WO2002061931A1

WO2002061931A1 - Boosting power circuit, liquid crystal display device, and portable electronic equipment

Info

Publication number: WO2002061931A1
Application number: PCT/JP2001/011233
Authority: WO
Inventors: Shinobu Nohtomi; Kazuya Endo; Kazuo Ookado
Original assignee: Hitachi, Ltd.; Hitachi Device Engineering, Co., Ltd.
Priority date: 2001-01-30
Filing date: 2001-12-21
Publication date: 2002-08-08
Also published as: JPWO2002061931A1

Abstract

A boosting power circuit, wherein an external power voltage is used as a reference voltage for charging the boosting power circuit formed of a charging pump, a voltage boosted by the charging pump is output as a liquid crystal drive voltage by using the reference voltage generated in a reference voltage generating circuit formed of a differential amplifier at the time of boosting, and a voltage obtained by resistively dividing an output voltage from the charging pump is allowed to feed back to the input terminal of the differential amplifier in the reference voltage generating circuit.

Description

Description Boost type power supply circuit, liquid crystal display device and portable electronic equipment

The present invention relates to a technology that is effective when applied to a boosting type power supply circuit that generates a voltage obtained by boosting a power supply voltage. For example, the present invention relates to a liquid crystal driving voltage generating circuit that generates a voltage for driving a liquid crystal display device, and a liquid crystal incorporating the same. The present invention relates to a display control device and a technique effective for use in a portable electronic device equipped with the display control device. '' Background technology

In recent years, as a display device of a portable electronic device such as a mobile phone or a pager, a dot matrix type liquid crystal panel in which a plurality of display pixels are two-dimensionally arranged in a matrix, for example, is generally used. The semiconductor device is provided with a semiconductor integrated circuit-based display control device for controlling the display of the liquid crystal panel, a driver for driving the liquid crystal panel, or a display control device incorporating such a driver. Such a display control device integrated into a semiconductor integrated circuit can operate at a voltage of 5 V or less, whereas a display drive of a liquid crystal panel requires a drive voltage of 5 to 40 V. In many cases, the display control device has a built-in liquid crystal drive voltage generation circuit that generates a voltage for driving the liquid crystal panel by boosting the power supply voltage.

The present inventors have studied a circuit as shown in FIGS. 11 and 12 as a liquid crystal drive voltage generation circuit built in such a liquid crystal display control device. The circuit in FIG. 11 includes a reference voltage generation circuit including a differential amplifier AMP and a charge pump CPM that boosts the reference voltage Va generated by the reference voltage generation circuit. The circuit is composed of a charge pump CPM that boosts the power supply voltage VDD, a reference voltage generation circuit 10 that operates using the voltage Vp boosted by the charge pump as a power supply, and a liquid crystal drive voltage, and a voltage follower 11. It is a thing. Fig. 11 and Fig. 12 show the charge pump CPM as an example. Although a circuit that boosts the voltage Va or VDD three times is shown, a charge pump such as a four-fold boost type or a five-fold boost type is used depending on the required voltage.

In addition, it has been clarified by a study conducted after the invention was made that there is a circuit as disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-260423. '

However, the booster-type liquid crystal drive voltage generation circuit as shown in Fig. 11 drives the liquid crystal panel directly with the voltage boosted by the charge pump CPM, so current efficiency is good, but the charge pump has a current supply capacity. It was found that the level of the output Vout of the charge pump CPM was reduced as shown in Fig. 13 due to the load of the panel being connected to the charge pump when the display on the liquid crystal panel was started. Since the amount of the voltage drop depends on the size of the load, that is, the size of the panel and the characteristics of the panel, the accuracy of the output voltage is poor and a DC voltage may be applied to the liquid crystal, which may cause deterioration of the liquid crystal. It was also found that there was a problem in that good image quality could not be obtained with the liquid crystal display panel, such as a shift in display color.

On the other hand, in the voltage-follower type liquid crystal drive voltage generation circuit as shown in Fig. 12, even when the load on the panel is connected to the voltage follower 11 when the LCD panel starts displaying, the voltage follower will have a current Since the supply capacity is high, a voltage is output that immediately drives the load sufficiently. As a result, as shown in Fig. 14, the liquid crystal drive voltage Vout output has high accuracy and good image quality can be obtained.However, a voltage Vp higher than the liquid crystal drive output voltage Vout boosted by the charge pump CPM is set to the reference voltage. Since it is used as an operating power supply for the generator circuit 10 and the voltage follower 11, it has been found that the power consumption is large, that is, the current loss is large. In addition, since the reference voltage generation circuit 10 and the voltage follower 11 operate using the voltage boosted by the charge pump CPM as a power supply, it is necessary to configure the circuit using a high withstand voltage element, and the circuit area is correspondingly reduced. It was found that there was a problem that the size and the process became complicated.

The present invention has been made in view of the above problems, and has as its object to provide a step-up power supply circuit capable of generating a highly accurate boosted voltage with a small current loss. . Another object of the present invention is to provide a liquid crystal display control device capable of generating a liquid crystal drive voltage with low power consumption and high accuracy and requiring a small circuit occupation area.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

Disclosure of the invention

The outline of a typical invention disclosed in the present application is as follows.

That is, the external power supply voltage (VDD) is used as the reference voltage for charging the booster circuit composed of the charge pump (20), and the voltage is generated by the reference voltage generator circuit (10) composed of a differential amplifier during boosting. Using the reference voltage (V a) thus obtained, the voltage boosted by the charge pump is output as the liquid crystal drive voltage, and the voltage obtained by dividing the output voltage of the charge pump by resistance is used as the differential voltage of the reference voltage generation circuit (10). It is configured to feed back to the input terminal of the amplifier.

More specifically, a reference voltage generating circuit having a differential amplifier that operates on an external power supply voltage, a plurality of capacitors, a switch for charging each of the capacitors, and a voltage connected by connecting the capacitors in series, and A booster circuit having a switch for addition, feedback means for feeding back a voltage corresponding to an output voltage of the booster circuit to an input terminal of the differential amplifier, and a smoothing capacitor connected to an output terminal of the booster circuit. In the booster power supply circuit thus configured, the booster circuit charges the capacitor based on the power supply voltage of the differential amplifier during a charging operation, and the plurality of capacitors are connected in series. When the operation of adding the charging voltage is performed, the voltage on the reference end side of the capacitor is boosted based on the reference voltage output from the differential amplifier.

