Drive circuit and method for driving capacitive load, and speaker device and electronic device including drive circuit

Abstract

The embodiment of the invention provides a driving circuit for driving a capacitive load, such as a piezoelectric MEMS acoustic transducer. The driving circuit comprises a booster circuit used for boosting the load voltage at the two ends of the capacitive load; the step-down circuit is used for reducing the load voltage; and a controller for receiving an input signal and controlling the boost circuit and the buck circuit such that the load voltage is an amplified version of the input signal. The driving circuit further comprises an energy storage device which is used for storing the electric energy released from the capacitive load. The boost circuit is electrically connected between a power supply and the capacitive load, and the step-down circuit is electrically connected between the capacitive load and the energy storage device. And the energy storage device is separated from the power supply.

Description

Technical Field

[0001] The present invention generally relates to a driving circuit, and more particularly to a driving circuit for driving a capacitive load. Background Art

[0002] Recently, piezoelectric microelectromechanical system (MEMS) acoustic transducers are becoming an important technology for speaker devices including earbuds, headphones, etc. in audio mobile applications such as smartphones, tablets, and wearable devices. At least one piezoelectric MEMS acoustic transducer is used to drive the diaphragm of the speaker device. Compared with traditional transducers such as electrodynamic acoustic transducers, piezoelectric MEMS acoustic transducers have a small unit size and can achieve precise vibration control, thereby achieving system miniaturization and high sound quality.

[0003] Some piezoelectric MEMS acoustic transducers require a high voltage input signal (e.g., a peak-to-peak voltage of 30V, i.e., 30Vpp) that is higher than the power supply voltage from the power supply in order to generate a sufficient sound pressure level. In addition, the input signal may need to carry a DC offset voltage. Such a signal is inconvenient for mobile devices with limited battery capacity. In addition, the piezoelectric MEMS acoustic transducer includes a piezoelectric layer disposed between a top electrode and a bottom electrode, and therefore, the piezoelectric MEMS acoustic transducer can be modeled as a capacitive load (i.e., a capacitor) in an equivalent circuit. Therefore, when the piezoelectric MEMS acoustic transducer is driven to vibrate the diaphragm to emit sound into the air, charging and discharging operations are repeatedly performed. However, most of the electrical energy transmitted to the piezoelectric MEMS acoustic transducer is not converted into acoustic energy, but is discharged to the ground. In other words, most of the electrical energy has no effect on the acoustic emission, and a large amount of apparent power is wastedly transmitted to the piezoelectric MEMS acoustic transducer. In addition, this large amount of apparent power causes a large amount of apparent current to flow through peripheral circuits such as amplifiers, thereby generating a large power loss. Therefore, it may be desirable to implement an energy recovery function or operation in the driving circuit to reuse the power delivered to the capacitive load for low power operation in mobile applications.Some energy recovery schemes have been proposed, however, the known schemes have their own disadvantages.

[0004] Therefore, there remains a need for an improved solution for energy recovery operation from such capacitive loads. Summary of the invention

[0005] The purpose of the embodiments of the present invention is to provide a driving circuit and method for driving a capacitive load to effectively realize energy recovery operation from the capacitive load. The embodiments of the present invention also provide a speaker device including such a driving circuit and an electronic device including such a speaker device.

[0006] According to a first aspect, a driving circuit for driving a capacitive load is provided. The driving circuit comprises: a boost circuit for increasing the load voltage across the capacitive load; a buck circuit for reducing the load voltage; and a controller for receiving an input signal and controlling the boost circuit and the buck circuit so that the load voltage is an amplified version of the input signal. The driving circuit also comprises: an energy storage device for storing electrical energy released from the capacitive load. The boost circuit is electrically connected between a power supply and the capacitive load, and the buck circuit is electrically connected between the capacitive load and the energy storage device. The energy storage device is separated from the power supply. In other words, the energy storage device is not electrically connected to a power supply.

[0007] An energy storage device separated from the power supply can store the electrical energy released from the capacitive load, realizing energy recovery operation without affecting the supply voltage of the power supply.

[0008] In a possible implementation of the first aspect, the energy storage device may be used to supply electrical energy to at least one other device or system separated from the drive circuit. Therefore, the electrical energy stored in the energy storage device may be reused for at least one other device or system.

[0009] In a possible implementation of the first aspect, the drive circuit may further include: a selection switch having two input terminals and an output terminal, one of the two input terminals being connected to the power supply, the other of the two input terminals being connected to the energy storage device, and the output terminal being connected to the boost circuit. The selection switch may be controlled so that the power supply or the energy storage device supplies electrical energy to the boost circuit. In this way, the electrical energy stored in the energy storage device may be reused in the drive circuit itself.

[0010] In a possible implementation of the first aspect, the drive circuit may further include: a sensing block for sensing the electric energy stored in the energy storage device and controlling the selection switch according to the sensed electric energy. The sensing block may be separated from the controller or integrated into the controller. In this way, the selection switch may be controlled according to the amount of actual electric energy stored in the energy storage device.

[0011] In a possible implementation of the first aspect, the sensing block may also be used to: compare the sensed electrical energy with a reference value; in response to the sensed electrical energy being greater than or equal to the reference value, control the selection switch so that the energy storage device supplies electrical energy to the boost circuit. In this way, the electrical energy stored in the energy storage device can be reused for the drive circuit only when the stored energy is sufficient to drive the capacitive load. In addition, by appropriately setting the reference value, a more efficient energy recovery operation can be achieved.

