JP2004102296A - Image processing circuit, image processing method, electro-optical device, and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To display a high-vividity and high-definition image by adjusting the range in which the signal level of an image signal changes according to the classification of electro-optical panels. <P>SOLUTION: In an image processing circuit, a D/A convertor 301 generates an image signal VID by converting input image data Da into an analog signal and its output range is controlled by an output range controlling signal CTLout whose signal level differs according to the classification of liquid crystal display panels 100A, 100B. Therefore, the change range of the signal level of the image signal VID can be adjusted according to the classification of the panels. Thereby, the electro-optical device can display the highly precise image because each data value of the input image data Da can be assigned to be within an expected impression voltage range even if several kinds of liquid crystal display panels 100A, 100B that have different V-T characteristics and an image signal processing circuit 300A are combined. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an image processing circuit and an image processing method suitable for an electro-optical device having an electro-optical material whose transmittance changes according to an applied voltage, an electro-optical device using the same, and an electronic apparatus.

A conventional electro-optical device, for example, an active matrix type liquid crystal display device will be described with reference to FIG. As shown in the figure, the conventional liquid crystal display device includes a liquid crystal display panel 100, a timing circuit 200, and an image signal processing circuit 300.

First, the liquid crystal display panel 100 is configured by sandwiching liquid crystal between an element substrate and a counter substrate. A plurality of data lines and a plurality of scanning lines are formed on the element substrate, and thin film transistors (Thin Film Transistors: hereinafter, referred to as TFTs) functioning as switching elements are provided in correspondence with their intersections. Since the liquid crystal has a property that the transmittance changes in accordance with the applied voltage, it is possible to display a desired gradation by controlling on / off of the TFT.

Next, the timing circuit 200 outputs a timing signal used in each unit. Further, the D / A conversion circuit 301 'of the image signal processing circuit 300 converts the input image data D supplied from the external device from a digital signal to an analog signal and outputs it as an image signal VID. Further, the phase expansion circuit 302 'receives one image signal VID, expands it into an N-phase (N = 6 in the figure) phase expansion image signal, and outputs it. Here, the reason why the image signal is developed into the N-phase is that the application time of the image signal supplied to the TFT is lengthened to sufficiently secure the sampling time and the charging / discharging time of the data signal supplied to the data line. It is.

The amplifying / inverting circuit 303 'inverts the polarity of the phase developed image signal under the following conditions, and adjusts the amplitude level in accordance with the VT characteristic (characteristic of the transmittance with respect to the applied voltage) of the liquid crystal display panel 100. The image signals VID1 to VID6 are supplied to the liquid crystal display panel 100. Here, the polarity inversion means that the voltage level is alternately inverted with the amplitude center potential of the output phase expanded image signal as a reference potential.

指標 Indicators representing the display performance of such a liquid crystal display device include a contrast ratio and a transmittance change amount per gradation. The contrast ratio is a value obtained by dividing the maximum transmittance of the liquid crystal by the minimum transmittance. The higher the contrast ratio, the sharper the displayed image can be. Further, the smaller the transmittance change amount per gradation, the higher the definition of the display.

However, the conventional image signal processing circuit 300 has the following problem due to the fact that the relationship between each data value of the input image data D and the signal level of the output phase expanded image signals VID1 to VID6 is determined on a one-to-one basis. was there.

First, the conventional image signal processing circuit 300 is supposed to be used in combination with a specific liquid crystal display panel 100. If the conventional image signal processing circuit 300 is used for another liquid crystal display panel having a different VT characteristic, a quantization error becomes large, and There was a problem that a fine image could not be displayed.

For example, the input image data D has 10 bits and the VT characteristic of the liquid crystal display panel 100 is as shown in FIG. 28A. In addition, the image signal processing circuit 300 has the maximum contrast ratio. In addition, it is assumed that the output phase expanded image signals VID1 to VID6 are generated such that the transmittance change amount per gradation is minimized.

で は In this VT characteristic, the transmittance changes sharply in the range of applied voltages Vw1 to Vb1, and the transmittance is saturated when the applied voltage is Vw1 or lower or Vb1 or higher. Here, when the input image data value changes from “0” to “1023” in order to maximize the contrast ratio and minimize the transmittance change amount per gradation, the image signal processing circuit 300 Output phase expanded image signals VID1 to VID6 are generated so as to change the voltage applied to the liquid crystal from Vb1 to Vw1. In this case, the amount of change in transmittance per bit is 90/1024.

Next, the liquid crystal display panel 100 having the VT characteristic shown in FIG. 2B is combined with the image signal processing circuit 300 instead of the liquid crystal display panel 100 having the VT characteristic shown in FIG. Consider when to use it. In the VT characteristic shown in FIG. 3B, the transmittance changes sharply in the range of the applied voltages Vw2 to Vb2. However, the image signal processing circuit 300 is adjusted to change the voltage applied to the liquid crystal from Vb1 to Vw1 when the input image data value changes from “0” to “1023”. Therefore, when the input image data value is "170", the voltage applied to the liquid crystal is Vb2, and when the input image data value is "853", the voltage applied to the liquid crystal is Vw2. In this VT characteristic, the transmittance is saturated when the applied voltage is equal to or lower than Vw2 and equal to or higher than Vb2. Therefore, even if the applied voltage is changed in such a range, the transmittance does not change. In other words, the effective range for changing the transmittance is within the range of the input image data value from “170” to “853”. In this case, the amount of change in transmittance per bit is 90/683. Therefore, when the liquid crystal display panel 100 having the VT characteristic shown in FIG. 4B and the image signal processing circuit 300 are combined, the liquid crystal display panel 100 having the VT characteristic shown in FIG. As compared with the case, the change amount of the transmittance per bit is about 3/2 times, the quantization error becomes large, and there is a problem that a high-definition image cannot be displayed. In other words, the conventional image signal processing circuit 300 can only be combined with a single liquid crystal display panel, and has a disadvantage of lacking versatility.

As input image data D supplied from the outside, there are those using so-called computer graphics generated digitally by a computer as a source, and A / D conversion of a video signal captured by a video camera. In some cases, what you get is the source. When the source is computer graphics, generally, the luminance level is high and the halftone display is low in many cases. On the other hand, when the source is a video signal, there are generally many halftone displays. As described above, the input image data D has a bias in possible data values depending on its type, that is, on what kind of source it is generated.

However, in the conventional image signal processing circuit 300, processing according to the type of the input image data D is not performed, and the processing is uniform, so that high-definition display according to the properties of the input image data D is performed. Cannot be performed.

(4) Further, when the input image data D is based on a video signal, a bias occurs in a data value that the input image data D can take depending on a shooting situation. For example, in a daytime beach scene, the data value is biased toward high luminance, in an indoor scene, the data value is biased toward halftone, and further, in a night road scene, the data value is biased toward low luminance.

However, in the conventional image signal processing circuit 300, the processing according to the data value of the input image data D is not performed, and the processing is uniform, so that the high definition corresponding to the data value of the input image data D is performed. Display cannot be performed.

The present invention has been made in view of the above-described circumstances, and has as its object to provide an image processing circuit, an image processing method, an electro-optical device, and an electronic apparatus which are versatile and capable of displaying high-definition images. .

In order to achieve the above object, in the image processing circuit of the present invention, one type selected from a plurality of predetermined types of electro-optical panels having an electro-optical material whose transmittance changes according to an applied voltage A control signal generating means for generating a control signal indicating a type of the electro-optical panel to be combined with the image processing circuit; and converting input image data from a digital signal to an analog signal to generate an image. D / A conversion means for generating a signal and adjusting a range in which the signal level of the image signal changes based on the control signal, and generating an output image signal to be supplied to the electro-optical panel based on the image signal And processing means for performing the processing.

(4) The transmittance of the electro-optical material is determined by the applied voltage, and the transmittance is saturated at a certain applied voltage. Therefore, in order to maximize the contrast ratio and minimize the amount of change in transmittance per gradation, the input image must be within the range of the applied voltage at which the transmittance is maximized to the applied voltage at which the transmittance is minimized. It is necessary to assign each data value of the data. According to the present invention, the range in which the signal level of the image signal changes can be adjusted in accordance with the type of the electro-optical panel, so that the electro-optical characteristics can be adjusted in accordance with various VT characteristics (transmittance characteristics with respect to applied voltage). The range of the applied voltage applied to the substance can be adjusted. As a result, even when the image processing circuit is used in combination with various electro-optical panels, a high-contrast and high-definition image can be displayed, and the performance of the panel can always be maximized.

In the above-described image processing circuit, the processing unit may include an image signal inverting unit that amplifies the image signal and inverts a signal polarity at a predetermined inversion cycle based on a certain potential to generate an inverted image signal. And generating a first reference voltage and a second reference voltage based on the control signal, and alternately selecting one of the first reference voltage and the second reference voltage in the inversion cycle. It is preferable to include a reference signal generation unit that generates a reference signal, and an output image signal generation unit that generates the output image signal by combining the inverted image signal and the reference signal. According to the present invention, since the first reference voltage and the second reference voltage can be generated according to the type of the electro-optical panel, the output image signal is adjusted according to the VT characteristic of the electro-optical panel used in combination. Can be generated. In addition, if a reference potential is supplied to one electrode sandwiching the electro-optical material and an output image signal is supplied to the other electrode, the polarity of the voltage applied to the electro-optical material can be inverted.

Here, the reference signal generation unit is configured such that each positive reference voltage higher than each reference potential predetermined according to the type of the electro-optical panel by each minimum applied voltage, A power supply unit that generates each negative polarity reference voltage lower by the minimum applied voltage, and a voltage corresponding to the electro-optical panel used in combination with the image processing circuit from among the respective positive polarity reference voltages based on the control signal. Selecting and generating the first reference voltage, selecting a voltage corresponding to the electro-optical panel to be used in combination with the image processing circuit from the negative reference voltages based on the control signal, and A first selection unit that generates the second reference voltage; and a first selection unit that alternately selects one of the first reference voltage and the second reference voltage at the inversion cycle to generate the reference signal. A selection unit, wherein each of the minimum applied voltages is specified for each of the electro-optical panels, and each of the lowest applied voltages that need to be applied to the electro-optical material to obtain the range of the transmittance used for image display. It is desirable that the applied voltage be used.
In addition, it is preferable that the minimum applied voltage is a voltage corresponding to a saturation transmittance of the electro-optical material.

Further, the power supply unit used for the reference signal generation unit, a first voltage source that generates each first voltage higher by each maximum applied voltage than each reference potential predetermined according to the type of the electro-optical panel, A second voltage source that generates a second voltage that is lower by a maximum applied voltage with respect to each of the reference potentials; and a change voltage that is predetermined from the first voltage according to the type of the electro-optical panel. A subtraction unit that subtracts to generate each of the positive reference voltages; and an addition unit that adds each of the change voltages to each of the second voltages to generate each of the negative reference voltages. May be the highest applied voltages that need to be applied to the electro-optical material in order to obtain each transmittance range used for image display according to the type of the electro-optical panel. According to the present invention, assuming that the electro-optical panel operates in a normally white mode, first, a positive first voltage and a negative second voltage corresponding to a black level are generated in consideration of AC driving, Next, a positive reference voltage and a negative reference voltage are obtained by subtracting and adding the change voltage.

