JP2013009176A - Driving driver, driving amplifier and information apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving driver, a driving amplifier and an information apparatus that generate driving signals of differential signals with a minimum number of switching elements and drive a capacitive load according to the driving signals.SOLUTION: A piezoelectric speaker driving amplifier 14 consumes less energy transferred from a capacitor 41 to a piezoelectric speaker 15 through a resistance and the like and reuses it as energy for driving the piezoelectric speaker 15. Specifically, a gate driver circuit 23 switches conduction states of PMOS transistors 45-49 of a switching drive circuit 24 according to each operational phase of the first phase to the fourth phase. The piezoelectric speaker driving amplifier 14 can thus generate driving signals of differential signals with a minimum number of switching elements and drive the piezoelectric speaker 15 according to the driving signals.

Description

  The present invention relates to a drive driver, a drive amplifier, and an information device, and more particularly to a drive driver, a drive amplifier, and an information device that can drive a capacitive load such as a piezoelectric element.

  In recent years, miniaturized information devices such as portable music players, mobile phones, and portable DVD players have been rapidly reduced in size and power consumption. From such a background, there are an increasing number of piezoelectric speakers that can be manufactured in a thin shape with a much better efficiency than conventional dynamic speakers and the like in speakers mounted on small information devices. These small information devices are equipped with a driving amplifier for driving a capacitive load such as a piezoelectric speaker.

  For example, in the digital amplifier of Patent Document 1, a PWM signal obtained by PWM-modulating an audio signal as an input signal and a power supply voltage are first input to a waveform conversion circuit, and the PWM signal is converted into an analog high voltage waveform by the waveform conversion circuit. The The analog high voltage waveform is input to a piezoelectric speaker as a load, that is, energy is charged in the piezoelectric speaker, and the piezoelectric speaker is driven. The energy charged in the piezoelectric speaker is consumed by a resistor connected in parallel with the piezoelectric speaker.

  As described above, in a general driving amplifier, energy is charged to a piezoelectric element from a driving power source or a DC-DC converter that boosts a power source voltage, and energy charged in a capacitive load is consumed by a resistor. The capacitive load such as a piezoelectric speaker is driven by repeatedly discharging to the ground.

JP 2006-60549 A

  By the way, the driving amplifier handles a relatively large current when driving a capacitive load such as a piezoelectric speaker. Therefore, a switching element that constitutes the circuit of the driving amplifier must have a high withstand voltage performance that can withstand the current. For this reason, it is preferable that the number of switching elements constituting the drive amplifier circuit is as small as possible.

  Therefore, in view of the above-described problems, the present invention generates a drive signal of a differential signal with as few switching elements as possible, and can drive a capacitive load with the drive signal, and a drive amplifier And to provide information equipment.

The drive driver, the drive amplifier, and the information device according to the present invention are configured as follows in order to achieve the above object.
The first driver for driving according to the present invention includes a first charge / discharge element charged with energy for driving a capacitive load, and energy charged in the first charge / discharge element or the capacitive load. A second charge / discharge element that is temporarily charged, a state in which the energy charged in the first charge / discharge element is charged to the capacitive load via the second charge / discharge element, and the capacitive The charging direction switching switching element for alternately switching the state in which the energy charged in the load is charged in the first charging / discharging element via the second charging / discharging element, and the charging direction switching switching element A state in which the energy charged in the first charge / discharge element is charged in the capacitive load, and a state in which the energy charged in the capacitive load is charged in the first charge / discharge element. When switching between each other, the state in which the energy charged in the first charge / discharge element or the capacitive load is charged from the positive terminal side of the capacitive load, and the first charge / discharge element or the capacitive load The polarity switching switching element for alternately switching the state in which the charged energy is charged from the negative electrode terminal side of the capacitive load, and the conduction state of the charging direction switching switching element and the polarity switching switching element are on. A control circuit that controls to switch to either one of the state and the off state, and the control circuit is a voltage of one of the drive signals that is a differential signal for driving the capacitive load A state in which the value is changed in accordance with the energy charged in the capacitive load, and the voltage value of the other signal is energy charged in the capacitive load And a state changing in such a manner are alternately repeated, and controlling the switching of the conducting state of the charging direction switching switching element and the polarity signal switching the switching element in accordance with the.

  According to the first driving driver, the control circuit switches each switching element in accordance with each operation phase of the driving driver from the first phase to the fourth phase. As a result, the energy transferred from the first charge / discharge element to the capacitive load via the second charge / discharge element is again consumed via the second charge / discharge element again without consuming as much as possible by resistance. By charging the discharge element, it is reused as energy for driving the capacitive load. At that time, the control circuit switches the conduction state of the polarity switching switching element. As a result, the drive driver can generate a differential signal drive signal with as few switching elements as possible and drive the capacitive load with the drive signal. In addition, the positive electrode terminal and the negative electrode terminal of the capacitive load do not indicate a voltage applied to the element like an electrolytic capacitor having a limitation on an applied voltage, but indicate a signal polarity.

  A second driver for driving according to the present invention includes an energy replenishing element for replenishing energy to the first charge / discharge element from a driving power supply that outputs a power supply voltage, and the control circuit includes the driving power supply. The conduction state of the energy replenishing element is controlled so that energy is replenished to the first charge / discharge element.

  According to the second driver for driving described above, the control circuit repeats the control circuit before the first phase first and when each operation phase from the first phase to the fourth phase is repeated a certain number of times in order. Before entering the phase, the operation phase of the driving driver is determined as the energy replenishment phase. Thus, the control circuit can further control the conduction state of the energy supplementing element in accordance with the energy supplementing phase.

  The third driver for driving according to the present invention compares the voltage value of one of the input signals which are differential signals with the voltage value of the other signal, and compares the voltage levels according to the comparison result. A first comparison circuit that outputs a result signal is compared with the voltage value of one of the drive signals and the voltage value of the other signal, and a comparison result signal having a voltage level corresponding to the comparison result is obtained. A second comparison circuit for outputting, and the control circuit includes at least the voltage level of the comparison result signal output from the first comparison circuit and the comparison result signal output from the second comparison circuit. Based on the combination of the voltage level and the voltage level of the modulation signal obtained by modulating the input signal, the voltage value of one of the drive signals is increased according to the energy charged in the capacitive load. , The other signal A first phase in which the value is set to an analog ground voltage level, which is a predetermined voltage level, and the voltage value of one of the drive signals is decreased according to the energy charged in the capacitive load, and the other A second phase in which the voltage value of the signal is set to the analog ground voltage level, and the voltage value of the other signal of the drive signal is increased in accordance with the energy charged in the capacitive load, And the voltage value of the other signal of the drive signal is decreased according to the energy charged in the capacitive load, and the voltage value of the other signal is reduced to the analog ground voltage level. The charging direction switching switching element and the polarity switching so that each operation phase with the fourth phase to be brought to the ground voltage level is repeated. It controls the switching of the conducting state of the switching element.

  According to the third driving driver, the control circuit determines the operation phase of the driving driver based on at least the combination of the comparison result by the first comparison circuit and the comparison result by the second comparison circuit. The operation phase is determined as any one of the first phase to the fourth phase. Thereby, the control circuit can control switching of the conduction state of the charging direction switching switching element and the polarity signal switching switching element in accordance with the operation phase of the driving driver.

  According to a fourth driver for driving according to the present invention, the control circuit starts again before the first phase and after each operation phase from the first phase to the fourth phase is repeated a predetermined number of times. Before entering the first phase, the conduction state of the energy replenishing element is controlled so that an energy replenishing phase for replenishing energy from the driving power supply to the first charging / discharging element is performed.

According to the fourth driving driver, the control circuit charges the energy from the driving power supply to the first charging / discharging element by controlling the operation of the energy supplementing element and the switching of the conduction state of the switching element. It becomes possible to make it.
The fifth driving driver according to the present invention monitors whether or not the current flowing through the second charging / discharging element starts to decrease until it reaches 0 (A), and the monitoring result And a current monitoring circuit that outputs a current monitoring result signal having a voltage level according to the control circuit, wherein the control circuit is output from the current monitoring circuit at least in each operation phase from the first phase to the fourth phase. On the basis of the combination of the voltage level of the current monitoring result signal and the voltage level of the modulation signal obtained by modulating the input signal, the energy charged in the first charge / discharge element or the capacitive load is changed to the second A charge phase for charging the charge / discharge element, a transfer phase for transferring the energy charged in the second charge / discharge element to the capacitive load or the first charge / discharge element, Energy charged in the first charge / discharge element, the second charge / discharge element, or the capacitive load between the first charge / discharge element, the second charge / discharge element, and the capacitive load The switching of the conduction state of the charging direction switching element and the polarity switching element is controlled so that each operation phase with the standby phase in which charging and transfer are not performed is repeated.

  According to the fifth driver for driving described above, the control circuit performs the operation phase of the driver for driving in more detail based on the combination of the signal modulated by the modulation circuit and the monitoring result signal by the current monitoring circuit. The operation phase is determined as any one of a charging phase, a transfer phase, and a standby phase. Thereby, the control circuit can control the switching of the conduction state of the charging direction switching switching element and the polarity signal switching switching element.

  In a sixth driving driver according to the present invention, the control circuit includes a charging phase for charging the first charge / discharge element with energy from the driving power source in the energy replenishment phase, and the driving power source. The switching of the conduction state of the energy replenishing element is controlled so as to be in each operation phase with a standby phase in which the first charge / discharge element is not charged with energy.

According to the sixth driving driver, the control circuit determines the energy replenishment phase in more detail as the operation phase of the charging phase or the standby phase. As a result, the control circuit can control switching of the conduction state of the energy supplementing element.
In a seventh driving driver according to the present invention, the first charging / discharging element is connected between the driving power source and the ground, and the second charging / discharging element is the first charging / discharging element. Connected to the positive terminal of the capacitive load, and the switching element for switching the charge direction includes a terminal on the capacitive load side of the second charge / discharge element and the first charge / discharge At least the second charge / discharge element between the negative electrode terminal of the element or between the positive electrode terminal of the first charge / discharge element and the terminal on the driving power supply side of the second charge / discharge element. Between the capacitive load side terminal of the first charge / discharge element and the negative charge terminal of the first charge / discharge element, and the polarity switching switching element is connected to the capacitive load side terminal of the second charge / discharge element, Connected between the positive terminal of the capacitive load and the capacitive load. A positive-side switching element connected between a pole terminal and a terminal on the drive power supply side of the second charge / discharge element, a capacitive load-side terminal of the second charge / discharge element, and the capacitance A negative-side switching element connected between the negative terminal of the capacitive load and connected between the positive terminal of the capacitive load and the terminal on the driving power source side of the second charge / discharge element; The control circuit is configured to switch the charge direction switching during the charge phase of the first phase, the transfer phase of the second phase, the charge phase of the third phase, and the transfer phase of the fourth phase. The device is controlled so that a closed circuit is formed by turning on the conduction state of the element. During the transfer phase of the first phase and the charge phase of the second phase, the positive side When the conduction state of the switching element is turned on, control is performed so that a closed circuit is formed. In the transfer phase of the third phase and the charge phase of the fourth phase, the conduction of the negative side switching element By controlling the state to be a closed circuit by turning on the state, the standby phase of the first phase, the standby phase of the second phase, the standby phase of the third phase, and the fourth phase In the standby phase, control is performed so that a closed circuit is not formed by turning off the conduction state of the charging direction switching element, the positive electrode side switching element, and the negative electrode side switching element.

