JP2009008958A - Liquid crystal display drive circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display drive circuit, capable of attaining simplification and reduction in power consumption of the circuit while allowing a wide gamma adjustment range. <P>SOLUTION: A gray scale voltage to be input to a decode circuit which selects and transmits the gray scale voltage according to display data to a liquid crystal display panel is formed in a voltage-dividing resistance circuit. A predetermined voltage adjusted to a predetermined value is transferred to a tap of the partial pressure resistant circuit so that the gray scale to the gradation voltage at an intermediate part of gamma characteristics including a pole part of a substantially S-shaped curve can be adjusted. The circuit includes a differential circuit part inputting the predetermined voltage and a plurality of output circuit parts having output terminals connected to a plurality of taps. An output signal of the differential circuit part is transmitted to an input of one output circuit part corresponding to the tap selected in conformation to the predetermined value through a first switch, the output signal is transmitted to a feedback input of the differential circuit part with a second switch being in ON state to form a voltage follower structure, and the predetermined voltage is transmitted to the predetermined tap. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display driving circuit that outputs a gradation voltage corresponding to display data indicating gradation to a TFT liquid crystal display panel in which a plurality of pixels are arranged, and more particularly to a liquid crystal display driving circuit capable of adjusting gamma characteristics. It is related to effective technology.

The applicant of the present application has previously proposed a drive device for a display device having gamma characteristic adjusting means inside a drive circuit in Japanese Patent Laid-Open No. 2006-146134. In an active matrix liquid crystal display device in which display luminance is controlled by gradation voltage, in order to perform accurate color reproduction, it is necessary to adjust display luminance characteristics with respect to gradation data, so-called gamma (γ) characteristics. In this display device drive device, as shown in FIG. 12, by dividing the reference voltage 107 by resistors 111 to 116, a plurality of gradation voltages corresponding to a plurality of gradations are generated. The plurality of gradation voltages are basically selected by the decoder circuit 106 according to display data. An amplitude adjustment register 103 for adjusting the division point or division ratio of the reference voltage is provided to adjust the amplitude of the gamma characteristic that defines the relationship between the gradation and the gradation voltage or the luminance in the display panel. In order to fix the end of the gamma characteristic and adjust the slope of the middle part of the gamma characteristic, a slope adjustment register 104 for adjusting the division point or division ratio of the reference voltage is provided. In order to finely adjust the intermediate portion of the gamma characteristic for each gradation, a fine adjustment register 105 for adjusting the division point or division ratio of the reference voltage is provided. In order to adjust the gradation with respect to the gradation voltage in the intermediate portion near the end of the gamma characteristic, a tap adjustment register 101 for adjusting the division point or division ratio of the reference voltage is provided. In order to adjust the ratio of gradation voltages between a plurality of gradations in an intermediate portion near the end of the gamma characteristic, a voltage division ratio adjustment register 102 for adjusting the division point or division ratio of the reference voltage is provided.
JP 2002-366112 A

  In the display device driving device disclosed in Patent Document 1, the switch elements constituting tap selectors (TAPSEL) 161 and 162 that are switch-controlled by the tap adjustment register 101 are inserted in series in the gradation voltage transmission path. Will be. When such a switch element is inserted, as shown in the equivalent circuit diagram of FIG. 13, the output voltage of the voltage follower circuit A 2 that receives the gradation voltage Vn provided in the amplifier circuit 141 is supplied to the tap selector 161. The signal is transmitted to the liquid crystal display panel through the on-resistance R1, the resistor R2 corresponding to the resistor 153 that forms the output gradation voltage, and the on-resistance R3 of the switch element constituting the decoding circuit 106, and is turned on by the scanning line selection operation. The data is written into the capacitor CPX constituting the pixel through the TFT transistor QS.

  The gradation voltage Vn must be written into the capacitor CPX constituting the pixel within a predetermined time. For example, in a relatively small liquid crystal display panel including a liquid crystal display panel for a mobile phone, the frame frequency is determined to be about 60 Hz. Since the number of scanning lines) increases, the time is shortened, and it is necessary to provide a buffer amplifier BA in the middle as shown in FIG. The tap selectors 161 and 162 are each composed of a total of 8 switches, 4 each in 2 locations corresponding to the gamma correction unit, and therefore it is sufficient to add 8 buffer amplifiers BA at the minimum. However, the balance with other gradation voltages not provided with the buffer amplifier BA becomes worse. Actually, the buffer amplifier BA is provided on the input side of the decoding circuit. If 64 gradation display is performed, 64 buffer amplifiers BA are provided, which may cause a problem that the circuit scale and current consumption increase. found.

  An object of the present invention is to provide a liquid crystal display driving circuit that realizes simplification of the circuit and low power consumption while enabling a wide gamma adjustment range. The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  One embodiment disclosed in the present application is as follows. A decoding circuit that selects a gradation voltage corresponding to the display data transmitted from the plurality of gradation voltages to the liquid crystal display panel; The gradation voltage input to the decoding circuit is formed by a voltage dividing resistor circuit. The voltage transmission circuit transmits a predetermined voltage adjusted by a predetermined value to the tap of the voltage dividing resistor circuit, and can adjust the gradation with respect to the gradation voltage in the intermediate portion of the gamma characteristic including the extreme point portion of the substantially S-shaped curve. And As this voltage transmission circuit, there are provided a differential circuit section that receives the predetermined voltage and a plurality of output circuit sections having output terminals connected to a plurality of taps. The input terminals of the plurality of output circuit units and the output terminals of the differential circuit unit are connected by a plurality of first switches. The output terminal of the output circuit unit and the feedback input terminal of the differential circuit unit are connected by a plurality of second switches. One of the first switch and the second switch corresponding to the tap selected corresponding to the predetermined value is turned on, and the differential circuit unit and the one output circuit unit are configured as a voltage follower configuration. Tell the tap.

  Since the resistance component of the switch that selects the tap for gamma adjustment is not included in the gradation voltage transmission path, the buffer in the preceding stage of the decoding circuit that selects the gradation voltage corresponding to the display data transmitted to the liquid crystal display panel An amplifier is unnecessary.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted. In the following embodiments, a liquid crystal display panel that displays an image by a normally black method will be described as an example of a display device using the liquid crystal display driving circuit of the present invention. However, by changing the pixel structure, Needless to say, the present invention can also be applied to a liquid crystal display device that displays an image in a white system.

  FIG. 3 is a block diagram showing an embodiment of the liquid crystal display driving circuit according to the present invention. Each circuit element in the figure is formed on one semiconductor substrate by a known semiconductor integrated circuit manufacturing technique. The liquid crystal display driving circuit path of this embodiment has a gradation voltage generation circuit 100 for generating a plurality of gradation voltages corresponding to a plurality of gradations by dividing the reference voltage 107. In order to adjust the gradation with respect to the gradation voltage in the intermediate portion near the end of the gamma characteristic, a tap adjustment register 101 for setting a value for adjusting the division point or division ratio of the reference voltage 107 is provided. A voltage dividing ratio for setting a division point or a value for adjusting the division ratio of the reference voltage 107 in order to adjust the ratio of gradation voltages between a plurality of gradations in an intermediate portion near the end of the gamma characteristic An adjustment register 102 is provided. In order to adjust the amplitude of the gamma characteristic, an amplitude adjustment register 103 for setting a value for adjusting the division point or the division ratio of the reference voltage 107 is provided. In order to adjust the slope of the intermediate portion of the gamma characteristic while fixing the end of the gamma characteristic, a slope adjustment register 104 for setting a value for adjusting the division point or division ratio of the reference voltage 107 is provided. In order to finely adjust the intermediate portion of the gamma characteristic for each gradation, a fine adjustment register 105 for setting a value for adjusting the division point or division ratio of the reference voltage 107 is provided. A decoding circuit 106 is provided for selecting a gradation voltage corresponding to display data from a plurality of gradation voltages.

