JP2012145848A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device which is capable of suppressing a current loss and ripple power by controlling whether or not to connect a resistor immediately after output of an amplifier circuit.SOLUTION: Upon inputting a mode switching signal or a channel switching signal, a load state discrimination circuit 112a of a T-CON 112 discriminates a load state of a liquid crystal panel 120 from a pixel pattern of the liquid crystal panel 120. When the load state discrimination circuit 112a determines that the liquid crystal panel 120 is under a normal load, "ON" is set to an output resistance switching signal and the output resistance switching signal is output to an output resistance circuit unit 152. When the load state discrimination circuit 112a determines that the liquid crystal panel 120 is under a heavy load, "OFF" is set to an output resistance switching signal and the output resistance switching signal is output to the output resistance circuit unit 152. When the output resistance switching signal is "ON", the output resistance circuit unit 152 short-circuits a resistor by closing a switch and, when the output resistance switching signal is "OFF", inserts the resistor by opening the switch.

Description

  The present invention relates to a liquid crystal display device including an amplifier circuit.

  A liquid crystal display device generally includes a control substrate (hereinafter referred to as “CTL substrate”) and a liquid crystal panel. In this CTL substrate, a power supply voltage for driving the liquid crystal panel is generated and supplied to the liquid crystal panel. In addition, since a large current is required to drive the liquid crystal panel, an amplifier circuit is provided on the CTL substrate. The amplifier circuit amplifies the current and supplies the current to the liquid crystal panel. By the way, depending on the pattern of the video signal displayed on the liquid crystal panel, a larger current than usual is required, and thus heat generation of the amplifier circuit may increase. In particular, when the display panel must be driven in accordance with a special video signal pattern, the power supply voltage of the liquid crystal panel pulsates, so that a larger current flows through the amplifier circuit in an attempt to suppress this pulsating voltage (ripple voltage). For this reason, the heat generation of the amplifier circuit may further increase. Conventionally, as a measure for suppressing the heat generation of the amplifier circuit, a resistor is connected in series immediately after the output of the amplifier circuit. However, power loss increases when the current output from the amplifier circuit passes through the resistor, and the ripple voltage of the voltage applied to the liquid crystal panel by the resistor further increases. For this reason, conventionally, a capacitor corresponding to the magnitude of the load of the amplifier circuit is connected immediately after the resistor, and the ripple voltage is suppressed by supplying a power supply voltage from this capacitor to the liquid crystal panel. JP-A-2001-282193 (Patent Document 1) can be cited as a technique for reducing the heat generated by such an amplifier circuit.

JP 2001-282193 A

  As described above, when the display panel has to be driven according to a special video signal pattern, there is a problem that heat generation of the amplifier circuit increases. In particular, in a liquid crystal display device, a display pattern in which lighting / non-lighting of signal electrodes is alternately repeated, for example, a checkered display in which lighting / non-lighting is performed for each dot, and lighting / non-lighting is repeated for each scanning line. In a so-called heavy load display such as a stripe display, a large loss occurs in the amplifier circuit as the output current changes greatly, and the elements such as the operational amplifier itself become high temperature. As a countermeasure, a resistor is connected, but the ripple voltage due to the resistor is increased as described above. In addition, in a normal video signal pattern, a resistor is connected immediately after the output of the amplifier circuit, although it is not necessary to suppress the heat generation of the amplifier circuit. This resistor causes power loss, and the ripple voltage is reduced. It was increasing. In the technique disclosed in Patent Document 1, the heat generation of the operational amplifier of the liquid crystal drive voltage generation circuit is reduced, and the liquid crystal drive voltage generation circuit is stably driven even in an environment where the ambient temperature is high. A liquid crystal display device that improves the above is presented. However, although the technique disclosed in Patent Document 1 reduces the heat generation of the operational amplifier, it cannot suppress the power loss due to the resistor connected immediately after the output of the amplifier circuit.

  The present invention has been made in view of such a situation, and an object thereof is to provide a liquid crystal display device capable of solving the above-described problems.

A liquid crystal display device according to the present invention includes a power supply voltage generation circuit that generates a power supply voltage for driving a liquid crystal panel, and an output resistance change circuit that changes an output resistance of the power supply voltage generation circuit.
Further, the output resistance changing circuit of the liquid crystal display device of the present invention is characterized in that one resistance value and 0 ohm are switched.
The liquid crystal display device of the present invention further includes a load state determination unit that determines a load state of the power supply voltage generation circuit, and controls the output resistance change circuit according to a determination result of the load state determination unit. It is a feature.
Further, when the load state determination unit of the liquid crystal display device of the present invention determines that the load state of the amplifier circuit is large, increases the resistance value of the output resistance change circuit and determines that the load state is small. The resistance value of the output resistance changing circuit is reduced.
Further, the load state determination unit of the liquid crystal display device of the present invention is characterized in that the determination is made based on the data fluctuation amount of each pixel of the liquid crystal panel.
Further, the load state determination unit of the liquid crystal display device of the present invention is characterized in that determination is made based on a mode switching signal or a channel switching signal.
Further, the load state determination unit of the liquid crystal display device of the present invention is characterized in that the determination is made based on the temperature of the power supply voltage generation circuit.

