JPH10233686A - A/d converter circuit and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the A/D converter circuit and the display device configured such that a gradation interval of an image displayed via a D/A converter and an A/D converter is uniformized without the need of high precision components and of an adjustment process. SOLUTION: The A/D converter circuit is configured of an A/D converter means 11 that converts an analog signal into digital data whose level corresponding to a voltage level of the analog signal and provides an output of the digital data, an automatic gain adjustment control circuit 13 that has a constant number data register and a data comparison means, uses the data comparison means comparing the constant data stored in the constant number register with data outputted from the A/D converter means 11 to provide an output of control data, a reference voltage generating D/A converter means 12 that generates a prescribed reference voltage based on the control data outputted from the automatic gain adjustment control circuit 13, and a means that adjusts a conversion means of the A/D converter means 11 based on the reference voltage. Furthermore, the display device is configured with the provision of the A/D converter circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AD conversion circuit and a display device, and more particularly to an analog-to-digital (A / D) conversion circuit and a display device such as a liquid crystal display device for displaying an image on a personal computer. A video signal AD in a display device having a configuration in which a video signal is converted into a digital signal and then converted into a drive signal for a display element
The present invention relates to a conversion circuit having a circuit for automatically adjusting a conversion gain when converting a video signal to a digital signal, and a display device including the video signal AD conversion circuit.

[0002]

2. Description of the Related Art Conventionally, a matrix type display device such as a liquid crystal display device for converting a video signal which is an analog signal output from a personal computer or the like into a digital signal by an AD converter and then converting the digital signal into a drive signal for a display element is known. However, since the apparatus does not have a function of automatically adjusting a conversion gain when converting a video signal, the following problem occurs.

A video signal output from a personal computer or the like is obtained by converting a digital signal into a video signal which is an analog signal by a DA converter. Therefore, it is desirable that the digital signal output from the AD converter built in the liquid crystal display device matches the digital signal input to the DA converter.

However, errors in the gain of the amplifier and D
If there is a difference between the reference voltage of the A converter and the reference voltage of the AD converter, the digital signal input to the DA converter and the digital signal output from the AD converter do not match.

For example, when the gain of the amplifier between the DA converter and the AD converter is smaller than a set value, or when the reference voltage of the AD converter is higher than the reference voltage of the DA converter, 2 which were adjacent to each other when inputting to
When a digital signal of a level is output from an AD converter, it may be converted into a digital signal of a single level.

When the gain of the amplifier is larger than the set value, or when the reference voltage of the AD converter is lower than the reference voltage of the DA converter, the amplifiers are adjacent to each other when inputting to the DA converter. Each of the two-level digital signals that have been output from the A / D converter may be converted to digital signals of separated levels.

FIG. 5 shows an example of the correspondence between the input signal voltage of the DA converter and the output signal voltage of the AD converter when the reference voltage of the AD converter is about 0.8 times the reference voltage of the DA converter. FIG. The horizontal axis in FIG.
The input data of the converter, the vertical axis is the output data of the AD converter,
The square frame in the graph indicates the correspondence between the input data of the AD converter and the output data of the AD converter. FIG. 5 (b)
FIG. 5A is a graph extracted from FIG. 5A and illustrating the correspondence between the digital signal input to the DA converter and the digital signal output from the AD converter.

When the input data of the DA converter is at level 2, the output data of the AD converter is at level 2, and when the input data of the DA converter is at level 3, the output data of the AD converter is at level 4, and the output data of the AD converter is at level 4. The condition of the input data of the DA converter in which the output data is level 3 does not exist. That is, D
Since the accuracy of the matching between the conversion gain of the A converter and the conversion gain of the AD converter is lower than the least weighted bit (LSB) of the DA converter or the AD converter, when the gray scale is displayed, FIG. As shown in b), the gray level becomes uneven. That is, if the accuracy of the gain of the amplifier is insufficient or if there is a difference between the reference voltage of the D / A converter and the reference voltage of the A / D converter, the D / A converter input data and the A / D converter output data do not match. On the other hand, when a gray scale is displayed, there is a problem that the intervals between gradations become unequal, and the number of gradations that can be expressed substantially decreases. Conventionally, in order to prevent this problem, high-precision parts and an adjustment process at the time of manufacturing have been required.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and does not require high-precision parts or an adjustment process, and has a uniform gradation interval of an image displayed through a DA converter and an AD converter. It is an object of the present invention to provide an AD conversion circuit and a display device having a configuration capable of achieving the structure.

