Driver circuit for a capacitive transducer

Abstract

The present disclosure relates to a circuit for driving a capacitive transducer based on an input signal. The circuit comprises a primary driver circuit configured to receive the input signal and output a primary drive signal to the capacitive transducer based on the input signal, and a secondary driver circuit configured to receive an error signal indicative of an error between the input signal and the primary drive signal and output a secondary drive signal to the capacitive transducer based on the error signal, wherein both the primary driver circuit and the secondary driver circuit comprise a switching converter circuit.

Description

Technical Field

[0001] This disclosure relates to a driver circuit for a capacitive transducer. Background Technology

[0002] Piezoelectric transducers are increasingly 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, thanks to their slim form factor, which can be advantageous in meeting the need for increased functionality in such devices without significantly increasing their size. Piezoelectric transducers are also increasingly being used as transducers in ultrasonic sensing and ranging systems.

[0003] Piezoelectric transducers can be voltage-driven. However, when voltage-driven, piezoelectric transducers exhibit hysteresis and creep, meaning that their displacement depends on both the currently applied voltage and the previously applied voltage. Therefore, for any given drive voltage, a variety of possible displacements exist for the piezoelectric transducer. In 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 varies with the applied charge.

[0005] Figure 1 is a schematic diagram of a circuit for driving a piezoelectric transducer with charge. As generally shown at 100 in Figure 1, the charge driving circuit 102 (e.g., it may be a charge pump circuit) can 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 the piezoelectric transducer 104 such that the piezoelectric transducer 104 produces an audible, ultrasonic or tactile output based on the electrical input signal. Summary of the Invention

[0006] According to a first aspect, the present invention provides a circuit for driving a capacitive transducer based on an input signal, the circuit comprising:

[0007] A primary driver circuit configured to receive the input signal and output a primary drive signal to the capacitive transducer based on the input signal; and

[0008] The secondary driver circuit is configured to receive an error signal indicating the error between the input signal and the primary drive signal, and to output a secondary drive signal to the capacitive transducer based on the error signal.

[0009] Both the primary driver circuit and the secondary driver circuit include a switch converter circuit.

[0010] In one example, the primary driver circuit includes a variable voltage power supply circuit, and the secondary driver circuit includes a charge pump circuit.

[0011] The variable voltage power supply circuit may include a switching network, an inductor, and a storage capacitor.

[0012] The charge pump circuit may include a switching network and a flying capacitor.

[0013] The flying capacitor can be variable.

[0014] The charge pump circuit can be configured to receive a power supply that varies based on parameters of the input signal.

[0015] The variable voltage power supply circuit can be configured to provide the power supply to the charge pump circuit.

[0016] The variable voltage power supply circuit may include a detector circuit configured to detect the level, envelope, or other parameters of the input signal and control the power supply voltage supplied to the charge pump circuit based on the detected level, envelope, or other parameters.

[0017] The charge pump circuit may include one or more supply capacitors, and the switching network is operable to transfer charge between the storage capacitor and the one or more supply capacitors.

[0018] In another example, the primary driver circuit includes a first variable voltage power supply circuit, and the secondary driver circuit includes a second variable voltage power supply circuit.

[0019] The primary driver circuit and the secondary driver circuit may each include a switching network and an inductor, and the inductor of the secondary driver circuit may be smaller than the inductor of the primary driver circuit.

[0020] The inductor of the secondary driver circuit can be embedded in an integrated circuit that implements the circuit.

[0021] The first variable voltage power supply circuit may include a first storage capacitor for storing charge.

[0022] The first storage capacitor can be shared by the first variable voltage power supply circuit and the second variable voltage power supply circuit.

[0023] The second variable voltage power supply circuit may include a second storage capacitor for storing charge.

[0024] The circuit may also include an auxiliary capacitor configured to receive charge from the primary driver circuit or the secondary driver circuit in order to adjust the voltage across the auxiliary capacitor.

[0025] The auxiliary capacitor can be:

[0026] Series coupling between the capacitive transducer and ground; or

[0027] Series coupling is performed between the output of the secondary driver circuit and the first terminal of the capacitive transducer; or

[0028] The capacitor transducer is coupled in parallel between the output of the secondary driver circuit and ground; or

[0029] It is coupled in parallel with the capacitor transducer between the output of the primary driver circuit and ground.

[0030] The circuit may include:

[0031] A first auxiliary capacitor is connected in parallel with the capacitive transducer between the output of the secondary driver circuit and ground; and

[0032] The second auxiliary capacitor is coupled in parallel with the capacitive transducer between the output of the primary driver circuit and ground.

[0033] The circuit may include:

[0034] A first auxiliary capacitor is connected in parallel with the capacitive transducer between the output of the secondary driver circuit and ground; and

[0035] A second auxiliary capacitor is coupled in series between the output of the secondary driver circuit and the first terminal of the capacitive transducer.

[0036] The primary driver circuit may be configured to be coupled to a terminal of the capacitive transducer, and the secondary driver circuit may be configured to be coupled to the same terminal of the capacitive transducer.

[0037] Alternatively, the primary driver circuit may be configured to be coupled to a first terminal of the capacitive transducer, and the secondary driver circuit may be configured to be coupled to a second terminal of the capacitive transducer.