  According to the present invention, it is possible to control whether or not a resistor is connected immediately after the output of the amplifier circuit based on the video signal pattern, and when a video signal pattern expected to increase the heat generation of the amplifier circuit is input. Providing a liquid crystal display that can suppress current loss and ripple voltage due to resistance by short-circuiting the resistor when a normal video pattern that does not increase the heat generation of the amplifier circuit is input by inserting a resistor To do.

It is a figure which shows the structure of the liquid crystal display device which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure of the CTL board | substrate and T-CON which concern on the 1st Embodiment of this invention. It is a figure which shows the connection relation of the signal line in the level shifter which concerns on the 1st Embodiment of this invention. It is a figure which shows the waveform of the input signal and output signal of a level shifter which concern on the 1st Embodiment of this invention. It is a figure which shows the structure of the output resistance connected immediately after the output of the amplifier circuit which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure of the amplifier circuit which concerns on the 2nd Embodiment of this invention.

  Hereinafter, a first embodiment for carrying out the present invention (hereinafter referred to as “embodiment 1”) will be described with reference to the drawings.

  FIG. 1 shows a configuration of a liquid crystal display device 100 according to the first embodiment. The video display device 100 includes a video circuit unit 110, a liquid crystal panel 120, a source driver 130, a gate driver 140, a CTL substrate 150 (power supply voltage generation circuit), and a power supply unit 160. The video circuit unit 110 includes an image processing unit 111 and a timing controller (hereinafter referred to as “T-CON”) 112. The source driver 130 and the gate driver 140 are drivers mounted on the liquid crystal panel 120.

  The video circuit unit 110 receives a video signal output from a video device such as a tuner unit of a television receiver or a DVD playback device as an external device, and performs processing for displaying the video signal on the liquid crystal panel 120. Circuit. When the video signal is input, the image processing unit 111 decodes the video signal, generates video signal data, a vertical synchronization signal, and a horizontal synchronization signal based on the decoded video data, and outputs them to the T-CON 112. The T-CON 112 sequentially outputs data for one pixel line of the video signal data input from the image processing unit 111 to the source driver 130.

  The source driver 130 is a circuit for driving source bus lines of TFTs (Thin Film Transisto) groups arranged in a matrix on the liquid crystal panel 120. The gate driver 140 is a circuit for driving gate bus lines of TFTs (Thin Film Transisto) groups arranged in a matrix of the liquid crystal panel 120. The gate driver 140 outputs one line (hereinafter referred to as “pixel line”) of a specific pixel output by the T-CON 112 when the T-CON 112 completes outputting the voltage data of one line of pixels to the source driver 130. select. Then, the source driver 130 outputs the data for one pixel line received from the T-CON 112 to the source bus line, and the data of all the pixels in the pixel line selected by the gate driver 140 is updated to the data from the source driver 130. The When the update of the pixel line data is completed, the gate driver 140 selects the next pixel line. Then, the source driver 130 outputs data for one pixel line newly received from the T-CON 112 to the source bus line, and the data of the next pixel line selected by the gate driver 140 is updated. As described above, the liquid crystal panel 120 performs data update for pixels in all pixel lines during one field period, and repeats pixel data update for all pixel lines in the liquid crystal panel 120 for each field period. As described above, the liquid crystal panel 120 displays the video by repeating the output of the video signal data, that is, the pixel data update at a certain timing, that is, every field period based on the vertical synchronization signal.

  When power is supplied from the power supply unit 160, the CTL substrate 150 generates a power supply voltage for driving the liquid crystal panel and supplies the power supply voltage to the liquid crystal panel 120. The T-CON 112 includes a signal for switching a mode such as a dynamic mode for game video and a standard mode such as television broadcasting (hereinafter referred to as a “mode switching signal”), a channel for television broadcasting, a channel for an external storage device, and the like. A signal for switching channels (hereinafter referred to as “channel switching signal”) is input. Based on the mode switching signal and the channel switching signal, the T-CON 112 is a signal for switching a resistor connected immediately after the output of the amplifier circuit provided on the CTL board 150 (hereinafter referred to as “output resistance switching signal”). Is output to the CTL substrate 150. When the output resistance switching signal is input from the T-CON 112, the CTL board 150 performs resistance switching control based on the output resistance switching signal. The configurations of the CTL substrate 150 and the T-CON 112 according to the present invention will be described later. The power supply unit 160 supplies power to the video circuit unit 110 and also supplies power to the liquid crystal panel 120 via the CTL substrate 150.

