Driver circuit for a capacitive transducer

Abstract

The present disclosure relates to a driver circuit for driving a capacitive transducer. The circuit comprises an output stage circuit (330) configured to receive an input signal and drive the capacitive transducer (340) to produce an output signal; a variable voltage power supply circuit (320) configured to output a supply voltage to power the output stage circuit, wherein the supply voltage output by the variable voltage power supply circuit varies based on the input signal; a supply capacitor (326, 328) to receive the supply voltage output by the variable voltage power supply circuit; a storage capacitor (360); and a circuit to transfer charge between the storage capacitor and the supply capacitor (400).

Description

Technical Field

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

[0002] Piezoelectric transducers are increasingly being seen as a viable alternative to transducers such as loudspeakers and resonant actuators for providing audio and / or haptic output in devices such as mobile phones, laptops, and tablets. 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 produce an audible 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. Summary of the Invention

[0006] According to a first aspect, the present invention provides a circuit for driving a capacitor transducer, the circuit comprising:

[0007] An output stage circuit, the output stage circuit being configured to receive an input signal and drive a capacitor transducer to generate an output signal;

[0008] A variable voltage power supply circuit configured to output a supply voltage for a charge-driven output stage circuit, wherein the supply voltage output by the variable voltage power supply circuit varies based on an input signal;

[0009] A power supply capacitor, the power supply capacitor being used to receive a power supply voltage output by a variable voltage power supply circuit;

[0010] Storage capacitors; and

[0011] A circuit used to transfer charge between a storage capacitor and a power supply capacitor.

[0012] The output stage circuit may include a charge drive circuit.

[0013] The circuit may also include circuitry configured to transmit control signals to a variable voltage power supply circuit so that the variable voltage power supply circuit adjusts the magnitude of the supply voltage to the output stage circuit based on the input signal.

[0014] For example, a circuit configured to transmit a control signal to a variable voltage power supply circuit so that the variable voltage power supply circuit adjusts the magnitude of the supply voltage of the output stage circuit based on the input signal may include a lead circuit.

[0015] The lead circuit can be configured to monitor the level of the input signal, and the control signal can be based on the level of the input signal.

[0016] The lead circuit can be configured to monitor the envelope of the input signal, and the control signal can be based on the envelope of the input signal.

[0017] A circuit used to transfer charge between a storage capacitor and a supply capacitor may include a switching network and one or more inductors.

[0018] The circuit may also include control circuitry for controlling the operation of the switching network to transfer charge between the storage capacitor and the supply capacitor via at least one of one or more inductors.

[0019] The variable voltage power supply circuit can be configured to drive the positive and negative supply voltages of the output stage circuit with output charge.

[0020] The circuit may include a first supply capacitor for a positive supply voltage and a second supply capacitor for a negative supply voltage.

[0021] The circuit may also include a signal processing circuit configured to process the input signal and output a processed version of the input signal to a charge-driven output stage circuit.

[0022] Signal processing circuitry may include one or more of the following:

[0023] Filter circuit;

[0024] Digital-to-analog converter circuit;

[0025] Envelope detector circuit; and

[0026] Delay circuit.

[0027] For example, the input signal can be an audio signal.

[0028] The input signal can be a tactile signal.

[0029] The input signal can be an ultrasonic signal.

[0030] The output stage circuit may include a charge pump circuit.

[0031] The output stage circuit may include a linear amplifier circuit.

[0032] The variable voltage power supply circuit can be configured to drive the positive and negative supply voltages of the output stage circuit with output charge, and the linear amplifier circuit may include:

[0033] The input stage receives a fixed supply voltage from a positive voltage supply and a reference voltage supply; and

[0034] The output stage receives a positive supply voltage and a negative supply voltage from a variable voltage power supply circuit.

[0035] The output stage circuit may include:

[0036] Current source;

[0037] Current tank; and

[0038] Control circuit,

[0039] Furthermore, the control circuit can be configured to control the operation of the current source and current tank to selectively charge and discharge the capacitor transducer based on the input signal.

[0040] The circuit may also include a commutator circuit coupled to the output stage circuit, the commutator circuit being configured to selectively couple a first or second terminal of the capacitor transducer to the output of the output stage circuit.

[0041] Capacitive transducers can include, for example, piezoelectric transducers, MEMS transducers, or electrostatic transducers.

[0042] According to a second aspect, the present invention provides an integrated circuit comprising the circuit of the first aspect.

[0043] According to a third aspect, the present invention provides an apparatus comprising the circuitry of the first aspect. For example, the apparatus may include a mobile phone, a tablet computer or laptop computer, a smart speaker, an accessory device, a headset, an earphone, or an in-ear headphone. Attached Figure Description

[0044] Embodiments of the invention will now be described strictly by way of example with reference to the accompanying drawings, in which:

[0045] Figure 1This is a schematic diagram illustrating the concept of using charge to drive a capacitor transducer;

[0046] Figure 2 This is a schematic diagram showing a circuit for driving a capacitor transducer that includes a variable voltage power supply circuit.