[0012] In a possible implementation of the first aspect, the drive circuit may further include an accumulation block for monitoring the input signal and / or control signal provided from the controller to the boost circuit and the buck circuit to estimate the electrical energy stored in the energy storage device. The accumulation block may also be used to control the selection switch based on the estimated electrical energy. The accumulation block may be separated from the controller or integrated into the controller. In this way, the selection switch may be controlled without sensing the actual amount of electrical energy stored in the energy storage device 140.

[0013] In a possible implementation of the first aspect, the accumulation block may also be used to: compare the estimated electric energy with a reference value; in response to the estimated electric energy being greater than or equal to the reference value, control the selection switch so that the energy storage device supplies electric energy to the boost circuit. In this way, the electric energy stored in the energy storage device can be reused for the drive circuit only when the stored energy is sufficient to drive the capacitive load. In addition, by appropriately setting the reference value, a more efficient energy recovery operation can be achieved.

[0014] In a possible implementation of the first aspect, the amplified version of the input signal may be a linear amplified version of the input signal. This may be advantageous in many applications. For example, if the driving circuit receives an audio signal as an input signal and drives the piezoelectric MEMS acoustic transducer according to the audio signal, the linear amplification of the audio signal may reduce acoustic distortion, thereby obtaining high-quality sound.

[0015] In a possible implementation of the first aspect, the controller may be further configured to receive or detect a value indicative of the load voltage as a feedback input. Using such a feedback input may minimize an error in the load voltage.

[0016] In a possible implementation of the first aspect, the boost circuit may include a first inductor having one end connected to the power supply, a first switch connected between the other end of the first inductor and the ground, and a second switch connected between the other end of the first inductor and the capacitive load. Similarly, the step-down circuit may also include a second inductor having one end connected to the energy storage device, a third switch connected between the other end of the second inductor and the capacitive load, and a fourth switch connected between the other end of the second inductor and the ground. Then, the controller may control the first switch, the second switch, the third switch, and the fourth switch based on the input signal. In this way, the drive circuit may provide a higher voltage than the voltage provided from the power supply to the capacitive load. In addition, the drive circuit may transfer electrical energy from the capacitive load to the energy storage device without any complex circuit.

[0017] In a possible implementation of the first aspect, the boost circuit may include a first inductor having one end connected to the power supply, a first switch connected between the other end of the first inductor and the ground, and a first diode having an anode connected to the other end of the first inductor and a cathode connected to the capacitive load. In addition, the buck circuit may include a second inductor having one end connected to the energy storage device, a second switch connected between the other end of the second inductor and the capacitive load, and a second diode having an anode connected to the ground and a cathode connected to the other end of the second inductor. Then, the controller may control the first switch and the second switch based on the input signal. In this way, the control of the drive circuit may be further simplified.

[0018] According to a second aspect, a method for driving a capacitive load is provided. The method comprises the steps of receiving an input signal and controlling a load voltage across the capacitive load so that the load voltage is an amplified version of the input signal. The step of controlling the load voltage comprises supplying electrical energy from a power supply to the capacitive load via a boost circuit to charge the capacitive load; and transferring electrical energy from the capacitive load to an energy storage via a step-down circuit to discharge the capacitive load. The energy storage is separate from the power supply.

[0019] In a possible implementation manner of the second aspect, the method may further include the following steps: switching a selection switch so that the power supply or the energy storage device supplies electrical energy to the capacitive load through the boost circuit.

[0020] In a possible implementation of the second aspect, the method may further include the following steps: sensing the electric energy stored in the energy storage device, and the step of switching the selection switch includes controlling the selection switch according to the sensed electric energy. In another possible implementation of the second aspect, the method may further include the following steps: monitoring the input signal and / or control signal provided to the boost circuit and the buck circuit to estimate the electric energy stored in the energy storage device, and the step of switching the selection switch includes controlling the selection switch according to the estimated electric energy.

[0021] The second aspect and possible implementations thereof may have the same advantages as described in conjunction with the first aspect.

[0022] According to a third aspect, a speaker device is provided. The speaker device includes a piezoelectric MEMS acoustic transducer. The speaker device also includes: a circuit for receiving an input signal and power and driving the piezoelectric MEMS acoustic transducer as a capacitive load. The circuit includes the driving circuit according to the first aspect or any possible implementation of the first aspect.

[0023] According to a fourth aspect, an electronic device is provided, the electronic device comprising the speaker device according to the third aspect. The electronic device further comprises: a processor, configured to provide the input signal to the speaker device; and a battery, configured to supply the power to the speaker device.

[0024] The third aspect and the fourth aspect may have the same advantages as described in conjunction with the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 4 is a circuit diagram of a driving circuit for driving a capacitive load provided by a first embodiment of the present invention.

[0026] Figure 2 4 is a circuit diagram of a driving circuit for driving a capacitive load provided by a second embodiment of the present invention.

[0027] Figure 3 4 is a circuit diagram of a driving circuit for driving a capacitive load provided by a third embodiment of the present invention.

[0028] Figure 4 4 is a circuit diagram of a driving circuit for driving a capacitive load provided by a fourth embodiment of the present invention.

[0029] Figure 5 4 is a circuit diagram of a driving circuit for driving a capacitive load provided by a fifth embodiment of the present invention.

[0030] Figure 6 is a flow chart of a method for driving a capacitive load provided by an embodiment of the present invention.

[0031] Figure 7 Schematic diagram of a speaker device provided by an embodiment of the present invention.

[0032] Figure 8 is a schematic diagram of an electronic device provided by an embodiment of the present invention.