  The gradation voltage generation circuit 100 includes the following circuits. A first ladder resistor composed of resistors 111 to 116 connected between the connection end of the reference voltage 107 and the connection end of the ground (GND) 108 is provided. The variable resistors 121 and 122 connected in series with the first ladder resistor on the connection end side of the reference voltage 107 or the connection end side of the ground 108 with respect to the first ladder resistor, and the first resistor at the intermediate portion of the first ladder resistor. There are provided variable resistors 123 and 124 connected in series with one ladder resistor. Selectors (SEL) 131 to 136 for selecting an output from the first ladder resistor are provided. Corresponding to the selectors 131 to 136, an amplifier circuit 141 composed of an amplifier connected to the output side of this selector is provided. A second ladder resistor composed of resistors 151 to 155 connected between a plurality of inputs of the decode circuit 106 is provided. Tap selectors (TAPSEL) 161 and 162 for selecting the input of the decoding circuit 106 and connecting the output from the amplifier circuit 141 to the input are provided. Variable resistors 171 and 172 connected in series with the second ladder resistor are provided between the second ladder resistor and the input of the decoding circuit 106. The decoding circuit 106 is a circuit that decodes a gradation voltage corresponding to display data from the gradation voltage generated by the gradation voltage generation circuit 100.

  A tap adjustment register 101, a voltage division ratio adjustment register 102, an amplitude adjustment register 103, a slope adjustment register 104, and a fine adjustment register 105 are provided outside the gradation voltage generation circuit 100. In this embodiment, the tap adjustment register 101 and the voltage division ratio adjustment register 102 store setting values for adjusting the tap selectors 161 and 162 and the variable resistors 171 and 172 of the gradation voltage generation circuit 100, respectively. is there. The amplitude adjustment register 103 stores a register value for adjusting the resistance values of the variable resistors 121 and 122. The inclination adjustment register 104 stores a register value for adjusting the resistance values of the variable resistors 123 and 124. The fine adjustment register 105 stores a register value for adjusting the selectors 131 to 136 for selecting a voltage level when the resistors 111 to 116 are divided.

  The operation of the gradation voltage generator 100 in the present embodiment is as follows. The reference voltage 107 input from the outside is resistance-divided by a first ladder resistor composed of resistors 111 to 116 with respect to the ground (GND) 108, and a desired gradation voltage is changed to variable resistors 121 to 124, It is generated by the setting of selectors 131-136. In the present embodiment, eight voltage levels V1 to V8 are generated by the configuration described above. Hereinafter, the generated voltage level is referred to as reference voltages V1 to V8 from the high voltage side. Here, the reference voltages V1 to V8 can be controlled by amplitude adjustment, inclination adjustment, and fine adjustment functions. Among the reference voltages V1 to V8, the reference voltages V1 and V8 (tap voltages 181 and 188) are output to the decoding circuit 106 as they are.

  The reference voltages V2 to V7 are buffered by the amplifiers A1 to A6 that perform the voltage follower operation of the amplifier circuit 141. Hereinafter, the reference voltages V2 to V7 buffered by the amplifiers A1 to A6 of the amplifier circuit 141 are referred to as tap voltages 182 to 187, respectively. The tap voltages 182 to 187 are divided by a second ladder resistor composed of resistors 151 to 155. Among these, the tap voltage 183 and the tap voltage 186 are configured such that the tap selectors 161 and 162 are selected corresponding to the set value of the tap adjustment register 101 and the tap destination to the second ladder resistor can be changed. Yes.

  In Patent Document 1, the internal configuration of the tap selector 161 (162) shown in FIG. 12 is that the tap voltage 183 (186) is a connection destination 191, 192, 193, 194 (195, 196) in the second ladder resistor. , 197, 198), and there is a select switch composed of two stages between them. First, in the first-stage select switch 1, the tap voltage 183 (186) is connected to the first data line for connecting to the connection destination 191 or 192 (195 or 196), or to the connection destination 193 or 194 (197 or 198). Select the second data line.

  Next, the second-stage select switch 2 connects the first data line from the first-stage select switch 1 to the connection destination 191 (195) or the data line connected to the connection destination 192 (196). Select. The other second-stage select switch 3 selects whether the second data line from the select switch 1 is connected to the connection destination 193 (197) or the data line connected to the connection destination 194 (198). .

  The select switches 1 to 3 are composed of 2to1 selectors, and the output of the first-stage select switch 1 is selected at the [0] bit of the register setting value, and the second-stage at the [1] bit. Select the output of select switches 2 and 3.

  When the register value of the tap adjustment register 101 is set to “00” [BIN], the tap selector 161 (162) is set to select the connection destination 191 (195). When the value is set to “11” [BIN], the tap selector 161 (162) is set to select the connection destination 194 (198). As described above, since the on-resistances of the two switches are connected in series in Patent Document 1, a buffer is provided on the input side of the decode circuit 106 in the large-screen or high-definition liquid crystal display panel as described above. An amplifier is required.

  In this embodiment, in order to solve such a problem, the on-resistance of the switch is not inserted into the voltage transmission path as a circuit configuration in which the tap selector 161 (162) is inserted into the feedback path of the amplifier A2 (A5). It has been devised.

  FIG. 1 shows a circuit diagram of an embodiment of a voltage transmission circuit according to the present invention. The voltage transmission circuit of this embodiment corresponds to the amplifier A2 (A5) and the tap selector 161 (162) shown in FIG.

  The voltage transmission circuit of this embodiment is composed of one differential circuit unit and four output circuit units. In the differential circuit section, N-channel MOSFETs Q1 and Q2 are made differential. The gate of the MOSFET Q1 serves as an input terminal and is supplied with an input voltage VIN corresponding to the tap voltage 183 (186). Between the common source of MOSFETs Q1 and Q2 and the circuit ground potential AVSS (GND), an N-channel MOSFET Q3 having a constant voltage BIAS supplied to the gate as a current source is provided. Between the drains of the MOSFETs Q1 and Q2 and the power supply voltage AVDD, P-channel MOSFETs Q4 and Q5 in the form of a current mirror as an active load circuit are provided.