[0010]

The above object can be achieved by automatically adjusting the gain when converting a signal with an AD converter.

In the AD conversion circuit according to the present invention, A
The conversion gain is adjusted by adjusting the voltage level of the reference voltage used for AD conversion in the D converter. The adjustment of the conversion gain is referred to by a DA converter (DA converter for generating a reference voltage) provided in the AD converter during a period when the video signal DA converter is outputting a video signal corresponding to specific digital data. This is automatically performed by adjusting the input data of the reference voltage generating DA converter so that a voltage is generated and a predetermined digital signal is output from the AD converter. Here, a minimum value and a maximum value at which a predetermined digital signal can be obtained are obtained, and the arithmetic average value or the geometric average value thereof is used as input data of the adjusted reference voltage generating DA converter.

Further, a display device according to the present invention has a configuration including the AD conversion circuit according to the present invention.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an AD conversion circuit and a display device according to the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of an AD converter according to a first embodiment of the present invention.

The A / D conversion circuit according to the first embodiment of the present invention comprises a video signal which is an analog signal and a reference voltage Vre.
f is input to the video AD converter 11,
A reference voltage generation DA converter 12 for generating a reference voltage Vref input to the converter 11, and a reference voltage generation DA converter based on an output signal of the video AD converter 11 and a synchronization signal 14.
And an automatic gain adjustment control circuit 13 for controlling the converter 12.

For example, in the case of a color liquid crystal display device, three sets of AD conversion circuits according to the present invention are provided in a signal input section, and convert input red, green, and blue video signals into digital signals.

The input video signal is, for example, a video signal generated by a 6-bit video signal D / A converter built in a personal computer. The video signal D / A converter here comprises, for example, 64 current sources, a current adding circuit, a circuit for controlling the number of current sources to be added according to a digital signal input, and a load resistor. Shall be The output current of each current source is adjusted by the reference voltage Vref.

On the other hand, the video AD converter 11, for example,
A 6-bit flash AD converter, comprising 63 voltage comparators, a voltage dividing circuit for the reference voltage Vref, and a priority encoder for converting the comparator output into a binary digital signal corresponding to the voltage level. By comparing the voltage level of the input analog video signal with the voltage level of the reference voltage Vref, the video signal is converted into a binary digital signal corresponding to the voltage level.

How the reference voltage Vref works in a video signal DA converter such as a personal computer
The manner of operation of the reference voltage Vref in the converter is different due to their configuration, and furthermore, since the video signal D / A converter and the A / D converter are disposed apart from each other, their respective environmental temperatures are different. Power is also supplied from another system. Therefore, it is difficult to obtain sufficient accuracy without adjusting the gain.

The reference voltage Vref of the video AD converter 11
Is generated by the reference voltage generating DA converter 12 controlled by the automatic gain adjustment control circuit 13. The reference voltage generating DA converter 12 is, for example, a substantially 12-bit DA converter.
This is a converter whose resolution is set higher than that of the video AD converter 11. The conversion time of the reference voltage generating DA converter 12 may be long, for example, about 1 μs.

The variable range of the reference voltage Vref of the video A / D converter 11 is a range that can cope with a variation in the performance of components.
For example, since a variable range of ± 5% is sufficient, the reference voltage generating DA converter 12 is configured by combining an 8-bit DA converter and an adder to form a substantially 12-bit DA converter. I have.

The automatic gain adjustment control circuit 13 controls the reference voltage generating DA converter 12 of the video A / D converter 11 and refers to the output signal of the video A / D converter 11 during, for example, a vertical blanking period of display. Then, a value to be set during the display period of the reference voltage generating DA converter 12 is determined.

During a display vertical blanking period, a predetermined digital signal is input to a video signal D / A converter built in a personal computer, and a video signal having an automatic gain adjustment voltage is output. Further, the personal computer transmits to the automatic gain adjustment control circuit 13 by the synchronization signal 14 that the automatic gain adjustment voltage is being output.

FIG. 4 shows the internal configuration of the automatic gain adjustment control circuit 13. That is, the whitening gain control adjustment circuit 13 stores the constant data and outputs the constant data at the timing designated by the synchronization signal 14.
1. The constant data 55 output from the constant data register 51 is compared with the data 54 output from the AD conversion means 11, and a predetermined value corresponding to whether the data 54 is larger than, equal to, or smaller than the constant data 55 is calculated. Control signal 5
6 and a search section control register 53 including a register A60, a register B61, and a register C62. As the constant data register 51, general storage means such as a register, a ROM, and a RAM can be used. As the comparison means 52, a well-known comparator circuit can be applied.