According to the above-described means, since the output voltage of the booster circuit is fed back to the input terminal of the differential amplifier that generates the reference voltage of the booster circuit, a highly accurate boosted voltage can be generated, and at the time of boosting, The differential amplifier that generates the reference voltage of Since the device operates with an external power supply voltage lower than the boosted voltage, power consumption can be reduced. Preferably, the feedback means includes: a resistance dividing means including a plurality of resistance elements connected in series between an output terminal of the booster circuit and a power supply voltage terminal; Selecting means for selecting the potential of the node and transmitting the selected potential to the input terminal of the differential amplifier. As a result, it becomes possible to select the feed voltage, and the output boost voltage can be adjusted according to the characteristics of a load or a circuit such as a liquid crystal display panel.

Preferably, a register is provided for designating a voltage to be fed back to the input terminal of the differential amplifier by the selection means. As a result, the output boost voltage can be adjusted by changing the set value of the register, and a boost power supply circuit with high adaptability to the system to be used can be obtained.

Further, a liquid crystal drive voltage generation circuit according to the present invention includes a reference voltage generation circuit having a differential amplifier operated by an external power supply voltage, a plurality of capacitors, a switch for charging each of the capacitors, and the capacitors in series. A booster circuit having a switch for adding the charged voltage connected thereto; feedback means for feeding back a voltage corresponding to an output voltage of the booster circuit to an input terminal of the differential amplifier; A first boosting power supply circuit configured to generate a voltage to be applied to the segment electrodes of the liquid crystal panel, the first boosting power supply circuit including a smoothing capacitor connected to the output terminal of A second step-up power supply circuit that generates a voltage applied to a common electrode of the liquid crystal panel based on a voltage; and wherein the second step-up power supply circuit includes a plurality of capacitors and the capacitors. The booster circuit has a switch for charging and a switch for adding the charged voltage by connecting the capacitors in series, and a smoothing capacitor connected to an output terminal of the booster circuit. . Thereby, when the load of the second booster type power supply circuit is small, the second booster type power supply circuit can generate a sufficiently accurate common electrode applied voltage by the second booster type power supply circuit, and the circuit area is reduced. In addition, a power supply circuit with low power consumption can be realized.

Also, a reference voltage generating circuit having a differential amplifier operated by an external power supply voltage, a plurality of capacitors, a switch for charging each of the capacitors, and the capacitor are connected in series. A booster circuit having a switch for adding the charged voltage, a feedback circuit for feeding back a voltage corresponding to an output voltage of the booster circuit to an input terminal of the differential amplifier, and an output terminal of the booster circuit. A first boosted power supply circuit configured to generate a voltage applied to the segment electrodes of the liquid crystal panel, the first boosted power supply circuit being configured from a connected smoothing capacitor, and a voltage generated by the first boosted power supply circuit. A second step-up power supply circuit for generating a voltage applied to a common electrode of the liquid crystal panel; wherein the second step-up power supply circuit includes a reference voltage generation circuit having a differential amplifier operating with an external power supply voltage; A booster circuit having a plurality of capacitors and a switch for charging each of the capacitors, and a switch for adding the charged voltage by connecting the capacitors in series; and A resistive dividing means for dividing the output voltage of the booster circuit is fee Dopakku to an input terminal of the differential amplifier, constituted by the connected smoothing capacitor to the output terminal of the booster circuit. Thus, even when the load on the second booster power supply circuit is large, a sufficiently accurate common electrode applied voltage can be generated by the second booster power supply circuit.

Further, another invention of the present application relates to a reference voltage generating circuit having a differential amplifier operated by an external power supply voltage, a plurality of capacitors, a switch for charging the capacitors, and a capacitor connected in series to be charged. A booster circuit having a switch for adding the boosted voltage, a feedpack means for feeding a voltage corresponding to an output voltage of the booster circuit to an input terminal of the differential amplifier, and a booster circuit connected to an output terminal of the booster circuit. A first step-up power supply circuit configured to generate a voltage to be applied to the segment electrode of the liquid crystal panel, the first step-up power supply circuit being configured by the first step-up power supply circuit. In a method for designing a liquid crystal driving voltage generating circuit including a second boosting type power supply circuit for generating a voltage applied to a common electrode of a liquid crystal panel, the load on the common electrode is small. In this case, the second boosting type power supply circuit may include a plurality of capacitors and a switch for charging the capacitors, and a switch for connecting the capacitors in series and adding a charged voltage. And a smoothing capacitor connected to the output terminal of the booster circuit. When the load on the common electrode is large, the second booster-type power supply circuit includes a reference voltage generating circuit having a differential amplifier. And multiple A booster circuit having a capacitor, a switch for charging the capacitor, and a switch for connecting the capacitor in series and adding a charged voltage; and dividing the output voltage of the booster circuit into the differential amplifier. And a smoothing capacitor connected to the output terminal of the booster circuit.

According to the above-described means, it is possible to generate a sufficiently accurate common electrode applied voltage by the second booster power supply circuit regardless of whether the load of the second booster power supply circuit is small or large. In addition, when the load of the second step-up power supply circuit is small, a power supply circuit having a small circuit area and low power consumption can be realized.

Still another aspect of the present invention provides a liquid crystal drive voltage generation circuit having the above-described configuration, a display memory for storing data to be displayed on the liquid crystal panel, and a method for generating data to be written in the display memory and for displaying the data. A control circuit for controlling data reading from the memory; and a control circuit for applying data to the segment electrodes of the liquid crystal panel based on data read from the display memory and a driving voltage generated by the liquid crystal driving voltage generating circuit. And a common electrode drive circuit that generates a signal to be applied to a common electrode of the liquid crystal panel based on the drive voltage generated by the liquid crystal drive voltage generation circuit and a predetermined timing signal. It constitutes a liquid crystal display control device. Thus, it is possible to realize a liquid crystal display device capable of displaying high-quality images without deterioration of the liquid crystal.

Preferably, the liquid crystal drive voltage generation circuit, the display memory, the control circuit, the segment drive circuit, and the common electrode drive circuit are formed on one semiconductor chip. As a result, the number of components of the electronic device including the liquid crystal display device can be reduced, the mounting density can be increased, and the size of the electronic device can be reduced.

