JP2009025665A - Gamma correction circuit and display control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gamma correction circuit capable of correcting gamma highly precisely without increasing a hardware scale, and to provide a display control circuit. <P>SOLUTION: The display control circuit 1 includes a source driver 1 and an MPU 3, wherein the source driver 2 includes an interface section 11 transmitting and receiving various kinds of data with the MPU 3, a set register 12 setting the first and second reference voltages and a specified gamma correction curve (scenario), a reference voltage generator 13 generating a reference voltage, a grayscale voltage generator 14 generating a plurality of grayscale voltages, and a decoder 15 selecting one voltage in a plurality of grayscale voltages. A grayscale voltage corresponding to the specified scenario is selected by the grayscale voltage generator 14, and the selected grayscale voltage is finely adjusted by changing the first and reference voltages set in the set register 12. Thus, gamma correction conforming with a desired gamma correction curve can be carried out. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a gamma correction circuit and a display control circuit that perform gamma correction in accordance with the characteristics of a display panel.

  The electrical characteristics of liquid crystal panels vary from manufacturer to manufacturer. This is because the physical phenomenon of driving the liquid crystal differs depending on the mode of the liquid crystal (PVA, IPS, OCB, etc.). The luminance characteristic for the gradation of the liquid crystal is defined by standards such as sRGB, ITU709, SMPTE240M, etc., but gamma correction is necessary to realize such a gradation number-luminance characteristic (gamma characteristic: gamma curve). Become. Gamma correction defines the voltage for gradation.

  A DAC using a resistor array is well known as a gamma correction circuit. For example, Patent Document 1 discloses a gamma correction circuit applicable to a wide variety of liquid crystal panels.

  The gradation number-gradation voltage characteristics (gamma correction voltage characteristics: gamma correction curve) vary greatly depending on the type of liquid crystal panel. For this reason, many adjustments such as amplitude adjustment, tilt adjustment, fine adjustment, tap adjustment, and voltage division ratio adjustment are required. This is because the electro-optical characteristics (VT curve: characteristics relating to the voltage V and the light transmittance T) of the liquid crystal are empirically recognized as “substantially S-shaped curves”, but are not quantitatively understood. It is. A value obtained by normalizing the luminance with the maximum luminance is the transmittance T.

  As described above, the adjustment range of the gamma correction voltage is determined empirically, and it is necessary to further expand the adjustment range of the gamma correction voltage in order to deal with a wide variety of liquid crystal panels. This results in an increase in design cost such as hardware scale and adjustment cost.

  On the other hand, as a technique for improving the yield of liquid crystal panels, a technique for correcting a gamma correction curve associated with manufacturing variations of liquid crystal panels has been proposed (see Non-Patent Document 1).

  In this non-patent document 1, the electro-optic characteristic (VT curve) of the liquid crystal is measured for each liquid crystal panel, and the voltage expected for the gradation is inversely calculated by interpolating the measured VT curve with the variation. The technology is disclosed. This technique has the problem that the liquid crystal panel characteristics must be measured each time. In order to improve this problem, Non-Patent Document 1 reduces the number of times of measurement by reducing the number of interpolation samples by inverse calculation, but does not solve the problem of measuring liquid crystal panel characteristics every time. Since the reaction of the liquid crystal takes time, it takes time to measure the liquid crystal panel characteristics, which is a big obstacle in practical use.

From the point of view of nominal design, design is performed with individual measurement data, so statistical variation cannot be clearly recognized and the design cannot be performed. Request adjustment.
JP 2006-146134 A Jaeho Oh, Seung-Woo Lee, Kwan-Young Oh, Taesung Kim, Brian H. Berkeley and Sang Soo Kim. Automatic LCD Gamma Curve Optimization, SID Symposium 2006, P-53, pp. 394-397.

  The present invention provides a gamma correction circuit and a display control circuit that can perform gamma correction with high accuracy without increasing the hardware scale.

  According to one aspect of the present invention, a gamma information setting unit that selects one of a plurality of gamma correction curves having different characteristics and sets a reference standard voltage, and a reference voltage based on the reference standard voltage. Reference voltage generation means for generating, gradation voltage generation means for generating a plurality of gradation voltages based on the reference voltage and the gamma correction curve selected by the gamma information setting means, and the plurality of gradation voltages And a gradation voltage selecting means for selecting a gradation voltage corresponding to the input pixel data.

  According to the present invention, gamma correction can be performed with high accuracy without increasing the hardware scale.

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

  First, the basic concept of this embodiment will be described. It is known that the electro-optical characteristic (VT curve) of the liquid crystal can be expressed by a behavior model such as a TRC curve or an S-shaped curve. Using this operation model, the variation of the liquid crystal is considered.

  First, as an example, an operation model based on TRC (Tone Reproduction Curve) is introduced. This behavior model is an example, and the present embodiment is not limited to this behavior model. Other behavior models (for example, behavior models based on S-curves) may be used, or a plurality of behavior models. May be combined.

The operation model by TRC is expressed by the following equations (1) and (2).
T = 1−EXP [−POWER (v, gamma)] (1)
v = C1 * V + C2 (2)

  Here, T is the light transmittance, V is the voltage applied to the liquid crystal, and gamma, C1, and C2 are parameters that characterize the VT curve of the liquid crystal. v is a virtual voltage, which is obtained by enlarging / reducing the actual physically meaningful applied voltage V as shown in equation (2).

  Here, gamma is a parameter characterizing the liquid crystal characteristics (VT curve), and is a gamma value of the visual characteristic curve (for example, a value such as 2.2 or 1.8: a value indicating gradation vs. luminance characteristics). Note that this is not the case. When writing a gamma value in katakana, it is a gamma as a visual characteristic, and when writing gamma in English, it is a gamma as a VT curve parameter.

  The parameters C1 and C2 specify voltage scaling when converting the actual applied voltage V to the virtual voltage v. The parameter gamma specifies the degree of inclination of the VT curve. EXP is an exponential function, and POWER is a power function.

  Since each liquid crystal panel is characterized by a parameter set <gamma, C1, C2>, considering the characteristics of a wide variety of liquid crystal panels means that there are a plurality of parameter sets <gamma, C1, C2>. Corresponding to For example, <gamma-a, C1a, C2a>, <gamma-b, C1b, C2b>, and so on.

Even with the same type of liquid crystal panel, it is known that the gamma characteristic varies for each liquid crystal panel, and the parameters vary. The variation in this case is a variation in the vicinity of the nominal value (nominal value), and the amount of parameter variation is relatively small compared to the difference in the panel itself. The amount of parameter fluctuation in this case is expressed by the following equations (3) to (5).
gamma = gamma_nominal ± Δgamma (3)
C1 = C1_nominal ± ΔC1 (4)
C2 = C2_nominal ± ΔC2 (5)

  Here, Δgamma, ΔC1, and ΔC2 give 3 sigma for each parameter. “gamma_nominal”, “C1_nominal”, and “C2_nominal” represent nominal values, respectively. In addition, a statistical distribution function may be explicitly taken into account.

  Perturbation with this type of variation parameter gives an isomorphic mapping between VT curves. The advantage of such an approach is that the VT curve can be specified globally, so that the variation variation of the curve can be reduced to a few parameter variations. When considering a curve with an approximation such as a polygonal line approximation, the number of parameters to be handled is large and it is difficult to handle variations: especially the handling of discontinuities in the curve becomes a problem.

