
In particular, 20 ° C. selected as the initial value is close to room temperature, which is convenient for trimming and other adjustment at the time of shipment. In addition, the liquid crystal panel has a characteristic change that deviates from linear at a high temperature part immediately before liquefaction in addition to a sudden characteristic change immediately before solidification. Therefore, when the temperature at the center is 20 ° C., the temperature compensation range is divided into four as a temperature region. Goes well with. Considering that the characteristic change is moderate at room temperature, the accuracy of the temperature sensor without calibration is about several degrees Celsius, and the temperature compensation range is about 120 degrees Celsius, the temperature code should be 6 bits. The effect of temperature quantization is less noticeable.
[Brief description of the drawings]
FIG. 1 is a graph (A) of nonlinear temperature compensation and a block diagram (B) of a liquid crystal drive voltage generation circuit according to an embodiment of the present invention.
FIG. 2 is a block diagram of a comparison operation unit of the code conversion unit according to the embodiment of this invention.
FIG. 3 is a table for determining an increment δ according to the embodiment of this invention.
[Explanation of symbols]
1,2,3,4 control voltage approximating line segments 100 threshold temperature characteristics 101, 102, 103 and 104 approximates segments of register 105 comparing unit 106 temperature code 107 A / D converter 108 Temperature Sensor of liquid crystal panel for 109 Compensation code 110 8-bit adder 111 Limiter 112 Trimming 113 Electronic volume 115 Comparator 122 High voltage 125 for driving the liquid crystal panel 125 Control voltage 126 Code conversion unit 201, 206, 208, 213 Add the register 204 1 to the register 203 1 Subtractor 205, 207, 210, 214 Selector 211 2-bit increment value adder 212 2-bit increment value subtractor

Claims (5)

A temperature sensor and an A / D converter that converts the output of the temperature sensor into a temperature code of a digital signal, and generates a driving voltage of the liquid crystal panel by calculation from the output value of the A / D converter, and In a liquid crystal display device that automatically adjusts the drive voltage,
The calculation is
Dividing the operating temperature range of the liquid crystal display device into a plurality of temperature ranges;
A specific temperature as an initial value, the temperature code at the initial value as a reference temperature code, and the compensation code at the initial value as a reference compensation code,
Read the temperature code output from the A / D converter,
An approximate line segment specified by a multi-bit parameter is provided for each temperature range, and the read temperature code corresponds to a temperature higher than the reference temperature code, or the read temperature code is When a temperature lower than the reference temperature code is supported, a new compensation code is newly added to the reference compensation code by repeatedly subtracting or adding the increment specified by the register corresponding to the approximate line segment. Calculate
Generating the drive voltage based on the calculated compensation code;
The drive voltage varies linearly with a predetermined slope value within each temperature range, and the drive voltage is continuous at a temperature that is a boundary between adjacent temperature ranges. A liquid crystal display device.   A digital value generated by a trimming circuit or an electronic volume is added to the calculated compensation code, a value obtained by the addition is converted into an analog voltage, and the analog voltage is amplified to generate the drive voltage. The liquid crystal display device according to claim 1. The liquid crystal display device according to claim 2 , wherein a switching regulator is used to amplify the analog voltage. The liquid crystal display device according to any one of claims 1 to 3, characterized in that dividing the temperature range into four temperature ranges. The width of the temperature range is the approximately 30 ° C, the liquid crystal display device according to claim 1, wherein in any one of the 4 in that the specific temperature is approximately 20 ° C.

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