Further, the liquid crystal drive voltage generation circuit, the display memory, the control circuit, and the segment drive circuit are configured as a semiconductor integrated circuit on one semiconductor chip (first chip). On the other hand, the common electrode drive circuit is mounted on a semiconductor chip (second chip) separate from the semiconductor chip on which the liquid crystal drive voltage generation circuit is formed. The common electrode drive circuit is configured as a conductor integrated circuit, and is configured by an element having a higher withstand voltage than an element configuring the liquid crystal drive voltage generation circuit. This makes it possible to simplify the manufacturing process of each of the first and second chips, thus lowering the packaging density of portable electronic devices, but reducing the manufacturing costs of the first and second chips. Can be achieved.

Further, the portable electronic device of the present invention includes a liquid crystal display control device configured as described above, a signal generated by the segment driving circuit, and a signal generated by the common electrode driving circuit. A liquid crystal panel that performs display in a dot matrix system and a battery that supplies a power supply voltage of the liquid crystal display control device are provided. This makes it possible to realize a portable electronic device that has good display image quality, low power consumption, and can be driven for a long time by a battery. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a circuit diagram showing a first embodiment of the booster circuit according to the present invention.

FIG. 2 is a waveform diagram showing a waveform example of a clock signal for operating the booster circuit of the embodiment.

FIG. 3 is an operation explanatory diagram for explaining the operation of the booster circuit according to the embodiment.

FIG. 4 is a circuit diagram showing a specific example of the variable resistance circuit of the booster circuit according to the embodiment.

FIG. 5 is a circuit diagram showing a preferred embodiment when the present invention is applied to a liquid crystal drive voltage generation circuit.

FIG. 6 is a circuit diagram showing another embodiment in which the present invention is applied to a liquid crystal drive voltage generation circuit.

FIG. 7 is a waveform diagram showing a waveform example of the segment applied voltage VSEG and the common applied voltage VC0M of the liquid crystal panel. '

FIG. 8 is a block diagram showing a configuration example of a liquid crystal display system including a liquid crystal control driver as a liquid crystal display control device incorporating a power supply circuit including a booster circuit according to the present invention and a liquid crystal panel driven by the driver. It is.

FIG. 9 shows an entire portable telephone equipped with a liquid crystal control driver to which the present invention is applied. It is a block diagram which shows a body structure.

FIG. 10 is a circuit diagram showing a specific example of a voltage inversion circuit that generates a negative voltage applied to the common electrode.

FIG. 11 is a circuit diagram showing a configuration example of a conventional liquid crystal drive voltage generation circuit.

FIG. 12 is a circuit diagram showing another configuration example of the conventional liquid crystal drive voltage generation circuit. FIG. 13 is a waveform diagram showing how the boosted voltage changes in the liquid crystal drive voltage generation circuit of FIG.

FIG. 14 is a waveform chart showing how the boosted voltage changes in the liquid crystal drive voltage generation circuit of FIG.

FIG. 15 is a waveform chart showing how the boosted voltage changes in the liquid crystal drive voltage generation circuit of the example. BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows a first embodiment of a step-up power supply circuit according to the present invention.

In FIG. 1, reference numeral 10 denotes a reference voltage generation circuit including a differential amplifier AMP, and reference numeral 20 denotes a charge pump circuit. In this embodiment, the voltage obtained by dividing the boosted output V out of the charge pump 20 by the variable resistor circuit 30 is fed back to the inverting input terminal of the differential amplifier AMP of the reference voltage generating circuit 10. I have.

The charge pump 20 has switches SW1 to SW4 that are turned on and off by the clock signal φ1 and a clock signal <ί) 2 formed so that the high-level period does not overlap with the clock signal φ1. (See Fig. 2) Switches SW5 to SW7 that are turned on and off by switches SW5 to SW7, step-up capacitors C1 and C2 that are connected in series by switches SW5 and SW6, and output capacitor C connected to output terminal OUT. It consists of three.

The low-potential side terminal C 1 _ of the boosting capacitor C 1 is connectable to the ground point or the first reference potential terminal T 1 via the switch SW 4 or SW 7, and is a boosting capacitor. The terminal C 1 + on the high potential side of 1 is connectable to the second reference potential terminal T 2 via the switch SW3. In addition, the terminal C 2— on the low potential side of the boosting capacitor C 2 is The terminal C 2 + on the high potential side of the step-up capacitor C 2 can be connected to the second reference potential terminal T 2 via the switch SW 1 while being connected to the ground point via the switch SW 2.

Further, the output terminal OUT and the terminal C 2 + on the high potential side of the boosting capacitor C 2 can be connected via the switch SW 5, and the terminal C 2 — The connection between the capacitor C 1 and the terminal C 1 + on the high potential side of the step-up capacitor C 1 can be connected via a switch SW 6. The reference voltage Va from the reference voltage generation circuit 10 is applied to the first reference potential terminal T1, and the operating power supply voltage VDD of the reference voltage generation circuit 10 is applied to the second reference potential terminal T2. I have.

The charge pump 20 configured as described above operates while the switch SW1 to SW4 is turned on (at this time, SW5 to SW7 are turned off) as shown in FIG. Then, the boost capacitors C 1 and C 2 are charged to the power supply voltage VDD. Next, when the switches SW1 to SW4 are turned off, the switches SW5 to SW7 are turned on instead, and as shown in FIG. The terminal C 1 on the reference end side, that is, the low potential side of the capacitor C 1 is connected to the first reference potential terminal T 1 via the switch SW7. As a result, the voltage of the output terminal OUT is boosted to (Va + 2VDD). By repeating the charging operation and the boosting operation, the electric charge charged in the boosting capacitor C2 is transferred to the smoothing capacitor C3 connected to the output terminal OUT, and the boosted voltage Vout of (Va + 2VDD) is obtained. Is output.

Further, the booster circuit of the embodiment of FIG. 1 is configured such that the voltage Vf obtained by dividing the boosted voltage Vout by the variable resistor circuit 30 is fed back to the inverting input terminal of the differential amplifier AMP of the reference voltage generating circuit 10. The reference voltage Vref is applied to the non-inverting input terminal of the differential amplifier AMP. Therefore, by adjusting the resistance value of the variable resistor circuit 30 and changing the voltage Vf to be fed back to the inverting input terminal of the differential amplifier AMP of the reference voltage generation circuit 10, the output voltage Vf of the reference voltage generation circuit 10 is changed. By changing a, the output voltage itself of the liquid crystal drive voltage generation circuit can be arbitrarily adjusted. The reference voltage Vref is, for example, Supplied from a reference voltage generation circuit such as a low-gap reference circuit with low temperature dependency and low power supply voltage dependency.

