JP6584266B2 - LCD drive circuit - Google Patents

Description

  The present invention relates to a liquid crystal driving circuit that applies a voltage corresponding to a luminance level to an electrode of a liquid crystal panel.

  Conventionally, a non-inverted signal having the same polarity as an input video signal and its inverted signal are generated, and synthesized so that they are targeted for each horizontal line, thereby generating a drive signal having no DC offset. Such a liquid crystal driving circuit is known (for example, see Patent Document 1). By using such a drive signal, it is possible to reduce liquid crystal burn-in that occurs when a DC level signal is continuously applied to the liquid crystal panel.

JP-A-5-61430

  By the way, although the DC offset applied to the liquid crystal panel can be reduced by using the liquid crystal driving circuit disclosed in Patent Document 1 described above, the DC level cannot be completely reduced to zero, and the time is long. There is a problem in that there is a possibility that the burn-in of the liquid crystal panel may occur with the use of. For example, in the configuration shown in FIG. 1 and FIG. 11 of Patent Document 1, the multiplex driver 18 generates a non-inverted signal having the same polarity as the video signal and its inverted signal. It is difficult to generate an inverted signal in which the signal is accurately inverted, and the DC offset cannot be completely eliminated. The same applies to the intermediate voltage Vp, and it is desirable to match the intermediate voltage level of the applied voltage V (= 1 / 2V). However, in reality, the intermediate voltage Vp has an error, so A DC offset occurs due to this error.

  The present invention was created in view of the above points, and an object of the present invention is to provide a liquid crystal driving circuit capable of preventing the occurrence of burn-in of a liquid crystal panel by eliminating a DC offset caused by a driving signal. It is in.

  In order to solve the above-described problem, the liquid crystal driving circuit of the present invention is a liquid crystal driving circuit that applies a driving voltage to a pair of electrodes of a display panel, and generates a common voltage to be applied to one of the pair of electrodes. Driving voltage for applying to the other of the pair of electrodes the first and second voltages having different polarities so that the potential difference between the voltage generation unit and the common voltage is a voltage value corresponding to the gradation indicated by the input signal A drive voltage generation unit configured as a drive voltage generation unit configured by a resistance voltage divider circuit having one end connected to the high potential side power supply terminal and the other end connected to the low potential side power supply terminal; And a drive voltage switching unit that switches the drive voltage so that the second voltage is alternately applied to the other of the pair of electrodes at a predetermined interval, and a resistance voltage division with each of the high potential side power supply terminal and the low potential side power supply terminal Both sides of the circuit The connection between the respective parts, and a power supply switching unit that switches repeatedly at a predetermined timing.

  By repeatedly switching the polarities of the first voltage and the second voltage generated by the resistance voltage dividing circuit, the potential difference between the first voltage and the common voltage and the potential difference between the second voltage and the common voltage can be accurately determined. Even when they do not match or when the center voltage of the first and second voltages does not exactly match the common voltage, the DC bias caused by these can be canceled out. As a result, the DC bias generated by the drive signal can be eliminated and the occurrence of burn-in of the liquid crystal panel can be prevented.

The power supply switching unit described above includes a first switch that selectively connects one end of the resistance voltage dividing circuit to one of the high potential side power supply terminal and the low potential side power supply terminal, and the other end of the resistance voltage dividing circuit. A second switch for selectively connecting the end to either the high potential side power supply terminal or the low potential side power supply terminal, and a connection state via the first switch and a connection via the second switch The state is changed at a predetermined timing . As a result, the polarities of the first and second voltages as drive voltages can be reliably switched.

  Moreover, it is desirable that the interval at which the first voltage and the second voltage are alternately switched by the drive voltage switching unit described above is a display frame switching interval. Further, it is desirable that the interval at which the connection is repeatedly switched by the power supply switching unit described above is longer than the interval at which the first and second voltages are alternately switched by the drive voltage switching unit. As a result, it is possible to reliably eliminate the DC bias that occurs when the use state in which the first voltage and the second voltage are alternately applied as the drive voltage continues.

  Further, it is desirable that the power supply switching unit described above switches the connection state every time the voltage application operation is started by the drive voltage switching unit. In particular, the above-described power supply switching unit desirably switches the connection state every time the input mode is switched. As a result, it is possible to make the image disturbance that occurs when switching the connection state of both ends of the resistance voltage dividing circuit inconspicuous, and to prevent the display quality from deteriorating.