  Conventionally, the VT characteristic of the liquid crystal panel is measured for each liquid crystal panel, and the VT characteristic is adjusted based on the measurement result, and statistical processing is not performed.

  In the present embodiment, as a statistical model, variation is reflected in parameters as Δgamma, ΔC1, and ΔC2, and a range related to variation is determined. Since the actual adjustment is performed in a scenario based on a range that has been predicted in advance, it can be performed efficiently.

An operation model based on TRC when a wide viewing angle is considered is expressed by the following equations (6) to (9).
T1 = 1-EXP [-POWER (v1, gamma1)] (6)
v1 = C11 * V1 + C12 (7)
T2 = 1−EXP [−POWER (v2, gamma2)] (7)
v2 = C21 * V2 + C22 (8)
T = m1 * T1 + m2 * T2 (9)

  Here, m1 and m2 are the mixture ratios of the operation models for one domain cell. For example, if the ratio of cell A to cell B is 2: 1, m1 = 2/3 and m2 = 1/3. This behavior model may be further divided into models.

  However, since it is difficult to handle discontinuities when the number of sections is increased, it is preferable that the number of section modeling is as small as possible. If possible, it is desirable to approximate with one curve. There is a trade-off between model and accuracy in this regard.

Here, 256 gradations are considered. In the fitting result with the actual measurement value, an error of 1% at the maximum occurs near the shoulder and skirt of the gamma curve. As a design of nominal value, the trend can be grasped without any problem. In order to further improve the accuracy, it may be possible to partially introduce other motion models, particularly in the low luminance region. Alternatively, as another operation model, there is an S-shaped model represented by the following equation (10).
T = POWER (V, α) / (POWER (V, β) + C) (10)

  Such an S-shaped model may be used. Here, α, β, and C are parameters characterizing the liquid crystal. Table interpolation can also approximate a curve with high accuracy if the number of samples is increased. In this respect, it is not necessary to consider only the above TRC and S-curve as an operation model. However, from the viewpoint that the curve can be grasped globally, the TRC and S-curve parameters are more preferable means.

  FIG. 1 is a flowchart conceptually showing a processing operation performed by the gamma correction circuit according to the present embodiment. First, the statistical distribution of the electrical characteristics (for example, VT curve) of the liquid crystal panel is measured using an electro-optic model (step S1).

  Next, based on the parameters of the electro-optic model, a plurality of candidates (hereinafter referred to as scenarios) representing the electrical characteristics are generated (step S2). In this step S2, for example, a plurality of VT curves are generated as a scenario.

  Next, a gradation voltage characteristic (gamma correction voltage) is calculated for each generated scenario (step S3). Next, based on the calculated gradation voltage characteristics, hardware for driving the liquid crystal panel (gamma correction circuit) is constructed (step S4).

  Next, an optimum scenario is selected for each liquid crystal panel, and hardware for driving the liquid crystal panel is adjusted based on the selected scenario (step S5).

  First, how the variation of the VT curve affects the gamma curve is first confirmed with reference to FIGS. Subsequently, correction of the gamma correction curve will be described with reference to FIGS.

  FIG. 2 is a diagram showing how the gamma curve changes due to variations in the VT curve. 2A is an ideal 2.2 power gamma correction curve, FIG. 2B is a variation in VT curve, and FIG. 2C is a gamma curve affected by the variation in FIG. 2B. Respectively. The variation in FIG. 2B is obtained by changing the parameter gamma that characterizes the VT curve.

  The gamma correction curve is calculated from the center curve (nominal curve) of the VT curve. At this time, since the gamma correction circuit has not been corrected yet, the gamma correction curve remains fixed. FIG. 2C shows a plurality of gamma curves obtained as a result of back calculation from the gamma correction curve and the changed VT curve.

  In summary, the fact that the VT curve varies means that the applied voltage obtained in the process of calculating the applied voltage from the VT curve varies. As a result, the gamma curve of FIG. 2 (c) also varies, and as a result, in FIG. 2 (a), the gamma distributed from the ideal power of 2.2 to the power of 2.1 to 2.4. It becomes a curve.

  The inventor examines a technique for expressing the variation of the gamma correction curve with two parameter pairs <C1, C2> and a parameter gamma. More precisely, as described above, it is characterized by the liquid crystal characteristics (VT curve) by the triplet <gamma, C1, C2>, so the two examinations here are (1) gamma fixed , <C1, C2> are variable (FIGS. 3 and 4), (2) When <C1, C2> is fixed and gamma is variable (FIG. 2), each is considered independently. That's what it means. Therefore, the change of the three parameters can be understood by combining the two cases. In this sense, consider two cases. If another behavior model is used, the same thing can be considered with the parameters that characterize it.

  3A to 3C are diagrams showing the results of changing the values of the parameter pair <C1, C2>. 3A is an ideal 2.2 power gamma correction curve, FIG. 3B is a VT curve obtained by changing the value of the parameter pair <C1, C2>, and FIG. 3C is a gamma changed corresponding to the VT curve shown in FIG. 3B. Each curve is shown (the gamma correction curve is still fixed).

  In the gamma curve of FIG. 3C, the amount of voltage fluctuation is reversely calculated from the VT curve of FIG. 3B. At this time, a voltage shift ΔV (also referred to as a field-through voltage) may be taken into consideration. Here, in order to facilitate understanding, it is simply expressed as “reverse calculation”.

As shown in the following equation (11), the voltage shift ΔV is a change amount ΔVG of the gate voltage VG when the liquid crystal display element is turned on and off, CGD (capacitance C between gate and drain), CLC (Voltage C of liquid crystal cell) and change amount of voltage determined by CS (auxiliary capacitor), and the applied voltage of liquid crystal changes by redistributing charges when the gate changes from on to off To occur.
ΔV = ΔVG * (CGD / (CGD + CLC + CS)) (11)

  There may be a choice that this voltage shift ΔV is not intentionally included in the inverse calculation. When this selection is adopted, the parameter pair <C1, C2> is adjusted by including the voltage shift ΔV in the variation of the liquid crystal panel.

  If gamma correction is performed for each polarity (positive electrode / negative electrode), such asymmetry due to ΔV is considerably reduced. In this sense, it may not be necessary to enter ΔV into the inverse calculation.

  Comparing FIG. 2C and FIG. 3C, by adjusting the parameter pair <C1, C2>, the gamma curve can be made larger than the actual gamma curve variation.

  4A and 4B are diagrams illustrating an example of generating a gamma curve by performing curve approximation based on a plurality of sample points. FIG. 4A shows the relationship between the values of nine types of parameter pairs <C, offset> and gamma values, and FIG. 4B shows the gamma curves corresponding to the nine types of parameter pairs <C, offset>.

  This is a calculated gamma curve on the assumption that the VT curve varies with the gamma correction curve fixed at the center CC = 2.2 gamma value. The gamma value (HH = 1.94 or LL = 2.44) at this time is obtained from the gamma curve using a logarithm-logarithmic graph.

