JP4541332B2 - Display device - Google Patents

Description

  The present invention relates to a power supply device for controlling the power supply of a liquid crystal display device and a liquid crystal display device including the power supply device, and more particularly to a power supply control device for a TFT (Thin Film Transistor) liquid crystal display device and the power supply device thereof. The present invention relates to a liquid crystal display device provided.

  As a power supply circuit of a conventional liquid crystal display device, for example, there is a power supply circuit disclosed in Japanese Patent Application Laid-Open No. 10-301087, “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 deterioration of the liquid crystal layer, AC driving that reverses the polarity of the writing voltage to the pixel electrode with respect to the common electrode (counter electrode) is necessary. There is a common inversion driving method as one of the driving methods. The common inversion driving method will be briefly described. In this driving method, the common electrode of the TFT liquid crystal panel is switched between a low potential and a high potential at regular time intervals, and the drain voltage is written to the pixel electrode.

  As a pixel structure of the 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 the common inversion driving method is applied, in this pixel structure, a driving method for maintaining the potential difference between both ends of the liquid crystal capacitor constant by alternating the off-voltage of the gate line so as to have the same amplitude and phase as the common voltage, Since it has an effect of suppressing the charge / discharge current of the storage capacitor and the liquid crystal capacitor, it is generally used.

  FIG. 13 shows a conventional power supply circuit, which generates the common voltage and the off-voltage of the gate line. 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 is 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.

JP 10-301087 A

  TFT liquid crystal panels are applied to small portable information devices that require particularly low power consumption, in addition to large TFT liquid crystal panels used in conventional notebook computers and the like.

  However, in the conventional power supply circuit, a constant current flows from the common voltage Vcom through the ZD, and the power consumption is high. Further, in order to change the amplitude and voltage level of Vcom and Vgoff according to the TFT liquid crystal panel to be applied, it is necessary to change each resistance value or to replace components such as ZD. Furthermore, the number of parts is large, which is disadvantageous in terms of cost.

  The objective of this invention is providing the power supply device which can reduce the power consumption of a liquid crystal display device, and its liquid crystal display device.

  Alternatively, an object of the present invention is to improve user convenience. To provide a power supply device and a liquid crystal display device thereof.

  The present invention relates to a setting value holding circuit for setting the amplitude and voltage level between the driving voltage of the common electrode of the liquid crystal display device and the non-scanning period voltage of the scanning line, and the driving voltage of the common electrode and the scanning line according to the setting value. An amplitude reference voltage generation circuit that generates an amplitude reference voltage with a non-scan period voltage, a common electrode drive circuit that AC drives the common electrode with an amplitude and a voltage level determined from the amplitude reference voltage and a set value, and the amplitude reference voltage And a non-scan period voltage generation circuit that generates a non-scan period voltage of the scan line having the same phase and the same amplitude as the drive voltage of the common electrode at an amplitude and voltage level determined from the set value. Preferably, the common electrode driving circuit generates one potential according to a set value, generates the other potential according to the amplitude reference voltage from one potential, and generates a driving voltage for the common electrode by switching both potentials. The non-scan period voltage generation circuit generates one potential according to a set value, generates the other potential according to the amplitude reference voltage from one potential, and switches both potentials to generate the non-scan period voltage of the scan line. Preferably, the low potential side voltage of the drive voltage of the common electrode to be generated can be set to any of a negative potential, a ground (ground), or a positive potential.

  Alternatively, according to the present invention, a set value holding circuit that sets a voltage level between the driving voltage of the common electrode of the liquid crystal display device and the non-scan period voltage of the scanning line, and one potential is fixed and the other potential is generated according to the set value A common electrode driving circuit for AC driving the common electrode, and generating one potential according to a set value and generating the other potential from the potential difference of the driving voltage of the common electrode and having the same phase as the driving voltage of the common electrode and A non-scanning period voltage generation circuit for generating a non-scanning period voltage of the scanning line having the same amplitude. Preferably, one potential at which the drive voltage of the common electrode is fixed is ground.

