Driver circuit for a capacitive transducer

Abstract

The present disclosure relates to a driver circuit (200) for driving a capacitive transducer (210), e.g. a piezoelectric or electrostatic transducer. The circuit (200) comprises a power supply (260), a storage capacitor (220), a switching network circuit (240), and a control circuit (270). The control circuit (270) is configured to control operation of the switching network circuit (240) so as to charge the storage capacitor (220) from the power supply (260) and transfer charge between the storage capacitor (220) and the capacitive transducer (210).

Description

Technical Field

[0001] This disclosure relates to driver circuitry for capacitor transducers. Background Technology

[0002] Piezoelectric transducers are increasingly seen as a viable alternative to transducers such as loudspeakers and resonant actuators due to their thin form factor, for providing audio and / or haptic output in devices such as mobile phones, laptops, and tablets. This could potentially meet the need to increase functionality in such devices without significantly increasing their size. Piezoelectric transducers are also increasingly being used as transducers in ultrasonic sensing and ranging systems.

[0003] Piezoelectric transducers can be voltage-driven. However, when voltage-driven, piezoelectric transducers exhibit hysteresis and creep, meaning that when voltage-excited, the displacement of the piezoelectric transducer depends on both the currently applied voltage and the previously applied voltage. Therefore, for any given drive voltage, there are multiple possible displacements of the piezoelectric transducer. In audio applications, this manifests as distortion.

[0004] One way to reduce hysteresis and creep, and related problems, in piezoelectric transducers is to drive the transducer with charge instead of voltage. When driven by charge, the displacement of the piezoelectric transducer varies with the applied charge.

[0005] Figure 1 This is a schematic diagram of a circuit used to drive a piezoelectric transducer with electrical charge. For example... Figure 1 The circuit 100, generally shown as 100, may be a charge-driven circuit 102, for example, a charge pump circuit, which may receive an electrical input signal (e.g., an input audio or ultrasonic signal or tactile waveform) from an upstream circuit (not shown), such as an amplifier circuit, and drive a piezoelectric transducer 104 to generate an audible, ultrasonic, or tactile output based on the electrical input signal. Circuit 100 is also suitable for driving other capacitive transducers, such as capacitive microelectromechanical systems (MEMS) transducers or electrostatic transducers.

[0006] It is desirable to transfer charge to the transducer efficiently to minimize power consumption, especially when the transducer and drive circuit 102 are part of a battery-powered device such as a mobile phone. When transferring charge to the piezoelectric transducer 104, charge can be drawn from a power source (e.g., a battery). However, when the charge on the transducer 104 is reduced, it is undesirable to transfer the charge back to the power source, especially when the power source is a battery, as this would shorten the battery's lifespan.

[0007] Additionally, for thin piezoelectric transducers comprising only a small number (e.g., 1) layers of piezoelectric material, a relatively large voltage (e.g., 70 volts) is required to drive the piezoelectric transducer 104 to cause displacement of the transducer. If the drive circuit 102 is powered by a low-voltage supply (e.g., a 3-volt battery), a mechanism is needed to increase the voltage available at the output of the drive circuit 102. Typically, a switching converter will be used for boosting. The duty cycle D of the switching converter for a given voltage gain g is determined by the equation... Therefore, for a voltage gain of 23.3V required to boost a 3V supply voltage to a 70V output voltage, a 96% duty cycle is needed if a single converter is used. This is difficult to achieve in practice, as will be understood by those skilled in the art. Using two or more converters to boost the supply voltage in multiple stages would reduce the duty cycle required per converter, but would require multiple inductors (one per converter) and multiple switches. Summary of the Invention

[0008] According to a first aspect, the present invention provides a circuit for driving a capacitive transducer based on an input signal, the circuit comprising:

[0009] power supply;

[0010] Storage capacitor;

[0011] Switching network circuits; and

[0012] A switching circuit configured to control the operation of a switching network circuit to charge a storage capacitor from a power source and transfer charge between the storage capacitor and a capacitor transducer.

[0013] The circuit may also include one or more inductors. The control circuit can be configured to control the operation of the switching network circuit to transfer charge between a storage capacitor and a capacitive transducer via one of the one or more inductors.

[0014] The control circuit can be configured to control the operation of the switching network circuit to transfer charge from the power source to the storage capacitor via one or more inductors.

[0015] Alternatively, the control circuit can be configured to control the operation of the switching network circuit to directly transfer charge between the storage capacitor and the capacitor transducer.

[0016] The capacitance value of the storage capacitor can be variable.

[0017] The control circuit can also be configured to control the operation of the switching network to transfer charge from the power source to the storage capacitor based on the indication of the level of the input signal.

[0018] The circuit may also include a monitoring circuit configured to monitor the level or magnitude of the input signal and output a signal indicating the level or magnitude of the input signal to the control circuit.

[0019] The circuit may also include a lead circuit configured to receive an input signal and output a signal indicating the level of the input signal to the control circuit.

[0020] The circuit may also include an envelope detector circuit configured to receive an input signal and output a signal indicating the envelope of the input signal to the control circuit.

[0021] The switching network circuit can be configured to couple to a single terminal of the capacitor transducer.

[0022] Alternatively, the switching network circuit can be configured to be coupled to the first and second terminals of the capacitor transducer.

[0023] The power supply can be configured to provide an output voltage that varies according to the level of the input signal.

[0024] The power supply can be configured to provide an output voltage that is greater than the voltage supplied to the power supply by the power source.

[0025] For example, a power supply may include a switching power supply.

[0026] The control circuit can be configured to receive a feedback signal that indicates the charge level of the capacitive transducer.

[0027] The feedback signal can be based on the voltage across the capacitor transducer.

[0028] The circuit may include one or more inductors, and the control circuit may be configured to control the operation of the switching network circuit to transfer charge between a storage capacitor and a capacitive transducer via one of the one or more inductors, and the feedback signal may be based on the current passing through one of the one or more inductors.