In FIG. 4A, voltage scaling conversion of the VT curve is performed according to the following equation (12).
New voltage = C × voltage + offset (12)

  In FIG. 4A, although not represented by the voltage scale parameter itself for the parameter pair <C1, C2> in TRC, the parameter pair <C1, C2> and <C, offset> are in a linear relationship. The pair <C, offset> can be handled in the same way as the parameter pair <C1, C2>.

  In FIG. 4A, the parameter C takes values of 0.96, 1, and 1.04, and is abbreviated as L, C, and H (L is low, C is center, and H is high). The parameter offset takes values of -0.1, 0, 0.1, and is abbreviated as L, C, H.

  When the parameter pair <C, offset> is abbreviated, C is set first and offset is set after. For example, LC indicates that the parameter C is L and the parameter offset is C. Among such combinations of parameter pairs, the gamma value and the maximum value are 2.45 as a combination of LL. The minimum gamma value is 1.94 for the combination of HH. This is because the parameter C and the parameter offset are set to values of about 2.05 to 2.4, respectively, which is the case of 3 sigma, which is an extreme case.

  As shown in FIG. 4B, the gamma curve corresponding to these nine parameter pairs <C, offset> has a large variation in the central portion.

  The correction of the gamma curve with respect to the variation is to further correct the curve that has not been raised to the 2.2th power, which is an ideal curve, in order to forcibly correct the curve to the 2.2th power curve. . FIG. 5 is a diagram for explaining an example of correcting the deviation of the gamma curve when the parameter pair is LL. In this case, as shown in FIG. 5, correction is performed to reduce the degree of bending of the gamma curve.

  FIG. 6 is a diagram for explaining the cause of the deviation of the gamma curve. 6A is a gamma correction curve indicating gradation-voltage characteristics, FIG. 6B is a plurality of VT curves taking into account variations in liquid crystal characteristics, and FIG. 6C is a VT curve of FIG. 6B. 2 shows a gamma curve indicating gradation-transmittance characteristics due to curve variation. If the gamma correction curve for generating the voltage applied to the liquid crystal is fixed, when the VT curve varies, the gamma curve also varies.

  FIG. 7 is a diagram for explaining a procedure for giving a desirable curve so as not to deviate from the power of 2.2. FIG. 7A is a gamma correction curve showing gradation-voltage characteristics, FIG. 7B is a plurality of VT curves taking into account variations in liquid crystal characteristics, and FIG. 7C is an ideal power of 2.2. 2 shows a gamma curve showing a good gradation-transmittance characteristic.

  First, based on FIG. 7C, the transmittance for a given gradation is obtained. For this transmittance, a plurality of voltages are generated based on the variation of the curve in FIG. Next, the gamma correction curve shown in FIG. 7A is generated by combining these voltages and the initially designated gradation. This is a calculation procedure in the reverse direction to FIG.

  FIG. 8 is a diagram corresponding to FIG. 7A and shows a gamma curve when TRC is used.

The voltage scaling in FIG. 8 is expressed by the following expression (12), and an expression for inversely converting this expression is expressed by the following expression (13).
Voltage = (new voltage−offset) / C (13)

  This equation (13) means that the voltages of all the gradations are naturally adjusted only by forcibly setting the voltages at the upper and lower ends of the DAC using the resistor string. This corresponds to the adjustment in the resistor string that generates the gamma reference voltage. Here, it can be considered that this includes the VCOM adjustment function.

  In FIG. 8, a curve CC is a correction voltage characteristic curve (gamma correction curve) that realizes the target value 2.2 (center gamma value). On the other hand, the other curve is a correction voltage characteristic curve that realizes the target value 2.2 when the liquid crystal panel changes due to VT characteristic fluctuation.

  Here, it is necessary to pay particular attention to the fact that the upper voltage (first reference reference voltage) greatly changes from 4.3029 V (in the case of HH) to 3.7796 V (in the case of LL), and the lower voltage (second The reference reference voltage) is greatly changed from 1.0420 V (in the case of HH) to 0.7696 V (in the case of LL). Regardless of such a large change in the end points (upper voltage, lower voltage), this change is a change caused by voltage scaling. By correcting only the end points, all other points will naturally return to their original center values. It is a great advantage to be able to return to.

  9A to 9C are diagrams illustrating an example in which gamma correction is performed by changing the parameter gamma. FIG. 9A shows variation in VT curve, FIG. 9B shows variation in gradation-transmittance characteristics, and FIG. 9C shows variation in gradation-voltage characteristics (gamma correction curve).

  FIG. 9A shows how the VT curve changes when the parameter gamma varies (the parameter gamma takes values such as 7.4, 7.7, and 8.6). FIG. 9B shows how the tone-transmittance characteristic curve varies between gamma values of 2.0 and 2.4 with the 2.2 power as the center. FIG. 9C shows a result of correcting the gamma curve so that the gamma curve is raised to the power of 2.2. The gamma correction curve in FIG. 9C is much smaller than the variation due to voltage scaling.

  FIG. 10 is an enlarged view of a gamma correction curve having a gradation value near 186. FIG. At the gradation 186, the difference is zero in any gamma correction curve, and this gradation 186 is a fixed point. As the gradation shifts to the end, the difference between each gamma correction curve increases proportionally.

  Actually, since it is approximated using two TRCs in a piecewise dual-TRC, it can be more approximated by two straight lines as described below in FIG.

  FIG. 11 is a diagram showing a gradation-voltage characteristic curve in which the correction voltage when the parameter gamma is changed is normalized by the center value and further corrected. Even if the gradation is forced and proportionally distributed to the voltages near the maximum and minimum (both ends), the deviation of the gradation-voltage characteristic curve is reduced.

  The maximum deviation in voltage in the gradation direction is 4 gradations, and the variation of the parameter gamma can be sufficiently dealt with by resetting the voltages at both ends.

  In the present embodiment, a plurality of gamma correction curves are generated by combining the parameter <C, offset> and the parameter gamma, and some characteristic gamma correction curves are prepared as scenarios. Then, for each of the plurality of scenarios, a voltage value (normalized gamma correction voltage) with respect to the gradation value is registered as a table.

  FIG. 12 is a diagram illustrating an example of five gamma correction curves selected as a scenario from the gamma correction curves obtained by the combination of the parameter <C, offset> and the parameter gamma. Note that the number of gamma correction curves selected as a scenario is not limited to five. GS on the horizontal axis in FIG. 12 represents gradation. CC, H3, H2, H1, and HC indicate gamma correction curves for different scenarios.

  FIG. 13 is a diagram showing an example of a table representing normalized gamma correction voltages corresponding to the respective gradations. The gamma correction voltages in this figure correspond to the gamma correction voltages corresponding to the respective gradations in FIG. A gamma correction circuit to be described later acquires a gamma correction voltage corresponding to the gradation with reference to the table of FIG. 13 and sets the gradation voltage.

  Hereinafter, specific configurations of the gamma correction circuit and the display control circuit according to the present embodiment will be described.

  FIG. 14 is a block diagram showing the internal configuration of the display control circuit incorporating the gamma correction circuit according to the present embodiment. The display control circuit 1 in FIG. 14 includes a source driver 2 and an MPU 3. The source driver 2 supplies an analog pixel voltage to the liquid crystal panel 4. The liquid crystal panel 4 drives a display element (not shown) in synchronization with the analog pixel voltage supplied from the source driver 2 in synchronization with the gate signal from the gate driver 5.