  Further, it is desirable that the above-described power supply switching unit switches the connection state when the accumulated time of voltage application by the drive voltage switching unit in the same connection state exceeds a predetermined value. As a result, it is possible to make the time until switching between the connection states at both ends of the resistance voltage dividing circuit substantially constant, and to reliably cancel the DC bias accumulated before switching.

It is a figure which shows the structure of the liquid crystal drive circuit of one Embodiment. It is a figure which shows the detailed structure of a drive voltage production | generation part, a drive voltage switching part, and a power supply switching part. It is a figure which shows the relationship between the gradation instruct | indicated with an input signal, and the voltages V1-V18 produced | generated by a drive voltage generation part. It is a figure which shows the relationship between each display frame and the voltage applied to the LCD panel applied. It is a figure which shows the voltage applied to an LCD panel at the time of odd-numbered starting, and even-numbered starting.

  Hereinafter, a liquid crystal driving circuit according to an embodiment to which the present invention is applied will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a configuration of a liquid crystal driving circuit according to an embodiment. A liquid crystal driving circuit 100 shown in FIG. 1 is for applying a driving voltage to a pair of electrodes arranged with a liquid crystal of an LCD panel 200 as a display panel interposed therebetween, and includes a common voltage generating unit 10 and a driving voltage generating unit. 20, a drive voltage switching unit 30 and a power supply switching unit 40 are provided.

  The common voltage generator 10 generates a common voltage Vcom applied to one of the pair of electrodes of the LCD panel 200.

The drive voltage generation unit 20 applies the first voltage Va and the second voltage Vb having different polarities so that the potential difference with the common voltage Vcom becomes a voltage value corresponding to the gradation indicated by the input signal. It is generated as a drive voltage applied to the other of the pair of electrodes of the LCD panel 200. The drive voltage generation unit 20 is configured by a resistance voltage dividing circuit. This resistance voltage dividing circuit has one end connected to a high potential side power supply terminal (for example, a positive terminal of a power supply circuit (not shown) to which the operating voltage V _DD is applied) and the other end connected to a low potential side power supply terminal (for example, a ground terminal). Terminal).

  The drive voltage switching unit 30 is configured such that the first voltage Va and the second voltage Vb generated by the drive voltage generation unit 20 alternate with the other of the pair of electrodes of the LCD panel 200 at a predetermined interval (for example, every display frame). The drive voltage is switched so as to be applied.

  The power supply switching unit 40 connects each of the high-potential-side power supply terminal and the low-potential-side power supply terminal to both ends of the resistance voltage dividing circuit at a predetermined timing (for example, when the liquid crystal driving circuit 100 is turned on). Switch repeatedly.

  FIG. 2 is a diagram illustrating detailed configurations of the drive voltage generation unit 20, the drive voltage switching unit 30, and the power supply switching unit 40.

  As shown in FIG. 2, the drive voltage generation unit 20 is configured by a resistance voltage dividing circuit 20A in which, for example, 19 resistors R1 to R19 are connected in series. In the resistance voltage dividing circuit 20A, nine pairs of resistors are arranged symmetrically across the resistor R10 arranged in the center. The two resistors constituting each pair have the same resistance value. Specifically, the resistor R1 and the resistor R19 have the same resistance value. The resistor R2 and the resistor R18 have the same resistance value. The resistor R3 and the resistor R17 have the same resistance value. The resistor R4 and the resistor R16 have the same resistance value. Resistor R5 and resistor R15 have the same resistance value. The resistor R6 and the resistor R14 have the same resistance value. The resistor R7 and the resistor R13 have the same resistance value. The resistor R8 and the resistor R12 have the same resistance value. The resistor R9 and the resistor R11 have the same resistance value. In the resistance voltage dividing circuit 20A having such a configuration, 18 types of voltages V1 to V18 are output from the connection points of the 19 resistors R1 to R19.

  The drive voltage switching unit 30 selects a pair of voltages from the 18 types of voltages V1 to V18 output from the drive voltage generation unit 20, and further supplies the pair of voltages (first and second voltages) at a predetermined interval. And switch to the other of the pair of electrodes of the LCD panel 200.