[0029] Input signals may include audio signals, tactile waveforms, or ultrasonic signals.

[0030] The circuit may also include a commutator circuit coupled to a switching network circuit, the commutator circuit being configured to selectively couple a first or second terminal of the capacitor transducer to the output of the switching network circuit.

[0031] Capacitive transducers can include, for example, piezoelectric transducers, MEMS transducers, or electrostatic transducers.

[0032] According to a second aspect, the present invention provides a circuit for driving a capacitive transducer based on an input signal, the circuit comprising:

[0033] power supply;

[0034] Storage capacitor;

[0035] Switching network circuits; and

[0036] A control circuit configured to control the operation of a switching network circuit to charge a storage capacitor from a power source based on an indication of an input signal.

[0037] According to a third aspect, the present invention provides a circuit for estimating the charge level on a capacitive transducer, the circuit comprising:

[0038] An inductor is used to transfer charge from a charge source to a capacitive transducer.

[0039] A control circuit, configured to control the transfer of charge to a capacitive transducer based on an input signal.

[0040] The control circuit is configured to receive indications of the current flowing through the inductor and the voltage across the capacitor transducer.

[0041] Furthermore, the control circuitry is configured to estimate the charge level on the capacitor transducer based on the following:

[0042] When the frequency of the input signal is within the first range, the indication of the voltage across the capacitor transducer, and

[0043] The indication of the current passing through the inductor when the frequency of the input signal is in the second range.

[0044] According to a fourth aspect, the present invention provides an integrated circuit comprising the circuitry of any one of the first to third aspects.

[0045] According to a fifth aspect, the present invention provides an apparatus comprising the circuitry of any one of the first to third aspects.

[0046] For example, the device may include a mobile phone, tablet computer or laptop computer, smart speaker, accessory device, headphones, earphones or earbuds. Attached Figure Description

[0047] Embodiments of the invention will now be described strictly by way of example with reference to the accompanying drawings, in which:

[0048] Figure 1 This is a schematic diagram illustrating the concept of using charge to drive a capacitor transducer;

[0049] Figure 2a This is a schematic diagram showing a circuit for transferring charge between a power source, a storage capacitor, and a capacitor transducer.

[0050] Figures 2b to 2g Show Figure 2a The operation of the circuit;

[0051] Figure 3a This is a schematic diagram illustrating an alternative circuit for transferring charge between a power source, a storage capacitor, and a capacitor transducer.

[0052] Figures 3b to 3h Show Figure 3a The operation of the circuit;

[0053] Figure 4 This is a schematic diagram showing another circuit for transferring charge between a power source, a storage capacitor, and a capacitor transducer.

[0054] Figure 5 This is a schematic diagram illustrating a circuit for transferring charge between a power source, a storage capacitor, and a capacitor transducer; and

[0055] Figure 6 This is a schematic diagram showing a commutator circuit that can be used to provide bipolar drive for a capacitor transducer. Detailed Implementation

[0056] Figure 2a This is a schematic representation of a circuit 200 used to drive piezoelectric transducer 210. It should be understood that although in this example, system 200 drives a piezoelectric transducer, system 200 is also suitable for driving other capacitive transducers. For example, system 200 can be used to drive MEMS transducers or electrostatic transducers.

[0057] System 200 includes a storage capacitor 220 for storing charge; an inductor 230; and a switching network 240 for transferring charge between the storage capacitor 220 and a piezoelectric transducer 210 (in this example, including first to fifth controllable switches 242-250, which may be, for example, MOSFET devices). The storage capacitor 220... Figure 2a The image shows a single capacitor, but it should be understood that the storage capacitance 220 can alternatively be provided by multiple capacitors coupled together.

[0058] System 200 also includes a power source 260 for selectively supplying charge to storage capacitor 220. In some examples, power source 260 may include a battery. In other examples, power source 260 may include a power supply circuit that receives power from a source such as a battery.

[0059] Although system 200 is shown to include only a single inductor 230 (and this is likely preferred to minimize the number of external components and thus reduce the cost and space requirements of system 200), in some examples, more than one inductor may be present. For example, a first inductor may be provided to transfer charge from power supply circuit 260 to storage capacitor 200, and a second inductor may be provided to transfer charge from storage capacitor 220 to piezoelectric transducer 210.

[0060] The first switching device 242 is coupled between the output of the power supply 260 and the first terminal of the inductor 230.

[0061] The second switching device 244 is coupled between the first terminal of the inductor 230 and the ground / reference voltage power supply rail.

[0062] The third switching device 246 is coupled between the second terminal of the inductor 230 and the ground / reference voltage power supply rail.

[0063] A fourth switching device 248 is coupled between the second terminal of the inductor 230 and the first terminal of the storage capacitor 220. The second terminal of the storage capacitor is coupled to the ground / reference voltage supply rail.

[0064] The fifth switching device 250 is coupled between the first terminal of the inductor 230 and the first terminal 212 of the piezoelectric transducer 210. The second terminal 214 of the piezoelectric transducer 210 is coupled to the ground / reference voltage supply rail.

[0065] System 200 also includes a control circuit 270 operable to control switching devices 242-250 to control charge transfer between power supply 260, storage capacitor 220, and piezoelectric transducer 210, as will now be referred to. Figures 2b to 2g The explanation.

[0066] When system 200 (or a host device incorporated into system 200) is started, charge is transferred from power supply 260 to storage capacitor 220 to raise the voltage across storage capacitor 220 to a level suitable for driving piezoelectric transducer 210.

[0067] In the first stage of the charging process ( Figure 2b As shown in the diagram, in response to an appropriate control signal transmitted by control circuit 270, first switch 242 and third switch 246 close, as indicated by the dashed lines. This creates a current path through inductor 230 (indicated by the dashed arrows). When current flows through inductor 230, a magnetic field is generated around the inductor, thereby storing energy.