  The source driver 2 includes an interface unit 11 that transmits and receives various data to and from the MPU 3, a setting register (gamma information setting unit) 12 that sets first and second reference reference voltages and a specific gamma correction curve (scenario), A reference voltage generator 13 that generates a reference voltage, a gradation voltage generator 14 that generates a plurality of gradation voltages, and a decoder (gradation voltage selection means) 15 that selects one of the plurality of gradation voltages. And have.

  The MPU 3 selects one of a plurality of scenarios corresponding to a plurality of gamma correction curves, and sends control data for setting the first and second reference reference voltages via the interface unit 11 to the setting register. 12 is supplied. The selected scenario and control data are set in the setting register 12. The first and second reference reference voltages set as initial values in the setting register 12 are the maximum and minimum values of the gamma correction voltage corresponding to the selected scenario. Thereafter, the first and second reference reference voltages set in the setting register 12 are corrected with a predetermined voltage gap. This will be described later.

  FIG. 15 is a block diagram showing an example of the internal configuration of the reference voltage generator 13. The reference voltage generator 13 of FIG. 15 includes a first resistor string (first resistor voltage dividing circuit) 21 composed of a plurality of resistors connected in series, and a plurality of voltages output from the first resistor string 21. A plurality of selectors (first selection circuits) 22 and 23 for selecting one of them, and a plurality of registers 24 and 25 for setting selection information of the selectors 22 and 23, respectively. At least two selectors 22 and 23 are provided, one of which outputs the first reference voltage, and the other outputs the second reference voltage.

  When the gamma characteristics are different for each color of RGB, two selectors 22 and 23 are provided for each color. If the gamma characteristics of each color are the same, a total of two selectors 22 and 23 used in common for each color are provided.

  Even when the selectors 22 and 23 are provided separately for each color, the first resistor string 21 can be shared. This is because the accuracy required as the reference voltage depends on the number of bits of each pixel even when the gamma characteristics of each color are different, and the number of bits is common to each color. Since the first resistor string 21 is a source of the reference voltage, it is hereinafter referred to as “original gamma”. The first resistor row 21 is a series connection of a plurality of unit resistors having the same resistance value.

  The first or second reference reference voltage supplied from the MPU 3 is set in each of the plurality of registers 24 and 25. Each of the selectors 22 and 23 selects one of a plurality of voltages output from the first resistor string 21 based on the first or second reference reference voltage set in the corresponding register 24 or 25. select.

  Although the wiring between the first resistor array 21 and the selectors 22 and 23 may be designed to be fixed, a master slicing method that makes it easy to change the wiring position during manufacturing may be employed. The master slice method is useful when the type of the liquid crystal panel 4 is changed. Even if the type of the liquid crystal panel 4 is changed, the process up to immediately before the first-layer aluminum wiring can be made common, and only this wiring process needs to be changed according to the type of the liquid crystal panel 4, so that the manufacturing cost is reduced. And the time required for the design change can be shortened. Alternatively, a part of the first resistor string 21 may be connected in parallel to extract the voltage in units of 0.5.

  The operation of the reference voltage generator 13 in FIG. 15 will be described with reference to the gamma correction curve in FIG. The power supply voltage VDD = 5V and the common voltage VCOM = 0V. In the case of HH, the maximum voltage is 4.3029V, the minimum voltage is 3.7796V, and the center is 4.00412V.

  As the accuracy of the first resistor string 21, 1/1000 = 5 mV is assumed. At this time, 4.3029V is rounded to 4.305V, 3.7796 is rounded to 3.780V, and the range is 525 mV. Assuming 6 bits = 64 scenarios, 525/64 = 8.2 mV, so 10 mV is a scratch in this case. In other words, 4.300V to 3.780V can be selected with a 10 mV dent (52 level voltage). Thus, 6 bits are sufficient for the registers 24 and 25.

  The wiring between the first resistor string 21 and the selectors 22 and 23 has a voltage of 52 levels, and the selectors 22 and 23 select one from these 52 levels. Assuming the use of the master slice method, 64 levels can be selected, and therefore the selectors 22 and 23 may be prepared assuming 64 wires.

  When the first resistor array 21 is designed with 5 mV accuracy, the selectors 22 and 23 can select a voltage in units of 5 mV, not 10 mV. For example, the selectors 22 and 23 may select a voltage with a 5 mV gap near the center, and further roughen the gap near the maximum / minimum voltage to have 5 bits (32 levels).

  The first and second reference reference voltages set in the registers 24 and 25 are maximum values and minimum values corresponding to the selected scenario as initial values. Thereafter, the first and second reference standard voltages are adjusted so that the gamma correction curve becomes an optimal curve. As a result, the first and second reference voltages output from the selectors 22 and 23 are adjusted with a predetermined voltage (for example, 5 mV or 10 mV).

  If selectors 22 and 23 are provided for each color, selectors 22 and 23 of 6 bits * 3 = 18 bits are required. Two sets of these selectors 22 and 23 are required for generating the first and second reference voltages.

  Note that the above description is merely an example, and it is possible to widen the range of variable scratches around the maximum and minimum voltages, or to vary the scratches. Further, the scratch may be expanded to about 50 mV. The final decision can be made in consideration of the hardware cost.

  FIG. 14 illustrates an example in which five types of scenarios are prepared. However, the number of scenarios is arbitrary, and for example, nine types of scenarios may be prepared as shown in FIG.

  In FIG. 14, the example in which the setting register 12 is provided in the source driver 2 has been described. However, the setting register 12 may be provided separately from the source driver 2. FIG. 16 is a block diagram showing an internal configuration of a first modification of the display control circuit 1. The display control circuit 1 of FIG. 16 includes a setting register 12 separately from the plurality of source drivers 2. The first and second reference reference voltages and the gamma curve set in the setting register 12 are supplied to each source driver 2. The data transfer from the setting register 12 to each source driver 2 may be performed by a dedicated wiring. However, the data may be transmitted using a transmission line that transmits pixel data, for example, during a return period. .

  In the case of the large-screen liquid crystal panel 4, the voltage shift ΔV varies depending on the pixel position. As the VCOM adjustment, a plurality of setting registers 12 may be required including a ΔV adjustment function depending on the screen position. Therefore, whether or not to share the setting register 12 as shown in FIG. 16 may be determined according to the type of the liquid crystal panel 4 to be connected.

  FIG. 17 is a block diagram showing an internal configuration of a second modification of the display control circuit 1. The display control circuit 1 in FIG. 17 does not set the first and second reference reference voltages in the setting register 12a but supplies them from the outside via the dedicated line 26. An advantage of supplying the first and second reference reference voltages directly from the outside is that the user can freely adjust.

  In FIG. 17, the first and second reference reference voltages common to the source drivers 2 are supplied, but separate first and second reference reference voltages may be supplied to the source drivers 2.

  Thus, when the first and second reference reference voltages are directly supplied from the outside, there is a problem that the magnitude of the voltage drop varies due to the resistance component of the dedicated line 26. For this reason, when the influence of variation in voltage drop is large, it is desirable to supply the first and second reference reference voltages separately for each source driver 2.