Next, in the image processing circuit according to the present invention, the image processing circuit is used in combination with an electro-optical panel having an electro-optical material whose transmittance changes according to an applied voltage, and controls the type of input image data. Control signal generation means for generating a signal, data conversion means for converting each data value of the input image data into each data value associated in advance based on the control signal to generate converted image data, A D / A converter that converts the converted image data from a digital signal to an analog signal to generate an image signal, and adjusts a range in which the signal level of the image signal changes based on the control signal; Processing means for generating an output image signal to be supplied to the electro-optical panel based on the output signal.

The input image data has a bias in the occurrence frequency of each data value depending on its type. This means that there is a bias in the transmittance of the electro-optical material to be controlled according to the type of the input image data. According to the present invention, while the converted image data is generated according to the type of the input image data, the range in which the signal level of the image signal changes can be adjusted according to the type of the input image data. Can be changed in accordance with the type of data. This makes it possible to display a high-definition image.

Here, the processing unit amplifies the image signal, and inverts the signal polarity at a predetermined inversion cycle with a certain potential as a reference to generate an inverted image signal. Generating a first reference voltage and a second reference voltage, each of which takes a voltage value corresponding to a type of the input image data, based on the first and second reference voltages. It is preferable to include a reference signal generation unit that generates a reference signal by alternately selecting the output image signal in a cycle, and an output image signal generation unit that generates the output image signal by combining the inverted image signal and the reference signal. According to the present invention, the first reference voltage and the second reference voltage can be generated according to the type of the input image data, so that the output image signal is generated in accordance with the frequency of occurrence of each data value that differs depending on the type. It is possible to do. In addition, if the reference potential is supplied to one electrode holding the electro-optical material and the output image signal is supplied to the other electrode, the polarity of the applied voltage applied to the electro-optical material can be inverted. The substance can be AC driven.

The reference signal generation unit may include: a positive reference voltage that is higher by a minimum applied voltage than each predetermined reference potential according to a type of the input image data; A power supply unit for generating each of the low negative polarity reference voltages; and a voltage corresponding to the type of the input image data is selected from the positive polarity reference voltages based on the control signal to generate the first reference voltage. A first selector for selecting a voltage corresponding to the type of the input image data from the negative reference voltages based on the control signal to generate the second reference voltage; A second selection unit that alternately selects one of a voltage and the second reference voltage at the inversion cycle to generate the reference signal, wherein each of the minimum applied voltages is a value of the input image data. Images for each type It is preferred that the lowest individual applied voltage needed to be applied to the electro-optical material in order to obtain the transmittance range used for display.

Here, the power supply unit of the reference signal generation unit is configured to generate a first voltage source that generates a first voltage that is higher by a maximum applied voltage than each reference potential that is predetermined according to a type of the input image data; A second voltage source that generates a second voltage that is lower by the maximum applied voltage with respect to each of the reference potentials, and a change voltage that is predetermined from the first voltage according to the type of the input image data. A subtraction unit that subtracts to generate each of the positive reference voltages; and an addition unit that adds each of the change voltages to each of the second voltages to generate each of the negative reference voltages. Is preferably the highest applied voltage that needs to be applied to the electro-optical material in order to obtain each transmittance range used for image display for each type of the input image data. According to the present invention, assuming that the electro-optical panel operates in a normally white mode, first, a positive first voltage and a negative second voltage corresponding to a black level are generated in consideration of AC driving, Next, a positive reference voltage and a negative reference voltage are obtained by subtracting and adding the change voltage.

Further, the control signal may indicate whether the input image data is based on computer graphics or a video signal.
When using computer graphics as a source, the frequency of occurrence of input image data values is biased toward high luminance, while when using a video signal as a source, the frequency of occurrence of input image data values is biased toward halftone.

Further, the input image data is supplied from the outside together with a vertical synchronization signal indicating the vertical blanking period, and the control signal generation means detects a period of the vertical synchronization signal and generates the control signal based on the detection result. Is preferred. Since computer graphics generally has a higher field frequency than a video signal, it is possible to determine the type of input image data based on the cycle of a vertical synchronization signal.

Next, the image processing circuit according to the present invention is used in combination with an electro-optical panel having an electro-optical material whose transmittance changes in accordance with an applied voltage, and uses an image gradation average based on input image data. Average value generation means for calculating a value, and generating an average value signal indicating the grayscale average value, and converting the input image data into a converted image according to a conversion rule corresponding to the grayscale average value based on the average value signal. Data conversion means for converting data into data, a D / A converter for converting the converted data from a digital signal to an analog signal to generate an image signal, and an output image signal to be supplied to the electro-optical panel based on the image signal And a processing means for generating

The captured image has a bright part and a dark part in one screen, but the gradation of each pixel constituting one screen is not distributed from the highest luminance (saturated white) to the lowest luminance (saturated black). Are distributed in a predetermined range centered on the average gradation of one screen. According to the present invention, the converted image data is generated according to the average gradation value of the image, and the converted image data is D / A converted to generate the image signal. The applied voltage range to which values are assigned can be changed. This makes it possible to display a high-definition image.

Here, it is preferable that the average value generation means calculates an average gradation value of an image based on input image data of one screen.

Further, the processing means, while amplifying the image signal, an image signal inverting unit that generates an inverted image signal by inverting the signal polarity at a predetermined inversion cycle with a certain potential as a reference, A first reference voltage and a second reference voltage, each of which takes a voltage value corresponding to the gradation average value based on the first reference voltage and the second reference voltage. It is preferable to include a reference signal generation unit that alternately selects a reference signal to generate a reference signal, and an output image signal generation unit that combines the inverted image signal and the reference signal to generate the output image signal.

According to the present invention, since the first reference voltage and the second reference voltage can be generated in accordance with the average gradation value of the image, the output is performed in accordance with the frequency of occurrence of each data value that differs depending on the average gradation value. An image signal can be generated. In addition, if the reference potential is supplied to one electrode holding the electro-optical material and the output image signal is supplied to the other electrode, the polarity of the applied voltage applied to the electro-optical material can be inverted. The substance can be AC driven.

In addition, the reference signal generation unit, based on the average value signal, a minimum applied voltage generation unit that generates a minimum applied voltage to be applied to the electro-optical material according to a rule according to the grayscale average value, A reference voltage generation unit that adds the minimum applied voltage to the obtained reference potential to generate the first reference voltage, and subtracts the minimum applied voltage from the reference potential to generate the second reference voltage; It is preferable that the apparatus further includes a selection unit that alternately selects one of the first reference voltage and the second reference voltage at the inversion cycle to generate the reference signal.

Next, in the image processing method according to the present invention, one type of electro-optical panel selected from a plurality of predetermined types of electro-optical panels having an electro-optical material whose transmittance changes according to an applied voltage Generating an output image signal to be supplied to a digital signal, converting an input image data from a digital signal to an analog signal to generate an image signal, and a signal level of the image signal according to a type of the electro-optical panel. Adjust the range of change, while amplifying the image signal, to generate an inverted image signal by inverting the signal polarity at a predetermined inversion cycle based on a certain potential, according to the type of the electro-optical panel A positive reference voltage higher by a predetermined minimum applied voltage according to the type of the electro-optical panel based on a predetermined reference potential, and the reference potential as a reference. One of the negative reference voltage lower by the minimum applied voltage is alternately selected at the inversion cycle to generate a reference signal, and the inverted image signal and the reference signal are combined to produce the output image signal. The minimum applied voltage is the lowest applied voltage that is specified for each of the electro-optical panels and needs to be applied to the electro-optical material to obtain the range of the transmittance used for image display. It is characterized by the following.

According to the present invention, the range in which the signal level of the image signal changes according to the type of the electro-optical panel can be adjusted, and the positive level and the negative level of the reference signal can be adjusted according to the type of the electro-optical panel. Therefore, it is possible to generate an output image signal in accordance with the VT characteristic of the electro-optical panel used in combination. In addition, if a reference potential is supplied to one electrode sandwiching the electro-optical material and an output image signal is supplied to the other electrode, the polarity of the voltage applied to the electro-optical material can be inverted.

Further, in the image processing method according to the present invention, an output image signal to be supplied to an electro-optical panel having an electro-optical material whose transmittance changes in accordance with an applied voltage is generated. According to a conversion rule according to the type, the input image data is converted into converted image data, the converted image data is converted from a digital signal to an analog signal to generate an image signal, and the image signal is being amplified. An inverted image signal is generated by inverting the signal polarity at a predetermined inversion cycle based on the potential, and according to the type of the input image data based on a reference potential predetermined according to the type of the input image data. One of a positive reference voltage higher by a predetermined minimum applied voltage and a negative reference voltage lower by the minimum applied voltage with respect to the reference potential. Are alternately selected at the inversion cycle to generate a reference signal, the inverted image signal and the reference signal are combined to generate the output image signal, and the minimum applied voltage is a type of the input image data. The lowest applied voltage that is specified every time and needs to be applied to the electro-optical material in order to obtain the range of the transmittance used for image display.

According to the present invention, the range in which the signal level of the image signal changes according to the type of the input image data can be adjusted, and the positive polarity level and the negative polarity level of the reference signal can be adjusted according to the type of the input image data. Therefore, it is possible to generate the output image signal so that the range of the VT characteristic to be used can be changed according to the type of the input image data. As a result, a high-definition image can be displayed. In addition, if a reference potential is supplied to one electrode sandwiching the electro-optical material and an output image signal is supplied to the other electrode, the polarity of the voltage applied to the electro-optical material can be inverted.

Also, the image processing method of the present invention generates an output image signal to be supplied to an electro-optical panel having an electro-optical material whose transmittance changes according to an applied voltage, and generates an image based on input image data. Calculating the gray-scale average value, converting the input image data into converted image data according to a conversion rule according to the gray-scale average value, and converting the converted data from a digital signal to an analog signal to generate an image signal. Generating an inverted image signal by inverting the signal polarity at a predetermined inversion cycle with a certain potential as a reference while amplifying the image signal, and responding to the average gradation value with a predetermined reference potential as a reference. One of a positive reference voltage that is higher by a predetermined minimum applied voltage and a negative reference voltage that is lower by the minimum applied voltage with respect to the reference potential. Alternately generating a reference signal, generating the output image signal by combining the inverted image signal and the reference signal, the minimum applied voltage is specified for each of the average gradation values, and The lowest applied voltage that needs to be applied to the electro-optical material in order to obtain the range of the transmittance used for display.

According to the present invention, it is possible to adjust the range in which the signal level of the image signal changes according to the average gradation value of the image, and to adjust the positive and negative levels of the reference signal according to the average gradation value of the image. Therefore, the output image signal can be generated so that the range of the VT characteristic to be used can be changed according to the grayscale average value of the image. As a result, a high-definition image can be displayed. In addition, if a reference potential is supplied to one electrode sandwiching the electro-optical material and an output image signal is supplied to the other electrode, the polarity of the voltage applied to the electro-optical material can be inverted.

