JP2006154670A - Gradation voltage signal supply device for liquid crystal display device, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gradation voltage signal supply device for driving a liquid crystal display device that can highly accurately set a gradation voltage nearby a center voltage where an influence on picture quality of a liquid crystal display means is large while securing a sufficient output voltage range without specially making a D/A converter high in resolution. <P>SOLUTION: The gradation voltage signal supply device is equipped with a plurality of D/A converters 10 each of which converts an inputted digital signal into an analog voltage and outputs it as a gradation voltage signal to the liquid crystal display device, and signal conversion characteristics of each D/A converter 10 is such nonlinear characteristics that variation of values V1 to Vn of the analog voltage signal with respect to variation of values D1 to Dn of the digital signal monotonously increases (or monotonously decreases) and the gradient of the analog voltage signal within a prescribed range nearby the center value of a range within which values of the digital signal can exist is gentler than those of ranges before and after it. Further, levels of analog voltage signals of the respective D/A converters are made variable (or different). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention includes a plurality of D / A converters for converting an input digital signal into an analog voltage signal and outputting the analog voltage signal, and each of the analog voltage signals output by each D / A converter is used as a plurality of gradation voltage signals. The present invention relates to a gradation voltage signal supply device for supplying to a liquid crystal display device and a liquid crystal display device including the same.

In a liquid crystal display device provided in a liquid crystal television receiver, a notebook personal computer, or the like, it is necessary to supply gradation voltage signals in multiple stages to the liquid crystal display means. (Voltage) has a great influence on the image quality of the liquid crystal display means, so it is necessary to set it to a predetermined voltage level with high accuracy. Hereinafter, an apparatus for supplying such a multi-stage gradation voltage signal to the liquid crystal display means is referred to as a gradation voltage signal supply apparatus.
Here, the gradation voltage to be set differs depending on the type and specification (purpose) of the liquid crystal display means, and it is necessary to supply a gradation voltage signal corresponding to the gradation voltage. Therefore, in order to enable adjustment of the gradation voltage with the same hardware configuration, the conventional gradation voltage signal supply device has a D / D that can adjust the output voltage by adjusting the setting value of the digital signal (adjustment by software). Some use an A converter.

FIG. 6A is a diagram illustrating an example of a schematic configuration of a main part of a conventional gradation voltage signal supply device A for a liquid crystal display device.
As shown in FIG. 6 (a), the conventional gradation voltage signal supply device A is provided for each gradation voltage signal of a plurality of levels of voltage levels Vi (i = 1 to n) to be supplied to the liquid crystal display means. N D / A converters 30 are provided one by one. The number of D / A converters 30 (= n) is the same as the number of gradation voltage signals to be supplied to the liquid crystal display means (= n), and may vary depending on the specifications of the liquid crystal display means.
FIG. 6B is a graph showing signal conversion characteristics (conversion characteristics from a digital signal to an analog voltage signal) of each D / A converter 30.
As shown in FIG. 6B, the signal conversion characteristic of each D / A converter 30 is linear, and the digital signal is converted into a voltage signal having a level proportional to the value. Here, the plurality of D / A converters 30 have the same signal conversion characteristics.
Further, the conventional gradation voltage signal supply device A is provided with a digital signal output means (not shown) composed of, for example, a microcomputer, and the digital signal output means allows each D / A converter 30 to have a desired level of gradation. Digital signals having different values (D1 to Dn) are input (set) within a predetermined range (Dmin to Dmax) so that signals of voltages V1 to Vn can be obtained.
Here, as shown in FIG. 6B, the plurality of gradation voltages V1 to Vn are not equally spaced, but are intermediate voltages (hereinafter referred to as center voltages) between the minimum gradation voltage V1 and the maximum gradation voltage Vn. For the gradation voltages in the vicinity (Vi, Vi + 1, Vi + 2, etc. in FIG. 6B), the voltage to be set is smaller than the gradation voltages near the minimum voltage V1 and the maximum voltage Vn. Closely concentrated.
On the other hand, Patent Document 1 discloses a liquid crystal display device that digitizes a video signal, converts a digital signal that has been subjected to nonlinear conversion using a lookup table into an analog signal by a D / A converter, and drives a liquid crystal display panel using the analog signal. Has been.
JP-A-4-142513 Japanese Patent Laid-Open No. 11-312977