[0033] Throughout the drawings, the same or similar elements are indicated by the same or similar reference numerals. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the purpose, features and advantages of the embodiments of the present invention, the technical solutions in the preferred embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0035] In the present invention, the terms "comprising", "having" and any other variations are meant to cover a non-exclusive inclusion, for example, a process, method, circuit, device or system that includes a series of steps or elements is not necessarily limited to those steps or elements, but may include other steps or elements that are not explicitly listed or are not inherent to these processes, methods, circuits, devices or systems. In addition, the articles "a" and "an" used in the present invention are intended to include one or more items and can be used interchangeably with "one or more".

[0036] Figure 1 1 is a circuit diagram of a driving circuit 100 for driving a capacitive load 190 according to a first embodiment of the present invention. The driving circuit 100 includes a boost circuit 110 , a buck circuit 120 , a controller 130 and an energy storage device 140 .

[0037] The driving circuit 100 has a power node 170, an output node 172 and an energy recovery node 174, which are respectively connected to a power source 180, a capacitive load 190 and an energy storage device 140. In this way, the boost circuit 110 is electrically connected between the power source 180 and the capacitive load 190, and the buck circuit 120 is electrically connected between the capacitive load 190 and the energy storage device 140.

[0038] The boost circuit 110 is used to increase the load voltage across the capacitive load 190, that is, the voltage at the output node 172. The buck circuit 120 is used to reduce the load voltage across the capacitive load 190. The controller 130 is used to receive the input signal 135 and control the boost circuit 110 and the buck circuit 120 so that the load voltage is an amplified version of the input signal 135. In other words, the drive circuit 100 can be used as an amplifier for receiving the input signal 135, amplifying the input signal 135 to an amplified voltage, and outputting the amplified voltage at the output node 172. In some implementations, the drive circuit 100 is used to linearly amplify the input signal 135 and output a linear amplified version of the input signal 135 to the capacitive load 190. The details of the construction and operation of these components 110, 120 and 130 will be described below.

[0039] The power supply 180 can be a battery, such as a lithium-ion battery, etc. Alternatively, the power supply 180 can be another type of DC power supply, such as a supercapacitor or a rectifier. The power supply 180 can include an internal or external capacitor 185. It is understood that the capacitor 185 can be considered as part of the power supply 180.

[0040] The capacitive load 190 is an object to be driven by the driving circuit 100. For example, the capacitive load 190 may be a piezoelectric MEMS transducer for a speaker device. In this case, the controller 130 receives an audio signal as an input signal 135 from an audio circuit (not shown), and controls the boost circuit 110 and the buck circuit 120 to provide an amplified audio signal to the piezoelectric MEMS transducer 190. However, it should be noted that the capacitive load 190 may also be other types of capacitive loads, such as a MEMS ultrasonic transducer, an ultrasonic motor, etc.

[0041] The energy storage 140 is used to store the electrical energy released from the capacitive load 190. The energy storage 140 can be a capacitor and is shown as such throughout the drawings, but is not limited thereto. For example, the energy storage 140 can have a capacitance in the range of 1 μF to 10 μF. However, the capacitance of the energy storage 140 can be determined according to a specific application and / or implementation. The energy recovery node 174 to which the energy storage 140 is connected can be additionally connected to an external circuit, device or system 195 (hereinafter referred to as "another circuit" 195) separated from the drive circuit 100. For example, the other circuit 195 can be a peripheral circuit, a microphone circuit, an RF circuit, etc. of the drive circuit 100.

[0042] The energy storage 140 can be used to supply the electrical energy stored therein to another circuit 195. The energy storage 140 is separate from the power supply 180 (which may include the capacitor 185). In other words, the energy storage 140 is not electrically connected to the power supply 180. Therefore, the energy storage 140 can be used as an additional power source separate from the power supply 180.

[0043] Now, still refer to Figure 1 , describing the construction and operation of the boost circuit 110, the buck circuit 120 and the controller 130.

[0044] The boost circuit 110 may include a first inductor 112, a first switch 114, and a second switch 116. Figure 1 As shown, one end of the first inductor 112 is connected to the power supply 180, and the other end forms a node 118, to which the first switch 114 and the second switch 116 are both connected. The node 118 may be referred to herein as the "first inductor terminal" 118. The first switch 114 is connected between the first inductor terminal 118 and the ground. The second switch 116 is connected between the first inductor terminal 118 and the output node 172, to which the capacitive load 190 is connected. The first switch 114 and the second switch 116 are controlled (i.e., opened and closed) by the boost control signals SU1 and SU2 provided by the controller 130, respectively.

[0045] The boost circuit 110 can assume three states according to the open / closed states of the first switch 114 and the second switch 116. The three states include a first operating state, a second operating state, and a non-operating state.

[0046] In a first operating state in which the first switch 114 is closed and the second switch 116 is open, the first inductor terminal 118 is shorted to ground. Therefore, power is transferred from the power source 180 to the first inductor 112, and a current 113 (also referred to as a "first inductor current" 113) flowing through the first inductor 112 increases. The first operating state is followed by a second operating state.

[0047] In the second operating state in which the first switch 114 is open and the second switch 116 is closed, when the first inductor current 113 flows into the capacitive load 190, electric energy is transferred from the first inductor 112 to the capacitive load 190. Therefore, the first inductor current 113 decreases, and the load voltage at the output node 172 increases. In this way, through the first operating state and the second operating state, including the state transition therebetween, electric energy is transferred from the power supply 180 to the capacitive load 190, and the load voltage increases. The first operating state and the second operating state may be repeated so as to reach a target load voltage based on the input signal 135. Then, the boost circuit 110 is switched to the non-operating state.

