JP2006098422A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device in which a plurality of kinds of gamma correction values can be switched in a hardware manner without using software control for gamma correction. <P>SOLUTION: The display device is provided with: a plurality of display pixel arranged in matrix; a reference voltage generation circuit for generating a reference voltage for gamma correction; and a D/A converter which performs D/A conversion of a digital image signal inputted according to the reference voltage for gamma correction from the reference voltage generation circuit, generates a gamma corrected analog gray scale signal and supplies the analog gray scale signal to each display pixel, wherein a reference voltage generation circuit section having the plurality of reference voltage generation circuits corresponding to gamma values different from each other, is formed and a switch means for switching and selecting the plurality of the reference voltages for gamma correction of the reference voltage generation circuit corresponding to a predetermined gamma correction value and for supplying them to the D/A converter, is provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a display device having γ correction means such as a liquid crystal display device, a plasma display, an LED (light emitting diode) display device, and the like, and particularly has γ correction means that can be switched to a predetermined γ correction value according to the use environment. The present invention relates to a display device.

In a cathode ray tube (CRT, cathode ray tube), the relationship between the drive voltage V and the light emitting luminance Y rather than proportional, is expressed by the relational expression Y = KV ^gamma. This constant γ is called gamma, and in Japan's television (TV) system, this characteristic is taken into consideration and γ = 2.2 is corrected in advance on the transmission side. The gamma correction added to the original signal on the transmitting side changes not only the brightness of the image but also the ratio of red, green, and blue (RGB), but the receiving side displays the gamma corrected signal on the CRT. Then, the relationship between the drive voltage V and the light emission intensity Y becomes a proportional relationship so that the original color can be reproduced.

  However, in a liquid crystal display device, a plasma display, an LED display device using LEDs of three primary colors of RGB, etc., the relationship between the drive voltage and the luminance or transmitted light amount is different from that in the case of a CRT. In the liquid crystal display device, plasma display, or LED display device, it is necessary to perform γ correction on the receiving side so that the same color as that displayed on the CRT can be reproduced.

  For example, FIG. 3 shows an example of the relationship between the voltage V applied to each liquid crystal cell of the liquid crystal display panel and the light transmittance T in the liquid crystal display device, that is, an VT characteristic. In this case, in order to obtain a liquid crystal display device capable of displaying gradation of 8 bits = 256, the applied voltage is equally divided to obtain a signal level of 256 gradations, the black level transmittance is 0, and the white level transmittance is Is normalized as 100%, the relationship between signal level and transmittance T is as shown in FIG. Here, a signal level of 0 means black, and a signal level of 256 means white.

On the other hand, it is known that the human eye feels naturally with a sense of incongruity in the image, because the relationship between the signal level of the image and the luminance must be a characteristic as shown in the TV mode curve of FIG. ing. In this case, the relationship between the signal level X and the transmittance T is represented by TαX ^γ. This constant γ is also called gamma, and it is said that γ = 2.0 to 2.6 is good for a liquid crystal display panel. The TV mode curve in FIG. 5 shows a curve when γ = 2.2.

  Therefore, in order to use the liquid crystal display panel having the characteristics shown in FIGS. 3 and 4 to obtain the liquid crystal display device having the TV mode characteristics shown in FIG. 5, the liquid crystal of the liquid crystal display panel having the characteristics shown in FIG. As a voltage applied to the cell, an analog voltage corresponding to a signal level that can obtain the same luminance as the output of the TV mode shown in FIG. 5 may be applied to the liquid crystal cell.

  Γ correction of a TV receiver using a recent liquid crystal display panel is performed by controlling a source signal (see Patent Documents 1 and 2 below). Therefore, in order to understand the present invention, γ correction of a conventional liquid crystal display device will be described below with reference to FIGS. 6 is a block diagram showing an internal configuration of a conventional liquid crystal display device, FIG. 7 is a specific block diagram of the source driver circuit in FIG. 6, and FIG. 8 is a reference voltage for gamma correction in FIG. FIG. 9 is a diagram showing a specific example of a generation circuit and an analog / digital (A / D) conversion circuit, and FIG. 9 is a diagram for obtaining the same curve as the ideal output shown in FIG. 5 for the liquid crystal display panel. It is a figure which shows the relationship between a signal level and applied voltage.

