JP2002366114A - Power unit and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of a conventional liquid crystal display device that a power circuit has large stationary power consumption, its component has to be replaced to vary a voltage level, and the number of components is large. SOLUTION: The liquid crystal display device is provided with a setting register 100 where the amplitudes and voltage levels of the driving voltage of a common electrode and the non-scanning period voltage of scanning lines are set, an amplitude reference generating circuit 101 which generates an amplitude reference voltage for the driving voltage of the common electrode and the non-scanning period voltage of the scanning lines according to the set values, a VcomH reference generating circuit 102 and a VcomL generating circuit 100 which performs the AC driving of the common electrode to the amplitude and voltage level determined according to the amplitude reference voltage and set values, and a VgoffH generating circuit 104 and a VgoffL reference generating circuit 105 which generate the non-scanning period voltage of the scanning lines in phase with and to the same amplitude with the driving voltage of the common electrode with the amplitude and voltage level determined by the amplitude reference voltage and set values.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for controlling a power supply of a liquid crystal display device and a liquid crystal display device provided with the power supply device.
The present invention relates to a power supply control device for a liquid crystal display device of the (m Transistor) type and a liquid crystal display device including the power supply device.

[0002]

2. Description of the Related Art As a conventional power supply circuit of a liquid crystal display device, there is, for example, a power supply circuit disclosed in Japanese Patent Application Laid-Open No. 10-31087 "Liquid crystal display device". This will be described with reference to FIG.

As is generally known, in a liquid crystal panel, in order to prevent the deterioration of a liquid crystal layer, an AC drive for inverting the polarity of a writing voltage to a pixel electrode with respect to a common electrode (counter electrode) is required. One of the driving methods of the TFT liquid crystal panel is a common inversion driving method. In brief, the common inversion driving method is a driving method in which a common electrode of a TFT liquid crystal panel is switched between a low potential and a high potential at regular intervals and a drain voltage is written to a pixel electrode.

Further, as a pixel structure of a TFT liquid crystal, there is a structure in which a storage capacitor is connected to a pixel electrode and a gate line one line before. When applying the common inversion driving method, in this pixel structure, a driving method in which the off voltage of the gate line is exchanged so as to have the same amplitude and the same phase as the common voltage, and the potential difference between both ends of the liquid crystal capacitor is kept constant, It is generally used because it has the effect of suppressing the charge / discharge current of the storage capacitor and the liquid crystal capacitor.

FIG. 13 shows a conventional power supply circuit which generates the common voltage and the gate line off voltage. In FIG. 13, OP is an operational amplifier, TR1 is an NPN transistor, TR2 is a PNP transistor, ZD is a Zener diode, R1 to R4 are resistors, and C1 is a capacitor.

In this circuit, an AC signal M is input, inverted and amplified by OP, and current amplified by a buffer composed of TR1 and TR2 to generate a common voltage Vcom. Further, the gate-off voltage Vgoff is generated by shifting the voltage from the common voltage Vcom to the negative voltage VEE side by ZD.

[0007]

The TFT liquid crystal panel is applied not only to a large TFT liquid crystal panel used in a conventional notebook personal computer and the like, but also to a small portable information device which requires particularly low power consumption.

However, the conventional power supply circuit has a common voltage Vc
The current steadily flowed from om via ZD, and the power consumption was high. Also, depending on the TFT liquid crystal panel to be applied, V
In order to change the amplitude and voltage level of “com” and “Vgoff”, it was necessary to change each resistance value and replace components such as ZD. Further, the number of parts is large, which is disadvantageous in cost.

An object of the present invention is to provide a power supply device capable of reducing the power consumption of a liquid crystal display device and a liquid crystal display device thereof.

[0010] Alternatively, it is an object of the present invention to improve user convenience. A power supply device and a liquid crystal display device thereof are provided.

[0011]

According to the present invention, there is provided a set value holding circuit for setting an amplitude and a voltage level of a drive voltage of a common electrode of a liquid crystal display device and a non-scanning period voltage of a scanning line, and the common value according to a set value. An amplitude reference voltage generation circuit for generating an amplitude reference voltage between an electrode drive voltage and a non-scanning period voltage of the scanning line; and a common AC drive for the common electrode with an amplitude and a voltage level determined from the amplitude reference voltage and a set value. An electrode driving circuit, a non-scanning period voltage generating circuit that generates a non-scanning period voltage of the scanning line having the same phase and the same amplitude as the driving voltage of the common electrode at an amplitude and a voltage level determined from the amplitude reference voltage and a set value. Is provided. Preferably, the common electrode drive circuit generates one potential according to a set value, and generates another potential from one potential according to an amplitude reference voltage,
Switching between both potentials to generate a drive voltage for the common electrode, preferably, the non-scanning period voltage generation circuit generates one potential according to a set value, and generates the other potential from one potential according to the amplitude reference voltage. Generating a non-scanning period voltage of the scanning line by switching both potentials. Preferably, the low potential side voltage of the driving voltage of the common electrode is set to a negative potential, a ground (ground) or a positive potential. It is possible.

