JPH07225368A - Driving method of liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device which has a temperature compensating circuit to absorb the adverse effect caused by parts dispersion during a production and to suppress degradation of liquid crystal caused by the application of a d.c. voltage. CONSTITUTION:During the temperature compensation of an active matrix liquid crystal display device which uses switching elements, the temperature compensation digital data read from a lookup table 102 are converted to analog voltage by D/A converters 706 and 707 and are amplified to provide liquid crystal driving voltages. During this amplification, an amplification factor K1 of an amplifier 108, which is used to amplify the voltage for a positive polarity writing, and an amplification factor K2 of an amplifier 109, which is used to amplify the voltage for an negative polarity writing, are made equal in terms of their absolute values and an application of a d.c. component to the liquid crystal caused by the errors of the amplifiers is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of setting a driving voltage of a liquid crystal display device, and more particularly to temperature compensation of a driving voltage of an active matrix liquid crystal panel.

[0002]

2. Description of the Related Art MIM (me) is used as an element often used as a switching element of an active matrix liquid crystal panel.
There are two-terminal type non-linear elements such as a tal insulator metal element. The MIM element has a sandwich structure in which a thin insulating layer is sandwiched between conductor layers and has bidirectional diode characteristics. The liquid crystal display panel using this MIM element has a shorter manufacturing process and higher productivity than a liquid crystal display panel using a three-terminal type TFT element, and is advantageous in increasing the size of the liquid crystal display panel. There are advantages.

As a driving method using this MIM element, a four-level driving method has been disclosed in which two kinds of positive and negative selection voltages and two kinds of positive and negative holding voltages are applied to scan electrodes (Japanese Patent Publication No.
-714). FIG. 11 shows the output waveform on the scan electrode side in the 4-level drive method. Va + is a positive write voltage that makes the forward diode of the MIM element conductive, and Va- is a negative write voltage that makes the reverse diode of the MIM element conductive. Further, Vb + is a voltage required to hold the electric charges written in the positive polarity writing, and Vb- is a voltage required to hold the electric charges written in the negative polarity writing.

The current-voltage characteristics of MIM elements are often asymmetrical between positive and negative. In particular, its characteristics change significantly with temperature, and the asymmetry changes greatly. Among the four-level drive waveforms, the positive write voltage Va + and the negative write voltage Va- largely contribute to the temperature change of the current-voltage characteristic of the MIM element. The holding voltages Vb + and Vb- do not contribute much to the temperature change because the current flowing during holding is basically small and has little influence on the driving of the liquid crystal panel. However, a large amount of current flows during positive and negative polarity writing, and its characteristic curve is also very steep like the diode characteristic. Therefore, if the characteristics of the MIM element change even slightly due to temperature changes, the positive and negative writing voltages will change. V
The optimum values of a + and Va- also change, and the absolute value of the charge that goes in and out of the pixel in the liquid crystal panel becomes significantly different between the positive polarity writing and the negative polarity writing, and the accumulated charge is stored in the liquid crystal in the pixel. DC component is applied. As a result, the liquid crystal is deteriorated due to uneven distribution of ions. Therefore, it is necessary to perform temperature compensation for always setting the positive polarity write voltage Va + and the negative polarity write voltage Va- to optimum values according to the temperature characteristics of the MIM element.

FIG. 10 shows the optimum voltage-temperature characteristics of the positive polarity write voltage Va + and the negative polarity write voltage Va- at which no DC component is applied to the liquid crystal even if the temperature changes. The voltage-temperature characteristics of both Va + and Va- become smaller as the temperature rises, and become larger as the temperature rises. Further, the slope of the characteristic is non-linear and has almost no regularity.

As a first possible method for controlling a voltage having an irregular characteristic as shown in FIG. 10 with temperature as a variable, there is a method in which a resistor and a temperature-sensitive component are combined. In this case, the obtained temperature compensation voltage characteristic basically depends on the temperature-voltage characteristic of the temperature-sensitive component, and in order to obtain an arbitrary characteristic, a temperature-sensitive component having a temperature-voltage characteristic corresponding to the characteristic must be used. I won't. However, most of the temperature-sensitive parts are designed with emphasis on linearity, and few have non-linear characteristics, and it is very difficult to obtain the characteristics shown in FIG.

As a second method, there is a temperature compensation circuit in which an active component such as a transistor and a temperature sensitive component are combined to perform analog processing. In the case of the analog processing temperature compensating circuit, it is impossible to faithfully control the voltage having the irregular characteristic as shown in FIG. 10, and the control is performed by the approximate characteristic in most cases. In addition, since the active component itself has temperature characteristics, the temperature variable increases and becomes very complicated.

As described above, the first method and the second method have basic problems in analog processing. At present, there is no effective means to solve this problem. Therefore, a method of performing temperature compensation by digital processing has been proposed.

