JPH10170885A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the picture quality and reliability of a liquid crystal display device at a low cost, by driving the device at an operation point where a tracking error is minimum, making the bias ratio always constant, making temperature correction of a liquid crystal panel, and making it easy to adjust the contrast. SOLUTION: A liquid crystal driving power circuit 17 provided with an operation reference voltage input terminal VM, which determines the operation point of the liquid crystal panel is provided with a temperature correction terminal, an ON/OFF terminal, a Vcont terminal, etc., the operation reference voltage VM is generated by voltage dividing resistances R1, R2, and R3 from a scanning driving voltage VxH as the output voltage of the liquid crystal driving power circuit 17 and fed back to the VM terminal of the liquid crystal driving power circuit 17, and this VM is inputted to a scanning line driving circuit 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device useful as a display for information equipment such as video equipment and computers.

[0002]

2. Description of the Related Art FIG. 15 shows a conventional liquid crystal display device, in which signal lines 11 and scanning lines 12 are arranged in a matrix.
The intersection of the signal line 11 and the scanning line 12 is a pixel electrode 13. The liquid crystal panel including the signal lines 11, the scanning lines 12, and the pixel electrodes 13 is driven by a signal line driving circuit 14 and a scanning line driving circuit 15. Driving voltages for the signal line driving circuit 14 and the scanning line driving circuit 15 are supplied from a signal line driving voltage generating circuit including a liquid crystal driving power supply circuit 20 and an operational amplifier 21. The control circuit 16 controls the signal line drive circuit 14, the scan line drive circuit 15, and the liquid crystal drive power supply circuit 20.

A scanning line driving circuit 15 sequentially scans the scanning lines 12 and applies a driving voltage of VxH or VxL to a selected scanning line 12 and an operation reference voltage VM to an unselected scanning line 12. . The signal line drive circuit 14 drives the signal line 11 with a signal line drive voltage of VyH or VyL as a first scan pulse in response to a control signal of the control circuit 16. The liquid crystal panel is driven as described above.

[0004] Vin represents a power supply voltage of the liquid crystal display device and is usually in a range of 3V to 5.5V. The liquid crystal drive power supply circuit 20 is Vx
It comprises an output circuit and a Vop output circuit. The Vx output circuit outputs the drive voltages VxH and VxL of the scanning line drive circuit 20. ON to turn on / off the output voltage to the Vx output circuit
ON / OFF terminal for inputting / OFF control signal and Vx
A Vcont terminal for inputting a control signal for optimizing the contrast of the liquid crystal display device by varying the voltages of H and VxL. A DC voltage of 0 to 3 V is input to the Vcont terminal. The ON / OFF control signal is used to control the display of the liquid crystal display device independently of the display data. When the display is performed, the display is turned on, and when the display is not performed, the display is turned off. Are also input to the signal line driving circuit 14 and the scanning line driving circuit 15.

When the display is turned off, the signal line drive circuit 14 and the scan line drive circuit 15 output VM according to the ON / OFF control signal, and the liquid crystal drive power supply circuit 20 turns off VxH and VxL.
In order to turn off the display, the signal line drive circuit 14
An analog switch that outputs M is required. FIG. 16 shows a configuration diagram of the signal line drive circuit 14. Here, 31 is a data latch. Reference numeral 30 denotes an output circuit, which includes VyH, VyL, and VM.
In order to select one value from the three values, the analog switch is configured by three analog switches.

The Vop output circuit outputs the voltages Vop + and Vop-, and uses them as the power supply for the operational amplifier 21 and the power supply for the operation reference voltage VM that determines the operating point of the liquid crystal panel. The input and output voltages of the power supply circuit are denoted by the same reference numerals as the terminals. V
M is determined by Vop + and the voltage dividing resistors Ra, Rb, Rc, and is represented by (Equation 1).

[0007]

## EQU00001 ## VM = (Vop +). Times. (Rb + Ra) / (Ra + Rb + Rc) As shown in FIG. 15, the voltage obtained from Vop + and the voltage dividing resistor is input to the voltage follower of the operational amplifier 21, and the output is VM.

The signal line driving voltage VyL is Vop + and the voltage dividing resistor R
It is determined by a, Rb, and Rc and is represented by (Equation 2).

[0009]

## EQU2 ## VyL = (Vop +). Times. (Rc) / (Ra + Rb + Rc) When the signal line drive voltage has two values, VxH and VyH, VyL is normally set to 0V, but crosstalk correction for improving image quality is performed. When a voltage is added to the signal line driving voltage and the signal line driving voltage is four or more, VyL is not set to 0V. (Equation 2) is a case where this correction voltage is added to the signal line driving voltage. (However, to simplify the description of the present invention, those relating to the correction voltage are omitted.) Further, the relationship between the scanning line driving voltage and the signal line driving voltage is represented by (Equation 3).
When the above condition is satisfied, the highest contrast of the liquid crystal panel can be obtained.