  According to the seventh driving driver, the control circuit controls switching of the conduction state of the charging direction switching switching element, the positive side switching element, and the negative side switching element in accordance with the operation phase of the driving driver. To do. Then, the driving driver exchanges energy between the first charging / discharging element and the second charging / discharging element by a closed circuit formed with the conduction state of the charging direction switching switching element turned on. . Further, the driver for driving is connected from the positive electrode terminal side of the capacitive load between the second charge / discharge element and the capacitive load by a closed circuit formed with the conduction state of the positive electrode side switching element turned on. Exchange energy. Further, the driving driver exchanges energy between the second charge / discharge element and the capacitive load via the negative electrode terminal of the capacitive load by the closed circuit with the conduction state of the negative electrode side switching element turned on. To do. The voltage value of one of the drive signals, which is a differential signal, and the voltage value of the other signal are alternately changed in accordance with the change in energy between the elements and the capacitive load. Is possible.

  In an eighth driver according to the present invention, the energy replenishing element is connected between the driving power source and a positive electrode terminal of the first charge / discharge element, and the control circuit includes the energy replenishing phase. The conduction state of the energy replenishing element is controlled to be in the on state during the charging phase, and the conduction state of the energy supplementing element is in the off state during the standby phase of the energy replenishment phase. Control.

According to the eighth driver, the control circuit performs control so that the conduction state of the energy supplementing element is turned on. This makes it possible to charge the energy from the driving power supply to the first charge / discharge element via the energy replenishing element.
In a ninth driving driver according to the present invention, when the control circuit performs control so that a closed circuit is formed by turning on a conduction state of the charging direction switching element, the closed circuit is When controlling to be connected to the ground and controlling the positive electrode side switching element and the negative electrode side switching element to be in the on state to form a closed circuit, the closed circuit is Control is performed so as to be connected to a power supply different from the drive power supply, the ground, or a ground different from the ground.

According to the ninth driver for driving described above, when the control circuit forms a closed circuit by turning on the conduction state of each switching element, the closed circuit is connected to the ground or the power source to perform circuit operation. It is possible to determine the upper reference voltage level.
The drive amplifier according to the present invention is a modulation circuit that outputs a modulation signal obtained by modulating the input signal, and a differential signal for driving the capacitive load based on the modulation signal output from the modulation circuit. A drive driver according to any one of claims 1 to 9, which generates a drive signal.

According to the driving amplifier described above, the number of switching elements having high withstand voltage performance for constituting the circuit of the driving amplifier can be reduced as much as possible.
An information device according to the present invention includes a capacitive load, an input signal generation circuit that generates an input signal, and a drive signal for driving the capacitive load based on the input signal generated by the input signal generation circuit. 11. The driving amplifier according to claim 10, wherein the driving amplifier outputs, and a driving power supply that supplies a predetermined power supply voltage to the input signal generation circuit and the driving amplifier.

  According to the above information device, it is configured to include the above driving amplifier. Further, the energy charged in the capacitive load is recharged to the first charge / discharge element through the second charge / discharge element without consuming as much waste as possible by the element such as a resistor. For this reason, it becomes possible to drive a capacitive load with low power consumption.

  According to the present invention, the drive amplifier for driving a capacitive load such as a piezoelectric speaker of an information device has a control circuit adapted to each operation phase of the drive amplifier from the first phase to the fourth phase. Switch each switching element. In particular, the drive amplifier generates a differential signal drive signal with as few switching elements as possible by switching the conduction state of the polarity switching switching element, and drives the capacitive load by the drive signal. Can do.

In addition, according to the present invention, the number of switching elements having a high withstand voltage performance for constituting a drive amplifier circuit can be reduced as much as possible.
Further, according to the present invention, the drive for driving includes the first charging / discharging element and the second charging / discharging element, and the energy charged in the capacitive load such as the piezoelectric speaker is wasted as much as possible by the element such as the resistor. The first charge / discharge element is charged again with energy through the second charge / discharge element without being consumed. And the drive for a drive uses the energy charged by the 1st charging / discharging element in the phase which drives a capacitive load. For this reason, the driving driver passes only the energy consumed mainly by the resistance of each wiring or each element or the kinetic energy of the capacitive load such as the piezoelectric speaker from the power source to the first charge / discharge element, Capacitive loads can be driven with low power consumption.

It is a block diagram which shows the apparatus structure of the portable music player 10 which concerns on this embodiment. 3 is a block diagram showing a device configuration of a piezoelectric speaker driving amplifier 14. FIG. 3 is a circuit diagram showing a circuit configuration of a switching drive circuit 24. FIG. 6 is a time chart showing voltage values of comparison result signals Sa and Sb and drive signals VCP and VCN in each operation phase of the piezoelectric speaker drive amplifier 14; 3 is a circuit diagram showing an equivalent circuit in an energy supplement phase, an energy supplement phase, a first phase, and a second phase of the switching drive circuit 24. FIG. 3 is a circuit diagram showing an equivalent circuit in a third phase and a fourth phase of the switching drive circuit 24. FIG. In the first energy replenishment phase of the piezoelectric speaker drive amplifier 14, the voltage value V _C41 between the two terminals of the capacitor 41 of the switching drive circuit 24, the current value I _L42 flowing through the inductor 42, and the voltage values of the drive signals VCP and VCN. It is a time chart which shows. Time indicating the voltage value V _C41 between both terminals of the capacitor 41 of the switching drive circuit 24, the current value I _L42 flowing through the inductor 42, and the voltage values of the drive signals VCP and VCN in the first phase of the piezoelectric speaker drive amplifier 14 It is a chart. Time indicating the voltage value V _C41 between both terminals of the capacitor 41 of the switching drive circuit 24, the current value I _L42 flowing through the inductor 42, and the voltage values of the drive signals VCP and VCN in the second phase of the piezoelectric speaker drive amplifier 14 It is a chart. Time indicating the voltage value V _C41 between both terminals of the capacitor 41 of the switching drive circuit 24, the current value I _L42 flowing through the inductor 42, and the voltage values of the drive signals VCP and VCN in the third phase of the piezoelectric speaker drive amplifier 14 It is a chart. Time indicating the voltage value V _C41 between both terminals of the capacitor 41 of the switching drive circuit 24, the current value I _L42 flowing through the inductor 42, and the voltage values of the drive signals VCP and VCN in the fourth phase of the piezoelectric speaker drive amplifier 14 It is a chart. The voltage value V _C41 between both terminals of the capacitor 41 of the switching drive circuit 24, the current value I _L42 flowing through the inductor 42, and the voltages of the drive signals VCP and VCN in the second and subsequent energy supplement phases of the piezoelectric speaker drive amplifier 14 It is a time chart which shows a value. 3 is a block diagram showing a circuit configuration of a gate driver circuit 23. FIG. 6 is a circuit diagram showing a circuit configuration of a switching drive circuit 100 which is a first modification of the switching drive circuit 24. FIG. FIG. 6 is a circuit diagram showing a circuit configuration of a switching drive circuit 200 which is a second modification of the switching drive circuit 24. FIG. 3 is a circuit diagram showing a circuit configuration of a switching drive circuit 300 when the switching drive circuit 24 is configured as an integrated circuit (hereinafter referred to as “IC (Integrated Circuit)”). It is a circuit diagram which shows the circuit structure of the switching drive circuit 400 at the time of comprising the switching drive circuit 100 as IC. It is a circuit diagram which shows the circuit structure of the switching drive circuit 500 at the time of comprising the switching drive circuit 200 as IC.

Hereinafter, preferred embodiments of a driving driver, a driving amplifier, and an information device according to the present invention will be described in detail with reference to the accompanying drawings.
(Device configuration of portable music player 10)
First, with reference to FIG. 1, a device configuration of a portable music player 10 will be described as an example of information equipment provided with a driving driver according to the present invention as a driving amplifier.

FIG. 1 is a block diagram showing a device configuration of the portable music player 10. A portable music player 10 shown in FIG. 1 includes a control unit 11, a touch panel 12, a memory 13, a piezoelectric speaker driving amplifier 14, a piezoelectric speaker 15, and a lithium ion battery 16.
The control unit 11 controls the overall portable music player 10 by transmitting and receiving control signals and the like to and from each unit constituting the portable music player 10. The control unit 11 is supplied with a predetermined power supply voltage VDD from the lithium ion battery 16. The control unit 11 also serves as an input signal generation circuit, generates audio signals VIP and VIN as input signals, and outputs the generated audio signals VIP and VIN to the piezoelectric speaker drive amplifier 14.

The touch panel 12 is used for the user to select a song to be played back and the volume, and to display the song being played, the current device status, and the like.
The memory 13 stores a program executed by the control unit 11 and a music file taken in from an external personal computer or the like.
The piezoelectric speaker driving amplifier 14 is a driving amplifier that drives the piezoelectric speaker 15 by inputting the power supply voltage VDD from the lithium ion battery 16 and the audio signals VIP and VIN output from the control unit 11.

  The piezoelectric speaker 15 includes a piezoelectric body and electrodes, and is a piezoelectric element that vibrates the piezoelectric body and outputs sound by applying a voltage to the electrodes sandwiching the piezoelectric body, that is, a capacitive load. The piezoelectric speaker 15 that is a capacitive load has a positive electrode terminal and a negative electrode terminal. The positive electrode terminal and the negative electrode terminal do not indicate a voltage to be applied to the element like an electrolytic capacitor having a limitation in applied voltage. It represents the polarity of the signal.

  The lithium ion battery 16 is a secondary battery that can be charged by a commercial power source or the like, and is a driving power source that supplies an operating voltage to the control unit 11 and the piezoelectric speaker driving amplifier 14. When the operating voltage of the piezoelectric speaker driving amplifier 14 is higher than the power supply voltage VDD output from the lithium ion battery 16, the power supply voltage VDD may be boosted using a booster circuit such as a DC-DC converter.

  Further, as described in the background art, in a general driving amplifier, energy is charged to a piezoelectric speaker or the like from a driving power source or a DC-DC converter that boosts a power source voltage. As an operation method of the DC-DC converter, there are a continuous current mode (hereinafter, referred to as “CCM (Continuous Conduction Mode)”) and a negative continuous current mode (hereinafter, referred to as “DCM (Discontinuous Conduction Mode)”). In the former CCM, in order to realize stable phase compensation, it is sometimes necessary to narrow the signal band, so when the driving amplifier handles audio signals, the driving amplifier is driven. As an operation method for boosting the driving power supply and the power supply voltage, CCM is relatively unsuitable, and DCM is more suitable than CCM.

  In the present embodiment, an information device provided with the piezoelectric speaker driving amplifier 14 according to the present invention will be described as a portable music player 10, but the information device may be a mobile phone, a portable DVD player, or the like. Also good. Further, the load driven by the piezoelectric speaker driving amplifier 14 may be a capacitive load, and is not limited to the piezoelectric speaker 15. For example, the capacitive load may be a capacitive load such as various piezoelectric elements or modulators other than the piezoelectric speaker 15.