[0048] In a non-operating state where both the first switch 114 and the second switch 116 are opened, electric energy is not transferred between the power source 180 and the capacitive load 190 .

[0049] It is understood that the first switch 114 and the second switch 116 should not be closed at the same time. If the first switch 114 and the second switch 116 are closed at the same time, the electric energy stored in the capacitive load 190 will flow to the ground through these switches by mistake. Therefore, the controller 130 is designed to avoid this situation.

[0050] The buck circuit 120 may include a second inductor 122, a third switch 124, and a fourth switch 126. Figure 1 As shown, one end of the second inductor 122 is connected to the energy storage 140, and the other end forms a node 128, to which the third switch 124 and the fourth switch 126 are both connected. The node 128 may be referred to herein as the "second inductor terminal" 128. The third switch 124 is connected between the second inductor terminal 128 and the output node 172, to which the capacitive load 190 is connected. The fourth switch 126 is connected between the second inductor terminal 128 and the ground. The third switch 124 and the fourth switch 126 are controlled (i.e., opened and closed) by the step-down control signals SD1 and SD2 provided by the controller 130, respectively.

[0051] The buck circuit 120 can assume three states according to the open / closed states of the third switch 124 and the fourth switch 126. The three states include a third operating state, a fourth operating state, and a non-operating state.

[0052] In the third operating state in which the first switch 124 is closed and the fourth switch 126 is open, electric energy is transferred from the capacitive load 190 to the second inductor 122, so that the potential at the second inductor terminal 128 becomes the same as the potential at the output node 172. Therefore, the current 123 (also referred to as "second inductor current" 123) flowing through the second inductor 122 increases, and the load voltage decreases. The third operating state is followed by a fourth operating state.

[0053] In the fourth operating state where the third switch 124 is open and the fourth switch 126 is closed, the electric energy accumulated in the second inductor supplies current to the energy storage 140 through the fourth switch 126. In this way, through the third operating state and the fourth operating state, including the state transition therebetween, the electric energy is transferred from the capacitive load 190 to the energy storage 140, and the load voltage is reduced. In other words, the electric energy released from the capacitive load 190 can be transferred to the energy storage 140 for energy recovery. The third operating state and the fourth operating state can be repeated to reach the target load voltage based on the input signal 135. Then, the buck circuit 120 is switched to the non-operating state.

[0054] In the non-operating state of the buck circuit 120 where both the third switch 124 and the fourth switch 126 are turned off, electric energy is not transferred between the capacitive load 190 and the energy storage 140 .

[0055] It is understood that the third switch 124 and the fourth switch 126 should not be closed at the same time. If the third switch 124 and the fourth switch 126 are closed at the same time, the electric energy stored in the capacitive load 190 will flow to the ground through these switches by mistake. Therefore, the controller 130 is designed to avoid this situation.

[0056] In order to implement the above operations of the boost circuit 110 and the buck circuit 120, the controller 130 is used to generate the boost control signal and the buck control signal SU1, SU2, SD1 and SD2 based on the input signal 135. Generally, the controller 130 can generate the control signals SU1, SU2, SD1 and SD2 using a pulse width modulation (PWM) scheme.

[0057] Preferably, the controller 130 is configured to receive or detect a value indicative of the load voltage as a feedback input FB, such as Figure 1. The controller 130 may compare the feedback input FB with the target load voltage, which may be an amplified version of the input signal 135. When the feedback input FB is lower than the target load voltage, the controller 130 generates boost control signals SU1 and SU2 to operate the boost circuit 110 as described above, thereby charging the capacitive load 190. When the feedback input FB is higher than the target load voltage, the controller 130 generates buck control signals SD1 and SD2 to operate the buck circuit 120 as described above, thereby discharging the capacitive load 190 and transferring the released energy to the energy storage device 140. The use of the feedback input FB may minimize the error in the load voltage. For example, the audio signal 135 may be linearly amplified, and acoustic distortion may be reduced, thereby obtaining high quality sound.

[0058] The energy recovery operation disclosed herein may provide several advantages as described below.

[0059] 1. The boost circuit 110 can act as a boost circuit to generate a high voltage (e.g., more than 30 Vpp) from a low voltage supplied by the power supply 180 without any additional power circuit or special power supply. For example, any waveform with a voltage up to 30 Vpp or higher can be generated from DC 3.7 V, which can be provided by a single lithium-ion battery. This high voltage can effectively drive capacitive loads, such as piezoelectric MEMS acoustic transducers.

[0060] 2. The energy stored in the capacitive load 190 can be transferred to the energy storage 140 without any complex circuitry and / or control. If additional circuitry is required, such as for polarity switching, level shifting, or electrical isolation, it may involve complex control, as well as additional energy consumption and space occupation.

[0061] 3. The energy stored in the capacitive load 190 can be recovered without affecting the supply voltage of the power supply 180.

[0062] In this regard, some known solutions suggest transferring the energy stored in the capacitive load back to the power supply by providing a circulation path between the capacitive load and the power supply. However, in practical applications, the energy flowing back to the power supply generates ripple noise, etc. on the power supply voltage. In high-performance audio applications or the operation of other components connected to the power supply, ripple noise on the supply voltage may cause serious problems.