[0010]

VxH-VM = a (VM-VyL) where a is a bias ratio, which differs depending on the driving method. By substituting VyL = 0 into (Equation 3), VxH = (a + 1)
Get VM. Therefore, when VxH changes, it is necessary to change VM, VyH, and VyL so as to satisfy (Equation 3). In the liquid crystal display device, the scanning line driving voltage is changed by Vcont so that the contrast is optimal for changes in ambient temperature, brightness, and the like. Yes, does not satisfy (Equation 3). Actually, in the range of the change of the scanning line driving voltage by Vcont, the contrast does not decrease so as to cause a practical problem, and therefore, VM and Vy determined by (Equation 1) and (Equation 2).
L, VyH can be used. However, this is a problem when a high-speed liquid crystal is used or in a high-quality liquid crystal display device.

VyL is the output of the voltage follower by the operational amplifier 21, like the VM. In addition, since the liquid crystal panel is driven by AC drive in which the polarity of the drive voltage is alternately inverted with reference to VM, VyH and VyL must satisfy (Equation 4), and VxH and VxL must satisfy (Equation 5).

[0012]

## EQU4 ## VyH-VM = VyL-VM

[0013]

VxH-VM = VM-VxL Also, the voltages normally used are VxH of 26 to 35V and VM
It is in the range of 1.5-2.5V. As shown in FIG. 15, VyH is obtained from the non-inverting amplifier by the operational amplifier 21 from VM and VyL. R6 and R7 are feedback resistors of the operational amplifier 21, and R6 = 2 × R7. Capacitors C5, C6, C7
Is a stabilizing capacitor for stabilizing the drive voltages of VM, VyH and VyL.

If VxH and VxL do not satisfy (Equation 5), flickers and beats occur on the screen, deteriorating the image quality and shortening the life of the liquid crystal panel. Practically, there is no problem as long as the tracking error between VxH and VxL based on the VM is δVx and (Equation 6) is satisfied.

[0015]

VxH + VxL−2VM = δVx | δVx | ≦ 0.1V As shown in FIG. 15, the liquid crystal drive power supply circuit 20 has no terminal for inputting a VM, and the reference voltage VpM built in the liquid crystal drive power supply circuit 20 is used. This is a configuration in which VxH and VxL satisfying (Equation 6) are preset and set to the same value as VM. Therefore,
The scanning line drive voltage of (Expression 7) is output from the liquid crystal drive power supply circuit 20.

[0016]

If VxH + VxL−2VpM = δVx VM = VpM, then (Equation 5) is satisfied. Is very difficult, the operation reference voltage of the signal line drive voltage VyH and the signal line drive voltage VyL, the scan line drive voltage VxH, and the scan line drive voltage VxL
Operating reference voltages cannot be the same.

[0017]

However, in the above-mentioned conventional configuration, since the liquid crystal drive power supply circuit 20 having the built-in reference voltage VpM does not have an operation reference voltage input terminal, the operation reference voltage VM of the signal line drive voltage is not provided. It cannot be used as an operation reference voltage for the scanning line drive voltage. The difference between VM and VpM is
If −VpM = △ / 2, (Expression 8) is obtained from (Expression 7).

[0018]

VxH + VxL−2VM = δVx− こ と Keeping the tracking error of the scanning line drive voltage of δVx− の within (Expression 8) within ± 0.1 V is extremely difficult due to variations in components, ambient temperature, fluctuations in Vop +, and the like. Have difficulty. δVx−
A liquid crystal driving power supply circuit in which Δ is within ± 0.1 V is very expensive.

Also, since VpM is preset in the liquid crystal drive power supply circuit, it is necessary to redesign the liquid crystal drive power supply circuit 20 when changing the value of VM due to a change in the specification of the liquid crystal panel, etc. And the value of the VM cannot be easily changed.

When the display is turned off by an ON / OFF control signal, an analog switch for selecting and outputting a VM to the signal line driving circuit 14 is required only for the display off function. Costs increase.

Since the contrast of the liquid crystal panel changes depending on the ambient temperature, it is necessary to increase the variable range of the scanning line driving voltage by Vcont in order to obtain the optimum contrast in the operating temperature range. Hard to do.

When the scanning line driving voltage changes,
(Equation 3) cannot be satisfied, and the bias ratio a changes.

The present invention has been made in view of such conventional problems, and has the same operation reference voltage for the signal line drive voltage and the scan line drive voltage, and supplies the operation reference voltage to the liquid crystal drive power supply circuit. By feeding back, the tracking error of the scanning line driving voltage is minimized, and the operation reference voltage VM
The scan line drive voltage for correcting the temperature characteristics of the liquid crystal panel is output, and the display on / off control is simplified.
It is an object of the present invention to provide a liquid crystal display device that significantly improves image quality and reliability at low cost.