FIG. 4 shows a specific example of the variable resistance circuit 30. In this embodiment, 24 unit resistors R 1 to R 24 each having a resistance value of r are connected in series between the output terminal OUT of the booster circuit and the ground point, and a connection node n 1 of R 16 and R 17 is connected. Switch SW1 1 to switch node n2 between R18 and R19, connection node n3 between R20 and R21, connection node n4 between R21 and R22, and connection node n5 between R22 and R23. One terminal of SW15 is connected, and the other terminals of switches SW11 to SW15 are connected to a common feedback voltage terminal Tfb.

Each of the switches SW11 to SW15 is configured so that one of the switches is turned on in accordance with the set value of the register REG. Therefore, when the switch SWl1 is turned on, the output voltage Vout is divided into three and the voltage of Vout / 3, and when any of SW12, SW13, SW14 and SW15 is turned on, the output voltage becomes The voltage Vout / 4, Vout / 6, Vout / 8, Vout / 12, which is obtained by dividing Vout into four, six, eight, and twelve, is transmitted to the terminal T fb, which generates the reference voltage as the feedback voltage V f Supplied to the inverting input terminal of the differential amplifier AMP of the circuit 10. Then, the output voltage Va of the differential amplifier AMP changes so that the potential of the inverting input terminal matches the reference voltage Vref of the non-inverting input terminal. As a result, the reference voltage Va generated by the reference voltage generation circuit 10 is changed according to the feedback voltage Vf, and the boosted voltage Vout (= Va + 2 VDD) itself is also changed.

As described above, in the step-up power supply circuit of the embodiment of FIG. 1, since the output of the charge pump 20 is used as the step-up voltage as it is, the loss of current is small, Is fed back to the differential amplifier AMP of the 1 ° reference voltage generation circuit that generates the boosted reference voltage.When the output Vout of the charge pump 20 drops, the differential amplifier AMP detects this and outputs the output V Works to raise a. Therefore, when the step-up power supply circuit of this embodiment is used as a liquid crystal drive voltage generation circuit in a liquid crystal display device, As shown in FIG. 15, the output Vout of the loop 20 hardly changes immediately after the start of display on the liquid crystal panel, and a highly accurate voltage can be generated and maintained. In this embodiment, since the differential amplifier AMP constituting the reference voltage generating circuit 10 operates at the external power supply voltage VDD, the differential amplifier AMP can be formed by low-withstand-voltage elements, and the circuit occupation area is reduced. can do.

5 and 6 show a preferred embodiment in which the present invention is applied to a liquid crystal drive voltage generation circuit. As is well known, in a display device using a liquid crystal panel, it is necessary to form a voltage applied to a segment electrode of the liquid crystal panel and a voltage applied to a common electrode, respectively. The voltage VC0M to be applied has an amplitude several times the amplitude of the voltage VSEG applied to the segment electrodes as shown in FIG. The liquid crystal drive voltage generation circuits shown in FIGS. 5 and 6 are examples of a circuit that generates a voltage applied to the segment electrode and a voltage applied to the common electrode. The circuit is suitable for a panel with a small load on the common electrode of the liquid crystal panel, and the liquid crystal drive voltage generation circuit in Fig. 6 is a circuit suitable for a panel with a large load on the common electrode of the liquid crystal panel.

Hereinafter, the configuration of each of the liquid crystal drive voltage generation circuit of FIG. 5 and the liquid crystal drive voltage generation circuit of FIG. 6 will be described. Note that both the liquid crystal drive voltage generation circuit in FIG. 5 and the liquid crystal drive voltage generation circuit in FIG. 6 use the booster circuit shown in FIG. 1 as a circuit for generating the voltage VSEG applied to the segment electrodes. A booster circuit 40 that generates the common applied voltage VC0M based on the voltage VSEG generated by the booster circuit for the segment applied voltage is provided, and the difference between the two is that a booster circuit 40 that generates the common applied voltage VC0M is provided in the subsequent stage. It is in.

Specifically, the booster circuit 40 at the subsequent stage in the liquid crystal drive voltage generator circuit of FIG. 5 is a charge pump circuit 20 omitting the reference voltage generator circuit 10 at the previous booster circuit for generating the segment applied voltage VSEG. 'It is the only circuit. On the other hand, the booster circuit 40 in the subsequent stage in the liquid crystal drive voltage generator circuit of FIG. 6 includes the reference voltage generator circuit 10 ′ and the charge pump circuit 20 ′ in the same manner as the booster circuit in the preceding stage that generates the segment applied voltage VSEG. , And the output voltage of the charge pump 20 'is variable The circuit is configured to feed-back to the reference voltage generation circuit 10 'via the circuit 30'.

Thereby, the booster circuit 40 at the subsequent stage in the liquid crystal drive voltage generating circuit of FIG. 5 receives the voltage VSEG generated by the booster circuit at the preceding stage and generates a voltage of three times, that is, 3 VSEG. On the other hand, the subsequent booster circuit 40 'in the liquid crystal drive voltage generation circuit of FIG. 6 generates a voltage of 2VSEG + Va' based on the voltage VSEG generated by the previous booster circuit and the power supply voltage VDD.

Here, the voltage of Va ′ is the output voltage of the reference voltage generating circuit 10 ′, and the voltage Va, can be adjusted according to the feedback voltage Vf, of the variable resistor circuit 30 ′. Also, the feedback voltage V f ′ can be changed by changing the set value of the register REG provided in the variable resistor circuit 30 configured in the same manner as in FIG. Further, in the booster circuits 40 and 40 in the subsequent stage, by changing the number of capacitors connected in series, the voltages m ′ VSEG and (m · VSEG + V a ′) obtained by raising the reference voltage to an arbitrary integral multiple are obtained. ) Can be generated respectively. Also in these embodiments, since the differential amplifiers constituting the reference voltage generating circuits 10 and 10 ′ of the booster circuits 40 and 40 operate at the external power supply voltage VDD, they must be formed of low withstand voltage elements. Thus, the area occupied by the circuit can be reduced.

By the way, as apparent from FIG. 7, in order to generate a signal to be applied to the common electrode, the boosted voltage V COM (for example, 20 V) and the polarity are centered around the liquid crystal center potential VMI (for example, 3 V). Requires the opposite negative voltage — VC0M (eg, 14 V). In this embodiment, a negative voltage VC0M is generated from the boosted voltage VC0M by using a voltage inverting circuit as shown in FIG. 10A shows a general voltage inversion circuit, and FIG. 10B shows a voltage inversion circuit with a reference voltage correction circuit.