According to another aspect of the present invention, there is provided a setting value holding circuit for setting a voltage level between a driving voltage of a common electrode of a liquid crystal display device and a non-scanning period voltage of a scanning line, and fixing one potential and setting the other potential. A common electrode drive circuit that generates according to a value and AC drives the common electrode, and generates one potential according to a set value and generates the other potential from a potential difference between the common electrode drive voltage and the common electrode drive voltage. A non-scanning period voltage generation circuit for generating a non-scanning period voltage of the scanning line having the same phase and the same amplitude. Preferably, the one potential for fixing the driving voltage of the common electrode is ground (ground), or the present invention provides a liquid crystal between a pixel electrode connected via a data line and a switching element. A liquid crystal panel in which a pixel portion having a common electrode sandwiching the same is arranged in a matrix at intersections of a plurality of data lines and a plurality of scanning lines, and a central processing unit for setting various setting values,
A liquid crystal drive circuit that temporarily holds a set value from the central processing unit; a scan circuit that drives a scan line of a liquid crystal panel according to a set value and a control signal from the liquid crystal drive circuit; A power supply circuit for generating a power supply for the circuit, a power supply for the scanning circuit, and a drive voltage for the common electrode of the liquid crystal panel in accordance with a set value from the liquid crystal drive circuit.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG.
The configuration and operation of the power supply circuit according to one embodiment of the present invention will be described with reference to FIGS. First, the overall configuration of the power supply circuit according to the present embodiment will be described with reference to FIG.

The power supply circuit according to the present embodiment includes a setting register 100 for holding a set value, an amplitude reference generating circuit 101 for generating a voltage Vamp from a reference voltage Vreg in accordance with the set value, and a voltage V in accordance with the set value from the reference voltage Vreg.
a VcomH reference generation circuit 102 that generates a comH;
A VcomL generating circuit 103 for generating a voltage VcomL from the VcomH and the Vamp, and a reference voltage Vreg
Generates a voltage VgoffL according to a set value from Vgo
ffL reference generation circuit 104, and VgoffH for generating voltage VgoffH from VgoffL and Vamp.
The generation circuit 105, VcomH, VcomL, and Vg
The buffers 106 to 109 receive currents offH and VgoffL and amplify the current.
A voltage selector 110 that switches between H and VcomL to generate a common voltage Vcom;
and a voltage selector 111 that switches between goffH and VgoffL to generate a gate-off voltage Vgoff.

Next, the operation of the power supply circuit according to the present embodiment will be described. First, an amplitude reference generation circuit 101, a VcomH reference generation circuit 102,
A set value for determining a voltage generated by each circuit of the VgoffL reference generation circuit 104 is held. When each set value is changed, the voltage generated by each circuit changes according to the changed set value. The amplitude reference generation circuit 101 uses the reference voltage Vreg as a reference in accordance with a set value and VcomL.
A voltage Vamp, which is a reference voltage of the generation circuit 103 and the VgoffH generation circuit 105, is generated to generate a common voltage Vco.
m and the voltage amplitude of the gate-off voltage Vgoff are determined. The VcomH reference generation circuit 102 outputs the reference voltage Vre
A voltage VcomH that is a high-potential-side voltage of the common voltage Vcom is generated according to a set value with g as a reference. Vco
The mL generation circuit 103 calculates VamH based on VcomH.
According to p, a voltage VcomL that is a low-potential-side voltage of the common voltage Vcom is generated. VcomH and VcomL
Is amplified by the buffers 106 and 107 so as to supply a current sufficient to drive the common electrode of the TFT liquid crystal panel. VcomH and VcomL amplified by the buffers 106 and 107 are input to the voltage selector 110 and switched by the AC signal M to output one as the common voltage Vcom. For example, if the drive voltage of the liquid crystal panel is positive when the AC signal M is low, the voltage selector 110
Select and output. VgoffL reference generation circuit 104
Is a voltage Vg that is a low-potential-side voltage of the gate-off voltage Vgoff according to a set value with reference to the reference voltage Vreg.
generate offL. The VgoffH generation circuit 105
A voltage Vgoff that is a high-potential-side voltage of the gate-off voltage Vgoff according to Vamp with VgoffL as a reference.
Generate H. Note that the voltage VgoffH is VgoffL
Is made equal to the amplitude of the common voltage Vcom. VgoffH and VgoffL are in buffer 1
08 and the buffer 109, the current is amplified so as to supply a current sufficient to drive the off period of the gate electrode of the TFT liquid crystal panel. VgoffH and VgoffL amplified by the buffers 108 and 109 are input to the voltage selector 111, and are switched by the AC signal M to output one as the gate-off voltage Vgoff. For example, if the drive voltage of the liquid crystal panel is positive when the AC signal M is low, the voltage selector 111
goffL is selected and output. Therefore, the common voltage Vc
om and the gate-off voltage Vgoff have the same phase and the same amplitude.