Automatic gain adjustment control circuit 1 in this embodiment
3 is a reference voltage generating D during the automatic gain adjustment period (set within the vertical blanking period) by the following procedure.
A value to be set in the A conversion means 12 is determined. Originally, the input data of the video D / A converter on the personal computer side is, for example, the data of the "62nd" gradation (hereinafter the gradation data is represented by ""), and the output data of the video AD conversion means is 61 The minimum reference voltage or the maximum reference voltage which becomes 62 is defined as the reference voltage-low, and the minimum reference voltage or 6 which the output data of the video AD conversion means becomes 62.
A maximum reference voltage of 3 is defined as a reference voltage-high, an average voltage of the reference voltage-low and a reference voltage-high is determined as a reference voltage-medium, and the reference voltage-middle is defined as a reference voltage for video signal AD conversion. . (1) First, a procedure for obtaining the reference voltage-low will be described below.
Video signal DA converters for personal computers, etc.
In addition, it is assumed that the offset voltage of the AD converter 11 is adjusted in advance. The input data to the video signal D / A converter of a personal computer or the like is a predetermined value (data corresponding to the gradation to be displayed on the liquid crystal display device;
The video signal D / A converter of a personal computer or the like outputs an analog voltage corresponding thereto. The constant data register 51 previously stores data of the 61st gradation which is one smaller than the data of the 62nd gradation.

Register 6 in search section control register 53
0 stores digital data corresponding to the lowest level of display gray scale, register 62 stores digital data corresponding to the highest level of display gray scale, and register 61 stores the data stored in register 60 and the register. The average value data of the data stored in 62 is calculated and stored in the addition circuit 63.

The data stored in the register 61 is output to the reference voltage generating DA converter 12 through the data selector 70 as input data 57 of the reference voltage generating DA converter 12. (2) When the data 54 output from the AD conversion means 11 is larger than the constant data 54 output from the constant data register 51 (for example, the data of the 62nd gradation), the comparing means 52 A control signal 56 for performing the following control is output to the control register 53.

First, the data of the register B61 is stored in the register A60, and then the data newly stored in the register A60 and the data previously stored in the register C62 are stored in the register A60.
The divided (average) data is stored in the register B61.
The search section control register 53 outputs the data newly stored in the register B61 as the control signal 57.

Conversely, if the data 54 is smaller than or equal to the data 55, the data in the register C62 is stored in the register A60, and the data in the register A60 and the data in the register C62 are averaged and stored in the register B61. . (3) The reference voltage generating DA converter 12 generates a reference voltage Vref corresponding to the control signal 57 output from the search section control register 53 and outputs the reference voltage Vref to the AD converter 11. The conversion gain of the AD conversion means 11 is equal to the reference voltage V
Adjusted based on ref.

At this time, in the procedure (1), the data 54
Is larger than the data 55, the data stored in the register B61 and the data stored in the register C62, which is larger than the data 55, are divided into two, so that the reference voltage Vref increases. AD
The voltage value is in the direction of decreasing the conversion gain of the conversion means 11. (4) The steps (2) and (3) are performed by using the reference voltage generation DA
This is repeated until the LSB of the conversion means 12 is set. For example, if the DA conversion means 12 has an 8-bit resolution, it repeats eight times, and if it has a 6-bit resolution, repeats six times. By this cycle, the reference voltage Vref is set to the lowest voltage at which the output of the AD converter 11 outputs the data 61 or the highest voltage at which the output of the AD converter 11 becomes the data 62. (5) The data in the register B61 at this time is saved in the save register 72. However, the save register 72 has
Since the sum of the output of the save register 72 and the data of the register B61 is stored, data 0 is stored in the register 72 in advance. (6) Next, the output data of the video A / D converter is "6
The reference voltage-high, which is the minimum reference voltage of "2" or the maximum reference voltage of "63", is obtained in the same procedure as that for determining the reference voltage-low. However, the difference is that the data stored in advance in the constant data register 51 is set to “62”. (7) The data stored in the save register 72 up to the procedure (5) and the data stored in the register B61 up to the procedure (6) are added and stored in the save register 72.
The divided data is used as an output 57 of the automatic gain adjustment control circuit 13 via the data selector 70. (8) By the procedures (1) to (7), the reference voltage Vre
f is automatically set to a voltage value at which the output of the AD converter 11 stably outputs 62, with higher accuracy than the LSB of the AD converter, and the conversion gain of the AD converter is adjusted.