By the way, among the plurality of gradation voltages, the gradation voltage near the center voltage has an error relative to the target voltage (the voltage that should be originally set) compared with the gradation voltage near the minimum voltage and the maximum voltage. Since the influence on the image quality of the means is particularly great, it is necessary to supply the gradation voltage signal with higher accuracy with respect to the target voltage. In addition, it is necessary to sufficiently secure the range of the gradation voltage (the difference between the maximum gradation voltage Vn and the minimum gradation voltage V1).
On the other hand, when a D / A converter having a linear signal conversion characteristic is used, a sufficient output voltage range (Vmax−Vmin) is ensured with respect to the gradation voltage range (Vn−V1), and the target voltage is not affected. To enable a very small output voltage setting (output voltage adjustment) so that an output voltage with a small error (voltage of an analog converted signal) can be obtained, it is necessary to use a D / A converter with a very high resolution. However, there was a problem that the equipment was complicated and the cost was increased.
This is the same even if non-linear conversion of a digital signal input to a D / A converter is performed as disclosed in Patent Document 1.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a liquid crystal display means while ensuring a sufficient output voltage range without particularly increasing the resolution of the D / A converter. An object of the present invention is to provide a gradation voltage signal supply device for driving a liquid crystal display device and a liquid crystal display device including the gradation voltage signal supply device, which can set a voltage with high accuracy with respect to the gradation voltage in the vicinity of the center voltage having a large influence on image quality. .

In order to achieve the above object, the present invention comprises a plurality of D / A converters for converting an input digital signal into an analog voltage signal and outputting the analog voltage signal, and a plurality of analog voltage signals output by each D / A converter. A gradation voltage signal is supplied to a liquid crystal display device as a stepwise gradation voltage signal, and is configured as a gradation voltage signal supply device in which the signal conversion characteristics of each of the D / A converters are nonlinear or a liquid crystal display device including the gradation voltage signal supply device It is what is done.
More specifically, the signal conversion characteristic of each of the D / A converters is a characteristic in which a change in the analog voltage signal monotonously increases or decreases with respect to a change in the value of the digital signal, The slope of the analog voltage signal (the slope of the change in the analog voltage value with respect to the change in the digital signal value) in a predetermined range near the median value in the possible range (hereinafter referred to as the range near the center input value) It can be considered that the characteristic is gentler than the slope of the analog voltage signal in the front and rear ranges.
As a result, when the value of the digital signal set in the D / A converter is changed in the vicinity of the center input value, the analog voltage signal is in the vicinity of the median value of the gradation voltages in a plurality of stages ( Since a signal conversion characteristic (that is, a characteristic with a gradual slope) that changes slightly in the vicinity of the center voltage is obtained, accuracy is particularly required (that is, the influence on the image quality in the liquid crystal display means is large). It is possible to improve the accuracy of the gradation voltage with respect to a target voltage (originally a voltage to be set) in the vicinity of the voltage.
On the other hand, if the value of the digital signal is changed in the range before and after the range near the center input value, that is, the range close to the minimum value or the maximum value of the digital signal, the analog voltage signal changes relatively greatly. Therefore, a sufficient output voltage range can be secured without particularly increasing the resolution of the D / A converter. Here, in a range other than the vicinity of the center voltage (a range close to the minimum value or the maximum value of the analog voltage signal), the signal conversion characteristic has a relatively steep slope, and therefore the level of the analog voltage signal (that is, the level) Although it is not possible to finely adjust (adjustment voltage), an error with respect to the target voltage within this range has little effect on the image quality, so it is not a problem.