  The output circuit unit includes four output circuits corresponding to the output taps VOUT1 to VOUT4. The four output circuits are constituted by P-channel amplification MOSFETs Q10, Q12, Q14 and Q16 and N-channel load MOSFETs Q11, Q13, Q15 and Q17, respectively. The drain nodes of the MOSFETs Q1 and Q4, which are the inverted outputs of the differential circuit section, are transmitted to the gate of the P-channel MOSFET Q10 constituting the output circuit corresponding to the output tap VOUT1 via the switch S1. The constant voltage BIAS is transmitted to the gate of the N-channel load MOSFET Q11 via the switch S3. Then, the output voltage of the output tap VOUT1 is transmitted to the gate of the MOSFET Q2, which is the feedback terminal of the differential circuit, via the switch S2.

  Corresponding to the remaining three output circuits Q12 and Q13, Q14 and Q15, and Q16 and Q17, switches S4 to S6, S7 to S9, and S10 to S12 are provided in the same manner as the switches S1 to S3. In the figure, the switches S1 to S3 are turned on to transmit the input voltage VIN to the output tap VOUT1, and the other switches S4 to S12 are turned off. In this embodiment, the differential circuit and the output circuits (Q10 and Q11) corresponding to the output tap VOUT1 are activated, and a voltage follower circuit is configured. At this time, the switch S2 is included in the feedback path of the voltage follower circuit, and the output nodes of the output circuits (Q10 and Q11) are directly connected to the output tap VOUT1. Thereby, the input voltage VIN is transmitted to the output tap VOUT1 with the low output impedance of the voltage follower circuit, and the voltage at the connection destination 191 (195) of the second ladder resistor 153 in FIG. 183 (186).

  The remaining three output circuits are in an output high impedance state due to the off states of the switches S4 to S6, S7 to S9, and S10 to S12. The voltages of the output taps VOUT2 to VOUT4 are the same as those shown in FIG. The voltage of the connection destinations 192 to 194 (196 to 198) of the ladder resistor 153 according to the voltage dividing operation of the ladder resistor 153 is set.

  FIG. 2 is a circuit diagram showing another embodiment of the voltage transmission circuit according to the present invention. In the voltage transmission circuit of this embodiment, the P-channel MOSFET and the N-channel MOSFET shown in FIG. That is, in the differential circuit section, MOSFETs Q1, Q2, and Q3 are P-channel MOSFETs, and MOSFETs Q4 and Q5 are N-channel MOSFETs. In the output circuit section, amplification MOSFETs Q10, Q12, Q14, and Q16 are configured by N-channel MOSFETs, and load MOSFETs Q11, Q13, Q15, and Q17 are configured by P-channel MOSFETs. Thus, even if the P-channel MOSFET and the N-channel MOSFET are interchanged, the same operation as in FIG. 1 can be performed.

  FIG. 4 shows an equivalent circuit diagram of the voltage transmission circuit of FIG. 1 (FIG. 2). In this embodiment, the on-resistance R1 of the tap selector 161, the resistor R2 corresponding to the resistor 153 that forms the output gradation voltage, and the on-resistance R3 of the switch element constituting the decoding circuit 106 are used, as in FIG. The resistor R1 corresponding to the switch S2 is included in the feedback path of the amplifier A2 (A5), and the output voltage of the amplifier A2 can be directly transmitted to the resistor R2 corresponding to the ladder resistor 153. The resistance component of the switch S1 is included in the signal transmission path that connects the differential circuit section and the output circuit section of the amplifier A2, and therefore does not affect the output impedance of the voltage follower circuit. As a result, the grayscale voltage passed through the amplifier A2 (A5) is transmitted to the liquid crystal display panel through the resistor R2 corresponding to the resistor 153 that forms the output grayscale voltage and the on-resistance R3 of the switch element constituting the decode circuit 106. Thus, the data is written into the capacitor CPX constituting the pixel through the TFT transistor QS turned on by the scanning line selection operation.

  The tap selectors 161 and 162 are selected from four selection destinations in this embodiment, but the selection destinations can be increased or decreased. In this embodiment, the tap destination is selected from consecutive gradation numbers. However, the selection destination can be arbitrarily selected as necessary, for example, by selecting from one skipped gradation number. You can change it.

  Furthermore, variable resistors 171 and 172 exist between the second ladder resistor and the tap voltage 182 and between the second ladder resistor and the tap voltage 187. The resistance values of the variable resistors 171 and 172 can be changed by setting the voltage dividing ratio adjustment register 102.

  By changing the value of the variable resistor 171, the resistance voltage dividing ratio between the tap voltage 182 and the connection destination of the tap voltage 183 selected by the tap selector 161 can be changed, and the value of the variable resistor 172 is changed. Thus, the resistance voltage division ratio between the tap voltage 186 and the connection destination where the tap voltage 187 is selected by the tap selector 162 can be changed.

  As described above, the eight tap voltages 181 to 188 can be resistance-divided by the second ladder resistor to generate gradation voltages corresponding to the necessary gradations (in this embodiment, as an example, 64 Tones). At this time, the so-called shoulder curve of the gamma characteristic can be changed in detail for the tap voltages 181 to 188 by further setting the tap selectors 161 and 162 and the variable resistors 171 and 172.

  FIG. 5A is a characteristic diagram showing gradation number-gradation voltage characteristics. In FIG. 5A, 201 is a characteristic diagram showing the gradation number-gradation voltage when various register settings are set to default settings. The tap voltages 181 to 188 described above correspond to 202 to 209 on the characteristic diagram.

  3, when the tap selector 161 and the tap adjustment register 101 are set so that the selection destination of the tap voltage 183 is the connection destination 191 in the gradation voltage generation unit 100 in FIG. 3, the characteristic 201 in FIG. The point 204 on the graph changes to move to 210. Further, when the tap selector 161 and the tap adjustment register 101 are set so that the selection destination of the tap voltage 183 is the connection destination 194, the characteristic of 201 in FIG. Change to move.

  Similarly, when the tap selector 162 and the tap adjustment register 101 are set so that the selection destination of the tap voltage 186 is the connection destination 195 in the gradation voltage generation unit 100 of FIG. 3, the characteristic 201 in FIG. Changes so that the point 207 on the characteristic diagram moves to 212. Further, when the tap selector 162 and the tap adjustment register 101 are set so that the selection destination of the tap voltage 186 is the connection destination 198, the point 207 on the characteristic diagram moves to 213 in the characteristic 201 in FIG. To change.

  As described above, with the tap adjustment function, the points 204 and 207 on the gradation number-gradation voltage characteristics can be changed in the horizontal direction. As a result, it is possible to set the curvature of the S-curve of the gamma characteristic to be shallow or deep.

  In the prior art of Japanese Patent Laid-Open No. 2002-366112, adjustment of the shoulder portion in the gamma characteristic S-curve was performed by a fine adjustment function. With this fine adjustment function, the points 202 to 209 on the gradation number-gradation voltage characteristic graph can be individually adjusted in the vertical direction. In this case, particularly when adjusting the so-called shoulder portion of the S-curve of the gamma characteristic, the curvature of the S-curve is made shallower by adjusting 203, 204, 205 (206, 207, 208) of the graph in the vertical direction. Or it can be deeper.

  However, in the case of the above prior art (Japanese Patent Laid-Open No. 2002-366112), the shoulder portion of the S-shaped curve of the gamma characteristic can only be adjusted one-dimensionally such as vertical adjustment, but in the present embodiment, it is a tap. Two-dimensional adjustment can be realized by adding horizontal adjustment using the adjustment function. As a result, it is possible to realize a wider range of adjustment than the conventional adjustment function.