[0047] Figure 3 This is a schematic diagram showing the circuit used to drive the capacitor transducer;

[0048] Figure 4a Showing the use of in Figure 3 An example of a switching network that transfers charge around a circuit;

[0049] Figures 4b to 4e Showing the charge in Figure 3 The transfer around the circuit.

[0050] Figure 5 This is a schematic diagram illustrating an example of a charge drive circuit for driving a capacitor transducer;

[0051] Figure 6 This is a schematic diagram illustrating an alternative example of a charge drive circuit for driving a capacitor transducer;

[0052] Figure 7 This is a schematic diagram illustrating another alternative example of a charge drive circuit for driving a capacitor transducer; and

[0053] Figure 8 This is a schematic diagram showing a commutator circuit that can be used to provide bipolar drive for a capacitor transducer. Detailed Implementation

[0054] exist Figure 1 In circuit 100, charge drive circuit 102 is powered by a fixed voltage supply provided by a positive supply voltage rail (e.g., VDD) and a reference supply voltage rail (e.g., 0V or ground). The power efficiency of this arrangement is limited because the supply voltage of charge drive circuit 102 may be significantly higher than the voltage required to drive piezoelectric transducer 104 to obtain an input signal of a given magnitude.

[0055] improve Figure 1 One way to improve the power efficiency of the circuit is to adjust the supply voltage of the charge drive circuit 102 according to the level (e.g., magnitude or envelope) of the electrical input signal, so that the supply voltage of the charge drive circuit 102 is sufficient to drive the piezoelectric transducer 104 without introducing distortion into the output signal, but excluding the excess voltage margin required to drive the piezoelectric transducer 104.

[0056] This concept is in Figure 2 The diagram illustrates that, Figure 2The diagram illustrates a circuit 200 including a variable voltage power supply circuit 210 having an input terminal 212 for receiving an input signal, and a first output terminal 214 and a second output terminal 216 for providing a positive supply voltage (Vp) and a negative supply voltage (Vn) to a charge drive circuit 220 (e.g., a charge pump circuit) driving a piezoelectric transducer 230. 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 could be used to drive a MEMS transducer or an electrostatic transducer.

[0057] The charge drive circuit 220 is configured to receive an input signal and drive the piezoelectric transducer 230 with charge so that the piezoelectric transducer 230 produces an audible or visual output based on the electrical input signal.

[0058] Variable voltage power supply 210 receives fixed supply voltages from a positive voltage rail (e.g., VDD) and a reference voltage rail (e.g., 0V or ground), and outputs variable positive supply voltage Vp and negative supply voltage Vn to charge drive circuit 220. The magnitudes of the variable positive supply voltage Vp and negative supply voltage Vn vary based on the level (e.g., magnitude or envelope) of the electrical input signal, such that the supply voltage of charge drive circuit 220 is sufficient to drive piezoelectric transducer 230 without introducing distortion into the output generated by the piezoelectric transducer, but without including unnecessary additional voltage margin, thereby... Figure 1 The power efficiency of circuit 200 is improved compared to circuit 100.

[0059] Figure 3 This is a schematic representation of a circuit used to drive a piezoelectric transducer. The circuit, shown generally as 300, includes an envelope detector circuit 310 that receives an electrical input signal (which can be a digital or analog signal), detects the size of the envelope of the electrical input signal, and outputs a control signal based on or indicating the size of the electrical input signal envelope to a variable voltage power supply circuit 320. It should also be understood that although in this example, system 300 drives a piezoelectric transducer, system 300 is also suitable for driving other capacitive transducers. For example, system 300 could be used to drive MEMS transducers or electrostatic transducers.

[0060] The variable voltage power supply circuit 320 receives a fixed supply voltage from a positive voltage rail (e.g., VDD) and a reference voltage rail (e.g., 0V or ground), and in the example shown, provides the positive supply voltage Vp and the negative supply voltage Vn to the charge drive output stage circuit 330 via corresponding first supply capacitor 326 and second supply capacitor 328. The first supply capacitor 326 (in...) Figure 3The capacitor 328 (labeled Cp) is coupled between the first output terminal 322 of the variable voltage power supply circuit 320 and the reference power supply voltage rail, while the second power supply capacitor 328 (in...) Figure 3 The part marked Cn is coupled between the second output terminal 324 of the variable voltage power supply circuit 320 and the reference power supply voltage rail.

[0061] exist Figure 3 In the example shown, the variable voltage power supply circuit 320 provides a positive voltage Vp and a negative voltage Vn to the charge-driven output stage circuit 330. However, as those skilled in the art will understand, if the charge-driven output stage circuit 330 is configured to operate on, for example, a ground reference power supply, the variable voltage power supply circuit 330 provides only the positive supply voltage to the charge-driven output stage circuit 330. In this arrangement, only a single supply capacitor would be required, coupled between the supply voltage output terminal of the variable voltage power supply circuit 320 and the reference supply voltage rail.