[0024]

In order to achieve the above object, according to the first aspect of the present invention, a plurality of signal lines and a plurality of scanning lines are arranged in a matrix and arranged at intersections thereof. Liquid crystal panel having a liquid crystal layer provided between pixel electrodes, a signal line driving circuit for driving the signal lines, a scanning line driving circuit for driving the scanning lines, an operational amplifier for supplying a driving voltage, and a liquid crystal driving power supply circuit And a control circuit for controlling the signal line drive circuit, the scan line drive circuit, and the liquid crystal drive power supply circuit, wherein the liquid crystal drive power supply circuit is provided with an operation reference voltage input terminal. An operation reference voltage that determines an operation point of the liquid crystal panel is created from a scanning line drive voltage that is an output voltage of the power supply circuit, and this operation reference voltage is fed back to the operation reference voltage input terminal of the liquid crystal drive power supply circuit. The operation reference voltage of the signal line drive voltage and the operation reference voltage of the scan line drive voltage are set to the same value, the operation reference voltage can be easily set and changed, and the bias ratio with respect to the change of the scan line drive voltage is changed. It is constant and has the effect of minimizing the tracking error of the driving voltage and realizing improvement in image quality and reliability of the liquid crystal display device at low cost.

Further, the invention according to claim 2 of the present invention provides:
A liquid crystal panel in which a plurality of signal lines and a plurality of scanning lines are arranged in a matrix, and a liquid crystal layer is provided between pixel electrodes arranged at intersections thereof, and a signal line driving circuit for driving the signal lines,
A scanning line driving circuit for driving the scanning line; an operational amplifier for supplying a driving voltage; and a liquid crystal driving power supply circuit; and a control circuit for controlling the signal line driving circuit, the scanning line driving circuit, and the liquid crystal driving power supply circuit. A liquid crystal display device, wherein an operation reference voltage input terminal is provided in the liquid crystal drive power supply circuit, and an operation reference voltage for determining an operation point of a liquid crystal panel is generated from a power supply of the operational amplifier which is an output of the liquid crystal drive power supply circuit. The reference voltage is fed back to an operation reference voltage input terminal of the liquid crystal drive power supply circuit, wherein the operation reference voltage of the signal line drive voltage and the operation reference voltage of the scan line drive voltage are set to the same value, and the operation reference voltage is set and changed. Can be easily done,
It has the effect of minimizing the tracking error of the driving voltage and realizing improvement of the image quality and reliability of the liquid crystal display device at low cost.

According to a third aspect of the present invention, in the liquid crystal driving power supply circuit for outputting the scanning line driving voltages VxH and VxL, the operation reference voltage is set to VM. VxH + VxL-2VM =
| δVx | ≦ ± 0.1 V as δVx,
This has the effect of making the tracking error of the scanning line drive voltage a value that can be practically ignored.

A fourth aspect of the present invention is the invention according to the first or second aspect, wherein a temperature correction terminal is provided in the liquid crystal drive power supply circuit, and the temperature correction terminal and the scanning line drive voltage output are provided. A series circuit of a thermistor and a resistor is inserted between the terminals to output a scanning line driving voltage for correcting the temperature characteristics of the liquid crystal panel. It has the function of improving the image quality of the device.

The invention according to claim 5 of the present invention is the invention according to claim 1 or 2, wherein a liquid crystal drive power supply circuit is provided with a scanning line driving voltage setting terminal, and the scanning line driving voltage setting terminal is provided. A predetermined scanning line drive voltage is obtained by inserting a resistor between the
This has the effect that the drive voltage can be easily set to the optimum value.

The invention according to claim 6 of the present invention is the invention according to claim 1 or claim 2, wherein two kinds of reference voltages are formed from a scanning line drive voltage or a power supply voltage of an operational amplifier, and one of them is a liquid crystal. The operation reference voltage input terminal of the driving power supply circuit is input to the other terminal, and the other is used as the operation reference voltage of the liquid crystal panel. This has the effect of minimizing the tracking error of the scanning line driving voltage.

The invention according to claim 7 of the present invention is the invention according to claim 1 or 2, wherein a liquid crystal drive power supply circuit is provided with a contrast adjustment terminal, and a control voltage input to the contrast adjustment terminal is provided. The present invention is characterized in that the scanning line driving voltage is varied and the contrast of the liquid crystal panel is optimized, and has an effect that the optimum contrast can be set according to the use condition of the liquid crystal display device.

An eighth aspect of the present invention is the invention according to the first or second aspect, wherein an integration circuit is provided at an operation reference voltage input terminal of the liquid crystal driving power supply circuit. And has an effect of removing noise superimposed on the operation reference voltage.

A ninth aspect of the present invention is the invention according to the eighth aspect, wherein the time constant of the integrating circuit provided at the operation reference voltage input terminal of the liquid crystal driving power supply circuit is 1 ms or more. There is an effect that the time constant of the integration circuit can be determined.

A tenth aspect of the present invention is the invention according to the first aspect, wherein an ON / OFF terminal for inputting an ON / OFF control signal for turning on / off a scanning line driving voltage is connected to a liquid crystal driving power supply. The liquid crystal display device is provided in a circuit, and has an effect that display on / off of a liquid crystal display device can be easily realized at low cost.

An eleventh aspect of the present invention is the invention according to the first or second aspect, wherein ON / O for simultaneously turning on / off the scanning line driving voltage and the power supply of the operational amplifier.
An on / off terminal for inputting an FF control signal is provided in the liquid crystal drive power supply circuit, and has an effect that on / off of the display of the liquid crystal display device can be easily realized at low cost.