(Circuit configuration of the piezoelectric speaker driving amplifier 14)
Next, with reference to FIG. 2, a device configuration of the piezoelectric speaker driving amplifier 14 of the portable music player 10 will be described as an example of the driving amplifier according to the present invention.
FIG. 2 is a block diagram illustrating a circuit configuration of the piezoelectric speaker driving amplifier 14. The piezoelectric speaker drive amplifier 14 shown in FIG. 2 includes an error suppression circuit 21, a PWM (Pulse Width Modulation) circuit 22, a gate driver circuit 23, a switching drive circuit 24, and LPF (Low Pass Filter) circuits 25a and 25b. And a current monitoring circuit 30, a first comparison circuit 31a, and a second comparison circuit 31b.

The error suppression circuit 21 detects an error between the amplitude of the audio signals VIP and VIN input as differential signals from the input terminals 26 and 27 and the amplitude of the drive signals VCP and VCN fed back as differential signals from the output side. This is a circuit that outputs audio signals VIP ′ and VIN ′ obtained by correcting the amplitudes of the audio signals VIP and VIN based on the detected amplitude error.
The PWM circuit 22 is a modulation circuit that performs PWM modulation on the audio signals VIP ′ and VIN ′ output from the error suppression circuit 21 and outputs a PWM signal that is a modulation signal. In addition, although the modulation system in this embodiment is PWM modulation, it is not limited to this. The modulation method may be other than PWM modulation, for example, PDM (Pulse Density Modulation) modulation including delta sigma modulation.

  The gate driver circuit 23 includes the PWM signal Sp output from the PWM circuit 22, the current monitoring result signal Si output from the current monitoring circuit 30, the comparison result signal Sa output from the first comparison circuit 31a, and the first Based on at least four signals with the comparison result signal Sb output from the second comparison circuit 31b, drive control signals φ0 to φ4 for driving the switching elements to be described later constituting the switching drive circuit 24 are generated. It is a circuit to output.

The switching drive circuit 24 is connected via the output terminals 28 and 29 because the conduction state of each switching element constituting the switching drive circuit 24 is operated by the drive control signals φ0 to φ4 output from the gate driver circuit 23. This is a circuit for outputting drive signals VCP and VCN to the piezoelectric speaker 15.
When the LPF circuits 25a and 25b feed back the drive signals VCP and VCN output from the switching drive circuit 24 to the input side, the LPF circuits 25a and 25b remove the high-frequency components of the drive signals VCP and VCN to reduce the low frequency of the drive signals VCP and VCN. It is a filtering circuit for extracting components.

  The current monitoring circuit 30 monitors a current value flowing in an inductor, which will be described later, constituting the switching drive circuit 24, and is a predetermined voltage level H level or lower than the H level according to the state of the current value flowing in the inductor. This is a circuit for outputting an L level current monitoring result signal Si which is a voltage level. The current monitoring circuit 30 outputs an L level current monitoring result signal while the value of the current flowing through the inductor is 0 (A) and from when the current value flowing through the inductor starts to increase from 0 (A) to when it starts to decrease. Si is output. On the contrary, the H level current monitoring result signal Si is output from the time when the value of the current flowing through the inductor starts to decrease after rising and until it becomes 0 (A) again.

  The first comparison circuit 31a is a circuit that compares the voltage value of the audio signal VIP ′ output from the error suppression circuit 21 with the voltage value of the audio signal VIN ′. Then, the first comparison circuit 31a outputs an H level or L level comparison result signal Sa according to the comparison result. For example, when the voltage value of one signal output as a differential signal from the error suppression circuit 21 is higher than the voltage value of the other signal, the first comparison circuit 31a outputs an H-level comparison result signal Sa. On the contrary, when the voltage value of the other signal becomes higher than the voltage value of one signal, the second comparison circuit 31b outputs an L level comparison result signal Sa.

  The second comparison circuit 31b is a circuit that compares the voltage value of the drive signal VCP output from the switching drive circuit 24 with the voltage value of the drive signal VCN. Then, the second comparison circuit 31b outputs a comparison result signal Sb of H level or L level according to the comparison result. For example, when the voltage value of the drive signal VCP becomes higher than the voltage value of the drive signal VCN, the second comparison circuit 31b outputs an L-level comparison result signal Sb. On the contrary, when the voltage value of the drive signal VCN becomes higher than the voltage value of the drive signal VCP, the second comparison circuit 31b outputs an H-level comparison result signal Sb.

  The drive signal VCP for driving the piezoelectric speaker 15 from the gate driver circuit 23, the switching drive circuit 24, the current monitoring circuit 30, the first comparison circuit 31a, and the second comparison circuit 31b described above. , VCN is output. The gate driver circuit 23 functions as a control circuit for the driving driver.

(Circuit configuration of the switching drive circuit 24)
Next, the circuit configuration of the switching drive circuit 24 according to the present invention will be described with reference to FIG.
FIG. 3 is a circuit diagram showing a circuit configuration of the switching drive circuit 24. The switching drive circuit 24 shown in FIG. 3 includes a capacitor 41, an inductor 42, PMOS transistors 43 and 45 to 47, and an NMOS transistor 44.
The capacitor 41 is connected between a drive power supply that outputs the power supply voltage VDD and the ground. The capacitor 41 is charged with energy corresponding to the power supply voltage VDD of the lithium ion battery 16. Then, the charged energy is discharged from the capacitor 41. The capacitor 41 functions as a first charge / discharge element.

In the present embodiment, the capacitance of the piezoelectric speaker 15 is about 1 μF, whereas the capacitance of the capacitor 41 is about 50 μF, which is larger than the capacitance of the piezoelectric speaker 15. Of course, each capacitance value is not limited to this.
The inductor 42 is connected between the positive terminal of the capacitor 41 and the positive terminal of the piezoelectric speaker 15. The inductor 42 is temporarily charged with energy corresponding to the value of the current flowing through the inductor 42. The charged energy is discharged from the inductor 42. The inductor 42 functions as a second charge / discharge element.

  The PMOS transistor 43 is connected between the driving power supply and the positive terminal of the capacitor 41. The PMOS transistor 43 is a switching element for replenishing the capacitor 41 with energy corresponding to the power supply voltage VDD by switching the conduction state between the on state and the off state by the drive control signal φ0. The PMOS transistor 43 is turned on when the drive control signal φ0 is at L level. At this time, the capacitor 41 is charged with energy from the power supply voltage VDD. On the contrary, the PMOS transistor 43 is turned off when the drive control signal φ0 becomes H level. At this time, energy is not charged to the capacitor 41 from the power supply voltage VDD.

The PMOS transistor 43 functions as an energy supplement switching element.
The NMOS transistor 44 is connected between the terminal on the capacitive load side of the inductor 42 and the negative terminal of the capacitor 41. The NMOS transistor 44 is a switching element for switching the conduction state between the on state and the off state by the drive control signal φ1. The NMOS transistor 44 is turned on when the drive control signal φ1 is at H level, and is turned off when the drive control signal φ1 is at L level.

The NMOS transistor 44 has a state in which the energy charged in the capacitor 41 is charged in the piezoelectric speaker 15 via the inductor 42 and a state in which the energy charged in the piezoelectric speaker 15 is charged in the capacitor 41 via the inductor 42. It functions as a charging direction switching element that switches alternately.
The PMOS transistor 45 is connected between a terminal on the capacitive load side of the inductor 42 and a terminal on the driving power source side of the PMOS transistor 46. The PMOS transistor 45 is a switching element for switching the conduction state between the on state and the off state by the drive control signal φ2. The PMOS transistor 45 is turned on when the drive control signal φ2 is at L level, and is turned off when the drive control signal φ2 is at H level.

  The PMOS transistor 45 is an element connected to adjust the breakdown voltage described in the background art. Even if the PMOS transistor 45 is not connected, the conduction state of the PMOS transistor 45 can be substantially controlled by the PMOS transistors 46 to 49. For this reason, the PMOS transistor 45 is not necessarily connected. In the case where the PMOS transistor 45 is not connected, it is sufficient that the portion is connected and is in a conductive state.

  The PMOS transistor 46 is connected between the terminal on the capacitive load side of the inductor 42 and the positive terminal of the piezoelectric speaker 15. The PMOS transistor 47 is connected between the negative terminal of the piezoelectric speaker 15 and the terminal on the driving power source side of the inductor 42. The PMOS transistors 46 and 47 are switching elements for switching the conduction state between the on state and the off state by the drive control signal φ3. The PMOS transistors 46 and 47 are turned on when the drive control signal φ3 is at the L level, and turned off when the drive control signal φ3 is at the H level.

  The PMOS transistor 48 is connected between the terminal on the capacitive load side of the inductor 42 and the negative terminal of the piezoelectric speaker 15. The PMOS transistor 49 is connected between the positive terminal of the piezoelectric speaker 15 and the terminal on the driving power source side of the inductor 42. The PMOS transistors 48 and 49 are switching elements for switching the conduction state between the on state and the off state by the drive control signal φ4. The PMOS transistors 48 and 49 are turned on when the drive control signal φ4 is at the L level, and turned off when the drive control signal φ4 is at the H level.

The PMOS transistors 45 to 49 are configured to switch between a state in which energy is charged in the piezoelectric speaker 15 and a state in which the capacitor 41 is charged with energy by the NMOS transistor 44 that is a switching element for switching the charging direction, and the piezoelectric speaker 15. It functions as a polarity switching switching element that alternately switches between a state in which energy is charged from the positive electrode terminal side and a state in which energy is charged through the negative electrode terminal of the piezoelectric speaker 15. In particular, the PMOS transistors 45 to 47 function as positive side switching elements, and the PMOS transistors 45, 48, and 49 function as negative side switching elements.
Of the MOS transistors described above, in the MOS transistor in which two bulks are illustrated, one of the bulks is selected depending on the operation phase of the piezoelectric speaker driving amplifier 14 described later.

(Operation phase of piezoelectric speaker drive amplifier 14)
Next, an operation phase of the piezoelectric speaker driving amplifier 14 will be described with reference to FIG.
FIG. 4 is a time chart showing voltage values of the comparison result signals Sa and Sb and the drive signals VCP and VCN in each operation phase of the piezoelectric speaker drive amplifier 14. 4 represents the voltage level of the comparison result signal Sa output from the first comparison circuit 31a, the voltage level of the comparison result signal Sb output from the second comparison circuit 31b, and the piezoelectric speaker driving amplifier 14. Shows the voltage values of the drive signals VCN and VCP output from. The horizontal axis represents time T.

There are four operating phases of the piezoelectric speaker driving amplifier 14 from the first phase to the fourth phase. When the fourth phase ends, the operation returns to the first phase, and each operation phase is repeated.
First, the first phase is a phase in which the voltage value of the drive signal VCP is increased to set the voltage value of the drive signal VCN to an analog ground voltage level VLP that is a predetermined voltage level. In the next second phase, the voltage value of the drive signal VCN is set to the analog ground voltage level VLP, and the voltage value of the drive signal VCP is decreased.

In contrast to the first phase and the second phase, the third phase is a phase in which the voltage value of the drive signal VCN is increased to set the voltage value of the drive signal VCP to the analog ground voltage level VLP. The next fourth phase is a phase in which the voltage value of the drive signal VCN is decreased to the analog ground voltage level VLP.
These operation phases are determined by the piezoelectric speaker driving amplifier 14 mainly by a combination of the voltage level of the comparison result signal Sa and the voltage level of the comparison result signal Sb. Since the piezoelectric speaker drive amplifier 14 needs to synchronize when determining the operation phase, the PWM signal Sp is also necessary, but the description is omitted here.