[0063] Still considering the known scheme of recovering the energy released by the capacitive load by transferring it back to the power supply, for ease of description, the power supply is considered as a capacitor (see Figure 1 When all the energy stored in the load is released and then charged in the power supply capacitor, the following equation applies:

[0064] C L V L 2 / 2(released energy) = C S V ripple 2 / 2 (charged energy, used for recycling)

[0065] Among them, C L is the capacitance of the load, V L is the voltage across the load, C S is the capacitance of the power supply capacitor, V ripple is the magnitude of the ripple voltage on the power supply capacitor. According to this equation, the magnitude of the ripple voltage is determined by the ratio of the capacitance (i.e., C L / C S ). If the load has a large capacitance, the power supply capacitor should also have a large capacitance. In other words, in order to effectively suppress ripple noise, a large power supply capacitor is required, which may hinder system miniaturization.

[0066] In contrast, the technical solution disclosed herein transfers the released energy of the capacitive load 190 to the energy storage 140 through the step-down circuit 120. As described above, the energy storage 140 is separated from the power supply 180. Therefore, the power supply voltage from the power supply 180 (and / or the capacitor 185) is not affected by the energy recovery operation and remains clean and constant without ripple noise, etc.

[0067] 4. As another advantage, the energy recovery operation can be performed without substantial restrictions on operating conditions. Since the energy storage device 140 is separated from the power supply 180, the voltage across the energy storage device 140 can take various values ​​within a wide range, which is different from the known technical solutions described above. If the released energy is transmitted back to a power supply with an approximately constant voltage, the energy recovery operation can be substantially limited to a certain range of the load voltage, and when the load voltage exceeds this range, the stored energy may be dissipated. Specifically, when the load voltage is lower than the power supply voltage, the energy stored in the capacitive load may not be efficiently transmitted to the power supply. In contrast, in the technical solution disclosed herein, the energy recovery operation can continue to occur within a wider range of the load voltage.

[0068] Figure 1 The first illustrated embodiment may be modified to construct other embodiments, some of which are described below.

[0069] Figure 22 is a circuit diagram of a drive circuit 200 for driving a capacitive load provided by a second embodiment of the present invention. The drive circuit 200 is the same as the drive circuit 100 provided by the first embodiment, except that the boost circuit 110, the buck circuit 120 and the controller 130 are replaced by a boost circuit 210, a buck circuit 220 and a controller 230, respectively. The same components are provided with the same reference numerals and are not described in detail again.

[0070] More specifically, the boost circuit 210 includes a first diode 216 instead of the second switch 116 of the boost circuit 110. Similarly, the buck circuit 220 includes a second diode 226 instead of the fourth switch 126 of the buck circuit 120. In this case, the switch 114 in the boost circuit 210 and the switch 124 in the buck circuit 220 (which may be the same as the first switch 114 and the third switch 124 in the first embodiment) may be referred to as the first switch 114 and the second switch 124, respectively. Accordingly, the controller 230 is modified to provide the boost control signal SU and the buck control signal SD to the first switch 114 and the second switch 124, respectively.

[0071] The boost circuit 210 can present a first operating state, a second operating state, and a non-operating state similar to those presented by the boost circuit 110 in the first embodiment. In addition, the buck circuit 220 can present a third operating state, a fourth operating state, and a non-operating state similar to those presented by the buck circuit 120 in the first embodiment.

[0072] In the first operating state, the boost control signal SU is provided to the first switch 114, so that the first switch 114 is closed, thereby shorting the first inductor terminal 118 to ground. As described above in conjunction with the first embodiment, power is transferred from the power source 180 to the first inductor 112, and the first inductor current 113 increases.

[0073] In the second operating state, the boost control signal SU is disabled to turn off the first switch 114. Since the voltage at the first inductor terminal 118 becomes higher than the load voltage at the output node 172, the first diode 216 can cause the first inductor current 113 to flow into the capacitive load 190. Therefore, the first inductor current 113 decreases and the load voltage increases. During other states, the first diode 216 blocks current conduction because the first inductor terminal 118 has a voltage lower than the load voltage.

[0074] In the third operation state, the step-down control signal SD is provided to the second switch 124, so that the second switch 124 is closed. As described above in conjunction with the first embodiment, electric energy is transferred from the capacitive load 190 to the second inductor 122, and the load voltage is reduced.

[0075] In the fourth operating state, the buck control signal SD is disabled to open the second switch 124. As the voltage at the second inductor terminal 128 becomes lower than the ground level, the second diode 226 automatically transmits current to the energy storage 140 through the second inductor 122. During other states, the diode 226 blocks current conduction because the second inductor terminal 128 has a voltage higher than the ground level.

[0076] The driving circuit 200 of the second embodiment utilizes the automatic switching operation of the diodes 216 and 226, thereby further simplifying the control of the driving circuit.

[0077] Figure 3 3 is a circuit diagram of a driving circuit 300 for driving a capacitive load provided by a third embodiment of the present invention. The driving circuit 300 is the same as the driving circuit 100 provided by the first embodiment, except that a selection switch 350 is provided. The same components are provided with the same reference numerals and are not described in detail. Figure 3 Not shown Figure 1 The power supply capacitor 185 and other circuits 195 in the Figure 1 The selector switch 350 is connected to the drive circuit 300 in the same manner as in the embodiment 2. In addition, the selector switch 350 can also be applied to the drive circuit 200 of the second embodiment.

[0078] The selection switch has two input terminals and one output terminal. One of the input terminals is connected to the power supply 180, and the other input terminal is connected to the energy storage 140. The output terminal is connected to the first inductor 112 in the boost circuit 110. The selection switch 350 can be controlled so that the power supply 180 or the energy storage 140 supplies electrical energy to the boost circuit 110. In other words, the selection switch 350 supports selection between the power supply 180 and the energy storage 140 to select as the energy source of the boost circuit 110.