  Alternatively, according to the present invention, a pixel portion having a pixel electrode that is connected to the data line via a switching element and a common electrode that sandwiches liquid crystal between the pixel electrode is defined as an intersection position of the plurality of data lines and the plurality of scanning lines. Liquid crystal panels arranged in a matrix, a central processing unit for setting various setting values, a liquid crystal driving circuit for temporarily holding setting values from the central processing unit, and setting values and control signals from the liquid crystal driving circuit A scanning circuit for driving a scanning line of the liquid crystal panel, and a reference power source is boosted to increase the power source of the liquid crystal driving circuit, the power source of the scanning circuit, and the driving voltage of the common electrode of the liquid crystal panel according to the set value from the liquid crystal driving circuit And a power supply circuit to be generated.

  According to the present invention, it is possible to suppress the steady current of the liquid crystal display device, thereby producing an effect of reducing power consumption.

  Alternatively, according to the present invention, it is possible to easily change the amplitude and voltage level of the common voltage Vcom and the gate-off voltage Vgoff, thereby improving the convenience for the user.

  Examples of the invention will be described below.

  Hereinafter, the configuration and operation of a power supply circuit according to an 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 that holds a set value, an amplitude reference generation circuit 101 that generates a voltage Vamp from the reference voltage Vreg according to the set value, and a VcomH that generates the voltage VcomH from the reference voltage Vreg according to the set value. A reference generation circuit 102, a VcomL generation circuit 103 that generates a voltage VcomL from the VcomH and the Vamp, a VgoffL reference generation circuit 104 that generates a voltage VgoffL from a reference voltage Vreg according to a set value, and a voltage VgoffH from the VgoffL and the Vamp VcomoffH generation circuit 105 for generating VcomH, VcommL, VgoffH and VgoffL, and buffers 106 to 109 that receive current amplification upon receiving VcomH, VcomL, and VcomH and VcomL are switched according to AC signal M. The voltage selector 110 which generates a Mont voltage Vcom, the voltage selector 111 which generates a gate-off voltage Vgoff switches the VgoffH and VgoffL accordance AC signal M, composed.

  Next, the operation of the power supply circuit according to the present embodiment will be described. First, the setting register 102 holds setting values for determining voltages generated by the amplitude reference generation circuit 101, the VcomH reference generation circuit 102, and the VgoffL reference generation circuit 104. 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 generates a voltage Vamp that is a reference voltage of the VcomL generation circuit 103 and the VgoffH generation circuit 105 according to a set value with the reference voltage Vreg as a reference, and determines the voltage amplitude of the common voltage Vcom and the gate-off voltage Vgoff. To do. The VcomH reference generation circuit 102 generates a voltage VcomH that is a high potential side voltage of the common voltage Vcom according to a set value with reference to the reference voltage Vreg. The VcomL generation circuit 103 generates a voltage VcomL that is a low potential side voltage of the common voltage Vcom according to Vamp with VcomH as a reference. VcomH and VcomL are amplified by a buffer 106 and a buffer 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 buffer 106 and the buffer 107 are input to the voltage selector 110, switched by the AC signal M, and one of them is output as the common voltage Vcom. For example, when the AC signal M is at a low level and the driving voltage of the liquid crystal panel is positive, the voltage selector 110 selects and outputs VcomL. The VgoffL reference generation circuit 104 generates a voltage VgoffL 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. The VgoffH generating circuit 105 generates a voltage VgoffH that is a high potential side voltage of the gate-off voltage Vgoff according to Vamp with VgoffL as a reference. The voltage VgoffH is set so that the potential difference from VgoffL is the same as the amplitude of the common voltage Vcom. VgoffH and VgoffL are amplified by the buffer 108 and the buffer 109 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 buffer 108 and the buffer 109 are input to the voltage selector 111, switched by the alternating signal M, and one of them is output as the gate-off voltage Vgoff. For example, when the AC signal M is at a low level and the driving voltage of the liquid crystal panel is positive, the voltage selector 111 selects and outputs VgoffL. Therefore, the common voltage Vcom and the gate-off voltage Vgoff have voltage waveforms having the same phase and the same amplitude.