[0038] The circuit may further include a commutation circuit configured to selectively couple one of the first and second terminals of the capacitive transducer to the primary driver circuit and the secondary driver circuit, and to couple the other of the first and second terminals of the capacitive transducer to a reference voltage supply.

[0039] The commutation circuit can be configured to selectively couple one of the first and second terminals of the capacitive transducer to the primary driver circuit and the secondary driver circuit based on the polarity of the input signal, and to couple the other of the first and second terminals of the capacitive transducer to a reference voltage supply.

[0040] The commutation circuit may be configured to selectively couple one of the primary driver circuit and the secondary driver circuit to a first terminal of the capacitive transducer, and to couple the other of the primary driver circuit and the secondary driver circuit to a second terminal of the capacitive transducer.

[0041] The commutation circuit can be configured to selectively couple one of the primary driver circuit and the secondary driver circuit to the first terminal of the capacitive transducer based on the polarity of the input signal, and to couple the other of the primary driver circuit and the secondary driver circuit to the second terminal of the capacitive transducer.

[0042] The circuit may further include a first control circuit for regulating the operation of the primary driver and a second control circuit for regulating the operation of the secondary driver circuit. The width of the second control circuit may be greater than the width of the first control circuit.

[0043] The secondary driver circuit can be selectively operated based on the parameters of the input signal.

[0044] The parameters of the input signal may include one or more of the signal level, envelope, and frequency of the input signal.

[0045] The primary driver circuit can be selectively operated based on the signal level or envelope of the input signal.

[0046] The primary driver circuit and / or the secondary driver circuit may be selectively operable based on the operating mode of the circuit.

[0047] The secondary driver circuit can be enabled in a first mode where the input signal includes an audio signal, and can be disabled in a second mode where the input signal includes a tactile signal or a waveform.

[0048] In another example, both the primary driver circuit and the secondary driver circuit include a charge pump circuit.

[0049] In another example, the primary driver circuit includes a charge pump circuit, and the secondary driver circuit includes a variable voltage power supply circuit.

[0050] For example, the capacitive transducer can be a piezoelectric transducer, a MEMS transducer, or an electrostatic transducer.

[0051] According to a second aspect, the present invention provides an integrated circuit comprising the circuit of the first aspect.

[0052] According to a second aspect, the present invention provides an apparatus comprising the circuitry of the first aspect.

[0053] The device may include, for example, a mobile phone, a tablet computer or a laptop computer, a smart speaker, an accessory, a headset, an in-ear headphone or an earbud. Attached Figure Description

[0054] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0055] Figure 1 is a schematic diagram illustrating the concept of a charge-driven capacitive transducer;

[0056] Figure 2 is a schematic diagram illustrating the concept of auxiliary amplifier arrangement;

[0057] Figure 3 is a schematic diagram illustrating an example of a driver circuit for driving a capacitor transducer;

[0058] Figure 4 is a schematic diagram showing an alternative example of a driver circuit for driving a capacitive transducer;

[0059] Figure 5 is a schematic diagram illustrating another alternative example of a driver circuit for driving a capacitive transducer.

[0060] Figure 6 is a schematic diagram illustrating another alternative example of a driver circuit for driving a capacitive transducer.

[0061] Figure 7 is a schematic diagram showing the control loop of the driver circuit in Figure 4;

[0062] Figure 8 is a schematic diagram showing an example of a primary driver circuit for the driver circuits of Figures 3 to 7;

[0063] Figure 9 is a schematic diagram showing an example of a secondary driver circuit used in the driver circuits of Figures 3 to 7;

[0064] Figure 10 is a schematic diagram of an alternative example of a secondary driver circuit for the driver circuits of Figures 3 to 7.

[0065] Figure 11 is a schematic diagram illustrating a commutator circuit that can be used to provide bipolar drive for a capacitor transducer; and

[0066] Figures 12 to 16 are schematic diagrams illustrating alternative examples of driver circuits for driving capacitive transducers. Detailed Implementation

[0067] Improving the power efficiency of the circuitry used to drive the transducer without adversely affecting the output signal fidelity is a persistent design goal, and many different techniques can be employed to enhance power efficiency. One concept that can be used in audio applications employing conventional audio output transducers (such as diaphragm-based loudspeakers) is the "auxiliary amplifier."

[0068] Figure 2 is a schematic diagram of an exemplary auxiliary amplifier arrangement 200 for driving a conventional audio output transducer 210, which is a loudspeaker in the illustrated arrangement.

[0069] An exemplary auxiliary amplifier arrangement 200 includes a primary amplifier 230 that receives a positive supply voltage VSup from a positive supply rail 220. The primary amplifier 230 may be, for example, a switching amplifier, such as a Class D amplifier, configured to receive an audio input signal and output a digital primary transducer drive signal to transducer 210 via a reconstruction filter 240 based on the audio input signal.

[0070] Reconstruction filter 240 is configured to convert the digital primary transducer drive signal output from primary amplifier 230 into an analog primary transducer drive signal suitable for driving transducer 210. Reconstruction filter 240 includes: an inductor 242, which is coupled in series between the output of primary amplifier 230 and a first terminal of transducer 210; and a capacitor 244, which is coupled in parallel with transducer 210 between inductor 242 and a reference voltage supply rail (e.g., ground). A second terminal of transducer 210 is coupled to the reference voltage supply rail (e.g., ground).