Each of the D / A converters fixes the minimum value and the maximum value of the analog voltage signal that can be output at the same value, and the analog signal for the value of the digital signal in the range from the minimum value to the maximum value. A configuration in which the overall level of the voltage signal is variable is conceivable.
Alternatively, in each of the D / A converters, the minimum value and the maximum value of the analog voltage signal that can be output are the same, and the entire analog voltage signal with respect to the value of the digital signal in the range from the minimum value to the maximum value. Different levels may be considered.
With these configurations, when each of the D / A converters receives the digital signal in the vicinity of the center input value, the D / A converter takes on (to output) the target voltage of the gradation voltage. The analog voltage signal having a value in a range that can normally be taken may be output.
That is, the D / A converter that is responsible for supplying the low-level gradation voltage has a signal conversion characteristic in which the low-level voltage is output when the digital signal in the vicinity of the center input value is input. The D / A converter responsible for supplying the high-level gradation voltage has a signal conversion characteristic that outputs the high-level voltage when the digital signal in the vicinity of the center input value is input. be able to. As a result, the gradation voltage signal with high accuracy can be obtained in a range other than the vicinity of the center voltage (a range close to the minimum value or the maximum value of the analog voltage signal) without particularly increasing the resolution of the D / A converter. Can supply.
Further, when using the D / A converter in which the level of the analog voltage signal is variably used, the analog voltage signal having a level closest to the target voltage to be output is output for each D / A converter. For D / A converters having a large error in the level of the analog voltage signal with respect to the target voltage after setting different values of the digital signal, fine adjustment in the direction to eliminate the error by adjusting the level of the analog voltage signal It is also possible to do.

  According to the present invention, the D / A converter is required to have a particularly high accuracy while ensuring a sufficient output voltage range (gradation voltage range) without increasing the resolution particularly (that is, in the liquid crystal display means). The accuracy of the gradation voltage with respect to the target voltage in the vicinity of the center voltage can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
FIG. 1 is a block diagram showing a schematic configuration of a main part of a liquid crystal display device X according to an embodiment of the present invention. FIG. 2 is a block diagram showing a schematic configuration of a gradation voltage signal supply device Z provided in the liquid crystal display device X. 3 is a graph schematically showing a first example of signal conversion characteristics of a D / A converter included in the gradation voltage signal supply device Z. FIG. 4 is a diagram showing a D / A included in the gradation voltage signal supply device Z. FIG. 5 is a graph schematically illustrating a third example of the signal conversion characteristics of the D / A converter included in the gradation voltage signal supply device Z. FIG. 5 is a graph schematically illustrating the second example of the signal conversion characteristics of the converter. 6 is a diagram showing a schematic configuration of a main part of a conventional gradation voltage signal supply device A and a signal conversion characteristic of a D / A converter constituting the same, and FIG. 7 is a circuit configuration of a basic D / A converter. It is an example.

First, the structure of the main part of the liquid crystal display device X according to the embodiment of the present invention will be described with reference to the block diagram shown in FIG.
As shown in FIG. 1, the liquid crystal display device X includes a liquid crystal display panel 1, a source driver 2 and a gate driver 3 for driving the liquid crystal display panel 1, a display control circuit 4 for controlling both drivers, and the source driver 2. A gradation voltage signal supply device Z for supplying gradation voltage signals at a plurality of levels is provided.
The display control circuit 4 is composed of a microcomputer (not shown) and its peripheral devices, etc., and externally input video signals (image signals for each of R, G, and B, horizontal synchronizing signals, vertical synchronizing signals, synchronizing clock signals). Etc.), the gate driver 3 is supplied with a gate start pulse signal, a gate clock signal, etc., and the source driver 2 is provided with a color display image signal, a data start pulse signal, a data clock signal, and an enable signal. Image display control on the liquid crystal display panel 1 is performed by outputting signals, output pulse signals, and the like.
Further, the display control circuit 4 is connected to the gradation voltage signal supply device Z via a bus control line such as I2C. For adjusting the voltage levels V1 to Vn of the gradation voltage signal output from the gradation control signal supply device Z to the source driver 2 from the display control circuit 4 to the gradation voltage signal supply device Z. The digital signal used is output.
The gradation voltage signal supply device Z inputs n (for example, about nine) digital signals corresponding to each of the n gradation voltage signals transmitted from the display control circuit 4, and the digital signal Are supplied to the source driver 2 which is the control unit of the liquid crystal display panel 1 on the basis of the values D1 to Dn of the voltage levels Vi (i = 1 to n).
The liquid crystal display panel 1, the source driver 2, and the gate driver 3 constitute an example of liquid crystal display means.