The invention described in claim 12 of the present invention
The invention according to claim 10 or claim 11, wherein the output circuit of the signal line drive circuit includes only an analog switch that selects and outputs one signal line drive voltage from a plurality of signal line drive voltages, and outputs an operation reference voltage. It is characterized by not having an analog switch for selecting and outputting, and has an effect that the number of analog switches in the signal line driver circuit can be reduced and the cost of the display device can be reduced.

The invention according to claim 13 of the present invention is the invention according to claim 1 or 2, wherein any one of the scanning line drive voltage and the power supply voltage of the operational amplifier is V, and A resistor R1 and a resistor R2 are connected between the V output terminal and ground.
, And V × R1 / (R1 + R2) is used as the input of the voltage follower, and the output voltage of the voltage follower is used as the operation reference voltage. Can be obtained by a simple method.

The invention described in claim 14 of the present invention
13. The invention according to 13, wherein the series resistance value of the resistor R1 and the resistor R2 is set to 1 MΩ or more, and an effect that the power consumption by the resistor R1 and the resistor R2 can be set to a practically negligible value. Have.

The invention according to claim 15 of the present invention is the invention according to claim 1 or claim 2, wherein any one of the scanning line drive voltage and the power supply voltage of the operational amplifier is V, and A resistor R1 and a resistor R2 are connected between the V output terminal and ground.
And a series resistor composed of a resistor R3 and V × (R1 + R2) /
(R1 + R2 + R3) and V × R2 / (R1 + R2 + R3) are input to respective voltage followers, and the output voltages of the voltage followers are used as an operation reference voltage and a signal line drive voltage, respectively. This has the effect that a high and stable operation reference voltage and signal line drive voltage can be obtained by a simple method.

Further, the invention according to claim 16 of the present invention is the invention according to claim 15, characterized in that the series resistance of the resistors R1, R2 and R3 is 1 MΩ or more. This has the effect that the power consumption by the resistors R1, R2 and R3 can be made practically negligible.

[0040]

Embodiments of the present invention will be described below in detail with reference to the drawings. (Embodiment 1) FIG. 1 shows the configuration of a liquid crystal display device according to Embodiment 1 of the present invention, and the same parts as those in the conventional example of FIG. Reference numeral 17 denotes a liquid crystal drive power supply circuit provided with an operation reference voltage input terminal VM that determines an operation point of the liquid crystal panel.

In FIG. 1, reference numeral 11 denotes a signal line, and 12 denotes a scanning line, which are arranged in a matrix. Reference numeral 13 denotes a pixel electrode arranged at the intersection of the signal line 11 and the scanning line 12. A liquid crystal layer is provided between the pixel electrodes to form a liquid crystal panel. Reference numeral 18 denotes a signal line driving circuit that drives the signal lines 11, and 15 denotes a scanning line driving circuit that drives the scanning lines 12. 16 is a signal line drive circuit 18,
This is a control circuit for controlling the scanning line drive circuit 15 and the liquid crystal drive power supply circuit 17.

The scanning line driving circuit 15 sequentially scans the scanning lines 12, applies a driving voltage of VxH or VxL to the selected scanning lines 12, and applies the operation reference voltage V to the unselected scanning lines 12.
Give M. The signal line drive circuit 18 drives the signal line 11 with a signal line drive voltage of VyH or VyL as a first scan pulse in response to the control signal of the control circuit 16. The liquid crystal panel is driven as described above.

Vin represents the power supply voltage of the liquid crystal display device and is usually in the range of 3 V to 5.5 V. The liquid crystal drive power supply circuit 17 is Vx
It comprises an output circuit and a Vop output circuit. The Vx output circuit outputs the drive voltages VxH and VxL of the scanning line drive circuit 15. The Vop output circuit outputs voltages of Vop + and Vop-, and is used as a power supply of the operational amplifier 21. The input and output voltages of the power supply circuit are denoted by the same reference numerals as the terminals.

The ON / OFF terminal of the liquid crystal drive power supply circuit 17 is a terminal for inputting an ON / OFF control signal for turning on / off the output voltages of the Vx output circuit and the Vop output circuit.
The ON / OFF control signal is output from the control circuit 16. V
The M terminal is an input terminal for the operation reference voltage VM of the liquid crystal panel,
cont is an input terminal for a control signal that varies the voltage value of VxH and VxL with a DC voltage of 0 to 3V. FB terminal is V
A temperature correction terminal for obtaining a scanning line driving voltage VxH and a scanning line driving voltage VxL for correcting a temperature characteristic of a liquid crystal panel by inserting a series circuit of a resistor R5 and a thermistor TH between the terminal and a terminal x. Is a given V at room temperature.
When cont is input, by inserting a resistor R4 between TS and ground, the scanning line driving voltage V
This is a preset terminal for setting xH and the scanning line drive voltage VxL. As described above, the VM, TS, and FB terminals are added as compared with the liquid crystal drive power supply circuit 20 of the conventional liquid crystal display device.
All output voltages can be turned on / off by the ON / OFF terminal.

The scanning line driving voltage VxH of the liquid crystal driving power supply circuit 17 having the above functions is divided by the resistors R1, R2 and R3 and is divided by the voltage follower of the operational amplifier 21.
An operation reference voltage VM and a signal line drive voltage VyL are obtained. VyL
And VM are input to a non-inverting amplifier having a gain of 2 by the operational amplifier 21 to obtain VyH. VM, VyH, and VyL satisfy (Equation 3), and VM and VyL are determined by (Equation 9).