  Next, the circuit for generating the common voltage Vcom of the power supply circuit according to the present embodiment will be described in detail using a specific example with reference to FIG. In FIG. 2, the amplitude reference voltage generation circuit 101 includes an operational amplifier OP1, a variable resistor R1a, and a resistor R1b. The VcomH reference generation circuit 102 includes an operational amplifier OP2, a variable resistor R2a, and a resistor R2b. The VcomL generation circuit 103 includes an operational amplifier OP3 and resistors R3a to R3d. The buffer 106 is composed of an operational amplifier OP6. The buffer 107 is composed of an operational amplifier OP7. 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 DDVDH, and the negative power supply is the ground GND. Since VcomL is normally set to a voltage value near GND, the positive power supply of OP3 and OP7 is DDVDH, and the negative power supply is the negative power supply voltage VCL. The positive power source of OP1 that generates the voltage Vamp related to the voltage amplitude is DDVDH, and the negative power source is the 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 that forms 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 according to the set value of the setting register 100. The VcomH reference voltage generation circuit 102 generates a voltage VcomH by buffering a voltage obtained by dividing the reference voltage Vreg by the variable resistor R2a and the resistor R2b with an operational amplifier OP2 that forms a voltage follower. The resistance value of the variable resistor R2a can be changed by the setting value of the setting register 100 in the same manner as the variable resistor R1a. The VcomL generation circuit 103 forms a differential amplifier circuit, and generates VcomL from VcomH and Vamp. The voltage of VcomL is expressed by the following equation.

VcomL = A.VcomH-B.Vamp (1)
(However, A = {(R3c + R3d) · R3b} / {(R3a + R3b) · R3d}, B = R3c / R3d).
In the buffer 106, VcomH is buffered by an operational amplifier OP6 that forms a voltage follower. In the buffer 107, VcomL is buffered by an operational amplifier OP7 that forms a voltage follower. As described above, VcomL can be generated from VcomH and Vamp, and the amplitude and voltage level of Vcom can be easily adjusted by adjusting VcomH and Vamp according to set values.

  Here, R3a = R3c and R3b = R3d are shown as the conditions for generating the amplitude of the common voltage Vcom only by setting Vamp regardless of the setting of VcomH, and these are substituted into Expression (1). The following formula is obtained.

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 the negative power supply voltage VCL, VcomL can be any of a negative voltage, GND, or a positive voltage. It is possible to correspond to.

  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 using a specific example with reference to FIG. In FIG. 3, the VgoffL reference generation circuit 104 includes an operational amplifier OP4, a variable resistor R4a, and a resistor R4b. The VgoffH generation circuit 105 includes an operational amplifier OP5 and resistors R5a to R5d. The buffer 108 is composed of an operational amplifier OP8. The buffer 109 is composed of an operational amplifier OP9. Note that VgoffH and VgoffL are in the range from the ground GND to the negative power supply voltage VGL.

  In the VgoffL reference voltage generation circuit 104, the operational amplifier OP4 generates VgoffL so that a voltage obtained by dividing the voltage VgoffL and the positive power supply voltage DDVDH by the variable resistor R4a and the resistor R4b is equal to the reference voltage Vreg. The resistance value of the variable resistor R4a can be changed by the setting value of the setting register 100, similarly to the variable resistor R1a. The VgoffH generation circuit 105 forms a differential amplifier circuit, and generates VgoffH from VgoffL and Vamp. The voltage VgoffH is expressed by the following equation.

VgoffH = C · VgoffL + D · Vamp (3)
(However, C = {(R4c + R4d) · R4a} / {(R4a + R4b) · R4c}, D = R4b / R4c).
In the buffer 108, VgoffH is buffered by an operational amplifier OP8 that forms a voltage follower. In the buffer 109, VgoffL is buffered by an operational amplifier OP9 that forms a voltage follower. As described 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 the set values.

  Here, the conditions for generating the amplitude of the gate-off voltage Vgoff by only setting Vamp regardless of the setting of VgoffL are R4a = R4c and R4b = R4d, and these are substituted into Expression (3). The following formula is obtained.