  The liquid crystal display device 10B includes an A / D conversion circuit unit 11 and a liquid crystal drive circuit unit 12 as shown in FIG. The A / D conversion circuit unit 11 includes an interface (I / F) circuit 13, an A / D converter 14, and a scaler IC 15, and is a device that generates analog RGB signals of a personal computer (PC) 16 or a TV tuner 17. The analog RGB signal (0.7 Vp-p) input from the A / D converter circuit 11 passes through the I / F circuit 13 of the A / D converter circuit 11 and the A / D converter 14 and the scaler IC 15, for example, RGB corresponding to red, green and blue Each signal is converted into an 8-bit digital signal and input to the liquid crystal drive circuit unit 12. If the PC 16 directly generates a digital RGB signal, the digital RGB signal is directly input to the liquid crystal drive circuit unit 12. Note that devices that generate analog RGB signals include not only TV tuners but also video tape players, DVD players, and the like. In this specification, devices that generate analog RGB signals are collectively referred to as TV tuners, etc. It expresses.

  On the other hand, the liquid crystal drive circuit unit 12 includes a liquid crystal display panel 18, an I / F circuit 19, a timing controller 20, a gate driver 21, and a source driver 22, and various digital RGB signals input to the liquid crystal drive circuit are A predetermined input source is selected via the / F circuit 19 and input to the timing controller 20, and the timing controller 20 converts the digitized RGB 8-bit display signals DR, DG, DB and the horizontal synchronization signal HS. A control signal such as a start pulse HSP signal and a source driver clock SCLK signal is output to the source driver 22, and a vertical synchronization signal VS and a gate driver clock signal GCLK are output to the gate driver 21.

  As shown in FIG. 7, the source driver 22 includes an 8 × 3 bit latch 23, a shift register 24, a sampling memory 25, a hold memory 26, a level shifter 27, a D / A converter 28, an output buffer 29, and a reference voltage generation circuit 30. I have.

The digitized RGB 8-bit display signals DR, DG, and DB input from the timing controller 20 to the source driver 22 are latched in the latch 23 in a time-sharing manner, and are sampled memory 25, hold memory 26, level shifter 27, the analog voltage for gradation display (gradation display voltage) is obtained by performing D / A conversion by the D / A converter 28 based on the reference voltage from the reference voltage generation circuit 30 in synchronization with the horizontal synchronization signal HS. ) And is supplied to n signal lines 31 composed of Y ₁ to Y _n of the liquid crystal display panel 18 via the output buffer 29. Further, the vertical synchronization signal VS and the gate driver clock signal GCLK supplied from the timing controller 20 to the gate driver 21 are processed by the gate driver 21 and _m scanning signals composed of X _{1 to} X _m of the liquid crystal display panel 18. Are supplied to the scanning line 32. Note that specific signal processing in the source driver 22 and the gate driver 21 is already well known (see Patent Documents 1 and 2 below), and thus detailed description thereof is omitted.

  In this way, the source driver 22 converts the gradation display voltage applied to the signal line 31 of the liquid crystal display panel 18 into an analog voltage, thereby changing the light transmittance of the liquid crystal display panel 18 for each of the RGB pixels. 8 bits, that is, 256 levels of gradation display.

  In this case, predetermined γ correction is performed when an analog voltage for gradation display is obtained by the D / A converter 28 based on the reference voltage from the reference voltage generation circuit 30. The reference voltage generation circuit 30 and the D / A A specific example of the A converter 28 will be described with reference to FIG.

The D / A converter 28 is a circuit that generates 2 ⁸ = 256 analog voltages when the display signals DR, DG, and DB are 8-bit digital signals. The reference voltage generating circuit 30 itself divides a constant voltage VR supplied from a constant voltage source (not shown) into eight by a resistor dividing circuit in which eight resistors R _{0 to} R ₇ are connected in series, for example, as shown in FIG. Eight reference voltages VR _{1 to} VR ₈ (9 including VR ₀ ) arbitrarily selected so as to obtain the indicated ideal output curve are obtained, and these VR _{0 to} VR ₈ are supplied to the D / A converter 28. Supply. _RVAR is a semi-fixed resistor for fine adjustment of the reference voltage. The reference voltage generation circuit 30 itself can generate any number of reference voltages as long as it is plural. However, if the number is too small, the correction interval becomes coarse, so usually six or more, particularly eight for high-precision correction. The above is used.

In the D / A converter 28, based on the nine reference voltages V _{0 to} V ₈ supplied from the reference voltage generating circuit 30, the voltages between the adjacent reference voltages are divided into 32 at equal intervals. 32 × 8 = 256 reference reference voltages V _{0 to} V ₂₅₅ are created. In this case, one reference voltage generation circuit 30 is provided and shared by one source driver IC, and a D / A converter 28 is provided for each signal line 31 of the source driver IC.