[0068] In the second stage of the charging process ( Figure 2cAs shown in the diagram, in response to an appropriate control signal transmitted by control circuit 270, first switch 242 and third switch 246 are opened, and second switch 244 and fourth switch 248 are closed, as indicated by... Figure 2c The dotted line indicates that the magnetic field around inductor 230 collapses, thereby inducing a current that flows from inductor 230 to storage capacitor 220, thereby charging storage capacitor 220.

[0069] The first and second phases are repeated until the voltage across the storage capacitor 220 has increased to a level suitable for driving the piezoelectric transducer 210, as determined by the control circuit 270 based on the feedback signal received from the piezoelectric transducer 210. Once the storage capacitor 220 has been charged to the required level, the first switch 242 is turned off, thereby decoupling the power supply 260 so that the piezoelectric transducer 210 can be driven by transferring charge from the storage capacitor 220.

[0070] When system 200 needs to increase the charge level on piezoelectric transducer 210, for example to drive piezoelectric transducer 210 to generate transducer output, system 200 again operates in two stages.

[0071] In the first stage of the charge transfer process ( Figure 2d As shown in the diagram, in response to an appropriate control signal transmitted by control circuit 270, the second switch 244 and the fourth switch 248 close, as indicated by... Figure 2d The dashed line indicates this. Therefore, a current path is established from the storage capacitor 220 through the inductor 230. When current flows through the inductor 230, a magnetic field is generated around the inductor, thereby storing energy.

[0072] In the second stage of the charge transfer process ( Figure 2e As shown in the diagram, in response to an appropriate control signal transmitted by control circuit 270, third switch 246 and fifth switch 250 close, as indicated by... Figure 2e The dotted line indicates that the second switch 244 and the fourth switch 248 are open. The magnetic field around the inductor 230 collapses, thereby inducing a current that flows from the inductor 230 to the piezoelectric transducer 210, thereby increasing the charge on the piezoelectric transducer 210.

[0073] When system 200 needs to reduce the charge level on piezoelectric transducer 210, the charge can be transferred from piezoelectric transducer 210 to storage capacitor 220, so that the charge is retained for future use instead of being lost. This improves the efficiency of system 200.

[0074] The process of transferring charge from the piezoelectric transducer 210 to the storage capacitor 220 occurs in two stages.

[0075] In the first stage ( Figure 2fAs shown in the diagram, in response to an appropriate control signal transmitted by control circuit 270, third switch 246 and fifth switch 250 close, as indicated by... Figure 2f The dashed line indicates this. Therefore, a current path is established from the piezoelectric transducer 210 through the inductor 230. When current flows through the inductor 230, a magnetic field is generated around the inductor, thereby storing energy.

[0076] In the second stage ( Figure 2g As shown in the diagram, in response to an appropriate control signal transmitted by control circuit 270, the second switch 244 and the fourth switch 248 close, as indicated by... Figure 2g The dotted line indicates that the third switch 246 and the fifth switch 250 are open. The magnetic field around the inductor 230 collapses, thereby inducing a current that flows to the storage capacitor 220, thereby charging the storage capacitor 220.

[0077] Therefore, in system 200, the piezoelectric transducer 210 can be driven by transferring charge from the storage capacitor 220, and the charge can be circulated between the piezoelectric transducer 210 and the storage capacitor 220 to improve power efficiency. The power supply 260 provides an initial charge to the storage capacitor 220 during the charging process and occasionally or periodically charges or recharges the storage capacitor 220 as needed.

[0078] As indicated above, system 200 is suitable for driving any capacitive transducer, and as those skilled in the art will understand, system 200 operates similarly whether driving a piezoelectric transducer or other capacitive transducers (e.g., MEMS transducers or electrostatic transducers).

[0079] Figure 2a A piezoelectric transducer in a single-ended configuration is shown, wherein a first terminal is coupled to a switching network 240 and a second terminal is coupled to ground or some other reference voltage. Figure 3a An alternative system is shown, in which a capacitor transducer (in this example, a piezoelectric transducer) is coupled in a bridged load configuration.

[0080] The system shown overall in Figure 3 (denoted by 300) includes: a piezoelectric transducer 310; a storage capacitor 320 for storing charge; an inductor 330; and a switching network 340 for transferring charge between the storage capacitor 320 and the piezoelectric transducer 310 (in this example, including first to eighth controllable switches 342-356, which may be, for example, MOSFET devices). Similarly, although the storage capacitor 320... Figure 3a The image shows a single capacitor, but it should be understood that the storage capacitance 320 can alternatively be provided by multiple capacitors coupled together.

[0081] System 300 also includes a power source 360 ​​for selectively supplying charge to storage capacitor 320. In some examples, power source 360 ​​may include a battery. In other examples, power source 360 ​​may include a power supply circuit that receives power from a source such as a battery.

[0082] System 300 also includes a control circuit 370 operable to control switching devices 342-356 to control charge transfer between power supply 360, storage capacitor 320, and piezoelectric transducer 310, as will now be referred to. Figures 3b to 3h The explanation.

[0083] When the system 300 (or the host device incorporated into the system 300) is started, charge is transferred from the power supply 360 to the storage capacitor 320 to raise the voltage across the storage capacitor 320 to a level suitable for driving the piezoelectric transducer 310.

[0084] In the first stage of the charging process ( Figure 3b As shown in the diagram, in response to an appropriate control signal transmitted by control circuitry 370, first switch 342 and third switch 346 close, as indicated by the dashed lines. This creates a current path through inductor 330 (indicated by the dashed arrows). As current flows through inductor 330, a magnetic field is generated around the inductor, thereby storing energy.