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

  Furthermore, when the condition that the amplitude of the common voltage Vcom is equal to the amplitude of the gate-off voltage Vgoff is (R3a / R3b) = (R4b / R4a).

  Accordingly, by selecting the resistance ratio so as to satisfy all the above-described conditions, the VcomH voltage and the VgoffL voltage are set to determine the reference potentials for the common voltage Vcom and the gate-off voltage Vgoff. By setting the voltage, it is possible to generate the common voltage Vcom having the same phase and the same amplitude and the gate-off voltage Vgoff.

  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 the set values of the amplitude reference generation circuit, the VcomH reference generation circuit, and the VgoffL reference generation circuit.

  Furthermore, since the power supply circuit according to this embodiment 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.

  Furthermore, since each voltage level and amplitude are determined by the resistance ratio, if the resistance value is increased, a steady current can be suppressed and power consumption can be reduced.

  Although the power supply circuit according to the first embodiment has been described above, the power supply circuit according to the second embodiment shows a method of further reducing the circuit scale and reducing power consumption.

  A power supply circuit according to the second embodiment of the present invention will be described below with reference to FIGS. This embodiment is characterized in that VcomL is fixed, and the method for determining the amplitudes of the common voltage Vcom and the gate-off voltage Vgoff of the power supply circuit according to the first embodiment is 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. In addition, VgoffL is generated from the VgoffL reference generation circuit 105 as in the power supply circuit according to the first embodiment. VgoffH is generated by inputting VcomH and VgoffL to the VgoffH generation circuit. That is, VcomH is input instead of Vamp input to the VgoffH generation circuit in the power supply circuit according to the first embodiment. The specific internal configuration of each circuit is the same as that of the power supply circuit according to the first embodiment. Therefore, VgoffH is expressed by the following equation.

VgoffH = C · VgoffL + D · VcomH (5)
(However, C = {(R4c + R4d) · R4a} / {(R4a + R4b) · R4c}, D = R4b / R4c).
Here, a condition for generating the amplitude of the gate-off voltage Vgoff only by setting VcomH regardless of the setting of VgoffL is R4a = R4c = R4b = R4d, which is substituted into the equation (5). The following formula is obtained.

VgoffH−VgoffL = VcomH (6)
Therefore, when VcomL is fixed to GND, the voltage values of VcomH and VgoffL are set by equalizing the resistance values of the VgoffH generation circuit, and the common voltage Vcom having the same phase and the same amplitude and the gate-off voltage are set. It is possible to generate Vgoff.

  Furthermore, the power supply circuit according to the present embodiment can reduce the circuit scale and power consumption as compared with the power supply circuit according to the first embodiment.

  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 switches the voltage Vamp and VcomH by the switching signal MODE and applies it to Vgoff, and switches the voltage VcomL and GND amplified by the buffer 107 to the voltage selector 110 by switching by the switching signal MODE. A voltage selector 202 is provided. All the resistance values of the VgoffH generation circuit are made equal. That is, R4a = R4c = R4b = R4d. In addition, 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 the respective power supplies.

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

  The power supply circuit according to the second embodiment has been described above. However, in the power supply circuit according to the third embodiment, a method of easily switching the same phase and the same amplitude even when the reference voltage is changed will be described.

  Hereinafter, a power supply circuit according to a third 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 that holds a setting value, an amplitude reference generation circuit 101 that generates a voltage Vamp from the reference voltage Vreg according to the setting value, and a VcomL that generates the voltage VcomL from the reference voltage Vreg according to the setting value. A reference generation circuit 301, a VcomH generation circuit 302 that generates a voltage VcomH from the VcomL and the Vamp, a VgoffH reference generation circuit 303 that generates a voltage VgoffH from a reference voltage Vreg according to a set value, and a voltage VgoffL from the VgoffH and the Vamp VcomoffL generation circuit 304 that generates VcomH, VcomH and VcommL, and buffers 106 to 109 that receive current amplification upon receiving VgoffH and VgoffL, and VcomH and VcomL are switched according to AC signal M The voltage selector 110 which generates a Mont voltage Vcom, the voltage selector 111 which generates a gate-off voltage Vgoff switches the VgoffH and VgoffL accordance AC signal M, composed.