Next, a circuit for generating the common voltage Vcom of the power supply circuit according to the present embodiment will be described in detail with reference to FIG. 2, an amplitude reference voltage generating circuit 101 includes an operational amplifier OP1 and a variable resistor R1.
a and a resistor R1b. The VcomH reference generation circuit 102 includes an operational amplifier OP2 and a variable resistor R2
a and a resistor R2b. The VcomL generation circuit 103 includes an operational amplifier OP3 and resistors R3a to R3a.
3d. The buffer 106 includes an operational amplifier OP6. The buffer 107 is an operational amplifier O
P7. Since VcomH is usually set to a voltage value near the positive power supply voltage DDVDH, OP2
, OP6 have a positive power supply of DDVDH and a negative power supply of ground GND. Also, since VcomL is normally set to a voltage value near GND, the positive power supply of OP3 and OP7 is
DVDH, the negative power supply is a negative power supply voltage VCL. The positive power supply of OP1 that generates the voltage Vamp related to the voltage amplitude is DDVDH, and the negative power supply is ground GND.

In the amplitude reference voltage generation circuit 101, a voltage obtained by dividing the reference voltage Vreg by the variable resistor R1a and the resistor R1b is buffered by an operational amplifier OP1 forming a voltage follower to generate a voltage Vamp. The variable resistor R1a is a so-called electronic volume resistor composed of a resistor and a MOS switch, and the resistance value can be changed by a setting value of the setting register 100. Also, VcomH
In the reference voltage generation circuit 102, a voltage obtained by dividing the reference voltage Vreg by the variable resistor R2a and the resistor R2b is buffered by an operational amplifier OP2 forming a voltage follower to generate a voltage VcomH. The resistance value of the variable resistor R2a can be changed by the setting value of the setting register 100, similarly to the variable resistor R1a. VcomL generation circuit 103
Forms a differential amplifier circuit, and VcH is derived from VcomH and Vamp.
Generate omL. The voltage of VcomL is represented by the following equation.

VcomL = A · VcomH−B · Vamp (1) (where, A = {(R3c + R3d) · R3b} /｝ (R
3a + R3b) · R3d｝, and B = R3c / R3d. In the buffer 106, VcomH is buffered by the operational amplifier OP6 forming a voltage follower. In the buffer 107, an operational amplifier O forming a voltage follower is used.
Buffer VcomL at P7. As described above, Vc
VcomL can be generated from omH and Vamp, and the amplitude and voltage level of Vcom can be easily adjusted by adjusting VcomH and Vamp according to set values.

Here, the amplitude of the common voltage Vcom is
If the conditions for generating only with the setting of Vamp irrespective of the setting of comH are shown, R3a = R3c, R3b = R3
d, which is substituted into equation (1) to obtain the following equation.

VcomH−VcomL = (R3a / R3b) · Vamp (2) That is, the amplitude of the common voltage Vcom is a voltage proportional to Vamp.

Here, the voltage value of VcomL will be described. VcomL is determined by the product of (R3a / R3b) and Vamp, and takes a value near GND. Since the positive power supply of OP3 and OP7 is DDVDH and the negative power supply is negative power supply voltage VCL, VcomL can be any one of negative voltage, GND, and positive voltage. It is possible to correspond to.

Next, a circuit for generating the gate-off voltage Vgoff of the power supply circuit according to the present embodiment will be described in detail with reference to FIG. In FIG. 3, Vgo
The ffL reference generation circuit 104 includes an operational amplifier OP4, a variable resistor R4a, and a resistor R4b. Vg
The offH generation circuit 105 includes an operational amplifier OP5 and resistors R5a to R5d. Buffer 108
Is composed of an operational amplifier OP8. The buffer 109 includes an operational amplifier OP9. Note that VgoffH
And VgoffL are the negative power supply voltage V from ground GND.
It is assumed to be in the range of GL.

In the VgoffL reference voltage generating circuit 104, the operational amplifier OP4 operates so that the voltage obtained by dividing the voltage VgoffL and the positive power supply voltage DDVDH by the variable resistors R4a and R4b becomes equal to the reference voltage Vreg.
Generate goffL. The variable resistor R4a is the variable resistor R1
Similarly to a, the resistance value can be changed by the set value of the setting register 100. The VgoffH generating circuit 105 forms a differential amplifier circuit, and calculates Vgoff from VgoffL and Vamp.
Generate fH. The voltage of VgoffH is represented by the following equation.

VgoffH = C · VgoffL + D · Vamp (3) (where C = {(R4c + R4d) · R4a} / ｛(R
4a + R4b) · R4c｝, and D = R4b / R4c. In the buffer 108, VgoffH is buffered by the operational amplifier OP8 forming a voltage follower. In the buffer 109, VgoffL is buffered by an operational amplifier OP9 forming a voltage follower. As mentioned above,
VgoffH can be generated from VgoffL and Vamp, and the amplitude and voltage level of Vgoff can be easily adjusted by adjusting VgoffL and Vamp according to set values.

Here, conditions for generating the amplitude of the gate-off voltage Vgoff only by setting Vamp without depending on the setting of VgoffL are as follows: R4a = R4c, R4b
= R4d, which is substituted into equation (3) to obtain the following equation.

VgoffH−VgoffL = (R4b / R4a) · Vamp (4) That is, the amplitude of the gate-off voltage Vgoff is a voltage proportional to Vamp.

Further, if the condition that the amplitude of the common voltage Vcom and the amplitude of the gate-off voltage Vgoff are equal is shown, (R3a / R3b) = (R4b / R4
a).