[0071] The auxiliary amplifier arrangement 200 also includes a secondary amplifier 250, which may be a linear amplifier, such as, for example, a Class AB amplifier. The secondary amplifier 250 is configured to receive an error signal output from the error block 260 and output a secondary transducer drive signal to the transducer 210 based on the error signal.

[0072] Error block 260 is configured to receive an input audio signal (or a signal indicating or representing the input audio signal) at its first input terminal and an analog primary transducer drive signal (or a signal indicating or representing the analog primary transducer drive signal) at its second input terminal, and generate an error signal based on the difference between the input audio signal and the analog primary transducer drive signal.

[0073] When using auxiliary amplifier arrangement 200, primary amplifier 230 provides the primary transducer drive signal to transducer 210 in a power-efficient manner. The primary transducer drive signal provides most of the power required to drive transducer 210 based on the input audio signal. Secondary amplifier 250 provides the secondary transducer drive signal to transducer 210 to compensate for any errors in the analog primary transducer drive signal. Although the power efficiency of secondary amplifier 250 may be lower than that of primary amplifier 230, its overall impact on the power efficiency of auxiliary amplifier arrangement 200 is small because the secondary transducer drive signal is smaller than the analog primary transducer drive signal, and therefore draws less power from the positive supply rail 220 by secondary amplifier 250.

[0074] Therefore, the auxiliary amplifier arrangement 200 can provide a high-fidelity output signal for driving the transducer 210 with high power efficiency. However, the auxiliary amplifier arrangement 200 of Figure 2 is unsuitable for driving piezoelectric transducers for a variety of reasons, including problems associated with hysteresis and creep discussed above.

[0075] Figure 3 is a schematic diagram of an example of a driver circuit 300 for driving a piezoelectric transducer 310. It should be understood that although the driver circuit 300 in this example drives a piezoelectric transducer, the driver circuit 300 is also suitable for driving other capacitive transducers. For example, the driver circuit 300 can be used to drive a MEMS transducer or an electrostatic transducer.

[0076] The driver circuit 300 includes a primary driver circuit 320 for driving the piezoelectric transducer 310. The primary driver circuit 320 includes a switch-converter circuit and may be, for example, a variable voltage power supply circuit, a charge pump circuit, or some other form of switch-converter circuit.

[0077] The primary driver circuit 320 receives a first positive supply voltage VSup from the first positive supply rail 330, which can be coupled directly or via a voltage regulator to a power source, such as the battery of the host device that combines the driver circuit 300 and the piezoelectric transducer 310.

[0078] The primary driver circuit 320 is configured to receive an input signal and output a primary transducer drive signal based on the input signal, such that charge is transferred to and from the piezoelectric transducer 310 to drive the piezoelectric transducer 310. A storage capacitor 322 (or multiple storage capacitors) is provided to store the charge that has been transferred from the piezoelectric transducer 310 to facilitate charge “recycling”, thereby reducing the need for additional charge to be supplied from the first positive power rail 330.

[0079] The driver circuit 300 also includes a secondary driver circuit 340 for driving the piezoelectric transducer 310. The secondary driver circuit 340 also includes a switch-converter circuit and may be, for example, a variable voltage power supply circuit, a charge pump circuit, or some other form of switch-converter circuit.

[0080] Therefore, this disclosure covers: embodiments of driver circuit 300 in which both primary driver circuit 320 and secondary driver circuit 340 include variable voltage power supply circuits, or in which both primary driver circuit 320 and secondary driver circuit 340 include charge pump circuits; and embodiments in which one of primary driver circuit 320 and secondary driver circuit 340 includes a variable voltage power supply circuit, and the other of secondary driver circuit 340 and primary driver circuit 320 includes a charge pump circuit.

[0081] The secondary driver circuit 340 receives a second positive supply voltage VBoost from the second positive supply rail 360. The second positive supply rail 360 may receive the second positive supply voltage VBoost from a boost converter or the like, which is configured to generate the second positive supply voltage VBoost from a lower voltage supply (such as the supply voltage provided by the host device's battery).

[0082] The driver circuit 300 also includes an error block 350, which is configured to receive an input signal (or a signal indicating or representing the input signal) at its first input terminal 352 and a signal indicating or representing a primary transducer drive signal, such as a digital signal representing the voltage across the piezoelectric transducer 310 output by the ADC 370, at its second input terminal 354, and generate an error signal based on the input signal and the primary transducer drive signal.

[0083] The secondary driver circuit 340 is configured to receive an error signal output by the error block 350 and output a secondary transducer drive signal based on the error signal, such that charge is transferred to and from the piezoelectric transducer 310 to compensate for any error between the input signal and the primary transducer drive signal.

[0084] In the example shown in Figure 3, the output of the primary driver circuit 320 is coupled to the first terminal 312 of the piezoelectric transducer 310, and the second terminal 314 of the piezoelectric transducer 310 is coupled to a reference voltage supply rail (e.g., ground rail). The output of the secondary driver circuit 340 is also coupled to the first terminal 312 of the piezoelectric transducer 310. Therefore, the piezoelectric transducer 310 is coupled in parallel with the primary driver circuit 320 and the secondary driver circuit 340.