[0085] In the second stage of the charging process ( Figure 3c As shown in the diagram, in response to an appropriate control signal transmitted by control circuit 370, first switch 342 and third switch 346 are opened, and second switch 344 and fourth switch 348 are closed, as indicated by... Figure 3c The dotted line indicates that the magnetic field around inductor 330 collapses, thereby inducing a current that flows from inductor 330 to storage capacitor 320, thereby charging storage capacitor 320.

[0086] The first and second phases are repeated until the voltage across the storage capacitor 320 has increased to a level suitable for driving the piezoelectric transducer 310, as determined by the control circuit 370 based on the feedback signal received from the piezoelectric transducer 310. Once the storage capacitor 320 has been charged to the required level, the first switch 342 is turned off, thereby decoupling the power supply 360 so that the piezoelectric transducer 310 can be driven by transferring charge from the storage capacitor 320.

[0087] When the system 300 needs to increase the charge level on the piezoelectric transducer 310 by supplying charge to the first terminal 312 of the piezoelectric transducer 310, for example to drive the piezoelectric transducer 310 to produce a transducer output, the system 300 again operates in two stages.

[0088] In the first stage of the charge transfer process ( Figure 3d As shown in the diagram, in response to an appropriate control signal transmitted by control circuit 370, the second switch 344 and the fourth switch 348 close, as indicated by... Figure 3d The dashed line indicates this. Therefore, a current path is established from the storage capacitor 320 through the inductor 330. When current flows through the inductor 330, a magnetic field is generated around the inductor, thereby storing energy.

[0089] In the second stage of the charge transfer process ( Figure 3e As shown in the diagram, in response to an appropriate control signal transmitted by control circuit 370, the third switch 346, the fifth switch 350, and the sixth switch 352 close, as indicated by... Figure 3e The dotted line indicates that the second switch 344 and the fourth switch 348 are open. The magnetic field around the inductor 330 collapses, thereby inducing a current that flows from the inductor 330 to the first terminal 312 of the piezoelectric transducer 310, thereby increasing the charge on the piezoelectric transducer 310.

[0090] When the system 300 needs to increase the charge level on the piezoelectric transducer 310 by supplying charge to the second terminal 314 of the piezoelectric transducer 310, for example to drive the piezoelectric transducer 310 to produce a transducer output, the system 300 again operates in two stages.

[0091] As referenced above Figure 3d Describe the first phase.

[0092] In the second stage of the charge transfer process ( Figure 3f As shown in the diagram, in response to an appropriate control signal transmitted by control circuit 370, the third switch 346, the seventh switch 354, and the eighth switch 356 are closed, as indicated by... Figure 3f The dotted line indicates that the second switch 344 and the fourth switch 348 are open. The magnetic field around the inductor 330 collapses, thereby inducing a current that flows from the inductor 330 to the second terminal 314 of the piezoelectric transducer 310, thereby increasing the charge on the piezoelectric transducer 310.

[0093] The process of transferring charge from the piezoelectric transducer 310 to the storage capacitor 320 occurs in two stages.

[0094] In the first stage ( Figure 3g As shown in the diagram, in response to an appropriate control signal transmitted by control circuit 270, the third switch 346, the seventh switch 354, and the eighth switch 356 are closed, as indicated by... Figure 2g The dashed line indicates this. Therefore, a current path is established from the piezoelectric transducer 310 through the inductor 330. When current flows through the inductor 330, a magnetic field is generated around the inductor, thereby storing energy.

[0095] In the second stage ( Figure 3h As shown in the diagram, in response to an appropriate control signal transmitted by control circuit 370, the second switch 344 and the fourth switch 348 close, as indicated by... Figure 3h The dotted line indicates that the third switch 346, the seventh switch 354, and the eighth switch 356 are open. The magnetic field around the inductor 330 collapses, thereby inducing a current that flows to the storage capacitor 320, thereby charging the storage capacitor 320.

[0096] Therefore, in system 300, the piezoelectric transducer 310 can be driven by transferring charge from the storage capacitor 320 to either terminal, and charge can be circulated between the piezoelectric transducer 310 and the storage capacitor 320 to improve power efficiency. The power supply 360 provides an initial charge to the storage capacitor 320 during the charging process and occasionally or periodically charges or recharges the storage capacitor 320 as needed.

[0097] Although in the above example, system 300 is used to drive a piezoelectric transducer, it should be understood that system 300 is suitable for driving any capacitive transducer, and as those skilled in the art will understand, system 300 operates similarly whether driving a piezoelectric transducer or some other capacitive transducer (e.g., a MEMS transducer or an electrostatic transducer).

[0098] In each of the above systems, in order to determine the correct timing of charge transfer between the storage capacitor and the transducer, and from the power source to the storage capacitor, the voltage across the storage capacitor and the charge stored on the transducer are monitored.

[0099] Return to reference Figure 2a The control circuit 270 receives a feedback signal indicating the voltage VRES across the storage capacitor 220, the voltage VPIEZO across the piezoelectric transducer 210, and the current IL through the inductor 230.

[0100] Similarly, in Figure 3a In system 300, control circuit 370 receives feedback signals indicating the voltage VRES across storage capacitor 320, the voltage VPIEZO across piezoelectric transducer 310, and the current IL through inductor 330.

[0101] The voltage across the piezoelectric transducer is not an accurate indication of the charge stored in the transducer at high input signal frequencies because the transducer is not purely capacitive but also includes resistive elements. However, at low input signal frequencies (e.g., 100 Hz or lower), the voltage across the transducer is an acceptablely accurate indication of the charge stored in the transducer. At higher frequencies, the integral of the current IL passing through inductors 230 and 330 is a more accurate indication of the charge stored in the transducer.