[0046]

## EQU9 ## VM = (VxH) .times. (R2 + R3) / (R1 + R2 + R3) VyL = (VxH) .times. (R3) / (R1 + R2 + R3) According to the present invention, according to the present invention, In order to obtain VM, VyL, and VyH, the bias ratio a in (Equation 3) is always constant even when the scanning line driving voltage changes.
The highest contrast that a liquid crystal panel has can always be obtained.

According to the present invention, the thus obtained VM
Is fed back to the VM terminal of the liquid crystal drive power supply circuit 17 and input to the scan line drive circuit 15 to obtain a scan line drive voltage VxH and a scan line drive voltage VxL satisfying (Equation 5). FIG. 2A shows signal line driving voltages VyH and Vy corresponding to image signals.
7 shows a signal line drive voltage waveform indicating a relationship between L and an operation reference voltage VM. 1H represents one horizontal scanning time. FIG. 2B shows a scan line drive voltage waveform indicating the relationship between the scan line drive voltages VxH, VxL and VM. 1V is one vertical scanning time. As shown in FIGS. 2 (a) and 2 (b), the drive voltage is AC-driven based on VM. FIG. 3 shows a configuration diagram of the liquid crystal drive power supply circuit 17. The Vop output circuit and the Vx output circuit shown in FIG. 3 are switching power supplies, and VxH−VM = VxL−VM
The Vx output circuit is composed of a tracking regulator with high accuracy satisfying + δVx, and | δVx |
It has performance of 0.1V or less in the operating temperature range of ° C. Also,
Temperature correction by thermistor, VxH and VxL by Vcont
(Equation 5) is always satisfied even when the variable is changed. As described above, according to the present invention, a decrease in image quality and a decrease in reliability due to a tracking error of a scanning line drive voltage can be ignored. FIG. 4 shows that when the input voltages Vin = 3.3 V and 5 V, δVx
The following shows an example of the temperature characteristic of the above, which sufficiently satisfies | δVx | ≦ 0.1V.

An integrating circuit including a resistor R6 and a capacitor C8 is inserted into the VM terminal. This integration circuit is inserted to remove noise superimposed on the VM and to operate the Vx output circuit stably. FIG. 5 shows that the noise superimposed on the VM is removed by the integration circuit. The superimposed noise is a spike-like pulse having a sharp peak as shown in FIG. 5 and is always generated when the liquid crystal panel is driven by an alternating current. Therefore, an integrating circuit is indispensable. Further, in the present invention, the time constant of the integrating circuit is set to 1 ms or more so that noise can be completely removed.

A liquid crystal driving power supply circuit by ON / OFF terminals
Since all 17 outputs can be controlled, when the display is off,
VxH, VxL, VyH, VyL, and VM all become 0V, and the signal line 11 and the scanning line 12 of the liquid crystal panel become 0V. Therefore, an analog switch for selecting a VM, which is required in the configuration of the conventional signal line drive circuit 14, can be eliminated. As shown in FIG. 6, the signal line drive circuit 18 has no VM terminal. In FIG. 6, reference numeral 40 denotes an output circuit, and 41 denotes a data latch. As described above, in the present invention, the number of analog switches in the signal line driving circuit can be reduced, so that the cost of the signal line driving circuit can be reduced. Further, wiring between the signal line driving circuit 18 and the liquid crystal driving power supply circuit 17 can be simplified.

FIG. 7 is a diagram showing an example of the correction of the temperature characteristic of the liquid crystal panel by the scanning line driving voltage of the present invention. The transmittance of the liquid crystal panel changes depending on the temperature, and the scanning line driving voltage must be changed depending on the temperature so as to obtain the optimum transmittance, that is, the optimum contrast. The broken line in FIG. 7 is the scanning line driving voltage at which the liquid crystal panel has the optimum contrast, and the solid line is the resistance characteristic of the liquid crystal panel when the resistor R5 and the thermistor are inserted into the FB terminal of the liquid crystal driving power supply circuit 17. Is corrected. in this way,
According to the present invention, the temperature of the liquid crystal panel can be corrected with high accuracy, and a display with an appropriate contrast can always be performed within the operating temperature range of the liquid crystal display device.

The liquid crystal driving power supply circuit 17 is provided with a contrast adjusting terminal Vcont, and the contrast of the liquid crystal display device can be set to an optimum state by a control voltage. FIG.
The change of the scanning line drive voltage VxH with respect to the control voltage of cont is shown.

In FIG. 1, the Vop output circuit of the liquid crystal drive power supply circuit has two outputs, Vop + and Vop-, but the present invention is not limited to this. Vop + only, Vop-only, or
Three or more outputs may be used.

As described above, according to the first embodiment,
By providing an operation reference voltage input terminal in the liquid crystal drive power supply circuit 17, the driving voltage with the minimum tracking error is always maintained at a constant bias ratio even when the operating conditions such as the ambient temperature and ambient brightness of the liquid crystal display device change. Can drive the liquid crystal panel, and can easily obtain the optimal contrast,
A liquid crystal display device with high image quality and high reliability can be realized at low cost, for example, setting and changing of the operation reference voltage and drive voltage can be easily performed at low cost.