[0079] In operation, if the energy stored in the energy storage 140 is insufficient to increase the load voltage as desired during the boost operation, the selection switch 350 may be used to select the power supply 180 as the energy source of the boost circuit 110. The power supply 180 then supplies additional energy to the first inductor 112. Conversely, if the energy stored in the energy storage 140 is sufficient, the selection switch 350 may be used to select the energy storage 140 as the energy source of the boost circuit 110. The energy storage 140 then supplies electrical energy to the first inductor 112.

[0080] In this way, the selection switch 350 enables the drive circuit 300 to reuse the energy stored in the energy storage 140 for the drive circuit 300 itself. It should be noted that, as described with reference to the first embodiment, the drive circuit 300 can also reuse the energy stored in the energy storage 140 for other circuits 195 ( Figure 3 not shown).

[0081] Figure 4 4 is a circuit diagram of a drive circuit 400 for driving a capacitive load provided by a fourth embodiment of the present invention. The drive circuit 400 is the same as the drive circuit 300 provided by the third embodiment, except that a sensing block 452 for controlling the selection switch 350 is additionally provided. The same components are provided with the same reference numerals and are not described in detail again.

[0082] The sensing block 452 may be used to continuously or periodically sense the amount of electrical energy stored in the energy storage 140 to obtain a sensing value 454. For example, the sensing block 452 may sense the voltage across the energy storage 140 to monitor the electrical energy stored in the energy storage 140. The sensing block 452 may then control the selection switch 350 based on the sensing value 454. Figure 4 4 is shown as being separated from the controller 130 , but the sensing block 452 may be integrated into the controller 130 to become a part of the controller 130 .

[0083] In addition, the sensing block 452 can be used to compare the sensing value 454 with the reference value 456. If the sensing value 454 is higher than or equal to the reference value 456, the sensing block 452 can control the selection switch 350 so that the energy storage 140 supplies electrical energy to the boost circuit 110. If the sensing value 454 is lower than the reference value 456, the sensing block 452 can control the selection switch 350 so that the power supply 180 supplies electrical energy to the boost circuit 110. The reference value 456 can be a preset value, a configurable value, or a variable value. For example, the reference value 456 can be set to a value lower than the power supply voltage of the power supply 180. For another example, the reference value 456 can be dynamically changed according to the load voltage.

[0084] In this way, the sensing block 452 is able to control the selection switch 350 according to the sensing value 454, which represents the actual amount of energy stored in the energy storage 140. This means that the driving circuit 400 can reuse the energy stored in the energy storage 140 for the driving circuit 400 itself based on the actual amount of stored energy.

[0085] Figure 5 1 is a circuit diagram of a driving circuit 500 for driving a capacitive load provided by a fifth embodiment of the present invention. The driving circuit 500 is the same as the driving circuit 300 provided by the third embodiment, except that an accumulation block 562 for controlling the selection switch 350 is additionally provided. The same components are provided with the same reference numerals and are not described in detail again.

[0086] The accumulation block 562 is used to accumulate the corresponding amounts of the boost operation and the buck operation based on the information 564 obtained from the controller 130 to estimate the amount of electric energy stored in the energy storage 140. For example, the accumulation block 562 may cumulatively monitor the control signals SU1, SU2, SD1, and SD2 provided from the controller 130 to the boost circuit 110 and the buck circuit 120. Alternatively or additionally, the accumulation block 562 may cumulatively monitor the input signal 135 provided to the controller 130. Then, the accumulation block 562 may control the selection switch 350 according to the estimated electric energy. Although the accumulation block 562 is Figure 5 562 is shown as being separate from the controller 130 , but the accumulation block 562 may be integrated into the controller 130 to become a part of the controller 130 .

[0087] In addition, like the sensing block 452 of the fourth embodiment, the accumulation block 562 can also be used to compare the estimated power with a reference value. For details of such a reference value, please refer to the above description of the reference value 456 in conjunction with the fourth embodiment.

[0088] In this way, the accumulation block 562 enables the selection switch 350 to be controlled without sensing the actual electrical energy stored in the energy storage 140. This means that the drive circuit 500 can reuse the energy stored in the energy storage 140 for the drive circuit 500 itself based on the information obtained from the controller 130.

[0089] Reference now Figure 6 , a flow chart of a method 600 for driving a capacitive load provided by an embodiment of the present invention is shown. For example, the capacitive load is a piezoelectric MEMS acoustic transducer for a speaker device. For another example, the capacitive load may be other types of capacitive loads, such as a MEMS ultrasonic transducer, an ultrasonic motor, etc.

[0090] The method 600 comprises a step of receiving an input signal 602. The input signal may be, for example, an audio signal.

[0091] The method 600 further includes step 604 of controlling a load voltage across the capacitive load so that the load voltage is an amplified version of the input signal. For example, the load voltage may be a linearly amplified version of the audio signal.

[0092] Step 604 may include a sub-step 606 of supplying power from the power source to the capacitive load through a boost circuit to charge the capacitive load and a sub-step 608 of transferring power from the capacitive load to an energy storage device through a buck circuit to discharge the capacitive load. The energy storage device is separate from the power source.

[0093] The electrical energy released from the capacitive load and stored in the energy storage device can be reused, for example, in other circuits, thereby achieving energy recovery from the capacitive load.

[0094] Optionally, the method 600 may further include the following step: switching the selection switch so that the power supply or the energy storage device supplies electrical energy to the capacitive load, which may allow the electrical energy stored in the energy storage device 140 to be reused to drive the capacitive load.