Therefore, by selecting the ratio of the resistances so as to satisfy all of the above conditions, the voltage of VcomH and
VgoffL and the common voltage Vcom
By determining the reference potential of the gate-off voltage Vgoff and further setting the voltage of Vamp, the common voltage Vcom having the same phase and the same amplitude and the gate-off voltage Vgoff
Can be generated.

As described above, the common voltage Vc having the same phase and the same amplitude is determined by the set values of the amplitude reference generation circuit, the VcomH reference generation circuit, and the VgoffL reference generation circuit.
om and the gate-off voltage Vgoff can be easily generated.

Further, the power supply circuit according to the present embodiment
Since it can be realized by a resistor, an operational amplifier, or the like, it can be integrated in an IC, and the number of components can be reduced.

Further, since each voltage level and amplitude are determined by the resistance ratio, a higher resistance value can suppress a steady current and reduce power consumption.

The power supply circuit according to the first embodiment has been described above. The power supply circuit according to the second embodiment will show a method for further reducing the circuit scale and reducing power consumption. (Second Embodiment) Hereinafter, a power supply circuit according to a second embodiment of the present invention will be described with reference to FIGS. This embodiment is characterized in that VcomL is fixed, and the common voltage Vc of the power supply circuit according to the first embodiment is set.
om and the method of determining the amplitude of the gate-off voltage Vgoff are different.

In FIG. 4, VcomL is fixed to GND, and VcomH is generated from the VcomH reference generation circuit 102 as in the power supply circuit according to the first embodiment. Further, VgoffL is generated from the VgoffL reference generation circuit 105 as in the power supply circuit according to the first embodiment. VgoffH is obtained by converting VcomH and VgoffL to Vgo
It is input to the ffH generation circuit and generated. That is, in the power supply circuit according to the first embodiment, VcomH is input instead of Vamp input to the VgoffH generation circuit. The specific internal configuration of each circuit is the same as the power supply circuit according to the first embodiment. Therefore, VgoffH is expressed by the following equation.

VgoffH = C · VgoffL + D · VcomH (5) (where C = {(R4c + R4d) · R4a} / ｛(R
4a + R4b) · R4c｝, and D = R4b / R4c. Here, the amplitude of the gate-off voltage Vgoff is defined as Vgof
If the conditions for generating only with the setting of VcomH regardless of the setting of fL are shown, R4a = R4c = R4b = R4d,
This is substituted into equation (5) to obtain the following equation.

VgoffH−VgoffL = VcomH (6) Therefore, when VcomL is fixed to GND, Vgoff
By making all resistance values of the H generation circuit equal, Vcom
By setting the voltage of H and the voltage of VgoffL, it is possible to generate the common voltage Vcom and the gate-off voltage Vgoff having the same phase and the same amplitude.

Further, the power supply circuit according to the present embodiment
Compared with the power supply circuit according to the first embodiment, the circuit scale can be reduced and power consumption can be reduced.

Next, a power supply circuit that can be used by switching between the power supply circuit according to the first embodiment and the power supply circuit shown in FIG. 4 will be described with reference to FIG. In FIG. 5, the power supply circuit according to the present embodiment includes Vamp and Vcom.
H by the switching signal MODE and Vgo
The voltage selector 201 includes a voltage selector 201 for giving to ff, and a voltage selector 202 for switching between VcomL and GND amplified by the buffer 107 with the switching signal MODE and for giving to the voltage selector 110. Note that the resistance values of the VgoffH generation circuit are all equal. That is, R4a = R4c =
R4b = R4d. When VcomL is fixed to GND, the power consumption of the amplitude reference generation circuit 101, the VcomL generation circuit 103, and the buffer 107 can be reduced by turning off each power supply.

As described above, VcomL is changed to GND.
, The common voltage Vcom and the gate-off voltage Vgoff having the same phase and the same amplitude can be easily generated by setting values of the low power consumption, the amplitude reference generation circuit, the VcomH reference generation circuit, and the VgoffL reference generation circuit. Can be done.

The power supply circuit according to the second embodiment has been described above. However, in the power supply circuit according to the third embodiment, even if the reference voltage is changed, a method of easily switching between the same phase and the same amplitude is similarly used. Is described. (Third Embodiment) A power supply circuit according to a third embodiment of the present invention will be described below with reference to FIGS. First, the overall configuration of the power supply circuit according to the present embodiment will be described with reference to FIG.

The power supply circuit according to the present embodiment includes a setting register 100 for holding a set value, an amplitude reference generating circuit 101 for generating a voltage Vamp from a reference voltage Vreg in accordance with the set value, and a voltage V in accordance with the set value from the reference voltage Vreg.
a VcomL reference generation circuit 301 that generates a comL;
A VcomH generation circuit 302 that generates a voltage VcomH from the VcomL and the Vamp, and a reference voltage Vreg.
Generates a voltage VgoffH according to a set value from Vgo
ffH reference generation circuit 303, and VgoffL for generating voltage VgoffL from VgoffH and Vamp
The generation circuit 304, VcomH, VcomL, and Vg
The buffers 106 to 109 receive currents offH and VgoffL and amplify the current.
A voltage selector 110 that switches between H and VcomL to generate a common voltage Vcom;
and a voltage selector 111 that switches between goffH and VgoffL to generate a gate-off voltage Vgoff.