  First, the piezoelectric speaker drive amplifier 14 determines whether it is a phase for increasing or decreasing the voltage value of the drive signal VCP or the drive signal VCN according to the voltage level of the comparison result signal Sa. For example, when the comparison result signal Sa is at the L level, the first phase or the third phase in which the voltage value of the drive signal VCP or the drive signal VCN is increased. On the contrary, when the comparison result signal Sa is at the H level, the second phase or the fourth phase in which the voltage value of the drive signal VCP or the drive signal VCN is decreased is entered.

  Further, the piezoelectric speaker driving amplifier 14 determines whether it is a phase for changing the voltage value of the driving signal VCP or a phase for changing the voltage value of the driving signal VCN according to the voltage level of the comparison result signal Sb. For example, when the comparison result signal Sb is at the L level, the first phase or the second phase in which the voltage value of the drive signal VCP is changed is entered. On the contrary, when the comparison result signal Sb is at the H level, the third phase or the fourth phase in which the voltage value of the drive signal VCN is changed is entered.

In short, when the comparison result signal Sa is at the L level and the comparison result signal Sb is at the L level, the operation phase of the piezoelectric speaker driving amplifier 14 is the first phase. When the comparison result signal Sa is at the H level and the comparison result signal Sb is at the L level, the operation phase of the piezoelectric speaker driving amplifier 14 is the second phase. When the comparison result signal Sa is at the L level and the comparison result signal Sb is at the H level, the operation phase of the piezoelectric speaker driving amplifier 14 is the third phase. When the comparison result signal Sa is at the H level and the comparison result signal Sb is at the H level, the operation phase of the piezoelectric speaker driving amplifier 14 is the fourth phase.
As will be described later, there is an energy replenishment phase as a phase for charging the capacitor 41 with energy corresponding to the power supply voltage VDD separately from the above-described operation phases.

(Change in energy of each element in each operation phase of the switching drive circuit 24)
Next, with reference to FIGS. 5 and 6, changes in energy of each element in each operation phase of the switching drive circuit 24 will be described.
5 and 6 are circuit diagrams showing an equivalent circuit of the switching drive circuit 24 in each operation phase of the switching drive circuit 24. FIG. An equivalent circuit (1a) shown in FIG. 5 shows an equivalent circuit of the switching drive circuit 24 in the energy replenishment phase. An equivalent circuit (1b) and an equivalent circuit (1c) shown in FIG. 5 are equivalent circuits of the switching drive circuit 24 in the first phase. An equivalent circuit (1d) and an equivalent circuit (1e) shown in FIG. 5 are equivalent circuits of the switching drive circuit 24 in the second phase. Further, an equivalent circuit (2a) and an equivalent circuit (2b) shown in FIG. 6 are equivalent circuits of the switching drive circuit 24 in the third phase. An equivalent circuit (2c) and an equivalent circuit (2d) shown in FIG. 6 are equivalent circuits of the switching drive circuit 24 in the fourth phase.

The switching drive circuit 24 changes the connection form of the switching drive circuit 24 by switching the conduction states of the PMOS transistors 43, 45 to 47 and the NMOS transistor 44 by the drive control signals φ0 to φ4 in accordance with the operation phases.
First, as shown in the equivalent circuit (1a), in the energy replenishment phase, the conduction state of the PMOS transistor 43 is turned on, the positive terminal of the capacitor 41 is connected to the driving power supply, and the negative terminal of the capacitor 41 is connected to the ground. Connected. Thereby, the energy corresponding to the power supply voltage VDD is charged in the capacitor 41.

Next, as shown in the equivalent circuit (1b), in the first phase, the conduction state of the NMOS transistor 44 and the PMOS transistor 45 is turned on, and the capacitor 41 and the inductor 42 are connected. By this closed circuit, the energy charged in the capacitor 41 moves to the inductor 42 and the energy is charged in the inductor 42.
Here, the voltage value between both terminals of the capacitor 41 before the energy of the capacitor 41 moves is V ₁ (V), and the voltage value between both terminals of the capacitor 41 after the energy of the capacitor 41 moves is V _2. Assuming (V), the voltage value between both terminals of the capacitor 41 decreases from V ₁ (V) to V ₂ (V) before and after energy transfer. For this reason, the energy ΔE _C1 (J) transferred from the capacitor 41 is
ΔE _C1 = (1/2) C ₁ (V ₁ ² −V ₂ ² ) Equation (1)
It becomes.

The current value flowing through the inductor 42 before the energy is transferred to the inductor 42 is 0 (A), and the current value flowing through the inductor 42 after the energy is transferred to the inductor 42 is I ₁ (A). At this time, the value of the current flowing through the inductor 42 increases from 0 (A) to I ₁ (A) before and after the energy is transferred. Therefore, the energy ΔE _L (J) transferred to the inductor 42 is
ΔE _L = (1/2) L (I ₁ ² −0)
= (1/2) LI ₁ ² ...... Formula (2)
It becomes.

When the inductance of the inductor is L (H), the capacitance of the capacitor is C (F), the voltage value is V (V), and the current value is I (A), impedance Z = √ (L / C) (Ω), V = IZ (V), so
V = I × √ (L / C) (3)
It becomes. When the capacitance C (F) of the capacitor 41 is C ₁ (F) and Equation (3) is substituted into Equation (1),
ΔE _C1 = (1/2) C ₁ (V ₁ ² −V ₂ ² )
= (1/2) C ₁ (I ₁ ² (L / C ₁ ) −0 ² (L / C ₁ ))
= (1/2) LI ₁ ² -0
= (1/2) LI ₁ ² ...... Formula (4)
It becomes. Therefore, the energy ΔE _C1 (J) transferred from the capacitor 41 and the energy ΔE _L (J) charged in the inductor 42 are equal. That is, when energy is transferred from the capacitor 41 to the inductor 42, it can be said that energy is not wasted if the wiring and resistance values of the respective elements are ignored. However, since energy is actually consumed by the resistance of the wiring and each element, etc., if the energy of the loss consumed by the resistance of the wiring and each element is E _LOSS (J), the law of conservation of energy The energy ΔE _C1 (J) transferred from the capacitor 41 by
ΔE _C1 = ΔE _L + E _LOSS ...... Formula (5)
It becomes.

Next, as shown in the equivalent circuit (1c), in the first phase, the conduction state of the PMOS transistors 46 and 47 is turned on, and the inductor 42 and the piezoelectric speaker 15 are connected. Due to this closed circuit, as in the second phase, the current value flowing through the inductor 42 before the energy is transferred to the piezoelectric speaker 15 is I ₁ (A), and the inductor after the energy is transferred to the piezoelectric speaker 15. Since the current value flowing through the inductor 42 becomes 0 (A), the current value flowing through the inductor 42 decreases from I ₁ (A) to 0 (A) before and after the energy is transferred. Therefore, the energy ΔE _L (J) transferred to the inductor 42 is
ΔE _L = (1/2) LI ₁ ² ...... Formula (6)
It becomes.

The voltage value between both terminals of the piezoelectric speaker 15 before the energy is transferred to the piezoelectric speaker 15 is V ₃ (V), and the voltage value between both terminals of the piezoelectric speaker 15 after the energy is transferred to the piezoelectric speaker 15. Is V ₄ (V), the voltage value between both terminals of the piezoelectric speaker 15 increases from V ₃ (V) to V ₄ (V) before and after energy transfer. Therefore, the energy ΔE _C2 (J) moved from the piezoelectric speaker 15 is
ΔE _C2 = (1/2) C ₂ (V ₄ ² −V ₃ ² ) (7)
It becomes.

When the capacitance C (F) in the expression (3) is C ₂ (F), the expression (7) is expanded by substituting the expression (3) into the expression (7), and is transferred to the inductor 42 shown in the expression (6). The energy ΔE _L (J) thus made becomes equal to the energy ΔE _C2 (J) moved to the piezoelectric speaker 15 shown by the equation (7). For this reason, when transferring energy from the inductor 42 to the piezoelectric speaker 15 in the third phase, it can be said that the energy is not wasted if the wiring and the resistance values of the respective elements are ignored as in the second phase. However, since energy is actually consumed by the resistance of the wiring and each element, etc., if the energy of the loss consumed by the resistance of the wiring and each element is E _LOSS (J), the law of conservation of energy The energy ΔE _C2 (J) moved from the piezoelectric speaker 15 by
ΔE _C2 = ΔE _L + E _LOSS ...... Formula (8)
It becomes.

Next, as shown in the equivalent circuit (1d), in the second phase, the conduction state of the PMOS transistors 46 and 47 remains unchanged and the inductor 42 and the piezoelectric speaker 15 are connected. Then, by this closed circuit, the energy charged in the piezoelectric speaker 15 is charged in the inductor 42.
The voltage value between both terminals of the piezoelectric speaker 15 before the energy of the piezoelectric speaker 15 moves is V ₅ (V), and the voltage value between both terminals of the capacitor 41 after the energy of the piezoelectric speaker 15 moves is V _6. Assuming (V), the voltage value between the two terminals of the piezoelectric speaker 15 decreases from V ₅ (V) to V ₆ (V) before and after energy transfer. For this reason, the energy ΔE _C3 (J) moved from the piezoelectric speaker 15 is
ΔE _C3 = (1/2) C ₂ (V ₅ ² −V ₆ ² ) (9)
It becomes.

Further, the current value flowing through the inductor 42 before the energy is transferred to the inductor 42 is 0 (A), and the current value flowing through the inductor 42 after the energy is transferred to the inductor 42 is I ₂ (A). For example, the value of the current flowing through the inductor 42 increases from 0 (A) to I ₂ (A) before and after the energy is transferred. Therefore, the energy ΔE _L (J) transferred to the inductor 42 is
ΔE _L = (1/2) LI ₂ ² ...... Equation (10)
It becomes.

When the capacitance C (F) in the equation (3) is C ₂ (F) and the equation (3) is substituted into the equation (9) and the equation (9) is developed, the energy ΔE _C3 (J ) And the energy ΔE _L (J) transferred to the inductor 42 are equal. For this reason, when charging the energy from the piezoelectric speaker 15 to the inductor 42 in the fourth phase, it can be said that energy is not wasted as in the second phase and the third phase. However, since energy is actually consumed by the resistance of the wiring and each element, etc., if the energy of the loss consumed by the resistance of the wiring and each element is E _LOSS (J), the law of conservation of energy The energy ΔE _C3 (J) moved from the piezoelectric speaker 15 by
ΔE _C3 = ΔE _L + E _LOSS ...... Formula (11)
It becomes.

Next, as shown in the equivalent circuit (1 e), in the second phase, only the conduction state of the NMOS transistor 44 and the PMOS transistor 45 is switched on, and the capacitor 41 is connected to the inductor 42. Then, the energy charged in the inductor 42 is transferred to the capacitor 41 by this closed circuit.
The voltage value between both terminals of the inductor 42 before the energy of the inductor 42 moves is V ₇ (V), and the voltage value between both terminals of the inductor 42 after the energy of the inductor 42 moves is V ₈ (V). Then, the voltage value between both terminals of the inductor 42 increases from V ₇ (V) to V ₈ (V) before and after energy transfer. Therefore, the energy ΔE _C4 transferred from the capacitor 41 is
ΔE _C4 = (1/2) C ₁ (V ₈ ² −V ₇ ² ) (12)
It becomes.