As a third method, digital temperature compensation using a microcomputer (hereinafter referred to as a microcomputer) will be described. FIG. 12 shows a block diagram of an 8-bit digital temperature compensation system. The output of the temperature sensor 704 is connected to the A / D converter 705 in the microcomputer 701. The microcomputer 701 includes a CPU 703, a look-up table 702, and an A / D converter 705. 8-bit digital data DATA + and DATA- are output from the output port of the microcomputer 701 to the D / A converter 1706 and the D / A converter 2707, respectively.
The reference voltage Vref is the same as that of the D / A converter 1706.
Connect to converter 2707. D / A converter 17
06, and the output voltage of the D / A converter 2707 is output to the amplifier 1708 and the amplifier 2709, respectively. Amplifier 1
The amplification factor of 708 is K1, and the amplification factor of amplifier 2709 is K.
It is 2. The output of each amplifier is connected to the liquid crystal panel 710.

Next, details of the operation will be described. The temperature sensor 704 has a function of converting temperature into voltage, and its temperature-voltage characteristic is linear. The output of the temperature sensor 704 is amplified to an output voltage of 0V at -20 ° C and 5V at + 60 ° C so that the maximum conversion range of the A / D converter 705 can be used (amplification part is not shown). The A / D converter 705 in the microcomputer 701 performs analog-digital conversion. The conversion range is set from -20 ℃ to + 60 ℃ because the recommended operating range of liquid crystal is generally 0-40 ℃.
This is because the compensation range is ± 20 ° C. The result after conversion is 8-bit data, where 0 is -20 ° C and 255 is +
Corresponding to 60 ° C, 1LSB is a step of + 0.3 ° C. For example, when the room temperature is 25 ° C., the A / D converter 70
The 8-bit data output from 5 is 144.

The contents of the lookup table 702 will be described. The storage format of the 8-bit data of the look-up table 702 is ROM (read only memory).
The storage area is divided into two, and one of the storage areas is D /
8-bit data DAT output to A converter 1706
A + is stored, and the D / A converter 27 is stored in the other storage area.
It stores 8-bit data DATA- to be output to 07. Each output data follows the following formula. DATA + = Va + ÷ K1 ÷ Vref × 256 (1) DATA- = Va- ÷ K2 ÷ Vref × 256 (2) Va + in the formula (1) is the optimum positive write voltage at each temperature shown in Fig. 6, ( Va- in the equation 2) is the optimum negative write voltage at each temperature shown in FIG.

The arrangement of addresses when writing the 8-bit data created by the equations (1) and (2) into the ROM constituting the lookup table will be described. The storage capacity of the ROM is 512 bytes because two storage areas of DATA + and DATA- each require 256 bytes. For the ROM address, the converted output value of the A / D converter 705 in the microcomputer 701 is used by associating the temperature of the temperature-voltage characteristic of FIG. In the first memory area, 8 of the positive write voltage Va + in FIG.
Since the bit data DATA + is written, DATA + at −20 ° C. is stored in the address 0, and 2
At address 55, DATA at + 60 ° C
Store +. Since the second memory area starts from the address of address 256 and the 8-bit data DATA- of the negative write voltage Va- in FIG. 10 is written,
At the 6th address, DATA- at -20 ° C
Is stored, and DATA- at + 60 ° C. is stored in the 512th address. Lookup table 702
The situation is shown in FIG.

The D / A converter 1706 and the D / A converter 2707 have 8-bit resolution and have a reference voltage Vr.
The voltage value of ef is 5V.

The amplifier 1708 is composed of a non-inverting amplifier, and its amplification factor K1 is such that the maximum output voltage of the D / A converter 1706 becomes 5 V which is the value of Vref, and the maximum value of the positive polarity write voltage Va + is-. 35 at 20 ° C
Since it becomes V, it is set to 7 times from the formula (3). K1 = 35V ÷ 5V = 7 (3) Further, the amplifier 1708 is composed of an inverting amplifier, and its amplification factor K2 is the maximum value of the negative polarity write voltage Va−.
Since it becomes −16 V when the temperature is −20 ° C. from 0, it is set to −2.2 times from the formula (4). K2 = −16 ÷ 5V = −2.2 (4)

Taking the above amplification factor into consideration, the 8-bit data of the lookup table 702 at 25 ° C. is
From Fig. 10, Va + is 28V and Va- is -9V at 25 ℃.
Substituting into equations (1) and (2), DATA + becomes 204.8 according to equation (5), rounds off to the decimal point and becomes 205, and DATA− becomes 20 according to equation (6).
It becomes 9.4, rounded down to the nearest whole number, and becomes 209. 28V ÷ 7 ÷ 5V × 256 = 204.8 (5) -9V ÷ -2.2 ÷ 5V × 256 = 209.4 (6)

Since the above two 8-bit data are at 25 ° C., the address of the lookup table 702 at 25 ° C. is the 144th address in the positive write memory area, and the negative write memory area. Then it will be number 400.

From the above, the DATA + value 205 is written in the 144th address of the lookup table 702, and the DATA- value 209 is written in the 400th address. This from 0 ℃ to 60
A lookup table 702 is created by going up to ℃.
This look-up table 702 is created only once during mass production, is written in the mask ROM of the microcomputer during mass production, and is common to all lots.