Next, the operation of the power supply circuit according to the present embodiment will be described. The amplitude reference generation circuit 101 outputs the reference voltage V
A voltage Vamp, which is a reference voltage of the VcomH generation circuit 302 and the VgoffL generation circuit 304, is generated in accordance with a setting value with reference to reg, and the voltage amplitude of the common voltage Vcom and the gate-off voltage Vgoff is determined. Vc
The omL reference generation circuit 301 generates a voltage VcomL that is a low-potential-side voltage of the common voltage Vcom according to a set value with reference to the reference voltage Vreg. The VcomH generation circuit 302 generates a voltage Vc that is a high-potential-side voltage of the common voltage Vcom according to Vamp based on VcomL.
omH is generated. Buffer 106 and buffer 107
The operation of the voltage selector 110 is the same as that of the power supply circuit according to the first embodiment. VgoffH reference generation circuit 30
3 is based on the reference voltage Vreg and according to the set value,
A voltage V that is a high-potential-side voltage of the gate-off voltage Vgoff
Generate goffH. VgoffL generation circuit 304
Is a voltage Vgo that is a lower potential side voltage of the gate-off voltage Vgoff according to Vamp with VgoffH as a reference.
Generate ffL. Note that the voltage VgoffL is equal to Vgoff.
The potential difference from fH is made equal to the amplitude of the common voltage Vcom. The operations of the buffer 108, the buffer 109, and the voltage selector 111 are the same as those of the power supply circuit according to the first embodiment.

Next, a circuit for generating the common voltage Vcom of the power supply circuit according to the present embodiment will be described in detail with reference to FIG. In FIG. 7, the amplitude reference voltage generation circuit 101 has the same configuration as that of the power supply circuit according to the first embodiment. VcomL reference generation circuit 301
Has the same configuration as the VcomH reference generation circuit 102,
The difference is that VcomL is generated instead of VcomH. The VcomH generation circuit 302 includes an operational amplifier OP10
And resistors R6a to R6d. In addition,
Since VcomH is normally set to a voltage value near the positive power supply voltage DDVDH, the positive power supply of OP2 and OP6 is DDV
DH and the negative power supply are ground GND. Also, Vco
Since mL is usually set to a voltage value near GND, OP
3 and OP7, the positive power supply is DDVDH, and the negative power supply is a negative power supply voltage VCL. The voltage Vam related to the voltage amplitude
The positive power supply of OP1 that generates p is DDVDH, and the negative power supply is ground GND.

The VcomH generation circuit 302 forms a differential amplifier circuit, and generates VcomH from VcomL and Vamp. The voltage of VcomH is represented by the following equation.

VcomH = E · VcomL + F · Vamp (7) (where E = {(R6c + R6d) · R6a} / ｛(R
6a + R6b) · R6c｝, and F = R6b / R6c. As described above, VcomH can be generated from VcomL and Vamp, and the amplitude and voltage level of Vcom can be easily adjusted by adjusting VcomL and Vamp according to the set values.

Here, the amplitude of the common voltage Vcom is
If the conditions for generating only with the setting of Vamp irrespective of the setting of comL are shown, R6a = R6c, R6b = R6
d, which is substituted into equation (7) to obtain the following equation.

VcomH−VcomL = (R6b /
R6a) · Vamp (8) That is, the amplitude of the common voltage Vcom is a voltage proportional to Vamp.

Next, the circuit for generating the gate-off voltage Vgoff of the power supply circuit according to the present embodiment will be described in detail with reference to FIG. In FIG. 8, Vgo
The ffH reference generation circuit 303 has the same configuration as the VgoffL reference generation circuit 104, and instead of VgoffL, V
GoffH is different. The VgoffL generation circuit 304 includes an operational amplifier OP7 and resistors R7a to R7a.
7d. Note that VgoffH and Vgoff
It is assumed that offL is in a range from the ground GND to the negative power supply voltage VGL.

The VgoffL generating circuit 604 forms a differential amplifier, and generates VgoffL from VgoffH and Vamp. The voltage of VgoffL is represented by the following equation.

VgoffL = G · VgoffH−H · Vamp (9) (where G = {(R7c + R7d) · R7a} /｝ (R
7a + R7b) · R7c｝, and H = R7d / R7c. As described above, from VgoffH and Vamp, Vgoff
L can be generated, and VgoffH and Vam
By adjusting p according to the set value, the amplitude and voltage level of Vgoff can be easily adjusted.

Here, conditions for generating the amplitude of the gate-off voltage Vgoff only by the setting of Vamp irrespective of the setting of VgoffH are as follows: R7a = R7c, R7b
= R7d, which is substituted into equation (9) to obtain the following equation.

VgoffH−VgoffL = (R7b / R7a) · Vamp (10) That is, the amplitude of the gate-off voltage Vgoff is a voltage proportional to Vamp.

Further, when the condition that the amplitude of the common voltage Vcom and the amplitude of the gate-off voltage Vgoff are equal is shown, (R6b / R6a) = (R7b / R7
a).