If the current value flowing through the inductor 42 before energy is transferred to the inductor 42 is I ₂ (A), and the current value flowing through the inductor 42 before energy is transferred to the inductor 42 is 0 (A). The current value flowing through the inductor 42 decreases from I ₂ to 0 (A) before and after the energy is transferred. Therefore, the energy ΔE _L (J) transferred to the inductor 42 is
ΔE _L = (1/2) LI ₂ ² ...... Formula (13)
It becomes.

When the capacitance C (F) of the capacitor in Expression (3) is C ₁ (F) and Expression (3) is substituted into Expression (12) and Expression (12) is developed, energy ΔE _L ( J) is equal to the energy ΔE _C4 (J) transferred to the capacitor 41. From this, it can be said that energy is not wasted even when energy is transferred from the inductor 42 to the capacitor 41 in the fifth phase. However, since energy is actually consumed by the resistance of the wiring and each element, etc., if the energy of the loss consumed by the resistance of the wiring and each element is E _LOSS (J), the law of conservation of energy The energy ΔE _C4 (J) transferred to the capacitor 41 by
ΔE _C4 = ΔE _L + E _LOSS ...... Formula (14)
It becomes.

As described above, when the energy moves, in the first phase, the voltage value of the drive signal VCP can be increased according to the energy charged in the piezoelectric speaker 15, and in the second phase, the drive signal The voltage value of VCP can be reduced.
In addition, as shown in the equivalent circuit (2a) to the equivalent circuit (2d), the flow of energy transfer between the elements in the third phase and the fourth phase is the energy between the elements in the first phase and the second phase. Is the same as the flow of moving. However, when energy moves to the piezoelectric speaker 15 in the third phase, and when energy moves from the piezoelectric speaker 15 in the fourth phase, not from the positive terminal side of the piezoelectric speaker 15 but from the negative terminal side of the piezoelectric speaker 15. Energy is exchanged. In short, the gate driver circuit 23 controls the conduction state of only the PMOS transistors 46 to 49 of the switching drive circuit 24, so that the piezoelectric speaker 15 has the first phase and the second phase, and the third phase and the fourth phase. Polarity is changing on the connection. By moving the energy in the closed circuit as described above, in the third phase, the voltage value of the drive signal VCN can be increased according to the energy charged in the piezoelectric speaker 15, and in the fourth phase, the drive is performed. The voltage value of the signal VCN can be reduced.

Thus, the number of switching elements having a high withstand voltage performance for constituting the circuit of the piezoelectric speaker driving amplifier 14 is as small as possible.
Then, after the operation phase of the piezoelectric speaker driving amplifier 14 first becomes the “energy replenishment phase”, the “first phase”, “second phase”, “third phase”, “fourth phase”, “ Each operation phase is repeated continuously like “first phase”, “second phase”, “third phase”, “fourth phase”. During this time, energy is gradually lost as heat or the like due to the wiring or resistance of each element. For this reason, for example, when a predetermined energy is lost or each operation phase from the first phase to the fourth phase is performed a predetermined number of times, the process returns to the “energy replenishment phase” again, and the resistance of the wiring and each element The capacitor 41 is charged with energy corresponding to the energy lost due to the above. Thereafter, each operation phase from the first phase to the fourth phase is similarly repeated. The piezoelectric speaker drive amplifier 14 alternately changes the voltage value of the drive signal VCP and the voltage value of the drive signal VCN in accordance with the change in energy at this time.

(Detailed operation phases in each operation phase of the piezoelectric speaker driving amplifier 14)
Next, detailed operation phases in each operation phase of the piezoelectric speaker drive amplifier 14 will be described with reference to FIGS.
FIG. 7 shows the voltage value V _C41 between the two terminals of the capacitor 41 of the switching drive circuit 24, the current value I _L42 flowing through the inductor 42, and the drive signal VCP, in the first energy replenishment phase of the piezoelectric speaker drive amplifier 14. It is a time chart which shows the voltage value of VCN. FIG. 8 is a time chart showing the voltage values and current values in the first phase of the piezoelectric speaker driving amplifier 14. FIG. 9 is a time chart showing the voltage values and current values in the second phase of the piezoelectric speaker driving amplifier 14. FIG. 10 is a time chart showing the above voltage values and current values in the third phase of the piezoelectric speaker driving amplifier 14. FIG. 11 is a time chart showing the voltage values and current values in the fourth phase of the piezoelectric speaker driving amplifier 14. FIG. 12 is a time chart showing the respective voltage values and current values in the second and subsequent energy replenishment phases of the piezoelectric speaker driving amplifier 14.

7 to 12, the vertical axis indicates the voltage level of the PWM signal Sp output from the PWM circuit 22, the voltage level of the comparison result signal Sa output from the first comparison circuit 31a, and the first level. 2 shows the voltage level of the comparison result signal Sb output from the second comparison circuit 31b and the voltage level of the current monitoring result signal Si output from the current monitoring circuit 30.
Furthermore, the vertical axis of each figure represents the conduction state of the PMOS transistors 43, 45 to 49 and the NMOS transistor 44, the voltage value V _C41 across the capacitor 41, the current value I _L42 flowing through the inductor 42, the voltage value of the drive signal VCP, The voltage value of the drive signal VCN is also shown.

In addition, the horizontal axis of each of the above drawings indicates time T.
As described above, the operation phase of the piezoelectric speaker drive amplifier 14 has four phases from the first phase to the fourth phase. However, first, it is necessary to charge the capacitor 41 with energy corresponding to the power supply voltage VDD. For this reason, the operation phase of the piezoelectric speaker drive amplifier 14 becomes an energy replenishment phase before the first phase.

As shown in FIG. 7, the energy replenishment phase is further divided into two operation phases, a standby phase and a charging phase.
Therefore, the operation phase of the piezoelectric speaker driving amplifier 14 becomes a standby phase of the energy supplementation phase. In this standby phase, the conduction states of all the MOS transistors of the PMOS transistors 43 and 45 to 49 and the NMOS transistor 44 are turned off by the voltage levels of the drive control signals φ0 to φ4. Thus, in the standby phase, energy is not transferred from the inductor 42 to each element, and the current value I _L42 flowing through the inductor 42 is completely maintained at 0 (A). For this reason, in the standby phase, the voltage value V _C41 across the capacitor 41 and the current value I _L42 flowing through the inductor 42 do not change. At this time, the voltage values of drive signals VCP and VCN do not change from analog ground voltage level VLP.

Subsequently, the operation phase of the piezoelectric speaker driving amplifier 14 becomes a charging phase of the energy supplementation phase. In this charging phase, according to the voltage level of drive control signal φ0, only the PMOS transistor 43 is turned on, and the other MOS transistors are turned off. Then, the capacitor 41 is charged with energy corresponding to the power supply voltage VDD. For this reason, the voltage value V _C41 across the capacitor 41 and the energy ΔE _{C41 of the} capacitor 41 gradually increase from 0 (J). At this time, the voltage values of drive signals VCP and VCN do not change from analog ground voltage level VLP.

Here, the operation phase of the piezoelectric speaker drive amplifier 14 becomes the standby phase of the energy replenishment phase again. For this reason, in the standby phase, the voltage value V _C41 across the capacitor 41 and the current value I _L42 flowing through the inductor 42 do not change. At this time, the voltage values of drive signals VCP and VCN do not change from analog ground voltage level VLP.
Next, the operation phase of the piezoelectric speaker drive amplifier 14 is changed from the energy replenishment phase to the first phase. As shown in FIG. 8, the first phase is further divided into three operation phases including a charge phase, a transfer phase, and a standby phase, and these operation phases are repeated.

First, in the charge phase of the first phase, the conduction state of the NMOS transistor 44 and the PMOS transistors 46 and 47 is turned on in accordance with the voltage level of the drive control signals φ0 to φ4, and the conduction states of the other MOS transistors. Turns off. Then, the energy charged in the capacitor 41 is charged in the inductor 42. For this reason, the voltage value V _C41 across the capacitor 41 and the energy of the capacitor 41 decrease. The current value I _L42 flowing through the inductor 42 increases from 0 (A) to I ₁ (A), and the energy of the inductor 42 increases from 0 (J) by the energy corresponding to the decrease of the capacitor 41. Note that the voltage value of the capacitor 41, that is, the energy changes as shown by the broken line in the figure if the wiring and resistance values of the elements are ignored, but the energy is consumed little by little due to the resistance of the wiring and each element. Therefore, it changes as shown by the solid line. At this time, the voltage values of drive signals VCP and VCN do not change from analog ground voltage level VLP.

Subsequently, in the transfer phase of the first phase, the PMOS transistors 45, 46, and 47 are turned on according to the voltage levels of the drive control signals φ0 to φ4, and the other MOS transistors are turned on. Turns off. Then, the energy charged in the inductor 42 is transferred to the piezoelectric speaker 15. Therefore, current I _L flowing through the inductor 42 with decreases from I ₁ (A) to 0 (A), the energy of the inductor 42 decreases. The voltage value V _{C15 at} both ends of the piezoelectric speaker 15 and the energy of the piezoelectric speaker 15 increase from 0 (J) by the energy corresponding to the decrease of the inductor 42. At this time, the voltage value of the drive signal VCP gradually increases from the analog ground voltage level VLP. However, the voltage value of the drive signal VCN does not change from the analog ground voltage level VLP.

Subsequently, in the standby phase of the first phase, the PMOS transistors 46 and 47 are turned on according to the voltage levels of the drive control signals φ0 to φ4, and the other MOS transistors are turned off. become. Thus, in the standby phase, energy is not transferred from the inductor 42 to each element, and the current value I _L42 flowing through the inductor 42 is completely maintained at 0 (A). Therefore, in the standby phase, the voltage value V _{C41 at} both ends of the capacitor 41, the current value I _L42 flowing through the inductor 42, the voltage value V _{C15 at} both ends of the piezoelectric speaker 15, the energy of the capacitor 41, the energy of the inductor 42, and the piezoelectric speaker. The energy of 15 does not change. At this time, the voltage value of the drive signal VCP does not change from the voltage increased in the immediately preceding transfer phase. Further, the voltage value of the drive signal VCN does not change from the analog ground voltage level VLP.

In the first phase, the voltage value of the drive signal VCP is increased as shown in FIG. 8 while repeating the charging phase, the transfer phase, and the standby phase. However, the voltage value of the drive signal VCN is not changed from the analog ground voltage level VLP.
Subsequently, the operation phase of the piezoelectric speaker driving amplifier 14 is changed from the first phase to the second phase. As shown in FIG. 9, the second phase is also divided into three operation phases of a charge phase, a transfer phase, and a standby phase, as in the first phase, and these operation phases are repeated.

