Driver circuitry for capacitive transducers

Abstract

The present disclosure relates to a driving network (200) for driving a capacitive converter (210), for example, a piezoelectric converter or an electrostatic converter. The network (200) includes a power supply (260); a storage capacitance (220); a switch network (240); and a control network (270). The control network (270) is configured to control the operation of the switch network (240) to charge the storage capacitance (220) from the power supply (260) and to transfer charge between the storage capacitance (220) and the capacitive converter (210).

Description

Technology Field

[0001] The present disclosure relates to a driver circuitry for a capacitive converter. Background Technology

[0002] Piezoelectric transducers are increasingly being seen as a viable alternative to transducers, such as speakers and resonant actuators, for providing audio and / or haptic output in devices such as mobile phones, laptops, and tablet computers, due to their thin form factor, which can be beneficial in meeting the demand for increased functionality in devices without significantly increasing their size. Piezoelectric transducers are also increasingly being used as transducers for ultrasonic sensing and distance measurement systems.

[0003] Piezoelectric transducers can be driven by voltage. However, when driven by voltage, piezoelectric transducers exhibit both hysteresis and creep, which means that when driven by voltage, the displacement of the piezoelectric transducer depends on both the currently applied voltage and the previously applied voltage. Therefore, for any given driving voltage, there are several possible displacements of the piezoelectric transducer. For audio applications, this manifests as distortion.

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

[0005] FIG. 1 is a schematic diagram of a circuitry for driving a piezoelectric transducer with electric charge. As generally illustrated as 100 in FIG. 1, a charge-driving circuitry (102), which may be, for example, a charge pump circuitry, receives an electrical input signal (e.g., an input audio or ultrasonic signal or haptic waveform) from an upstream circuitry (not shown), such as an amplifier circuitry, and can drive the piezoelectric transducer (104) to produce an audio, ultrasonic, or haptic output based on the electrical input signal. The circuitry (100) is also suitable for driving other capacitances, such as a capacitive micro-electromechanical system (MEMS) transducer or an electrostatic transducer.

[0006] In particular, when the converter and driving network (102) are part of a battery-powered device such as a mobile phone, it is desirable to transfer charge to the converter with high efficiency to minimize power consumption. When transferring charge to the piezoelectric converter (104), the charge may be drawn from a power supply (e.g., a battery). However, when reducing charge in the converter (104), especially when the power supply is a battery, it is not desirable to transfer charge back to the power supply, as this may shorten the battery's lifespan.

[0007] Additionally, for a thin piezoelectric transducer comprising only a small number (e.g., 1) of layers of piezoelectric material, a relatively large voltage (e.g., 70 V) is required to drive the piezoelectric transducer (104) to induce displacement of the transducer. If the driving network (102) is powered by a low-voltage power supply (e.g., a 3 V battery), a mechanism is required to increase the available voltage at the output of the driving network (102). Typically, a switching converter is used to boost the voltage. The duty cycle (D) of the switching converter for a given voltage gain (g) is given by the equation It is given by. Therefore, for a voltage gain of 23.3 required to step up a 3V supply voltage to a 70V output voltage, a 96% duty cycle was required when a single converter was used. As understood by those skilled in the art, this is difficult to achieve in practice. Using two or more converters to step up the supply voltage at multiple stages reduces the duty cycle required for each converter, but requires multiple inductors (one for each converter) and many switches.

[0008] According to a first aspect, the present invention provides a circuit network for driving a capacitive converter based on an input signal, and the circuit network is,

[0009] Power supply;

[0010] Storage capacitance;

[0011] Switch network circuitry; and

[0012] It includes a control network configured to control the operation of a switch network to charge the storage capacitance from a power supply and to transfer charge between the storage capacitance and the capacitive converter.

[0013] The circuit network may include one or more additional inductors. The control circuit network may be configured to control the operation of the switch network to transfer charge between the storage capacitance and the capacitive converter through one of the one or more inductors.

[0014] The control network can be configured to control the operation of the switch network to transfer charge from the power supply to the storage capacitance through one or more inductors.

[0015] Alternatively, the control network can be configured to control the operation of the switch network to directly transfer charge between the storage capacitance and the capacitive converter.

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

[0017] The control network may be further configured to control the operation of the switch network to transfer charge from the power supply to the storage capacitance based on the level indication of the input signal.

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

[0019] The circuitry may further include a look-ahead circuitry configured to receive an input signal and output a signal indicating the level of the input signal to a control circuitry.

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

[0021] The switch network circuitry can be configured to be coupled to a single terminal of a capacitive converter.

[0022] Alternatively, the switch network circuitry can be configured to be coupled to the first and second terminals of the capacitive converter.

[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 greater than the voltage supplied to the power supply by the power source.

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

[0026] The control network can be configured to receive a feedback signal indicating the charge level of the capacitive converter.

[0027] The feedback signal can be based on the voltage across the capacitive converter.

[0028] The circuit network may include one or more inductors, and the control circuit network may be configured to control the operation of the switch network to transfer charge between the storage capacitance and the capacitive converter through one of the one or more inductors, and the feedback signal may be based on the current through one of the one or more inductors.

[0029] The input signal may include an audio signal, a haptic waveform, or an ultrasonic signal.

[0030] The circuit network may further include a commutator circuit connected to a switch network, and the commutator circuit is configured to selectively connect a first or second terminal of a capacitive converter to the output of the switch network.