Next, an actual temperature compensating operation will be described by taking 25 ° C. as an example. First, the temperature of the liquid crystal panel 710 is measured by the temperature sensor 704, and the analog-digital conversion is performed by the A / D converter 705 in the microcomputer 701.
The 8-bit digital value 144 of ° C is input to the CPU 703. The CPU 703 uses the address 144 as the address and the DATA + 8-bit data (20
5) and 400 are taken as addresses and DATA- 8-bit data (209) is taken out, and D / A converter 1706 outputs D
ATA + is output to the D / A converter 2707 and DATA- is output to each. In each D / A converter, the reference voltage Vref (5
V) performs digital-analog conversion, and the output is an amplifier 1
Output to 708 and amplifier 2709.

Amplifier 1708 (amplification factor 7 times) and amplifier 2
709 (amplification rate −2.2 times) amplifies the input analog voltage by each amplification rate, and sets the positive polarity write voltage Va + and the negative polarity write voltage Va− as the liquid crystal panel 7.
Output to 10. The value of each write voltage Va +, Va- is obtained by the following equation. Va + = 205 × 5V ÷ 256 × 7 = 28.03V (7) Va- = 209 × 5V ÷ 256 × −2.2 = −8.98 (8) 28.03V by the equations (7) and (8) Is output to the liquid crystal panel 710 as a positive write voltage, and a voltage of −8.98 V as a negative write voltage.

A lookup table is provided in this way,
The liquid crystal panel 7 takes out the data with the output of the temperature sensor as a variable, amplifies the data after digital-analog conversion.
By outputting to 10, the write voltage is temperature-compensated.

[0021]

However, some problems have been pointed out in the above-mentioned prior art. In general, when configuring an amplifier, a method of setting an amplification factor by a feedback resistor using an operational amplifier is used. The same applies to the conventional case, and an amplifier configured by an operational amplifier is used from the viewpoint of cost reduction and circuit simplification. When an amplifier with an operational amplifier structure is used, the accuracy of the amplification factor is determined by the relative error of the resistance value of the feedback resistor. Since the amplifier 1708 and the amplifier 2709 have different amplification factors, the value of the feedback resistor for setting the amplification factor is naturally different, so that the manufacturing lot of the resistors used is also different. If the manufacturing lots are different, variations between lots will occur in addition to variations within the lots, and the relative error of the amplification factor will be further increased. According to the experiments conducted by the inventor, the error range of the amplification factor is ± 1% when a resistor having a resistance tolerance of 0.5% is used. Considering the case of 25 ° C., from (7) and (8), the error range of Va + is ± 0.28V,
The error range of Va- is ± 0.09V. Therefore, the error range of the offset voltage of the write voltage due to the error of the resistance value is in the range of 9.71V to 9.34V. The actually desired offset voltage is 9.53 from the equations (7) and (8).
Since it is V, the error of the offset voltage becomes maximum when the error of Va + is -0.28V and the error of Va- is -0.09V.
At that time, the offset voltage is 9.34V, and the error is -0.19V. In this way, the error in the resistance value of the amplifier greatly affects the offset voltage.

It is known that the voltage applied to the liquid crystal in the liquid crystal panel 710 is determined by the capacitance ratio of the MIM element and the liquid crystal cell, but when the capacitance ratio is about 1: 1, it is applied to the liquid crystal panel 710. Half of the applied voltage will be applied to the liquid crystal cell. Therefore, when there is an offset error of 0.19V, half of that, 0.095V, is applied to the liquid crystal cell. When a direct current component is applied to the liquid crystal, the liquid crystal is deteriorated and the quality is greatly impaired. According to the inventor's experiment, it is known that the direct current component that does not cause deterioration even when applied to the liquid crystal needs to be suppressed to within 0.05 V, and when the direct current component of 0.095 V is applied, the quality remarkably deteriorates. .

Further, there is a method of controlling the write voltage of the liquid crystal panel 710 when the bright adjustment is provided for the image adjustment of the liquid crystal panel 710. In the case of bright adjustment, since only the brightness of the image is changed, the positive write voltage and the negative write voltage are increased / decreased with the same voltage value.
When this is performed by the conventional technique, it is necessary to increase / decrease Va + and Va- by an equivalent voltage. However, since the amplification factor of the amplifier 1708 is 7 times and the amplification factor of the amplifier 2709 is -2.2 times, which is not an integral multiple, the 8-bit data DATA + that determines the voltage of Va + is increased or decreased by ± 1. In between, 8-bit data DATA that determines the voltage of Va-
Even when − is increased or decreased by ± 3, the change amount of the offset voltage is 5 ÷ 256 × (7−2.2 × 3) = 8 mV. Furthermore, DATA + is ± 2, 3, 4, 5
When increasing or decreasing, it is necessary to increase or decrease DATA- with an increasing or decreasing value that minimizes the offset voltage. Bright adjustment in this manner affects the offset voltage. Further, it is necessary to calculate the increase / decrease value in order to suppress it to the minimum, and the load on the software also increases.

In this way, when considering even mass production, a desired voltage cannot be obtained due to component variations and brightness adjustment problems, and as a result, a direct current component is applied to the liquid crystal to deteriorate the quality. Therefore, temperature compensation of asymmetric MIM is performed. Was said to be very difficult.

An object of the present invention is to provide a liquid crystal display device provided with a temperature compensating circuit which suppresses the deterioration of the liquid crystal due to the application of a DC voltage, absorbs component variations during mass production, and can easily carry out bright adjustment. Is.