Next, in an electro-optical device according to the present invention, an electro-optical panel including the above-described image processing circuit and an electro-optical material whose output image signal is supplied and whose transmittance changes in accordance with an applied voltage And characterized in that:

Here, the electro-optical panel includes a plurality of data lines, a plurality of scanning lines, switching elements corresponding to intersections of the data lines and the scanning lines, and pixel electrodes connected to the switching elements. An element substrate, a counter substrate on which a counter electrode is formed, and an electro-optical material sandwiched between the element substrate and the counter substrate, wherein the reference potential is the potential of the counter electrode, and the output image signal Is preferably supplied sequentially to each of the data lines.

Next, an electronic apparatus according to the present invention includes the above-described electro-optical device, and includes, for example, a video projector, a notebook personal computer, and a mobile phone.

As described above, according to the present invention, the range in which the signal level of the image signal changes can be adjusted according to the type of the electro-optical panel. Applied voltage range can be adjusted. As a result, it is possible to always maximize the performance of the panel.

According to the present invention, the applied voltage range to which each data value is assigned can be changed according to the type of the input image data. This makes it possible to display a high-definition image.

According to the present invention, the applied voltage range to which each data value of the input image data is assigned can be changed according to the gradation average value of the image. This makes it possible to display a high-definition image.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<1. First Embodiment>
<1-1: Overview of Liquid Crystal Display>
First, an active matrix type liquid crystal display device according to the first embodiment will be described as an example of an electro-optical device.

FIG. 1 is a block diagram showing the overall configuration of the liquid crystal display device. The liquid crystal display device according to the present embodiment includes a liquid crystal display panel 100A, a control circuit 200A, and an image signal processing circuit 300A. Further, the liquid crystal display device can be used in combination with another liquid crystal display panel instead of the liquid crystal display panel 100A. Although the number of panel types is not limited, in this example, it is assumed that a liquid crystal display panel 100B having a different VT characteristic can be used in addition to the liquid crystal display panel 100A. In the following description, the VT characteristic of the liquid crystal display panel 100A is referred to as a first VT characteristic, and the VT characteristic of the liquid crystal display panel 100B is referred to as a second VT characteristic.

FIG. 2A shows the first VT characteristic, and FIG. 2B shows the second VT characteristic. Here, the range of transmittance used for gradation display is the range of Ta and Tb shown in the figure, and the range of applied voltage (change voltage) corresponding thereto is Va and Vb. The transmittance ranges Ta and Tb are set to a range in which the transmittance with respect to the applied voltage changes sharply, in order to obtain high contrast. The liquid crystal display panels 100A and 100B of this example operate in a normally white mode in which the transmittance increases when the applied voltage is low as shown in FIGS. 2A and 2B. Needless to say, a device operating in a normally black mode in which the transmittance is low may be used.
<1-2: Liquid crystal display panel>
Next, the liquid crystal display panel 100A will be described. FIG. 3 is a block diagram showing a configuration of the liquid crystal display panel 100A. Note that the liquid crystal display panel 100B has the same configuration as the liquid crystal display panel 100A except for the VT characteristics, and thus description thereof is omitted. The liquid crystal display panel 100A has a configuration in which an element substrate and a counter substrate are opposed to each other with a gap, and liquid crystal is sealed in the gap. Here, the element substrate and the opposing substrate are made of a quartz substrate, hard glass, or the like.

Among them, on the element substrate, a plurality of scanning lines 112 are arranged in parallel along the X direction in FIG. 3 and a plurality of data lines are formed in parallel along the Y direction orthogonal to this. A line 114 has been formed. Here, each data line 114 is divided into blocks in units of six, and these are referred to as blocks B1 to Bm. Hereinafter, for convenience of explanation, when a general data line is pointed out, the reference numeral is shown as 114, but when a specific data line is pointed out, the reference numeral is shown as 114a to 114f.

At each intersection between the scanning line 112 and the data line 114, each TFT 116 is provided as a switching element. The gate electrode of the TFT 116 is connected to the scanning line 112, its source electrode is connected to the data line 114, and its drain electrode is connected to the pixel electrode 118. Each pixel includes a pixel electrode 118, a common electrode formed on a counter substrate, and a liquid crystal sandwiched between the two electrodes. Then, each pixel is arranged in a matrix at each intersection of the scanning line 112 and the data line 114. In addition, a storage capacitor (not shown) is formed in a state connected to each pixel electrode 118.

The scanning line driving circuit 120 is formed on an element substrate, and outputs a pulse-like scanning signal to each scanning line based on a clock signal CLY from the timing circuit 200A, its inverted clock signal CLYinv, a transfer start pulse DY, and the like. The data is sequentially output to the MPU 112. More specifically, the scanning line driving circuit 120 sequentially shifts the transfer start pulse DY supplied at the beginning of the vertical scanning period in accordance with the clock signal CLY and its inverted clock signal CLYinv and outputs it as a scanning line signal. The scanning lines 112 are sequentially selected.

On the other hand, the sampling circuit 130 includes a sampling switch 131 at one end of each data line 114 for each data line 114. The switch 131 is formed of a TFT similarly formed on an element substrate, and the output electrode of the switch 131 is supplied with output phase expanded image signals VID1 to VID6 via image signal supply lines L1 to L6. The gate electrodes of the six switches 131 connected to the data lines 114a to 114f of the block B1 are connected to signal lines to which the sampling signal S1 is supplied, and connected to the data lines 114a to 114f of the block B2. The gate electrodes of the switches 131 are connected to signal lines to which the sampling signal S2 is supplied, and similarly, the gate electrodes of the six switches 131 connected to the data lines 114a to 114f of the block Bm are connected to the sampling signal S2. It is connected to a signal line to which Sm is supplied. Here, the sampling signals S1 to Sm are signals for sampling the output image signals VID1 to VID6 for each block within the horizontal effective display period.

The shift register circuit 140 is also formed on the element substrate and sequentially outputs the sampling signals S1 to Sm based on the clock signal CLX from the timing circuit 200, its inverted clock signal CLXinv, the transfer start pulse DX, and the like. Things. More specifically, the shift register circuit 140 sequentially shifts the transfer start pulse DX supplied at the beginning of the horizontal scanning period according to the clock signal CLX and its inverted clock signal CLXinv, and sequentially outputs the sampling signals S1 to Sm. It is.

In such a configuration, when the sampling signal S1 is output, the output phase expanded image signals VID1 to VID6 are sampled on the six data lines 114a to 114f belonging to the block B1, respectively, and these output phase expanded images are output. The signals VID1 to VID6 are respectively written to the six pixels in the currently selected scanning line by the TFT 116.

Thereafter, when the sampling signal S2 is output, the output phase expanded image signals VID1 to VID6 are sampled on the six data lines 114a to 114f belonging to the block B2, respectively. VID1 to VID6 are written to the six pixels on the selected scanning line at that time by the TFT 116, respectively.

Similarly, when the sampling signals S3, S4,..., Sm are sequentially output, the image signals VID1 to VID6 are sampled on the six data lines 114a to 114f belonging to the blocks B3, B4,. Then, these image signals VID1 to VID6 are respectively written to six pixels in the selected scanning line at that time. Then, after that, the next scanning line is selected, and similar writing is repeatedly executed in the blocks B1 to Bm.

In this driving method, the number of stages of the shift register circuit 140 for controlling the driving of the switch 131 in the sampling circuit 130 is reduced to 1/6 as compared with the method of driving each data line in a dot sequential manner. Further, since the frequency of the clock signal CLX to be supplied to the shift register circuit 140 and the inverted clock signal CLXinv thereof can be reduced to １ ／, the power consumption can be reduced along with the reduction in the number of stages.

Next, a counter electrode is formed on the counter substrate, and a counter electrode voltage is supplied from the timing circuit 200 to the counter electrode. Since the liquid crystal is sandwiched between the pixel electrode 118 and the counter electrode, the potential difference between the pixel electrode 118 and the counter electrode becomes the voltage applied to the liquid crystal.
<1-3: Timing circuit>
Next, the timing circuit 200A generates various timing signals based on the dot clock signal DCLK, the vertical synchronization signal VB, and the horizontal blanking signal HB, and also controls the panel type indicating the type of the liquid crystal display panels 100A and 100B. Generate the signal CTLp. The dot clock signal DCLK is a signal synchronized with the sampling cycle of the input image data Da. The vertical synchronization signal VB is at the L level during the vertical blanking period, and is at the H level during the other periods. The horizontal blanking signal goes low during the horizontal blanking period, and goes high during the other periods.

The panel type control signal CTLp indicates that the panel type control signal CTLp is used in combination with the liquid crystal display panel 100A when it is at the H level, and indicates that it is used in combination with the liquid crystal display panel 100B when it is at the L level. In this example, a DIP switch (not shown) is connected to the timing circuit 200A, and the user can switch the operation element to input a panel type. Then, the timing circuit 200A detects the state of the dip switch and generates the panel type control signal CTLp.

In addition, the timing circuit 200A selects one of the first common electrode voltage Vc1 and the second common electrode voltage Vc2 based on the panel type control signal CTLp, and supplies it to the liquid crystal display panel 100A or 100B. It has become.
Specifically, the timing circuit 200A selects the first counter electrode voltage Vc1 when the panel type control signal CTLp is at the H level, and selects the second counter electrode voltage Vc2 when the panel type control signal CTLp is at the L level. .
<1-4: Image signal processing circuit>
Next, the image signal processing circuit 300A includes a D / A converter 301, a phase expansion circuit 302, an amplification / inversion circuit 303, an output range control signal generation circuit 304, and a reference signal generation circuit 305. The input image data Da is supplied from an external device (not shown). The input image data Da is a 10-bit parallel format, and is a data sequence in which the sampling cycle is the cycle of the dot clock signal DCLK.

FIG. 4 is a block diagram showing a detailed configuration of the image signal processing circuit 300A. The D / A converter 301 has a control input terminal 301T, converts 10-bit input image data Da from a digital signal to an analog signal, and outputs it as an image signal VID. The D / A converter 301 controls an output range of the D / A converter 301 by a voltage supplied to the control input terminal 301T. Here, the output range refers to the signal level of the image signal VID corresponding to the minimum value “0” of the input image data Da from the signal level of the image signal VID corresponding to the maximum value “1023” of the input image data Da. The range up to. That is, the output range is a change range of the signal level of the image signal VID, and is determined by the minimum value and the maximum value of the image signal VID. However, in this example, the minimum value of the image signal VID is fixed to the ground potential, and the maximum value of the image signal VID and the amount of change per bit are adjusted by the voltage supplied to the control input terminal 301T. ing.

The output range control signal generation circuit 304 includes a first power supply circuit 3041 and a selection circuit 3042. The first power supply circuit 3041 includes a constant voltage source that generates the first output range setting voltage V1 and the second output range setting voltage V2. The first output range setting voltage V1 is selected such that when the first output range setting voltage V1 is applied to the control input terminal 301T, the range of the voltage finally applied to the liquid crystal becomes the range Va shown in FIG. On the other hand, the second output range setting voltage V2 is selected such that when it is applied to the control input terminal 301T, the range of the final voltage applied to the liquid crystal becomes the range Vb shown in FIG. 2B.