  If the function of the fine adjustment function as the prior art is expanded (when the voltage range in which the tap voltage can be set is expanded, or when the selector is set in more detail), the settings of the points 202 to 209 on the characteristic diagram Although it is possible to widen the range, it is impossible to have the same function as tap adjustment because it is only set in the vertical direction on the characteristic diagram. On the other hand, in the tap adjustment function of this embodiment, the size of the so-called S-shaped curve of the gamma characteristic can be changed.

  An example of the effect of the voltage division ratio adjustment function will be described with reference to FIG. FIG. 5B is a characteristic diagram showing a gradation number-gradation voltage characteristic. In FIG. 5B, since the characteristic 201 in FIG. 5A and the points 202 to 209 on the characteristic diagram are the same, the description is omitted.

  When the voltage division ratio adjustment register 102 is set so that the resistance value of the variable resistor 171 is reduced in the gradation voltage generation unit 100 in FIG. 3, the characteristic 201 in FIG. 5B is a point 203-204 in the characteristic diagram. The partial pressure ratio between them changes so as to be a partial pressure ratio of 221. Further, when the voltage division ratio adjustment register 102 is set so that the resistance value of the variable resistor 171 is increased, the characteristic 201 in FIG. 5B is obtained by dividing the voltage division ratio between points 203 and 204 on the characteristic diagram by 222. It changes to become pressure ratio.

  When the voltage division ratio adjustment register 102 is set so that the resistance value of the variable resistor 172 is reduced in the gradation voltage generation unit 100 of FIG. 3, the characteristic 201 of FIG. The partial pressure ratio between them changes so as to be a partial pressure ratio of 223. Further, when the voltage division ratio adjustment register 102 is set so that the resistance value of the variable resistor 172 is increased, the characteristic 201 in FIG. 5B shows that the voltage division ratio between points 207 to 208 on the characteristic diagram is 224. It changes to become pressure ratio. As described above, in the voltage dividing ratio adjustment function, by adjusting the variable resistors 171, 172, the resistance division ratio between the points 203-204 and 207-208 on the characteristic diagram is changed, and the point 203 on the characteristic diagram is displayed. The voltage setting of each gradation number between -204 and 207-208 can be changed.

  In the prior art (Japanese Patent Laid-Open No. 2002-366112), the gradation voltage value between tap voltages is determined by the tap voltage value, and the resistance division ratio of the ladder resistor that connects the tap voltages is It was fixed. Therefore, when the gradation voltage value between 203 and 204 (between 207 and 208) is lifted up, the points 203 and 204 (points 207 and 208) need to be lifted up. If the point 204 (207) is lifted up, the shoulder portion of the gamma characteristic S-shaped curve will be lifted up. Similarly, when lowering the gradation voltage value between 203 and 204 (between 207 and 208), it is necessary to lower points 203 and 204 (points 207 and 208). If the point 204 (207) is lowered, the shoulder portion of the S curve of the gamma characteristic is lowered. In the voltage division ratio adjustment function of this embodiment, voltage settings near the reference voltage and near the ground can be set over a wide range without changing the S-shaped curve of the gamma characteristic.

  Even if the fine adjustment function in the prior art (Japanese Patent Application Laid-Open No. 2002-366112) is extended, the shoulder portion of the gamma characteristic S-curve is also deformed for the above reason, so that the fine adjustment function is expanded. Therefore, it is impossible to provide the same function as the partial pressure ratio adjustment. As described above, the voltage setting near the reference voltage and the ground can be set in a wide range by the voltage division ratio adjustment function.

  In the foregoing, the effects of the tap adjustment function and the voltage division ratio adjustment function have been described. These two functions are the amplitude adjustment, inclination adjustment, and fine adjustment functions of the prior art as shown in FIGS. 5 (c) to 5 (e). It is also possible to combine the effects obtained in. The variable resistors 121 and 122 of the gradation voltage generator adjust the voltage value at both ends of the gradation number by referring to the resistance value setting data included in the amplitude adjustment register 103 and changing the resistance value. As shown in FIG. 5C, the gradation number-gradation voltage characteristic obtained from the result of the amplitude adjustment function is such that the characteristic 231 increases the resistance value of the variable resistor 121 with respect to the default setting of the characteristic 201. In this example, the resistance value of the variable resistor 122 is set small. A characteristic 232 indicates a case where the resistance value of the variable resistor 121 is set small and the resistance value of the variable resistor 122 is set large. As described above, the amplitude voltage of the gradation voltage can be adjusted.

  The variable resistors 123 and 124 of the gradation voltage generation unit 100 adjust the inclination characteristics of the intermediate part of the gradation voltage by referring to the resistance value setting data included in the inclination adjustment register 104 and changing the resistance value. As shown in FIG. 5D, the gradation number-gradation voltage characteristic obtained from the result of the tilt adjustment function is such that the characteristic 241 has a smaller resistance value of the variable resistor 123 than the default setting of the characteristic 201. In this example, the resistance value of the variable resistor 124 is set large. A characteristic 242 indicates a case where the resistance value of the variable resistor 123 is set large and the resistance value of the variable resistor 124 is set small. As described above, the halftone portion of the gradation voltage can be adjusted.

  The selectors 131 to 136 of the gradation voltage generation unit 100 perform fine adjustment by selecting a desired gradation voltage with reference to the setting value of the fine adjustment register 105 from the voltage values divided by the resistors 111 to 116. I do. As shown in FIG. 5E, the gradation number-gradation voltage characteristic obtained from the result of this fine adjustment function is the characteristic 251 of the selection voltage of the selectors 131 to 136 with respect to the default setting of the graph 201. Of these, the case where a value close to the reference voltage is selected is shown. A characteristic 252 indicates a case where a value close to GND is selected from the selection voltages of the selectors 131 to 136. As described above, the gradation voltage can be finely adjusted.

  As described above, by combining these functions, in addition to the conventional gamma characteristic adjustment function, a function that can further expand the adjustment range of the so-called shoulder portion in the S-curve indicating the gamma characteristic is realized. In a liquid crystal panel, accurate color reproducibility can be realized. In general, in the gradation number-gradation voltage characteristics, the optimum curve differs depending on the liquid crystal display panel used at the shoulder portion of the so-called S-shaped curve close to the reference voltage and the ground. For this reason, a wide range of adjustment is necessary to support a wide variety of liquid crystal display panels, and the grayscale voltage generation unit 100 of the present application can cope with such a requirement.

  FIG. 6 shows an overall block diagram of an embodiment of a liquid crystal display device equipped with a gradation voltage generator according to the present invention. The liquid crystal display device 300 in this embodiment includes a liquid crystal panel 301, a signal line driver circuit 302 equipped with a gradation voltage generation unit in FIG. 3 that outputs gradation voltages corresponding to display data to signal lines of the liquid crystal panel 301, liquid crystal A scanning line driving circuit 303 for applying a scanning signal to the scanning lines of the panel 301, a signal line driving circuit 302, and a power supply circuit 304 for supplying operation power to the scanning line driving circuit 303. The power supply voltage supplied from the power supply circuit 304 to the signal line driver circuit 302 includes the reference voltage shown in FIG. Connected to the liquid crystal display device 300 is an MPU (microprocessor unit) 305 that performs various processes for displaying an image on the liquid crystal panel 301.