FIG. 2 shows a configuration of the CTL substrate 150 and the T-CON 112 according to the first embodiment. In FIG. 2, only the part which concerns on this invention is shown in figure in the CTL board | substrate 150 and T-CON112. The CTL substrate 150 includes an amplification circuit 151, an output resistance circuit unit 152 (output resistance change circuit), and a level shifter 153. The T-CON 112 includes a load state determination circuit 112a (load state determination unit). The amplifier circuit 151 constitutes a voltage follower, and outputs a voltage corresponding to the input voltage when a predetermined voltage V ₁ is input. The outputtable current is amplified by the amplifier circuit 151. The output of the amplifier circuit 151 is output to the output resistance circuit unit 152. The output resistance circuit unit 152 is a circuit for switching whether or not to insert a resistance based on an output resistance switching signal output from the load state determination circuit 112a of the T-CON 112. Switching between one resistance value and 0 ohms I do. The structure of the output resistance circuit unit 152 will be described later. The level shifter 153 adjusts the output potential of the output resistance circuit unit 152 and outputs it to the liquid crystal panel 120. When the mode switching signal and the channel switching signal are input, the load state determination circuit 112a of the T-CON 112 determines the load state of the liquid crystal panel 120 based on these signals, and uses the determined result as an output resistance switching signal. It outputs to 152. When the load state determination circuit 112a determines that the load state of the amplifier circuit 151 is large, the load state determination circuit 112a increases the resistance value of the output resistance circuit unit 152, and when the load state determination unit 112a determines that the load state is small, the resistance of the output resistance circuit unit 152 Try to reduce the value.

  FIG. 3 shows a specific example of the level shifter 153 according to the first embodiment. As shown in FIG. 3, the level shifter 153 inputs signals for six pairs of an input signal A and an input signal B (hereinafter, referred to as one pair of input signals) that are out of phase with each other from the T-CON 112. Further, the level shifter 153 receives the voltage (VCS + 1) of the amplifier circuit 151a, the voltage (VCS + 2) of the amplifier circuit 151b, the voltage (VCS-2) of the amplifier circuit 151c, and the amplifier from the power supply unit 160 via the output resistance circuit unit 152. When the voltage (VCS-1) of the circuit 151d is input, an output signal obtained by level shifting the waveforms of the input signal A and the input signal B is output to the liquid crystal panel 120. FIG. 4 shows waveforms of the input signal and the output signal of the level shifter according to the first embodiment. FIG. 4A shows waveforms of the input signal A and the input signal B whose phases are shifted from each other. The level shifter 153 applies a voltage (VCS + 1), a voltage (VCS + 2), a voltage (VCS-2), and a voltage (VCS-1) to the input signal A and the input signal B as shown in FIG. The level-shifted output signal shown in FIG.

  FIG. 5 shows a structure of the output resistance circuit unit 152 connected to the amplifier circuit 151 according to the first embodiment. As shown in FIG. 5, the output resistance circuit unit 152 includes a resistor 152a and a switch 152b connected in parallel to the resistor 152a. The switch 152b is opened and closed based on the output resistance switching signal, and the connection of the resistor 152a is controlled. That is, the resistor 152a is inserted when the switch 152b is turned off, and the resistor 152a is short-circuited when the switch 152b is turned on.

  Next, a process from when the T-CON 112 inputs a mode switching signal or a channel switching signal until the output resistance switching signal is output to the output resistance circuit unit 152 of the CTL substrate 150 will be described with reference to FIGS. 2 and 5. . When the display mode of the liquid crystal display device 100 is switched, a mode switching signal is output to the T-CON 112. Further, when the channel of the liquid crystal display device 100 is switched, a channel switching signal is output to the T-CON 112. When the load state determination circuit 112a of the T-CON 112 receives the mode switching signal or the channel switching signal, the load state of the liquid crystal panel 120 is determined based on the mode switching signal or the channel switching signal. As a method of determining the load state of the liquid crystal panel 120, the difference in brightness between the pixels of the liquid crystal panel 120 is large, the difference in data between adjacent pixels is large, and the displayed frame and the next frame are displayed. Discriminating by detecting the amount of data fluctuation in pixel units, such as when there is a large difference in data from the previous frame, or when there is a large difference in data when focusing on the same pixel in the displayed frame and the next displayed frame Do. As an example of a video pattern with a heavy load state, for example, a staggered pattern with a narrow repetition interval can be cited. In other words, in the case of a staggered pattern in which the brightness of pixels is repeated at a high speed, the number of pixel data that can be switched per unit time, in other words, the number of pixels in which current flows increases, and the current flowing in the liquid crystal panel increases Will do.