[0085] In this arrangement, particularly when the piezoelectric transducer 310 is composed of a single layer or a few layers of piezoelectric material, the secondary driver circuit 340 may need to provide a relatively large output voltage (e.g., approximately 100V) at its output to provide the charge required to compensate for errors in the primary transducer drive signal, thereby generating the desired displacement of the piezoelectric transducer 310. To provide the required output voltage, the supply voltage VBoost may need to be significantly higher than the output voltage provided by the battery of the host device in conjunction with circuit 300, and therefore the secondary supply voltage VBoost may need to be provided by a boost converter as described above.

[0086] Figure 4 is a schematic diagram of an alternative example of the driver circuit 400 for driving the piezoelectric transducer 310. The driver circuit 400 is similar to the driver circuit 300 of Figure 3, and therefore, in Figures 3 and 4, the same elements are indicated by the same reference numerals. Similarly, it can be understood that although the driver circuit 400 in this example drives a piezoelectric transducer, the driver circuit 400 is also suitable for driving other capacitive transducers. For example, the driver circuit 400 can be used to drive MEMS transducers or electrostatic transducers.

[0087] The difference between the driver circuit 400 in Figure 4 and the driver circuit 300 in Figure 3 is that the output of the primary driver circuit 320 is coupled to the first terminal 312 of the piezoelectric transducer 310, while the output of the secondary driver circuit 340 is coupled to the second terminal 314 of the piezoelectric transducer 310. Therefore, the piezoelectric transducer 310 is coupled in series with the primary driver circuit and the secondary driver circuit 340.

[0088] Compared to the parallel coupling arrangement of the driver circuit 300 in Figure 3, the series coupling arrangement of the driver circuit 400 in Figure 4 has the advantage that, since the voltage across the piezoelectric transducer 310 is based on the difference between the primary transducer drive signal voltage and the secondary transducer drive signal voltage when using the driver circuit 400, the relatively small voltage output by the secondary driver circuit 340 is sufficient to provide the necessary compensation for errors in the primary transducer drive signal. Therefore, the second positive supply voltage VSup to the secondary driver circuit 340 does not need to be high and can therefore be supplied by the host device's battery (directly or indirectly, e.g., via a voltage regulator). Because the supply voltage to the secondary driver circuit 340 is relatively low, the secondary driver circuit can use physically smaller, low-power devices (e.g., transistors), which helps to minimize the silicon area occupied by the secondary driver circuit 340 in the integrated circuit implementation of the driver circuit 400.

[0089] Figure 5 is a schematic diagram of another alternative example of the driver circuit 500 for driving the piezoelectric transducer 310. Similarly, it should be understood that although the driver circuit 500 in this example drives a piezoelectric transducer, it is also suitable for driving other capacitive transducers. For example, the driver circuit 500 can be used to drive MEMS transducers or electrostatic transducers. The driver circuit 500 is similar in some respects to the driver circuit 400 of Figure 4, and therefore the same components are indicated by the same reference numerals in Figures 4 and 5. For clarity and simplicity, some components of the driver circuit 400 of Figure 4 are not shown in Figure 5.

[0090] The difference between the driver circuit 500 in Figure 5 and the driver circuit 400 in Figure 4 is that the driver circuit in Figure 5 includes an "auxiliary" capacitor 510 coupled between node 512 and ground, said node being located between the second terminal 314 of the piezoelectric transducer 310 and the output terminal of the secondary driver circuit 340. Therefore, the auxiliary capacitor 510 is coupled in series between the piezoelectric transducer 310 and ground. The capacitance of the auxiliary capacitor 510 can be approximately ten times the nominal capacitance of the piezoelectric transducer 310.

[0091] The driver circuit 500 includes an input signal path 520 that couples the input node 522 of the driver circuit 500 to the input terminal of the primary driver circuit 320. The input signal path 520 includes an adder circuit 524. The output signal path 530 couples the output terminal of the primary driver circuit 320 to the first terminal 312 of the piezoelectric transducer 310 at node 532.

[0092] The primary driver feedback path 540 couples the output signal path 530 to the first input of the first subtractor circuit 542. The second input of the first subtractor circuit 542 is coupled to the output of the adder circuit 524. The first subtractor circuit 542 is configured to output a primary driver feedback signal FBPRIM to the primary driver circuit 320, which indicates the difference between the voltage at the input of the primary driver circuit 320 and the voltage at the output of the primary driver circuit 320.

[0093] The driver circuit 500 also includes an error signal path 550, which couples node 532 to the input of the secondary driver circuit 340 via a second subtractor circuit 552. A first input of the second subtractor circuit 552 is coupled to input node 522 of the input signal path 520, and a second input of the second subtractor circuit 552 is coupled to node 532. The output of the second subtractor circuit 552 is coupled to the input of the secondary driver circuit 340 to provide a first error signal, Error1, to the secondary driver circuit 340.

[0094] The driver circuit 500 also includes a secondary driver feedback path 560, which couples the output of the secondary driver circuit 340 to the secondary driver circuit 340 via a third subtractor circuit 562. Therefore, the output of the secondary driver circuit 340 is coupled to the first input of the third subtractor circuit 562. The second input of the third subtractor circuit 562 receives a signal indicating the target voltage VH_TARGET across the auxiliary capacitor 510. The third subtractor circuit 562 therefore outputs a signal to the secondary driver circuit 340 indicating the difference between the target voltage VH_TARGET and the actual voltage VH across the auxiliary capacitor 510.