(Embodiment 2) In the circuit of FIG. 1, the ON / OFF terminal of the liquid crystal drive power supply circuit 17 may be provided only in the Vx output circuit. FIG. 9 shows a second embodiment of the present invention. Only the Vx output circuit of the liquid crystal drive power supply circuit 50 has ON / OFF terminals. Operating reference voltage V
Since M and the signal line driving voltage are obtained from the scanning line driving voltage, when the scanning line driving voltage is turned off by ON / OFF control, VxH and VxL become 0 V, and therefore, VM, VyH, VyL Also becomes 0V.

When a commercially available standard switching regulator can be used for the Vop output circuit of the liquid crystal drive power supply circuit 50, the configuration of FIG. 9 is useful, and has exactly the same effect as that of FIG.

(Embodiment 3) In the circuit of FIG. 1, a configuration in which the operation reference voltage VM and the signal line drive voltage are obtained from Vop + may be used. It is suitable for a reflection type liquid crystal display device or a normal liquid crystal display device, but is not suitable for a high quality liquid crystal display device using a high-speed liquid crystal.

FIG. 10 shows a third embodiment of the present invention. In this case, VM and VyL are obtained from (Equation 10).

[0058]

## EQU10 ## VM = (Vop +) × (R2 + R3) / (R1 + R2 + R3) VyL = (Vop +) × (R3) / (R1 + R2 + R3) In this case, although the bias ratio is not constant with respect to the change in the scanning line driving voltage, Otherwise, the same effects as in FIG. 1 are obtained. However, the ON / OFF terminal cannot be omitted in the Vop output circuit of the liquid crystal drive power supply circuit 17.

(Embodiment 4) By changing the circuit of FIG. 1, a voltage VM slightly different from the operation reference voltage VM of the liquid crystal panel
M may be fed back to the VM terminal of the liquid crystal drive power supply circuit 17 so as to have an adjustment circuit for minimizing the tracking error of the scanning line drive voltage. FIG. 11 shows a fourth embodiment of the present invention.

In the configuration shown in FIG. 11, the liquid crystal drive power supply circuit 17
The scanning line driving voltage of (Expression 11) is output.

[0061]

VxH + VxL-2 VMM = δVx VM and VMM are determined by resistors R1a, R2a, R3a, R7a and variable resistor VR1, and VMM can be adjusted by VR1. Here, if VM−VMM = △ V, then (Equation 11)
(Equation 12) is obtained.

[0062]

VxH + VxL-2VM = δVx-2 △ V Therefore, if δVx-2 △ V = 0 in (Equation 12), a scanning line drive voltage without tracking error can be obtained. δV
Since x−2 △ V cannot be measured directly, the variable resistor VR1 is adjusted to determine the minimum level of flicker visually or to detect the flicker electrically to determine the minimum level.

By changing the circuit of FIG.
And VyL may be obtained from the power supply of the operational amplifier. However, the bias ratio changes with a change in the scanning line driving voltage.

(Embodiment 5) In the circuit of FIG.
A configuration in which yL = 0V may be used. FIG. 12 shows a fifth embodiment of the present invention. In FIG. 12, by setting VyL = 0 V, the wiring between the signal line drive circuit 18 and the operation reference voltage VM terminal can be simplified, and the cost can be reduced. The operation reference voltage VM is determined by VxH × R1a / (R1b + R2b). The series resistance value of the resistor R1a and the resistor R1b is set to 1 MΩ.
By doing so, the power loss due to the resistance can be made very small. Vy
L = 0V indicates that the signal line drive voltage does not require a correction voltage for correcting crosstalk, that is, the signal line drive voltage is V
This is very effective when only H and VL are used.

(Embodiment 6) In the circuit of FIG. 12, ON / OFF control may be provided only for the Vx output circuit of the liquid crystal drive power supply circuit 17, and a signal line drive circuit 14 having an input terminal for the VM may be used. . FIG. 13 shows a sixth embodiment of the present invention. In FIG. 13, the ON / OFF terminal is provided only in the Vx output circuit of the liquid crystal drive power supply circuit 50, and
A signal line driving circuit 14 having an M terminal is used. It is very effective when a standard switching power supply can be used at low cost for the Vop output circuit, especially when Vop− = 0V. The liquid crystal drive power supply circuit 50 is the same as the liquid crystal drive power supply circuit 17 except that the Vop output circuit has no ON / OFF terminal.

(Embodiment 7) In the circuit of FIG. 12, a configuration may be adopted in which an operation reference voltage is obtained from the Vop output of the liquid crystal drive power supply circuit 17. FIG. 14 shows a seventh embodiment of the present invention. As in the case of FIG. 12, this is very effective when the signal line drive voltage does not require a compensation voltage for correcting crosstalk, but the bias ratio changes with a change in the scan line drive voltage.