[0026]

In order to achieve the above object, in a temperature compensating circuit of a liquid crystal display device including a liquid crystal panel including pixels switched by a two-terminal system non-linear element represented by MIM, The two digital data for the positive write voltage and the negative write voltage corresponding to are fetched from the lookup table,
The amplifier 1 for amplifying the positive write voltage and the negative write voltage by the amplifier 2 after the digital-analog conversion is performed by the D / A converter.
The amplification factor K1 and the amplification factor K2 of the amplifier 2 are equal in absolute value.

[0027]

Since the amplification factors of the amplifier 1 and the amplifier 2 are equal in absolute value, the resistors that determine the amplification factor of the amplifier are the same resistance value combination of the amplifier 1 and the amplifier 2. Therefore, the resistors used in the amplifier 1 and the amplifier 2 can be resistors manufactured in the same lot. It is known that the variation of the resistance value within the same lot is very small compared to the tolerance of the resistance value, so the error of the resistance value is controlled only by the variation between the lots, and the amplification factor of the amplifier 1 The error and the error in the amplification factor of the amplifier 2 are the same. Therefore, the difference between the positive polarity write voltage Va + and the negative polarity write voltage Va- from the desired voltage is that if Va + increases from 0V, Va- increases in amplitude, and if Va + decreases in amplitude, V increases.
The amplitude of a- also tends to decrease. When the writing voltages of both polarities increase / decrease in the same amplitude direction, the offset voltage of the writing voltage does not change, so that no DC component is applied to the liquid crystal panel. Further, during the brightness adjustment, since the amplification factors are the same, it is possible to easily make the increase and decrease of the write voltage constant in both the positive polarity and the negative polarity.

[0028]

【Example】

(Embodiment 1) Hereinafter, Embodiment 1 according to the present invention will be described with reference to FIGS.
Will be described with reference to FIG. FIG. 1 is a block diagram of this embodiment. The output of the temperature sensor 704 is the microcomputer 701.
Is connected to the A / D converter 701 inside. Microcomputer 7
01 is the CPU 703, the lookup table 102 and A
It is composed of a / D converter 705. 8-bit digital data DATA +, D from the output port of the microcomputer 701
ATA- to D / A converter 1706 and D / A respectively
Output to converter 2707. Reference voltage Vref is D
The A / A converter 1706 and the D / A converter 2707 are connected. The output voltages of the D / A converter 1706 and the D / A converter 2707 are output to the amplifier 1108 and the amplifier 2109, respectively. Up to this point, it is the same as the conventional example. The difference from the conventional one is that the amplification factor K1 of the amplifier 1108 is 7
The point is that the amplification factor K2 of the amplifier 2109 is set to -7 times and the absolute values are set to be equal in absolute value. The output of each amplifier is connected to the liquid crystal panel 710.

Next, detailed operation will be described. Temperature sensor 7
04, A / D converter 701, C in the microcomputer 701
Since the operation of the PU 703 is basically the same as that of the conventional technique, detailed description will be omitted.

As the storage format of the look-up table 102, a storage medium composed of a ROM is used as in the prior art, and R
In the OM, the storage area is divided into two, and 8-bit data D to be output to the D / A converter 1706 in one storage area.
ATA + is stored, and 8-bit data DATA- output to the D / A converter 2707 is stored in the other storage area. The 8-bit data DATA + output to the D / A converter 1706 follows the following equation. DATA + = Va + ÷ K1 ÷ Vref × 256 (9) 8-bit data D output to the D / A converter 2707
ATA− follows the following equation. DATA− = Va− ÷ K2 ÷ Vref × 256 (10) Va + in the equation (9) is the optimum positive write voltage at each temperature shown in FIG. 10, and Va− in the equation (10) is each shown in FIG. It is the optimum negative write voltage at temperature.

The appearance of the lookup table 102 is shown in FIG.
Shown in. As in the prior art, the temperature of the temperature-voltage characteristic of FIG. 10 is associated with the address of the ROM. The actual address arrangement is to store DATA + 8-bit data at address -20 ° C at address 0, and at address +255 at address +60.
Stores DATA + 8-bit data when the temperature is ° C. D
ATA- 8-bit data is stored in the other storage area 25
Store DATA- at -20 ° C at the 6th address and DA at + 60 ° C at the 512th address
Store TA-.

Next, the amplification factors of the amplifier 1108 and the amplifier 2109 will be described. The maximum conversion range of the D / A converter 1706 and the D / A converter 2707 is Vref.
It becomes 5V decided by the value of. When determining the amplification factor, normally, the maximum conversion range of the D / A converter is made to correspond to the conversion ranges of Va + and Va-, and the amplification factor of the amplifier 1708 is increased seven times as in the prior art, and the amplification factor of the amplifier 2709 is increased. -2.2 times. However, in the present embodiment, the amplification factors of the amplifier 1108 and the amplifier 2109 are made equal in absolute value, so that the amplification factor is unified to the larger absolute value. Therefore, the amplifier 1108
The amplification factor K1 is set to 7 times, and the amplification factor K2 of the amplifier 2109 is set to -7 times.