First, in the charge phase of the second phase, the PMOS transistors 45, 46, and 47 are turned on according to the voltage levels of the drive control signals φ0 to φ4, and the other MOS transistors are turned off. It becomes a state. Then, the energy charged in the piezoelectric speaker 15 is charged in the inductor 42. For this reason, the voltage value V _C15 across the piezoelectric speaker 15 and the energy of the piezoelectric speaker 15 are reduced. Then, the current value I _L42 flowing through the inductor 42 increases from 0 (A) to I ₂ (A), and the energy of the inductor 42 increases by the energy corresponding to the decrease of the piezoelectric speaker 15. Even in the second phase, the energy of the capacitor 41 is indicated by a broken line in the figure if the wiring and the resistance of each element are ignored, but the energy is consumed little by little by the wiring and the resistance of each element. To go. For this reason, the difference between the theoretical energy indicated by the broken line and the actual energy indicated by the solid line gradually increases. At this time, the voltage value of the drive signal VCP gradually decreases from the voltage value increased in the immediately preceding first phase. Further, the voltage value of the drive signal VCN does not change from the analog ground voltage level VLP.

Subsequently, in the transfer phase of the second phase, the conduction state of the NMOS transistor 44 and the PMOS transistors 46 and 47 is turned on according to the voltage level of the drive control signals φ0 to φ4, and the conduction state of each MOS transistor is changed. Turns off. Then, the energy charged in the inductor 42 is transferred to the capacitor 41. Therefore, the voltage value V _{C41 at} both ends of the capacitor 41 and the energy of the capacitor 41 increase, the current value I _L42 flowing through the inductor 42 decreases from I ₂ (A) to 0 (A), and the energy of the inductor 42 is The energy corresponding to the increase of the capacitor 41 decreases. At this time, the voltage value of the drive signal VCP does not change from the voltage value decreased in the immediately preceding charging phase. Further, the voltage value of the drive signal VCN does not change from the analog ground voltage level VLP.

Subsequently, in the standby phase of the second phase, the PMOS transistors 46 and 47 are turned on according to the voltage levels of the drive control signals φ0 to φ4, and the other MOS transistors are turned off. become. Then, the current value I _L42 flowing through the inductor 42 becomes 0 (A). Therefore, in the standby phase, the voltage value V _{C41 at} both ends of the capacitor 41, the current value I _L42 flowing through the inductor 42, the voltage value V _{C15 at} both ends of the piezoelectric speaker 15, the energy of the capacitor 41, the energy of the inductor 42, and the piezoelectric speaker. The energy of 15 does not change. At this time, the voltage value of the drive signal VCP does not change from the voltage decreased in the immediately preceding charging phase. Further, the voltage value of the drive signal VCN does not change from the analog ground voltage level VLP.

In the second phase, the voltage value of the drive signal VCP is decreased to the analog ground voltage level VLP as shown in FIG. 9 while repeating the charging phase, the transfer phase, and the standby phase. However, the voltage value of the drive signal VCN is not changed from the analog ground voltage level VLP.
Subsequently, the operation phase of the piezoelectric speaker driving amplifier 14 is changed from the second phase to the third phase. As shown in FIG. 10, the third phase is also divided into three operation phases of a charging phase, a transfer phase, and a standby phase, as with each phase, and these operation phases are repeated.

First, in the charge phase of the third phase, the conduction state of the NMOS transistor 44 and the PMOS transistors 48 and 49 is turned on according to the voltage level of the drive control signals φ0 to φ4, and the conduction states of the other MOS transistors. Turns off. Then, the energy charged in the capacitor 41 is charged in the inductor 42. For this reason, the voltage value V _C41 across the capacitor 41 and the energy of the capacitor 41 decrease. The current value I _L42 flowing through the inductor 42 increases from 0 (A) to I ₁ (A), and the energy of the inductor 42 increases from 0 (J) by the energy corresponding to the decrease of the capacitor 41. Even in the third phase, the energy of the capacitor 41 changes as shown by broken lines in the figure if the resistance value of the wiring and each element is ignored, but the energy is little by little due to the resistance of the wiring and each element. Since it is consumed, it changes as shown by the solid line. At this time, the voltage values of the drive signals VCP and VCN do not change from the analog ground voltage level VLP.

Subsequently, in the transfer phase of the third phase, according to the voltage level of the drive control signals φ0 to φ4, the PMOS transistors 45, 48, and 49 are turned on, and the other MOS transistors are turned on. Turns off. Then, the energy charged in the inductor 42 is transferred to the piezoelectric speaker 15. Therefore, current I _L flowing through the inductor 42 with decreases from I ₁ (A) to 0 (A), the energy of the inductor 42 decreases. The voltage value V _{C15 at} both ends of the piezoelectric speaker 15 and the energy of the piezoelectric speaker 15 increase from 0 (J) by the energy corresponding to the decrease of the inductor 42. At this time, the voltage value of the drive signal VCP does not change from the analog ground voltage level VLP. However, the voltage value of the drive signal VCN gradually increases from the analog ground voltage level VLP.

Subsequently, in the standby phase of the third phase, the PMOS transistors 48 and 49 are turned on according to the voltage levels of the drive control signals φ0 to φ4, and the other MOS transistors are turned off. become. Thus, in the standby phase, energy is not transferred from the inductor 42, and the current value I _L42 flowing through the inductor 42 is completely maintained at 0 (A). Therefore, in the standby phase, the voltage value V _{C41 at} both ends of the capacitor 41, the current value I _L42 flowing through the inductor 42, the voltage value V _{C15 at} both ends of the piezoelectric speaker 15, the energy of the capacitor 41, the energy of the inductor 42, and the piezoelectric speaker. The energy of 15 does not change. At this time, the voltage value of the drive signal VCP does not change from the analog ground voltage level VLP. Further, the voltage value of the drive signal VCN does not change from the voltage value increased in the immediately preceding charging phase.

In the third phase, the voltage value of the drive signal VCN is increased as shown in FIG. 10 while repeating the charging phase, the transfer phase, and the standby phase. However, the voltage of the drive signal VCP is not changed from the analog ground voltage level VLP.
Subsequently, the operation phase of the piezoelectric speaker driving amplifier 14 is changed from the third phase to the fourth phase. As shown in FIG. 11, the fourth phase is also divided into three operation phases, a charge phase, a transfer phase, and a standby phase, as in the operation phases from the first phase to the fourth phase. The operation phase is repeated.

First, in the charge phase of the fourth phase, the PMOS transistors 45, 48, and 49 are turned on according to the voltage levels of the drive control signals φ0 to φ4, and the ground MOS transistors are turned off. It becomes a state. Then, the energy charged in the piezoelectric speaker 15 is charged in the inductor 42. For this reason, the voltage value V _C15 across the piezoelectric speaker 15 and the energy of the piezoelectric speaker 15 are reduced. Then, the current value I _L42 flowing through the inductor 42 increases from 0 (A) to I ₂ (A), and the energy of the inductor 42 increases by the energy corresponding to the decrease of the piezoelectric speaker 15. However, in the fourth phase, the energy of the capacitor 41 is indicated by a broken line in the figure if the wiring and the resistance of each element are ignored, but the energy is consumed little by little by the wiring and the resistance of each element. To go. For this reason, the difference between the theoretical energy indicated by the broken line and the actual energy indicated by the solid line gradually increases. At this time, the drive signal VCP does not change from the analog ground voltage level VLP. The drive signal VCN gradually decreases from the voltage value increased in the immediately preceding third phase.

Subsequently, in the transfer phase of the fourth phase, the conduction state of the NMOS transistor 44 and the PMOS transistors 48 and 49 is turned on according to the voltage level of the drive control signals φ0 to φ4, and the conduction of the other MOS transistors. The state is turned off. Then, the energy charged in the inductor 42 is transferred to the capacitor 41. Therefore, the voltage value V _{C41 at} both ends of the capacitor 41 and the energy of the capacitor 41 increase, the current value I _L42 flowing through the inductor 42 decreases from I ₂ (A) to 0 (A), and the energy of the inductor 42 is The energy corresponding to the increase of the capacitor 41 decreases. At this time, the voltage value of the drive signal VCN does not change from the voltage value decreased in the immediately preceding charging phase. Further, the voltage value of the drive signal VCP does not change from the analog ground voltage level VLP.

Subsequently, in the standby phase of the fourth phase, the PMOS transistors 48 and 49 are turned on according to the voltage levels of the drive control signals φ0 to φ4, and the other MOS transistors are turned off. become. Then, the current value I _L42 flowing through the inductor 42 becomes 0 (A). Therefore, in the standby phase, the voltage value V _{C41 at} both ends of the capacitor 41, the current value I _L42 flowing through the inductor 42, the voltage value V _{C15 at} both ends of the piezoelectric speaker 15, the energy of the capacitor 41, the energy of the inductor 42, and the piezoelectric speaker. The energy of 15 does not change. At this time, the voltage value of the drive signal VCP does not change from the analog ground voltage level VLP. Further, the voltage value of the drive signal VCN does not change from the decreased voltage value.

In the fourth phase, the voltage value of the drive signal VCN is decreased to the analog ground voltage level VLP as shown in FIG. 11 while repeating the charging phase, the transfer phase, and the standby phase. However, the voltage value of the drive signal VCP is not changed from the analog ground voltage level VLP.
As described above, the voltage value of the drive signal VCP and the voltage value of the drive signal VCN are alternately changed while repeating each operation phase from the first phase to the fourth phase. However, the voltage value of the drive signal VCN is not changed from the analog ground voltage level VLP while the voltage value of the drive signal VCP is changed. Further, while the voltage value of the drive signal VCN is changed, the voltage value of the drive signal VCP is not changed from the analog ground voltage level VLP.

  Since the energy of the capacitor 41 is consumed by the wiring and the resistance of each element in each operation phase, it is necessary to charge the capacitor 41 with energy corresponding to the consumed energy. For this reason, as shown in FIG. 12, before the fourth phase is finished and the first phase is reached, the operation phase of the piezoelectric speaker driving amplifier 14 becomes the energy supplement phase again.

As described with reference to FIG. 7, the energy replenishment phase is divided into two operation phases, a standby phase and a charging phase.
First, the operation phase of the piezoelectric speaker driving amplifier 14 is the charging phase of the energy replenishment phase. In this charging phase, according to the voltage levels of drive control signals φ0 to φ4, only the PMOS transistor 43 is turned on and the other MOS transistors are turned off. Then, energy is charged in the capacitor 41 from the driving power supply. However, the switching drive circuit 24 drives the capacitive load by charging the capacitor 41 again via the inductor 42 of the switching drive circuit 24 without wastefully consuming the energy transferred to the piezoelectric speaker 15 by a resistor or the like. It is reused to do. Therefore, in this energy replenishment phase, it is only necessary to charge only the energy consumed by the wiring, the resistance of each element, and the like, instead of charging the capacitor 41 with all the energy corresponding to the power supply voltage VDD. When the capacitor 41 starts to be charged again with energy corresponding to the power supply voltage VDD, the energy charged in the capacitor 41 increases to the same energy as when the first energy replenishment phase is completed. At this time, the voltage values of drive signals VCP and VCN do not change from analog ground voltage level VLP.