[0095] The driver circuit 500 also includes a filter signal path 570, which includes a low-pass filter 572 having an input coupled to node 526 and an output coupled to a first input of adder circuit 524. A second input of adder circuit 524 receives an input voltage VSig representing the signal (e.g., an audio or haptic signal) to be output by piezoelectric transducer 310. Adder circuit 524 is configured to add the signals received at its input and output the result of the addition. Therefore, adder circuit 324 outputs the signal VSig + VH* (where VH* is a filtered version of the voltage VH across auxiliary capacitor 510) to primary driver circuit 320.

[0096] The primary driver circuit 320 is configured to output a primary voltage VPRIM_OUT to the piezoelectric transducer 310 to transfer charge to the piezoelectric transducer 310 so as to cause the piezoelectric transducer 310 to be displaced.

[0097] The secondary driver circuit 340 is configured to selectively charge or discharge the auxiliary capacitor 510 to adjust the voltage VH across the auxiliary capacitor 510 to facilitate the transfer of charge to or from the piezoelectric transducer 310 to correct any errors in the primary output voltage VPRIM_OUT.

[0098] The instantaneous voltage VP across the piezoelectric transducer 310, generated by the primary voltage VPRIM_OUT, is equal to the difference between VPRIM_OUT and VH, i.e., VP – VPRIM_OUT – VH. Therefore, the auxiliary capacitor 510 provides a “buffer” voltage VH, which can be adjusted upwards or downwards (through appropriate action of the secondary driver circuit 340) to adjust the voltage VP across the piezoelectric transducer 310 to compensate for errors in the primary voltage VPRIM_OUT output by the primary driver circuit 320.

[0099] For the displacement of the piezoelectric transducer 310 to correctly represent the input signal, the voltage VP should be equal to the voltage VSig. Therefore, VPRIM_OUT should be as close as possible to VSig + VH so that the voltage VP equals VSig (because VP = VPRIM_OUT – VH). However, as will be understood, if only VH is added to VSig, high-frequency transient changes in VH can cause undesirable oscillations in the voltage VP. A low-pass filter 572 is operable to attenuate such high-frequency transients and provides a filtered version VH* of the voltage VH, which is added to VSig by the adder circuit 524.

[0100] Therefore, in the absence of any error, VPRIM_OUT = VSig + VH*, and VP = VPRIM_OUT – VH ≈ VSig.

[0101] The primary driver circuit 320 is operable to adjust its output signal VPRIM_OUT based on the primary driver feedback signal FBPRIM to keep VPRIM_OUT as close as possible to VSig + VH*, thereby minimizing the error of VPRIM_OUT.

[0102] To correct for any error in voltage VP (i.e., to correct any difference between VSig and VP), the secondary driver circuit 340 receives a first error signal Error1 from the subtractor circuit 552, which indicates the difference between VP and VSig, and adjusts the voltage VH across the auxiliary capacitor 510 accordingly by adding or removing charge from the auxiliary capacitor 510. Therefore, if VP is greater than VSig, charge can be added to the auxiliary capacitor 510 to increase voltage VH for compensation. Similarly, if VP is less than VSig, charge can be removed from the auxiliary capacitor 510 to decrease voltage VH for compensation.

[0103] As will be understood, repeatedly correcting the error of VP by reducing the voltage VH across the auxiliary capacitor 510 may eventually cause the voltage VH to drop to zero, which would make it impossible to further reduce VP without a negative voltage supply.

[0104] To avoid this possibility, the secondary driver feedback path 560 provides a second error signal, Error2, which indicates the difference between the target voltage VH_TARGET across the auxiliary capacitor 510 and the actual voltage VH across the auxiliary capacitor 510. The secondary driver circuit 340 is operable to adjust its output to minimize the second error signal Error2 over a long period. Therefore, the secondary driver circuit 340 can operate (almost) instantaneously to adjust the voltage VH to compensate for the error in VPRIM_OUT to achieve the correct VP for a given input signal, but over a longer duration, the secondary driver circuit 340 is operable to maintain the voltage VH across the auxiliary capacitor 510 at the target voltage VH_TARGET, such that after any adjustment to VH to compensate for the error in VPRIM_OUT, VH returns to VH_TARGET.

[0105] As those skilled in the art will understand, the control loop implemented by the error signal path 550 should operate faster (i.e. have higher bandwidth) than the control loop implemented by the secondary driver feedback path 560.

[0106] In addition, the control loop implemented by the error signal path 550 should operate faster (i.e. have higher bandwidth) than the control loop implemented by the primary driver feedback path 540 in order to quickly compensate for the error of VPRIM_OUT.

[0107] More generally, in all the disclosed examples, the control loop that controls or regulates the operation of the secondary driver circuit 340 will have a higher bandwidth than the control loop that controls or regulates the operation of the primary driver circuit 320, in order to quickly compensate for errors in the primary drive signal output by the primary driver circuit 320.