In the A / D converter 28, the display signals DR, DG, DB supplied from the 256 reference standard voltages V _{0 to} V ₂₅₅ via the latch 23, sampling memory 25, hold memory 26 and level shifter 27 are supplied. One reference standard voltage corresponding to each digital signal is selected and output as an analog gradation output value, and supplied to n signal lines 31 composed of Y ₁ to Y _n of the liquid crystal display panel 18. It has become.

As described above, since the reference reference voltages V _{0 to} V ₂₅₅ corresponding to the analog voltage for gradation display are determined by the resistance ratio of the eight resistors R _{0 to} R ₇ in the reference voltage generation circuit 30, D / A When the analog voltage for gray scale display corrected by the converter 28 is obtained, a constant voltage is generated by the reference voltage generation circuit 30 so as to obtain the relationship between the signal level and the applied voltage as shown in FIG. In general, a method of generating the reference voltages VR _{0 to} VR ₈ by dividing VR into non-equal parts is performed.
JP 2002-175060 A (paragraphs [0002] to [0039], FIG. 9, FIG. 13, FIG. 17) JP 2002-250908 A (paragraphs [0002] to [0004], [0011] to [0019], FIG. 13 to FIG. 15, FIG. 17)

  By the way, for example, in a TV mass retailer, an image is displayed in a dynamic mode in order to emphasize the vividness of the screen display. However, in a home, an image is generally displayed in a normal TV mode. Also, images such as PCs and car navigation systems have a large dynamic range and many high-contrast signals, so they are used for γ correction of γ = 2.5. However, halftone signals are especially used for video signals such as cinema. Since there are many components, it is possible to display in a natural color tone with γ correction of γ = 2.2 or less. Therefore, for example, when an image of a TV or the like is displayed on a liquid crystal display device that has been subjected to γ correction suitable for a PC display, the image becomes slightly dark. Therefore, it is desired to change the γ correction according to each video source to be displayed or a required display effect.

  Conventionally, the above-described γ correction is fixed to a predetermined constant value, and contrast control and color shift are supported by software. For example, in a liquid crystal display device in which γ correction suitable for TV is made, When the video signal of the TV is used as the dynamic mode display screen or the cinema mode display screen, the software control is used. However, such software control requires calculation processing for the control memory, which makes the configuration complicated and increases the cost.

  The present invention has been made to solve the above-described problems of the prior art, and its purpose is not to use software control for γ correction, but to provide a plurality of gamma correction values in hardware. An object of the present invention is to provide a display device that can be switched.

  The above object of the present invention can be achieved by the following constitution. That is, a display device according to claim 1 of the present application includes a plurality of display pixels arranged in a matrix, a reference voltage generation circuit that generates a reference voltage for γ correction, and a reference for γ correction from the reference voltage generation circuit. A display including a D / A converter that generates a γ-corrected analog gradation signal by D / A converting a digital image signal input according to a voltage and supplies the analog gradation signal to each display pixel. In the apparatus, a plurality of reference voltage generation circuits are provided corresponding to different γ correction values to form a reference voltage generation circuit unit, and a plurality of γ corrections of the reference voltage generation circuit corresponding to a predetermined γ correction value are provided. Switch means for simultaneously switching and selecting the reference voltage for supply to the D / A converter is provided.

  Further, according to claim 2 of the present application, in the display device according to claim 1, the reference voltage generation circuit divides a predetermined reference voltage into a plurality of γ correction voltages by a resistance voltage dividing circuit. It is characterized by being.

  The invention according to claim 3 of the present application is characterized in that, in the display device according to claim 1, the switch means is an analog switch.

  Further, according to a fourth aspect of the present invention, in the display device according to the first aspect, at least two of the reference voltage generation circuits are provided, and a plurality of γ corrections generated by the respective reference voltage generation circuits are provided. The combination of the reference voltages is at least two selected from the PC mode, the dynamic mode, the TV mode, and the cinema mode.

 By providing the above configuration, the present invention has the following excellent effects. That is, according to the first aspect of the present invention, when the γ correction value of the display device is switched, it can be directly switched by the switch means, so that it is necessary for the γ correction by the soft control as in the prior art. It becomes possible to provide a display device that can switch the γ correction value at a low cost with a simple configuration, and a plurality of signals input to the D / A converter. Since the γ correction reference voltage is directly switched, the color can be easily changed, and the color reproducibility is improved.

  According to the second aspect of the present invention, since the resistance voltage dividing circuit can arbitrarily select a resistance value to be combined, a desired combination of a plurality of γ correction reference voltages can be easily generated.