Here, the operation phase of the piezoelectric speaker driving amplifier 14 becomes the standby phase of the energy replenishment phase again. In this standby phase, the conduction states of all the MOS transistors of the PMOS transistors 43 and 45 to 49 and the NMOS transistor 44 are turned off by the voltage levels of the drive control signals φ0 to φ4. For this reason, in the standby phase, the voltage value V _C41 across the capacitor 41 and the current value I _L42 flowing through the inductor 42 do not change. At this time, drive signals VCP and VCN are not changed from analog ground voltage level VLP.

In the operation phase of the piezoelectric speaker drive amplifier 14, after the energy replenishment phase, each operation phase from the first phase to the fourth phase is repeated as described above.
In the description here, the piezoelectric speaker driving amplifier 14 repeats the charging phase, the transfer phase, and the standby phase three times in each operation phase from the first phase to the fourth phase. However, the number of times the charge phase, transfer phase, and standby phase are repeated is not limited to this, and may be any number. Then, after the operation phases from the first phase to the fourth phase are repeated an arbitrary number of times, the energy replenishment phase may be performed to charge only the energy consumed by the wiring, the resistance of each element, and the like. Therefore, the piezoelectric speaker drive amplifier 14 can drive the piezoelectric speaker 15 with low power consumption.

(Circuit configuration of the gate driver circuit 23)
Next, the circuit configuration of the gate driver circuit 23 of the piezoelectric speaker driving amplifier 14 will be described with reference to FIG.
FIG. 13 is a block diagram showing a circuit configuration of the gate driver circuit 23 of the piezoelectric speaker driving amplifier 14. Note that the gate driver circuit 23 described below is merely an example of a logic circuit for executing each operation phase as shown in FIG. The gate driver circuit 23 shown in FIG. 13 includes a first phase determination circuit 23a and a second phase determination circuit 23b.

  First, the first phase determination circuit 23a receives at least the PWM signal Sp, the current monitoring result signal Si, and the comparison result signal Sb, and the voltage level of the current monitoring result signal Si and the voltage of the comparison result signal Sb. The operation phase of the piezoelectric speaker drive amplifier 14 is determined based on the combination with the level. Then, the first phase determination circuit 23a outputs the drive control signals φ0 to φ2 at the H level or the L level.

When the comparison result signal Sb is at the L level, the first phase determination circuit 23a selects the operation phase of the piezoelectric speaker drive amplifier 14 as the first phase for increasing the voltage value of the drive signal VCP, or the drive signal VCN. The third phase for increasing the voltage is determined.
At this time, the first phase determination circuit 23a outputs the drive control signal φ1 at the H level while the PWM signal Sp is at the H level (the charging phase of the first phase or the charging phase of the third phase). On the other hand, the first phase determination circuit 23a operates while the PWM signal Sp is at the L level (the transfer phase of the first phase, the standby phase of the first phase, the transfer phase of the third phase, and the third phase). In the standby phase), the drive control signal φ1 is output at the L level.

  Further, the first phase determination circuit 23a outputs the drive control signal φ2 at the L level while the current monitoring result signal Si is at the H level (the transfer phase of the first phase and the transfer phase of the third phase). On the other hand, the first phase determination circuit 23a determines that the current monitoring result signal Si is at the H level (the charge phase of the first phase, the standby phase of the first phase, the charge phase of the third phase, and the third phase). During the standby phase, the drive control signal φ2 is output at the H level.

On the other hand, when the comparison result signal Sb is at the H level, the first phase determination circuit 23a performs the operation phase of the piezoelectric speaker drive amplifier 14 in the second phase in which the voltage value of the drive signal VCP is decreased, or in the drive The fourth phase in which the voltage value of the signal VCN is decreased is determined.
At this time, the first phase determination circuit 23a outputs the drive control signal φ2 at the L level while the PWM signal Sp is at the H level (the charging phase of the second phase and the charging phase of the fourth phase). On the other hand, the first phase determination circuit 23a operates while the PWM signal Sp is at the L level (the second phase transfer phase, the second phase standby phase, the fourth phase transfer phase, and the fourth phase transfer phase). In the standby phase), the drive control signal φ2 is output at the H level.

  Further, the first phase determination circuit 23a outputs the drive control signal φ1 at the H level while the current monitoring result signal Si is at the H level (the second phase transfer phase and the fourth phase transfer phase). On the contrary, the first phase determination circuit 23a determines that the current monitoring result signal Si is at L level (second phase charging phase, second phase standby phase, fourth phase charging phase, and fourth phase During the standby phase, the drive control signal φ1 is output at the L level.

  The first phase determination circuit 23a outputs the drive control signal φ0 at H level when the operation phase of the piezoelectric speaker drive amplifier 14 is determined to be any operation phase from the first phase to the fourth phase. To do. However, after each operation phase from the first phase to the fourth phase is repeated an arbitrary number of times, the first phase determination circuit 23a determines the operation phase of the piezoelectric speaker drive amplifier 14 as the energy supplement phase. To do. At that time, the first phase determination circuit 23a outputs the drive control signal φ0 at the L level while the PWM signal Sp is at the H level (charging phase of the energy replenishment phase). On the contrary, the first phase determination circuit 23a outputs the drive control signal φ0 at the H level while the PWM signal Sp is at the L level (standby phase of the energy replenishment phase). The first phase determination circuit 23a outputs the drive control signal φ1 at the L level and outputs the drive control signal φ2 at the H level during the energy replenishment phase.

  The second phase determination circuit 23b receives at least the PWM signal Sp and the comparison result signals Sa and Sb, and is based on a combination of the voltage level of the comparison result signal Sa and the voltage level of the comparison result signal Sb. Thus, the operation phase of the piezoelectric speaker driving amplifier 14 is determined. Then, the second phase determination circuit 23b outputs the drive control signal φ3 at the H level or the L level.

  When the comparison result signal Sa is at the L level, the second phase determination circuit 23b performs the operation phase of the piezoelectric speaker driving amplifier 14, the first phase for increasing the voltage value of the driving signal VCP, or the driving signal VCP. The second phase for decreasing the voltage value is determined. At this time, the second phase determination circuit 23b outputs the drive control signal φ3 at the L level and outputs the drive control signal φ4 at the H level in accordance with the cycle of the PWM signal Sp.

  On the other hand, when the comparison result signal Sa is at the H level, the second phase determination circuit 23b performs the operation phase of the piezoelectric speaker drive amplifier 14 in the third phase in which the voltage value of the drive signal VCN is increased, or in the drive The fourth phase in which the voltage value of the signal VCN is decreased is determined. At this time, the second phase determination circuit 23b outputs the drive control signal φ3 at the H level and the drive control signal φ4 at the L level in accordance with the cycle of the PWM signal Sp.

  The first phase determination circuit 23a determines the operation phase of the piezoelectric speaker driving amplifier 14 as an energy supplement phase. Then, in response to the fact that the second phase determination circuit 23b is in the energy replenishment phase from the first phase determination circuit 23a, the second phase determination circuit 23b outputs the drive control signals φ3 and φ4 in accordance with the period of the PWM signal Sp during the energy replenishment phase. Output at H level.

(Circuit configuration of the switching drive circuits 100 and 200)
Next, the circuit configuration of the switching drive circuits 100 and 200 according to the modification of the switching drive circuit 24 will be described with reference to FIGS. 14 and 15.
FIG. 14 is a circuit diagram showing a circuit configuration of a switching drive circuit 100 according to a first modification of the switching drive circuit 24. FIG. 15 is a circuit diagram showing a circuit configuration of a switching drive circuit 200 according to a second modification of the switching drive circuit 24. In the drawings, the same elements and the like are denoted by the same reference numerals, and the description of these overlapping circuits is omitted.

The switching drive circuit 100 shown in FIG. 14 includes the same elements as the switching drive circuit 24 shown in FIG. However, the switching drive circuit 100 is different from the switching drive circuit 24 in that it further includes an NMOS transistor 101 and a PMOS transistor 102.
The NMOS transistor 101 is connected between the positive terminal of the capacitor 41 and the terminal on the driving power supply side of the inductor 42. The NMOS transistor 101 is an element for switching the conduction state between the on state and the off state by the drive control signal φ1 just like the NMOS transistor 44. Similar to the NMOS transistor 44, the NMOS transistor 101 functions as a charging direction switching element.

  The PMOS transistor 102 is connected between the negative terminal of the piezoelectric speaker driving amplifier 14 and the terminal on the driving power source side of the inductor 42. The PMOS transistor 102 is an element for switching the conduction state between the on state and the off state by the drive control signal φ2 just like the PMOS transistor 45. Similar to the PMOS transistors 45 to 49, the PMOS transistor 102 functions as a polarity switching switching element, and serves as both a positive side switching element and a negative side switching element. It is not always necessary to connect the PMOS transistor 102 as in the case of the PMOS transistor 45.

In the switching drive circuit 24, the NMOS transistor 44 is one of a circuit formed with the conduction state of the NMOS transistor 44 turned on and a circuit formed with the conduction state of the PMOS transistors 45 to 49 turned on. Only the circuit formed when the conductive state is turned on is connected to the ground. However, in the switching drive circuit 100, the switching drive is that the circuit formed by turning on the PMOS transistors 45 to 49, 102 is connected to a power supply different from the drive power supply. Different from the circuit 24. That is, the switching drive circuit 100 is different in the reference voltage level in circuit operation from the switching drive circuit 24. However, in the switching drive circuit 100 as well as the switching drive circuit 24, the first to fourth phases described above are used. The piezoelectric speaker 15 can be driven while the voltage values of the drive signals VCP and VCN are alternately changed in accordance with the operation phases described above.

  As another modification, the switching drive circuit 200 shown in FIG. 15 includes the same elements as the switching drive circuit 100 shown in FIG. However, the switching drive circuit 200 is different from the switching drive circuit 100 in the connection relationship between the elements constituting the circuit. The switching drive circuit 200 includes a closed circuit formed when the NMOS transistors 44 and 101 are turned on, and a closed circuit formed when the PMOS transistors 45 to 49 and 102 are turned on. Are connected to a common ground.

Also in the switching drive circuit 200, the piezoelectric speaker 15 can be driven by alternately changing the voltage values of the drive signals VCP and VCN by the above-described control method. Of course, the closed circuit formed by the conductive state of the NMOS transistors 44 and 101 and the closed circuit formed by the conductive state of the PMOS transistors 45 to 49 and 102 may be connected to different grounds.
Note that each of the switching drive circuits 24, 100, and 200 described above can be configured by an IC and an external element connected to the IC.

(Circuit configuration of the switching drive circuits 300, 400, 500 when configured as an IC)
Next, the circuit configuration of the switching drive circuits 300, 400, 500 in which the switching drive circuits 24, 100, 200 are configured as ICs will be described with reference to FIGS.
FIG. 16 is a circuit diagram showing a circuit configuration of the switching drive circuit 300 when the switching drive circuit 24 is configured as an IC. FIG. 17 is a circuit diagram showing a circuit configuration of the switching drive circuit 400 when the switching drive circuit 100 is configured as an IC. FIG. 18 is a circuit diagram showing a configuration of the switching drive circuit 500 when the switching drive circuit 200 is configured as an IC.

  First, in the switching drive circuit 300 shown in FIG. 16, three elements of the capacitor 41, the inductor 42, and the PMOS transistor 43 of the switching drive circuit 24 are external elements connected to the IC 310. In the switching drive circuit 300, the remaining elements constituting the switching drive circuit 24 excluding the external elements are ICs 310.