[0108] Figure 6 is a schematic diagram of an alternative example of a driver circuit 600 for driving a piezoelectric transducer 310. As in the previous examples, it should be understood that although the driver circuit 600 in this example drives a piezoelectric transducer, the driver circuit 600 is also suitable for driving other capacitive transducers. For example, the driver circuit 600 can be used to drive a MEMS transducer or an electrostatic transducer. The driver circuit 600 is similar to the driver circuit 300 of Figure 3, and therefore, in Figures 3 and 6, the same elements are indicated by the same reference numerals.

[0109] In the driver circuit 600 of Figure 6, the positive supply voltage Vp and negative supply voltage Vn supplied by the primary driver circuit 320 to the secondary driver circuit 340 vary according to the level, envelope or other parameters of the input signal.

[0110] For this purpose, the primary driver circuit 320 of the variable voltage power supply, which includes or is implemented in this example as described in detail below with reference to FIG8, may include a detector circuit 610 that receives an input signal, detects the signal level (e.g., amplitude), envelope, or some other parameter of the input signal, and controls the positive supply voltage Vp and the negative supply voltage Vn based on the detected parameters of the input signal. The positive supply voltage Vp and the negative supply voltage Vn are supplied to the secondary driver circuit via corresponding first (positive) supply voltage rail 620 and second (negative) supply voltage rail 630.

[0111] The driver circuit 600 also includes a first supply capacitor 640 and a second supply capacitor 650. The first supply capacitor 640 (labeled Cp in FIG. 6) is coupled between the first (positive) supply voltage rail 620 and ground, while the second supply capacitor 650 (labeled Cn in FIG. 6) is coupled between the second (negative) supply voltage rail 630 and ground.

[0112] In the example shown in Figure 6, the primary driver circuit 320 provides a positive voltage Vp and a negative voltage Vn to the secondary driver circuit 340. However, as those skilled in the art will understand, if the secondary driver circuit 340 is configured to operate on a power supply referenced to ground, for example, the primary driver circuit 320 will only provide a positive supply voltage to the secondary driver circuit 340. In such an arrangement, only a single supply capacitor coupled between the first (positive) supply voltage rail 620 and ground would be required.

[0113] The voltage output by the primary driver circuit 320 depends on the detected signal level, envelope, or other parameters of the input signal. Therefore, if the detected signal level, envelope, or other parameters indicate that the input signal is increasing, the amplitude of the voltage output by the primary driver circuit 320 supplying power to the secondary driver circuit 340 increases. Conversely, if the detected level, envelope, or other parameters indicate that the input signal is decreasing, the amplitude of the voltage output by the primary driver circuit supplying power to the secondary driver circuit 340 decreases.

[0114] The secondary driver circuit 340 is coupled to the primary driver circuit 320 to receive variable positive voltage Vp and negative voltage Vn as a power supply. The secondary driver circuit 340 can also be operated to receive an error signal output from the error block 350 and provide a compensating second drive signal to drive the piezoelectric transducer 310, as discussed above.

[0115] Using a variable supply voltage to power the secondary driver circuit 340 helps improve the power efficiency of the secondary driver circuit 340 by reducing or minimizing unnecessary margins in the supply voltage.

[0116] The storage capacitor 322 and the primary driver circuit 320 can be used to further improve the power efficiency of the circuit 600 by transferring charge between the storage capacitor 322 and the first supply capacitor 640 and the second supply capacitor 650 when the power supply requirements of the secondary driver circuit 340 change.

[0117] For example, when the level or envelope of the input signal decreases, the charge stored in the first supply capacitor 640 and the second supply capacitor 650 may exceed the charge required to supply the secondary driver circuit 340 to provide a compensating second drive signal to the piezoelectric transducer 310. In this case, instead of wasting power by discharging the first supply capacitor 640 and the second supply capacitor 650 to ground, the excess charge can be transferred to the storage capacitor 322 using the switching network and inductor of the primary driver circuit 320: first, the switching network is controlled to establish a current path between the first supply capacitor 640 or the second supply capacitor 650 and ground via the inductor, such that a magnetic field is formed around the inductor; then, the switching network is controlled to decouple the first supply capacitor 640 or the second supply capacitor 650 from the inductor and establish a current path from the inductor to the storage capacitor 322, such that when the magnetic field around the inductor collapses, a current is induced to flow to the storage capacitor 322, thereby charging the storage capacitor 322.

[0118] Conversely, as the level or envelope of the input signal increases, it may be necessary to increase the amount of charge stored in the first supply capacitor 640 and the second supply capacitor 650 to supply the secondary driver circuit 340 to support the required output signal level. The stored charge can be transferred from the storage capacitor 332 to at least partially achieve the required increase by reusing the switching network and inductor of the primary driver circuit 320: first, the switching network is controlled to establish a current path between the storage capacitor 322 and ground via the inductor, such that a magnetic field is formed around the inductor; then, the switching network is controlled to decouple the storage capacitor 322 from the inductor and establish a current path from the inductor to the first supply capacitor 640 or the second supply capacitor 650, such that when the magnetic field around the inductor collapses, a current is induced to flow to the first supply capacitor 640 or the second supply capacitor 650, thereby charging the first supply capacitor 640 or the second supply capacitor 650.