  The signal line driving circuit 302 includes a system interface 306 for exchanging display data and control data with the MPU 305, a display data memory 307 for storing display data output from the system interface 306, The control register 308 including the various registers of the tap adjustment register 101, the voltage division ratio adjustment register 102, the amplitude adjustment register 103, the inclination adjustment register 104, and the fine adjustment register 105, the gradation voltage generation circuit 100, and the decode circuit 106 shown in FIG. It becomes the composition including.

  The system interface 306 receives display data and instructions output from the MPU 305 and outputs them to the control register 308. Details of the operation are based on, for example, a 68-system 16-bit bus interface, and a CS (Chip Select) signal indicating chip selection and an RS (Register Select) for selecting whether to specify the address of the control register 308 or data. ) Signal, an E (Enable) signal for instructing the start of processing operation, a WR (Write Read) signal for selecting writing or reading of data, and a DATA signal which is an address or data set value of the control register 308.

  The instructions are information for determining internal operations of the signal line driving circuit 302, the scanning line driving circuit 303, and the power supply circuit 304, and include various parameters such as a frame frequency, the number of driving lines, and a driving voltage. In addition, information regarding amplitude adjustment, inclination adjustment, fine adjustment, tap adjustment, and voltage division ratio adjustment, which are features of the present invention, is also included. The control register 308 stores instruction data and outputs the instruction data to the blocks of the driving circuits.

  The set value of each register of the control register 308 can be easily changed independently from the outside, facilitating each adjustment of the gamma characteristic, and in addition to the gamma characteristic adjustment function, an S-shaped curve indicating the gamma characteristic further has a so-called shoulder shape. A function capable of further expanding the adjustment range of the part is realized, and accurate color reproducibility can be realized in various liquid crystal panels.

  In this embodiment, in order to simplify the explanation, the concept relating to polarity inversion driving necessary for driving liquid crystal or the like is omitted, but it can be easily applied to various methods such as common inversion, column-by-column inversion, and dot inversion. The correspondence to the common inversion drive will be described in detail in an embodiment described later. Although the number of bits of the display data is six, it is not limited to this.

  In this embodiment, the concept of color is omitted for the sake of simplicity of description, but the color display is realized by, for example, displaying display data for one pixel in R (red), G (green), and B (blue). However, this can be easily realized by applying a so-called vertical stripe structure to the display portion. The correspondence to R (red), G (green), and B (blue) will be described in detail in an embodiment described later.

  In the present embodiment, the description has been made on the assumption that various types of information relating to the adjustment of the gamma characteristic are stored in the register. However, the present invention is not limited to this, and for example, terminal setting may be used.

  FIG. 7 is a block diagram showing another embodiment of the liquid crystal display driving circuit according to the present invention. In the liquid crystal display panel, in order to prevent the image quality deterioration of the video display, it is necessary to perform AC driving that inverts the polarity of the applied voltage every certain period. In this case, switching of the applied voltage polarity is performed by an AC signal (hereinafter referred to as an M signal). For example, the low state and the high state of the M signal are inverted every scanning period. Here, depending on the liquid crystal display panel, the characteristics of gradation number-gradation voltage may differ depending on the positive polarity (for example, M = low state) and the negative polarity (for example, M = high state). It is necessary to adjust the gamma characteristic.

  In the configuration of the gradation voltage generation circuit 100 shown in FIG. 3, in order to change the setting of the gradation voltage for each polarity, two register settings for the positive polarity and the negative polarity are stored in the liquid crystal display device. Then, by synchronizing it with the M signal and switching the register value input to the gradation voltage generation unit, positive and negative gradation voltages can be generated. However, in this case, the set time from when the grayscale voltage is switched to when it converges depends on the values of the first and second ladder resistors, and if these resistance values are too large, within a certain period (for example, 1H May not be able to converge within the period. In order to improve this, the value of the ladder resistance may be reduced, but there is a problem that a side effect of increasing the steady current occurs.

  In order to solve this problem, this embodiment has an amplitude adjustment function, a tilt adjustment function, a fine adjustment function, a tap adjustment function, and a voltage division ratio adjustment function in a liquid crystal display drive circuit having a gamma characteristic adjustment function. The first ladder resistor shown in FIG. 3 is provided with two systems, and in particular, the first ladder resistor for positive polarity and negative polarity is set in advance during AC driving, and two systems are switched by switching the polarity. By switching the existing first ladder resistor, the positive and negative gradation voltage setting switching time can be increased.

  The gradation voltage generation unit 100 in the liquid crystal display driving circuit of this embodiment has two systems of the first ladder resistor shown by the gradation voltage generation unit 100 in FIG. 3, that is, an A ladder resistor 401 and a B ladder resistor 402. . Further, independent A ladder setting register 411 for performing desired gamma characteristic setting (amplitude adjustment, inclination adjustment, fine adjustment) for positive polarity and negative polarity for A ladder resistor 401 and B ladder resistor 402, respectively. A B ladder setting register 412 is provided, and selectors 421 to 428 for selecting one of tap voltages generated from the A ladder resistor 401 and the B ladder resistor 402 are additionally provided. Other than the above, the amplifier circuit 141, the tap selectors 161 and 162, the variable resistors 171 and 172, and the second ladder resistor have the same configuration as in FIG. 3 (FIGS. 1 and 2).

  Corresponding to the two systems of A ladder resistor 401 and B ladder resistor 402, the first ladder resistor composed of resistors 111 to 116, variable resistors 121 to 124, and selectors 131 to 136 shown in FIG. There are two systems, and the outputs from the two systems of selectors 131 to 136 are selected by the added selectors 421 to 428 and output to the amplifier circuit 141.

  A tap voltage is also generated in the A ladder resistor 401 and the B ladder resistor 402 in the same manner as the first ladder resistor described in the embodiment of FIG. Here, it is assumed that the A ladder resistor 401 has a positive polarity register setting, and the B ladder resistor 402 has a negative polarity register setting. Each gamma characteristic adjustment (amplitude adjustment, inclination adjustment, fine adjustment) of the A ladder resistor 401 and the B ladder resistor 402 can be performed in the same manner as in the embodiment of FIG.

  The tap voltages generated by the A and B ladder resistors 401 and 402 are input to the selectors 421 to 428, and the M signal is switched as a ladder switching signal 431. For example, when the M signal is in the low state, among the tap voltages input to the selectors 421 to 428, all the positive polarity setting tap voltages (the tap voltage output from the A ladder resistor 401) are selected. On the other hand, when the M signal is in the high state, the tap voltages set to the negative polarity (the tap voltage output from the B ladder resistor 402) are selected from the tap voltages input to the selectors 421 to 428. The subsequent operation (from the generation of the tap voltage to the generation of the gradation voltage) is the same as in the embodiment of FIG.