[0062] The voltage output by the variable voltage power supply circuit 320 depends on the control signal output by the envelope detector circuit 310. Therefore, if the control signal indicates that the envelope of the input signal is increasing, the magnitude of the voltage output by the variable voltage power supply circuit increases. Conversely, if the control signal indicates that the envelope of the input signal is decreasing, the magnitude of the voltage output by the variable voltage power supply circuit decreases.

[0063] For example, the variable voltage power supply circuit 330 can implement a switching power supply, wherein the first capacitor 326 and the second capacitor 328 are charged and discharged when the switching power supply is turned on and off at a switching frequency. Therefore, the magnitudes of the positive output voltage Vp and the negative output voltage Vn depend on the switching frequency of the switching power supply. If the switching frequency is constant, the magnitudes of the positive output voltage Vp and the negative output voltage Vn are...

[0064] The control signal output by the envelope detector circuit 310 can control the switching frequency of the switching power supply, so that when the envelope of the input signal remains constant, the positive output voltage Vp and the negative output voltage Vn also remain constant. However, when the size of the input signal envelope decreases, the values ​​of the positive output voltage Vp and the negative output voltage Vn also decrease, and when the size of the input signal envelope increases, the values ​​of the positive output voltage Vp and the negative output voltage Vn also increase.

[0065] The charge-driven output stage circuit 330 is coupled to the variable voltage power supply circuit 320 to receive variable positive voltage Vp and negative voltage Vn as power. The charge-driven output stage circuit 330 can also operate to receive an electrical input signal and drive the piezoelectric transducer 340. The charge-driven output stage circuit 330 supplies charge to the piezoelectric transducer 340 based on the received electrical input signal and may include, for example, a charge pump circuit, a linear amplifier circuit, or a current source circuit.

[0066] Circuit 300 may further include signal processing circuitry 350, operable to receive an electrical input signal and output a processed version of the electrical input signal to charge-driven output stage circuitry 330. Signal processing circuitry 350 may include, for example, filter circuitry, digital-to-analog (DAC) circuitry, delay circuitry, etc., for modifying or otherwise processing the received input signal before transmitting it to charge-driven output stage circuitry 330.

[0067] The signal processing circuit 350 processes the input signal, causing a delay in the arrival of the processed version of the received signal at the charge drive circuit. This delay is useful because it allows the envelope detector circuit 310 time to send appropriate control signals to the variable voltage power supply circuit 320 to ensure that the magnitudes of the positive voltage Vp and negative voltage Vn supplied to the charge drive output stage circuit 330 are sufficient to enable the charge drive output stage circuit 330 to drive the piezoelectric transducer 340 without introducing distortion, but without providing unnecessary and power-inefficient margins in the voltage supplied to the charge drive output stage circuit 330.

[0068] Therefore, the envelope detector circuit 310 provides a lead circuit, which is configured to transmit a control signal to the variable voltage power supply circuit 320 based on the input signal, so that the variable voltage power supply circuit 320 adjusts the magnitudes of the positive voltage Vp and negative voltage Vn supplied to the charge drive output stage circuit 330 to adapt to the input signal to be received by the charge drive output stage circuit 330.

[0069] In an alternative example, the envelope detector circuit 310 can be replaced by a level detector circuit that detects the level of the electrical input signal, such as the voltage value, and outputs a control signal based on or indicating the level of the electrical input signal to the variable voltage power supply circuit 320 to control or adjust the voltage value output by the variable voltage power supply circuit 320.

[0070] Circuit 300 also includes a storage capacitor 360 (in Figure 3 The storage capacitor 360 (marked Cr) and the inductor 370 associated with the variable voltage power supply circuit 320. The storage capacitor 360 and the inductor 370 can be connected to the switching network 400 (in... Figure 3 (Shown as being integrated into the variable voltage power supply circuit, but can also be provided separately from the variable voltage power supply circuit) for use in combination to further improve the power efficiency of circuit 300 by transferring charge between storage capacitor 360 and first capacitor 326 and second capacitor 328 when the power supply requirements of charge-driven output stage circuit 330 change. Although Figure 3Only one inductor is shown, but the circuit may include two or more inductors, such as a first inductor for transferring charge from the variable voltage power supply circuit 320 to the storage capacitor 360, and a second inductor for transferring charge between the storage capacitor 360 and the first capacitor 326 and the second capacitor 328.

[0071] For example, when the level or envelope of the input signal decreases, the charge stored in the first capacitor 326 and the second capacitor 328 may exceed the charge required to drive the output stage circuit 330 and power the piezoelectric transducer 340. Instead of wasting power by discharging the first and second power supply capacitors 326 and 328 to ground in this case, the excess charge is transferred to the storage capacitor 360 using the switching network 400 and the inductor 370. Conversely, when the level or envelope of the input signal increases, the amount of charge stored in the first and second power supply capacitors 326 and 328 needs to be increased to power the charge-driven output stage circuit 330 to support the required output signal level. This increase can be achieved, at least in part, by transferring the stored charge from the storage capacitor 360 again using the switching network 400 and the inductor 370.