FIG. 2 is a block diagram showing a schematic configuration of the gradation voltage signal supply device Z. As shown in FIG.
The gradation voltage signal supply device Z includes n (plurality) of D (one) for each gradation voltage signal of n stages of voltage levels Vi (i = 1 to n) to be supplied to the source driver 2. / A converter 10 is provided.
Each of the n D / A converters 10 converts each of the n digital signals input from the display control circuit 4 into an analog voltage signal and outputs the analog voltage signal (voltage V1). ... To Vn) are supplied to the source driver 2 (part of the liquid crystal display means) through the buffer 12 as n-level (n) gradation voltage signals.

(First example of signal conversion characteristics)
FIG. 3 is a graph schematically showing a first example of signal conversion characteristics of the D / A converter 10. The horizontal axis of the graph represents the value of the digital signal, and the vertical axis represents the value of the analog voltage signal.
As shown in FIG. 3, the signal conversion characteristics of each D / A converter 10, that is, the correspondence relationship of the value of the analog voltage signal to the value of the digital signal is non-linear.
In this first example, the signal conversion characteristic of each of the D / A converters 10 is a characteristic that the change in the value of the analog voltage signal monotonously increases with respect to the change in the value of the digital signal. The slope of the analog voltage signal in the predetermined range Dw (hereinafter referred to as the center input value vicinity range Dw) in the vicinity of the median value in the possible ranges Dmin to Dmax (that is, the slope of the change in the analog voltage value with respect to the change in the digital signal value). , The characteristic is gentler than the slope of the analog voltage signal in the range before and after the center input value vicinity range Dw.
In this example, each of the D / A converters 10 has the same signal conversion characteristics, and each D / A converter 10 has the analog voltage at the level closest to the target voltage to be output (target value of the gradation voltage). The digital signal is set so that the signal is output. Normally, the digital signals having different values are set (input) to each of the n D / A converters 10.
As a result, the value of the digital signal set in the D / A converter 10 at the time of initial adjustment according to the specifications of the liquid crystal panel 1 (parameter adjustment in the control program of the display control circuit 4) is input to the center input. When the value is changed in the value vicinity range Dw, the value of the analog voltage signal is in the vicinity of the median value of the n gradation voltages V1 to Vn (near the center voltage, Vi, Vi + 1, A signal conversion characteristic (that is, a characteristic with a gentle slope) that changes slightly can be obtained.
As a result, a target voltage (originally to be set as a gradation voltage to be supplied to the source driver 2) near the center voltage that requires particularly high accuracy (that is, has a large influence on the image quality in the liquid crystal display panel 1). The accuracy of the gradation voltage with respect to (voltage) should be improved.

On the other hand, in the range before and after the center input value vicinity range Dw, that is, in the range close to the minimum value Dmin or the maximum value Dmax of the digital signal, the value of the analog voltage signal is compared when the value of the digital signal is changed. Change significantly. Therefore, a sufficient output voltage range (Vmin to Vmax) can be secured without particularly increasing the resolution of the D / A converter 10.
For this reason, in the range other than the vicinity of the center voltage (the range close to the minimum value or the maximum value of the analog voltage signal), the signal conversion characteristic has a relatively steep slope. Although it is not possible to finely adjust (gradation voltage), an error with respect to the target voltage within this range is not particularly problematic because it has a small effect on the image quality.
Here, the signal conversion characteristic shown in FIG. 3 is a characteristic in which the change in the value of the analog voltage signal monotonously increases with respect to the change in the value of the digital signal. If the magnitude relation is reversed and given, the same effect is obtained.