FIG. 3 shows the configuration of each amplifier. Amplifier 1
Reference numeral 108 is composed of two inverting amplifiers using operational amplifiers. R1 of the first-stage amplifier is 2 kΩ, R2 is 14 kΩ, and the amplification factor is -7 times. The R3 and R4 of the second stage amplifier are both 14 kΩ, and the amplification factor is −1 times. The amplifier 2109 is composed of one inverting amplifier using an operational amplifier. R5 is 2 kΩ and R6 is 14 kΩ, and the amplification factor is -7 times.

Here, for the resistance of 14 kΩ, the amplifier 1108 and the amplifier 2109 are manufactured in the same lot, and the resistance of 2 kΩ is manufactured in the same lot.

Next, the 8-bit data stored in the lookup table 102 will be described by taking 25 ° C. as an example. From FIG. 10, it is desired to set the positive write voltage Va + at 25 ° C. to 28V and the negative write voltage Va− to −9V.
In equations (9) and (10), K1 = 7, K2 = −7, Vref
= 5 V, the positive write voltage is 8
The bit data DATA + is 204.8 from the equation (11) and is rounded off to the decimal point to be 205, and the 8-bit data DATA− of the negative write voltage is 6 from the equation (12).
At 5.8, it is rounded down to the nearest whole number, which is 66. 28V ÷ 7 ÷ 5V × 256 = 204.8 (11) -9V ÷ -7 ÷ 5V × 256 = 65.8 (12) These two 8-bit data are looked up table 10.
Store in 2. The address to be stored is D as in the prior art.
ATA + becomes the 144th address and DATA- becomes the 400th address. The state of the stored data in the lookup table 102 is shown in FIG.

The lookup table 102 is created by performing the above calculation from 0 ° C. to 60 ° C. The look-up tables 102 are created at the design stage, and the same data are used for all the subsequent mass production unless the characteristics of the liquid crystal panels 710 are changed.

Next, the actual temperature compensation operation will be described by taking 25 ° C. as an example. First, the temperature of the liquid crystal panel 710 is measured by the temperature sensor 704, analog-digital conversion is performed by the A / D converter 705 in the microcomputer 101, and an 8-bit digital value 144 of 25 ° C. is input to the CPU 703. C
The PU 703 uses the address 144 as the address and the DATA + 8-bit data (205) from the lookup table 102.
DATA- 8-bit data (6
6) is taken out, and DATA is input to the D / A converter 1706.
It outputs + and outputs DATA- to the D / A converter 2707. Each of the D / A converters performs digital-analog conversion with the reference voltage Vref (5V) according to the input 8-bit data, and outputs the output from the amplifier 1108.
(Amplification factor 7 times) and the amplifier 2109 (amplification factor -7 times). Expressions (13) and (14) show the positive write voltage Va + and the negative write voltage Va- after passing through the D / A converter and the amplifier. Va + = 205 × 5V ÷ 256 × 7 = 28.03V (13) Va- = 66 × 5V ÷ 256 × -7 = −9.02V (14)

According to the equations (13) and (14), the liquid crystal panel 710 has Va + of 28.03 V as the positive write voltage and Va- of -9.02 V as the negative write voltage.
Is output to.

Next, the influence of component variations during mass production will be described. The error in the amplification factor between the amplifier 1108 and the amplifier 2109 is determined by the resistance tolerance of the resistors used, and is ± 0.5%.
When the product is used, it reaches up to ± 1% as described in the prior art. As a result, an error in the amplification factor contributes to the positive polarity write voltage Va + and the negative polarity write voltage Va-, and at 25 ° C, Va + is ± 0.28 V at maximum and Va- is ± 0.09 at maximum.
This is the error range of V.

However, in the present embodiment, the same manufacturing lot product having the same resistance value is used for R1 of the amplifier 1108 and R5, R2 to R4 and R6 of the amplifier 2109 shown in FIG. In the same manufacturing lot, the error from the nominal resistance value is relatively uniform, there is almost no variation in the resistance value within the lot, and R1 is +
If it deviates from the nominal resistance value by 0.5%, R5 also tends to deviate by approximately + 0.5%. Similarly, R2 to R4
And R6, if R6 is deviated by -0.5%, R2 to R2
4 also shifts by -0.5%. Taking this as an example, the amplification factor of the first stage inverting amplifier of the amplifier 1108 has an error of -1%. The second stage amplifier has an error of −0.5% for both R3 and R4, so there is no change in the amplification factor. The amplifier 2109 is-
There is an error of 1%. That is, the error in the amplification factor of the amplifier 1108 and the error in the amplification factor of the amplifier 2109 are the same, and a correlation occurs between the two. At this time, the positive write voltage Va + has an error of −0.28 V, the negative write voltage Va− has an error of +0.09 V, and Va + is 27.75 V.
Va- becomes -8.93V. FIG. 4 shows the amount of change in voltage. V1 is the desired write voltage at 25 ° C. in FIG. 10, V2 is the actual output voltage after temperature compensation shown in equations (13) and (14), and V3 is the maximum error in this embodiment. Write voltage. Offset voltages from 0V are V1 for VO1, V2 for VO2, and V3.
Becomes VO3, and VO4 is the maximum error of the offset voltage in the conventional technique.