  According to the invention of claim 3, since the analog switch is small, it is possible to easily obtain a multi-stage and multi-contact switch, so that it corresponds to a desired γ correction value without complicating the wiring structure. A plurality of γ correction reference voltages can be simultaneously selected and switched.

  Furthermore, according to the invention of claim 4, it is possible to switch and select an optimal γ correction value corresponding to each input image signal such as a PC mode, a dynamic mode, a normal TV mode, and a cinema mode as necessary. Therefore, it is possible to display an image that looks natural to human eyes.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. However, in the following embodiments, an example of a liquid crystal display device will be described as a display device for embodying the technical idea of the present invention. However, the present invention is not limited to the liquid crystal display device and is arranged in a matrix. The present invention is equally applicable to display devices having a plurality of display pixels, such as plasma display panels and LED display devices.

  FIG. 1 is a block diagram showing an internal configuration of the liquid crystal display device of this embodiment, and FIG. 2 is a diagram showing a specific example of the reference voltage generation circuit and the A / D conversion circuit in the source driver circuit of FIG. 1 and 2, the same reference numerals are given to the same components as those of the conventional liquid crystal display panel 10B shown in FIGS. 3 to 6, and the detailed description thereof is omitted. To do.

The liquid crystal display device 10A in this embodiment is different from the conventional liquid crystal display device 10B shown in FIG. 6 in that the source driver 22 has a γ correction switching terminal 33, and this γ correction switching terminal. All the combinations of a plurality of γ correction reference voltages VR _{0 to} VR ₈ input to the D / A converter 28 of the source driver 22 in accordance with the γ correction switching input input to 33 are for a predetermined γ correction value. It is a point that can be switched to.

A specific configuration of the reference voltage generation circuit unit 34 in the source driver 22 of this embodiment and a connection relationship with the D / A converter 28 will be described with reference to FIG. The reference voltage generation circuit unit 34 of the present embodiment includes, for example, a first reference voltage generation circuit 34-1 and a second reference that generate a combination of a plurality of γ correction reference voltages respectively corresponding to three different γ correction values. An arbitrary set of references from a combination of the voltage generation circuit 34-2, the third reference voltage generation circuit 34-3, and three sets of γ correction reference voltages from these reference voltage generation circuits 34-1 to 34-3 A γ correction voltage switching circuit 35 that selects and sends voltage combinations VR _{0 to} VR ₈ to the D / A converter 28 is provided.

The first reference voltage generation circuit 34-1, the second reference voltage generation circuit 34-2, and the third reference voltage generation circuit 34-3 include, for example, eight resistors R _{01 to} R ₇₁ , R _{02 to} R ₇₂ , and It consists of a resistance voltage dividing circuit composed of R _{03 to} R ₇₃ , and one end of each of the voltage dividing resistors R ₇₁ , R ₇₂ and R ₇₃ is connected in parallel via a semi-fixed resistor V _VAR for reference voltage fine adjustment. A constant voltage VR supplied from a constant voltage source (not shown) is applied. The combinations of these resistors R _{01 to} R ₇₁ , R _{02 to} R ₇₂ , and R _{03 to} R ₇₃ are selected so that a combination of reference voltages corresponding to predetermined γ correction values is obtained.

The combination of the eight resistors of each of the reference voltage generation circuits 34-1 to 34-3 is generally shown in the case where they are connected in parallel, but a specific resistor in each reference voltage circuit is used. There is also a method of selecting each and selecting any one of VR ₀ to VR ₈ .

  As the γ correction value in this case, for example, an optimal numerical value corresponding to each input image signal such as a PC mode, a dynamic mode, a normal TV mode, and a cinema mode can be appropriately selected.

The voltage dividing points of the respective resistors are connected in parallel to the fixed terminals of, for example, 8 circuits and 3 contact analog switches SW _{0 to} SW ₇ of the γ correction voltage switching circuit 35. Based on the γ correction switching input signal input to the γ correction input switching terminal 33, a set of reference voltage combinations VR _{0 to} VR ₈ corresponding to a predetermined γ correction value is selected and sent to the D / A converter 28. .

2 shows an example in which the combination of the γ correction reference voltages generated by the first reference voltage generation circuit 34-1 is selected and sent to the D / A converter 28. In FIG. 2, buffer circuits are connected to the selection output units of the analog switches SW _{0 to} SW ₇ , respectively, which lowers the output impedance of the reference voltage generation circuit unit 34 and supplies a sufficient output current. This can be omitted if the input impedance of the D / A converter 28 is sufficiently larger than the output impedance of the reference voltage generation circuit section 34.