[0102] Therefore, at low input signal frequencies (e.g., when the input signal frequency is within a first range or below a threshold), control circuits 270 and 370 can use the voltage across piezoelectric transducers 210 and 310 directly as an indication of the charge stored on piezoelectric transducers 210 and 310, or to estimate the charge stored on piezoelectric transducers 210 and 310, in order to determine whether charge should be transferred from storage capacitors 220 and 320 to piezoelectric transducers 210 and 310 in response to the input signal received by control circuits 270 and 370. At higher input signal frequencies (e.g., when the input signal frequency is in the second range or above a threshold), control circuits 270, 370 can use the current IL passing through inductors 230, 330 (or the integral of the current IL passing through inductors 230, 330) directly as an indication of the charge stored on piezoelectric transducers 210, 310, or to estimate the charge stored on piezoelectric transducers 210, 310, in order to determine whether charge should be transferred from storage capacitors 220, 320 to piezoelectric transducers 210, 310 in response to the received input signal.

[0103] In system 200, control circuit 270 monitors the charge stored on piezoelectric transducer 210 (indicated by voltage VPIEZO for low input signal frequencies and by current IL for higher input signal frequencies) and controls switching network 240 to transfer charge between storage capacitor 220 and piezoelectric transducer 210 as needed.

[0104] Therefore, if the magnitude of the input signal increases, requiring charge to be transferred to the piezoelectric transducer 210 to produce a suitable output, the switching network 240 can be controlled by the control circuit 270 to transfer charge from the storage capacitor 220 to the piezoelectric transducer 210. If the magnitude of the input signal decreases, requiring charge to be transferred from the piezoelectric transducer 210 to produce a suitable output, the switching network 240 can be controlled by the control circuit 270 to transfer charge from the piezoelectric transducer 210 to the storage capacitor 220.

[0105] Control circuit 270 also monitors the charge stored on storage capacitor 220 (as indicated by the voltage VRES across the storage capacitor) and controls switching network 240 to transfer charge from power source 260 and storage capacitor 220 as needed to maintain the charge level on storage capacitor 220 required to supply the necessary charge to piezoelectric transducer 210. For example, control circuit 270 may periodically compare the charge level on storage capacitor 220 with a threshold, and if the charge level on storage capacitor is below the threshold, it may control switching network 240 to transfer charge from power source 270 to storage capacitor 220 to charge or recharge storage capacitor 220 to compensate for losses that may cause the charge level on storage capacitor 220 to decrease over time, such as resistive losses in switching network 240, etc. This charge transfer from power source 270 to storage capacitor 220 occurs when switching network 240 is not used to transfer charge between storage capacitor 220 and piezoelectric transducer 210.

[0106] The control circuit 370 of system 300 operates in a similar manner to control the switching network 340 to transfer charge between the storage capacitor 320 and the piezoelectric transducer 310 and, if necessary, transfer charge from the power source 360 ​​to the storage capacitor 320.

[0107] In some examples, additional circuitry may be provided to detect the level of the input signal (e.g., the magnitude or envelope of the input signal) and to enable the switching network to transfer charge from the power source to the storage capacitor based on the expected level of the input signal, ensuring that there is sufficient charge on the storage capacitor to drive a piezoelectric transducer (or another capacitive transducer) to generate an output based on the input signal.

[0108] Figure 4 This is a schematic diagram showing a system including this additional circuitry. Figure 4 The system shown in the figure as 400 is based on the above reference. Figure 2a The system 200 described herein, and therefore those components common to system 200, are indicated by common reference numerals and will not be described in detail here. Of course, those skilled in the art will understand that the principles described herein also apply to… Figure 3a System 300.

[0109] The difference between system 400 and system 200 is that it includes additional circuitry 410 for monitoring the level of the input signal received by control circuitry 270. For example, the additional circuitry may include circuitry for monitoring the level or magnitude of the input signal (e.g., voltage or current level or magnitude), a lead circuit, or an envelope detector circuit. Additional circuitry 410 receives the input signal and outputs a signal indicating the level (e.g., magnitude or envelope) of the input signal to control circuitry 270. Control circuitry 270 controls switching network 240 based on the signal received from additional circuitry 410 to transfer charge from power source 260 to storage capacitor 260 if necessary, ensuring sufficient charge on storage capacitor 260 to accommodate the expected level of the input signal, i.e., driving piezoelectric transducer 210 to generate an output based on the input signal.

[0110] System 400 may further include signal processing circuitry 420 configured to process the input signal. Signal processing circuitry 420 may include upsampling circuitry to convert the input signal (which may be at an audio sampling rate of, for example, 48 kHz) to a higher rate (e.g., 12.28 MHz, which is equal to 256 times the sampling rate of the input signal) corresponding to the operating frequency of switching network 240 and / or control circuitry 270. Signal processing circuitry 420 may also include an upsampled version of interpolation circuitry for interpolating the input signal.

[0111] As those skilled in the art will understand, this signal processing circuitry introduces a delay into the input signal, such that the control circuitry 270 receives a delayed version of the input signal in addition to the signal output by the additional circuitry 410. Alternatively, the signal processing circuitry 420 includes dedicated delay circuitry to introduce a delay or additional delay into the input signal. This delay is advantageous because it allows the additional circuitry 410 time to output a signal used by the control circuitry 270 to control the charge transfer from the power supply 260 to the storage capacitor 220 if necessary, ensuring that sufficient charge is available on the storage capacitor 220 to adapt the level of the input signal before the delayed input signal is received by the control circuitry 270.

[0112] Therefore, the additional circuit 410 provides a lead circuit, which is configured to output a control signal to the control circuit 270 based on the input signal, so that the control circuit 270 controls the switching network 240 to transfer charge from the power supply 260 to the storage capacitor 220 as needed to accommodate the input signal.

[0113] In the two-stage charge transfer process for transferring charge from the power source to the storage capacitor and in the two-stage charge transfer process for transferring charge between the storage capacitor and the transducer, the aforementioned systems 200 and 300 use inductors as intermediate energy storage devices.