  When the first and second reference reference voltages are set in the setting register 12 as shown in FIG. 16, the problem of voltage drop does not occur, but the first and second reference reference voltages are within a predetermined range. Can only be set with.

  As a general tendency, FIG. 14 is suitable for driving a small liquid crystal panel 4 such as a mobile phone, and FIGS. 16 and 17 are suitable for driving a large liquid crystal panel 4 such as a liquid crystal television. Yes.

  13 to 17, the example in which the display control circuit 1 such as the source driver 2 is provided separately from the liquid crystal panel 4 has been described. However, the source driver 2 and the like may be formed on the same glass substrate as the liquid crystal panel 4. .

  FIG. 18 is a block diagram showing a schematic configuration of the gradation voltage generator 14 of FIG. As shown in the figure, the gradation voltage generator 14 has a gradation generator 31 for each color. Note that when all the colors have the same gamma characteristics, the same gradation generator 31 may be shared by each color.

  FIG. 18 shows an example in which individual processing circuits are prepared because the characteristics differ depending on RGB. In general, the characteristic change is not only RGB, but also the temperature, polarity (positive electrode / negative electrode), and the impulse accompanying the backlight control. It changes for various reasons such as driving, choice of indoor or outdoor environment. In the present embodiment, such a change is similarly handled. The same applies to these combinations.

  In this embodiment, the gamma characteristic at the positive electrode and the gamma characteristic at the negative electrode are individually adjusted. Conventionally, the gamma characteristics of the positive electrode and the negative electrode were simultaneously handled as VCOM adjustment. In the present embodiment, since the gamma characteristics of the positive electrode and the negative electrode can be individually adjusted, the accuracy can be further improved. In addition, adjustment is easy because of independent control.

  FIG. 19 is a block diagram showing the internal configuration of the gradation generator 31 of FIG. As shown in the figure, the gradation generator 31 selects a second resistor string (second resistor voltage dividing circuit) 32 and a plurality of voltages selected from the plurality of voltages output from the second resistor string 32. Selector (second selection circuit) 33 and a curve register 34 for setting selection information of the selector 33. Each of the three gradation generators 31 shown in FIG. 18 has the same configuration as that of FIG.

  The second resistor string 32 is formed by connecting a plurality of unit resistors having the same resistance value in series. A first reference voltage is applied to one end of the second resistor string 32 and a second resistor is connected to the other end. The reference voltage is applied. The second resistor string 32 is referred to as “post-gamma” because it generates a grayscale voltage as post-processing from a given reference voltage.

  Each of the plurality of selectors 33 receives a plurality of different voltages output from the second resistor row 32, and each selector 33 converts any one of the voltages according to the setting information of the curve register 34 into a gradation. Select as voltage. The number of voltages input from the second resistor string 32 to each selector 33 is equal to the total number of scenarios to be selected. Therefore, each selector 33 selects a voltage corresponding to one scenario from a plurality of scenarios as a gradation voltage.

  Since each of the selectors 33 outputs a separate gradation voltage, 256 selectors 33 are required to generate a gradation voltage of 256 gradations. In the curve register 34, control data for scenario selection is set. This setting information is supplied from the setting register 12 of FIG. The voltage selected by each selector 33 is output as a gradation voltage from the output line.

  The value set in the curve register 34 can be a separate value for each color when the gamma characteristics are different for each color.

  FIG. 20 is a block diagram showing an internal configuration of the selector 33 of FIG. As illustrated, the selector 33 has a plurality of switches 35 therein. These switches 35 are turned on / off by the value of the curve register 34 to switch whether or not to supply the voltage output from the second resistor string 32 to the output line. In the curve register 34, control data 36 indicating whether or not to select each of the five types of scenarios CC, H3, H2, H1, and HC is set.

  Hereinafter, an example of the voltage from the second resistor string 32 input to the selector 33 will be described. The voltage input to the selector 33 is set based on the table of FIG. For example, the gradation GS = 3 will be described as an example. Each unit resistance is numbered with the unit resistance at the top of the second resistor row 32 as 1.

  The values of the five types of scenarios when the gradation GS = 3 are as follows as shown in FIG.

  GS = 3, CC = 33, H3 = 32, H2 = 31, H1 = 30, HC = 30.

  In accordance with these values, the output terminal of the second resistor string 32 and the input terminal of the selector 33 are wired. The switch 35 in the selector 33 switches whether to select the voltage 33 output from the second resistor string 32 and supply it to the output line by the register 23 value CC in the curve register 34. The switch 35 switches whether the voltage 32 output from the second resistor string 32 is selected and supplied to the output line by the register 23 value H3 in the curve register 34. The switch 35 switches whether to select the voltage 31 output from the second resistor string 32 and supply it to the output line by the register 23 value H2 in the curve register 34. Since the values of H1 and HC are the same, the switch 35 switches whether the voltage 30 output from the second resistor string 32 is supplied to the output line by H1 and HC in the curve register 34.

  Here, it is conceivable that the selector 33 is arranged immediately after the second resistor string 32 or just before the decoder 15. When the selector 33 is disposed immediately before the decoder 15, the output line of the second resistor string 32 must be routed until just before the decoder 15, which increases the amount of wiring.

  In general, the voltage level to be referenced is 2 bits more than the number of gradations. For this reason, even if the output of the second resistor string 32 can be shared with the input related to the adjacent gradation, the number of outputs of the second resistor string 32 is very large. For this reason, it is not desirable to arrange the selector 33 immediately before the decoder 15.

  On the other hand, if the selector 33 is arranged immediately after the second resistor row 32, only the output line of the selector 33 needs to be routed to the decoder 15, so that the number of wirings to be routed can be reduced.

  In this embodiment, the electro-optical characteristics of a liquid crystal panel 4 are statistically grasped, and gamma correction is performed assuming voltage scaling and gamma parameter distribution. Since the voltage extraction from the second resistor array 32 used for the post-gamma processing is based on the assumption of one gamma parameter, it is not a general voltage extraction.

  If another liquid crystal panel 4 is used, a new voltage extraction is determined through the same design procedure. However, only the wiring between the second resistor string 32 and the selector 33 may be changed using the same hardware configuration. In order to make hardware common, it is desirable to provide an extra number of unit resistors constituting the second resistor row 32. As a result, it is possible to deal with a plurality of types of liquid crystal panels 4 by changing only the wiring between the second resistor row 32 and the selector 33.

  As described above, the reference voltage generator 13 in the gamma correction circuit of FIG. 14 generates the first and second reference voltages based on the first and second reference reference voltages set in the setting register 12. Then, the gradation voltage generator 14 selects the voltage output from the second resistor string 32 with the selector 33 in a state where the first and second reference voltages are applied to both ends of the second resistor string 32. Thus, a gradation voltage is generated. The selector 33 selects a voltage based on the scenario information set in the setting register 12. The gradation voltage generator 14 selects a gradation voltage corresponding to a specific scenario, and changes the first and second reference reference voltages set in the setting register 12 for fine adjustment of the selected gradation voltage. To do. Thereby, gamma correction matching a desired gamma correction curve can be performed.