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

[0032] According to a second aspect, the present invention provides a circuit network for driving a capacitive converter based on an input signal, and the circuit network is,

[0033] Power supply;

[0034] Storage capacitance;

[0035] Switch network circuitry; and

[0036] It includes a control network configured to control the operation of a switch network to charge storage capacitance from a power supply based on the indication of an input signal.

[0037] According to a third aspect, the present invention provides a circuit network for estimating the level of charge in a capacitive converter, and the circuit network is,

[0038] An inductor for transferring charge from a charge source to a capacitive converter;

[0039] It includes a control network configured to control the transfer of charge to a capacitive converter based on an input signal,

[0040] The control network is configured to receive an indication of current through an inductor and an indication of voltage across a capacitive converter, and

[0041] The control network is,

[0042] Indication of voltage across a capacitive converter when the frequency of the input signal is within a first range, and

[0043] Indication of current through the inductor when the frequency of the input signal is within the second range

[0044] Based on this, it is configured to estimate the charge level in a capacitive converter.

[0045] According to a fourth embodiment, the present invention provides an integrated circuit network comprising any one of the first to third embodiments.

[0046] According to the fifth embodiment, the present invention provides a device comprising a circuit network of any one of the first to third embodiments.

[0047] The device may include, for example, a mobile phone, a tablet or laptop computer, a smart speaker, an accessory device, headphones, earphones, or earbuds. Brief explanation of the drawing

[0048] Now, embodiments of the present invention will be described strictly by example with reference to the accompanying drawings: FIG. 1 is a schematic diagram illustrating the concept of driving a capacitive converter with electric charge; FIG. 2a is a schematic diagram illustrating a circuit network for transferring charge between a power supply, a storage capacitance, and a capacitive converter; FIGS. 2b to 2g illustrate the operation of the circuit network of FIG. 2a; FIG. 3a is a schematic diagram illustrating an alternative circuit network for transferring charge between a power supply, a storage capacitance, and a capacitive converter; FIGS. 3b to 3h illustrate the operation of the circuit network of FIG. 3a; FIG. 4 is a schematic diagram illustrating an additional circuit network for transferring charge between a power supply, a storage capacitance, and a capacitive converter; FIG. 5 is a schematic diagram illustrating a circuit network for transferring charge between a power supply, a storage capacitance, and a capacitive converter; and FIG. 6 is a schematic diagram illustrating a commutator network that can be used to provide a bipolar drive for a capacitive converter. Specific details for implementing the invention

[0049] FIG. 2a is a schematic diagram of a system (200) for driving a piezoelectric transducer (210). Although in this example the system (200) drives a piezoelectric transducer, it will be understood that the system (200) is also suitable for driving other capacitive transducers. For example, the system (200) can be used to drive a MEMS transducer or an electrostatic transducer.

[0050] The system (200) includes a storage capacitance (220) for storing charge, an inductor (230), and a switch network (240) for transferring charge between the storage capacitance (220) and the piezoelectric transducer (210) (including, in this example, first to fifth controllable switches (242 to 250) which may be, for example, MOSFET devices). Although the storage capacitance (220) is shown in FIG. 2a as a single capacitor, it will be understood that the storage capacitance (220) may alternatively be provided by a plurality of capacitors connected together.

[0051] The system (200) also includes a power supply (260) for optionally providing charge to the storage capacitance (220). In some examples, the power supply (260) may include a battery. In other examples, the power supply (260) may include a power supply network that receives power from a power supply such as a battery.

[0052] Even though the system (200) is depicted as comprising only a single inductor (230) (and this may be desirable to minimize the number of external components and thus reduce the cost and space requirements of the system (200)), in some examples, there may be one or more inductors. For example, a first inductor may be provided to transfer charge from the power supply network (260) to the storage capacitance (200), and a second inductor may be provided to transfer charge from the storage capacitance (220) to the piezoelectric transducer (210).

[0053] The first switching device (242) is connected between the output of the power supply (260) and the first terminal of the inductor (230).

[0054] The second switching device (244) is connected between the first terminal of the inductor (230) and the ground / reference voltage supply rail.

[0055] The third switching device (246) is connected between the second terminal of the inductor (230) and the ground / reference voltage supply rail.

[0056] The fourth switching device (248) is connected between the second terminal of the inductor (230) and the first terminal of the storage capacitance (220). The second terminal of the storage capacitance is connected to the ground / reference voltage supply rail.

[0057] The fifth switching device (250) is connected 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 connected to a ground / reference voltage supply rail.

[0058] The system (200) further includes a control network (270) operable to control switching devices (242 to 250) to control the transfer of charge between a power supply (260), a storage capacitance (220), and a piezoelectric transducer (210), as described with reference to FIGS. 2b through 2g.

[0059] At the start of the system (200) (or a host device including the system (200)), the charge is transferred from the power supply (260) to the storage capacitance (220) to raise the voltage across the storage capacitance (220) to a level suitable for driving the piezoelectric transducer (210).

[0060] In the first stage of the charging process (exemplified in FIG. 2b), in response to an appropriate control signal transmitted by the control network (270), the first and third switches (242, 246) are closed as indicated by dashed lines. This creates a current path (indicated by dashed arrows) through the inductor (230). As current flows through the inductor (230), a magnetic field is deployed around it to store energy.

[0061] In the second stage of the charging process (exemplified in FIG. 2c), in response to an appropriate control signal transmitted again by the control network (270), the first and third switches (242, 246) are opened and the second and fourth switches (244, 248) are closed, as indicated by dashed lines in FIG. 2c. The magnetic field around the inductor (230) collapses, inducing a current flowing from the inductor (230) to the storage capacitance (220), thereby charging the storage capacitance (220).