Desired offset voltage VO1 in FIG.
The error between and becomes a DC component as it is, and a voltage of about half the error is applied to the liquid crystal in consideration of the capacitance ratio between MIM and the liquid crystal. In VO2, an offset error of 5 mV is applied to the write voltage due to an error caused by the resolution of the D / A converter, and the liquid crystal receives a DC component of 2.5 mV which is half that of the liquid crystal in consideration of the capacitance ratio. According to the conventional method, an offset error of 0.18V is applied to the writing voltage like VO4, and a direct current component of 0.09V is applied to the liquid crystal. However, in this embodiment, the error of the offset voltage of VO3 is 0.09V.
Thus, the DC component applied to the liquid crystal can be suppressed to 0.045V. As a result, the direct current component is suppressed within 0.05 V, and the condition for preventing deterioration of the liquid crystal can be satisfied.

Further, since parts having the same resistance value can be unified, cost reduction can be realized. According to the above offset error, the tolerance of the resistance value of the resistor is twice as accurate as the conventional one in the embodiment. Therefore, the tolerance of the resistance value required to achieve the desired accuracy may be doubled as compared with the conventional one, resulting in cost reduction as well. The relationship between the resistance tolerance and the cost is a big problem, and if the tolerance range is halved, the unit price of the resistance becomes five times or more. Therefore, this embodiment is very effective in cost reduction.

Although the resistors of the same manufacturing lot were used in this embodiment, it was found that the same effect can be obtained for the same reason even if the collective resistors are used when the lot control during mass production is difficult. There is.

Also, in the brightness adjustment, DATA +
If DATA- is increased or decreased by ± 1 while ± is increased or decreased by 1, the amplification factor is equal in absolute value, so that the voltage is equivalently increased and the offset voltage does not change.

In this embodiment, the temperature compensation of the write voltage Va ± of the liquid crystal panel 710 has been described.
The temperature compensation of the holding voltage Vb ± in FIG. Further, in the case of a liquid crystal display device, a signal voltage is applied to the signal electrode of the liquid crystal panel 710 to control the writing amount of liquid crystal by the amplitude of the signal electrode, but the same method can be used for temperature compensation of this signal voltage. it can.
When the holding voltage, the signal voltage, and the writing voltage are all temperature-compensated according to this embodiment, the removal of the DC component from the liquid crystal becomes more effective.

Example 2 Hereinafter, Example 2 according to the present invention will be described.
Will be described with reference to FIGS. A driving method using an oscillating power source for driving a liquid crystal display device is disclosed in Japanese Patent Laid-Open No. 60-2491.
91. Even if the oscillating power supply is used, digital temperature compensation is possible, so an embodiment will be shown.

FIG. 5 shows a block diagram of the liquid crystal display device according to this embodiment. The power supply circuit 1608 is a circuit that generates a rectangular wave by switching a reference voltage of 0 V and a DC voltage of 5 V as a function of time, and outputs the rectangular wave to one terminal of a capacitor 1606 and a capacitor 2607. The other terminal of the capacitor 1606 outputs to the clamp circuit 2602, and the other terminal of the capacitor 2607 outputs to the clamp circuit 1601. Clamp circuit 2
In 602, the low potential side of the input rectangular wave is clamped by the positive side clamp voltage 605 and output to the liquid crystal panel 710 as the positive side power supply VDD of the scan electrode drive circuit 610. Similarly, in the clamp circuit 1601, the high potential side of the input rectangular wave is clamped by the negative side clamp voltage 604 and the liquid crystal panel 71 is used as the negative side power supply VSS of the scan electrode drive circuit 610.
Output to 0. The scan electrode drive circuit 610 uses the positive power supply VD.
The high potential side of the rectangular wave of D is applied to the liquid crystal as a positive write voltage, and the low potential side of the rectangular wave of the negative power supply VSS is applied to the liquid crystal as a negative write voltage.

A block diagram of the power supply circuit 2603 is shown in FIG. 6 is almost the same as FIG. 1 of the first embodiment, except that the contents of the lookup table 501 and the amplifier 150 are different.
2, the amplification factor of the amplifier 2503. Also, the output connected to the liquid crystal panel 710 in FIG.
Is output to the clamp circuit 1601. Amplifier 1502
And the amplifier 2503 have the same circuit configuration as in FIG. 3. In FIG. 3, R1 is 2 kΩ, R2 is 12 kΩ, and R3 and R4 are 12 kΩ.
With kΩ, the amplification factor K1 ′ of the amplifier 1502 becomes 6 times. R
5 is 2 kΩ, R6 is 12 kΩ, and the amplification factor K2 ′ of the amplifier 2503 is −6. Note that each resistor is in the same manufacturing lot as in the first embodiment.