The selection circuit 3042 selects the first output range setting voltage V1 and the second output range setting voltage V2 based on the panel type control signal CTLp, generates an output range control signal CTLout, and supplies this to the control input terminal 301T. I do.

As described later, the gain of the phase expansion circuit 302 is 1, and the gain of the amplification / inversion circuit 303 is A or -A. Here, considering the input / output characteristics of the D / A converter 301, the range of the voltage to be finally applied to the liquid crystal is Va shown in FIG. 2A when the liquid crystal display panel 100A is used, When the liquid crystal display panel 100B is used, the voltage is Vb shown in FIG. Therefore, when the liquid crystal display panel 100A is used, the signal level of the image signal VID needs to be changed by Va / A, while when the liquid crystal display panel 100B is used, the signal level of the image signal VID needs to be changed by Vb / A.

FIG. 5 is a graph showing the input / output characteristics of the D / A converter 301. Note that a characteristic W1 shown in the figure is an input / output characteristic when the first output range setting voltage V1 is supplied to the control input terminal 301T, and a characteristic W2 is that the second output range setting voltage V2 is supplied to the control input terminal 301T. This is the input / output characteristic when the operation is performed. As is clear from the drawing, when the first output range setting voltage V1 is supplied to the control input terminal 301T, the output range of the D / A converter 301 becomes 0 to Va / A, while the second output range setting voltage V2 becomes When power is supplied to the control input terminal 301T, the output range of the D / A converter 301 becomes 0 to Vb / A. That is, the output range of the D / A converter 301 is obtained by dividing the applied voltage ranges Va and Vb used in the liquid crystal display panels 100A and 100B by the gain A. This makes it possible to adjust the output range of the D / A converter 301 according to the applied voltage range determined by the type of the liquid crystal display panel.

Next, the phase expansion circuit 302 performs serial-parallel conversion on the image signal VID to generate six-phase expanded phase expanded image signals VID1 to VID6. Specifically, the phase expansion circuit 302 samples and holds the image signal VID based on the six-phase sample-and-hold pulses SP1 to SP6 that are activated every six periods of the dot clock signal DCLK, and sets the time of the image signal VID. The axis is expanded by a factor of six, and the system is divided into six systems to generate the phase developed image signals VID1 to VID6. The gain of the phase expansion circuit 302 is 1.

Next, the amplification / inversion circuit 303 includes six processing units U1 to U6 provided for each of the phase developed image signals VID1 to VID6. Since each of the processing units U1 to U6 has the same configuration, here, only the processing unit U1 corresponding to the phase expanded image signal VID1 will be described, and the description of the other processing units U2 to U6 will be omitted.

First, the processing unit U1 includes a normal amplification circuit 3031, an inversion amplification circuit 3032, and a selection circuit 3033. The forward amplification circuit 3031 forwardly amplifies the phase expanded image signal VID1, while the inversion amplification circuit 3032 inverts and amplifies the phase expanded image signal VID1. Here, the gain of the non-inverting amplifier circuit 3031 is A, and the gain of the inverting amplifier circuit 3032 is -A.

The selection circuit 3033 selects one of the output signal of the non-inverting amplifier circuit 3031 and the output signal of the inverting amplifier circuit 3032 based on the polarity control signal CTLx, and outputs the selected signal as the inverted image signal vid '. The selection circuit 3033 selects the output signal of the non-inverting amplification circuit 3031 when the inversion control signal CTLx is at the H level, and selects the output signal of the inversion amplification circuit 3032 when it is at the L level. In this example, the polarity is inverted for each scanning line. Therefore, the polarity control signal CTLx is a signal in which one cycle is two horizontal scanning periods 2H. The signal level of the inverted image signal vid 'is inverted every horizontal scanning period.

From these facts, it can be said that the normal amplification circuit 3031, the inversion amplification circuit 3032, and the selection circuit 3033 have a function of inverting the signal level at a predetermined inversion cycle while amplifying the image signal.

(4) The processing unit U1 further includes an adding circuit 3034. The addition circuit 3034 adds (combines) the inverted image signal vid 'and the reference signal Sref to generate an output phase expanded image signal.

Next, the reference signal generation circuit 305 generates the reference signal Sref. The reference signal generation circuit 305 includes a second power supply circuit 3051, a positive polarity reference voltage selection circuit 3052, a negative polarity reference voltage selection circuit 3053, and a positive / negative polarity selection circuit 3054. The second power supply circuit 3051 includes a plurality of constant voltage sources. Each constant voltage source generates a first positive reference voltage Vp1, a second positive reference voltage Vp2, a first negative reference voltage Vn1, and a second negative reference voltage Vn2, respectively.

Here, as shown in FIG. 2A, the minimum applied voltage corresponding to the maximum transmittance tamax in the first VT characteristic is defined as Vamin, and the maximum applied voltage corresponding to the minimum transmittance tamin is defined as Vamax. As shown in FIG. 5, the minimum applied voltage corresponding to the maximum transmittance tbmax in the second VT characteristic is Vbmin, and the maximum applied voltage corresponding to the minimum transmittance tbmin is Vbmax.

In this case, the first positive reference voltage Vp1 is obtained by adding the first minimum applied voltage Vamin to the first common electrode voltage Vc1, while the first negative reference voltage Vn1 is the minimum value of the first common electrode voltage Vc1. This is a value obtained by subtracting the applied voltage Vamin. The first counter electrode voltage Vc1 is a voltage supplied to a counter electrode formed on a counter substrate of the liquid crystal display panel 100A. On the other hand, the second positive polarity reference voltage Vp2 is obtained by adding the second minimum applied voltage Vbmin to the second common electrode voltage Vc2, while the second negative polarity reference voltage Vn2 is the minimum applied voltage from the second common electrode voltage Vc2. The voltage Vbmin is subtracted. The second counter electrode voltage Vc2 is a voltage supplied to a counter electrode formed on a counter substrate of the liquid crystal display panel 100B described later.

Next, the positive polarity reference voltage selection circuit 3052 selects the first positive polarity reference voltage Vp1 when the panel type control signal CTLp is at the H level, and selects the second positive polarity reference voltage Vp1 when the panel type control signal CTLp is at the L level. The reference voltage Vp2 is selected to generate a positive polarity reference voltage Vp. The negative polarity reference voltage selection circuit 3053 selects the first negative polarity reference voltage Vn1 when the panel type control signal CTLp is at the H level, and selects the second negative polarity reference voltage when the panel type control signal CTLp is at the L level. The voltage Vn2 is selected to generate the negative reference voltage Vn.

Next, the positive / negative polarity selection circuit 3054 selects the selected positive polarity reference voltage Vp when the polarity control signal CTLx is at the H level, and selects the selected negative polarity reference voltage Vn when the polarity control signal CTLx is at the L level. Generate a reference signal Sref.

FIG. 6 is a timing chart showing waveforms of the polarity control signal CTLx and the reference signal Sref. As shown in this figure, when the liquid crystal display panel 100A is used (CTLp = H), the reference signal Sref is inverted with the first counter electrode voltage Vc1 as the center voltage in synchronization with the polarity control signal CTLx. When the polarity control signal CTLx indicates a positive polarity, the first reference voltage Vp1 is higher than the first counter electrode voltage Vc1 by the minimum applied voltage Vamin. On the other hand, when the polarity control signal CTLx indicates a negative polarity, the reference signal is negative. Sref becomes the first negative reference voltage Vn1 lower than the first counter electrode voltage Vc1 by the minimum applied voltage Vamin.

When the liquid crystal display panel 100B is used (CTLp = L), the reference signal Sref is inverted in synchronization with the polarity control signal CTLx, and the polarity control signal CTLx has a positive polarity with the second counter electrode voltage Vc2 as the center voltage. When the polarity control signal CTLx indicates a negative polarity, the second reference voltage Vp2 is higher than the second counter electrode voltage Vc2 by the minimum applied voltage Vbmin. The second negative reference voltage Vn2 becomes low.

As described above, the output phase expanded image signal VID1 is obtained by adding the inverted image signal vid1 'and the reference signal Sref. Therefore, when the image signal processing circuit 300A is used in combination with the liquid crystal display panel 100A, the image signal processing is performed. The input / output characteristics of the entire circuit 300A are as shown in FIG. On the other hand, when this is used in combination with the liquid crystal display panel 100B, its input / output characteristics are as shown in FIG. Therefore, the image signal processing circuit 300A can be used in combination with a plurality of liquid crystal display panels 100A and 100B having different VT characteristics.
<1-5: Operation of liquid crystal display device>
Next, the operation of the liquid crystal display device will be described. First, when the timing circuit 200A generates the panel type control signal CTLp, the output range control signal generation circuit 304 outputs one of the first output range setting voltage V1 and the second output range setting voltage V2 based on the panel type control signal CTLp. One of them is selected to generate the output range control signal CTLout.

Since the input / output characteristics of the D / A converter 301 are determined by the output range control signal CTLout supplied to the control input terminal 301T, when the liquid crystal display panel 100A is used, the characteristic becomes W1 while the liquid crystal display panel 100B is used. In this case, the characteristic becomes W2 (see FIG. 5). Therefore, according to the present embodiment, the output range of the D / A converter 301 can be adjusted according to the VT characteristics of each liquid crystal display panel. In other words, the output range of the D / A converter 301 can be adjusted according to the transmittance range of the liquid crystal display panel used in combination with the image signal processing circuit 300A.

As shown in FIG. 5, the output range of the D / A converter 301 is 0 to Va / A for the characteristic W1, and the output range is 0 to Vb / A for the characteristic W2. On the other hand, the gain of the phase expansion circuit 302 is 1, and the gain of the amplification / inversion circuit 303 is A or -A. Therefore, if the polarity inversion is ignored, when the input / output characteristics of the D / A converter 301 are the characteristics W1, the signal levels of the output phase expanded image signals VID1 to VID6 are changed by Va, and the input / output characteristics are the characteristics W2. For example, the signal levels of the output phase expanded image signals VID1 to VID6 change by Vb. This means that each data value (0 to 1023) of the input image data Da is assigned to the applied voltage range Va or Vb according to the type of the VT characteristic. Therefore, the contrast ratio can be maximized by using the image signal processing circuit 300A in combination with any of the liquid crystal display panels 100A or 100B.

Here, as shown in FIG. 2, when the first VT characteristic and the second VT characteristic are compared, there is a relationship of Tb> Ta for the transmittance range and a relationship of Va> Vb for the applied voltage range. In the present embodiment, each data value from 0 to 1023 of the input image data Da is assigned to the applied voltage range Va or Vb. Therefore, the amount of change in transmittance per bit is smaller in the liquid crystal display panel 100B. Therefore, when the liquid crystal display panel 100B is used, a higher definition image can be displayed.