  As described above, by generating the tap voltage for positive polarity and negative polarity in advance by the first ladder resistance of the two systems of A ladder resistance 401 and B ladder resistance 402, the polarity switching can be prevented. Therefore, it is possible to generate gradation voltages corresponding to necessary gradations at high speed.

  Also in this embodiment, it is possible to obtain the effects of the amplitude adjustment, inclination adjustment, fine adjustment, tap adjustment, and voltage division ratio adjustment functions as shown in FIGS. 5A to 5E in the embodiment of FIG. By combining these functions, it is possible to further expand the so-called shoulder adjustment range of the S-shaped curve indicating the conventional gamma characteristic adjustment function and the gamma characteristic in both the positive polarity and the negative polarity. It is possible to achieve accurate color reproducibility in a wide variety of liquid crystal display panels.

  FIG. 8 shows an overall block diagram of an embodiment of a liquid crystal display device on which the gradation voltage generation unit of FIG. 7 is mounted. The liquid crystal display device 300 in this embodiment has a configuration in which only the control register 308 and the gradation voltage generation circuit 100 are changed from the embodiment of FIG. The gradation voltage generation circuit 100 is the voltage generation circuit 100 described with reference to FIG.

  The control register 308 includes a positive polarity control register 501 including a positive polarity amplitude adjustment register, a tilt adjustment register, and a fine adjustment register, and a negative polarity amplitude adjustment register, a tilt adjustment register, and a fine adjustment register. The control register 502 includes a positive polarity control register 503 including a positive polarity tap adjustment register and a voltage division ratio adjustment register, and a negative polarity control register 504 including a negative polarity tap adjustment register and a voltage division ratio adjustment register. Is done.

  The A ladder setting register value from the positive polarity control register 501 and the B ladder setting register value from the negative polarity control register 502 are input from the control register 308 to the gradation voltage generation circuit 100. The positive control register 503 and the negative control register 504 are switched by the M signal in the selector 505. In this embodiment, when the M signal is in a low state, the positive register setting value (control register 503) is selected. Conversely, when the M signal is in the high state, the negative register setting value (control register 504) is selected.

  In FIG. 8, an example of the timing of the register setting value input from the control register 308 to each register of the gradation voltage generation circuit 100 will be described with reference to the timing chart shown in FIG. FIG. 9 shows an operation of the control register at the time of polarity inversion driving for each line as an example. At the time of polarity inversion driving for each line, the output data is switched between positive polarity and negative polarity every horizontal cycle. Therefore, the A ladder resistor 401 to which the register setting value of the positive polarity control register 501 is input and the B ladder resistor 402 to which the register setting value of the negative polarity control register 502 is input alternately every horizontal cycle. In order to use it, it is necessary to change the ladder switching signal 431 every horizontal period.

  In this embodiment, the A ladder resistor 401 is selected when the ladder switching signal 431 is in the high state, and the B ladder resistor 402 is selected when the ladder switching signal 431 is in the low state. In this embodiment, since the timing of the ladder switching signal 431 and the M signal is the same, the M signal may be used as the ladder switching signal.

  As for the tap adjustment register and the voltage division ratio adjustment register, the register setting value input from the control register 308 to each register of the gradation voltage generation circuit 100 is the register setting value of the positive polarity control register 503 and the negative polarity every horizontal cycle. It is necessary to switch the register setting value of the sex control register 504. As described above, this can be realized by switching using the M signal.

  According to the liquid crystal display device 300 according to the present embodiment described above, two systems of positive and negative gamma characteristic adjustments are prepared in advance, and these are switched in accordance with the M signal instructing AC conversion. It has become possible to speed up the switching of the gradation voltage corresponding to the negative polarity. The liquid crystal display device 300 is also configured with various setting registers such as amplitude adjustment, tilt adjustment, fine adjustment, tap adjustment, and voltage division ratio adjustment. In addition to the conventional gamma characteristic adjustment function, in addition to the conventional gamma characteristic adjustment function, the S-shaped curve showing the gamma characteristic realizes a function that can further expand the adjustment range of the so-called shoulder part. Accurate color reproducibility can be realized.

  FIG. 10 is a block diagram showing still another embodiment of the liquid crystal display driving circuit according to the present invention. As a driving method of the color liquid crystal display device, the signal line driving circuit outputs gradation voltages corresponding to the respective colors of R (red), G (green), and B (blue) in a time division manner within one scanning period. There is a method in which the built-in circuit on the LCD panel side demultiplexes. The object of the present embodiment is to improve the image quality by individually adjusting the gamma characteristics of each of the R, G, and B colors in the above-described driving method.

  In realizing this, the circuit configuration shown in FIG. 7 is applied. Specifically, the present embodiment is a liquid crystal display device having a gamma characteristic adjustment function, which has an amplitude adjustment function, a tilt adjustment function, a fine adjustment function, a tap adjustment function, and a voltage division ratio adjustment function. The first ladder resistance of the two systems shown in FIG. 2 is provided, and the positive polarity and the negative polarity are switched every scanning period, and the R, G, and B gamma characteristic settings are switched during one scanning period. Shall. Then, switching between positive and negative gamma characteristic settings and switching of gamma characteristic settings for each of R, G, and B data is realized by alternately using two systems of first ladder resistors.

  In FIG. 10, the liquid crystal panel 301 is provided with a changeover switch 751 between the signal line of the R / G / B pixel and the signal line input from the signal line driver circuit 302. At this time, the signal line data input from the signal line driver circuit 302 to the liquid crystal panel 301 is input R / G / B data in a time division manner within one horizontal period. Then, a signal line switching signal 752 is used to switch the input destination of the signal line input from the liquid crystal panel 301 and the signal line driving circuit 302 by the changeover switch 751.

  The control register 308 includes a negative polarity R control register 701 for negative polarity R, G, and B data, a negative polarity G control register 703, a negative polarity B control register 705, and registers for amplitude adjustment, inclination adjustment, and fine adjustment. A positive R control register 702 for positive R, G, and B data, a positive G control register 704, and a positive B control register 706 are provided. In addition, a negative polarity R control register 707, a negative polarity G control register 709, a negative polarity B control register 711 for negative polarity R, G, B data including a register relating to tap adjustment and a voltage dividing ratio, and positive polarity R, G, It has a positive R control register 708 for B data, a positive G control register 710, and a positive B control register 712.

  The register values of the negative R control register 701 and the positive R control register 702 are switched using a selector 731 in accordance with a 2to1 switching signal 722 output from the register switching timing generation circuit 721. The same applies to other control registers, and the positive and negative registers are switched using selectors 732 to 736 according to the 2to1 switching signal 722. Here, the switching timings of the selectors 731 to 733 are different from those of the selectors 734 to 736. This timing will be described in detail with reference to FIG.

  The register setting value selected by the selectors 731 to 733 is input to the selector 741, and one of the three register values is selected according to the 3to1 switching signal 723 output from the register switching timing generation circuit 721, and the A ladder setting is set. It is input to the gradation voltage generation circuit 100 as a register value.

  Similarly, the register setting value selected by the selectors 731 to 733 is input to the selector 742 and selects one of the three register values according to the 3to1 switching signal 723 output from the register switching timing generation circuit 721. The value is input to the gradation voltage generation circuit 100 as a B ladder setting register value.