[0114] In another example, charge can be transferred from the power source to the storage capacitor and directly between the storage capacitor and the transducer, i.e., without any intermediate energy storage device, as will now be referenced. Figure 5 describe, Figure 5 A system 500 for direct charge transfer used to drive a piezoelectric transducer 510 is schematically illustrated. It should be understood that although in this example, system 500 drives a piezoelectric transducer, it is also suitable for driving other capacitive transducers. For example, system 500 could be used to drive a MEMS transducer or an electrostatic transducer.

[0115] System 500 includes a storage capacitor 520 for storing charge (as in systems 200 and 300 described above, the storage capacitor may be provided as a single capacitor or multiple capacitors coupled together); and a switching network 540 for transferring charge between the storage capacitor 520 and the piezoelectric transducer 510 (in this example, including first to third controllable switches 542-546, which may be, for example, MOSFET devices).

[0116] Figure 5 The system shown as 500 includes a piezoelectric transducer 510, a storage capacitor 520, a switching network circuit 540, a power supply 560, and a control circuit 570.

[0117] System 500 also includes a power supply 560 for selectively supplying charge to storage capacitor 520. In other examples, power supply 560 may include a power supply circuit that receives power from a power source (e.g., a battery) external to system 500. Power supply 560 may be configured to generate an output voltage VSUP for charging storage capacitor 520 based on a lower voltage supplied to power supply 560 from the external power source. Therefore, the output voltage VSUP provided by power supply 560 is greater than the supply voltage received by power supply 560 from the external power source, and thus power supply 560 may be referred to as a boost power supply.

[0118] The first switching device 542 is coupled between the output of the power supply 560 and the first terminal 522 of the storage capacitor 520. The second terminal 524 of the storage capacitor is coupled to the ground / reference voltage power supply rail.

[0119] The second switching device 544 is coupled between the first terminal 512 of the storage capacitor 520 and the ground / reference voltage power supply rail.

[0120] A third switching device 546 is coupled between the first terminal of the storage capacitor 520 and the first terminal 512 of the piezoelectric transducer. The second terminal 514 of the piezoelectric transducer 510 is coupled to the ground / reference voltage supply rail.

[0121] System 500 also includes a control circuit 570 operable to control switching devices 542-546 to control charge transfer between power supply 560, storage capacitor 520, and piezoelectric transducer 510, so as to generate an output at piezoelectric transducer 510 based on an input signal received by control circuit 570. Control circuit 570 is coupled to a first terminal 512 of piezoelectric transducer 510 to receive a feedback signal indicating the voltage VPIEZO across piezoelectric transducer 510.

[0122] Power supply 560 may be a tracking power supply, which outputs a voltage VSUP that varies based on the level (e.g., magnitude or envelope) of the input signal or based on a control signal output from control circuit 570 to power supply 560.

[0123] When using system 500, power supply 560 outputs voltage VSUP, which is the same as or slightly higher than the voltage required to produce the desired output at piezoelectric transducer 510 based on the input signal.

[0124] To generate the desired output (based on the input signal) at the piezoelectric transducer 510, a first charge transfer operation is performed, wherein the control circuit 570 outputs an appropriate control signal to the switching network 540 to close the first switch 542 for a predetermined time period, while the second switch 544 and the third switch 546 remain open. Thus, charge is transferred from the power supply 560 to the storage capacitor 520. A second charge transfer operation is then performed, wherein the control circuit 570 outputs an appropriate control signal to the switching network 540 to close the third switch 546 for a predetermined time period, while the first switch 542 and the second switch 544 remain open. Thus, charge is transferred from the storage capacitor 520 to the piezoelectric transducer 510.

[0125] This first and second charge transfer operation is repeated as needed until the voltage VPIEZO across the piezoelectric transducer 510 (determined by the control circuit 570 based on the feedback signal) reaches the desired level. At this point, the control circuit 570 transmits a control signal to open the first, second, and third switches 542-546.

[0126] Transferring charge to the piezoelectric transducer 510 via the storage capacitor 520 in this manner has the effect of filtering out any ringing or overshoot in the voltage VSUP output by the power supply 560. Therefore, the switching network 540 and the storage capacitor 520 effectively function as a low-pass filter.

[0127] By transmitting appropriate control signals from control circuit 570 to close the third switch 546 and open the first switch 542 and the second switch 544, charge can be transferred from piezoelectric transducer 510 to storage capacitor 520.

[0128] When it is necessary to discharge the storage capacitor 520 (e.g., when the system is off to reduce the risk of potentially harmful accidental discharge events), the control circuit 570 transmits a control signal to the switch network 540 to open the first switch 542 and the third switch 546 and close the second switch 544, thereby allowing the storage capacitor to discharge to the ground / reference voltage supply rail. Similarly, when it is necessary to discharge the piezoelectric transducer 510 (e.g., when the system is off to reduce the risk of potentially harmful accidental discharge events), the control circuit 570 transmits a control signal to the switch network 540 to open the first switch 542 and close the second switch 544 and the third switch 546, thereby allowing the piezoelectric transducer 510 to discharge to the ground / reference voltage supply rail.

[0129] If the storage capacitor 520 is small, the first and second charge transfer operations will need to be repeated a relatively large number of times in order for the voltage VPIEZO across the piezoelectric transducer 510 to reach the desired level. This, in turn, requires the control circuitry 570 and the switching network 540 to operate at high speeds to accommodate high input signal frequencies. However, using a small storage capacitor 520 allows for precise control of the voltage across the piezoelectric transducer 510.

[0130] Conversely, a larger storage capacitor 520 requires fewer repetitions of the first and second charge transfer operations and allows for the use of a lower-speed switching network 540 and control circuitry 570, at the cost of reduced control accuracy across the voltage of the piezoelectric transducer 510.