The control method of the search section control register 53 is a so-called binary search method, which is the same as a binary search method that is sometimes used when searching for a solution of an equation by a computer program. .

In the above procedure, the video DA converter 11
Only one constant was selected and used for the input data of the video DA converter, the video AD converter, the video AD converter, or the video DA converter.
If the video amplifier between the converter and the video A / D conversion means does not have sufficient linearity, a plurality of data are input to the video D / A converter 11 to generate a reference voltage corresponding to each data. Input data 5 for DA conversion means
It is desirable that the average value of 7 be the final data 57. For example, data values “1”, “20”, “41”, “6”
The minimum reference voltage for each of "2" is obtained and averaged to obtain data 57. In this case, the odd data value and the even data value are selected and used by the same number. In this case, even if the offset voltage is not adjusted in advance,
The conversion gain can be adjusted.

In the above procedure, the binary search method is used to shorten the time for setting the reference voltage Vref.
The reference voltage Vref may be sequentially increased to find the reference voltage Vref (the input data 57 of the reference voltage generating DA converter 12) at which the output 54 of the AD converter changes, and the conversion gain may be automatically adjusted. However, the AD converter 11
When the output signal voltage of the AD converter 11 becomes larger than the target value, the reference voltage Vref is increased, and the AD converter 11 If the output signal voltage of No. 11 is lower than the target value, the reference voltage Vref is lowered to approach the target value.

The above-described automatic gain adjustment procedure can be modified as follows.

In the above-described procedure, when searching for a boundary, it is not fixed whether the value corresponding to the boundary approaches from the higher side or the lower side. Therefore, the transient response of the DA converter 12 for generating reference voltage is not fixed. Is not sufficiently short, the detection of the boundary may be erroneously determined to be higher or lower. If the detection error of the boundary is roughly determined, it is possible to correct the detection error by obtaining the detection error by an experiment or the like.
Therefore, in the above-described procedure, the boundary is not searched for the minimum resolution by the binary search method, and the boundary is searched by always changing the reference voltage Vref sequentially from the lowest one, for example, near the minimum resolution. It is also possible. here,
Although it is assumed that the transient response of the reference voltage generating DA converter 12 is long, the same applies to the case where the video A / D converter 11 has a long response to the reference voltage Vref.

Further, as a modification of the above-described automatic gain adjustment procedure, if the automatic adjustment is not completed within one vertical blanking period, the procedure can be divided into a plurality of vertical blanking periods.

In the above procedure, one of the values smaller than the full scale of the input signal voltage of the video signal DA converter or the video AD converter 11 of the personal computer or the like and close to the full scale is selected for automatic adjustment. Normal,
Video signal DA converters for personal computers, etc.
Since the relationship between the input signal voltage and the output signal voltage of the video AD converter 11 does not have ideal linearity, a plurality of input digital signals of the D / A converter for automatic gain adjustment are selected, and the video signal is selected for each of them. It is desirable that the set value of the reference voltage Vref of the AD converter 11 be obtained, and the average value thereof be used as the set value of the reference voltage Vref of the video AD converter 11 during the display period.

The above-described automatic gain adjustment is performed independently for each channel of the red, green, and blue video signals. The automatic gain adjustment does not need to be performed every vertical blanking period. For example, the adjustment operation may be performed only for 30 minutes after the power is turned on, or may be adjusted every hour. In the above procedure, the time required for the automatic adjustment is shortened by the binary search method. However, the set value of the automatic adjustment is not searched for in the entire adjustment range every time the automatic adjustment is performed, but the previous set value is set. May be stored, and the set value may be searched only in the vicinity of the previous set value.

In the above configuration of the automatic gain adjustment circuit, it is assumed that the offset voltage is compensated in advance. However, an addition circuit for adjusting the offset voltage and a DA converter are provided on the input side of the AD converter. Also, the offset voltage can be automatically adjusted by slightly changing the procedure.

FIG. 2 is a block diagram showing a configuration of an AD conversion circuit according to a second embodiment of the present invention.