Various specific configurations of the D / A converter are conceivable. For example, a weight resistor type D / A converter having the circuit configuration shown in FIG. 7A or a ladder having the circuit configuration shown in FIG. A resistance type D / A converter or the like can be considered.
Here, in the case of the weight resistance type D / A converter shown in FIG. 7A, when the voltage of each bit signal constituting the 4-bit digital signal is E1 to E4, the output voltage Eo (the level of the analog voltage signal) ) Is expressed by the following equation (1).
Eo = -Ro (E1 / R1 + E2 / R2 + E3 / R3 + E4 / R4) (1)
Further, in the case of the ladder resistor type D / A converter shown in FIG. 7B, when each 4-bit voltage is E1 to E4, the output voltage Eo is expressed by the following equation (2).
Eo = 1/24 (8E1 + 4E2 + 2E3 + E4) (2)
A D / A converter that realizes nonlinear signal conversion characteristics can be configured by previously setting a combination of resistance values in such a D / A converter and a voltage of each bit signal to a predetermined value.
The specific configuration of the D / A converter that realizes such nonlinear signal conversion characteristics is also described in detail, for example, in Patent Document 2.

(Second example of signal conversion characteristics)
Next, another example (second example) of the signal conversion characteristics of the D / A converter 10 will be described with reference to FIG.
FIG. 4 is a graph schematically showing a second example of signal conversion characteristics of the D / A converter 10. In the second example, similarly to the first example, the signal conversion characteristics of each of the D / A converters 10 are nonlinear, and the slope of the analog voltage signal in the center input value vicinity range Dw is The characteristic is gentler than the slope of the analog voltage signal in the range before and after the range Dw.
In each of the D / A converters 10 in the second example, the minimum value Vmin and the maximum value Vmax of the analog voltage signal that can be output are fixed at the same value, and the range from the minimum value Vmin to the maximum value Vmax. The overall level of the analog voltage signal with respect to the digital signal values Dmin to Dmax is variable. In FIG. 4, the state where the level of the analog voltage signal is changed is indicated by a broken line. The level adjustment of the analog voltage signal in each of the D / A converters 10 is performed based on a control signal from the display control circuit 4 or the like, for example.

The n D / A converters 10 having the signal conversion characteristics according to the second example are preferably used as follows.
For example, as in the case of the first example described above, the digital signals having different values are output so that the analog voltage signals at levels closest to the target voltage to be output are output for each D / A converter 10. Set. In addition, the D / A converter 10 having a large level error of the analog voltage signal with respect to the target voltage is finely adjusted to eliminate the error by adjusting the level of the analog voltage signal.
In addition, when each of the D / A converters 10 receives the digital signal in the range Dw near the center input value, each D / A converter 10 out of the n gradation voltages takes charge (outputs). The level adjustment is performed so that the analog voltage signal having a value in a range that can normally be taken according to the specification or the like is output to the liquid crystal display panel 1 as the target voltage of the gradation voltage Vi. That is, for the D / A converter 10 that is responsible for supplying the low-level gradation voltage (for example, V1 etc.), when the digital signal in the range Dw near the center input value is inputted, The level is adjusted so that the signal conversion characteristic for outputting the voltage is obtained. Similarly, for the D / A converter 10 that is responsible for supplying the high-level gradation voltage (for example, Vn), when the digital signal in the range Dw near the center input value is input, The level is adjusted so that the signal conversion characteristic for outputting the voltage is obtained. In this case, the digital signal having the same value can be set in each of the D / A converters 10.
As described above, the D / A converter 10 does not have a particularly high resolution, and the level with high accuracy can be obtained in a range other than the vicinity of the center voltage (a range close to the minimum value Vmin or the maximum value Vmax of the analog voltage signal). A regulated voltage signal can be supplied.
Here, as a configuration for changing the overall level of the analog voltage signal, for example, a weight resistance type D / A converter shown in FIG. 7A or a ladder resistance type shown in FIG. When the D / A converter has a basic configuration, a configuration in which a bit voltage level adjustment circuit that can adjust (variably) the levels of the voltages E1 to E4 of each bit signal can be considered.