[0095] Optionally, the method 600 may further include the following steps: sensing the electrical energy stored in the energy storage device, and the step of switching the selection switch includes controlling the selection switch according to the sensed electrical energy. This may enable the energy stored in the energy storage device to be reused to drive the capacitive load based on the actual amount of stored energy.

[0096] Alternatively, the method 600 may further include the following steps: monitoring the input signal and / or the control signal provided to the boost circuit and the buck circuit to estimate the electric energy stored in the energy storage device, and the step of switching the selection switch includes controlling the selection switch according to the estimated electric energy. This may enable the energy stored in the energy storage device to be reused to drive the capacitive load based on the input signal and / or the control signal.

[0097] Figure 7 is a schematic diagram of a speaker device 700 provided in an embodiment of the present invention. The speaker device 700 includes a piezoelectric MEMS acoustic transducer 790, which is used as a capacitive load. The speaker device 700 also includes a drive circuit 705, which is used to receive an input signal 735, which can be an audio signal, and the speaker device 700 drives the piezoelectric MEMS acoustic transducer 790 according to the audio signal 735. Advantageously, the drive circuit 705 can linearly amplify the audio signal 735 and provide the amplified signal to the piezoelectric MEMS acoustic transducer 790. The drive circuit 705 also receives power from a power supply 780. The power supply 780 can, for example, be a low-voltage power supply, such as a single lithium-ion battery.

[0098] The driving circuit 705 may be any one of the driving circuits 100, 200, 300, 400, and 500 described above. Thus, the driving circuit 705 may generate a high voltage (e.g., more than 30 Vpp) from a DC voltage (e.g., about 3.7 V) supplied by the low voltage power supply 780. In addition, the driving circuit 705 may transmit the electrical energy released from the piezoelectric MEMS acoustic transducer 790 and store the electrical energy in the energy storage (see Figures 1 to 5The energy storage device 140 in the energy storage device 140 is used for energy recovery. This energy recovery operation can be performed without any complex circuits and / or controls. In addition, this energy recovery operation does not affect the power supply voltage of the low-voltage power supply 780, thereby achieving higher sound quality. In addition, this energy recovery operation can continue to occur over a wider load voltage range, thereby achieving more efficient energy recovery. The electrical energy stored in the energy storage device can be reused to drive another circuit and / or the piezoelectric MEMS acoustic transducer 790 itself, as described above.

[0099] The speaker device 700 may be, but is not limited to, an earphone, a headset, a headset, a headphone, or a built-in speaker of an electronic device. Examples of built-in speakers of electronic devices include Figure 8 shown.

[0100] Figure 8 8 is a schematic diagram of an electronic device 800 provided in an embodiment of the present invention. In one example, the electronic device 800 may be a mobile device, such as a smart phone, a tablet computer, etc. The electronic device 800 includes a processor 810, a memory 820, a battery 830, a display panel 840, and a speaker 850. The display panel 840 may be assembled with the housing of the electronic device 800 so that the front surface of the display panel 840 is visible to the user of the electronic device 800, such as Figure 8 The speaker 850 can emit sound to the external environment (i.e., air), and in this sense is also represented by a solid line. The processor 810, the memory 820, and the battery 830 can be completely contained in the housing, as shown in FIG. Figure 8 The processor 810, the memory 820, the battery 830, the display panel 840 and the speaker 850 may be electrically connected.

[0101] Although not shown, the electronic device 800 may optionally include a radio frequency (RF) circuit, a camera, a microphone, an input device, a sensor, an antenna, a near field communication module, and the like.

[0102] The processor 810 can be used to call software programs and data stored in the memory 820, and execute the software programs to perform various functions and / or data processing of the electronic device 800. The processor 810 may include any suitable dedicated or general processing device or unit. In addition, the processor 810 may include any appropriate number of processors. For example, the processor 810 may include a microprocessor, a microcontroller, an application processor, a central processing unit (CPU), a graphics processing unit (GPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), etc. One or more.

[0103] The memory 820 can be used to store software programs and data, and can include any suitable media that can be accessed by the processor 810. In addition, the memory 820 can include any suitable number of memories. The memory 820 may include volatile memory and / or non-volatile memory, and may include, for example, random access memory (RAM), read-only memory (ROM), and / or flash memory. It should be noted that the term "memory" used in this article may refer to a large-capacity memory capable of storing a large amount of data (e.g., multimedia data). Therefore, the memory 820 may also include, for example, a hard disk drive (HDD), a solid state drive (SDD), an optical drive, etc.

[0104] The battery 830 may be used to supply power to various components (e.g., the processor 810, the memory 820, the display panel 840, the speaker 850) of the electronic device 800. The processor 810 may run a power management program or module stored in the memory 820 to control the power consumption of one or more components and the charging and discharging of the battery 830. In addition to the battery 830, or in place of the battery 830, the electronic device 800 may have a power connector, an adapter, etc. connected to an external power source (e.g., mains power).

[0105] The display panel 840 may be used to display various information and content, including information input by a user and information provided to the user. The display panel 840 may include a user input device, such as a touch screen, on at least a portion of a surface exposed from the housing.

[0106] Speaker 850 may include, for example, Figure 7 The speaker device 700 shown (specifically the drive circuit 705 and the piezoelectric MEMS sound transducer 790). However, the electronic device 800 can include multiple different types of speakers. In an example, the speaker 850 can combine the speaker device 700 with the piezoelectric MEMS sound transducer 790 with another type of speaker device with, for example, an electrodynamic sound transducer.