[0062] The first and second steps are repeated until the voltage across the storage capacitance (220) increases to a level suitable for driving the piezoelectric transducer (210), as determined by the control network (270) based on the feedback signal received from the piezoelectric transducer (210). When the storage capacitance (220) is charged to a desired level, the first switch (242) is opened, and thus the power supply (260) is disconnected, so that the piezoelectric transducer (210) can be driven by transferring the charge from the storage capacitance (220).

[0063] When the system (200) is required to increase the level of charge in the piezoelectric transducer (210) to drive the piezoelectric transducer (210) to generate a transducer output, for example, the system (200) operates again in two steps.

[0064] In the first stage of the charge transfer process (exemplified in FIG. 2d), in response to an appropriate control signal transmitted by the control network (270), the second and fourth switches (244, 248) are closed as indicated by dashed lines in FIG. 2d. Thus, a current path is established from the storage capacitance (220) through the inductor (230). As current flows through the inductor (230), a magnetic field is deployed around it to store energy.

[0065] In the second stage of the charge transfer process (exemplified in FIG. 2e), in response to an appropriate control signal transmitted by the control network (270), the third and fifth switches (246, 250) are closed as indicated by dashed lines in FIG. 2e, and the second and fourth switches (244, 248) are opened. The magnetic field around the inductor (230) collapses, inducing a current flowing from the inductor (230) to the piezoelectric transducer (210), thereby increasing the charge in the piezoelectric transducer (210).

[0066] When the system (200) is required to reduce the level of charge in the piezoelectric transducer (210), the charge can be transferred from the piezoelectric transducer (210) to the storage capacitance (220) so that the charge remains available for future use rather than being lost. This improves the efficiency of the system (200).

[0067] The process of transferring charge from the piezoelectric transducer (210) to the storage capacitance (220) occurs in two steps.

[0068] In the first step (exemplified in FIG. 2f), in response to an appropriate control signal transmitted by the control network (270), the third and fifth switches (246, 250) are closed as indicated by dashed lines in FIG. 2f. Thus, a current path is established from the piezoelectric transducer (210) through the inductor (230). As current flows through the inductor (230), a magnetic field is deployed around it to store energy.

[0069] In the second step (exemplified in FIG. 2g), in response to an appropriate control signal transmitted by the control network (270), the second and fourth switches (244, 248) are closed as indicated by dashed lines in FIG. 2g, and the third and fifth switches (246, 250) are opened. The magnetic field around the inductor (230) collapses, inducing a current to flow into the storage capacitance (220), and thus charging the storage capacitance (220).

[0070] Accordingly, in the system (200), the piezoelectric transducer (210) can be driven by receiving a charge from the storage capacitance (220), and the charge can be recirculated between the piezoelectric transducer (210) and the storage capacitance (220) to improve power efficiency. The power supply (260) provides an initial charge to the storage capacitance (220) during the charging process and charges or recharges the storage capacitance (220) from time to time or periodically as needed.

[0071] As shown above, the system (200) is suitable for driving any capacitive converter, and as understood by those skilled in the art, the operation of the system (200) is similar regardless of whether a piezoelectric converter or some other capacitive converter (e.g., a MEMS converter or an electrostatic converter) is being driven.

[0072] FIG. 2a illustrates a piezoelectric transducer in a single-ended configuration having a first terminal connected to a switch network (240) and a second terminal connected to ground or some other reference voltage. FIG. 3a illustrates an alternative system in which a capacitive transducer (in this example, a piezoelectric transducer) is connected in a bridge-connected load configuration.

[0073] The system generally depicted as (300) in FIG. 3 comprises a piezoelectric transducer (310), a storage capacitance (320) for storing charge, an inductor (330), and a switch network (340) for transferring charge between the storage capacitance (320) and the piezoelectric transducer (310) (including first to eighth controllable switches (342 to 356) which may be, for example, MOSFET devices in this example). Again, it will be understood that although the storage capacitance (320) is depicted as a single capacitor in FIG. 3a, the storage capacitance (320) may alternatively be provided by a plurality of capacitors connected together.

[0074] The system (300) also includes a power supply (360) for optionally providing charge to the storage capacitance (320). In some examples, the power supply (360) may include a battery. In other examples, the power supply (360) may include a power supply network that receives power from a power supply such as a battery.

[0075] The system (300) further includes a control network (370) operable to control switching devices (342-356) to control the transfer of charge between a power supply (360), a storage capacitance (320), and a piezoelectric transducer (310), as described with reference to FIGS. 3b through 3h.

[0076] When starting the system (300) (or a host device including the system (300)), the charge is transferred from the power supply (360) to the storage capacitance (320) to raise the voltage across the storage capacitance (320) to a level suitable for driving the piezoelectric transducer (310).

[0077] In the first stage of the charging process (exemplified in FIG. 3b), in response to an appropriate control signal transmitted by the control network (370), the first and third switches (342, 346) are closed as indicated by dashed lines. This creates a current path (indicated by dashed arrows) through the inductor (330). As current flows through the inductor (330), a magnetic field is developed around it to store energy.

[0078] In the second stage of the charging process (exemplified in FIG. 3c), in response to an appropriate control signal transmitted again by the control network (370), the first and third switches (342, 346) are opened and the second and fourth switches (344, 348) are closed, as indicated by dashed lines in FIG. 3c. The magnetic field around the inductor (330) collapses, inducing a current flowing from the inductor (330) to the storage capacitance (320), thereby charging the storage capacitance (320).