Next, when the phase expansion circuit 302 phase-expands the image signal VID to generate phase expansion image signals vid1 to vid6, the amplification / inversion circuit 303 amplifies the phase expansion image signals vid1 to vid6 and a predetermined value. The inverted image signals vid1 ′ to vid6 ′ inverted at the inversion cycle and the reference signal Sref are respectively added to generate output phase expanded image signals VID1 to VID6. Here, the reference signal Sref is generated by alternately selecting one of the positive reference voltage Vp and the negative reference voltage Vn at an inversion cycle. In addition, the center voltage of the positive reference voltage Vp and the negative reference voltage Vn match the common electrode voltage Vc1 or Vc2, and an offset is given to the common electrode voltage Vc1 or Vc2 by the minimum applied voltage Vamin or Vbmin. . Therefore, by adding the reference signal Sref, it becomes possible to always apply the minimum applied voltage Vamin or Vbmin to the liquid crystal in synchronization with the polarity inversion.

If the counter electrode voltage Vc1 or Vc2 and the inverted image signals vid1 'to vid6' are added instead of the reference signal Sref to generate output phase expanded image signals VID1 to VID6, the D / A converter 301 Must be set to 0 to (Va + Vmin) / A or 0 to (Vb + Vbmin) / A. This means that each data value of the input image data Da is assigned to a range below the minimum applied voltage Vamin or Vbmin. When such an assignment is performed, the range of data values assigned to the applied voltage range is reduced, so that the amount of change in transmittance per bit increases.

However, in the present embodiment, the minimum applied voltage Vamin or Vbmin according to the type of the liquid crystal display panel used as described above is given as an offset with respect to the counter electrode voltage Vc1 or Vc2. Therefore, it is not necessary to assign each data value of the input image data Da to a range lower than the minimum applied voltage Vamin or Vbmin, and it is possible to assign all of them to the applied voltage range Va or Vb used for gradation display. As a result, high-definition display is possible.
<2. Second Embodiment>
<2-1: Overview of Liquid Crystal Display>
Next, a liquid crystal display device according to a second embodiment will be described. The liquid crystal display device according to the second embodiment changes the transmittance range to which each data value of the input image data is allocated according to the type of the input image data.

FIG. 8 is a block diagram illustrating a configuration of a liquid crystal display device according to the second embodiment.
The liquid crystal display device shown in the figure uses an image signal processing circuit 300B instead of the image signal processing circuit 300A, and shows the type of data instead of the panel type control signal CTLp indicating the type of the liquid crystal display panel in the timing circuit 200A. Except for generating the data type control signal CTLd, the configuration is substantially the same as the liquid crystal display device of the first embodiment shown in FIG.

The input image data Db supplied to the liquid crystal display device is in an 11-bit parallel format. There are various types of input image data Db. In this example, two types are assumed, that is, a case where the source of the input image data Db is computer graphics and a case where the source is a video signal. In the following description, when distinguishing these, the former will be referred to as graphics data Db1, and the latter will be referred to as video data Db2.

Next, properties of the graphics data Db1 and the video data Db2 will be described. Since computer graphics often display images vividly, the saturation and brightness of display colors are often high. For this reason, the data value of the graphics data Db1 is generally biased toward high luminance. In this example, it is assumed that the data values of the graphics data Db1 are distributed with the probability density shown in FIG. On the other hand, the video data Db2 generated based on the video signal often has a data value that is biased toward an intermediate gradation. In this example, it is assumed that each data value of the video data Db2 is distributed with the probability density shown in FIG. The probability density shown in FIG. 9 is normalized by the maximum value.

The field frequency of graphics data Db1 generated by a personal computer or the like is 120 Hz, while the field frequency of video data Db2 such as a moving image is 60 Hz. The timing circuit 200A detects the frequency of the vertical synchronization signal VB supplied from the outside together with the input image data Db, compares the frequency with a predetermined threshold frequency (for example, 90 Hz), and generates the data type control signal CTLd. It has become. The timing circuit 200A sets the data type control signal CTLd to the H level when the input image data Db is the graphics data Db1, and sets the data type control signal CTLd to the L level when the input image data Db is the video data Db2. .
In the present embodiment, it is assumed that one type of liquid crystal display panel 100A is used. Therefore, the timing circuit 200A selects the first common electrode voltage Vc1 and the second common electrode voltage Vc2 as in the first embodiment. The first counter electrode voltage Vc1 is directly supplied to the liquid crystal display panel 100A from a power supply circuit (not shown).
<2-2: Image signal processing circuit>
FIG. 10 is a block diagram illustrating a configuration of an image signal processing circuit 300B used in the liquid crystal display device according to the second embodiment. The image signal processing circuit 300B includes a data value conversion circuit 306, and the first power supply circuit 3041 uses the third and fourth output range setting voltages V3 and V4 instead of the first and second output range setting voltages V1 and V2. The point of generation, the second power supply circuit 3051 generates the third and fourth positive reference voltages Vp3 and Vp4 instead of the first and second positive reference voltages Vp1 and Vp2, and the first and second negative polarities This is the same as the image signal processing circuit 300A of the first embodiment shown in FIG. 4, except that third and fourth negative reference voltages Vn3 and Vn4 are generated instead of the reference voltages Vn1 and Vn2. Hereinafter, differences will be described.

The data value conversion circuit 306 generates 10-bit converted image data Dx according to the data type of the 11-bit input image data Db. The data value conversion circuit 306 includes a first conversion table 3061, a second conversion table 3062, and a selection circuit 3063 as shown in FIG.

The first and second conversion tables 3061 and 3062 are configured by a ROM having 11 input bits and a 10 bit output bit, using 11-bit input image data Db as a read address, and using a corresponding storage area. , And 10-bit first conversion data Dx1 or second conversion data Dx2, respectively. The selection circuit 3063 selects the first conversion data Dx1 when the data type control signal CTLd is at the H level, and selects the second conversion data Dx2 when it is at the L level to generate the conversion image data Dx. .

Here, the first conversion table 3061 is used to convert the graphics data Db1, and the second conversion table 3062 is used to convert the video data Db2. FIG. 11A is a graph showing the input / output characteristics of the first conversion table, and FIG. 11B is a graph showing the input / output characteristics of the second conversion table.

As shown in FIG. 11A, the first conversion table 3061 converts the graphics data Db1 having data values of 768 to 2047 into the first conversion data Dx1 having data values of 1 to 1023 on a one-to-one basis. The graphics data Db1 having a value of 0 to 767 is converted to first conversion data Dx1 having a data value of 0. The input / output characteristics of the first conversion table 3061 are determined as described above. As shown in FIG. 9A, the data values of the graphics data Db1 are mostly distributed in the range of 767 to 2047. Is extremely low to be 767 or less.

Also, as shown in FIG. 2B, the second conversion table 3062 converts the video data Db2 having data values of 512 to 1533 into the second conversion data Dx2 having data values of 1 to 1022 on a one-to-one basis. The video data Db2 having a data value of 0 to 511 is converted into second conversion data Dx2 having a data value of 0, and the video data Db2 having a data value of 1534 to 2047 is converted into second conversion data Dx2 having a data value of 1023. The reason why the input / output characteristics of the second conversion table 3062 are determined as described above is that the data values of the video data Db2 are mostly distributed in the range of 511 to 1534 as shown in FIG. This is because the probability of becoming 510 or less or 1535 or more is extremely low.

That is, the data value conversion circuit 306 extracts a frequently occurring data value (0 to 2047) from the input image data Db and converts it into 10-bit converted image data Dx. Accordingly, the data value conversion circuit 306 can generate the 10-bit converted image data Dx without deteriorating the quality of the 11-bit input image data Db.

Next, in the output range control signal generation circuit 304, the selection circuit 3042 selects the third output range setting voltage V3 when the data type control signal CTLd is at the H level, and selects the fourth output range setting voltage V3 when it is at the L level. V4 is selected to generate an output range control signal CTLout, which is supplied to the control input terminal 301T of the D / A converter 301. Therefore, when the input image data Db is the graphics data Db1, the output range of the D / A converter 301 is determined by the third output range setting voltage V3, and when the input image data Db is the video data Db2, The output range of the D / A converter 301 is determined by the four output range setting voltage V4.

FIG. 12 is a graph showing the first VT characteristic of the liquid crystal display panel 100A. As described above, the data value conversion circuit 306 converts the data value of the input image data Db according to the data type to generate converted image data Dx. If the input image data Db is the graphics data Db1, the data values 767 to 2047 of the graphics data Db1 corresponding to the transmittance range Ta1 are assigned to the converted image data values 0 to 1023. On the other hand, if the input image data Db is the video data Db2, the data values 511 to 1534 of the video data Db2 corresponding to the transmittance range Ta2 are assigned to the converted image data values 0 to 1023. Therefore, when the input image data Db is the graphics data Db1, the applied voltage range of the liquid crystal is set to Va1, and when it is the video data Db2, the applied voltage range of the liquid crystal is set to Va2. .

The third output range setting voltage V3 is selected so that when it is applied to the control input terminal 301T, the final range of the voltage applied to the liquid crystal becomes the range Va1 shown in FIG. The fourth output range setting voltage V4 is selected such that when the fourth output range setting voltage V4 is applied to the control input terminal 301T, the range of the final voltage applied to the liquid crystal becomes the range Va2 shown in FIG.

Since the gains of the phase expansion circuit 302 and the amplification / inversion circuit 303 are A or −A, the output range of the D / A converter 301 is determined in consideration of the gain A. FIG. 13 is a graph showing the input / output characteristics of the D / A converter 301. In the figure, a characteristic W3 is an input / output characteristic when the third output range setting voltage V3 is supplied, and a characteristic W4 is an input / output characteristic when the fourth output range setting voltage V4 is supplied. As is clear from the characteristics W3 and W4, the output range of the D / A converter 301 is obtained by dividing the applied voltage ranges Va1 and Va2 according to the data type by the gain A. This makes it possible to adjust the output range of the D / A converter 301 according to the applied voltage range determined by the data type.

Next, the third positive reference voltage Vp3, the fourth positive reference voltage Vp4, the third negative reference voltage Vn3, and the fourth negative reference voltage Vn4 generated by the second power supply circuit 3051 of the reference signal generation circuit 305 are described. explain. First, the third positive reference voltage Vp3 is obtained by adding the minimum applied voltage Va1min shown in FIG. 12 to the first counter electrode voltage Vc1 that supplies power to the opposite substrate of the liquid crystal display panel 100A. The voltage Vn3 is obtained by subtracting the minimum applied voltage Va1min from the first common electrode voltage Vc1. The fourth positive reference voltage Vp4 is obtained by adding the minimum applied voltage Va2min to the first common electrode voltage Vc1, while the fourth negative reference voltage Vn4 is obtained by adding the minimum applied voltage Va2min to the first common electrode voltage Vc1. Is subtracted.