  When the load state of the liquid crystal panel 120 is determined by the load state determination circuit 112a and it is determined that the liquid crystal panel 120 is a normal load, the load state determination circuit 112a sets the output resistance switching signal to “ON” and outputs it. Output to the resistance circuit unit 152. When the load state determination circuit 112 a determines that the liquid crystal panel 120 is a heavy load, the load state determination circuit 112 a sets “OFF” in the output resistance switching signal and outputs the signal to the output resistance circuit unit 152. The output resistance circuit unit 152 receives the output resistance switching signal and determines whether the output resistance switching signal is “ON” or “OFF”. When the output resistance switching signal is “ON”, the output resistance circuit unit 152 switches so as to close the switch 152b. Thus, by closing the switch 152b of the output resistance circuit unit 152, the resistor 152a is short-circuited. Further, when the output resistance switching signal is “OFF”, the output resistance circuit unit 152 switches so as to open the switch 152b. Thus, the resistor 152a is inserted by opening the switch 152b of the output resistance circuit unit 152.

  Thus, the resistor 152a of the output resistor circuit unit 152 is inserted when the liquid crystal panel 120 is a heavy load, and the resistor 152a of the output resistor circuit unit 152 is short-circuited when the liquid crystal panel 120 is a normal load. . That is, when the liquid crystal panel 120 is heavily loaded, the heat generation of the amplifier circuit 151 increases. Therefore, the increase in heat generation is suppressed by passing through the resistor 152a, and when the heat generation of the amplifier circuit 151 does not increase, the resistor 152a is not passed. Thus, current loss and ripple voltage due to the resistor 152a can be suppressed.

  In the first embodiment, the resistor 152a may be a variable resistor such as a field effect transistor (FET), and the value of the variable resistor may be changed. In this case, the variable resistance value of the output resistance circuit unit 152 is set high when the load is heavy, and the variable resistance value of the output resistance circuit unit 152 is set low when the liquid crystal panel 120 is a normal load. In this way, by changing the value of the variable resistor in accordance with the load state of the liquid crystal panel 120, the resistance value can be set low when it is not necessary to pass through the resistor, thereby suppressing current loss and ripple voltage. it can.

  Next, a second embodiment (hereinafter referred to as “second embodiment”) for carrying out the present invention will be described with reference to the drawings. The configuration of the liquid crystal display device according to the second embodiment is the same as that shown in FIG. 1 except that the CTL substrate 150 is changed to the CTL substrate 150a and no output resistance switching signal is output from the T-CON 112 to the CTL substrate 150. 1 is the same as the configuration of the one liquid crystal display device 100. The structure of the output resistance circuit unit 152 according to the second embodiment is the same as the structure of the output resistance 152 of the first embodiment shown in FIG.

FIG. 6 shows a configuration of a CTL substrate 150a according to the second embodiment. FIG. 6 illustrates only a portion according to the present invention in the CTL substrate 150a. The CTL substrate 150 a includes an amplifier circuit 151, an output resistance circuit unit 152, a level shifter 153, and a temperature sensor 154. The amplifier circuit 151 constitutes a voltage follower, and outputs a voltage corresponding to the input voltage when a predetermined voltage V ₁ is input. The outputtable current is amplified by the amplifier circuit 151. The output of the amplifier circuit 151 is output to the output resistance circuit unit 152. The output resistance circuit unit 152 is a circuit that switches whether to insert a resistor based on an output resistance switching signal output from the temperature sensor 154. The level shifter 153 adjusts the output potential of the amplifier circuit 151 and outputs it to the liquid crystal panel 120. The temperature sensor 154 can determine whether or not the heat generation of the amplifier circuit 151 is increasing by measuring the temperature inside the CTL substrate 150a. That is, if the heat generation of the amplifier circuit 151 is increased, the temperature inside the CTL substrate 150a becomes high. Therefore, the temperature sensor 154 determines the measured temperature, and outputs the determined result to the output resistance circuit unit 152 as an output resistance switching signal.