  Next, the operation of the power supply circuit according to the present embodiment will be described. The amplitude reference generation circuit 101 generates a voltage Vamp that is a reference voltage of the VcomH generation circuit 302 and the VgoffL generation circuit 304 according to a set value with the reference voltage Vreg as a reference, and determines the voltage amplitude of the common voltage Vcom and the gate-off voltage Vgoff. To do. The VcomL reference generation circuit 301 generates a voltage VcomL that is a low potential side voltage of the common voltage Vcom in accordance with a set value with reference to the reference voltage Vreg. The VcomH generation circuit 302 generates a voltage VcomH that is a high potential side voltage of the common voltage Vcom according to Vamp with VcomL as a reference. The operation of the buffer 106, the buffer 107, and the voltage selector 110 is the same as that of the power supply circuit according to the first embodiment. The VgoffH reference generation circuit 303 generates a voltage VgoffH that is a high-potential-side voltage of the gate-off voltage Vgoff according to a set value with reference to the reference voltage Vreg. The VgoffL generation circuit 304 generates a voltage VgoffL that is a low potential side voltage of the gate-off voltage Vgoff according to Vamp with VgoffH as a reference. The voltage VgoffL is set such that the potential difference from VgoffH is the same as the amplitude of the common voltage Vcom. The operation of the buffer 108, the buffer 109, and the voltage selector 111 is the same as that of the power supply circuit according to the first embodiment.

  Next, the circuit for generating the common voltage Vcom of the power supply circuit according to the present embodiment will be described in detail using a specific example with reference to FIG. In FIG. 7, an amplitude reference voltage generation circuit 101 has the same configuration as that of the power supply circuit according to the first embodiment. The VcomL reference generation circuit 301 has the same configuration as the VcomH reference generation circuit 102, and differs in that VcomL is generated instead of VcomH. The VcomH generation circuit 302 includes an operational amplifier OP10 and resistors R6a to R6d. 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 DDVDH, and the negative power supply is the ground GND. Since VcomL is normally set to a voltage value near GND, the positive power supply of OP3 and OP7 is DDVDH, and the negative power supply is the negative power supply voltage VCL. The positive power source of OP1 that generates the voltage Vamp related to the voltage amplitude is DDVDH, and the negative power source is the ground GND.

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

VcomH = E · VcomL + F · Vamp (7)
(However, E = {(R6c + R6d) · R6a} / {(R6a + R6b) · R6c}, 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 VcommL and Vamp according to set values.

  Here, the conditions for generating the amplitude of the common voltage Vcom by only setting Vamp regardless of the setting of VcomL are R6a = R6c, R6b = R6d, and these are substituted into Expression (7). The following formula is obtained.

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 using a specific example with reference to FIG. In FIG. 8, a VgoffH reference generation circuit 303 has the same configuration as the VgoffL reference generation circuit 104, and differs in that VgoffH is generated instead of VgoffL. The VgoffL generation circuit 304 includes an operational amplifier OP7 and resistors R7a to R7d. Note that VgoffH and VgoffL are in the range from the ground GND to the negative power supply voltage VGL.

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

VgoffL = G · VgoffH−H · Vamp (9)
(However, G = {(R7c + R7d) · R7a} / {(R7a + R7b) · R7c}, H = R7d / R7c).
As described above, VgoffL can be generated from VgoffH and Vamp, and the amplitude and voltage level of Vgoff can be easily adjusted by adjusting VgoffH and Vamp according to the set values.

  Here, the conditions for generating the amplitude of the gate-off voltage Vgoff by only setting Vamp regardless of the setting of VgoffH are R7a = R7c, R7b = R7d, and these are substituted into the equation (9). The following formula is obtained.

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

  Furthermore, when the condition that the amplitude of the common voltage Vcom is equal to the amplitude of the gate-off voltage Vgoff is (R6b / R6a) = (R7b / R7a).