[0079] The first and second steps are repeated until the voltage across the storage capacitance (320) increases to a level suitable for driving the piezoelectric transducer (310), as determined by the control network (370) based on the feedback signal received from the piezoelectric transducer (310). When the storage capacitance (320) is charged to a desired level, the first switch (342) is opened, and thus the power supply (360) is disconnected, so that the piezoelectric transducer (310) can be driven by transferring the charge from the storage capacitance (320).

[0080] When the system (300) is required to increase the charge level in the piezoelectric transducer (310) by supplying a charge to the first terminal (312) of the piezoelectric transducer (310) to drive the piezoelectric transducer (310) to generate a transducer output, for example, the system (300) operates again in two steps.

[0081] In the first stage of the charge transfer process (exemplified in FIG. 3d), in response to an appropriate control signal transmitted by the control network (370), the second and fourth switches (344, 348) are closed as indicated by dashed lines in FIG. 3d. Thus, a current path is established from the storage capacitance (320) through the inductor (330). As current flows through the inductor (330), a magnetic field is deployed around it to store energy.

[0082] In the second stage of the charge transfer process (exemplified in FIG. 3e), in response to an appropriate control signal transmitted by the control network (370), the third, fifth, and sixth switches (346, 350, 352) are closed as indicated by dashed lines in FIG. 3e, and the second and fourth switches (344, 348) are opened. The magnetic field around the inductor (330) collapses, inducing a current to flow from the inductor (330) to the first terminal (312) of the piezoelectric transducer (310), thereby increasing the charge in the piezoelectric transducer (310).

[0083] When the system (300) is required to increase the level of charge in the piezoelectric transducer (310) by supplying charge to the second terminal (314) of the piezoelectric transducer (310) to drive the piezoelectric transducer (310) to generate a transducer output, for example, the system (300) operates again in two steps.

[0084] The first step is as described above with reference to Fig. 3d.

[0085] In the second stage of the charge transfer process (exemplified in FIG. 3f), in response to an appropriate control signal transmitted by the control network (370), the third, seventh, and eighth switches (346, 354, 356) are closed as indicated by dashed lines in FIG. 3f, and the second and fourth switches (344, 348) are opened. The magnetic field around the inductor (330) collapses, inducing a current to flow from the inductor (330) to the second terminal (314) of the piezoelectric transducer (310), thereby increasing the charge in the piezoelectric transducer (310).

[0086] The process of transferring charge from the piezoelectric transducer (310) to the storage capacitance (320) occurs in two steps.

[0087] In the first step (exemplified in FIG. 3g), in response to an appropriate control signal transmitted by the control network (270), the third, seventh, and eighth switches (346, 354, 356) are closed as indicated by dashed lines in FIG. 2g. Thus, a current path is established from the piezoelectric transducer (310) through the inductor (330). As current flows through the inductor (330), a magnetic field is deployed around it to store energy.

[0088] In the second step (exemplified in FIG. 3h), in response to an appropriate control signal transmitted by the control network (370), the second and fourth switches (344, 348) are closed as indicated by dashed lines in FIG. 3h, and the third, seventh, and eighth switches (346, 354, 356) are opened. The magnetic field around the inductor (330) collapses, inducing a current to flow into the storage capacitance (320), and thus charging the storage capacitance (320).

[0089] Accordingly, in the system (300), any terminal of the piezoelectric transducer (310) can be driven by receiving a charge from the storage capacitance (320), and the charge can be recirculated between the piezoelectric transducer (310) and the storage capacitance (320) to improve power efficiency. The power supply (360) provides an initial charge to the storage capacitance (320) during the charging process and charges or recharges the storage capacitance (320) as needed, from time to time or periodically.

[0090] In the example described above, although the system (300) is used to drive a piezoelectric transducer, the system (300) is suitable for driving any capacitive transducer, and as recognized by those skilled in the art, the operation of the system (300) is similar regardless of whether a piezoelectric transducer or some other capacitive transducer (e.g., a MEM transducer or an electrostatic transducer) is being driven.

[0091] In each of the systems described above, the voltage across the storage capacitance and the charge stored in the converter are monitored to determine the precise timing for transferring charge between the storage capacitance and the converter, and from the power supply to the storage capacitance.

[0092] Referring again to FIG. 2a, the control network (270) receives a feedback signal representing the voltage (VRES) across the storage capacitance (220), the voltage (VPIEZO) across the piezoelectric transducer (210), and the current (IL) through the inductor (230).

[0093] Similarly, in the system (300) of FIG. 3a, the control network (370) receives feedback signals representing the voltage (VRES) across the storage capacitance (320), the voltage (VPIEZO) across the piezoelectric transducer (310), and the current (IL) through the inductor (330).

[0094] The voltage across the piezoelectric transducer is not an accurate indication of the charge stored by the piezoelectric transducer at high input signal frequencies because the piezoelectric transducer contains resistive components as well as being purely capacitive. However, at lower input signal frequencies (e.g., 100 Hz or less), the voltage across the piezoelectric transducer is an acceptablely accurate indication of the charge stored by the piezoelectric transducer. At higher frequencies, the integral of the current (IL) through the inductor (230, 330) is a more accurate indication of the charge stored by the piezoelectric transducer.