FIG. 14 shows a reference signal Sref that selects these voltages Vp3, Vp4, Vn3, and Vn4 based on the data type control signal CTLd and the polarity control signal CTLx. Further, since the output phase expanded image signal VID1 is obtained by adding the inverted image signal vid1 ′ and the reference signal Sref, if the input image data Db is the graphics data Db1, the output phase expanded image signal VID1 is input from the D / A converter 301 The input / output characteristics up to the output of the amplifying / inverting circuit 303 are as shown in FIG. 15A. On the other hand, when the input image data Db is the video data Db2, the input / output characteristics are as shown in FIG. It becomes.
<2-3: Operation of liquid crystal display device>
Next, the operation of the liquid crystal display device will be described. First, when the timing circuit 200A generates the data type control signal CTLd based on the vertical synchronization signal VB, the data value conversion circuit 306 converts the 11-bit input image data Db into the 10-bit converted image based on the data type control signal CTLd. Convert to data Dx. In this conversion process, the converted image data Dx is assigned in consideration of the data value distribution of the input image data Db, so that the converted image data Dx has substantially 11-bit accuracy.

Next, based on the data type control signal CTLd, the output range control signal generation circuit 304 selects one of the third output range setting voltage V3 and the fourth output range setting voltage V4 to generate the output range control signal CTLout. I do. Since the input / output characteristics of the D / A converter 301 are determined by the output range control signal CTLout supplied to the control input terminal 301T, when the input image data Db is the graphics data Db1, the characteristics become W3, If it is the video data Db2, the characteristic becomes W4 (see FIG. 13). The input image data Db has different characteristics for each data type, and its data value is biased. According to the present embodiment, since the output range of the D / A converter 301 can be adjusted according to the data type, the output range of the D / A converter 301 is adjusted according to the bias of the data value. can do.

Further, since the range of transmittance used for gradation display differs depending on the data type of the input image data Db, the minimum applied voltage of the liquid crystal also differs, but the reference signal Sref takes into account the third positive reference voltage Vp3 , The fourth positive reference voltage Vp4, the third negative reference voltage Vn2, and the fourth negative reference voltage Vn4. Thereby, as shown in FIG. 12, if the input image data Db is the graphics data Db1, the transmittance range can be set to Ta1, and if the input image data Db is the video data Db2, the transmittance range is set to Ta2. be able to.

Here, as a comparative example, it is assumed that the upper 10 bits are extracted from the 11-bit input image data Db to generate converted image data Dx and assign the converted image data Dx to the applied voltage range Va. In this comparative example, since 1-bit information is lost in the conversion process, the applied voltage change per bit of the input image data Db is Va / 1024. On the other hand, according to the present embodiment, the information of the input image data Db is not lost in the data value conversion process, and the voltage range applied to the liquid crystal can be set to Va1 or Va2. The amount of applied voltage change per bit can be reduced. When the input image data Db is the graphics data Db1, the applied voltage change amount is Va1 / 2048, and when the input image data Db is the video data Db2, it is Va2 / 2048. Here, if Va1 / Va = 3/4 and Va2 / Va = 1/4, when displaying the graphics data Db1, the applied voltage change amount per bit is 3/8 times that of the comparative example. In the case of displaying the video data Db2, the applied voltage change amount per bit can be reduced to 1/8 times as compared with the comparative example.

Therefore, according to the present embodiment, it is possible to display a high-definition image according to the data type.
<3. Third embodiment>
<3-1: Overview of liquid crystal display device>
Next, a liquid crystal display device according to a third embodiment will be described. The liquid crystal display device according to the third embodiment changes the transmittance range based on the average value of the input image data Da.

FIG. 16 is a block diagram illustrating a configuration of a liquid crystal display device according to the third embodiment. The liquid crystal display device shown in the figure uses an image signal processing circuit 300C instead of the image signal processing circuit 300A, except that the timing circuit 200A does not generate a panel type control signal CTLp indicating the type of the liquid crystal display panel. This is substantially the same as the liquid crystal display device of the first embodiment shown in FIG.

Here, the input image data Dc supplied to the liquid crystal display device is in an 11-bit parallel format. The input image data Dc is video data obtained by A / D converting a video signal obtained by imaging a subject with a video camera. The captured image has a bright part and a dark part in one screen, but the gradation of each pixel constituting one screen is not distributed from the highest luminance (saturated white) to the lowest luminance (saturated black). Are distributed in a predetermined range centered on the average gradation of one screen. FIG. 17 is a graph showing distribution characteristics of input image data values of one screen. In this graph, the input image data values are normalized by setting the average data value of one screen to 0, and the probability density is normalized by setting the maximum value to 1.

As shown in the figure, most of the data values of the input image data Dc are distributed in a range of ± 511 around the average value of one screen. From this, it can be seen that the difference between the maximum value and the minimum value of the input image data Dc of the first screen is 1024 or less, and the distribution range of the data value can be specified from the average value of the input image data Dc. .
<3-2: Image signal processing circuit>
As shown in FIG. 16, the image signal processing circuit 300C according to the third embodiment includes an average value calculation circuit 307, a data value conversion circuit 308, and a reference signal generation circuit 309, but does not include an output range control circuit 304. Except for this point, this embodiment is different from the image signal processing circuit 300A of the first embodiment shown in FIG. Further, a predetermined voltage is supplied to the control input terminal 301T of the D / A converter 301. Therefore, the output range of the D / A converter 301 does not fluctuate as in the first and second embodiments, and is fixed. The output range of this example is Vx / A when the applied voltage range finally applied to the liquid crystal is Vx (Vx1 to Vx2). Note that A is a gain obtained by integrating the phase expansion circuit 302 and the amplification / inversion circuit 303 as in the first and second embodiments.

First, the average value calculation circuit 307 calculates an average value of the input image data Dc of one screen, and generates average value data Dh indicating the calculated average value.

Next, the data value conversion circuit 308 converts the 11-bit input image data Dc into 10-bit converted image data Dy based on the average value data Dh. FIG. 18 is a block diagram showing a configuration of the data value conversion circuit 308. As shown in this figure, the data value conversion circuit 308 includes a correction table 3081, a subtraction circuit 3082, and a lower bit separation circuit 3083.

The correction table 3081 is constituted by a ROM of 11-bit input and 10-bit output, and stores 10-bit correction data Dk in association with each data value of the average value data Dh. Therefore, when certain average value data Dh is used as a read address, correction data Dk corresponding to the average value indicated by average value data Dh is read from correction table 3081.

FIG. 19 is a graph showing the input / output characteristics of the correction table. As shown in this figure, when the data value of the average value data Dh is 511 or less, the data value of the correction data Dk is 0, and when the data value of the average value data Dh is in the range of 512 to 1533, the data value of the correction data Dk is When the data value of the average value data Dh is 1534 or more, the data value of the correction data Dk is 1023.

Next, the subtraction circuit 3082 subtracts the correction data Dh from the input image data Dc and outputs the result. Next, the lower bit separation circuit 3083 separates the lower 10 bits of the data output from the subtraction circuit 3082, and outputs this as converted image data Dy.

Thereby, the 11-bit input image data Dc can be converted into the 10-bit converted image data Dy according to the average value of one screen. FIG. 20 is a graph showing a range in which input image data is allocated to converted image data. In this figure, the hatched portion indicates the range of the converted image data Dy extracted from the original input image data Dc.

For example, if the value of the average value data Dh is 1023, the data value of the correction data Dk is 511 (see FIG. 19). As described above, since the data values of the input image data Dc are distributed in a range of ± 511 around the average value on a certain screen, the data values of the input image data Dc are 511 to 1534 on the screen where the average value is 511. It will be distributed within the range.

Since the converted image data Dy is obtained by subtracting the correction data Dk from the input image data Dc, if the value of the input image data Dc is 511, the value of the converted image data Dy is 0, and the value of the input image data Dc is If it is 1534, the value of the converted image data Dy is 1023.

Next, the reference signal generation circuit 309 generates a reference signal Sref whose polarity is inverted in synchronization with the polarity control signal CTLx based on the average value data Dh and the first common electrode voltage Vc1. FIG. 21 is a block diagram showing a configuration of the reference signal generation circuit 309.
As shown in this figure, the reference signal generation circuit 309 includes a minimum applied voltage generation circuit 3091, an addition circuit 3092, a subtraction circuit 3093, and a positive / negative polarity selection circuit 3094.

First, the minimum applied voltage generation circuit 3094 generates a minimum applied voltage Vmin to be applied to the liquid crystal based on the average value data Dh. When the liquid crystal display panel 100A operates in the normally white mode as in this example, the maximum transmittance, that is, the maximum value of the gradation is determined by the minimum applied voltage Vmin. Further, as described above, the maximum value of the gradation in a certain screen is determined by the average value of the gradation in the entire screen.
Therefore, if the average value of a certain screen is known, the minimum applied voltage Vmin can be specified. The minimum applied voltage generation circuit 309 includes a storage unit that stores the average value data Dh and the minimum applied voltage data in association with each other and a D / A converter (not shown). Then, the minimum applied voltage generation circuit 309 performs D / A conversion of the minimum applied voltage data to generate the minimum applied voltage Vmin. The minimum applied voltage Vmin in this example is Vx2 when the value of the average value data Dh is 0 to 511 as shown by a dashed line in FIG. It becomes.

Next, the adder circuit 3092 adds the minimum applied voltage Vmin and the first common electrode voltage Vc1 to output a positive reference voltage Vp, while the subtraction circuit 3092 subtracts the minimum applied voltage Vmin from the first common electrode voltage Vc1. To output a negative polarity reference voltage Vn.

Next, the positive / negative polarity selection circuit 3094 selects the positive polarity reference voltage Vp when the polarity control signal CTLx is at the H level, and selects the negative polarity reference voltage Vn when the polarity control signal CTLx is at the L level to generate the reference signal Sref.

Therefore, the polarity of the reference signal Sref is inverted with respect to the first counter electrode voltage Vc1. FIG. 22 is a timing chart showing waveforms of the reference signal Sref and the polarity inversion signal CTLx. Since the value of the minimum applied voltage Vmin changes according to the value of the average value data Dh, the waveform of the reference signal Sref dynamically changes according to the value of the average value data Dh as shown in FIG.
<3-3: Operation of liquid crystal display device>
Next, the operation of the liquid crystal display device will be described. First, when the input image data Dc is supplied from an external device to the average value calculation circuit 307, the average value calculation circuit 307 calculates the average value of the input image data Dc during one field period and generates the average value data Dh. I do. The data value conversion circuit 308 converts the 11-bit input image data Dc into 10-bit converted image data Dx based on the average value data Dh. In this conversion processing, since the converted image data Dy is assigned in consideration of the data value distribution of the input image data Dc corresponding to the average value of one screen, the converted image data Dy has substantially 11-bit accuracy. ing.

As shown in FIG. 20, the range in which the 11-bit input image data Dc is assigned to the 10-bit converted image data Dx changes according to the value of the average value data Dh. It is necessary to change according to the value of the data Dh. This will be described with reference to FIG. FIG. 23 is a diagram illustrating a correlation between the first VT characteristic, the effective range of the input image data, and the average value data.