  Accordingly, by selecting the resistance ratio so as to satisfy all of the above-described conditions, the VcomL voltage and the VgoffH voltage are set to determine the reference potentials of the common voltage Vcom and the gate-off voltage Vgoff. By setting the voltage, it is possible to generate the common voltage Vcom having the same phase and the same amplitude and the gate-off voltage Vgoff.

  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.

  Although the power supply circuit according to the third embodiment has been described above, the power supply circuit according to the fourth embodiment shows a method of easily generating two voltages having the same phase and the same amplitude with fewer operational amplifiers. .

  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 only in the circuit that generates VgoffH of the power supply circuit according to the first embodiment. As shown in FIG. 9, instead of the VgoffH generation circuit 105 and the buffer 108 of the power supply circuit according to the first embodiment, a capacitor 901, VcomH amplified by the buffer 106, and VgoffH connected to the voltage selector are converted into an AC signal. A voltage selector 902 that is switched by M and connected to the + electrode of the capacitor 901, and a voltage that is switched between VcomL amplified by the buffer 107 and VgoffL amplified by the buffer 109 by the AC signal M and connected to the − electrode of the capacitor 901. And a selector 903.

  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 positive, and the voltage selectors 110 and 111 select and output VcomL and VgoffL, respectively. At this time, the voltage selector 902 connects the + electrode of the capacitor 902 and VcomH, and the voltage selector 903 connects the − electrode of the capacitor 902 and VcomL to charge the capacitor 901. When fully charged, the potential difference across 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, when the AC signal M becomes high level and becomes negative, the voltage selectors 110 and 111 select and output VcomH and VgoffH, respectively. At this time, the voltage selector 902 connects the + electrode of the capacitor 902 and VgoffH, and the voltage selector 903 connects the − electrode of the capacitor 902 and VgoffL. Therefore, the voltage of VgoffH becomes higher from VgoffL by the amplitude of the common voltage Vcom, and the gate-off voltage Vgoff can output a voltage having the same amplitude and the same phase as the common voltage Vcom.

  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 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 can be integrated in the IC.

  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.

  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, the liquid crystal display device includes a microprocessor (hereinafter referred to as MPU) 10, a power supply circuit 20, a liquid crystal driving circuit 30, a scanning circuit 40, and a liquid crystal panel 50. Furthermore, the liquid crystal driving 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. The power supply circuit 100 is a power supply circuit according to the first to fourth embodiments.

  Next, the operation of the liquid crystal display device including the power supply circuit according to the present embodiment will be described. First, after the power is turned on, the MPU 10 outputs a command for setting the operation of each circuit to the liquid crystal drive circuit 30. The liquid crystal driving circuit 30 that has received the command by the interface unit 31 holds it in the register unit 32. Among the setting values held in the register unit 32, the setting values of the power supply circuit 20 and the scanning circuit 40 are output to the respective values in response to a transmission command from the MPU 10.

  Here, a method for 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, then data is sent and written to the register unit 32 for each index. If the set value of the power supply circuit 20 is set to bits 1 to 0 of the index 01h, bits 3 to 2 of the index 02h, and bits 2 to 0 of the index 03h among the sent data, a transmission command from the MPU 10 is sent. At that time, the bits are collectively transmitted to the power supply circuit 20. Similarly, the set value can be transmitted to the scanning circuit 40. Therefore, it is possible to reduce the circuit scale of the power supply circuit 20 and the scanning circuit 40 by consolidating the interface unit with the MPU 10 in the liquid crystal driving circuit 30.

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

  Further, the liquid crystal driving circuit 30 outputs a control signal and plays the role of a controller. The power supply circuit 20 generates and outputs a boosting clock DCCLK and an alternating signal M. The power supply circuit 20 takes the set value from the liquid crystal drive circuit 30 into the setting register 100 and sets each voltage inside the power supply circuit 20. Similarly, the scanning circuit 40 receives the set value and performs setting in the scanning circuit 40. In the power supply circuit 20, each voltage is generated by boosting from the reference power supply Vci based on the boosting clock DCCLK according to the setting value of the setting register, and for the liquid crystal driving circuit 30, the gradation voltage power supply DDVDH, A gradation reference voltage VDH is output. Further, a positive high voltage power supply VGH (which becomes a gate-on voltage Vgon) and a negative high voltage power supply VGL are output to the scanning circuit 40, and a gate-off voltage Vgoff is output. Further, the common voltage Vcom is output to the common electrode of the liquid crystal panel 50 for 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, and the liquid crystal drive circuit 30 uses a gradation voltage power supply DDVDH as a power supply. ), A voltage level of each gradation is generated from the gradation reference voltage VDH, converted into a gradation voltage according to display data, and output to the data line of the liquid crystal panel 50.