  The register setting value selected by the selectors 734 to 736 is input to the selector 734, and one of the three register values is selected by the 3to1 switching signal 723 output from the register switching timing generation circuit 721, and tap adjustment is performed. The grayscale voltage generation circuit 100 inputs the register value and the voltage division ratio adjustment register value.

  In the above three selectors 741, 742, and 743, the timing for switching register values is independent. The register value switching timing will be described in detail with reference to FIG.

  In FIG. 10, the timing of the register setting values input from the control register 308 to each register of the gradation voltage generation circuit 100 will be described with reference to the timing chart shown in FIG. In FIG. 11, polarity inversion drive is performed for each line, and data transfer is performed in RGB time division. Therefore, the A ladder resistor 401 and the B ladder resistor 402 are switched every RGB time division within one horizontal cycle. At this time, for example, when the output data from the signal line driving circuit 302 is positive G data and the selected ladder resistor is the B ladder resistor 402 (period 801 in FIG. 11), the register setting of the B ladder resistor 402 is a gamma characteristic. It is necessary to perform in the setting period 802. By setting at the above timing, the grayscale voltage generation in the B ladder resistor 402 is already fixed at the timing 801 when the B ladder resistor 402 is used. Therefore, as in the embodiments of FIGS. 7 and 8, there is no problem in the convergence time at the time of switching. Further, the same effect can be obtained by setting the register for the A ladder resistor 401 at the same timing.

  Regarding the tap adjustment register and the voltage division ratio adjustment register, the control register is also changed in synchronization with the RGB output data. For example, at the timing when the positive electrode R data is output from the signal line driving circuit 302, the tap adjustment register value and the voltage division ratio adjustment register value are also set to the register value of the positive electrode R data.

  According to the present embodiment described above, positive and negative gamma characteristic adjustment and gamma characteristic adjustment for each R, G, B data can be individually adjusted. In addition, it is possible to set gradation voltage generation at a high speed by alternately using the first ladder resistors of the two systems at the time of switching the gamma characteristic setting (at the time of switching the positive polarity, the negative polarity, and at the time of RGB switching). It becomes feasible. The liquid crystal display device 300 is also configured with various setting registers such as amplitude adjustment, tilt adjustment, fine adjustment, tap adjustment, and voltage division ratio adjustment. In addition to the conventional gamma characteristic adjustment function, in addition to the conventional gamma characteristic adjustment function, the S-shaped curve showing the gamma characteristic realizes a function that can expand the adjustment range of the so-called shoulder part, and in various liquid crystal display panels Accurate color reproducibility can be realized.

  As a result, according to each of the embodiments, the gamma characteristic has five types of gamma characteristic adjustment functions such as tap adjustment and partial pressure adjustment in addition to amplitude adjustment, inclination adjustment, and fine adjustment as in the prior art. Therefore, the gamma characteristic can be adjusted optimally and easily in various liquid crystal panels, and high image quality and versatility can be realized.

  The switches S1 to S12 shown in FIG. 1 and FIG. 2 are constituted by a select switch formed by a Metal-Oxide Field-Effect Transistor (hereinafter referred to as a MOSFET).

  The invention made by the inventor has been specifically described based on the embodiments. However, the present invention is not limited to the embodiments, and various modifications can be made without departing from the scope of the invention. Not too long. For example, the output circuit section of FIGS. 1 and 2 has a three-state output function including an output high impedance by forming an inverting amplifier circuit with a CMOS inverter circuit and providing a switch MOSFET between the power supply voltages AVDD and AVSS. It may be a thing. In this case, the output signal of the differential circuit section is constantly connected to the input terminal of the CMOS inverter circuit. The switch MOSFET provided between the power supply voltages AVDD and AVSS can serve as the switches S1 and S3. The present invention can be widely applied to a liquid crystal display driving circuit that forms a gradation voltage that is transmitted to a liquid crystal display panel by inputting a gradation voltage formed by the resistance voltage dividing circuit having the gamma characteristic adjusted to a decoding circuit.

1 is a circuit diagram of an embodiment of a voltage transmission circuit according to the present invention. FIG. It is a circuit diagram of another embodiment of the voltage transmission circuit according to the present invention. It is a block diagram of one Example of the liquid crystal display drive circuit based on this invention. FIG. 4 is an equivalent circuit diagram using the voltage transmission circuit of FIG. 1 (FIG. 2). It is explanatory drawing of the gamma characteristic adjustment which concerns on this invention. FIG. 4 is an overall block diagram of an embodiment of a liquid crystal display device on which the grayscale voltage generator shown in FIG. 3 is mounted. It is a block diagram of other one Example of the liquid crystal display drive circuit based on this invention. FIG. 8 is an overall block diagram of an embodiment of a liquid crystal display device on which the gradation voltage generation unit illustrated in FIG. 7 is mounted. FIG. 9 is a timing chart illustrating an example of timing of register setting values in FIG. 8. FIG. It is a block diagram of further another embodiment of the liquid crystal display drive circuit according to the present invention. 11 is a timing chart illustrating an example of timing of register setting values in FIG. 10. It is a block diagram which shows an example of the conventional drive device for display apparatuses. FIG. 13 is an equivalent circuit diagram of the gradation voltage transmission path in FIG. 12.

Explanation of symbols

Q1-Q17 ... MOSFET, S1-A12 ... switch,
DESCRIPTION OF SYMBOLS 100 ... Grayscale voltage generation circuit, 101 ... Tap adjustment register, 102 ... Voltage division ratio adjustment register, 103 ... Amplitude adjustment register, 104 ... Inclination adjustment register, 105 ... Fine adjustment register, 106 ... Decode circuit, 107 ... Reference voltage, 108 ... ground, 111-116 ... resistor, 121-124 ... variable resistor, 131-136 ... selector, 141 ... amplifier circuit, 151-155 ... resistor, 161,162 ... tap selector, 171,172 ... variable resistor, 181-188 DESCRIPTION OF SYMBOLS ... Tap voltage, 191-198 ... Connection destination, 300 ... Liquid crystal display device, 301 ... Liquid crystal panel, 302 ... Signal line drive circuit, 303 ... Scanning line drive circuit, 304 ... Power supply circuit, 305 ... MPU, 306 ... System interface, 307: Display data memory, 308: Control register, 401: A ladder resistor 402, B ladder resistance, 411 ... A ladder setting register, 412 ... B ladder setting register, 421-428 ... selector, 431 ... ladder switching signal, 501 ... positive polarity control register, 502 ... negative polarity control register, 503 ... Positive polarity control register, 504 ... Negative polarity control register, 505 ... Selector, 701 ... Negative polarity R control register, 702 ... Positive polarity R control register, 703 ... Negative polarity G control register, 704 ... Positive polarity G control register 705 ... Negative electrode B control register, 706 ... Positive electrode B control register, 707 ... Negative electrode R control register, 708 ... Positive electrode R control register, 709 ... Negative electrode G control register, 710 ... Positive electrode G control register, 711 ... Negative B control register, 712 ... Positive B control register, 721 ... Register switching timing generation Circuit, 722... 2 to 1 switching signal, 723... 3 to 1 switching signal, 731 to 736... Selector, 741 to 743... Selector, 751. Registers 902, 903... Variable resistor group, 904, 905... Resistor, 906, 907... Variable resistor group, 908 to 927... Variable resistor, 928 to 933. 1001-1011 ... Characteristic curve.