First, when the value of the average value data Dh is in the range of 0 to 511, the possible values of the input image data Dc are in the range of 0 to 1023. The transmittance range corresponding to this range is Tc1 as shown in FIG. In order to obtain the transmittance range Tc1, it is necessary to change the voltage applied to the liquid crystal from Vx2 to Vx3. As described above, when the value of the average value data Dh is in the range of 0 to 511, the value of the minimum applied voltage Vmin is Vx2, while the output range of the D / A converter 301 is Vx / A. This condition can be satisfied.

Next, when the value of the average value data Dh is in the range of 512 to 1533, the possible value of the input image data Dc changes from the range of 0 to 1023 to the range of 1023 to 2047. In this case, since the transmittance range changes from Tc1 to Tc2, it is necessary to change the voltage range applied to the liquid crystal from Vx2 to Vx3 from Vx1 to Vx2. As described above, when the value of the average value data Dh is in the range of 512 to 1533, the value of the minimum applied voltage Vmin changes from Vx2 to Vx1, while the output range of the D / A converter 301 is Vx / A. Therefore, this condition can be satisfied.

Next, when the value of the average value data Dh is in the range of 1534 to 2047, the possible values of the input image data Dc are in the range of 1023 to 2047. The transmittance range corresponding to this range is Tc2 as shown in FIG. In order to obtain the transmittance range Tc2, it is necessary to change the voltage applied to the liquid crystal from Vx1 to Vx2.
As described above, when the value of the average value data Dh is in the range of 1534 to 2047, the value of the minimum applied voltage Vmin is Vx1, while the output range of the D / A converter 301 is Vx / A. This condition can be satisfied.

That is, according to the present embodiment, according to the average value of the image, the input image data Dc is converted to generate the converted image data Dy, and the converted image data Dy is converted by the D / A converter 301 having a fixed output range. Since the A signal is converted to generate the image signal VID, the minimum applied voltage Vmin is generated based on the average value of the image, and the reference signal Sref is generated based on the minimum applied voltage Vmin. This is effective for displaying an image. The bits of the input image data Dc can be assigned to the range of the transmittance.
<4. Modification>
The present invention is not limited to the above embodiments, and for example, the following modifications are possible.
(1) In the first embodiment described above, the power supply circuit 3051 of the reference signal generation circuit 305 generates each of the positive voltages Vp1 and Vp2 and each of the negative voltages Vn1 and Vn2. There is. In the first mode, the second power supply circuit 3051 is configured by voltage sources that generate the voltages Vp1, Vp2, Vn1, and Vn2. In this mode, if the display panel 100 operates in the normally white mode, each voltage corresponding to the white level is directly generated.

は In the second mode, the second power supply circuit 3051 is configured by first and second voltage sources, a subtraction unit, and an addition unit. The first voltage source generates each first voltage that is higher than each reference potential predetermined according to the type of the electro-optical panel by each maximum applied voltage. The second voltage source generates each second voltage lower by each maximum applied voltage with respect to each reference potential. The subtracting unit generates each positive polarity reference voltage by subtracting each change voltage predetermined according to the type of the electro-optical panel from each first voltage. On the other hand, the adder adds each of the change voltages to each of the second voltages to generate each of the negative reference voltages. Here, each maximum applied voltage is the highest applied voltage that needs to be applied to the electro-optical material in order to obtain each transmittance range used for image display according to the type of the electro-optical panel.

In this mode, if the display panel 100 operates in the normally white mode, the first voltage and the second voltage corresponding to the black level (minimum transmittance) are generated, and these voltages and the electro-optical Each positive polarity reference voltage and each negative polarity reference voltage are generated based on the change voltage applied to the substance.
(2) Also, the power supply circuit 3051 in the above-described second embodiment has two modes in its configuration method, similarly to the above-described modification. In the first mode, the second power supply circuit 3051 is composed of voltage sources that generate the voltages Vp3, Vp4, Vn3, and Vn4. In this mode, if the display panel 100 operates in the normally white mode, each voltage corresponding to the white level is directly generated.

In a second mode, the second power supply circuit 3051 includes first and second voltage sources, a subtraction unit, and an addition unit. The first voltage source generates each first voltage that is higher by each maximum applied voltage than each reference potential predetermined according to the type of input image data. The second voltage source generates each second voltage lower by each maximum applied voltage with respect to each reference potential. The subtraction unit generates each positive polarity reference voltage by subtracting each change voltage predetermined according to the type of input image data from each first voltage. On the other hand, the adder adds each of the change voltages to each of the second voltages to generate each of the negative reference voltages. Here, each maximum applied voltage is the highest applied voltage that needs to be applied to the electro-optical material in order to obtain each transmittance range used for image display according to the type of input image data.
In this mode, if the display panel 100 operates in the normally white mode, the first voltage and the second voltage corresponding to the black level (minimum transmittance) are generated, and these voltages and the electro-optical Each positive polarity reference voltage and each negative polarity reference voltage are generated based on the change voltage applied to the substance.
<5. Application>
Next, some examples in which the liquid crystal display device described in each of the above-described embodiments is used for an electronic device will be described.
<5-1: Projector>
First, a projector using the liquid crystal display device as a light valve will be described. FIG. 24 is a plan view showing a configuration example of this projector.

As shown in this figure, a lamp unit 1102 including a white light source such as a halogen lamp is provided inside the projector 1100. The projection light emitted from the lamp unit 1102 is separated into three primary colors of RGB by four mirrors 1106 and two dichroic mirrors 1108 arranged in a light guide 1104, and is used as a light valve corresponding to each primary color. The light enters the liquid crystal panels 1110R, 1110B, and 1110G.

The configurations of the liquid crystal panels 1110R, 1110B, and 1110G are the same as those of the above-described liquid crystal display panel 100A or 100B, and are driven by R, G, and B primary color signals supplied from an image signal processing circuit (not shown). Now, the light modulated by these liquid crystal panels enters the dichroic prism 1112 from three directions. In the dichroic prism 1112, the R and B lights are refracted at 90 degrees, while the G light travels straight. Accordingly, as a result of combining the images of the respective colors, a color image is projected on a screen or the like via the projection lens 1114.

Since light corresponding to the primary colors of R, G, and B is incident on the liquid crystal panels 1110R, 1110B, and 1110G by the dichroic mirror 1108, it is not necessary to provide a color filter on the opposing substrate.
<5-2: Mobile computer>
Next, an example in which the liquid crystal display device is applied to a mobile computer will be described. FIG. 25 is a front view showing the configuration of this computer. In the figure, a computer 1200 includes a main body 1204 having a keyboard 1202 and a liquid crystal display 1206. The liquid crystal display 1206 is configured by adding a backlight to the back surface of the above-described liquid crystal display panel 100A or 100B.
<5-3: Mobile phone>
Further, an example in which the liquid crystal display device is applied to a mobile phone will be described. FIG. 26 is a perspective view showing the configuration of the mobile phone. In the figure, a mobile phone 1300 includes a plurality of operation buttons 1302 and a reflective liquid crystal panel 1005. In this reflection type liquid crystal panel 1005, a front light is provided on the front surface as needed.

Note that, in addition to the electronic devices described with reference to FIGS. 24 to 26, a liquid crystal television, a viewfinder type, a monitor direct-view type video tape recorder, a car navigation device, a pager, an electronic notebook, a calculator, a word processor, a work Stations, videophones, POS terminals, devices equipped with touch panels, and the like. Needless to say, the present invention can be applied to these various electronic devices.

FIG. 1 is a block diagram illustrating an entire configuration of a liquid crystal display device according to a first embodiment of the present invention. (A) is a graph showing the first VT characteristic of the liquid crystal display panel 100A used in the device, and (b) is a graph showing the second VT characteristic of the liquid crystal display panel 100B used in the device. FIG. 2 is a block diagram illustrating an electrical configuration of a liquid crystal display panel used in the device. FIG. 3 is a block diagram showing a configuration of an image processing circuit 300A used in the same device. 4 is a graph showing input / output characteristics of a D / A converter 301 in the same device. 6 is a timing chart showing waveforms of a polarity control signal CTLx and a reference signal Sref in the same device. (A) shows input / output characteristics of the image signal processing circuit 300A when the liquid crystal display panel 100A is used, and (b) shows input / output characteristics of the image signal processing circuit 300A when the liquid crystal display panel 100B is used. It is a block diagram showing the whole composition of the liquid crystal display concerning a 2nd embodiment of the present invention. (A) is a graph showing a probability density distribution of each data value of the graphics data Db1, and (b) is a graph showing a probability density distribution of each data value of the video data Db2. FIG. 2 is a block diagram illustrating a configuration of an image signal processing circuit used in the device. FIG. 11A is a graph showing the input / output characteristics of the first conversion table 3061 used in the apparatus, and FIG. 11B is a graph showing the input / output characteristics of the second conversion table 3062. 4 is a graph showing first VT characteristics of a liquid crystal display panel 100A used in the same device. 3 is a graph showing input / output characteristics of a D / A converter 301 used in the device. 6 is a timing chart showing waveforms of a polarity control signal CTLx and a reference signal Sref in the same device. (A) shows the input / output characteristics of the image signal processing circuit 300B when the input image data Db is the graphics data Db1, and (b) shows the image signal processing circuit when the input image data Db is the graphics data Db1. This is an input / output characteristic of 300B. It is a block diagram showing the whole composition of the liquid crystal display concerning a 3rd embodiment of the present invention. 9 is a graph showing distribution characteristics of input image data values of one screen. FIG. 3 is a block diagram of a data value conversion circuit 308 used in the device. 4 is a graph showing input / output characteristics of a correction table 3081 used in the apparatus. 4 is a graph showing a range in which input image data Dc is allocated to converted image data Dy in the device. FIG. 3 is a block diagram of a reference signal generation circuit 309 used in the device. 6 is a timing chart showing waveforms of a polarity control signal CTLx and a reference signal Sref in the same device. FIG. 4 is a diagram illustrating a correlation between a first VT characteristic, an effective range of input image data, and average value data. FIG. 14 is a cross-sectional view illustrating a configuration of a projector as an example of an electronic apparatus to which the liquid crystal display device is applied. FIG. 2 is a perspective view illustrating a configuration of a personal computer as an example of an electronic apparatus to which a liquid crystal display device is applied. FIG. 2 is a perspective view illustrating a configuration of a mobile phone as an example of an electronic apparatus to which a liquid crystal display device is applied. FIG. 11 is a block diagram illustrating the entire configuration of a conventional liquid crystal display device. (A) is a graph showing an example of VT characteristics of a liquid crystal display panel used in the same device, and (b) is a graph showing another example of VT characteristics.