The AD conversion circuit according to the second embodiment of the present invention comprises a video signal which is an analog signal and a reference voltage Vre.
f is input to the video AD converter 21,
A reference voltage generating DA converter 22 for generating a reference voltage Vref input to the converter 21, an offset voltage adjusting DA converter 25 for adjusting an offset voltage of a video signal input to the video AD converter 21, An automatic gain adjustment control circuit 23 controls the reference voltage generation DA converter 22 and the offset voltage adjustment DA converter 25 based on the output signal of the video AD converter 21 and the synchronization signal 24.

The automatic adjustment of the offset voltage and the gain by the AD conversion circuit according to the second embodiment of the present invention is performed according to the following procedure. (1) A level 1 is set to an input signal voltage of a video signal D / A converter of a personal computer or the like that outputs a video signal, and an output signal voltage corresponding thereto is output. (2) The output signal voltage of the offset voltage adjusting DA converter 25 is adjusted so that the output signal of the video AD converter 21 becomes
The setting of the boundary between the setting of level 0 and the setting of level 1 and the setting of the boundary between the setting of level 1 and the setting of level 2 are searched. As a search method, a binary search method is used similarly to the automatic gain adjustment described above. And
The average of the set values of the respective boundaries is set as a temporary offset voltage adjustment set value. (3) Next, automatic gain adjustment is performed using any of the above-described methods. (4) In steps (1) and (2), the offset voltage was adjusted with reference to the level 1 of the output signal voltage of the DA converter such as a personal computer, so that the gain adjustment in step (3) was performed. Apparently, the offset voltage changes. Therefore, the procedure after the procedure (2) is repeated again.
This repetition is performed until the set value of the offset voltage no longer changes or until the result of the repetition of the previous procedure becomes inconsistent. For example, if the increasing / decreasing direction of the offset voltage is opposite to the previous direction, it is determined that there is a contradiction, and the repetition of the procedure is stopped.

As described above, according to the configuration of the AD conversion circuit according to the second embodiment of the present invention, not only the gain of the AD conversion of the video signal but also the offset voltage of the video signal is automatically adjusted. Can be.

Next, the configuration of the entire display system in which the AD conversion circuit according to the present invention is incorporated will be described.

FIG. 3 is a block diagram showing an example of the configuration of a display device and a display system according to the present invention. The display device and the display system having the configuration in which the AD conversion circuit according to the present invention is incorporated are described. FIG. 2 is a block diagram illustrating an example configuration. In FIG. 3, components unnecessary for the description of the present invention, such as a power supply circuit and control signals, are omitted. Here, a liquid crystal display device is shown as an example of a display device according to the present invention, and a personal computer is shown as an example of a video signal source.

The display device according to the present invention is a liquid crystal display device 4.
0, a video A / D conversion circuit 41R with an automatic gain adjustment function provided for each of the red, green, and blue video signals;
41G, 41B, a liquid crystal display element control circuit 42 to which a digital signal converted from a video signal by the video AD conversion circuits 41R, 41G, 41B with an automatic gain adjustment function is input, and a digital signal through the liquid crystal display element control circuit 42. A scanning line driving IC 43 and a signal line driving IC 44 to which signals are inputted, and a liquid crystal display panel 47 for displaying an image are provided. The video A / D conversion circuits 41R, 41G, and 41B with the automatic gain adjustment function correspond to the above-described A / D converter according to the present invention.
The signal line driving IC 44 is a conversion circuit.
And a DA converter 46.

The source of the video signal for the liquid crystal display device 40 is the personal computer 30. The personal computer 30 generates an image signal which is a digital signal represented by red, green and blue video signals. A graphics controller 31 and a video signal DA converter 3 for converting each of the red, green, and blue image signals from the graphics controller 31 into a video signal.
2R, 32G, and 32B, and the personal computer 30 and the liquid crystal display device 40 constitute a display system according to the present invention.

The operation of the display device and the display system according to the present invention is as follows. That is, personal
Graphics controller 3 in computer 30
The image signal generated in 1 is red,
A video signal DA converter 32R corresponding to each color of green and blue,
The signal is converted into a video signal which is an analog signal at 32G and 32B, and is input to the liquid crystal display device 40. The three video signals input to the liquid crystal display device 40 are converted into AD conversion circuits 41R, 41G, and 41B with an automatic gain adjustment function according to the present invention.
And converted into digital signals. AD conversion circuits 41R, 4 with automatic gain adjustment function according to the present invention
The 1G, 41B converts the video signal into a digital signal by adjusting the conversion gain so that its output data corresponds to the input data of the video signal DA converters 32R, 32G, 32B as possible as possible. The converted digital signal is passed through a liquid crystal display element control circuit 42 to a signal line driving IC.
44. The signal line drive ICs 44 store the input digital signals for one horizontal scanning line in a register 45 inside the IC, and convert the digital signals into analog signals by a DA converter 46 at an appropriate timing to convert the signal lines of the liquid crystal display element. Drive. This is repeated for each scanning line by the scanning line driving IC 43 to display an image on the liquid crystal display panel 47.