The voltage inversion circuit shown in Fig. 10 (A) has a voltage terminal Ta to which the positive boosted voltage VC0M generated by the liquid crystal drive voltage generation circuit shown in Fig. 5 or Fig. 6 is applied, and a liquid crystal center potential VMI. A voltage terminal Tb, a voltage inverting capacitor C21, and switches connected between one terminal of the capacitor C21 and the voltage terminal Ta and the voltage terminal Tb. Switches SW21 and SW22, switches SW23 and SW24 respectively connected between the other terminal of the voltage inverting capacitor C21 and the output terminal Tc between the voltage terminal Tb and the output terminal Tc. And a smoothing capacitor C22 for negative voltage connected between the grounding point and the grounding point.

The voltage inversion circuit of this embodiment turns on the switches SW21 and SW23 and turns off the switches SW22 and SW24 by the clocks (see φ1 and φ2 in FIG. 2) in which the high-level periods do not overlap each other. After charging the voltage inverting capacitor C 21 with a voltage corresponding to the potential difference between the positive step-up voltage VC0M and the liquid crystal center potential VMI, the switches SW21 and SW23 are turned off, and the switches SW22 and SW24 are turned on. An operation is performed to charge the smoothing capacitor C22 with a negative voltage VC0M having a polarity opposite to that of the boosted voltage VC0M around the center potential VMI.

By the way, the voltage inverting circuit shown in Fig. 10 (Α) uses the boosted voltage VC0M and the liquid crystal center potential VMI to generate a negative voltage. The voltage drop occurs due to the current consumption in the liquid crystal panel to which the voltage is supplied, and the voltage level of the negative voltage is expressed as [(positive voltage)-(reference voltage)] = [(reference voltage)-(negative voltage)]. We need to be aware that in some cases we may not be able to fully satisfy them. When driving a liquid crystal panel, the positive voltage V COM and the negative voltage-V COM need to be symmetrical with respect to the liquid crystal center potential V Ml, and when the negative voltage drops, the display becomes thin, The image quality deteriorates and the liquid crystal deteriorates. For this reason, the voltage inversion circuit shown in Fig. 10 (A) may not be suitable for use in color LCD panels that require highly accurate symmetry of the positive and negative voltages or large LCD panels with large output loads. The voltage inverting circuit in Fig. 10 (B) is an improvement of the circuit in Fig. 10 (A). The voltage inverting circuit in Fig. 10 (A) has a reference for correcting the liquid crystal center potential VMI as a reference voltage. A voltage correction circuit is added. Specifically, the liquid crystal center potential VMI applied to the voltage terminal Tb is input to its non-inverting input terminal, and the inverting input terminal has a resistor connected in series between the voltage terminal Ta and the output terminal Tc. A differential amplifier AMP20 to which the voltage divided by R31 and R32 is input is provided. The operation of the switches SW21 to SW24 is the same as that of the circuit of FIG. In the voltage inverting circuit of Fig. 10 (B), a voltage is output such that the intermediate voltage of the output that is fed back to the inverting input terminal becomes equal to the liquid crystal center potential VMI by the operation of the differential amplifier AMP20. You. As a result, the reference voltage input terminal of the voltage inverting circuit is supplied with a direction for correcting the negative voltage drop, that is, a voltage lower than the center potential VMI. As a result, in this voltage inversion circuit, even when the output load increases, the output voltage can be kept constant because the reference voltage correction circuit lowers the reference voltage of the voltage inversion circuit in a direction to cancel the voltage drop. Therefore, the voltage inverting circuit of FIG. 10 (B) can supply a more accurate negative voltage than the voltage inverting circuit of FIG. 10 (A), improving the display quality of the liquid crystal panel and improving the liquid crystal display. There is an advantage that deterioration can be prevented.

FIG. 8 is a block diagram showing a configuration of a liquid crystal display device including a liquid crystal control driver as a liquid crystal display control device incorporating the power supply circuit of the embodiment as a liquid crystal drive voltage generation power supply circuit and a liquid crystal panel driven by the driver. FIG.

In FIG. 8, 100 is a liquid crystal control driver, and 200 is a liquid crystal panel driven by the liquid crystal control driver 100. The LCD control driver 100 has a segment driver 110 that drives the segment electrodes of the liquid crystal panel 200, and a common driver 120 that drives the common electrodes of the liquid crystal panel 200. The liquid crystal drive voltage generating circuit 130 of the above-described embodiment for generating the required drive voltage, a display RAM 140 for storing image data to be displayed on the liquid crystal panel 200 in a bitmap manner, and an external It has a controller 150 that controls the entire inside of the chip based on commands from a microprocessor (hereinafter also referred to as a microcomputer (CPU)), etc. These circuits are mounted on a single semiconductor chip such as single crystal silicon. Is configured.

Although not shown, the LCD control driver 100 has an address counter for generating an address for the display RAM 140, and data read from the display RAM 140 and an external microcomputer. Logical operation means for performing a logical operation for watermark display and superimposed display based on the supplied new display data, operation timing for the segment driver 10 and the common driver 120 T / JP01 / 11233

15 A timing generation circuit for generating signals is provided.

In the liquid crystal drive voltage generation circuit of the embodiment, the register R EG for setting the feedback voltage V f provided in the variable resistance circuit 30 is configured to be rewritable by the control unit 150. Then, the control unit 150 sets the register REG based on a command supplied from an external microcomputer or the like. In general, the control section 150 is provided with a control register for controlling the operation state of the entire chip such as the operation mode of the liquid crystal control panel 100 in the liquid crystal panel control panel 100. Therefore, the register REG for setting the feedback voltage Vf may be provided as a part of the control register.

The control method of the control unit 150 includes a method of receiving a command code from an external microcomputer and decoding the command to generate a control signal, and a method of executing a plurality of command codes and a command to be executed in the control unit in advance. An instruction register (referred to as an index register) is provided, and the microcomputer can take any control method such as a method of generating a control signal by specifying a command to be executed by writing to the index register. .