[0067]

As described above, according to the first, second and third aspects of the present invention, the operation reference voltage input terminal is provided in the liquid crystal drive power supply circuit, so that the operation of the signal line and scan line drive voltages can be performed. The same reference voltage makes it easy to set and change the operation reference voltage and realizes practically negligible scanning line drive voltage tracking errors, thereby improving the image quality and reliability of liquid crystal display devices at low cost it can. In particular, according to the first aspect of the invention, the bias ratio can be made constant with respect to the change in the scanning line driving voltage, and the highest contrast of the liquid crystal panel can always be obtained.

According to the fourth and fifth aspects of the present invention, a temperature correction terminal and a voltage setting terminal are provided in a liquid crystal driving power supply circuit, and a scanning line driving voltage capable of correcting a temperature characteristic of a liquid crystal panel by a thermistor is obtained. And the scanning drive voltage at which the contrast is optimal can be easily set.
The decrease in contrast due to temperature can be minimized.

According to the sixth aspect of the present invention, an operation reference voltage and a voltage to be fed back to the liquid crystal drive power supply circuit are separately obtained from the scan line drive voltage, thereby obtaining a scan line drive voltage with a minimum tracking error. Can be.

According to the seventh aspect of the present invention, the contrast adjusting terminal is provided in the liquid crystal driving power supply circuit, and the contrast of the liquid crystal display device can always be extremely easily adjusted to the optimum state by the control voltage of the contrast adjusting terminal. Can be.

According to the present invention, the time constant of the integration circuit can be determined by inserting the integration circuit into the operation reference voltage input terminal of the liquid crystal driving power supply circuit, and the operation reference voltage can be easily set. Can be removed, and the liquid crystal drive power supply circuit can operate stably.

According to the tenth, twelfth and twelfth aspects of the invention, the number of analog switches in the signal line drive circuit can be reduced by providing the control terminal for turning on / off the liquid crystal drive power supply circuit. Turn on the LCD display
Off can be easily configured at low cost.

According to the thirteenth and fourteenth aspects of the present invention, it is possible to easily obtain a high-precision operation reference voltage with a small power by using a resistor and an operational amplifier from either the scanning line driving voltage or the power supply of the operational amplifier. Can be.

According to the inventions described in claim 15 and claim 16, the operating reference voltage and the signal line driving voltage can be easily and accurately obtained by using the resistor and the operational amplifier from either the scanning line driving voltage or the power supply of the operational amplifier. Can be obtained with a very small power.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a liquid crystal display device according to Embodiment 1 of the present invention.

FIG. 2A illustrates an example of a signal line drive voltage waveform. (b) is a diagram showing an example of a scanning line drive voltage waveform.

FIG. 3 is a configuration diagram of a liquid crystal drive power supply circuit 17;

FIG. 4 is a diagram showing a temperature characteristic of a tracking error δVx.

FIG. 5 is a diagram showing how noise superimposed on an operation reference voltage VM and noise are removed by an integration circuit;

FIG. 6 is a configuration diagram of a signal line driving circuit 18.

FIG. 7 is a diagram illustrating a temperature characteristic of a liquid crystal panel and a scanning line driving voltage whose temperature is corrected.

FIG. 8 shows a scanning line driving voltage VxH with respect to a Vcont control voltage.
FIG.

FIG. 9 is a circuit configuration diagram of a liquid crystal display device according to Embodiment 2 of the present invention.

FIG. 10 is a circuit configuration diagram of a liquid crystal display device according to Embodiment 3 of the present invention.

FIG. 11 is a circuit configuration diagram of a liquid crystal display device according to Embodiment 4 of the present invention.

FIG. 12 is a circuit configuration diagram of a liquid crystal display device according to a fifth embodiment of the present invention.

FIG. 13 is a circuit configuration diagram of a liquid crystal display device according to a sixth embodiment of the present invention.

FIG. 14 is a circuit configuration diagram of a liquid crystal display device according to a seventh embodiment of the present invention.

FIG. 15 is a circuit configuration diagram of a conventional liquid crystal display device.

FIG. 16 is a configuration diagram of a signal line driving circuit 14.

[Explanation of Signs] 11: Signal line, 12: Scan line, 13: Pixel electrode, 14, 18
... Signal line drive circuit, 15 ... Scan line drive circuit, 16 ... Control circuit, 17,50 ... Liquid crystal drive power supply circuit, 21 ... Operational amplifier, 40 ... Output circuit of signal line drive circuit 18, 41 ... Signal line drive circuit 18 Data latch of VM, VM: Operation reference voltage (input terminal), VxH, VxL: Scan line drive voltage (output terminal), Vop +, Vop-: Power supply voltage of operational amplifier, FB
... Temperature correction terminal, TS ... Scan line drive voltage setting terminal, V
cont: contrast adjustment terminal, TH: thermistor.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masahito Matsunami 1006 Oaza Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (16)