  When the temperature sensor 154 determines the heat generation state of the amplifier circuit 151 and determines that the heat generation of the amplifier circuit 151 has not increased, the temperature sensor 154 sets the output resistance switching signal to “ON” and the output resistance circuit unit 152. Output to. Further, when the temperature sensor 154 determines that the heat generation of the amplifier circuit 151 is increasing, the temperature sensor 154 outputs the output resistance switching signal to the output resistance circuit unit 152 as “OFF”. The output resistance circuit unit 152 receives the output resistance switching signal and determines whether the output resistance switching signal is “ON” or “OFF”. When the output resistance switching signal is “ON”, the output resistance circuit unit 152 switches so as to close the switch 152b. Thus, by closing the switch 152b of the output resistance circuit unit 152, the resistor 152a is short-circuited. Further, when the output resistance switching signal is “OFF”, the output resistance circuit unit 152 switches so as to open the switch 152b. Thus, the resistor 152a is inserted by opening the switch 152b of the output resistance circuit unit 152.

  In this way, the resistor 152a of the output resistance circuit unit 152 is passed when the heat generation of the amplifier circuit 151 is increasing, and the resistor 152a of the output resistor circuit unit 152 is set when the heat generation of the amplifier circuit 151 is not increasing. Do not pass through. That is, when the liquid crystal panel 120 is heavily loaded, the heat generation of the amplifier circuit 151 increases. Therefore, the increase in heat generation is suppressed by passing through the resistor 152a, and when the heat generation of the amplifier circuit 151 does not increase, the resistor 152a is not passed. Thus, current loss and ripple voltage due to the resistor 152a can be suppressed. Conventionally, when an increase in heat generation of the amplifier circuit 151 is detected by the temperature sensor 154, the liquid crystal display device 100 is also stopped by stopping the amplifier circuit 151 itself. In this way, the resistor 152a is stopped by the switch 152b. By switching, the number of times that the liquid crystal display device 100 stops can be reduced.

  In the second embodiment, the amplifier circuit 151, the output resistor circuit unit 152, the level shifter 153, and the temperature sensor 154 are provided on the CTL substrate 150a. However, the amplifier IC includes an amplifier circuit 151, a resistor 152a, and a switch. 152b, a level shifter 153, and a temperature sensor 154 may be provided, and the amplifier IC may be installed on the CTL board 150a.

  As described above, according to the present embodiment, the output resistance circuit unit 152 connected immediately after the output of the amplifier circuit 151 can be controlled. Therefore, when the display panel 120 is driven according to the special video signal pattern, the amplifier circuit generates heat. When it increases, heat can be suppressed because resistance is passed. Further, when the display panel 120 is driven in accordance with a normal video signal pattern and the heat generation of the amplifier circuit does not increase, the resistor is not passed, so that current loss and ripple voltage due to the resistor can be suppressed.

  As mentioned above, although it demonstrated based on embodiment of this invention, this embodiment is an illustration, Various modifications are possible for the combination of each of those component, and such a modification is also in the scope of the present invention. This will be understood by those skilled in the art.

DESCRIPTION OF SYMBOLS 100 ... Liquid crystal display device 110 ... Video circuit part 111 ... Image processing part 112 ... T-CON
112a... Load state determination circuit (load state determination unit)
120... Liquid crystal panel 130... Source driver 140... Gate driver 150... CTL substrate (power supply voltage generation circuit)
150a ... CTL board (power supply voltage generation circuit)
151... Amplifier circuit 151 a... Amplifier circuit 151 b... Amplifier circuit 151 c... Amplifier circuit 151 d. circuit)
152a... Resistor 152b... Switch 153... Level shifter 154 temperature sensor 160.

Claims (7)

A liquid crystal display device comprising: a power supply voltage generation circuit that generates a power supply voltage for driving a liquid crystal panel; and an output resistance change circuit that changes an output resistance of the power supply voltage generation circuit. The liquid crystal display device according to claim 1, wherein the output resistance changing circuit switches between one resistance value and 0 ohm. A load state determination unit for determining a load state of the power supply voltage generation circuit;
The liquid crystal display device according to claim 1, wherein the output resistance changing circuit is controlled according to a determination result of the load state determination unit.   The load state determination unit increases the resistance value of the output resistance change circuit when determining that the load state of the amplifier circuit is large, and determines the resistance value of the output resistance change circuit when it is determined that the load state is small. The liquid crystal display device according to claim 3, wherein:   5. The liquid crystal display device according to claim 3, wherein the load state determination unit performs determination based on a data fluctuation amount of a pixel unit of the liquid crystal panel.   The liquid crystal display device according to claim 3, wherein the load state determination unit determines based on a mode switching signal or a channel switching signal.   5. The liquid crystal display device according to claim 3, wherein the load state determination unit determines based on a temperature of the power supply voltage generation circuit.

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