With the control of the control unit 150 configured as described above, the liquid crystal control driver 100 is configured to perform display on the above-described liquid crystal panel 200 based on command data from an external microcomputer. In addition, a drawing process for sequentially writing display data to the display RAM I 40 is performed, and a reading process for sequentially reading display data from the display RAM 140 is performed, and the segment of the liquid crystal panel 200 is performed. The signals to be applied to the electrodes and the signals to be applied to the common electrode are output by Dryno 110 and 120. FIG. 9 is a block diagram showing an overall configuration of a mobile phone as an application example of the liquid crystal display device including the liquid crystal control driver 100 and the liquid crystal panel 200 of FIG. The mobile phone of this embodiment has a liquid crystal panel 200 as a display unit, a transmitting / receiving antenna 321, a voice output speaker 32, a voice input microphone 32, and the present invention. LCD control driver 100, speaker 3 22 and audio interface 3 30 for input / output of microphone and microphone signals, and antenna 3 2 1 High-frequency interface 340 for input / output of signals between DSPs, DSP (Digital Signal Processor) 351 for signal processing related to audio signals and transmission / reception signals, ASIC (Application Specific Integrated) providing custom functions (user logic) Circuits) 352, a system controller 353 composed of a microprocessor or microcomputer for controlling the entire apparatus including display control, and a memory 360 for storing data and programs. The DSP 351, the ASIC 352, and the microcomputer 353 as a system control device constitute a so-called base band section 350.

Although not particularly limited, the liquid crystal panel 200 is a dot matrix type panel in which a large number of display pixels are arranged in a matrix. In the case of a color LCD panel, one pixel consists of three dots: red, blue, and green. The memory 360 is composed of, for example, flash memory that can be erased in batches in predetermined blocks, and stores a control program and control data of the entire mobile phone system including display control, and a two-dimensional memory. It also has a function as a CGROM (Character Generator Read Only Memory), which is a pattern memory that stores display data such as character fonts and other display patterns.

Further, in the system of this embodiment, the liquid crystal control driver 100 is configured as a liquid crystal control driver including the segment driver 110 and the common driver 120, but drives the common electrode of the liquid crystal panel. The common driver 120 is formed on a separate semiconductor chip, and the driving voltage is supplied to the common driver chip from the liquid crystal drive voltage generation circuit 140 in the liquid crystal control driver 100. Is also good.

Usually, the voltage of the common electrode signal is higher than that of the segment electrode signal, so that the common driver is composed of elements having a relatively high withstand voltage. Therefore, if a segment driver and a common driver are formed on the same chip, a process for forming a high withstand voltage element and a process for forming a low withstand voltage element become necessary, which complicates the process. The use of a chip eliminates the need for a process for forming a high withstand voltage element constituting a common driver. Moreover, the liquid crystal drive voltage generation of the above-described embodiment is performed. If a circuit is applied, the liquid crystal drive voltage generation circuit itself can be configured without using a high voltage element, so that a liquid crystal control driver with a built-in liquid crystal drive voltage generation circuit can be manufactured by a simple process. it can.

Although the invention made by the inventor has been specifically described based on the embodiments, the present invention is not limited to the above-described embodiment, and it can be said that various modifications can be made without departing from the gist of the invention. Not even. For example, in the booster circuit of the above embodiment, boosting is performed by charging the two capacitors CI and C2 to the power supply voltage VDD and then switching the switches to connect them in series, but in series. The number of connected capacitors is not limited to two, but may be three or more.

In the above description, the invention made by the present inventor has been mainly described with respect to the liquid crystal control driver for driving the liquid crystal panel of the mobile phone, which is the field of application, but the present invention is not limited to this. For example, the present invention can be applied to various portable electronic devices having a liquid crystal panel such as a pager, a pager, and a PDA (Personal Digital Assistants). Industrial applicability

According to the present invention, it is possible to realize a power supply circuit capable of generating a boosted voltage with a small current loss and high accuracy, and thereby a liquid crystal driving voltage generation for generating a voltage for driving a liquid crystal panel. When applied to a circuit, it is possible to provide a liquid crystal display device and a portable electronic device that can display a high-quality image without deterioration of the liquid crystal, can consume less power, and can be driven by a battery for a long time.

Claims

The scope of the claims

1. A reference voltage generating circuit having a differential amplifier that operates with an external power supply voltage, a plurality of capacitors, a switch for charging the capacitors, and a switch for connecting the capacitors in series to add a charged voltage. A booster circuit having a switch; feedback means for feeding back a voltage corresponding to an output voltage of the booster circuit to an input terminal of the differential amplifier; and a smoothing capacitor connected to an output terminal of the booster circuit. The circuit performs charging to the capacitor based on an operation power supply voltage of the differential amplifier during a charging operation, and performs an operation in which the plurality of capacitors are connected in series to add a charging voltage. A step-up power supply circuit configured to boost a voltage on a reference end side of the capacitor based on a reference voltage output from the differential amplifier.

2. The feedback means includes: a resistance dividing means including a plurality of resistance elements connected in series between an output terminal of the booster circuit and a power supply voltage terminal; and a potential at a connection node of any one of these resistance elements. Selecting means for selecting the voltage and transmitting the selected voltage to the input terminal of the differential amplifier, wherein the output voltage of the booster circuit can be adjusted by switching the feedback voltage. The boost type power supply circuit described.

3. The step-up power supply circuit according to claim 2, further comprising a register for designating a voltage fed back to an input terminal of the differential amplifier by the selection unit.

4. A reference voltage generating circuit having a differential amplifier that operates with an external power supply voltage, a plurality of capacitors, a switch for charging each of the capacitors, and a capacitor for connecting the capacitors in series to add a charged voltage. A booster circuit having a switch, and a voltage corresponding to an output voltage of the booster circuit is fed back to an input terminal of the differential amplifier. A first step-up power supply circuit configured to generate a voltage applied to a segment electrode of a liquid crystal panel, the first step-up power supply circuit including a feed pack unit, and a smoothing capacitor connected to an output terminal of the step-up circuit;

A second step-up power supply circuit that generates a voltage applied to a common electrode of the liquid crystal panel based on a voltage generated by the first step-up power supply circuit. A booster circuit having a plurality of capacitors, a switch for charging each of the capacitors, and a switch for connecting the capacitors in series to add a charged voltage; and a switch connected to an output terminal of the booster circuit. A liquid crystal drive voltage generating circuit, comprising: a smoothing capacitor;

5. A reference voltage generating circuit having a differential amplifier operating on an external power supply voltage, a plurality of capacitors, a switch for charging each of the capacitors, and a capacitor for connecting the capacitors in series to add a charged voltage A liquid crystal comprising a booster circuit having a switch, feedback means for feeding back a voltage corresponding to an output voltage of the booster circuit to an input terminal of the differential amplifier, and a smoothing capacitor connected to an output terminal of the booster circuit A first step-up power supply circuit for generating a voltage applied to a panel segment electrode;