[0107] The speaker 850 including the speaker device 700 (driving circuit 705 and piezoelectric MEMS acoustic transducer 790) can provide the advantages described above. Specifically, the speaker 850 allows reuse of power released from the piezoelectric MEMS acoustic transducer 790, thereby saving power stored in the battery 830 of limited capacity.

[0108] Although some preferred embodiments of the present invention have been described, those skilled in the art may make changes and modifications to these embodiments without departing from the scope of the present invention. Therefore, the appended claims are intended to be interpreted as covering all changes and modifications within the scope of the present invention.

Claims

1. A driving circuit for driving a capacitive load, characterized in that: The driving circuit comprises: A boost circuit, used for increasing the load voltage across the capacitive load; A step-down circuit, used for reducing the load voltage; a controller for receiving an input signal and controlling the voltage-boosting circuit and the voltage-dropping circuit so that the load voltage is an amplified version of the input signal; an energy storage device for storing the electrical energy released from the capacitive load, The boost circuit is electrically connected between the power supply and the capacitive load, the buck circuit is electrically connected between the capacitive load and the energy storage device, and Wherein, the energy storage device is separated from the power supply.

2. The driving circuit according to claim 1, characterized in that: The energy storage device is used to supply electrical energy to at least one other device or system separate from the drive circuit.

3. The driving circuit according to claim 1, characterized in that: Also includes: A selection switch having two input terminals and an output terminal, one of the two input terminals being connected to the power supply, the other of the two input terminals being connected to the energy storage device, and the output terminal being connected to the boost circuit, The selection switch is controlled so that the power supply or the energy storage device supplies electrical energy to the boost circuit.

4. The driving circuit according to claim 3, characterized in that: Also includes: A sensing block is used to sense the electric energy stored in the energy storage device and control the selection switch according to the sensed electric energy.

5. The driving circuit according to claim 4, characterized in that: The sensing block is also used for: comparing the sensed electrical energy with a reference value; In response to the sensed electric energy being greater than or equal to the reference value, the selection switch is controlled so that the energy storage supplies electric energy to the boost circuit.

6. The driving circuit according to claim 3, characterized in that: Also includes: Cumulative blocks for: monitoring the input signal and / or control signal provided from the controller to the boost circuit and the buck circuit to estimate the electrical energy stored in the energy storage device; The selection switch is controlled according to the estimated electric energy.

7. The driving circuit according to claim 6, characterized in that: The accumulation block is also used to: comparing the estimated electrical energy with a reference value; In response to the estimated electric energy being greater than or equal to the reference value, the selection switch is controlled so that the energy storage supplies electric energy to the boost circuit.

8. The driving circuit according to any one of claims 1 to 7, characterized in that: The amplified version of the input signal is a linearly amplified version of the input signal.

9. The driving circuit according to any one of claims 1 to 8, characterized in that: The controller is further configured to receive or detect a value indicative of the load voltage as a feedback input.

10. The driving circuit according to any one of claims 1 to 9, characterized in that: The boost circuit includes a first inductor having one end connected to the power supply, a first switch connected between the other end of the first inductor and the ground, and a second switch connected between the other end of the first inductor and the capacitive load. The step-down circuit includes a second inductor having one end connected to the energy storage device, a third switch connected between the other end of the second inductor and the capacitive load, and a fourth switch connected between the other end of the second inductor and the ground. The controller controls the first switch, the second switch, the third switch and the fourth switch based on the input signal.

11. The driving circuit according to any one of claims 1 to 9, characterized in that: The boost circuit includes a first inductor having one end connected to the power supply, a first switch connected between the other end of the first inductor and the ground, and a first diode having an anode connected to the other end of the first inductor and a cathode connected to the capacitive load. The step-down circuit includes a second inductor having one end connected to the energy storage device, a second switch connected between the other end of the second inductor and the capacitive load, and a second diode having an anode connected to the ground and a cathode connected to the other end of the second inductor. The controller controls the first switch and the second switch based on the input signal.

12. A method for driving a capacitive load, characterized in that: The method comprises the following steps: receiving an input signal; controlling a load voltage across the capacitive load so that the load voltage is an amplified version of the input signal; Wherein, the step of controlling the load voltage comprises: supplying electric energy from a power source to the capacitive load through a voltage boost circuit to charge the capacitive load; The electric energy is transferred from the capacitive load to an energy storage device through a step-down circuit to discharge the capacitive load, and the energy storage device is separated from the power source.

13. The method according to claim 12, characterized in that The following steps are also included: The selection switch is switched so that the power source or the energy storage device supplies electric energy to the capacitive load through the boost circuit.

14. The method according to claim 13, characterized in that The following steps are also included: sensing electrical energy stored in the energy storage device, Wherein, the step of switching the selection switch includes controlling the selection switch according to the sensed electric energy.

15. The method according to claim 13, characterized in that The following steps are also included: monitoring the input signal and / or control signal provided to the boost circuit and the buck circuit to estimate the electrical energy stored in the energy storage device, The step of switching the selection switch includes controlling the selection switch according to the estimated electric energy.

16. A speaker device, characterized in that: include: Piezoelectric MEMS acoustic transducer; Circuit for: receiving input signals and power; The piezoelectric MEMS acoustic transducer is driven as a capacitive load, Wherein, the circuit comprises a driving circuit according to any one of claims 1 to 11.

17. An electronic device, characterized in that: include: The speaker device according to claim 16; a processor, configured to provide the input signal to the speaker device; A battery is used to supply the power to the speaker device.

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