  The power supply switching unit 40 is connected to one end of the resistance voltage dividing circuit 20A constituting the drive voltage generation unit 20, and selectively connects one of the high potential side power supply terminal and the low potential side power supply terminal to this one end 2 A switching unit 40A having two switches 42a and 44a, and two switches that are connected to the other end of the resistance voltage dividing circuit 20A and selectively connect the other of the high potential side power supply terminal and the low potential side power supply terminal to the other end. And a switching unit 40B having 42b and 44b.

  Next, 18 types of voltages V1 to V18 generated by the drive voltage generation unit 20 will be described.

  FIG. 3 is a diagram illustrating the relationship between the gray scale indicated by the input signal and the voltages V <b> 1 to V <b> 18 generated by the drive voltage generation unit 20. In FIG. 3, the horizontal axis indicates the gradation, and it is assumed that nine gradations from black to white are designated by the input signal. The vertical axis indicates the driving voltage corresponding to each gradation so as to reproduce the gamma characteristic. The voltages V1 to V9 correspond to the first voltage Va and the voltages V18 to V10 correspond to the second voltage Vb. ing. Further, the characteristic shown in FIG. 3 is that in one switching unit 40A, the switch 42a is turned on, the switch 44a is turned off, one end of the resistance voltage dividing circuit 20A is connected to the high potential side power supply terminal, and the other switching unit It is assumed that the switch 42b is turned off at 40B, the switch 44b is turned on, and the other end of the resistance voltage dividing circuit 20A is connected to the low potential side power supply terminal.

  The voltages V9 and V10 corresponding to black (the gradation indicating the darkest luminance) have a potential difference of ΔV9 and ΔV10 with respect to the common voltage Vcom, and these potential differences ideally have the same absolute value and only polarity. Is different. Further, the voltages V1 and V18 corresponding to white (the gradation indicating the brightest luminance) have a potential difference of ΔV1 and ΔV18 from the common voltage Vcom, and these potential differences are ideally the same in absolute value. Only the polarity is different. The same applies to the other two voltages corresponding to the halftone between white and black. Ideally, the absolute value of the potential difference from the common voltage Vcom is the same and only the polarity is different.

  When a certain gradation is designated by the input signal, the drive voltage switching unit 30 determines a pair of voltages corresponding to the gradation, and switches between these voltages to be applied every time the display frame is switched. For example, when the voltage V4 as the first voltage Va and the voltage V15 as the second voltage Vb are considered as a pair of voltages, the voltage as the first voltage Va is used as a drive voltage when displaying an odd frame. V4 is used, and the voltage V15 as the second voltage Vb is used as a drive voltage when displaying an even frame. These voltages V4 and V15 have a potential difference of ΔV4 and ΔV15 from the common voltage Vcom. Ideally, the absolute values of these potential differences are the same, and the same gradation is maintained in successive frames.

  FIG. 4 is a diagram showing the relationship between each display frame and the voltage applied to the LCD panel 200 to be applied. When displaying odd frames, the common voltage Vcom is applied to one of the pair of electrodes of the LCD panel 200, and the voltage V4 output from the drive voltage switching unit 30 is applied to the other of the pair of electrodes. Further, when displaying an even frame, the common voltage Vcom is applied to one of the pair of electrodes of the LCD panel 200, and the voltage V15 output from the drive voltage switching unit 30 is applied to the other of the pair of electrodes.

  By the way, the absolute values of the potential difference ΔV4 between the voltage V4 and the common voltage Vcom and the potential difference ΔV15 between the voltage V15 and the common voltage Vcom are ideally designed to be the same. Must not.

  Therefore, in the liquid crystal drive circuit 100 of the present embodiment, the resistance voltage dividing circuit that configures the drive voltage generation unit 20 using the power supply switching unit 40 every time the power is turned on, that is, at the time of odd-numbered activation and even-numbered activation. The connection state between 20A and the high potential side power supply terminal and the low potential side power supply terminal is switched.

  For example, at the start of an odd number of times, the switching unit 40A turns on the switch 42a and turns off the switch 44a, thereby connecting one end of the resistance voltage dividing circuit 20A to the high potential side power supply terminal. In the switching unit 40B, the switch 42b is turned off and the switch 44b is turned on to connect the other end of the resistance voltage dividing circuit 20A to the low potential side power supply terminal.