(Third example of signal conversion characteristics)
Next, another example (third example) of signal conversion characteristics of the D / A converter 10 will be described with reference to FIG.
FIG. 5 is a graph schematically showing a third example of the signal conversion characteristics of the D / A converter 10. In this third example as well, the signal conversion characteristic of each D / A converter 10 is non-linear, and the slope of the analog voltage signal in the vicinity of the center input value Dw is the same as the first example. The characteristic is gentler than the slope of the analog voltage signal in the range before and after the range Dw.
Each of the D / A converters 10 in the third example has the same minimum value Vmin and maximum value Vmax of the analog voltage signal that can be output, and the digital signal is within the range from the minimum value Vmin to the maximum value Vmax. The overall level of the analog voltage signal with respect to the signal values Dmin to Dmax is different. FIGS. 5A, 5B, and 5C show examples of signal conversion characteristics in which the overall level of the analog voltage signal is different. 5A shows the signal conversion characteristics of the D / A converter 10 that supplies the maximum gradation voltage Vn. FIG. 5B shows the D / A that supplies a certain gradation voltage voltage Vi near the center voltage. Signal conversion characteristics of the converter 10 and (c) show examples of signal conversion characteristics of the D / A converter 10 that supplies the minimum gradation voltage V1.
As described above, when n D / A converters 10 having different signal conversion characteristics are used, each of the D / A converters 10 is set in the range near the center input value, as in the case of the second example. When the Dw digital signal is input, the output level is set such that the analog voltage signal is output in a range that can normally be taken by the target voltage of the gradation voltage Vi that the D / A converter 10 is responsible for. . In this case, the digital signal having the same value can be set in each of the D / A converters 10.
As a result, the D / A converter 10 does not have a particularly high resolution, and the level with high accuracy can be obtained in a range other than the vicinity of the center voltage (a range close to the minimum value Vmin or the maximum value Vmax of the analog voltage signal). A regulated voltage signal can be supplied.

  The present invention can be applied to a gradation voltage signal supply device that supplies gradation voltages to liquid crystal display means.

1 is a block diagram illustrating a schematic configuration of a main part of a liquid crystal display device X according to an embodiment of the present invention. FIG. 3 is a block diagram illustrating a schematic configuration of a gradation voltage signal supply device Z included in the liquid crystal display device X. The graph which represented typically the 1st example of the signal conversion characteristic of the D / A converter with which the gradation voltage signal supply apparatus Z is provided. The graph which represented typically the 2nd example of the signal conversion characteristic of the D / A converter with which the gradation voltage signal supply apparatus Z is provided. The graph which represented typically the 3rd example of the signal conversion characteristic of the D / A converter with which the gradation voltage signal supply apparatus Z is provided. The figure showing the schematic structure of the principal part of the conventional gradation voltage signal supply apparatus A, and the signal conversion characteristic of the D / A converter which comprises it. An example of a circuit configuration of a basic D / A converter.

Explanation of symbols

X ... Liquid crystal display device Z ... Gradation voltage signal supply device 1 ... Liquid crystal display panel 2 ... Source driver 3 ... Gate driver 4 ... Display control circuit 10 ... D / A converter

Claims (5)

A plurality of D / A converters for converting an input digital signal into an analog voltage signal and outputting the analog voltage signal are output, and each analog voltage signal output by each of the D / A converters is supplied to a liquid crystal display device as a plurality of gradation voltage signals. A gradation voltage signal supply device for supplying
A gradation voltage signal supply device, wherein the signal conversion characteristic of each of the D / A converters is non-linear.   A signal conversion characteristic of each of the D / A converters is a characteristic in which a change in the analog voltage signal with respect to a change in the value of the digital signal is monotonously increased or monotonically decreased, and a median value in a range that the value of the digital signal can take 2. The gradation voltage signal supply device according to claim 1, wherein a slope of the analog voltage signal in a predetermined range near is a characteristic that is gentler than a slope of the analog voltage signal in a range before and after the predetermined range near the median value.   The analog voltage signal corresponding to the value of the digital signal in the range from the minimum value to the maximum value while fixing the minimum value and the maximum value of the analog voltage signal that each D / A converter can output to the same value. The gradation voltage signal supply device according to claim 1, wherein the overall level is variable.   In each D / A converter, the minimum value and the maximum value of the analog voltage signal that can be output are the same, and the overall value of the analog voltage signal with respect to the value of the digital signal in the range from the minimum value to the maximum value. 3. The gradation voltage signal supply device according to claim 1, wherein the levels are different.   5. A liquid crystal comprising: a liquid crystal display means; and a gradation voltage signal supply device according to claim 1, which supplies a plurality of gradation voltage signals to the liquid crystal display means. Display device.

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