[0072] Figure 4a Showing the use of in Figure 3 An example switching network 400 in circuit 300 that transfers charge between storage capacitor 360 and first capacitor 326 and second capacitor 328.

[0073] In the example shown, the switch network 400 includes first to fifth controllable switches 402-410, which may be, for example, MOSFET devices.

[0074] The first switch 402 is coupled between the first plate of the storage capacitor 360 (the second plate of the storage capacitor 360 is coupled to the reference voltage rail) and the first terminal of the inductor 370, and is selectively operable to couple the first plate of the storage capacitor 360 to the first terminal of the inductor 370.

[0075] The second switch 404 is coupled between the first terminal of the inductor 370 and the reference voltage rail, and is selectively operable to couple the inductor 370 to the reference voltage rail.

[0076] The third switch 406 is coupled between the second terminal of the inductor 370 and the first power supply capacitor 326, and is selectively operable to couple the first power supply capacitor 326 to the second terminal of the inductor 370.

[0077] The fourth switch 408 is coupled between the second terminal of the inductor 370 and the second power supply capacitor 328, and is selectively operable to couple the second power supply capacitor 328 to the second terminal of the inductor 370.

[0078] The fifth switch 406 is coupled between the second terminal of the inductor 370 and the reference voltage rail, and is selectively operable to couple the inductor 370 to the reference voltage rail.

[0079] A control circuit 420 may be provided to control the operation of the switch to transfer charge between the storage capacitor 360 and the first capacitor 326 and the second capacitor 328.

[0080] Figure 4b The use of a switching network 400 for transferring excess charge from the first power supply capacitor 326 to the storage capacitor 360 is shown, for example, when the input signal level or envelope decreases, reducing the power supply requirements of the charge drive output stage circuit 330.

[0081] In the first phase of operation, in response to an appropriate control signal from control circuit 420, third switch 406 and second switch 404 are closed, and first switch 402, fourth switch 408 and fifth switch 410 are open (e.g., ...). Figure 4b (Indicated by the dashed line in the diagram). Therefore, a current path is established via inductor 370 from the first supply capacitor 326 to the reference voltage supply rail, and current flows out of the first supply capacitor 326, as shown in the diagram. Figure 4b As indicated by the dashed arrow in the diagram. Current flowing out of the first power supply capacitor 326 causes a magnetic field to be generated around the inductor 370, thereby storing energy from the first power supply capacitor 326.

[0082] In the second stage following the first stage, in response to an appropriate control signal from control circuit 420 (with fourth switch 408 remaining open), third switch 406 and second switch 404 are opened, and first switch 402 and fifth switch 410 are closed (as shown in the image). Figure 4b (Indicated by the dashed line in the diagram). Now, there is a current path from the first inductor 370 to the storage capacitor 360. The magnetic field around the inductor 370 collapses, thereby inducing a current in the inductor 370, which flows from the inductor 370 to the storage capacitor 360, as shown in the diagram. Figure 4b As indicated by the dashed arrow, the storage capacitor 360 is thus charged. Therefore, during the first and second phases, charge is transferred from the first power supply capacitor 326 to the storage capacitor 360.

[0083] Figure 4cThe use of a switching network 400 for transferring excess charge from the second power supply capacitor 328 to the storage capacitor 360 is shown, as may also occur when the input signal level or envelope decreases.

[0084] In the first stage, in response to an appropriate control signal from control circuit 420, fourth switch 408 and second switch 404 are closed, and first switch 402, third switch 406 and fifth switch 410 are open (e.g., Figure 4c (Indicated by the dashed line in the diagram). Therefore, a current path is established via inductor 370 from the second supply capacitor 328 to the reference voltage supply rail, and current flows out of the second supply capacitor 328, as shown in the diagram. Figure 4c As indicated by the dashed arrow in the diagram. Current flowing out of the second power supply capacitor 328 causes a magnetic field to be generated around the inductor 370, thereby storing energy from the second power supply capacitor 328.

[0085] In the second stage following the first stage, in response to an appropriate control signal from control circuit 420 (with the third switch 406 remaining open), the fourth switch 408 and the second switch 404 are opened, and the first switch 402 and the fifth switch 410 are closed (as shown in the image). Figure 4c (Indicated by the dashed line in the diagram). Now, there is a current path from the first inductor 370 to the storage capacitor 360. The magnetic field around the inductor 370 collapses, thereby inducing a current in the inductor 370, which flows from the inductor 370 to the storage capacitor 360, as shown in the diagram. Figure 4c As indicated by the dashed arrow, the storage capacitor 360 is thus charged. Therefore, during the first and second phases, charge is transferred from the second power supply capacitor 328 to the storage capacitor 360.

[0086] Figure 4d The use of a switching network 400 for transferring charge from storage capacitor 360 to first power supply capacitor 326 is shown, as may occur when an increase in the input signal level or envelope increases the power supply requirements of the charge drive output stage circuit 330.