Claims (10)

A gradation voltage generation circuit that divides the reference voltage to generate a plurality of gradation voltages corresponding to a plurality of gradations;
A decoding circuit that selects a gradation voltage corresponding to the display data transmitted from the plurality of gradation voltages to the liquid crystal display panel;
The gradation voltage generation circuit includes:
A first value for adjusting the amplitude of the gamma characteristic of the substantially S-curve that defines the relationship between the gradation and the gradation voltage or the luminance in the liquid crystal display panel by adjusting the division point or division ratio of the reference voltage. A first register for setting
A second register that sets a second value that adjusts a slope of an intermediate portion of the gamma characteristic by adjusting a division point or a division ratio of the reference voltage;
A third register that sets a third value for adjusting a division point or a division ratio of the reference voltage and finely adjusting an intermediate portion of the gamma characteristic for each gradation;
A voltage dividing resistor circuit that transmits a voltage corresponding to the amplitude of the gamma characteristic adjusted by the first value and the second value to both ends and forms a gradation voltage input to the decoding circuit;
A fourth value for adjusting a gradation with respect to a gradation voltage formed by the voltage dividing resistor circuit in an intermediate portion near the end of the gamma characteristic by adjusting a dividing point or a dividing ratio of the reference voltage is set. 4 registers,
The predetermined voltage adjusted by the third value is transmitted to the tap of the voltage dividing resistor circuit selected by the fourth value set in the fourth register, and includes the extreme point portion of the substantially S-shaped curve. A voltage transmission circuit capable of adjusting a gradation with respect to a gradation voltage in an intermediate portion of the gamma characteristic,
The voltage transmission circuit is
A differential circuit section that receives the predetermined voltage;
A plurality of output circuit units having output terminals connected to a plurality of taps;
A plurality of first switches that connect input terminals of the plurality of output circuit units and output terminals of the differential circuit unit;
A plurality of second switches for connecting the output terminal of the output circuit section and the feedback input terminal of the differential circuit section;
The liquid crystal display driving in which one first switch and second switch corresponding to the tap selected corresponding to the fourth value is turned on, and the differential circuit unit and the one output circuit unit are configured as a voltage follower. circuit. In claim 1,
A fifth register that sets a fifth value for adjusting a ratio of gradation voltages between a plurality of gradations in an intermediate portion near the end of the gamma characteristic by adjusting a division point or a division ratio of the reference voltage Further comprising
The fifth value is a liquid crystal display driving circuit that adjusts a voltage transmitted to both ends of the voltage dividing resistor circuit. In claim 2,
A liquid crystal display driving circuit, wherein the values of the first to fifth registers can be set independently from the outside. In claim 3,
The differential circuit section is
First and second MOSFETs of a first conductivity type in differential form;
A third MOSFET of a first conductivity type provided between a common source of the first and second MOSFETs and a first operating voltage and performing a constant current operation;
A load circuit comprising fourth and fifth MOSFETs of the second conductivity type provided between the drains of the first and second MOSFETs and a second operating voltage;
The gate of the first MOSFET is used as an input terminal to supply the predetermined voltage,
The gate of the second MOSFET is a feedback terminal,
The output circuit section is
An output MOSFET of a second conductivity type in which an output signal of the differential circuit section is supplied to the gate via the first switch;
A load MOSFET of a first conductivity type provided between the output MOSFET and the first operating voltage;
A plurality of third switches;
The connection point between the output MOSFET and the load MOSFET is an output terminal,
The second switch is provided between the output terminal and the gate of the second MOSFET;
The load MOSFET is a liquid crystal display driving circuit in which the third switch corresponding to the tap selected by the fourth value is turned on and a constant voltage is transmitted to perform a constant current operation. In claim 4,
The gradation voltage generation circuit includes:
A ladder resistor connected between the connection end of the first reference voltage and the connection end of the second reference voltage;
A first variable resistor connected in series with the ladder resistor on the connection end side of the first reference voltage or the connection end side of the second reference voltage with respect to the ladder resistor;
A second variable resistor connected in series with the first ladder resistor at an intermediate portion of the first ladder resistor;
A first selector for selecting an output from the ladder resistor;
When,
The resistance value of the first variable resistor is changeable based on the first value in the first register,
The resistance value of the second variable resistor can be changed based on the second value in the second register;
The liquid crystal display driving circuit, wherein the first selector can select an output from the first ladder resistor based on the third value in the third register. In claim 5,
An amplifier having a voltage follower configuration connected to the output side of the first selector;
The voltage transmission circuit is a liquid crystal display driving circuit also serving as the amplifier. In claim 6,
A third variable resistor connected in series with the voltage dividing resistor circuit;
The liquid crystal display driving circuit, wherein the resistance value of the third variable resistor can be changed based on the fifth value in the fifth register. In claim 7,
The gradation voltage generation circuit includes:
The first ladder resistor, the first variable resistor, the second variable resistor, and the first selector each have two systems,
A third selector for selecting an output from the first selector of the two systems and outputting it to the amplifier;
The resistance values of the first variable resistors of the two systems are based on the first value in the first register and the sixth value in the sixth register having the same function as the first register. Changeable,
The resistance values of the second variable resistors of the two systems are based on the second value in the second register and the seventh value in the seventh register having the same function as the second register. Changeable,
The first selectors of the two systems are based on the third value in the third register and the eighth value in an eighth register having the same function as the third register. The output from the ladder resistor can be selected,
The third selector can select an output from the first selector based on a first switching signal,
A liquid crystal display driving circuit in which the two systems are alternately used at fixed intervals, and one is used during a period in which one is used and the other is switched to a setting corresponding to the next use period. In claim 8,
The period in which the two systems are alternately used is a liquid crystal display driving circuit which is each period corresponding to the positive polarity and the negative polarity in the polarity inversion driving of the liquid crystal display panel. In claim 9,
The predetermined period of the two systems is a period of three divisions corresponding to each color of R, G, and B in driving the color liquid crystal display device,
The gradation voltage generation circuit selects the third selector for selecting the outputs from the first selectors of the two systems and the three-divided output from the third selector to the amplifier. A fourth selector for outputting,
The resistance values of the first variable resistors of the two systems and the three divisions are the first value in the first register, the sixth value in the sixth register, and the first register. Changeable based on the ninth to twelfth values in the ninth to twelfth registers having the same function,
The resistance values of the second variable resistors of the two systems and the three divisions are the second value in the second register, the seventh value in the seventh register, and the second register. Can change based on the thirteenth to sixteenth values in the thirteenth to sixteenth registers having the same function,
The first selector of the two systems / three divisions has the same function as the third value in the third register, the eighth value in the eighth register, and the third register. The output from the first ladder resistor can be selected based on the 17th to 20th values in the 17th to 20th registers,
The third selector can select an output from the first selector based on the first switching signal,
The liquid crystal display driving circuit, wherein the fourth selector can select an output from the third selector based on a second switching signal.

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