[0119] Although in the example shown in Figure 6, the primary driver circuit 320 and the secondary driver circuit 340 are coupled in parallel with the piezoelectric transducer 310, those skilled in the art will understand that the principle of using one or more supply voltages that vary according to the signal level, envelope, or other parameters of the input signal to power the secondary driver circuit 340 is also applicable to the series coupling arrangement shown in Figures 4 and 5, in which the primary driver circuit 320 and the secondary driver circuit 340 are coupled in series with the piezoelectric transducer 310.

[0120] Figure 7 is a schematic diagram showing a driver circuit 700 including a control loop 710 for a secondary driver circuit 340. The control loop 710 shown in Figure 7 and described below applies to driver circuits 300, 400, 500, and 600 of Figures 3 through 6.

[0121] The driver circuit 700 is similar to the driver circuit 400 in FIG4, and therefore the same components are indicated by the same reference numerals and will not be described in detail here. For clarity and brevity, the first positive power supply rail 330 and the second positive power supply rail 360 are not shown in FIG7, but those skilled in the art will readily understand that the primary driver circuit 320 and the secondary driver circuit 340 receive the corresponding first and second power supply voltages from the respective first and second positive power supply rails.

[0122] The control loop 710 includes an analog-to-digital converter (ADC) 720 having an input terminal coupled to a second terminal 314 and an output terminal coupled to a second input terminal 354 of an error block 350. The ADC 720 is configured to convert an analog signal (e.g., the voltage across the piezoelectric transducer 310) indicating the charge on the piezoelectric transducer 310 generated by a primary drive signal output from the primary driver circuit 320 into a digital signal, which is output to the error block 350. The error block 350 receives the input signal at its first input terminal 352 via a feedforward signal path and outputs a digital error signal to a loop filter 730, indicating the difference between the input signal and the signal output by the ADC 720 (and thus the error between the input signal and the primary drive signal output by the primary driver circuit 320).

[0123] The loop filter 730 (e.g., a digital integrator) provides a filtered version of the error signal output by the error block 350 to the Delta-Sigma digital-to-analog converter 740, which in turn outputs a control signal to the secondary driver circuit 340 to control the operation of the secondary driver circuit 340 to increase or decrease the charge on the piezoelectric transducer 310 as needed to compensate for the error between the input signal and the primary drive signal output by the primary driver circuit 320.

[0124] The control loop 710 may also include a filter 750 in the feedforward signal path to the first input terminal 352 of the error block 350 to introduce a delay and transfer function into the input signal, which corresponds to the delay and transfer function of the ADC 720 in the feedback path between the second terminal 314 of the piezoelectric transducer 310 and the second input terminal 354 of the error block 350.

[0125] As indicated above regarding circuit 500 in Figure 5, in order to quickly compensate for errors in the primary drive signal output by the primary driver circuit, control loop 710 should have a larger bandwidth than control loop (not shown) that regulates the operation of primary driver circuit 320.

[0126] In the above examples, the primary driver circuit 320 and the secondary driver circuit 340 are described as operating continuously and simultaneously. However, in some examples, the secondary driver circuit 340 and / or the primary driver circuit 320 may be selectively operable based on some predetermined conditions (i.e., selectively enabled / activated or disabled / deactivated).

[0127] For example, a secondary driver circuit can be selectively operable based on parameters of the input signal, such as frequency or level, or amplitude or envelope of the input signal.

[0128] At low input signal levels, the output of the primary driver circuit 320 may be accurate enough to drive the piezoelectric transducer 310, and therefore, when the input signal level is below a first threshold, the secondary driver circuit 340 can be disabled or deactivated to reduce power consumption of the driver circuit. At higher input signal levels, the primary driver circuit 320 may not be able to output a sufficiently accurate signal to drive the piezoelectric transducer 310 accurately, and therefore, if the input signal level meets or exceeds the first threshold, the secondary driver circuit 340 can be enabled or activated to compensate for errors in the primary drive signal output by the primary driver circuit 320.

[0129] Similarly, for input signals within a specific frequency range, the output of the primary driver circuit 320 may be accurate enough to drive the piezoelectric transducer 310, and therefore, when the input signal frequency is within the specific frequency range, the secondary driver circuit 340 can be disabled or deactivated to reduce the power consumption of the driver circuit. For signals outside the specific frequency range, the primary driver circuit 320 may not be able to output a sufficiently accurate output signal to accurately drive the piezoelectric transducer 310, and therefore, if the frequency of the input signal shifts outside the specific frequency range, the secondary driver circuit 340 can be enabled or activated to compensate for errors in the primary drive signal output by the primary driver circuit 320.

[0130] Alternatively or concurrently, in some examples, the secondary driver circuit 340 and / or the primary driver circuit 320 may be selectively operable in different operating modes of the driver circuit. For example, when the driver circuit operates in a first mode to output an audio signal to the piezoelectric transducer, both the primary driver circuit 320 and the secondary driver circuit 340 may be enabled or activated, while when the driver circuit operates in a second mode to output a tactile signal or waveform to the piezoelectric transducer, the primary driver circuit 320 may be enabled or activated and the secondary driver circuit 340 may be disabled or deactivated to reduce power consumption.

[0131] In another example, when the level (e.g., amplitude or envelope) of the input signal is very low, the output signal power provided by the primary driver circuit 320 may not be required. Therefore, when the level or envelope of the input signal is below a second threshold (which may be below the first threshold mentioned above), the primary driver circuit 320 can be disabled or deactivated, allowing the secondary driver circuit 340 to drive the piezoelectric transducer 310. When the input signal level meets or exceeds the second threshold, the primary driver circuit 320 can be enabled or activated.