Next, the contents of the lookup table 501 are shown in FIG. The calculation formula of the lookup table 501 is as follows. DATA + '= (Va + -5V) ÷ K1' ÷ Vref × 256 (15) DATA-'= (Va- + 5V) ÷ K2' ÷ Vref × 256 (16) (15), of the first term of the equation (16) 5V is power supply circuit 160
8 is the amplitude voltage of the rectangular wave generated in 8. According to this calculation formula, 8-bit data of DATA + ′ at −20 ° C. is stored in the 0th address of the lookup table 501 and D at + 60 ° C. is stored in the 255th address.
8-bit data of ATA + 'is -2 at address 256
512-bit DATA-'data at 0 ° C
At the address, 8-bit data of DATA-'at + 60 ° C is stored. When 8-bit data at 25 ° C. is obtained as in the first embodiment, Va + is 28V and Va− is -9V.
From equations (15) and (16), DATA + ′ is 196 (16
C4) in decimal, 34 for DATA- '(22 in hexadecimal)
Becomes C4 at the storage address 144 at 25 ℃, 40
22 is stored in the 0th address.

Next, an actual temperature compensation operation will be described by taking 25 ° C. as an example. In FIG. 6, the temperature of the liquid crystal panel 710 is measured by the temperature sensor 704, and A in the microcomputer 101 is measured.
A / D converter 705 performs analog-to-digital conversion, and 2
The 8-bit digital value 144 at 5 ° C. is input to the CPU 703. The CPU 703 fetches the DATA + '8-bit data (196) and the DATA-' 8-bit data (34) from the lookup table 501 with the address 144 and the address 400, and the D / A converter 17
DATA + 'to 06 and DA to D / A converter 2707
Output TA- '. In each D / A converter, digital-analog conversion is performed with the reference voltage Vref, and each output is connected to the amplifier 1502 and the amplifier 2503. Equations (17) and (18) show equations for calculating the positive clamp voltage 605 and the negative clamp voltage 604 after passing through the D / A converter and the amplifier. Positive side clamp voltage = 196 × 5V ÷ 256 × 6 = 22.97V (17) Negative side clamp voltage = 34 × 5V ÷ 256 × -6 = -3.98V (18) (17) Equation (18) Positive side clamp voltage 60
22.97 V is output to the clamp circuit 2602 as 5, and −3.98 V is output to the clamp circuit 1601 as the negative clamp voltage 604.

Next, the influence of component variations during mass production will be described. The difference in amplification factor between the amplifier 1502 and the amplifier 2503 depends on the resistance tolerance of the resistors used. Where ±
When the 0.5% product is used, the resistors of the same manufacturing lot are used as in the first embodiment. Therefore, the amplification factor of the amplifier 1502 is ± 1%, and the amplification factor of the amplifier 2503 is ± 1%. . That is, the error of the amplification factor of the amplifier 1502 and the amplifier 2
The error of the amplification factor of 503 is the same. Now, in the case of an error of -1%, the positive clamp voltage 60
5 is an error of -0.23V, and the negative clamp voltage 604 is +
There is an error of 0.04V and the positive clamp voltage 605 is 2
2.74V, the negative side clamp voltage 604 becomes -3.94V. FIG. 8 shows the amount of change in voltage. V1 is 25 in FIG.
The desired write voltage at C, V2 'is (17),
VDD, VSS, and V3 ′ when clamped with the clamp voltage shown in the equation (18) are VDD and VSS when clamped with the clamp voltage of (−1%) when the error in this embodiment is maximum. . Offset voltages from 0V are V1 for VO1 and V2 'for VO2', V2.
3'becomes VO3 ', and VO4 is the maximum offset voltage error in the prior art.

In FIG. 8, according to the conventional method, VO4 has an error of 0.16 V from VO1. However, according to this embodiment, VO3 'has an error of 0.1V with respect to VO1, and the error can be suppressed by 0.06V as compared with the conventional example. As described in the first embodiment, a voltage which is about half the error of the offset voltage is applied to the liquid crystal as a direct current component, so that in the present embodiment, the direct current component of 0.05 V can be suppressed. If the voltage is within 0.05 V, the liquid crystal can satisfy the conditions for preventing the liquid crystal from deteriorating.

[0053]

According to the liquid crystal display device of the present invention, the amplification factor K1 and the negative electrode of the amplifier for producing the positive writing voltage when the digital temperature compensation data is digital-analog converted and the output thereof is amplified to the writing voltage. The amplification factor K2 of the amplifier for generating the write voltage is set to have the same absolute value. As a result, the resistors of the same manufacturing lot can be used as the resistors that determine the amplification factor of the amplifier. When the manufacturing lot is the same, the error range of the resistance value is much smaller than the tolerance of the resistance value, and the error appears relatively uniformly in the lot. Therefore, the error of the amplification factor is also the amplification factor K1 and the amplification factor K2.
The same error occurs in and, and the positive and negative write voltages have the same increase and decrease in the amplitude direction as the write voltage, and the influence on the error of the offset voltage that corrects the asymmetry of MIM is significantly reduced. be able to. Further, even during the bright adjustment, it becomes easy to control the positive write voltage and the negative write voltage with the same increase / decrease value, and no error occurs. As a result, the direct current component applied to the liquid crystal can be reduced, so that the deterioration of the liquid crystal can be remarkably reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 shows the contents of a lookup table 102.

FIG. 3 is a configuration diagram of an amplifier.

FIG. 4 is a voltage value of each output.

FIG. 5 is a block diagram of a second embodiment of the present invention.

FIG. 6 is a block diagram of a power supply circuit 2603.