  The initial values of the first and second reference reference voltages set in the setting register 12 are values corresponding to the gamma correction curves (scenarios) set in the setting register 12. Based on the gamma correction curve set in the setting register 12, the gradation voltage generator 14 generates a gradation voltage to check whether the gamma correction curve is a desired curve. The gradation voltage is finely adjusted by changing the first and second reference reference voltages in the setting register 12. Thereby, a desired gamma correction curve is obtained.

  In this embodiment, when performing gamma correction according to the individual liquid crystal panel 4, only the wiring between the second resistor array 32 and the selector 33 may be changed in a master slice manner. There is no need to change itself. In this way, considering the master slice, the selector 33 does not need to be particular about 256 gradation outputs, and may be prepared in excess. By preparing extra, it is possible to employ a selector 33 close to a voltage node serving as a post-gamma extraction port corresponding to the increased resistance.

  FIG. 21 is a block diagram showing an internal configuration of a modified example of the gradation voltage generator 14. In FIG. 18, the gradation generator 31 is provided separately for each RGB, but in FIG. 21, the gradation generator 31 is used in common for all colors. The gradation generator 31 in FIG. 21 generates a gradation voltage unique to each color by time division.

  FIG. 22 is a block diagram showing a detailed configuration of the gradation generator 31 of FIG. The gradation generator 31 of FIG. 22 includes a second resistor string 32, a plurality of selector units 37 for selecting one from among a plurality of voltages output from the second resistor string 32, and a first A switch 38 for switching between the first and second reference voltages is provided.

  Each selector unit 37 has three selectors 33 for selecting gradation voltages for each color, and a curve R register 23, a curve G register 23, and a curve B register 23 for setting selection information of these selectors 33.

  These three selectors 33 sequentially select voltages in a time division within one horizontal period, and supply them to the output line as gradation voltages. As a result, the gradation voltage unique to each color can be generated with only one gradation generator 31.

  The output lines do not need to be provided for each color, and the gradation voltages of the respective colors may be supplied to the common output line in a time division manner. In this case, serial / parallel conversion processing for separating time-division gradation voltages is required immediately before the decoder 15.

  Next, a method for selecting a scenario for gamma correction for each individual liquid crystal panel 4 will be described. Information (scenario information) related to the scenario selected by the following method is set in the setting register 12 of FIG.

  It is a natural idea to extract the parameters of the operation model such as TRC and select the closest parameter combination for each liquid crystal panel 4. However, it is also possible to select one from a plurality of scenarios without determining parameters one by one. Although it does not deny parameter determination every time, a simpler and more efficient method is desirable.

  Therefore, hereinafter, a method for easily detecting an optimum scenario from a plurality of assumed scenarios will be described. A scenario closest to the actual characteristics of the liquid crystal panel 4 is searched from a plurality of assumed scenarios. Searching for parameters that characterize these curves from the scenarios related to voltage scaling and parameter gamma is the content of the scenario search.

  23A to 23F are diagrams for explaining a method of searching for the nine types of scenarios in FIG. FIG. 23A to FIG. 23F show how the tone transmittance characteristics (gamma curve) are obtained with respect to the parameter pair <C, offset> relating to voltage scaling. FIG. 23A, FIG. 23B, and FIG. 23C show the cases of <C, *>, <H, *>, <L, *>. The value * means that one of H (High), C (Center), and L (Low) is taken. Similarly, FIGS. 23D, 23E, and 23F show <*, C>, <*, H>, <*, L>.

  First, it can be seen from FIGS. 23A to 23F that the influence of the parameter C is large. Finding the best-fitting scenario from these curves is the challenge here.

  It is possible to check everything in order and select the scenario with the smallest error, but it takes time. Therefore, here, the transmittance in each scenario is first summarized as a table, and this is used as a scenario search candidate. Choose the best from this candidate.

  FIG. 24 is a diagram showing a table in which the transmittance of each scenario for a specific gradation value is summarized for three gradations of 64 gradations, 128 gradations, and 192 gradations. In FIG. 24, three types of gradations are shown, but the number of gradations can be appropriately increased or decreased. Although one gradation may be sufficient in essence, a method of calculating a plurality of values and selecting a candidate from the plurality is used here just in case.

  FIG. 24 shows the transmittance for the gradation 128, and the value of the transmittance is larger in the first scenario. Similar results are obtained for gradation 64 and gradation 192.

  FIG. 25 is a flowchart showing a scenario selection processing procedure. First, a table as shown in FIG. 24 showing the correspondence between gradation and transmittance for several gradation values is created (step S11).

  Next, the transmittance is actually measured (step S12). The transmittance is a value normalized to 1, and the maximum light amount needs to be measured as gradation 255 (or gradation 0) according to normally black or normally white. In addition, the amount of light is similarly measured for the gradation 128, and the normalized transmittance is obtained.

  Next, scenario candidates are selected using the table of FIG. 24 (step S13). For example, when the measured transmittance is 0.225, the CC and LH scenarios are close, so these are candidates. There is no particular limitation on the number of scenarios to be selected as candidates. For example, a plurality may be selected based on a certain range.

  For example, if the difference is within 0.03, the range is 0.195 to 0.0255, and HL can be included in the candidates. Here, the description will be continued with CC and LH as candidates.

Next, an error is calculated (step S14). The transmittance is also measured for gradation 64 and gradation 192. For example, it is assumed that 64 gradation is 0.048 and 192 gradation is 0.550. The error in this case is, for example, the sum of squared differences.
E1 = Error E (64 gradations, CC) = (0.048−0.0478) ² = 4 * 10 ⁻⁸
E2 = Error E (64 gradations, LH) = (0.048−0.0492) ² = 1.4 * 10 ⁻⁶
E3 = Error E (128 gradations, CC) = (0.225−0.2195) ² = 3.0 * 10 ⁻⁵
E4 = Error E (128 gradations, LH) = (0.225−0.2388) ² = 1.9 * 10 ⁻⁴
E5 = Error E (192 gradations, CC) = (0.550−0.5336) ² = 2.7 * 10 ⁻⁴
E6 = Error E (192 gradations, LH) = (0.550−0.5820) ² = 1.0 * 10 ⁻³
Therefore, the error is E (CC) = 2 * 10 ⁻⁸ + 3 * 10 ⁻⁵ + 2.7 * 10 ⁻⁴
E (LH) = 1.4 * 10 ⁻⁶ + 1.9 * 10 ⁻⁴ + 1.0 * 10 ⁻³
It becomes.

  Next, the smaller scenario is selected from the calculated errors (step S15). In this case, since E (CC) <E (LH), the scenario CC is selected.

  When the scenario is determined by the procedure of FIG. 25, the setting register 12 and the curve register 34 are set accordingly.

  Here, the number of scenarios is reduced to simplify the explanation, but in reality, by increasing the number of scenarios, errors can be reduced and an optimal scenario can be selected. If the idea is to put the gamma curve within the allowable range, it is sufficient to enter the target range even if there are some errors, rather than accurately reducing the error. (For example, it enters 2.2 ± 0.1 as the gamma value). For such a request, it is desirable to cover the assumed scenarios at the same interval with as few as possible without increasing the number of scenarios unnecessarily.

  The advantages of performing such a scenario selection will be described. In order to measure electro-optical characteristics for each liquid crystal panel 4, a sufficient number of sample points are required. For example, it is necessary to provide sample points mainly in the black portion, and about 20 samples are required only in the black portion. It is necessary to perform measurement at such sample points for each liquid crystal panel 4.