A second step-up power supply circuit that generates a voltage applied to a common electrode of the liquid crystal panel based on a voltage generated by the first step-up power supply circuit. A reference voltage generating circuit having a differential amplifier operating on an external power supply voltage, a plurality of capacitors and a switch for charging each of the capacitors, and adding the charged voltages by connecting the capacitors in series. Circuit, a resistor dividing means for dividing an output voltage of the booster circuit and feeding it back to an input terminal of the differential amplifier, and a smoothing capacitor connected to an output 'terminal of the booster circuit. A liquid crystal drive voltage generation circuit, comprising:

6. A first voltage input terminal to which the first voltage is applied, a second voltage input terminal to which the second voltage is applied, a capacitor, and a capacitor connected to one terminal of the capacitor. 1 A second terminal to which the other terminal of the capacitive element is connected; a voltage output terminal; a differential amplifier having the first voltage input terminal connected to its non-inverting input terminal; A first switch element connected between the first voltage input terminal and the first terminal; and a second switch connected between the first terminal and the output terminal of the differential amplifier. A switch element, a third switch element connected between the second terminal and the output terminal of the differential amplifier, and a fourth switch element connected between the second terminal and the output terminal. A switch element, and a resistance dividing circuit connected between the first input terminal and the output terminal,

The voltage divided by the resistance dividing circuit is applied to an inverting input terminal of the differential amplifier, and the first switch element and the fourth switch element are turned off in a state where the second switch element and the fourth switch element are turned off. After the third switch element is turned on and the capacitor element is charged with a charge corresponding to the difference voltage between the first voltage and the second voltage, the first switch element and the third switch are turned on. When the element is turned off and the second switch element and the fourth switch element are turned on, a voltage obtained by inverting the polarity of the first voltage with respect to the second voltage is output to the output terminal. A voltage inverting circuit characterized by being configured as described above.

7. A reference voltage generating circuit having a differential amplifier that operates on an external power supply voltage, a plurality of capacitors and a switch for charging the capacitors, and a switch for connecting the capacitors in series to add a charged voltage A booster circuit having a switch; a feed pack means for feeding a voltage corresponding to an output voltage of the booster circuit to an input terminal of the differential amplifier; and a smoothing capacitor connected to an output terminal of the booster circuit. A first step-up power supply circuit for generating a voltage applied to the segment electrodes of the liquid crystal panel;

A method for designing a liquid crystal driving voltage generating circuit comprising: a second boosting type power supply circuit for generating a voltage applied to a common electrode of the liquid crystal panel based on a voltage generated by the first boosting type power supply circuit And

When the load on the common electrode is small, the second booster type power supply circuit A booster circuit having a switch for charging the capacitor, a switch for charging the capacitor, and a switch for adding the charged voltage by connecting the capacitor in series; and a smoothing circuit connected to an output terminal of the booster circuit. With capacity,

When the load on the common electrode is large, the second boosting type power supply circuit includes a reference voltage generating circuit having a differential amplifier, a plurality of capacitors, a switch for charging each of the capacitors, and the capacitor. A booster circuit having a switch for adding a charged voltage connected in series; a resistor dividing means for dividing an output voltage of the booster circuit and feeding it back to an input terminal of the differential amplifier; A method for designing a liquid crystal drive voltage generating circuit, comprising: a smoothing capacitor connected to an output terminal.

8. The liquid crystal drive voltage generation circuit according to claim 4 or claim 5,

A display memory for storing data to be displayed on the liquid crystal panel;

A control circuit for controlling generation of data to be written to the display memory and reading of data from the display memory;

A segment drive circuit that generates a signal to be applied to a segment electrode of the liquid crystal panel based on data read from the display memory and a drive voltage generated by the liquid crystal drive voltage generation circuit;

A common electrode driving circuit that generates a signal to be applied to a common electrode of the liquid crystal panel based on the driving voltage generated by the liquid crystal driving voltage generating circuit and a predetermined timing signal;

A liquid crystal display control device comprising:

9. The liquid crystal drive voltage generation circuit, the display memory, the control circuit, the segment drive circuit, and the common electrode drive circuit are formed on one semiconductor chip. 9. The liquid crystal display control device according to claim 8, wherein:

10. The liquid crystal drive voltage generation circuit, the display memory, and the control circuit, The segment drive circuit is configured as a semiconductor integrated circuit on a first semiconductor chip, and the common electrode drive circuit is a second semiconductor separate from the semiconductor chip on which the liquid crystal drive voltage generation circuit is formed. 10. The liquid crystal device according to claim 9, wherein the liquid crystal device is configured as a semiconductor integrated circuit on a chip, and the common electrode drive circuit is configured by an element having a higher withstand voltage than an element configuring the liquid crystal drive voltage generation circuit. Display control device.

1 1. A reference voltage generating circuit having a differential amplifier that operates with an external power supply voltage, a plurality of capacitors and a switch for charging each of the capacitors, and a capacitor connected in series to add the charged voltages A booster circuit having the following switches: feedback means for feeding back a voltage corresponding to the output voltage of the booster circuit to an input terminal of the differential amplifier; and a smoothing capacitor connected to an output terminal of the booster circuit. A first step-up power supply circuit for generating a voltage applied to a segment electrode of the liquid crystal panel; and a voltage applied to a common electrode of the liquid crystal panel based on a voltage generated by the first step-up power supply circuit. And a second boost type power supply circuit for generating a plurality of capacitances, and a switch for charging each of the plurality of capacitances. A boosting circuit having a Sui' switch for adding the voltage charged by connecting an amount in series, the liquid crystal driving voltage generation circuit constituted by a connected smoothing capacitor to an output terminal of said booster circuit,

A display memory for storing data to be displayed on the liquid crystal panel; a control circuit for controlling generation of data to be written to the display memory and reading of data from the display memory; and a control circuit for reading data from the display memory. A segment drive circuit for generating a signal to be applied to the segment electrode of the liquid crystal panel based on the data obtained and the drive voltage generated by the liquid crystal drive voltage generation circuit; and a drive voltage generated by the liquid crystal drive voltage generation circuit. A liquid crystal display control device comprising: a common electrode driving circuit that generates a signal to be applied to the common electrode of the liquid crystal panel based on the predetermined timing signal and

A liquid crystal panel that performs display in a dot matrix system based on the signal generated by the segment drive circuit and the signal generated by the common electrode drive circuit Flannel,

A portable electronic device comprising: a battery that supplies a power supply voltage of the liquid crystal display control device.