Therefore, by selecting the ratio of the resistances so as to satisfy all of the above conditions, the voltage of VcomL and
VgoffH and the common voltage Vcom
By determining the reference potential of the gate-off voltage Vgoff and further setting the voltage of Vamp, the common voltage Vcom having the same phase and the same amplitude and the gate-off voltage Vgoff
Can be generated.

As described above, even when VcomH is generated based on VcomL and VgoffL is generated based on VgoffH, the common voltage Vcom and the gate-off voltage Vgoff having the same phase and the same amplitude can be easily generated. I can do it.

Although the power supply circuit according to the third embodiment has been described above, the power supply circuit according to the fourth embodiment uses two or more operational amplifiers having the same phase and the same amplitude.
An example of how to easily generate two voltages is shown. (Fourth Embodiment) Hereinafter, a power supply circuit according to a fourth embodiment of the present invention will be described with reference to FIG.

The power supply circuit according to the present embodiment is different from the power supply circuit according to the first embodiment only in the circuit for generating VgoffH. As shown in FIG. 9, the VgoffH generation circuit 105 of the power supply circuit according to the first embodiment and the buffer 1
08, the capacitor 901 and the buffer 106
And Vg connected to the voltage selector
offH and the voltage selector 902 connected to the + electrode of the capacitor 901 by switching with the AC signal M, and VcomL amplified by the buffer 107 and VgoffL amplified by the buffer 109 with the AC signal M to switch the capacitor 901. And a voltage selector 903 connected to the electrodes.

Next, the operation of the power supply circuit according to the present embodiment will be described. Here, when the AC signal M is at a low level, the driving voltage of the liquid crystal panel is set to a positive polarity, and the voltage selector 1
10 and 111 are VcomL and VgoffL, respectively.
Will be selected and output. At this time, the voltage selector 902 connects the + electrode of the capacitor 902 to VcomH, the voltage selector 903 connects the − electrode of the capacitor 902 to VcomL, and charges the capacitor 901. When charged sufficiently, the potential difference between both ends of the capacitor 901 becomes equal to the amplitude of the common voltage Vcom. At this time, VgoffH is separated by the voltage selector 902, but there is no problem because the voltage selector 111 selects and outputs VgoffL. Next, the AC signal M
Becomes high level and becomes negative, the voltage selector 11
0 and 111 select and output VcomH and VgoffH, respectively. At this time, the voltage selector 902 connects the + electrode of the capacitor 902 to VgoffH, and the voltage selector 903 connects the − electrode of the capacitor 902 to VgoffH.
fL. Therefore, the voltage of VgoffH is Vg
offL to a potential higher by the amplitude of the common voltage Vcom, and the gate-off voltage Vgoff becomes higher than the common voltage Vcom.
It is possible to output a voltage having the same amplitude and the same phase.

As described above, the common voltage Vcom and the gate-off voltage Vgoff having the same phase and the same amplitude can be easily generated by using the capacitor. The capacitor 901 can be an external component of the IC. However, if the load capacity of the gate line is small, the capacitance value of the capacitor 901 can be reduced, and the capacitor 901 can be integrated in the IC. (Fifth Embodiment) Hereinafter, a liquid crystal display device including a power supply circuit according to a fifth embodiment of the present invention will be described with reference to FIGS.
2 will be described.

FIG. 10 shows a schematic configuration of the liquid crystal display device including the power supply circuit according to the present embodiment. In FIG. 10, a liquid crystal display device includes a microprocessor (hereinafter, MPU) 10
, Power supply circuit 20, liquid crystal drive circuit 30, and scanning circuit 4
0 and a liquid crystal panel 50. Further, the liquid crystal drive circuit 30 includes an interface unit 31 that receives setting data from the MPU 10 and a register unit 32 that holds the setting data. In addition, the power supply circuit 100
To the power supply circuit according to the fourth embodiment.

Next, the operation of the liquid crystal display device including the power supply circuit according to the present embodiment will be explained. First, after turning on the power,
The MPU 10 outputs a command for setting the operation of each circuit to the liquid crystal drive circuit 30. The liquid crystal drive circuit 30 that has received the command at the interface unit 31 stores the command in the register unit 32. Of the setting values held in the register unit 32, the setting values of the power supply circuit 20 and the scanning circuit 40 are determined by the MPU 10
The set value is output to each by the transmission command from.

Here, a method of transmitting the set value of the power supply circuit 20 from the liquid crystal drive circuit 30 will be described in detail with reference to FIG. First, an index of data to be written is sent from the MPU 10, and then data is sent and written to the register unit 32 for each index. Among the transmitted data, the set value of the power supply circuit 20 is index 01h.
, Bits 3 to 2 of index 02h and bits 2 to 0 of index 03h,
When the transmission command is sent from the MPU 10, the bits are collectively transmitted to the power supply circuit 20. The set value can be transmitted to the scanning circuit 40 in the same manner. Therefore, the interface section with the MPU 10 is integrated into the liquid crystal drive circuit 30, and the power supply circuit 20 and the scanning circuit 4
0 circuit scale can be reduced.

As shown in FIG. 10, the setting value transmitted from the liquid crystal driving circuit 30 is held in the setting register 100 in the power supply circuit 20 in particular. In this way, MPU
10 outputs a set value of each circuit and outputs only necessary data from the liquid crystal drive circuit 30 to the power supply circuit 20 and the scanning circuit 40 to determine the operation of each circuit.