[Claims] 1. A liquid crystal panel in which a plurality of signal lines and a plurality of scanning lines are arranged in a matrix, and a liquid crystal layer is provided between pixel electrodes arranged at intersections thereof, and a signal line driving circuit for driving the signal lines A scanning line driving circuit for driving the scanning line;
A liquid crystal display device comprising: an operational amplifier that supplies a driving voltage; and a liquid crystal driving power supply circuit; and a control circuit that controls the signal line driving circuit, the scanning line driving circuit, and the liquid crystal driving power supply circuit. Provide an operation reference voltage input terminal in the power supply circuit,
An operation reference voltage that determines an operation point of the liquid crystal panel is created from a scanning line driving voltage that is an output voltage of the liquid crystal driving power supply circuit,
A liquid crystal display device wherein the operation reference voltage is fed back to the operation reference voltage input terminal of the liquid crystal drive power supply circuit. 2. A liquid crystal panel in which a plurality of signal lines and a plurality of scanning lines are arranged in a matrix and a liquid crystal layer is provided between pixel electrodes arranged at intersections thereof, and a signal line driving circuit for driving the signal lines A scanning line driving circuit for driving the scanning line;
A liquid crystal display device comprising: an operational amplifier that supplies a driving voltage; and a liquid crystal driving power supply circuit; and a control circuit that controls the signal line driving circuit, the scanning line driving circuit, and the liquid crystal driving power supply circuit. Provide an operation reference voltage input terminal in the power supply circuit,
Generating an operation reference voltage that determines an operation point of the liquid crystal panel from a power supply voltage of the operational amplifier, which is an output of the liquid crystal drive power supply circuit, and feeding back the operation reference voltage to the operation reference voltage input terminal of the liquid crystal drive power supply circuit. A liquid crystal display device characterized by the above-mentioned. 3. In a liquid crystal drive power supply circuit that outputs scanning line drive voltages VxH and VxL, | δVx | ≦ where VxH + VxL−2VM = δVx as an operation reference voltage.
3. The liquid crystal display device according to claim 1, wherein the voltage is set to ± 0.1 V. 4. A scanning line for correcting a temperature characteristic of a liquid crystal panel by providing a temperature correcting terminal in a liquid crystal driving power supply circuit and inserting a series circuit of a thermistor and a resistor between the temperature correcting terminal and the scanning line driving voltage output terminal. 3. The liquid crystal display device according to claim 1, wherein the liquid crystal display device outputs a driving voltage. 5. A scanning line driving voltage setting terminal is provided in a liquid crystal driving power supply circuit, and a predetermined scanning line driving voltage is obtained by inserting a resistor between the scanning line driving voltage setting terminal and ground. The liquid crystal display device according to claim 1. 6. Generating two kinds of reference voltages from a scanning line drive voltage or a power supply voltage of an operational amplifier, inputting one of them to an operation reference voltage input terminal of a liquid crystal drive power supply circuit and the other as an operation reference voltage of a liquid crystal panel. The liquid crystal display device according to claim 1 or 2, wherein: 7. A liquid crystal driving power supply circuit comprising a contrast adjusting terminal, wherein a scanning line driving voltage is varied by a control signal voltage input to the contrast adjusting terminal to optimize the contrast of the liquid crystal panel. 3. The liquid crystal display device according to claim 1 or 2. 8. The liquid crystal display device according to claim 1, wherein an integration circuit is provided at an operation reference voltage input terminal of the liquid crystal drive power supply circuit. 9. The liquid crystal display device according to claim 8, wherein a time constant of an integration circuit provided at an operation reference voltage input terminal of the liquid crystal drive power supply circuit is 1 ms or more. 10. An O for turning on / off a scanning line driving voltage.
2. The liquid crystal display device according to claim 1, wherein an ON / OFF terminal for inputting an N / OFF control signal is provided in the liquid crystal drive power supply circuit. 11. A liquid crystal drive power supply circuit having an ON / OFF terminal for inputting an ON / OFF control signal for simultaneously turning on / off a scan line drive voltage and a power supply voltage of an operational amplifier. The liquid crystal display device according to claim 2. 12. An analog switch for selecting and outputting an operation reference voltage, wherein an output circuit of the signal line driving circuit is constituted by only an analog switch for selecting and outputting one signal line driving voltage from a plurality of signal line driving voltages. 12. The liquid crystal display device according to claim 10, wherein the liquid crystal display device does not have a liquid crystal display. 13. A voltage of either the scanning line driving voltage or the power supply voltage of the operational amplifier is set to V, and a series resistor including a resistor R1 and a resistor R2 is inserted between an output terminal of the voltage V and the ground, and V × R1 / 3. The method according to claim 1, wherein (R1 + R2) is an input of a voltage follower, and an output voltage of the voltage follower is an operation reference voltage.
The liquid crystal display device as described in the above. 14. The series resistance value of the resistor R1 and the resistor R2 is 1M.
14. The liquid crystal display device according to claim 13, wherein the value is Ω or more. 15. A voltage of either the scanning line driving voltage or the power supply voltage of the operational amplifier is set to V, and a series resistor including a resistor R1, a resistor R2, and a resistor R3 is inserted between an output terminal of the voltage V and ground, V × (R1 + R2) / (R1 + R2 + R3) and V
3. The liquid crystal display according to claim 1, wherein × R3 / (R1 + R2 + R3) is input to each voltage follower, and each output voltage of the voltage follower is an operation reference voltage and a signal line drive voltage. apparatus. 16. The liquid crystal display device according to claim 15, wherein a series resistance value of the resistors R1, R2, and R3 is 1 MΩ or more.