  In the present embodiment, in order to measure the statistical properties of the electro-optical characteristics in advance, for example, 40 liquid crystal panels 4 are preliminarily measured, and the statistical distribution as a parameter of the operation model is grasped. Therefore, 20 samples are required for this pre-processing. However, once the statistical distribution is known, the liquid crystal panel 4 can be adjusted while covering the entire range in a scenario using the statistical distribution. In this adjustment, sample points are 4 (64 gradations, 128 gradations, 192 gradations, 255 gradations), for example, and can be reduced to 1/5. Regarding the manufacture of the liquid crystal panel 4, the adjustment time of the liquid crystal panel 4 is overwhelmingly long, and it can be seen that this effect is great even if it takes time for advance preparation (ascertaining statistical variation).

  Also, the effort for adjusting the curve is short. Conventionally, fitting was performed by individually adjusting individual adjustment functions of amplitude adjustment, inclination adjustment, fine adjustment, tap adjustment, and partial pressure ratio adjustment. In this case, since the curve moves by performing some adjustment, a trial-and-error-like search is necessary until all wrinkles occur, and the adjustment time tends to be long.

  In this embodiment, after all the possibilities are enumerated as scenarios, candidates are then selected and selected, so that no backtracking such as trial and error is performed. Since the statistical variation range is pre-analyzed, it can always be within the range.

  Furthermore, in the present embodiment, since a high-precision liquid crystal electro-optical operation model using the parameter <C, offset> and the parameter gamma is used, the post-gamma can be realized by the selector 33 in a LUT rather than a linear approximation. Gamma correction can be performed smoothly.

  In the above description, a method for preparing a scenario and selecting it from the scenario has been described as an optimal scenario selection method. However, there are other methods. In this method, flicker levels are measured for three scenarios, and voltage scaling parameters for an optimum scenario are predicted from the results.

  There are many scenarios with a set of first and second reference reference voltages. For example, the first reference reference voltage is adjusted within a range of ± 300 mV with a 10 mV dent, and the second reference reference voltage is adjusted within a range of ± 150 mV within a 10 mV dent.

  This is a combination of 6 bits for the first reference reference voltage selection and 5 bits for the second reference reference voltage selection. If this combination is simply performed, 6 + 5 = 11 bits, that is, 2048 combinations. This is a big number. If there is so much, it takes time to measure in each scenario, which is a problem. In order to solve this problem, the following method can be considered.

  FIG. 26 is a flowchart showing a processing procedure for selecting a scenario based on the flicker level measurement result. This processing procedure uses the reference voltage generator 13 more actively as a VCOM adjustment function.

  First, the first reference standard voltage is set to the maximum, the second reference standard voltage is set to the minimum (step S21), and the second reference standard voltage is fixed.

  Next, three scenario options are prepared for the first reference reference voltage, and the respective flicker levels are measured (step S22). Next, an optimal first reference reference voltage scenario is predicted from the three flicker levels thus measured (step S23). With respect to the predicted scenario, the flicker level is measured and it is determined whether or not it is smaller than the allowable threshold (step S24).

  If the flicker level is smaller than the allowable threshold, the scenario is adopted and the process ends. If the flicker level is equal to or greater than the allowable threshold, three scenario options are prepared for the second reference reference voltage, and the respective flicker levels are measured (step S25).

  Next, the first reference reference voltage determined in step S23 is fixed, three types of second reference reference voltage scenarios are prepared, and flicker levels are measured for them (step S26). Next, it is determined whether or not the measured flicker level is smaller than an allowable threshold (step S27). If the flicker level is smaller than the allowable threshold, this scenario is terminated as an optimal scenario. Otherwise, the process returns to step S22 and a similar search is performed. The above is an outline.

  To search for the optimum scenario, it is necessary to narrow down the range where the scenario exists. Therefore, in order to handle the scenario range, three combinations of <UL, UC, UH> with respect to the first reference reference voltage and <LL, LC, LH> with respect to the second reference reference voltage are considered. UL represents the lower limit of the first reference standard voltage, UC represents the center of the first reference standard voltage, and UU represents the upper limit of the first reference standard voltage. Similarly, LL is the lower limit of the second reference standard voltage, LC is the center of the second reference standard voltage, and LU is the upper limit of the second reference standard voltage.

  First, the first reference reference voltage given by 6 bits is VU1, VU2,..., VU64 from the top, and the second reference reference voltage given by 5 bits is VL1, VL2,. The purpose is to find one optimal combination of VU and VL.

  In step S21 described above, UL ← VU64, UC ← VU32, and UH ← VU1 are set. In addition, LL ← VL32, LC ← VL16, and LU ← VL1 are set. In the next step S22, first, the second reference reference voltage is premised on the median value of LC = VL16, and the set <UL, UC, UH> = <VU64, VU32, VU1> <UL , LC> = <VU64, VL16>, <UC, LC> = <VU32, VL16>, <UH, LC> = <VU1, VL16>.

  In the next step S23, for example, it is assumed that VU40 is predicted. Since the scenario range is halved, a range of 64 → 32 is considered and ± 16 is considered. That is, <UL, UC, UH> ← <VU24, VU40, VU56>. Of course, the range should be within the range from VU1 to VU64.

  In the next step S24, determination is made with respect to the center <VU40, VL16>. The explanation of step S25 is continued assuming that it is larger than the allowable threshold. Here, the second reference reference voltage is examined. <LL, LC, LH> = <VL32, VL16, VL1>, and the first reference reference voltage is combined with the central VU40. Therefore, the following three scenarios are considered: <UC, LL> = <VU40, VL32>, <UC, LC> = <VU40, VL16>, <UC, LH> = <VU40, VL1>.

  In step S25, for example, assume that VL10 is predicted to be optimal. Reduce the range from 32 to 16 to ± 8. Therefore, LL ← VL18, LC ← VL10, and LH ← VL2. In step 212, determination is made regarding <VU40, VL10>. Thereafter, the same is repeated.

  Here, it supplements about the specific method of scenario prediction in step S23 and step S26. The flicker level can be approximated as a graph expressed by a quadratic expression that is substantially symmetrical about the optimum level. Therefore, if there are 3 points of samples, the coefficient of this quadratic equation can be uniquely determined. From this determined coefficient, the voltage that minimizes the quadratic expression can be calculated backward.

  Here, the scenario range is narrowed in half in steps S23 and S26. Since the first setting is the first reference standard voltage 6 bits and the second reference standard voltage 5 bits, it can be seen that the range is narrowed by repeating at least 6 times, so that it always converges. That is, a maximum of 3 scenarios * (6 + 5) = 33 measurements are required. Actually, since the accuracy of prediction by the quadratic equation is good, there is a high possibility that sufficient accuracy is obtained after several iterations. Speaking of the statistical distribution, most of the distributions are center values, and the frequency of end values is extremely low.