In this way, a set of reference voltages VR _{0 to} VR ₈ corresponding to the predetermined γ correction value is set to the predetermined γ correction value set in advance by the γ correction switching input input to the γ correction switching terminal 33. Since the selected signal is sent to the D / A converter 28, the analog signal output having the selected predetermined gamma correction is applied to the n signal lines 31 composed of Y ₁ to Y _n of the liquid crystal display panel 18. Since the value is supplied, an image having a desired color tone can be displayed. In this case, since one set of reference voltage combinations VR _{0 to} VR ₈ corresponding to a desired γ correction value is directly selected by the analog switches SW _{0 to} SW ₇ , the color can be easily changed. In addition, color reproducibility is improved.

  In the present embodiment, the first to third reference voltage generation circuits 34-1 to 34-3 are each configured as a resistance voltage dividing circuit using eight resistors. However, it is desired to correct γ with higher accuracy. In such a case, more reference voltages for gamma correction may be created using more resistors. Further, in this embodiment, an example is shown in which three reference voltage generation circuits of the first to third reference voltage generation circuits 34-1 to 34-3 are used, but the number of reference voltage generation circuits is two. Any number may be used as long as it is greater than or equal to the number, and a person skilled in the art may appropriately determine.

  In the present embodiment, the reference voltage generating circuit unit 34 has been exemplified to generate a reference voltage of one polarity. However, as a driving method of a liquid crystal display panel, in general, AC driving is used to prevent polarization of the liquid crystal cell. In such a case, the reference voltage generation circuit unit 34 may generate a positive and negative output.

It is a block diagram which shows the internal structure of the liquid crystal display device of an Example. FIG. 2 is a diagram illustrating a specific example of a reference voltage generation circuit and an A / D conversion circuit in the source driver circuit of FIG. 1. It is a figure which shows the relationship between the voltage V applied to each liquid crystal cell of the liquid crystal display panel in a liquid crystal display device, and the transmittance | permeability T of light. FIG. 4 is a diagram showing the relationship between the signal level and the transmittance T obtained by normalizing the curve of FIG. 3 with a black level transmittance of 0 and a white level transmittance of 100%. It is a figure which shows the relationship between the signal level of the image of various modes, and a brightness | luminance. It is a block diagram which shows the internal structure of the conventional liquid crystal display device. It is a specific block diagram of the source driver circuit in FIG. FIG. 8 is a diagram illustrating a specific example of a reference voltage generation circuit and an A / D conversion circuit in FIG. 7. It is a figure which shows the relationship between the signal level and applied voltage for obtaining the same curve as the ideal output shown in FIG. 5 with respect to the liquid crystal display panel.

Explanation of symbols

10A, 10B Liquid crystal display device 11 A / D conversion circuit unit 12 Liquid crystal drive circuit unit 18 Liquid crystal display panel 20 Timing controller 21 Gate driver 22 Source driver 23 Latch 24 Shift register 25 Sampling memory 28 D / A converter 30 Reference voltage generation circuit 31 Signal line 32 Scan line 33 γ correction switching terminal 34 Reference voltage generation circuit unit 34-1 to 34-3 Reference voltage generation circuit 35 γ correction voltage switching circuit VR _{0 to} VR ₈ Reference voltage V _{0 to} V ₂₅₅ Reference reference voltage SW ₀ ~ SW ₇ analog switch

Claims (4)

A plurality of display pixels arranged in a matrix, a reference voltage generation circuit for generating a γ correction reference voltage, and a digital image signal input according to the γ correction reference voltage from the reference voltage generation circuit In a display device including a D / A converter that generates an analog gradation signal that is γ-corrected by A conversion and supplies the analog gradation signal to each display pixel, each of the reference voltage generation circuits has a different γ correction. A plurality of reference voltages generating circuits corresponding to the values are formed to form a reference voltage generating circuit unit, and a plurality of reference voltages for γ correction of the reference voltage generating circuit corresponding to a predetermined γ correction value are simultaneously switched and selected, and the D / A display device provided with a switch means for supplying to the A converter. The display device according to claim 1, wherein the reference voltage generation circuit is obtained by dividing a predetermined reference voltage into a plurality of γ correction voltages by a resistance voltage dividing circuit. 2. A display device according to claim 1, wherein the switch means is an analog switch. At least two reference voltage generation circuits are provided, and a combination of a plurality of γ correction reference voltages generated by each reference voltage generation circuit is at least two selected from a PC mode, a dynamic mode, a TV mode, and a cinema mode. The display device according to claim 1, wherein the display device is one.

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