The piezoelectric speaker 15 is connected to the IC 310 via the external connection pins 301 and 302 of the IC 310. The capacitor 41 is connected to the IC 310 via the external connection pins 303 and 304 of the IC 310. The inductor 42 is connected to the IC 310 via the external connection pins 304 and 305.
In short, in the switching drive circuit 300, the external elements of the capacitor 41, the inductor 42 and the PMOS transistor 43 are connected to the IC 310 to function as a switching drive circuit.

  In this switching drive circuit 300, only a part of the elements of the switching drive circuit 24 is provided as an external element, and the operation and the connection relation between the elements are the operation and connection relation of the switching drive circuit 24. And not really different. However, in the switching drive circuit 300, the capacitor 41, the inductor 42, and the PMOS transistor 43 are external elements connected to the IC 310. Therefore, for example, in the case of the capacitor 41, the switching drive circuit 300 can be configured by selecting an element having a desired capacitance value.

  Similarly, in the switching drive circuit 400 shown in FIG. 17, the capacitor 41, the inductor 42, and the PMOS transistor 43 of the switching drive circuit 200 are external elements. Further, the switching drive circuit 400 forms an IC 410 from the remaining elements constituting the switching drive circuit 24 other than the external elements. Also in the switching drive circuit 400, the external elements of the capacitor 41, the inductor 42 and the PMOS transistor 43 are connected to the IC 410 via the external connection pins 301 to 306.

Also in the switching drive circuit 500 shown in FIG. 18, external elements of the capacitor 41, the inductor 42, and the PMOS transistor 43 are connected to the IC 510 via the external connection pins 301 to 306.
The operations of the switching drive circuits 400 and 500 are substantially the same as the operations of the switching drive circuits 100 and 200.

(Summary)
The piezoelectric speaker drive amplifier 14 described in the present embodiment uses the inductor 42 to charge the capacitor 41 again by using the inductor 42 without consuming the energy transferred to the piezoelectric speaker 15 as much as possible. It is reused as energy for driving 15. At that time, the gate driver circuit 23 switches the conduction state of each MOS transistor of the switching drive circuit 24 in accordance with each operation phase from the first phase to the fourth phase. In particular, when the gate driver circuit 23 switches the conduction state of the PMOS transistors 45 to 49, the speaker driving amplifier 14 generates a differential signal drive signal with as few switching elements as possible, and the drive signal Thus, the piezoelectric speaker 15 can be driven.

  The driving amplifier and the driving driver of the present invention are a driving amplifier and a driving driver capable of driving a capacitive load such as a piezoelectric speaker included in an information device such as a portable music player, a mobile phone, and a portable DVD player. Can be used.

DESCRIPTION OF SYMBOLS 10 ... Portable music player 11 ... Control part 12 ... Touch panel 13 ... Memory 14 ... Piezoelectric speaker drive amplifier 15 ... Piezoelectric speaker 16 ... Lithium ion battery 21 ... Error suppression circuit 22 ... PWM circuit 23 …… Gate driver circuit 23a …… First phase determination circuit 23b …… Second phase determination circuit 24 …… Switching drive circuit 25a, 25b …… LPF circuit 30 …… Current monitoring circuit 31a …… First comparison circuit 31b …… Second comparison circuit 41 …… Capacitor 42 …… Inductor 43, 45 to 47 …… PMOS transistor 44 …… NMOS transistor 100 …… Switching drive circuit 101 …… NMOS transistor 200, 300, 400, 500 …… Switching drive circuit

Claims (11)

A first charge / discharge element charged with energy for driving the capacitive load;
A second charging / discharging element in which energy charged in the first charging / discharging element or the capacitive load is temporarily charged;
A state in which the energy charged in the first charge / discharge element is charged into the capacitive load via the second charge / discharge element; and the energy charged in the capacitive load in the second charge / discharge element A charging direction switching element that alternately switches the state of charging the first charging / discharging element via
The state in which the energy charged in the first charge / discharge element by the charge direction switching element is charged in the capacitive load, and the energy charged in the capacitive load in the first charge / discharge element When alternately switching the state to be performed, the state in which the energy charged in the first charge / discharge element or the capacitive load is charged from the positive terminal side of the capacitive load, and the first charge / discharge element or A switching element for polarity switching that alternately switches between a state in which the energy charged in the capacitive load is charged from the negative electrode terminal side of the capacitive load;
A control circuit that controls the conduction state of the charging direction switching switching element and the polarity switching switching element to be switched to either an on state or an off state; and
The control circuit is configured to change a voltage value of one of driving signals, which is a differential signal for driving the capacitive load, according to energy charged in the capacitive load, Switching of the conduction state of the charging direction switching switching element and the polarity signal switching switching element is performed so that a state in which a voltage value of a signal is changed alternately according to energy charged in the capacitive load is repeated. A drive driver characterized by controlling. An energy replenishing element for replenishing energy to the first charge / discharge element from a driving power supply that outputs a power supply voltage;
The control circuit includes:
The driving driver according to claim 1, wherein a conduction state of the energy replenishing element is controlled so that energy is replenished to the first charge / discharge element from the driving power supply. A first comparison circuit that compares the voltage value of one of the input signals, which is a differential signal, with the voltage value of the other signal, and outputs a comparison result signal having a voltage level corresponding to the comparison result; ,
A second comparison circuit that compares a voltage value of one of the drive signals with a voltage value of the other signal and outputs a comparison result signal having a voltage level according to the comparison result;
The control circuit includes:
At least the voltage level of the comparison result signal output from the first comparison circuit, the voltage level of the comparison result signal output from the second comparison circuit, and the voltage level of the modulation signal obtained by modulating the input signal Based on the combination of
A voltage value of one of the driving signals is increased according to energy charged in the capacitive load, and a voltage value of the other signal is set to an analog ground voltage level that is a predetermined voltage level. Phase,
A second phase in which the voltage value of one of the drive signals is decreased according to the energy charged in the capacitive load, and the voltage value of the other signal is brought to the analog ground voltage level;
A third phase in which the voltage value of the other signal of the drive signal is increased according to the energy charged in the capacitive load, and the voltage value of the other signal is set to the analog ground voltage level;
Each of the operation phases includes a fourth phase in which the voltage value of the other signal of the drive signal is decreased according to the energy charged in the capacitive load and the voltage value of the other signal is set to the analog ground voltage level. 3. The driving driver according to claim 1, wherein switching of the conduction state of the charging direction switching element and the polarity switching element is controlled to be repeated. 4. The control circuit includes:
Before the first phase, and after each operation phase from the first phase to the fourth phase is repeated a predetermined number of times and before the first phase again, the drive power supply 4. The driving driver according to claim 3, wherein a conduction state of the energy replenishing element is controlled so that an energy replenishing phase for replenishing energy to the first charge / discharge element is performed. It is monitored whether or not the current flowing through the second charge / discharge element is in a state from when it starts to decrease until it reaches 0 (A), and a current monitoring result signal having a voltage level corresponding to the monitoring result is obtained. An output current monitoring circuit;
With
The control circuit includes:
At least in each operation phase from the first phase to the fourth phase, based on the combination of the voltage level of the current monitoring result signal output from the current monitoring circuit and the voltage level of the modulation signal obtained by modulating the input signal And
A charging phase for charging the second charging / discharging element with the energy charged in the first charging / discharging element or the capacitive load;
A transfer phase for transferring energy charged in the second charge / discharge element to the capacitive load or the first charge / discharge element;
Energy charged in the first charge / discharge element, the second charge / discharge element, or the capacitive load between the first charge / discharge element, the second charge / discharge element, and the capacitive load The switching of the conduction state of the switching element for switching the charge direction and the switching element for switching the polarity is controlled so that each operation phase is repeated with a standby phase in which charging and transfer are not performed. Or the driving driver according to 4; The control circuit includes:
In the energy replenishment phase,
A charging phase for charging the first charging / discharging element from the driving power source;
The switching of the conduction state of the energy replenishing element is controlled so as to be in each operation phase with a standby phase in which the first charging / discharging element is not charged with energy from the driving power supply. 5. The driving driver according to 5. The first charge / discharge element is:
Connected between the driving power supply and the ground,
The second charge / discharge element is:
Connected between the positive terminal of the first charge / discharge element and the positive terminal of the capacitive load;
The charging direction switching element is
Between the capacitive load side terminal of the second charge / discharge element and the negative electrode terminal of the first charge / discharge element, or the positive terminal of the first charge / discharge element, and the second charge / discharge element. Among the terminals on the drive power supply side, and is connected at least between the capacitive load side terminal of the second charge / discharge element and the negative electrode terminal of the first charge / discharge element,
The polarity switching switching element is:
Connected between the capacitive load side terminal of the second charge / discharge element and the positive terminal of the capacitive load, and the negative terminal of the capacitive load, and the second charge / discharge element A positive-side switching element connected between the terminal on the drive power supply side;
Connected between the capacitive load side terminal of the second charge / discharge element and the negative terminal of the capacitive load, and the positive terminal of the capacitive load, and the second charge / discharge element A negative-side switching element connected between the terminals on the drive power supply side,
The control circuit includes:
In the charging phase of the first phase, the transfer phase of the second phase, the charging phase of the third phase, and the transfer phase of the fourth phase, the conduction state of the switching element for switching the charging direction is turned on. By controlling so that a closed circuit is formed,
At the time of the transfer phase of the first phase and the charge phase of the second phase, control is performed so that a closed circuit is formed by turning on the conduction state of the positive-side switching element,
In the transfer phase of the third phase and the charge phase of the fourth phase, control is performed so that a closed circuit is formed by turning on the conductive state of the negative side switching element,
In the standby phase of the first phase, the standby phase of the second phase, the standby phase of the third phase, and the standby phase of the fourth phase, the switching element for switching the charge direction, the positive-side switching element, and The driver for driving according to claim 5 or 6, wherein control is performed so that a closed circuit is not formed when the conduction state of the negative-side switching element is turned off. The energy replenishing element is:
Connected between the driving power source and the positive terminal of the first charge / discharge element;
The control circuit includes:
During the charge phase of the energy replenishment phase, control so that the conduction state of the energy replenishment element is turned on,
The driving driver according to claim 7, wherein, in the standby phase of the energy replenishment phase, control is performed so that the conduction state of the energy replenishment element is turned off. The control circuit includes:
When controlling so that a closed circuit is formed by turning on the conduction state of the switching element for charging direction switching, the closed circuit is controlled to be connected to the ground,
When controlling the positive-side switching element and the negative-side switching element to be turned on to form a closed circuit, the closed circuit is a power supply different from the driving power supply, the ground The drive driver according to claim 7, wherein the driver is controlled to be connected to a ground different from the ground. A modulation circuit that outputs a modulated signal obtained by modulating the input signal;
The drive driver according to any one of claims 1 to 9, wherein a drive signal that is a differential signal for driving the capacitive load is generated based on the modulation signal output from the modulation circuit. A driving amplifier comprising the driving amplifier. Capacitive load,
An input signal generation circuit for generating an input signal;
The drive amplifier according to claim 10, wherein a drive signal for driving the capacitive load is output based on an input signal generated by the input signal generation circuit;
An information device comprising: a drive power supply that supplies a predetermined power supply voltage to the input signal generation circuit and the drive amplifier.

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