[0087] In the first stage, in response to an appropriate control signal from control circuit 420, first switch 402 and fifth switch 410 are closed and second switch 404, third switch 406 and fourth switch 408 are open (e.g., Figure 4d (Indicated by the dashed line in the diagram). Therefore, a current path is established from the storage capacitor 360 to the reference voltage supply rail via the inductor 370, and current flows out of the storage capacitor 360, as shown in the diagram. Figure 4d As indicated by the dashed arrow in the diagram. Current flowing out of storage capacitor 360 causes a magnetic field to be generated around inductor 370, thereby storing energy from storage capacitor 360.

[0088] In the second stage following the first stage, in response to an appropriate control signal from control circuit 420 (with fourth switch 408 remaining open), first switch 402 and fifth switch 410 are opened and second switch 404 and third switch 406 are closed (as shown in the image). Figure 4d (Indicated by the dashed line in the diagram). Now, there is a current path from inductor 370 to the first supply capacitor 326. The magnetic field around inductor 370 collapses, thereby inducing a current in inductor 370, which flows from inductor 370 to the first supply capacitor 326, as shown in the diagram. Figure 4d As indicated by the dashed arrow, the first power supply capacitor 326 is thus charged. Therefore, during the first and second phases, charge is transferred from the storage capacitor 360 to the first power supply capacitor 326.

[0089] Figure 4e The use of a switching network 400 for transferring charge from storage capacitor 360 to second power supply capacitor 328 is shown, as may also occur when an increase in the input signal level or envelope increases the power supply requirements of the charge drive output stage circuit 330.

[0090] In the first stage, in response to an appropriate control signal from control circuit 420, first switch 402 and fifth switch 410 are closed and second switch 404, third switch 406 and fourth switch 408 are open (e.g., Figure 4e (Indicated by the dashed line in the diagram). Therefore, a current path is established from the storage capacitor 360 to the reference voltage supply rail via the inductor 370, and current flows out of the storage capacitor 360, as shown in the diagram. Figure 4e As indicated by the dashed arrow in the diagram. Current flowing out of storage capacitor 360 causes a magnetic field to be generated around inductor 370, thereby storing energy from storage capacitor 360.

[0091] In the second stage following the first stage, in response to an appropriate control signal from control circuit 420 (with the third switch 406 remaining open), the first switch 402 and the fifth switch 410 are opened, and the second switch 404 and the fourth switch 408 are closed (as shown in the image). Figure 4e (Indicated by the dashed line in the diagram). Now, there is a current path from inductor 370 to the second supply capacitor 328. The magnetic field around inductor 370 collapses, thereby inducing a current in inductor 370, which flows from inductor 370 to the second supply capacitor 328, as shown in the diagram. Figure 4e As indicated by the dashed arrow, the second power supply capacitor 328 is thus charged. Therefore, during the first and second phases, charge is transferred from the storage capacitor 360 to the second power supply capacitor 328.

[0092] The control circuit 420 receives the control signal output by the envelope detector circuit 310 and accordingly controls the operation of switches 402-410 to transfer charge between the storage capacitor 360 and the first capacitor 326 and the second capacitor 328. This allows excess charge from the first capacitor 326 and the second capacitor 328 to be stored in the storage capacitor 360 when the input signal level or envelope decreases, and charges to be supplied from the storage capacitor 360 to the first capacitor 326 and the second capacitor 328 when the input signal level or envelope increases. This reduces the amount of additional power that must be supplied to the first capacitor 326 and the second capacitor 328 by the variable voltage power supply circuit 320 to accommodate the increased input signal, and increases the power efficiency of the circuit 300.

[0093] The charge-driven output stage circuit 330 can be implemented in a variety of different ways.

[0094] Figure 5 This is a schematic representation of a charge pump circuit that serves as a charge-driven output stage circuit 330 to drive a piezoelectric transducer 340 (or another capacitive transducer, such as a MEMS transducer or an electrostatic transducer) to generate an output signal based on the input signal of the charge-driven output stage circuit 330.

[0095] Figure 5 The charge pump circuit shown in the figure as 500 includes a capacitor 510, a switching network 520, and a control circuit 530.

[0096] The switch network 520 includes first to fourth controllable switches 522-528, which may be, for example, MOSFET devices.

[0097] A first switch 522 is coupled between a positive power rail 540 and a first (upper) plate of a capacitor 510, the positive power rail receiving a positive supply voltage Vp provided by a first power supply capacitor 326. The first switch 522 is selectively operable to couple the first plate of the capacitor 510 to the positive power rail 540.

[0098] A second switch 524 is coupled between the second (lower) plate of capacitor 510 and a negative power rail 550, which receives a positive supply voltage Vp provided by the second power supply capacitor 328. The second switch 524 is selectively operable to couple the second plate of capacitor 510 to the negative power rail 550.

[0099] The third switch 526 is coupled between the first plate of capacitor 510 and the first (upper) terminal of piezoelectric transducer 340, and is selectively operable to couple the first plate of capacitor 510 to piezoelectric transducer 340.