As described above, the display image is generated as an image signal which is a digital signal, is converted into a video signal which is an analog signal, is again converted into a digital signal, is again converted into an analog signal, and is again converted into an analog signal. The lines are sequentially driven and displayed as an image on the liquid crystal display panel 47.

[0050]

According to the AD conversion circuit and the display device according to the present invention, a video signal D of a personal computer or the like can be obtained.
Since the A converter and the gain of the video A / D converter of the display device are automatically adjusted to match, the liquid crystal display can be used without using high-precision parts and without requiring a gain adjustment step at the time of manufacturing. It is possible to prevent unevenness between the gradation levels of the image displayed on the element, and it is not necessary to use an amplifier whose gain can be adjusted. The automatic adjustment of the gain is based on the video signal DA.
The least weighted bit (LS) of the converter or video A / D converter
Since it is performed with higher precision than in B), the output signal voltage level of the video A / D converter and the input signal voltage level of the video signal D / A converter can be made to correspond almost one-to-one.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an AD conversion circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an AD conversion circuit according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of an example of a display device and a display system according to the present invention.

FIG. 4 is a block diagram showing an internal configuration of an automatic gain adjustment control circuit.

FIG. 5 shows an example of the correspondence between the input signal voltage of the DA converter and the output signal voltage of the AD converter when the reference voltage of the AD converter is about 0.8 times the reference voltage of the DA converter. Graph.

[Explanation of symbols]

11, 21 Video AD converter 12, 22 Reference voltage generation DA converter 13, 23 Automatic gain adjustment control circuit 14, 24 Synchronization signal 25 Offset voltage adjustment DA converter 30 Personal computer 31 Graphics controller 32R, 32G , 32B Video signal DA converter 40 Liquid crystal display device 41R, 41G, 41B Video AD conversion circuit with automatic gain adjustment function 42 Liquid crystal display element control circuit 43 Scan line drive IC 44 Signal line drive IC 45 Register 46 DA converter 47 Liquid crystal display panel

Claims (5)

[Claims] An analog-to-digital converter for converting an analog signal into digital data corresponding to the voltage level of the analog signal and outputting the digital data; a constant data register and a data comparing means; and a constant stored in the constant data register. An automatic gain adjustment control circuit that outputs control data by comparing and referencing the data and the data output from the AD conversion means by the data comparison means; and a predetermined control based on the control data output from the automatic gain adjustment control circuit. Reference voltage generation DA for generating reference voltage
An AD conversion circuit comprising: conversion means; and means for adjusting a conversion gain of the AD conversion means based on the reference voltage. 2. The A / D conversion circuit according to claim 1, wherein a plurality of pieces of constant data and a plurality of output data of the A / D conversion means are compared and referenced by the data comparison means. 3. The A / D converter according to claim 1, further comprising an offset voltage adjusting DA converter for adjusting an offset voltage of an analog voltage input to the A / D converter based on output data of the automatic gain adjustment control circuit. The A / D conversion circuit according to claim 1. 4. A pixel driven by a plurality of scanning lines and signal lines, A / D conversion means for converting an analog signal into digital data corresponding to a voltage level of the analog signal and outputting the digital data, a constant data register, and a data comparison circuit. An automatic gain adjustment control circuit having means for comparing and referring to constant data stored in the constant data register with data output from the AD conversion means by the data comparison means and outputting control data; AD conversion having reference voltage generation DA conversion means for generating a predetermined reference voltage based on control data output from the adjustment control circuit, and means for adjusting the conversion gain of the AD conversion means based on the reference voltage A circuit for generating a predetermined gradation signal based on output data of the scanning line driving circuit for driving the scanning line and the AD conversion circuit; And a signal line driving circuit for driving the signal line. 5. The display device according to claim 4, wherein a synchronization signal for controlling a timing of a vertical blanking period is input to said automatic gain adjustment control circuit.