[0095] Accordingly, at a low input signal frequency (e.g., when the input signal frequency is within a first range or below a threshold), the control network (270, 370) may use a voltage across the piezoelectric transducer (210, 310) directly as an indication of the charge stored in the piezoelectric transducer (210, 310) or to estimate the charge stored in the piezoelectric transducer (210, 310) in order to determine whether the charge should be transferred from the storage capacitance (220, 320) to the piezoelectric transducer (210, 310) in response to an input signal received by the control network (270, 370). At a higher input signal frequency (e.g., when the input signal frequency is within a second range or higher than a threshold), the control network (270, 370) may use a current (IL) (or an integer of the current (IL) through the inductor (230, 330) as an indication of the charge stored in the piezoelectric transducer (210, 310) or to estimate the charge stored in the piezoelectric transducer (210, 310) in order to determine whether the charge should be transferred from the storage capacitance (220, 320) to the piezoelectric transducer (210, 310) in response to the received input signal.

[0096] In the system (200), the control network (270) monitors the charge stored in the piezoelectric transducer (210) (indicated as voltage (VPIEZO) for a low input signal frequency and as current (IL) for a higher input signal frequency) and controls the switch network (240) to transfer the charge as required between the storage capacitance (220) and the piezoelectric transducer (210).

[0097] Accordingly, when the magnitude of the input signal increases and charges must be transferred to the piezoelectric transducer (210) to generate an appropriate output, the switch network (240) can be controlled by the control network (270) to transfer charges from the storage capacitance (220) to the piezoelectric transducer (210). When the magnitude of the input signal decreases and charges must be transferred from the piezoelectric transducer (210) to generate an appropriate output, the switch network (240) can be controlled by the control network (270) to transfer charges from the piezoelectric transducer (210) to the storage capacitance (220).

[0098] The control network (270) also monitors the charge stored in the storage capacitance (220) (as indicated by the voltage (VRES) across the storage capacitance) and controls the switch network (240) to transfer charge from the power supply (260) and the storage capacitance (220) as needed to maintain the level of charge in the storage capacitance (220) required to supply the charge required to the piezoelectric transducer (210). For example, the control network (270) can periodically compare the level of charge in the storage capacitance (220) with a threshold value and control the switch network (240) to transfer charge from the power supply (270) to the storage capacitance (220) when the charge level of the storage capacitance falls below the threshold value, so as to replenish or recharge the storage capacitance (220) to compensate for losses, such as resistance losses in the switch network (240) that cause the level of charge in the storage capacitance (220) to drop over time. This transfer of charge from the power supply (270) to the storage capacitance (220) occurs while the switch network (240) is not in use to transfer charge between the storage capacitance (220) and the piezoelectric transducer (210).

[0099] The control network (370) of the system (300) operates in a manner similar to controlling the switch network (340) to transfer charge between the storage capacitance (320) and the piezoelectric transducer (310) and to transfer charge from the power supply (360) to the storage capacitance (320) as needed.

[0100] In some examples, an additional circuit network may be provided to monitor the level of the input signal (e.g., the amplitude or envelope of the input signal) and to allow a switch network to transfer charge from the power supply to the storage capacitance based on the expected level of the input signal, so as to ensure that sufficient charge is available in the storage capacitance to drive a piezoelectric transducer (or other capacitive transducer) to generate an output based on the input signal.

[0101] FIG. 4 is a schematic diagram illustrating a system including such additional circuitry. The system generally denoted as (400) in FIG. 4 is based on the system (200) described above with reference to FIG. 2a, and therefore, elements common to system (200) are indicated by common reference numerals and are not described in detail herein. Of course, it will be understood by those skilled in the art that the principles described herein are equally applicable to the system (300) of FIG. 3a.

[0102] The system (400) differs from the system (200) in that it includes an additional network (410) for monitoring the level of an input signal received by the control network (270). The additional network may include, for example, a network for monitoring the level or magnitude of the input signal (e.g., voltage or current level or magnitude), a forecast network, or an envelope detector network. The additional network (410) receives the input signal and outputs a signal indicating the level (e.g., amplitude or envelope) of the input signal to the control network (270). The control network (270) controls the switch network (240) based on a signal received from the additional network (410) to transfer charge from the power supply (260) to the storage capacitor (260) as needed, so as to ensure that sufficient charge is available in the storage capacitance (260) to drive the piezoelectric transducer (210) to receive the expected level of the input signal, that is, to generate an output based on the input signal.

[0103] The system (400) may further include a signal processing network (420) configured to process an input signal. The signal processing network (420) may include an upsampling network for converting an input signal, which may be at an audio sampling rate such as 48 kHz, to a higher rate (e.g., 12.28 MHz, which is 256 times the sample rate of the input signal) corresponding to the operating frequency of the switch network (240) and / or control network (270). The signal processing network (420) may further include an interpolation network for interpolating an upsampled version of the input signal.

[0104] As understood by those skilled in the art, such a signal processing network introduces a delay into the input signal, so that the control network (270) receives a delayed version of the input signal in addition to the signal output by the additional network (410). The signal processing network (420) may additionally or alternatively include a dedicated delay network for introducing a delay or additional delay into the input signal. Such a delay is beneficial as it allows time for the additional network (410) to output the signal used by the control network (270) to control the transfer of charge from the power supply (260) to the storage capacitance (220) as needed, so as to ensure that sufficient charge is available in the storage capacitance (220) to accommodate the level of the input signal before the delayed input signal is received by the control network (270).

[0105] Therefore, the additional circuit network (410) provides a predictive circuit network configured to output a control signal to the control circuit network (270) based on the input signal so that the control circuit network (270) controls the switch network (240) to transfer charge from the power supply (260) to the storage capacitance (220) to receive the input signal as needed.