[0100] The fourth switch 528 is coupled between the second plate of capacitor 510 and the first (upper) terminal of piezoelectric transducer 340, and is selectively operable to couple the second plate of capacitor 510 to piezoelectric transducer 340.

[0101] The second (lower) terminal of the piezoelectric transducer is coupled to the reference voltage supply rail.

[0102] When using the charge pump circuit 500, the control circuit 530 receives the input signal and transmits the control signal to the controllable switches 522-528, causing the switches 522-528 to open and close as needed to charge the capacitor 510 and transfer charge from the capacitor 510 to the piezoelectric transducer 430. Therefore, the piezoelectric transducer 340 can generate the desired output signal based on the received input signal.

[0103] In the first phase of operation, capacitor 510 is charged by closing the first switch 522 and the second switch 524. During this phase, the third switch 526 and the fourth switch 528 are closed.

[0104] Then, by opening the first switch 522 and closing the third switch 526, charge can be transferred to the piezoelectric transducer 340. The second switch 524 remains closed and the fourth switch 528 remains open. When the voltage across the capacitor 510 is greater than the voltage across the piezoelectric transducer 340, current flows from the capacitor 510 to the piezoelectric transducer 340, thereby charging the piezoelectric transducer 340 and discharging the capacitor 510.

[0105] When charge is transferred from the piezoelectric transducer 340, the first switch 522 and the fourth switch 528 are closed, and the second switch 524 and the third switch 526 are opened. Therefore, current can flow from the piezoelectric transducer 340 to the capacitor 510, thereby discharging the piezoelectric transducer 340 and charging the capacitor 510.

[0106] By controlling the operation of switches 522-528 according to the received input signal, the charge-driven output stage circuit 500 can drive the piezoelectric transducer 340 to generate an output signal based on the input signal.

[0107] During operation of the charge pump circuit 500, the control circuit 530 monitors the voltage across the piezoelectric transducer 340 and the voltage across the capacitor 510, and transmits a control signal to a switch to prevent the charge transfer direction from reversing, as the voltage across the capacitor 510 drops during charge transfer to the piezoelectric transducer 340, or vice versa. For example, when transferring charge from the capacitor 510 to the piezoelectric transducer 340, there may be moments when the voltage across the capacitor 510 drops below the voltage across the piezoelectric transducer 340 and the current flow direction reverses. This can cause undesirable undershoot or overshoot in the signal output by the piezoelectric transducer 340 (which may appear as damped oscillations). By monitoring the voltages across the capacitor 510 and the piezoelectric transducer 340, the control circuit 530 can transmit an appropriate control signal to a switch, such as to open a third switch 526, thereby decoupling the piezoelectric transducer 340 from the capacitor 510 and preventing charge transfer from the piezoelectric transducer 340 to the capacitor 510, and thus preventing undesirable overshoot or undershoot.

[0108] Figure 6 This is a schematic representation of a linear amplifier circuit that serves as a charge-driven output stage circuit 330 to drive a piezoelectric transducer 340 (or another capacitive transducer, such as a MEMS transducer or an electrostatic transducer) to generate an output signal based on the input signal of the charge-driven output stage circuit 330.

[0109] Figure 6 The linear amplifier circuit shown at 600 includes an input stage 610 and an output stage 620. The input stage 610 is powered by a fixed voltage supply provided through a positive voltage rail (e.g., VDD) and a reference voltage rail (e.g., 0V or ground), while the output stage 620 receives its power supply from a positive supply voltage Vp and a negative supply voltage Vn provided by a first supply capacitor 326 and a second supply capacitor 328.

[0110] The first input of input stage 610 receives an input signal (or a version of the input signal already processed by signal processing circuit 350). The output of input stage 610 is coupled to the input of output stage 620, and the output of output stage 620 is coupled to piezoelectric transducer 340. The output of output stage 620 is also coupled to a second input of input stage 620, thereby forming a negative feedback loop that feeds back at least a portion of the signal output by output stage 620 to the input stage.

[0111] This arrangement allows the positive and negative supply voltages of the output stage 620 to be adjusted as needed to accommodate specific input signal levels without causing distortion in the signal output from the output stage to the piezoelectric transducer, and without requiring excess supply voltage margin.

[0112] Figure 7This is a schematic representation of an alternative charge-driven output stage circuit 330, which uses a current source and a current slot to drive a piezoelectric transducer 340 (or another capacitive transducer, such as a MEMS transducer or an electrostatic transducer) to generate an output signal based on the input signal of the charge-driven output stage circuit 330.

[0113] Figure 7 The charge-driven circuit, shown as 700, includes a controllable current source 710 coupled in series with a controllable current tank 720 between a positive supply voltage rail 730 and a negative supply voltage rail 740. The positive supply voltage rail receives a positive supply voltage Vp provided by a first supply capacitor 326, and the negative supply voltage rail receives a negative supply voltage Vn provided by a second supply capacitor 328. A first terminal of a piezoelectric transducer 340 is coupled to a node between the current source 710 and the current tank 720, while a second terminal of the piezoelectric transducer 340 is coupled to a reference voltage supply rail.