The liquid crystal drive circuit 30 outputs a control signal and plays the role of a controller. For the power supply circuit 20, a boosting clock DCCLK, an AC conversion signal M,
Is generated and output. The power supply circuit 20 is a liquid crystal drive circuit 30
Is input to the setting register 100 and each voltage inside the power supply circuit 20 is set. The scanning circuit 40 similarly receives the set value and performs the setting inside the scanning circuit 40. The power supply circuit 20 generates each voltage by boosting the voltage from the reference power supply Vci based on the boosting clock DCCLK in accordance with the setting value of the setting register. It outputs a gradation reference voltage VDH. Further, it outputs a positive high-voltage power supply VGH (to be a gate-on voltage Vgon), a negative high-voltage power supply VGL, and a gate-off voltage Vgoff to the scanning circuit 40. Further, for the liquid crystal panel 50, the common voltage Vcom is output to the common electrode of the liquid crystal panel 50.

Next, when the power supply becomes stable,
The MPU 10 outputs display data to the liquid crystal drive circuit 30,
The liquid crystal drive circuit 30 generates a voltage level of each gradation from a gradation reference voltage VDH in a gradation voltage generation unit (not shown) using a power supply for gradation voltage DDVDH as a power supply, and converts the voltage level into a gradation voltage according to display data. The data is converted and output to the data line of the liquid crystal panel 50.

The scanning circuit 40 includes a positive high voltage power supply VG
H and a negative high voltage power supply VGL,
In response to the line clock CL1, the gate-off voltage Vgoff is output during the non-scanning period, and the scanning of the gate line of the liquid crystal panel 50 is performed using the positive high voltage power supply VGH as the scanning voltage during the scanning period. Therefore, a display is made on the liquid crystal panel 50.

Next, the internal configuration of the power supply circuit 20 will be described in detail with reference to FIG. 12, a power supply circuit 20 includes 100 to 111 elements of the power supply circuit according to the first embodiment, and in addition, a voltage adjustment circuit 1100.
, The regulator 1101, and the booster circuits 1102 to 1
105, VDH reference generation circuit 1106, and buffer 1
107 and boosting capacitors C11, C12, C2
1, C22, C23, C31, and C32. Each voltage output has a capacitor C for stabilization.
b is added.

Next, the operation of each unit will be described. First,
The voltage adjustment circuit 1100 generates and outputs a reference voltage VregP and a reference voltage VregN from the reference power supply Vci. The reference voltage VregP and the reference voltage VregN are the first
Performs the same function as the reference voltage Vreg of the power supply circuit according to the embodiment. The regulator 1101 is connected to the reference power supply Vci.
Is regulated by the reference voltage VregP to supply a stable voltage Vci1. The booster circuit 1102 is a charge pump circuit, and boosts the voltage Vci1 two or three times using the boosting capacitors C11 and C12 and outputs the boosted voltage Vci1 as the power supply voltage DDVDH. Also, the booster circuit 110
Reference numeral 3 denotes a charge pump circuit, which includes a step-up capacitor C2.
1, the power supply voltage DDVDH is increased by 2 using C22 and C23.
Double or triple or quadruple the power supply voltage VG
Output as H. The booster circuit 1104 is a charge pump circuit, and uses a booster capacitor C31 to
The voltage VGH is multiplied by -1 and output as the power supply voltage DDVDH. The booster circuit 1105 is a charge pump circuit, and uses a booster capacitor C41 to generate a reference voltage V
Ci is multiplied by -1 and output as the power supply voltage VCL. V
The DH reference generation circuit 1106 amplifies the voltage from the reference voltage VregP according to a set value. The amplified voltage is current-amplified by the buffer 1107 and output as a voltage VDH.
Reference numerals 104 to 111 are circuits having the same function as the power supply circuit according to the first embodiment, and the power supply of each circuit uses the power supply voltage generated by the booster circuits 1102 to 1105. Accordingly, each power supply voltage is generated from the stable reference voltage Vci1, and the common voltage Vcom and the gate-off voltage Vgoff
Is generated and supplied to the liquid crystal driving circuit 30, the scanning circuit 40, and the liquid crystal panel 50 to perform display.

As described above, the common voltage Vc having the same phase and the same amplitude is set according to the set values of the amplitude reference generation circuit, the VcomH reference generation circuit, and the VgoffL reference generation circuit.
om and the gate-off voltage Vgoff can be easily generated, and if the setting data is updated from the MPU 10, the voltage level and the amplitude can be easily changed.

The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention. For example, although the reference voltage Vreg of the power supply circuit according to the first embodiment is a voltage common to the amplitude reference generation circuit 101, the VcomH reference generation circuit 102, and the VgoffL reference generation circuit 105, the reference voltage Vreg is changed to different voltage levels. No problem at all.

According to the first to fifth embodiments of the present invention, the steady-state current is suppressed, low power consumption is achieved, and Vco
An easy-to-use, low-cost power supply circuit and a liquid crystal drive circuit using the same can be realized by easily changing the amplitudes and voltage levels of m and Vgoff.

[0071]

According to the present invention, the steady-state current of the liquid crystal display device can be suppressed, and the power consumption can be reduced.