[0131] In some examples, the storage capacitor 520 can respond to a control signal transmitted by the control circuit 570 (by... Figure 5 The value (indicated by the dashed arrow in the diagram) is variable, allowing for greater flexibility in terms of precise control requirements for the balanced voltage VPIEZO and the operating speed of the control circuit 570 and the switching network 540.

[0132] The above reference Figure 2a , Figure 4 and Figure 5 The examples described all use a piezoelectric transducer (or another capacitive transducer) driven as a single-ended load, i.e., the first terminal of the transducer is coupled to the output of the switching network, and the second terminal of the transducer is coupled to the ground / reference voltage supply rail.

[0133] It may be advantageous to be able to manufacture a driving bipolar circuit, i.e., drive either terminal of the transducer. This can be achieved by using a commutator circuit coupled to the transducer, as will now be referred to. Figure 6 As described, Figure 6A system 600 for driving a piezoelectric transducer 610 is shown. It should also be understood that although in this example, system 600 drives a piezoelectric transducer, system 600 is also suitable for driving other capacitive transducers. For example, system 600 can be used to drive MEMS transducers or electrostatic transducers.

[0134] System 600 includes a storage capacitor 620, a switching network 650, a power supply circuit 660, and a control circuit 670, which can be similar to... Figure 2a The corresponding components of System 200, or similar to Figure 5 The corresponding components of system 500. Therefore, the structure and operation of the switch network 650, power supply circuit 660 and control circuit 670 will not be described in detail here.

[0135] System 600 also includes a commutator circuit 680, which, in the illustrated example, includes first to fourth controllable switches 682-688. The commutator circuit 680 is coupled to a control circuit 670 to receive control signals for controlling the operation of the controllable switches 682-688 based on input signals.

[0136] A first controllable switch 682 is coupled between a first node 690 of the commutator circuit 680 and a first terminal 610 of the piezoelectric transducer 612. The first node 690 of the commutator circuit 680 is coupled to the output of a switching network 640, which is operable via an intermediate inductor (as described above). Figure 2a In system 200) or directly (i.e., without any intermediate inductors, as described above) Figure 5 In system 500, charge is transferred between storage capacitor 620 and piezoelectric transducer 610.

[0137] The second controllable switch 684 is coupled between the first terminal 612 of the piezoelectric transducer 610 and the ground / reference voltage power supply rail.

[0138] The third controllable switch 686 is coupled between the first node 690 of the commutator circuit 680 and the second terminal 614 of the piezoelectric transducer 610.

[0139] The fourth controllable switch 688 is coupled between the second terminal 614 of the piezoelectric transducer 610 and the ground / reference voltage power supply rail.

[0140] By selectively opening and closing controllable switches 682-688, one of the first terminal 612 and the second terminal 614 of the piezoelectric transducer 610 can be coupled to the output of the switch network 640, and the other of the first terminal 612 and the second terminal 614 of the piezoelectric transducer 610 can be coupled to the ground / reference voltage supply rail.

[0141] The control circuit 670 controls the operation of the controllable switches 682-688 according to the polarity of the input signal (relative to the ground or reference voltage supplied by the ground / reference voltage power supply rail), as shown in the table below.

[0142]

[0143] Therefore, when the input signal is positive, the fourth switch 688 closes, thereby coupling the second terminal 614 of the piezoelectric transducer 610 to the reference voltage supply rail. The second switch 684 and the third switch 686 are open. When charge is transferred to the first terminal 612 of the piezoelectric transducer 610, the first switch 682 closes, thereby coupling the first terminal 612 of the piezoelectric transducer 610 to the output of the switching network 640.

[0144] When the input signal is negative, the second switch 884 closes, thereby coupling the first terminal 612 of the piezoelectric transducer 610 to the ground / reference voltage supply rail. The first switch 682 and the fourth switch 688 are open. When charge is transferred to the second terminal 614 of the piezoelectric transducer 610, the third switch 686 closes, thereby coupling the second terminal 614 of the piezoelectric transducer 610 to the output of the switching network 640.

[0145] Therefore, the first terminal 612 or the second terminal 614 of the piezoelectric transducer 610 can be driven by the charge transferred through the switching network 640, depending on the polarity of the input signal.

[0146] As will be understood from the foregoing discussion, the circuitry of this disclosure provides a power-efficient component for using a charge-driven piezoelectric transducer (or another capacitive transducer) that reduces hysteresis and creep that may occur when such a piezoelectric transducer is voltage-driven. Power efficiency is improved due to charge cycling between the storage capacitor and the piezoelectric transducer, and the use of the storage capacitor helps reduce the effects of ringing or overshoot in the voltage output from the power supply used to charge the storage capacitor.

[0147] The implementation can be implemented as an integrated circuit, which in some examples may be a codec, an audio DSP, or the like. The implementation can be incorporated into an electronic device, which may be, for example, a portable device and / or a device that can be operated by battery power. The device may be a communication device, such as a mobile phone or a smartphone, or the like. The device may be a computing device, such as a laptop, laptop, or tablet. The device may be a wearable device, such as a smartwatch. The device may be a device with voice control or activation functionality, such as a smart speaker. In some instances, the device may be an accessory device to be used with another product, such as headphones, headsets, earphones, in-ear headphones, etc.

[0148] Those skilled in the art will recognize that some aspects of the aforementioned devices and methods (e.g., discovery and configuration methods) can be embodied as processor control code, for example, on non-volatile media such as disks, CD-ROMs, or DVD-ROMs, on programmable memory such as read-only memory (firmware), or on data carriers such as optical or electrical signal carriers. For many applications, implementations will be carried out on DSPs (Digital Signal Processors), ASICs (Application-Specific Integrated Circuits), or FPGAs (Field-Programmable Gate Arrays). Therefore, the code can include conventional program code or microcode, or, for example, code for setting up or controlling an ASIC or FPGA. The code can also include code for dynamically configuring reconfigurable devices (e.g., reprogrammable logic array gates). Similarly, the code can include code for, for example, Verilog... TM Alternatively, it may use code in a hardware description language such as VHDL (Very High Speed ​​Integrated Circuit Hardware Description Language). As those skilled in the art will understand, the code can be distributed among multiple coupled components that communicate with each other. Where appropriate, implementations may also utilize code that runs on a field-programmable analog array or similar device to configure the analog hardware.