[0114] A control circuit 750 is also provided to control the operation of the current source 710 and the current tank 720 based on the received input signal and the feedback signal received from the first terminal of the piezoelectric transducer 340. To charge the piezoelectric transducer 340, the circuit 750 transmits a control signal to activate the current source 710 and deactivate the current tank 720. Therefore, current flows from the current source 710 to the piezoelectric transducer 340 to charge it. To discharge the piezoelectric transducer, the control circuit 750 transmits a control signal to activate the current tank 720 and deactivate the current source 710. Therefore, current flows from the piezoelectric transducer 340 to the current tank, thereby discharging the piezoelectric transducer.

[0115] By controlling the current source 710 and the current tank 720 according to the received input signal and feedback signal, the charge-driven output stage circuit 700 can drive the piezoelectric transducer 340 to generate an output signal based on the input signal.

[0116] Although systems 200, 300, 500, 600, and 700 are used to drive piezoelectric transducers in the examples above, it should be understood that systems 200, 300, 500, 600, and 700 are suitable for driving any capacitive transducer, and as those skilled in the art will appreciate, systems 200, 300, 500, 600, and 700 operate similarly whether driving a piezoelectric transducer or some other capacitive transducer (e.g., a MEMS transducer or an electrostatic transducer).

[0117] In the examples above, the piezoelectric transducer 340 (or another capacitive transducer) is driven as a single-ended load, that is, the first terminal of the transducer 340 is coupled to the output of the charge drive circuit 330, and the second terminal of the transducer 340 is coupled to the reference voltage supply rail.

[0118] It may be advantageous to be able to manufacture a drive bipolar circuit, i.e., drive either terminal of the transducer 340. This can be achieved by using a commutator circuit coupled to the transducer 340, as will now be referred to. Figure 8 As described.

[0119] Figure 8 The commutator circuit shown in the figure at 800 includes first to fourth controllable switches 812-818 and control circuit 820 for controlling the operation of controllable switches 812-818 according to input signals. Figure 8 Also shown is the reference above. Figures 3 to 7 The described type includes a variable voltage power supply circuit 320 and a charge drive circuit 330 for driving the piezoelectric transducer 340. It should also be understood that although the commutator circuit 800 drives the piezoelectric transducer in this example, the commutator circuit 800 is also suitable for driving other capacitive transducers. For example, the commutator circuit 800 can be used to drive a MEMS transducer or an electrostatic transducer.

[0120] A first controllable switch 812 is coupled between a first node 830 of the commutator circuit 800 and a first terminal 342 of the piezoelectric transducer 340. The first node 830 of the commutator circuit 800 is coupled to the output of a charge drive circuit 330, which drives the piezoelectric transducer 340 as described above.

[0121] The second controllable switch 814 is coupled between the first terminal 342 of the piezoelectric transducer 340 and the reference voltage power supply rail.

[0122] The third controllable switch 816 is coupled between the first node 830 of the commutator circuit 800 and the second terminal 344 of the piezoelectric transducer 340.

[0123] The fourth controllable switch 818 is coupled between the second terminal 344 of the piezoelectric transducer 340 and the reference voltage power supply rail.

[0124] By selectively opening and closing controllable switches 812-816, one of the first terminal 342 and the second terminal 344 of the piezoelectric transducer 340 can be coupled to the output of the charge drive circuit 330, and the other of the first terminal 342 and the second terminal 344 of the piezoelectric transducer 340 can be coupled to the reference voltage supply rail.

[0125] The control circuit 820 controls the operation of the controllable switches 812-818 according to the polarity of the input signal (relative to the reference voltage), as shown in the table below.

[0126]

[0127] Therefore, when the input signal is positive, the fourth switch 818 closes, thereby coupling the second terminal 344 of the piezoelectric transducer 340 to the reference voltage supply rail. The second switch 814 and the third switch 816 are open, and the first switch 812 is controlled by the variable voltage power supply circuit 320. When charge is transferred to the first terminal 342 of the piezoelectric transducer 340, the first switch 812 closes, thereby coupling the first terminal 342 of the piezoelectric transducer 340 to the output of the charge drive circuit 330.

[0128] When the input signal is negative, the second switch 814 closes, thereby coupling the first terminal 342 of the piezoelectric transducer 340 to the reference voltage supply rail. The first switch 812 and the fourth switch 818 are open, and the third switch 816 is controlled by the variable voltage power supply circuit 320. When charge is transferred to the second terminal 344 of the piezoelectric transducer 340, the third switch 816 closes, thereby coupling the second terminal 344 of the piezoelectric transducer 340 to the output of the charge drive circuit 330.

[0129] Therefore, the first terminal 342 or the second terminal 344 of the piezoelectric transducer 340 can be driven by the charge drive circuit 330, depending on the polarity of the input signal.