  In FIG. 25 and FIG. 26 described above, the scenario in the case of voltage scaling has been described as an example. However, the parameter gamma can be similarly considered. In fact, in the processing procedure of FIG. 25, it is only necessary to construct a scenario with three parameters of voltage scaling and gamma, so the algorithm itself is not changed. In general, from the viewpoint of search technology, it can be easily predicted that more effective methods can be used than the simple search method here. In the processing procedure of FIG. 26, the same processing can be considered for the three scenarios for the parameter gamma by considering the range of the parameter gamma next to the first reference standard voltage and the second reference standard voltage.

  Considering that it corresponds to the function of VCOM adjustment, there is no need to add an adjustment circuit such as DVR as an external linear IC on the PCB, so there is an effect of reducing the number of parts. This is an effect of reducing hardware costs.

6 is a flowchart conceptually showing a processing operation performed by the gamma correction circuit according to the present embodiment. (A)-(c) is a figure which shows a mode that a gamma curve changes with the dispersion | variation in VT curve. The figure which shows the ideal gamma curve of the power of 2.2. The figure which shows the VT curve which fluctuated the value of parameter pair <C1, C2>. The figure which shows the gamma curve which changes corresponding to the VT curve of FIG. 3B. The figure which shows the relationship between the value of nine types of parameter pairs <C, offset> and a gamma value. The figure which shows the gamma curve corresponding to nine types of parameter pairs <C, offset>. The figure explaining the example which correct | amends the shift | offset | difference of the gamma curve when a parameter pair is LL. (A) is a gamma correction curve indicating gradation-voltage characteristics, FIG. 6 (b) is a plurality of VT curves taking into account variations in liquid crystal characteristics, and FIG. 6 (c) is a VT curve of FIG. 6 (b). The figure which shows the gamma curve which shows the gradation-transmittance characteristic by dispersion | variation. (A) is a diagram showing a gamma correction curve indicating gradation-voltage characteristics, (b) is a diagram showing a plurality of VT curves taking into account variations in liquid crystal characteristics, and (c) is an ideal power of 2.2. The figure which shows the gamma curve which shows a favorable gradation-transmittance | permeability characteristic. It is a figure corresponding to Fig.7 (a), and is a figure which shows a gamma curve at the time of using TRC. The figure which shows the dispersion | variation in a VT curve. The figure which shows the dispersion | variation in a gradation-transmittance characteristic (gamma curve). The figure which shows the dispersion | variation in a gradation-voltage characteristic (gamma correction curve). The figure which expanded the gamma correction curve whose gradation value is 186 vicinity. The figure which shows the gradation-voltage characteristic (gamma correction curve) which correct | amended further by correcting the correction voltage at the time of changing parameter gamma with a center value. The figure which shows an example of five types of gamma correction curves selected as a scenario from the gamma correction curve obtained by the combination of parameter <C, offset> and parameter gamma. The figure which shows an example of the table showing the normalized gamma correction voltage corresponding to each gradation. FIG. 3 is a block diagram showing an internal configuration of a display control circuit incorporating a gamma correction circuit according to the present embodiment. FIG. 3 is a block diagram illustrating an example of an internal configuration of a reference voltage generator 13. The block diagram which shows the internal structure of the 1st modification of the display control circuit 1. FIG. The block diagram which shows the internal structure of the 2nd modification of the display control circuit 1. FIG. The block diagram which shows schematic structure of the gradation voltage generator 14 of FIG. FIG. 19 is a block diagram showing an internal configuration of the gradation generator 31 of FIG. The block diagram which shows the internal structure of the selector 33 of FIG. The block diagram which shows the internal structure of the modification of the gradation voltage generator. The block diagram which shows the detailed structure of the gradation generator 31 of FIG. The figure which shows the mode of the change about what gradation transmittance | permeability characteristic (gamma curve) is obtained regarding parameter pair <C, offset> regarding voltage scaling. The figure which shows the mode of the change what kind of gradation transmittance characteristic is obtained regarding parameter pair <C, offset> regarding voltage scaling. The figure which shows the mode of the change what kind of gradation transmittance characteristic is obtained regarding parameter pair <C, offset> regarding voltage scaling. The figure which shows the mode of the change what kind of gradation transmittance characteristic is obtained regarding parameter pair <C, offset> regarding voltage scaling. The figure which shows the mode of the change what kind of gradation transmittance characteristic is obtained regarding parameter pair <C, offset> regarding voltage scaling. The figure which shows the mode of the change what kind of gradation transmittance characteristic is obtained regarding parameter pair <C, offset> regarding voltage scaling. The figure which shows the table | surface which put together the transmittance | permeability of each scenario about a certain specific gradation value regarding three of 64 gradations, 128 gradations, and 192 gradations. The flowchart which shows the process sequence of scenario selection. The flowchart which shows the process sequence which selects a scenario based on the measurement result of a flicker level.

Explanation of symbols

1 Display control circuit 2 Source driver 3 MPU
4 Liquid Crystal Panel 11 Interface Unit 12 Setting Register 13 Reference Voltage Generator 14 Gradation Voltage Generator 15 Decoder 21 First Resistor Row 22, 23 Selector 24, 25 Register 31 Gradation Generator 32 Second Resistor Row 33 Selector 34 Curve register

Claims (5)

Gamma information setting means for selecting one of a plurality of gamma correction curves having different characteristics and setting a reference standard voltage;
Reference voltage generating means for generating a reference voltage based on the reference standard voltage;
Gradation voltage generating means for generating a plurality of gradation voltages based on the reference voltage and the gamma correction curve selected by the gamma information setting means;
A gamma correction circuit, comprising: a gradation voltage selection unit that selects a gradation voltage corresponding to input pixel data from the plurality of gradation voltages. The gradation voltage selection means is provided in each pixel,
The gamma correction circuit according to claim 1, wherein the gamma information setting unit, the reference voltage generation unit, and the gradation voltage generation unit are shared by a plurality of pixels. The gamma information setting means sets two types of reference standard voltages having different voltage levels,
The reference voltage generation means includes
A first resistance voltage dividing circuit having a plurality of resistors connected in series to generate a plurality of reference voltages by resistance voltage division;
3. The gamma according to claim 1, further comprising: a first selection circuit that selects two types of reference voltages corresponding to the two types of reference reference voltages from among the plurality of reference voltages. Correction circuit. The reference voltage generation means outputs two types of reference voltages having different voltage levels,
The gradation voltage generating means includes
A second resistance voltage dividing circuit having a plurality of resistors connected in series to generate a plurality of reference voltages by resistance-dividing the two types of reference voltages;
A second selection circuit for selecting a plurality of gradation voltages from the plurality of reference voltages output from the second resistance voltage dividing circuit based on the gamma correction curve selected by the gamma information setting means. The gamma correction circuit according to claim 1, further comprising: A gamma correction circuit that generates gradation voltages according to pixel data in accordance with the characteristics of a specific gamma correction curve;
Gamma information supply means for supplying information related to the specific gamma correction curve to the gamma correction circuit,
The gamma correction circuit is
Gamma information setting means for selecting one of a plurality of gamma correction curves having different characteristics and setting a reference standard voltage;
Reference voltage generating means for generating a reference voltage based on the reference standard voltage;
Gradation voltage generating means for generating a plurality of gradation voltages based on the reference voltage and the gamma correction curve selected by the gamma information setting means;
A display control circuit, comprising: gradation voltage selection means for selecting a gradation voltage corresponding to input pixel data from the plurality of gradation voltages.

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