  The scanning circuit 40 uses a positive high voltage power supply VGH and a negative high voltage power supply VGL as power supplies, and outputs a gate-off voltage Vgoff during the non-scanning period according to the line clock CL1 from the liquid crystal driving circuit 30, and a positive high voltage power supply VGH during the scanning period. Is used as a scanning voltage to scan the gate lines of the liquid crystal panel 50. Accordingly, 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. In FIG. 12, a power supply circuit 20 includes each element of the power supply circuit 100 to 111 according to the first embodiment, a voltage adjustment circuit 1100, a regulator 1101, booster circuits 1102 to 1105, and VDH reference generation. A circuit 1106, a buffer 1107, and boost capacitors C11, C12, C21, C22, C23, C31, and C32 are included. A capacitor Cb for stabilization is added to each voltage output.

  Next, the operation of each unit will be described. First, the voltage adjustment circuit 1100 generates and outputs the reference voltage VregP and the reference voltage VregN from the reference power supply Vci. The reference voltage VregP and the reference voltage VregN perform the same function as the reference voltage Vreg of the power supply circuit according to the first embodiment. The regulator 1101 regulates the reference power supply Vci with the reference voltage VregP, and supplies a stable voltage Vci1. The booster circuit 1102 is a charge pump circuit, and boosts the voltage Vci1 twice or three times using the boosting capacitors C11 and C12, and outputs the boosted voltage as the power supply voltage DDVDH. The booster circuit 1103 is a charge pump circuit that boosts the power supply voltage DDVDH by 2 times, 3 times, or 4 times using the boost capacitors C21, C22, and C23, and outputs the boosted voltage as a power supply voltage VGH. The booster circuit 1104 is a charge pump circuit, which multiplies the voltage VGH by −1 using the booster capacitor C31 and outputs it as the power supply voltage DDVDH. The booster circuit 1105 is a charge pump circuit, which uses the boosting capacitor C41 to multiply the reference voltage Vci by −1 and outputs it as the power supply voltage VCL. The VDH 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 the voltage VDH. Reference numerals 104 to 111 denote circuits having the same functions as those of the power supply circuit according to the first embodiment, and the power supply voltage generated by the booster circuits 1102 to 1105 is used as the power supply of each circuit. Accordingly, each power supply voltage is generated from the stable reference voltage Vci1, and the common voltage Vcom and the gate-off voltage Vgoff are generated and supplied to the liquid crystal driving circuit 30, the scanning circuit 40, and the liquid crystal panel 50, and display is performed.

  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 the set values of the amplitude reference generation circuit, the VcomH reference generation circuit, and the VgoffL reference generation circuit. If the setting data is updated, the voltage level and amplitude can be easily changed.

  It goes without saying that the present invention is not limited to the embodiment described above, and various modifications can be made without departing from the spirit of the present invention. For example, 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, but this is changed to different voltage levels. There is no problem.

  According to the first to fifth embodiments of the present invention, low power consumption is achieved by suppressing steady current, and the amplitude and voltage level of Vcom and Vgoff can be easily changed, and the usability is low. A power supply circuit and a liquid crystal driving circuit using the power supply circuit can be realized.