[0130] As will be understood from the foregoing discussion, the circuitry of this disclosure provides a power-efficient component for driving a piezoelectric transducer, which reduces hysteresis and creep that may occur when such a piezoelectric transducer is voltage-driven. Improved power efficiency results from charge cycling between the storage capacitor and the supply capacitor when the supply voltage of the charge-driven output stage changes based on the level or envelope of the input signal. The circuitry of this disclosure is also suitable for driving other capacitive transducers, such as MEMS transducers and electrostatic transducers.

[0131] The implementation scheme can be implemented in a range of applications and is particularly well-suited for audio applications.

[0132] 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.

[0133] 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, programmable memory such as read-only memory (firmware), or 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 hardware description languages ​​such as Verilog™ or 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 can also be carried out using code that runs on a field-programmable analog array or similar device to configure analog hardware.

[0134] 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, the circuit comprising: A charge-driven output stage circuit, configured to receive an input signal and drive the capacitor transducer to generate an output signal; A variable voltage power supply circuit configured to output a power supply voltage for a charge-driven output stage circuit, wherein the power supply voltage output by the variable voltage power supply circuit varies based on the input signal; A power supply capacitor, the power supply capacitor being used to receive the power supply voltage output by the variable voltage power supply circuit; Storage capacitors; as well as A circuit for transferring charge between the storage capacitor and the power supply capacitor; The charge-driven output stage circuit mentioned above includes a charge pump circuit.

2. The circuit of claim 1, further comprising circuitry configured to transmit a control signal to the variable voltage power supply circuitry to cause the variable voltage power supply circuitry to adjust the magnitude of the supply voltage of the charge drive output stage circuitry based on the input signal.

3. The circuit of claim 2, wherein the circuit configured to transmit a control signal to the variable voltage power supply circuit to cause the variable voltage power supply circuit to adjust the magnitude of the supply voltage of the charge drive output stage circuit based on the input signal includes a lead circuit.

4. The circuit of claim 3, wherein the lead circuit is configured to monitor the level of the input signal, and wherein the control signal is based on the level of the input signal.

5. The circuit of claim 3 or claim 4, wherein the lead circuit is configured to monitor the envelope of the input signal, and wherein the control signal is based on the envelope of the input signal.

6. The circuit according to any one of claims 1 to 4, wherein the circuit for transferring charge between the storage capacitor and the power supply capacitor comprises a switching network and one or more inductors.

7. The circuit of claim 6, further comprising control circuitry for controlling the operation of the switching network to transfer charge between the storage capacitor and the supply capacitor via at least one of the one or more inductors.

8. The circuit according to any one of claims 1 to 4, wherein the variable voltage power supply circuit is configured to output the positive supply voltage and the negative supply voltage of the charge drive output stage circuit.

9. The circuit of claim 8, comprising a first supply capacitor for the positive supply voltage and a second supply capacitor for the negative supply voltage.

10. The circuit according to any one of claims 1 to 4, further comprising a signal processing circuit configured to process the input signal and output a processed version of the input signal to the charge-driven output stage circuit.

11. The circuit of claim 10, wherein the signal processing circuit comprises one or more of the following: Filter circuit; Digital-to-analog converter circuit; Envelope detector circuit; and Delay circuit.

12. The circuit according to any one of claims 1 to 4, wherein the input signal is an audio signal, a tactile signal, or an ultrasonic signal.

13. The circuit according to any one of claims 1 to 4, wherein the charge-driven output stage circuit comprises a linear amplifier circuit.

14. The circuit of claim 13, wherein the variable voltage power supply circuit is configured to output a positive supply voltage and a negative supply voltage to the charge-driven output stage circuit, and wherein the linear amplifier circuit comprises: The input stage receives a fixed supply voltage from a positive voltage supply and a reference voltage supply. as well as The output stage receives the positive supply voltage and the negative supply voltage from the variable voltage power supply circuit.

15. The circuit according to any one of claims 1 to 4, wherein the charge-driven output stage circuit comprises: Current source; Current tank; as well as Control circuit, The control circuit is configured to control the operation of the current source and the current tank to selectively charge and discharge the capacitor transducer based on the input signal.

16. The circuit according to any one of claims 1 to 4, further comprising a commutator circuit coupled to the charge-driven output stage circuit, the commutator circuit being configured to selectively couple a first or second terminal of the capacitor transducer to the output of the charge-driven output stage circuit.

17. The circuit according to any one of claims 1 to 4, wherein the capacitor transducer comprises a piezoelectric transducer, a MEMS transducer, or an electrostatic transducer.

18. An integrated circuit comprising the circuit according to any one of the preceding claims.

19. An apparatus comprising circuitry according to any one of the preceding claims, wherein the apparatus comprises a mobile phone, a tablet computer or laptop computer, a smart speaker, or an accessory device.

20. The apparatus of claim 19, wherein the accessory device includes headphones.

21. The device of claim 20, wherein the headphones comprise over-ear headphones or in-ear headphones.

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