[0106] The system (200, 300) described above uses an inductor as an intermediate energy storage device in a two-stage charge transfer process for transferring charge from a power supply to a storage capacitance and a two-stage charge transfer process for transferring charge between the storage capacitance and a converter.

[0107] In another example, the charge can be transferred from a power supply to a storage capacitance, and directly between the storage capacitance and the converter, that is, without any intermediate energy storage device, as described now with reference to FIG. 5, which schematically illustrates a system (500) for directly transferring the charge to drive a piezoelectric converter (510). It will be understood that although the system (500) drives a piezoelectric converter in this example, the system (500) is also suitable for driving other capacitive converters. For example, the system (500) can be used to drive a MEMS converter or an electrostatic converter.

[0108] The system (500) includes a storage capacitance (520) for storing charge (which may be provided as a single capacitor or a plurality of capacitors connected together, as in the systems (200, 300) described above), and a switch network (540) for transferring charge between the storage capacitance (520) and the piezoelectric transducer (510) (in this example, first to third controllable switches (542 to 546) which may be MOSFET devices, for example).

[0109] The system generally depicted as (500) in FIG. 5 includes a piezoelectric transducer (510), a storage capacitance (520), a switch network circuit (540), a power supply (560), and a control network (570).

[0110] The system (500) also includes a power supply (560) for optionally providing charge to the storage capacitance (520). In some examples, the power supply (560) may include a power supply network that receives power from a power source, such as a battery, located outside the system (500). The power supply (560) may be configured to generate an output voltage (VSUP) for charging the storage capacitance (520) based on a lower voltage supplied to the power supply (560) from an external power source. Thus, the output voltage (VSUP) provided by the power supply (560) is greater than the supply voltage received by the power supply (560) from the external power source, and so the power supply (560) may be referred to as a boosted power supply.

[0111] The first switching device (542) is connected between the output of the power supply (560) and the first terminal (522) of the storage capacitance (520). The second terminal (524) of the storage capacitance is connected to the ground / reference voltage supply rail.

[0112] The second switching device (544) is connected between the first terminal (512) of the storage capacitance (520) and the ground / reference voltage supply rail.

[0113] The third switching device (546) is connected between the first terminal of the storage capacitance (520) and the first terminal (512) of the piezoelectric transducer. The second terminal (514) of the piezoelectric transducer (510) is connected to the ground / reference voltage supply rail.

[0114] The system (500) further includes a control network (570) operable to control switching devices (542 to 546) to control the transfer of charge between a power supply (560), a storage capacitance (520), and a piezoelectric transducer (510) in order to generate an output from the piezoelectric transducer (510) based on an input signal received by the control network (570). The control network (570) is connected to a first terminal (512) of the piezoelectric transducer (510) to receive a feedback signal representing a voltage (VPIEZO) across the piezoelectric transducer (510).

[0115] The power supply (560) may be a tracking power supply that outputs a voltage (VSUP) that changes based on the level (e.g., amplitude or envelope) of an input signal or based on a control signal output to the power supply (560) by the control network (570).

[0116] When the system (500) is in use, the power supply (560) outputs a voltage (VSUP) that is equal to or slightly higher than the voltage required to produce a desired output from the piezoelectric transducer (510) based on the input signal.

[0117] To generate a desired output from the piezoelectric transducer (510) (based on an input signal), a first charge transfer operation is performed in which the control network (570) outputs an appropriate control signal to the switch network (540) so that the first switch (542) is closed for a predetermined period while the second and third switches (544, 546) are open. Thus, charge is transferred from the power supply (560) to the storage capacitance (520). Then, a second charge transfer operation is performed in which the control network (570) outputs an appropriate control signal to the switch network (540) so that the third switch (546) is closed for a certain period while the first and second switches (542, 544) are open. Thus, charge is transferred from the storage capacitance (520) to the piezoelectric transducer (510).

[0118] These first and second charge transfer operations are repeated as needed until the voltage (VPIEZO) across the piezoelectric transducer (510) (as determined by the control network (570) based on the feedback signal) reaches a required level at the time when the control network (570) transmits a control signal to cause the first, second, and third switches (542 to 546) to open.

[0119] In this way, transferring charge to the piezoelectric transducer (510) through the storage capacitance (520) has the effect of filtering any ringing or overshoot in the voltage (VSUP) output by the power supply (560). Thus, the switch network (540) and the storage capacitance (520) effectively act as a low-pass filter.

[0120] The charge can be transferred from the piezoelectric transducer (510) to the storage capacitance (520) by transmitting an appropriate control signal from the control network (570) to close the third switch (546) and open the first and second switches (542, 544).

[0121] When it is necessary to discharge the storage capacitance (520) (e.g., during a shutdown of the system to reduce the risk of potentially harmful accidental discharge events), the control network (570) transmits a control signal to the switch network (540) to open the first and third switches (542, 546) and close the second switch (544), thereby allowing the storage capacitance to discharge to the ground / reference voltage supply rail. Similarly, when it is necessary to discharge the piezoelectric transducer (510) (e.g., during a shutdown of the system to reduce the risk of potentially harmful accidental discharge events), the control network (570) transmits a control signal to the switch network (540) to open the first switch (542) and close the second and third switches (544, 546), thereby allowing the piezoelectric transducer (510) to discharge to the ground / reference voltage supply rail.