12. The liquid crystal drive voltage generation circuit, the display memory, the control circuit, the segment drive circuit, and the common electrode drive circuit are formed on one semiconductor chip. The portable electronic device according to claim 11, wherein

13. The liquid crystal drive voltage generation circuit, the display memory, the control circuit, and the segment drive circuit are configured as a semiconductor integrated circuit on a first semiconductor chip, and the common electrode drive circuit is The liquid crystal driving voltage generation circuit is formed as a semiconductor integrated circuit on a second semiconductor chip separate from the semiconductor chip on which the liquid crystal driving voltage generation circuit is formed, and the common electrode driving circuit is smaller than an element forming the liquid crystal driving voltage generation circuit. 12. The portable electronic device according to claim 11, wherein the portable electronic device is configured by a device having a high withstand voltage.

14. A voltage inverting circuit for inverting the polarity of the voltage generated by the second boosting type power supply circuit and generating a voltage of the opposite polarity applied to the common electrode of the liquid crystal panel is further provided. 14. The portable electronic device according to claim 11, wherein the portable electronic device is a portable electronic device.

15. The voltage inverting circuit includes a first voltage input terminal to which a voltage generated by the second step-up power supply circuit is applied, a second voltage input terminal to which a reference voltage is applied, and a capacitor A first terminal to which one terminal of the capacitive element is connected; a second terminal to which the other terminal of the capacitive element is connected; a voltage output terminal; and a first voltage input terminal. A differential amplifier to which a non-inverting input terminal is connected; a first switch element connected between the first voltage input terminal and the first terminal; a first terminal and the differential A second switch element connected between an output terminal of the amplifier, a third switch element connected between the second terminal and an output terminal of the differential amplifier, and the second terminal A fourth switch element connected between the output terminal and A resistor dividing circuit connected between the first input terminal and the output terminal, wherein a voltage divided by the resistance dividing circuit is applied to an inverting input terminal of the differential amplifier; The first switch element and the third switch element are turned on in a state where the fourth switch element is turned off, and the difference voltage between the first voltage and the second voltage is applied to the capacitor element. After the electric charge corresponding to the above is charged, the first switch element and the third switch element are turned off and the second switch element and the fourth switch element are turned on. 15. The portable device according to claim 14, wherein a voltage obtained by inverting the polarity of the voltage of the first voltage input terminal around the reference voltage is output to the output terminal. Electronics.

16. A reference voltage generating circuit having a differential amplifier that operates with an external power supply voltage, a plurality of capacitors, a switch for charging the capacitors, and a capacitor connected in series to add the charged voltages A booster circuit having the following switches: feedback means for feeding back a voltage corresponding to an output voltage of the booster circuit to an input terminal of the differential amplifier; and a smoothing capacitor connected to an output terminal of the booster circuit. A first boosted power supply circuit for generating a voltage to be applied to a segment electrode of the liquid crystal panel; and a voltage applied to a common electrode of the liquid crystal panel based on a voltage generated by the first boosted power supply circuit. A second step-up power supply circuit that generates a voltage, wherein the second step-up power supply circuit has a reference voltage generation circuit that includes a good operating amplifier that operates with an external power supply voltage; A booster circuit having a plurality of capacitors, a switch for charging each of the capacitors, and a switch for connecting the capacitors in series to add a charged voltage; dividing the output voltage of the booster circuit into A liquid crystal drive voltage generation circuit configured by a resistance dividing unit that feeds back to an input terminal of the differential amplifier, and a smoothing capacitor connected to an output terminal of the booster circuit;

A display memory for storing data to be displayed on the liquid crystal panel; a control circuit for controlling generation of data to be written to the display memory and reading of data from the display memory; and a control circuit for reading data from the display memory. Segment of the liquid crystal panel based on the data thus obtained and the driving voltage generated by the liquid crystal driving voltage generating circuit. A segment drive circuit for generating a signal to be applied to the common electrode; and a common electrode for generating a signal to be applied to the common electrode of the liquid crystal panel based on the drive voltage generated by the liquid crystal drive voltage generation circuit and a predetermined timing signal. A liquid crystal display control device having a drive circuit;

A liquid crystal panel that performs display in a dot matrix system based on a signal generated by the segment driving circuit and a signal generated by the common electrode driving circuit;

17. The liquid crystal drive voltage generation circuit, the display memory, the control circuit, the segment drive circuit, and the common electrode drive circuit are formed on one semiconductor chip. 17. The portable electronic device according to claim 16, wherein:

18. The liquid crystal drive voltage generation circuit, the display memory, the control circuit, and the segment drive circuit are configured as a semiconductor integrated circuit on a first semiconductor chip, and the common electrode drive circuit is The liquid crystal driving voltage generation circuit is formed as a semiconductor integrated circuit on a second semiconductor chip separate from the semiconductor chip on which the liquid crystal driving voltage generation circuit is formed, and the common electrode driving circuit is smaller than an element forming the liquid crystal driving voltage generation circuit. 18. The portable electronic device according to claim 17, wherein the portable electronic device is configured with a high withstand voltage element.

19. A voltage inverting circuit for inverting the polarity of the voltage generated by the second step-up power supply circuit and generating a voltage of the opposite polarity applied to the common electrode of the liquid crystal panel is further provided. 19. The portable electronic device according to claim 16, wherein the portable electronic device is a portable electronic device.

20. The voltage inverting circuit includes a first voltage input terminal to which a voltage generated by the second step-up power supply circuit is applied, a second voltage input terminal to which a reference voltage is applied, and a capacitor A first terminal to which one terminal of the capacitive element is connected; A second terminal to which the other terminal of the element is connected; a voltage output terminal; a differential amplifier having the non-inverting input terminal connected to the first voltage input terminal; and a first voltage input terminal. A first switch element connected between the first terminal, a second switch element connected between the first terminal and an output terminal of the differential amplifier, A third switch element connected between the second terminal and the output terminal of the differential amplifier; a fourth switch element connected between the second terminal and the output terminal; A resistor divided circuit connected between the input terminal of the differential amplifier and the output terminal of the differential amplifier; a voltage divided by the resistor divided circuit is applied to an inverting input terminal of the differential amplifier; And the first switch element and the fourth switch element are turned off. After the third switch element is turned on and the capacitor element is charged with a charge corresponding to the difference voltage between the first voltage and the second voltage, the first switch element and the third switch element Is turned off and the second switch element and the fourth switch element are turned on, so that a voltage obtained by inverting the polarity of the voltage of the first voltage input terminal around the reference voltage is output to the output terminal. 10. The portable electronic device according to claim 19, wherein the portable electronic device is configured to output.