[0149] It should be noted that the above embodiments are illustrative and not limiting of the invention, and those skilled in the art will be able to devise many alternative embodiments without departing from the scope of the appended claims. The word "comprising" does not exclude the presence of elements or steps other than those listed in the claims, and "a" or "an" does not exclude a plurality, and a single feature or other unit may perform the function of several units listed in the claims. Any reference numerals or markings in the claims should not be construed as limiting their scope.

Claims

1. A circuit for driving a capacitor transducer based on an input signal, the circuit being configured to receive power from a power source, the circuit comprising: Storage capacitor; Switching network circuit; A monitoring circuit configured to monitor the level of the input signal and output a signal indicating the level of the input signal; as well as A control circuit configured to control the operation of the switching network circuit to charge the storage capacitor from the power source and transfer charge between the storage capacitor and the capacitor transducer; The control circuit is further configured to control the operation of the switching network circuit to transfer charge from the power source to the storage capacitor based on a signal indicating the level of the input signal.

2. The circuit of claim 1, further comprising one or more inductors, wherein the control circuit is configured to control the operation of the switching network circuit to transfer charge between the storage capacitor and the capacitive transducer via one of the one or more inductors.

3. The circuit of claim 2, wherein the control circuit is configured to control the operation of the switching network circuit to transfer charge from the power source to the storage capacitor via one of the one or more inductors.

4. The circuit according to any one of claims 1 to 3, wherein the control circuit is configured to control the operation of the switching network circuit to directly transfer charge between the storage capacitor and the capacitor transducer.

5. The circuit according to claim 4, wherein the capacitance value of the storage capacitor is variable.

6. The circuit of claim 1, wherein the circuit further comprises a lead circuit configured to receive the input signal and output a signal indicating the level of the input signal to the control circuit.

7. The circuit of claim 1, wherein the circuit further comprises an envelope detector circuit configured to receive the input signal and output a signal indicating the envelope of the input signal to the control circuit.

8. The circuit according to any one of claims 1 to 3, wherein the switching network circuit is configured to be coupled to a single terminal of the capacitor transducer.

9. The circuit according to any one of claims 1 to 3, wherein the switching network circuit is configured to be coupled to the first and second terminals of the capacitor transducer.

10. The circuit according to any one of claims 1 to 3, wherein the power supply is configured to provide an output voltage that varies according to the level of the input signal.

11. The circuit according to any one of claims 1 to 3, wherein the power supply is configured to provide an output voltage greater than the voltage supplied to the power supply by the power source.

12. The circuit according to any one of claims 1 to 3, wherein the power supply comprises a switching power supply.

13. The circuit according to any one of claims 1 to 3, wherein the control circuit is configured to receive a feedback signal indicating the level of charge of the capacitive transducer.

14. The circuit of claim 13, wherein the feedback signal is based on the voltage across the capacitor transducer.

15. The circuit of claim 13, wherein the circuit includes one or more inductors, wherein the control circuit is configured to control the operation of the switching network circuit to transfer charge between the storage capacitor and the capacitive transducer via one of the one or more inductors, and wherein the feedback signal is based on the current passing through one of the one or more inductors.

16. The circuit according to any one of claims 1 to 3, wherein the input signal includes an audio signal, a tactile waveform, or an ultrasonic signal.

17. The circuit according to any one of claims 1 to 3, further comprising a commutator circuit coupled to the switching network circuit, the commutator circuit being configured to selectively couple a first or second terminal of the capacitor transducer to the output of the switching network circuit.

18. The circuit according to any one of claims 1 to 3, wherein the capacitor transducer comprises a piezoelectric transducer, a MEMS transducer, or an electrostatic transducer.

19. A circuit for driving a capacitor transducer based on an input signal, the circuit being configured to receive a power supply from a power source, the circuit comprising: Storage capacitor; Switching network circuit; A monitoring circuit configured to monitor the level of the input signal and output a signal indicating the level of the input signal; as well as A control circuit configured to control the operation of the switching network circuit so as to charge the storage capacitor from the power supply based on a signal indicating the level of the input signal.

20. A circuit for estimating the charge level on a capacitive transducer, the circuit comprising: An inductor used to transfer charge from a charge source to the capacitive transducer; A control circuit configured to control the transfer of charge to the capacitive transducer based on an input signal. The control circuit is configured to receive an indication of the current flowing through the inductor and an indication of the voltage across the capacitive transducer. And the control circuit is configured to estimate the charge level on the capacitor transducer based on the following: When the frequency of the input signal is within a first range, the indication of the voltage across the capacitive transducer, and The indication of the current passing through the inductor when the frequency of the input signal is within the second range.

21. An integrated circuit comprising the circuit according to any one of claims 1 to 20.

22. An electronic device comprising the circuitry according to any one of claims 1 to 20.

23. The electronic device of claim 22, wherein the electronic device is a mobile phone.

24. The electronic device of claim 22, wherein the electronic device is a tablet computer.

25. The electronic device of claim 22, wherein the electronic device is a laptop computer.

26. The electronic device of claim 22, wherein the electronic device is a smart speaker.

27. The electronic device of claim 22, wherein the electronic device is an accessory device.

28. The electronic device of claim 22, wherein the electronic device is a headset.

29. The electronic device of claim 22, wherein the electronic device is an earphone.

30. The electronic device of claim 22, wherein the electronic device is an earphone.

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