FIG. 7 shows the contents of a lookup table 501.

FIG. 8 is a voltage value of each output.

FIG. 9 shows the contents of a lookup table 702.

FIG. 10 is a voltage-temperature characteristic of a write voltage.

FIG. 11 is a 4-level drive waveform.

FIG. 12 is a block diagram of the related art.

[Explanation of symbols]

DATA + 8-bit digital data for positive write voltage DATA- 8-bit digital data for negative write voltage Va + Positive write voltage Va- Negative write voltage Vb + Positive holding voltage Vb- Negative hold Voltage K1 Amplification factor of the amplifier 1108 K2 Amplification factor of the amplifier 2109 V1 Write voltage V2 of FIG. 6 Write voltage V3 of the embodiment Maximum error of write voltage of the embodiment VO1 V1 offset voltage VO2 V2 offset voltage VO3 V3 offset voltage VO4 Maximum offset voltage error of prior art DATA + '8-bit digital data for positive side clamp voltage DATA-' 8-bit digital data for negative side clamp voltage V2 'VDD, VSS V3' of Example 2 of Example 2 Maximum error between VDD and VSS VO2 'V2' Amplification factor of the amplifier 2503 'amplification factor K2 of the amplifier 1502' offset voltage K1 set voltage VO3 'V3'

Claims (4)

[Claims] 1. A method for driving a liquid crystal display device, wherein in an active matrix liquid crystal panel, digital information is taken out with temperature as a variable and temperature compensation of a driving voltage is performed. At least two digital-analog converters, a voltage amplifier 1 and a voltage amplifier 2 are provided. And the two digital-to-analog converters output two temperature-compensated digital data corresponding to temperature.
The analog voltage is converted into two analog voltages, one of the analog voltages is output to the voltage amplifier 1, and the other of the analog voltages is output to the voltage amplifier 2. The voltage amplifier 1 amplifies the analog voltage with an amplification factor K1 and outputs a positive voltage. A negative writing voltage is applied to the liquid crystal panel, the voltage amplifier 2 amplifies the analog voltage with an amplification factor K2, and a negative writing voltage is applied to the liquid crystal panel to obtain the amplification factor K1 and the amplification factor K2. A method for driving a liquid crystal display device, wherein the two take the same absolute value. 2. An active matrix liquid crystal panel, wherein in a method of driving a liquid crystal display device for extracting digital information with temperature as a variable and compensating the temperature of a driving voltage, at least two digital-analog converters, a voltage amplifier 1 and a voltage amplifier 2 are provided. And the two digital-to-analog converters output two temperature-compensated digital data corresponding to temperature.
The analog voltage is converted into two analog voltages, one of the analog voltages is output to the voltage amplifier 1, and the other analog voltage is output to the voltage amplifier 2. The voltage amplifier 1 amplifies the analog voltage with an amplification factor K1, A rectangular wave having a constant peak value is clamped by the amplified voltage and applied to the scan electrode driving circuit in the liquid crystal panel, the voltage amplifier 2 amplifies the analog voltage with an amplification factor K2, and the amplified voltage is used to A method of driving a liquid crystal display device, wherein a rectangular wave is clamped and applied to the scan electrode driving circuit in the liquid crystal panel, and the amplification factor K1 and the amplification factor K2 are equal in absolute value. 3. A method of driving a liquid crystal display device, wherein in an active matrix liquid crystal panel, digital information is taken out by using temperature as a variable and temperature compensation of a driving voltage is performed. At least two digital-analog converters, a voltage amplifier 1 and a voltage amplifier 2 are provided. And the two digital-to-analog converters output two temperature-compensated digital data corresponding to temperature.
The analog voltage is converted into two analog voltages, one of the analog voltages is output to the voltage amplifier 1, and the other of the analog voltages is output to the voltage amplifier 2. The voltage amplifier 1 amplifies the analog voltage with an amplification factor K1 and outputs a positive voltage. A negative polarity signal voltage is applied to the liquid crystal panel, the voltage amplifier 2 amplifies the analog voltage with an amplification factor K2, and a negative polarity signal voltage is applied to the liquid crystal panel to obtain the amplification factor K1 and the amplification factor K2. A method for driving a liquid crystal display device, wherein the two take the same absolute value. 4. A method of driving a liquid crystal display device, wherein digital information is taken out with temperature as a variable and temperature compensation of a driving voltage is performed in an active matrix liquid crystal panel, and at least two digital-analog converters, a voltage amplifier 1 and a voltage amplifier 2 are provided. And the two digital-to-analog converters output two temperature-compensated digital data corresponding to temperature.
The analog voltage is converted into two analog voltages, one of the analog voltages is output to the voltage amplifier 1, and the other of the analog voltages is output to the voltage amplifier 2. The voltage amplifier 1 amplifies the analog voltage with an amplification factor K1 and outputs a positive voltage. Negative holding voltage is applied to the liquid crystal panel, the voltage amplifier 2 amplifies the analog voltage with an amplification factor K2, and a negative holding voltage is applied to the liquid crystal panel to obtain the amplification factor K1 and the amplification factor K2. A method for driving a liquid crystal display device, wherein the two take the same absolute value.