[0122] If the storage capacitance (520) is small, the first and second charge transfer operations need to be repeated a relatively large number of times to reach the required level of the voltage (VPIEZO) across the piezoelectric transducer (510), which in turn requires the control network (570) and the switch network (540) to operate at high speed to accommodate a high input signal frequency. However, using a small storage capacitance (520) enables accurate control of the voltage across the piezoelectric transducer (510).

[0123] In contrast, a larger storage capacitance (520) requires fewer repetitions of the first and second charge transfer operations and allows the use of a low-speed switch network (540) and a control network (570) at the cost of reduced accuracy in controlling the voltage across the piezoelectric transducer (510).

[0124] In some examples, the storage capacitance (520) may be variable in response to a control signal (indicated by a dashed arrow in FIG. 5) transmitted by the control network (570) to allow greater flexibility in balancing the requirements of the precise control of the voltage (VPIEZO) and the operating speed of the control network (570) and the switch network (540).

[0125] With reference to FIGS. 2a, FIGS. 4, and FIGS. 5, the examples described above all drive a piezoelectric transducer (or other capacitive transducer) as a single-ended load, that is, the first terminal of the transducer is connected to the output of a switch network, and the second terminal of the transducer is connected to a ground / reference voltage supply rail.

[0126] It may be advantageous to be able to drive a bipolar, that is, one of the terminals of the converter. This can be achieved by using a commutator network connected to the converter, as described now with reference to FIG. 6, which illustrates a system (600) for driving a piezoelectric converter (610). Again, although the system (600) drives a piezoelectric converter in this example, the system (600) is also suitable for driving other capacitive converters. For example, the system (600) can be used to drive a MEMS converter or an electrostatic converter.

[0127] The system (600) includes a storage capacitance (620), a switch network (650), a power supply network (660), and a control network (670) that may be similar to the corresponding element of the system (200) of FIG. 2a or the corresponding element of the system (500) of FIG. 5. Therefore, the structure and operation of the switch network (650), the power supply network (660), and the control network (670) will not be described in detail herein.

[0128] The system (600) further includes a commutator network (680) comprising first to fourth controllable switches (682 to 688) in the illustrated example. The commutator network (680) is connected to a control network (670) to receive a control signal for controlling the operation of the controllable switches (682 to 688) according to an input signal.

[0129] The first controllable switch (682) is connected between the first node (690) of the commutator network (680) and the first terminal (612) of the piezoelectric transducer (610). The first node (690) of the commutator network (680) is connected to the output of a switch network (640) which operates to transfer charge between the storage capacitance (620) and the piezoelectric transducer (610) either through an intermediate inductor (as in the system (200) of FIG. 2a described above) or directly (i.e., without any intermediate inductor, as in the system (500) of FIG. 5 described above).

[0130] The second controllable switch (684) is connected between the first terminal (612) of the piezoelectric transducer (610) and the ground / reference voltage supply rail.

[0131] A third controllable switch (686) is connected between the first node (690) of the commutator network (680) and the second terminal (614) of the piezoelectric transducer (610).

[0132] The fourth controllable switch (688) is connected between the second terminal (614) of the piezoelectric transducer (610) and the ground / reference voltage supply rail.

[0133] By selectively opening and closing the controllable switches (682-688), one of the first and second terminals (612, 614) of the piezoelectric transducer (610) can be connected to the output of the switch network (640), and the other of the first and second terminals (612, 614) of the piezoelectric transducer (610) can be connected to the ground / reference voltage supply rail.

[0134] The operation of the controllable switches (682 to 688) is controlled by the control network (670) according to the polarity of the input signal (ground or ground or reference voltage supplied by the ground / reference voltage supply rail) as shown in the table below.

[0135]

[0136] Accordingly, when the input signal is positive, the fourth switch (688) is closed, thereby connecting the second terminal (614) of the piezoelectric transducer (610) to the reference voltage supply rail. The second and third switches (684, 686) are opened. When a charge is transferred to the first terminal (612) of the piezoelectric transducer (610), the first switch (682) is closed, thereby connecting the first terminal (612) of the piezoelectric transducer (610) to the output of the switch network (640).

[0137] When the input signal is negative, the second switch (884) is closed, thereby connecting the first terminal (612) of the piezoelectric transducer (610) to the ground / reference voltage supply rail. The first and fourth switches (682, 688) are opened. When a charge is to be transferred to the second terminal (614) of the piezoelectric transducer (610), the third switch (686) is closed, thus connecting the second terminal (614) of the piezoelectric transducer (610) to the output of the switch network (640).

[0138] Accordingly, either the first terminal (612) or the second terminal (614) of the piezoelectric transducer (610) can be driven by a charge delivered by the switch network (640) depending on the polarity of the input signal.

[0139] As is evident from the foregoing discussion, the circuitry of the present disclosure provides a power-efficient means for driving a piezoelectric transducer (or other capacitive transducer) using electric charge, which reduces hysteresis and creep that may occur when such a piezoelectric transducer is voltage-driven. Power efficiency is improved due to the recirculation of electric charge between the storage capacitance and the piezoelectric transducer, and the use of the storage capacitor helps to reduce the effects of ringing or overshoot in the voltage output from the power supply used to charge the storage capacitance.

[0140] The embodiment may be implemented as an integrated circuit, which in some examples may be a codec or an audio DSP or similar. The embodiment may be integrated into an electronic device, for example, which may be a portable device and / or a battery-powered device. The device may be a communication device, such as a mobile phone or a smartphone or similar. The device may be a computing device, such as a notebook, laptop, or tablet computing device. The device may be a wearable device, such as a smartwatch. The device may be a device with activation functions, such as voice control or a smart speaker. In some cases, the device may be an accessory device, such as a headset, headphones, earphones, earbuds, etc., to be used with some other products.