Alternatively, according to the present invention, the common voltage Vco
By making it possible to easily change the amplitude and the voltage level of m and the gate-off voltage Vgoff, there is an effect that user convenience is improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a power supply circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a detailed configuration of a circuit that generates a common voltage Vcom of the power supply circuit according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a detailed configuration of a circuit that generates a gate-off voltage Vgoff of the power supply circuit according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating a schematic configuration of a power supply circuit according to a second embodiment of the present invention.

FIG. 5 is a diagram illustrating a schematic configuration of a power supply circuit according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating a schematic configuration of a power supply circuit according to a third embodiment of the present invention.

FIG. 7 is a diagram illustrating a detailed configuration of a circuit that generates a common voltage Vcom of a power supply circuit according to a third embodiment of the present invention.

FIG. 8 is a diagram illustrating a detailed configuration of a circuit that generates a gate-off voltage Vgoff of a power supply circuit according to a third embodiment of the present invention.

FIG. 9 is a diagram showing a schematic configuration of a power supply circuit according to a fourth embodiment of the present invention.

FIG. 10 is a diagram illustrating a schematic configuration of a liquid crystal display device including a power supply circuit according to a fifth embodiment of the present invention.

FIG. 11 is a diagram illustrating a method for transmitting setting data of a liquid crystal display device including a power supply circuit according to a fifth embodiment of the present invention.

FIG. 12 is a diagram showing a detailed internal configuration of a power supply circuit according to a fifth embodiment of the present invention.

FIG. 13 is a diagram showing a schematic configuration of a conventional power supply circuit.

[Explanation of symbols]

100: setting register, 101: amplitude reference generating circuit, 1
02 ... VcomH reference generation circuit, 103 ... VcomL generation circuit, 104 ... VgoffL reference generation circuit, 105 ...
VgoffH generation circuit, 106 buffer, 107 buffer, 108 buffer, 109 buffer, 110
... voltage selector, 111 ... voltage selector.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) G09G 3/20 624 G09G 3/20 624C (72) Inventor Kazuo Daimon 5-chome, Kamimizuhoncho, Kodaira-shi, Tokyo No. 1 Hitachi Semiconductor Group (72) Inventor Kazunari Kurokawa 3300 Hayano Mobara-shi, Chiba Prefecture Hitachi Display Group (72) Inventor Atsuhiro Higa 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture F term in Hitachi Image Information System Co., Ltd. (reference)

Claims (7)

[Claims] 1. A power supply device for AC driving a drive voltage of a common electrode and a non-scanning period voltage of a scanning line of a liquid crystal display device, wherein an amplitude of the driving voltage of the common electrode and a non-scanning period voltage of the scanning line is provided. And a setting value holding circuit for setting a voltage level; an amplitude reference voltage generating circuit for generating an amplitude reference voltage between a drive voltage of the common electrode and a non-scanning period voltage of the scanning line according to the set value; A common electrode drive circuit that AC drives the common electrode at an amplitude and a voltage level determined by a set value; and the same phase and the same amplitude as the drive voltage of the common electrode at an amplitude and a voltage level determined by the amplitude reference voltage and the set value. And a non-scanning period voltage generating circuit for generating a non-scanning period voltage of the scanning line. 2. The common electrode driving circuit generates one potential according to a set value, generates the other potential from one potential according to an amplitude reference voltage, and switches both potentials to generate a driving voltage for the common electrode. The power supply device according to claim 1. 3. The non-scanning period voltage generating circuit generates one potential according to a set value, generates the other potential from one potential according to an amplitude reference voltage, and switches both potentials to perform non-scanning of the scanning line. The power supply according to claim 1, wherein the power supply generates a period voltage. 4. The power supply device according to claim 1, wherein the low-potential-side voltage of the drive voltage of the common electrode can be set to a negative potential, a ground, or a positive potential. 5. A power supply device for AC-driving a drive voltage of a common electrode and a non-scanning period voltage of a scanning line of a liquid crystal display device, wherein a voltage between the driving voltage of the common electrode and the non-scanning period voltage of the scanning line is provided. A set value holding circuit for setting a level; a common electrode driving circuit for fixing one potential and generating the other potential according to the set value to drive the common electrode in an alternating current; And a non-scanning period voltage generating circuit for generating a non-scanning period voltage of the scanning line having the same phase and the same amplitude as the driving voltage of the common electrode by generating the potential of the common electrode from the potential difference of the driving voltage of the common electrode. . 6. The power supply device according to claim 5, wherein one of the fixed potentials of the drive voltage of the common electrode is ground. 7. A pixel section having a pixel electrode connected to a data line via a switching element and a common electrode sandwiching a liquid crystal between the pixel electrode and an intersection of a plurality of data lines and a plurality of scanning lines. A liquid crystal display device comprising a liquid crystal panel arranged in a matrix at positions, a central processing unit for setting various set values, a liquid crystal driving circuit for temporarily holding set values from the central processing unit, and the liquid crystal A scanning circuit for driving a scanning line of a liquid crystal panel according to a set value and a control signal from a driving circuit; A liquid crystal display device, comprising: a power supply circuit that generates power according to a set value from the liquid crystal drive circuit.