It is a figure which shows schematic structure of the power supply circuit by the 1st Embodiment of this invention. It is a figure which shows the detailed structure of the circuit which produces | generates the common voltage Vcom of the power supply circuit by the 1st Embodiment of this invention. It is a figure which shows the detailed structure of the circuit which produces | generates the gate-off voltage Vgoff of the power supply circuit by the 1st Embodiment of this invention. It is a figure which shows schematic structure of the power supply circuit by the 2nd Embodiment of this invention. It is a figure which shows schematic structure of the power supply circuit by the 2nd Embodiment of this invention. It is a figure which shows schematic structure of the power supply circuit by the 3rd Embodiment of this invention. It is a figure which shows the detailed structure of the circuit which produces | generates the common voltage Vcom of the power supply circuit by the 3rd Embodiment of this invention. It is a figure which shows the detailed structure of the circuit which produces | generates the gate-off voltage Vgoff of the power supply circuit by the 3rd Embodiment of this invention. It is a figure which shows schematic structure of the power supply circuit by the 4th Embodiment of this invention. It is a figure which shows schematic structure of the liquid crystal display device containing the power supply circuit by the 5th Embodiment of this invention. It is a figure which shows the transmission method of the setting data of the liquid crystal display device containing the power supply circuit by the 5th Embodiment of this invention. It is a figure which shows the detailed structure inside the power supply circuit by the 5th Embodiment of this invention. It is a figure which shows schematic structure of the conventional power supply circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Setting register, 101 ... Amplitude reference generation circuit, 102 ... 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.

Claims (6)

A pixel portion is formed in a matrix corresponding to the intersections of a plurality of data lines and a plurality of scanning lines, and the pixel portion includes a pixel electrode, a common electrode facing the pixel electrode, and a switching element, and the data line Is connected to the pixel electrode through the switching element, and the scanning line is connected to a control terminal of the switching element;
A data driving circuit for outputting a gradation voltage corresponding to display data to the switching element via the data line;
A scan driving circuit for outputting a gate-on voltage for turning on the switching element and a gate-off voltage for turning off the switching element to the switching element via the scanning line;
In the display device comprising: a gray-level reference voltage is used to generate the gray scale voltages, and the gate-on voltage, and the gate-off voltage, and a power supply circuit for outputting a common voltage applied to the common electrode,
The common voltage includes a first common voltage and a second common voltage having a lower potential than the first common voltage,
The gate-off voltage has a first gate-off voltage and a second gate-off voltage having a lower potential than the first gate-off voltage,
The power supply circuit is
A first circuit for generating a reference voltage by converting a power supply voltage input from the outside ;
A second circuit for generating the gradation reference voltage from the reference voltage;
A third circuit for generating the first common voltage from the gradation reference voltage;
A fourth circuit for generating the second common voltage from the first common voltage;
A fifth circuit for generating the second gate-off voltage from the reference voltage;
A holding circuit for holding a voltage corresponding to a potential difference between the first common voltage and the second common voltage;
And a sixth circuit for generating the first gate-off voltage by superimposing the voltage held in the holding circuit on the second gate-off voltage. The display device according to claim 1,
The power supply circuit is
A seventh circuit for outputting one of the first common voltage and the second common voltage by switching a predetermined timing;
And an eighth circuit for switching between the first gate-off voltage and the second gate-off voltage at a constant timing and outputting either of them. The display device according to claim 2,
The timing at which the seventh circuit switches the first common voltage and the second common voltage, and the timing at which the eighth circuit switches the first gate off voltage and the second gate off voltage are the pixel A display device according to an alternating signal for inverting the polarity of a voltage applied to an electrode. The display device according to claim 2 or 3,
The eighth circuit selects the first gate-off voltage when the seventh circuit selects the first common voltage, and the seventh circuit selects the second common voltage. A display device for selecting the second gate-off voltage. The display device according to any one of claims 2 to 4,
It said holding circuit is a capacitor,
Charging the capacitor by connecting an output terminal of the third circuit to a first terminal of the capacitor, and connecting an output terminal of the fourth circuit to a second terminal of the capacitor;
A display device that discharges the capacitor by switching the connection of the first terminal of the capacitor to the input terminal of the eighth circuit and switching the connection of the second terminal of the capacitor to the output terminal of the fifth circuit. . The display device according to claim 5,
The timing for switching the connection of the capacitor is a display device according to the alternating signal.

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