[0141] Those skilled in the art will recognize that some aspects of the aforementioned apparatus and method, for example, the discovery and configuration method, may be implemented as processor control code in a non-volatile carrier medium, such as a disk, CD- or DVD-ROM, read-only memory (firmware), or a data carrier, such as an optical or electrical signal carrier. For many applications, the embodiments will be implemented in a digital signal processor (DSP), an application-specific integrated circuit (ASIC), or a field programmable gate array (FPGA). Therefore, the code may include conventional program code or code for setting up or controlling a microphone, or, for example, an ASIC or FPGA. The code may also include code for dynamically configuring a reconfigurable device, such as a reprogrammable logic gate array. Similarly, the code may include code for a hardware description language, such as Verilog™ or VHDL (Very High Speed ​​Integrated Circuit Hardware Description Language). As those skilled in the art will recognize, the code may be distributed among a plurality of connected components that communicate with each other. Where appropriate, the embodiment may also be implemented using code executed on a field-(re)programmable analog array or similar device to configure analog hardware.

[0142] It should be noted that the embodiments mentioned above are illustrative rather than limiting of the invention, and that those skilled in the art can design 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, the singular expression does not exclude the plural, and a single feature or other unit may perform the function of several units cited in the claims. Drawing symbols or labels in the claims should not be interpreted as limiting the scope thereof.

Claims

Claim 1 A circuitry for driving a piezoelectric transducer based on an input signal, comprising: a power supply; a storage capacitance; a switch network; and a control circuitry configured to control the operation of the switch network to charge the storage capacitance from the power supply and to transfer charge between the storage capacitance and the piezoelectric transducer, wherein the control circuitry is further configured to control the operation of the switch network to transfer charge from the power supply to the storage capacitance based on an indication of the level of the input signal, and further comprising a look-ahead circuitry configured to receive the input signal and output a signal indicating the level of the input signal to the control circuitry. Claim 2 A circuit according to claim 1, further comprising one or more inductors, wherein the control circuit is configured to control the operation of the switch network circuit to transfer charge between the storage capacitance and the piezoelectric transducer through one of the one or more inductors. Claim 3 In paragraph 2, the control network is configured to control the operation of the switch network to transfer charge from the power supply to the storage capacitance through one of the one or more inductors. Claim 4 A circuit according to claim 1, wherein the control circuit is configured to control the operation of the switch network circuit to directly transfer charge between the storage capacitance and the piezoelectric transducer. Claim 5 In claim 1, the capacitance value of the storage capacitance is variable, circuit network. Claim 6 A circuit network according to claim 1, wherein the circuit network further comprises a monitoring circuit network 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 network. Claim 7 In claim 1, the switch network circuit is configured to be coupled to a single terminal of the piezoelectric transducer. Claim 8 In claim 1, the switch network circuit is configured to be coupled to the first and second terminals of the piezoelectric transducer. Claim 9 In claim 1, the power supply is configured to provide an output voltage that varies according to the level of the input signal. Claim 10 In claim 1, the circuit network is configured such that the power supply unit provides an output voltage greater than the voltage supplied to the power supply unit by the power source. Claim 11 In paragraph 1, the power supply unit comprises a switching power supply unit, forming a circuit network. Claim 12 In claim 1, the control network is configured to receive a feedback signal indicating the charge level of the piezoelectric transducer. Claim 13 In paragraph 12, the feedback signal is a circuit based on the voltage across the piezoelectric transducer. Claim 14 In claim 12, the circuit network comprises one or more inductors, and the control circuit network is configured to control the operation of the switch network to transfer charge between the storage capacitance and the piezoelectric transducer through one of the one or more inductors, and the feedback signal is based on the current through one of the one or more inductors. Claim 15 In claim 1, the input signal comprises an audio signal, a haptic waveform, or an ultrasonic signal, forming a circuit network. Claim 16 A circuit according to claim 1, further comprising a commutator circuit connected to the switch network circuit, wherein the commutator circuit is configured to selectively connect a first or second terminal of the piezoelectric transducer to the output of the switch network circuit. Claim 17 A circuit network for driving a piezoelectric transducer based on an input signal, wherein the circuit network comprises: a power supply; a storage capacitance; a switch network; and a control network configured to control the operation of the switch network to charge the storage capacitance from the power supply and to transfer charge between the storage capacitance and the piezoelectric transducer, wherein the control network is further configured to control the operation of the switch network to transfer charge from the power supply to the storage capacitance based on an indication of the level of the input signal, and the circuit network further comprises an envelope detector network configured to receive the input signal and output a signal indicating the envelope of the input signal to the control network. Claim 18 A circuit network for driving a piezoelectric transducer based on an input signal, wherein the circuit network comprises: a power supply; a storage capacitance; a switch network; and a control network configured to control the operation of the switch network to charge the storage capacitance from the power supply and to transfer charge between the storage capacitance and the piezoelectric transducer, wherein the capacitance value of the storage capacitance is variable. Claim 19 An integrated circuit network including the circuit network of claim 1. Claim 20 A device comprising the circuit network of claim 1. Claim 21 In paragraph 20, the device comprises a mobile phone, a tablet or laptop computer, a smart speaker, an accessory device, headphones, earphones, or earbuds.

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