  At the time of even-number activation, in the switching unit 40A, the switch 42a is turned off and the switch 44a is turned on to connect one end of the resistance voltage dividing circuit 20A to the low potential side power supply terminal. In the switching unit 40B, the switch 42b is turned on and the switch 44b is turned off, thereby connecting the other end of the resistance voltage dividing circuit 20A to the low potential side power supply terminal.

  FIG. 5 is a diagram illustrating voltages applied to the LCD panel 200 at the time of odd-numbered activation and even-numbered activation. FIG. 5A shows an applied voltage at the start of odd times, and FIG. 5B shows an applied voltage at the start of even times.

When an image is displayed using the LCD panel 200 for a long time at the start of an odd number of times, an error in the resistance value of each resistor constituting the common voltage Vcom, the resistance voltage dividing circuit 20A, a difference in the lengths and shapes of various wirings, etc. due to, not the absolute value of ΔV4 and ΔV15 same, DC bias [Delta] V _DC occurs (FIG. 5 (a)).

In addition, the common voltage Vcom does not change at the time of even-number activation, but the voltages V4 (+) and V15 (−) (+ in the parentheses indicate that the polarity is positive, and − indicates that the polarity is negative. ) Changes in polarity, the voltage between the pair of electrodes of the LCD panel 200 becomes ΔV4 (−) and ΔV15 (+) from ΔV4 (+) and ΔV15 (−) so far. .DELTA.V4 (-) and ΔV15 (+) is that the absolute value is not the same of the same as the case of startup odd times as described above, DC bias - [Delta] V _DC occurs (FIG. 5 (B)).

Thus the display startup behavior odd times startup of the display operation and even number of times in the repeats, the DC bias [Delta] V _DC occurring odd startup, the DC bias - [Delta] V _DC generated even number of times startup cancel each other .

  As described above, in the liquid crystal driving circuit 100 according to the present embodiment, the first voltage Va and the common voltage are switched by repeatedly switching the polarities of the first voltage Va and the second voltage Vb generated by the resistance voltage dividing circuit 20A. The potential difference between Vcom and the potential difference between the second voltage Vb and the common voltage Vcom do not exactly match, or the center voltage of the first voltage Va and the second voltage Vb does not exactly match the common voltage Vcom. Even in this case, the DC bias due to these can be canceled. As a result, the DC bias generated by the drive signal can be eliminated and the occurrence of burn-in of the liquid crystal panel can be prevented.

  In addition, a switching unit 40A having two switches 42a and 44a and a switching unit 40B having two switches 42b and 44b are provided and connected to both ends of the resistance voltage dividing circuit 20A by switching these switches. The connection state of the high potential side power supply terminal and the low potential side power supply terminal is switched. As a result, the polarities of the first voltage Va and the second voltage Vb as drive voltages can be reliably switched.

  In addition, an interval at which the first voltage Va and the second voltage Vb having the same absolute value and different polarities corresponding to the same gradation are alternately switched is set as a display frame switching interval, and the switching units 40A and 40B are configured to generate a high potential. The interval for repeatedly switching the connection state between the side power supply terminal and the low potential side power supply terminal and the resistance dividing circuit 20A is set to be longer. As a result, it is possible to reliably eliminate the DC bias that occurs when the use state in which the first voltage Va and the second voltage Vb are alternately applied as the drive voltage continues.

  In addition, the switching of the connection state by the switching units 40A and 40B is performed every time the power supply voltage is applied by the switching units 40A and 40B, that is, every time the liquid crystal driving circuit 100 is turned on, so that the resistance voltage dividing circuit 20A is switched. Disturbances in the video that occur when switching the connection state of both ends can be made inconspicuous, and deterioration in display quality can be prevented.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation implementation is possible within the range of the summary of this invention. For example, in the above-described embodiment, the connection state of the high potential side power supply terminal and the low potential side power supply terminal applied to both ends of the resistance voltage dividing circuit 20A is switched every time the liquid crystal driving circuit 100 is turned on. Whenever the input mode is switched, that is, when the LCD panel 200 is used as a display device such as a navigation device, an audio device, a terrestrial digital broadcast receiver, or a radio receiver, the device that is the source of the input signal is changed. The connection state of the high potential side power supply terminal and the low potential side power supply terminal applied to both ends of the resistance voltage dividing circuit 20A may be switched in accordance with “when the input mode is switched”. Since the content of the video changes greatly before and after the input mode is switched, it is possible to make the video disturbance inconspicuous when switching the connection state of both ends of the resistance voltage dividing circuit 20A, and to prevent the display quality from deteriorating. be able to.