Explanation of reference numerals

100A, 100B ... Liquid crystal display panel (electro-optical panel)
200A timing circuit (control signal generation means)
300A, 300B, 300C ... image signal processing circuit (image processing circuit)
CTLp: Panel type control signal (control signal)
Da: input image data
VID image signal 301 D / A converter (D / A conversion means)
302... Phase expansion circuit (processing means)
303 ... Amplifying / inverting circuit (processing means)
VID1 to VID6 …… Output phase expanded image signal
vid '... inverted image signal 3034 ... addition circuits 305, 309 ... reference signal generation circuit (reference signal generation unit)
306, 308... Data value conversion circuit (data conversion means)
Da, Db, Dc ... Input image data Db1 ... Graphics data Db2 ... Video data VB ... Vertical synchronization signal 307 ... Average value calculation circuit (average value generation means)

Claims (21)

An image processing circuit used in combination with one type of electro-optical panel selected from a plurality of predetermined types of electro-optical panels having an electro-optical material whose transmittance changes according to an applied voltage,
Control signal generating means for generating a control signal indicating the type of the electro-optical panel combined with the image processing circuit,
D / A conversion means for converting input image data from a digital signal to an analog signal to generate an image signal, and adjusting a range in which the signal level of the image signal changes based on the control signal;
Processing means for generating an output image signal to be supplied to the electro-optical panel based on the image signal. The processing means includes:
While amplifying the image signal, an image signal inverting unit that generates an inverted image signal by inverting the signal polarity at a predetermined inversion cycle based on a certain potential,
A first reference voltage and a second reference voltage are generated based on the control signal, and one of the first reference voltage and the second reference voltage is alternately selected at the inversion cycle to generate a reference signal. A reference signal generator that generates
The image processing circuit according to claim 1, further comprising: an output image signal generation unit configured to generate the output image signal by combining the inverted image signal and the reference signal. The reference signal generator,
From each reference potential predetermined according to the type of the electro-optical panel, each positive reference voltage higher by each minimum applied voltage, and each negative reference voltage lower by each minimum applied voltage with respect to each reference potential And a power supply for generating
Based on the control signal, a voltage corresponding to the electro-optical panel used in combination with the image processing circuit is selected from the respective positive polarity reference voltages to generate the first reference voltage, and based on the control signal, A first selection unit that selects a voltage corresponding to the electro-optical panel used in combination with the image processing circuit from among the negative reference voltages, and generates the second reference voltage;
A second selection unit that alternately selects one of the first reference voltage and the second reference voltage at the inversion cycle to generate the reference signal; The lowest applied voltage that is specified for each electro-optical panel and needs to be applied to the electro-optical material in order to obtain the range of the transmittance used for displaying an image. Image processing circuit. The image processing circuit according to claim 3, wherein the minimum applied voltage is a voltage corresponding to a saturation transmittance of the electro-optical material. A first voltage source that generates a first voltage that is higher than each of the reference potentials predetermined according to the type of the electro-optical panel by a maximum applied voltage,
A second voltage source that generates a second voltage that is lower by a maximum applied voltage with respect to each of the reference potentials;
A subtraction unit that subtracts each of the predetermined change voltages according to the type of the electro-optical panel from each of the first voltages to generate each of the positive polarity reference voltages;
An adding unit that adds each of the change voltages to each of the second voltages to generate each of the negative reference voltages;
The maximum applied voltage is the highest applied voltage that needs to be applied to the electro-optical material to obtain each transmittance range used for image display according to the type of the electro-optical panel. The image processing circuit according to claim 3. An image processing circuit used in combination with an electro-optical panel having an electro-optical material whose transmittance changes according to an applied voltage,
Control signal generating means for generating a control signal indicating a type of the input image data,
Based on the control signal, data conversion means for converting each data value of the input image data into each data value associated in advance to generate converted image data,
A D / A converter that converts the converted image data from a digital signal to an analog signal to generate an image signal, and adjusts a range in which the signal level of the image signal changes based on the control signal;
Processing means for generating an output image signal to be supplied to the electro-optical panel based on the image signal. The processing means includes:
While amplifying the image signal, an image signal inverting unit that generates an inverted image signal by inverting the signal polarity at a predetermined inversion cycle based on a certain potential,
A first reference voltage and a second reference voltage, each of which has a voltage value corresponding to a type of the input image data, are generated based on the control signal, and one of the first reference voltage and the second reference voltage is generated. A reference signal generation unit that alternately selects the inversion cycle to generate a reference signal,
The image processing circuit according to claim 6, further comprising: an output image signal generation unit configured to generate the output image signal by combining the inverted image signal and the reference signal. The reference signal generator,
Generating each positive reference voltage higher than each predetermined reference potential by each minimum applied voltage according to the type of the input image data and each negative polarity reference voltage lower than each each reference potential by each minimum applied voltage Power supply section,
The first reference voltage is generated by selecting a voltage corresponding to the type of the input image data from the respective positive reference voltages based on the control signal, and the respective negative reference voltages are selected based on the control signal. A first selector that selects a voltage corresponding to the type of the input image data from the voltages to generate the second reference voltage;
A second selection unit that alternately selects one of the first reference voltage and the second reference voltage at the inversion cycle to generate the reference signal,
Each of the minimum applied voltages is the lowest applied voltage that needs to be applied to the electro-optical material in order to obtain each transmittance range used for image display for each type of the input image data. The image processing circuit according to claim 7, wherein: A first voltage source that generates each first voltage that is higher than each of the reference potentials predetermined according to the type of the input image data by each maximum applied voltage;
A second voltage source that generates a second voltage that is lower by a maximum applied voltage with respect to each of the reference potentials;
A subtraction unit that subtracts each of the predetermined change voltages according to the type of the input image data from each of the first voltages to generate each of the positive polarity reference voltages;
An adding unit that adds each of the change voltages to each of the second voltages to generate each of the negative reference voltages;
The maximum applied voltages are the highest applied voltages that need to be applied to the electro-optical material in order to obtain each transmittance range used for image display for each type of the input image data. An image processing circuit according to claim 8. The image processing circuit according to claim 8, wherein the control signal indicates whether the input image data is based on computer graphics or a video signal. The input image data is supplied from the outside together with a vertical synchronization signal indicating the vertical blanking period,
The image processing circuit according to claim 10, wherein the control signal generation unit detects a period of a vertical synchronization signal, and generates the control signal based on a detection result. An image processing circuit used in combination with an electro-optical panel having an electro-optical material whose transmittance changes according to an applied voltage,
An average value generation unit that calculates an average value of the tone of the image based on the input image data and generates an average value signal indicating the average value of the tone,
Data conversion means for converting the input image data into converted image data according to a conversion rule according to the grayscale average value based on the average value signal,
A D / A converter that converts the converted data from a digital signal to an analog signal to generate an image signal;
Processing means for generating an output image signal to be supplied to the electro-optical panel based on the image signal. 13. The image processing circuit according to claim 12, wherein the average value generation unit calculates an average value of the gradation of the image based on input image data of one screen. The processing means includes:
While amplifying the image signal, an image signal inverting unit that generates an inverted image signal by inverting the signal polarity at a predetermined inversion cycle based on a certain potential,
A first reference voltage and a second reference voltage each having a voltage value corresponding to the gradation average value are generated based on the average value signal, and one of the first reference voltage and the second reference voltage is generated. A reference signal generation unit that alternately selects the inversion cycle to generate a reference signal,
The image processing circuit according to claim 12, further comprising: an output image signal generation unit configured to generate the output image signal by combining the inverted image signal and the reference signal. The reference signal generator,
Based on the average value signal, a minimum applied voltage generation unit that generates a minimum applied voltage applied to the electro-optical material according to a rule according to the grayscale average value,
A reference voltage generation unit that adds the minimum applied voltage to a predetermined reference potential to generate the first reference voltage, and subtracts the minimum applied voltage from the reference potential to generate the second reference voltage; ,
15. The selector according to claim 14, further comprising: a selector configured to alternately select one of the first reference voltage and the second reference voltage at the inversion cycle to generate the reference signal. 16. Image processing circuit. An image processing method for generating an output image signal to be supplied to one type of electro-optical panel selected from a plurality of predetermined types of electro-optical panels having an electro-optical material whose transmittance changes according to an applied voltage. hand,
Converting the input image data from a digital signal to an analog signal to generate an image signal, and adjusting a range in which the signal level of the image signal changes according to the type of the electro-optical panel,
While amplifying the image signal, to generate an inverted image signal by inverting the signal polarity at a predetermined inversion cycle based on a certain potential,
A positive reference voltage higher by a predetermined minimum applied voltage according to the type of the electro-optical panel based on a reference potential predetermined according to the type of the electro-optical panel; and Either one of the negative reference voltage lower than the applied voltage is alternately selected in the inversion cycle to generate a reference signal,
Generating the output image signal by synthesizing the inverted image signal and the reference signal;
The minimum applied voltage is specified for each of the electro-optical panels, and is the lowest applied voltage that needs to be applied to the electro-optical material in order to obtain the range of the transmittance used for image display. Image processing method. An image processing method for generating an output image signal to be supplied to an electro-optical panel having an electro-optical material whose transmittance changes according to an applied voltage,
According to a conversion rule according to the type of the input image data, the input image data is converted to converted image data,
Converting the converted image data from a digital signal to an analog signal to generate an image signal,
While amplifying the image signal, to generate an inverted image signal by inverting the signal polarity at a predetermined inversion cycle based on a certain potential,
A positive reference voltage higher by a predetermined minimum applied voltage according to the type of the input image data, based on a reference potential predetermined according to the type of the input image data; Either one of the negative reference voltage lower than the applied voltage is alternately selected in the inversion cycle to generate a reference signal,
Generating the output image signal by synthesizing the inverted image signal and the reference signal;
The minimum applied voltage is specified for each type of the input image data, and is the lowest applied voltage that needs to be applied to the electro-optical material in order to obtain the range of the transmittance used for image display. Image processing method. An image processing method for generating an output image signal to be supplied to an electro-optical panel having an electro-optical material whose transmittance changes according to an applied voltage,
Calculate the average gradation value of the image based on the input image data,
Converting the input image data to converted image data according to a conversion rule according to the gradation average value,
The conversion data is converted from a digital signal to an analog signal to generate an image signal,
While amplifying the image signal, to generate an inverted image signal by inverting the signal polarity at a predetermined inversion cycle based on a certain potential,
A positive reference voltage higher by a predetermined minimum applied voltage according to the average gradation value based on a predetermined reference potential; and a negative reference voltage lower by the minimum applied voltage based on the reference potential. Either one is alternately selected at the inversion cycle to generate a reference signal,
Generating the output image signal by synthesizing the inverted image signal and the reference signal;
The minimum applied voltage is specified for each of the average gradation values, and is the lowest applied voltage that needs to be applied to the electro-optical material in order to obtain the range of the transmittance used for image display. Image processing method. An electro-optical panel having an electro-optical material whose transmittance changes according to an applied voltage,
An image processing circuit according to any one of claims 1 to 15,
And an electro-optical panel having an electro-optical material whose transmittance changes according to an applied voltage while the output image signal is supplied. The electro-optical panel,
An element substrate including a plurality of data lines, a plurality of scanning lines, a switching element corresponding to an intersection of the data line and the scanning line, and a pixel electrode connected to the switching element; The opposing substrate,
Comprising an electro-optical material sandwiched between the element substrate and the counter substrate,
20. The electro-optical device according to claim 19, wherein the reference potential is a potential of the counter electrode, and the output image signal is sequentially supplied to the data lines. An electronic apparatus comprising the electro-optical device according to claim 19.

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