  Further, the accumulated time of voltage application to the LCD panel 200 by the drive voltage switching unit 30 in the same connection state (a state in which the connection state between the high potential side power supply terminal and the low potential side connection terminal is not changed) is a predetermined value (for example, 50 hours). When the power of the liquid crystal driving circuit 100 is turned on or when the input mode is switched, the connection between the high potential side power supply terminal and the low potential side power supply terminal applied to both ends of the resistance voltage dividing circuit 20A is performed. You may make it change a state. As a result, the time every time until the connection state of both ends of the resistance voltage dividing circuit 20A is switched can be made substantially constant, and the DC bias accumulated before the switching can be surely canceled.

  Further, in the above-described embodiment, the first voltage Va (V1 to V9) is applied in the odd-numbered frame, and the second voltage Vb (V18 to V10) is applied in the even-numbered frame. Instead of switching Va and the second voltage Vb in units of frames, switching may be performed in units of lines, and moreover, switching may be performed in units of frames when focusing on the same line.

  As described above, according to the present invention, by repeatedly switching the polarities of the first voltage and the second voltage generated by the resistance voltage dividing circuit, the potential difference between the first voltage and the common voltage and the second voltage are changed. Even when the potential difference between the voltage and the common voltage does not exactly match, or when the center voltage of the first and second voltages does not exactly match the common voltage, the DC bias caused by them is canceled out. be able to. As a result, the DC bias generated by the drive signal can be eliminated and the occurrence of burn-in of the liquid crystal panel can be prevented.

DESCRIPTION OF SYMBOLS 10 Common voltage generation part 20 Drive voltage generation part 20A Resistance voltage dividing circuit 30 Drive voltage switching part 40 Power supply switching part 40A, 40B Switching part 42a, 42b, 44a, 44b Switch 100 Liquid crystal drive circuit 200 LCD panel

Claims (6)

A liquid crystal driving circuit for applying a driving voltage to a pair of electrodes of a display panel,
A common voltage generator that generates a common voltage applied to one of the pair of electrodes;
First and second voltages having different polarities from which the potential difference from the common voltage becomes a voltage value corresponding to the gradation indicated by the input signal are generated as drive voltages to be applied to the other of the pair of electrodes. A drive voltage generation unit comprising a resistance voltage divider circuit having one end connected to the high potential side power supply terminal and the other end connected to the low potential side power supply terminal;
A drive voltage switching unit that switches the drive voltage so that the first and second voltages are alternately applied to the other of the pair of electrodes at a predetermined interval;
A power supply switching unit that repeatedly switches the connection between each of the high-potential-side power supply terminal and the low-potential-side power supply terminal and both ends of the resistance voltage dividing circuit at a predetermined timing;
The power supply switching unit includes a first switch that selectively connects one end of the resistance voltage dividing circuit to either the high-potential-side power supply terminal or the low-potential-side power supply terminal; A second switch for selectively connecting the other end of the voltage circuit to one of the high potential side power supply terminal and the low potential side power supply terminal, and a connection state via the first switch; liquid crystal drive circuit, wherein that you change the connection state via the second switch at the predetermined timing. In claim 1 ,
The liquid crystal driving circuit according to claim 1, wherein an interval at which the first and second voltages are alternately switched by the driving voltage switching unit is a display frame switching interval. In claim 1 or 2 ,
The liquid crystal driving circuit characterized in that an interval at which the connection is repeatedly switched by the power source switching unit is longer than an interval at which the first voltage and the second voltage are alternately switched by the driving voltage switching unit. In any one of Claims 1-3 ,
The liquid crystal driving circuit, wherein the power source switching unit switches a connection state every time a voltage application operation is started by the driving voltage switching unit. In any one of Claims 1-3 ,
The liquid crystal driving circuit, wherein the power source switching unit switches the connection state every time the input mode is switched. In claim 4 or 5 ,
The liquid crystal driving circuit according to claim 1, wherein the power source switching unit switches the connection state when a cumulative voltage application time by the driving voltage switching unit in the same connection state exceeds a predetermined value.

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