[0132] Figure 8 is a schematic diagram of an exemplary variable voltage power supply circuit 800 used as a primary or secondary driver circuit in driver circuits 300, 400, 500, and 600.

[0133] The variable voltage power supply circuit 800 includes a storage capacitor 322 for storing charge, an inductor 810, and a switching network 820 (in this example, it may include first switching devices 822 to fifth switching devices 830, which are controllable switches, such as MOSFET devices). The switching network is used to transfer charge between the storage capacitor 322 and the piezoelectric transducer 310. The storage capacitor 332 is shown as a single capacitor in FIG. 8; however, it should be understood that the storage capacitor 332 may alternatively be provided by multiple capacitors coupled together.

[0134] The variable voltage power supply circuit 800 is configured to receive power from the power supply circuit 840 and selectively supply charge to the storage capacitor 322. The power supply circuit 840 may include a boost power supply circuit configured to receive a relatively low voltage power supply (e.g., power supply from the host device's battery) and output a higher (boosted) supply voltage VSup.

[0135] Although the variable voltage power supply circuit 800 is shown as including only a single inductor 810 (and this may be preferred to minimize the number of external components and thus reduce the cost and space requirements of the primary driver circuit), in some examples, more than one inductor may be present. For example, a first inductor may be provided for transferring charge from the power supply circuit 840 to the storage capacitor 322, and a second inductor may be provided for transferring charge from the storage capacitor 322 to the piezoelectric transducer 310.

[0136] Furthermore, when the secondary driver circuit 340 is implemented using the variable voltage power supply circuit 800, the inductor 810 may be physically small (because the secondary driver circuit only needs to provide a relatively small voltage to compensate for the output error of the primary driver circuit), and therefore, when the secondary power supply circuit is implemented as an integrated circuit, the inductor 810 can be embedded in the integrated circuit rather than provided as a separate off-chip component.

[0137] In contrast, when the primary driver circuit is implemented using the variable voltage power supply circuit 800, the inductor 810 is typically physically large, i.e. too large to be embedded in the integrated circuit (because the primary driver circuit needs to provide a relatively large output voltage), and therefore, when the primary power supply circuit is implemented as an integrated circuit, the inductor 810 is typically not embedded in the integrated circuit, but is provided as a separate off-chip component.

[0138] The first switching device 822 is coupled between the output terminal of the power supply circuit 840 and the first terminal of the inductor 810.

[0139] The second switching device 824 is coupled between the first terminal of the inductor 810 and the reference voltage supply rail (e.g., the ground rail).

[0140] The third switching device 826 is coupled between the second terminal of the inductor 810 and the reference voltage supply rail.

[0141] A fourth switching device 828 is coupled between the second terminal of the inductor 810 and the first terminal of the storage capacitor 332. The second terminal of the storage capacitor 332 is coupled to the reference voltage supply rail.

[0142] The fifth switching device 830 is coupled between the first terminal of the inductor 810 and the first terminal 312 of the piezoelectric transducer 310. The second terminal 314 of the piezoelectric transducer 310 is coupled to the reference voltage supply rail.

[0143] The variable voltage power supply circuit 800 also includes a control circuit 850, which is operable to control the first switching device 822 to the fifth switching device 830 to control the charge transfer between the power supply circuit 840, the storage capacitor 322 and the piezoelectric transducer 310.

[0144] When the variable voltage power supply circuit 800 (or the host device combined with the primary driver circuit) is started, charge is transferred from the power supply circuit 840 to the storage capacitor 322 to raise the voltage across the storage capacitor 322 to a level suitable for driving the piezoelectric transducer 310.

[0145] In the first stage of the charging process, in response to an appropriate control signal transmitted by the control circuit 850, the first switching device 822 and the third switching device 826 are closed. This forms a current path through the inductor 810. When current flows through the inductor 810, a magnetic field is formed around it, thereby storing energy.

[0146] In the second stage of the charging process, also in response to an appropriate control signal transmitted by the control circuit 850, the first switch device 822 and the third switch device 826 are opened, and the second switch device 824 and the fourth switch device 828 are closed. The magnetic field around the inductor 810 collapses, thereby inducing a current flowing from the inductor 810 to the storage capacitor 322, thereby charging the storage capacitor 322.

[0147] The first and second stages are repeated until the voltage across the storage capacitor 322 increases to a level suitable for driving the piezoelectric transducer 310, as determined by the control circuit 850 based on the feedback signal received from the piezoelectric transducer 310. Once the storage capacitor 322 has been charged to the desired level, the first switching device 822 is disconnected, thereby decoupling the power supply circuit 840 so that the piezoelectric transducer 310 can be driven by transferring charge from the storage capacitor 322.

[0148] When the variable voltage power supply circuit 800 needs to increase the charge level on the piezoelectric transducer 310, for example, to drive the piezoelectric transducer 310 to produce a transducer output, the variable voltage power supply circuit 800 again operates in two stages.

[0149] In the first stage of the charge transfer process, in response to an appropriate control signal transmitted by control circuit 850, second switching device 824 and fourth switching device 828 are closed. This establishes a current path from storage capacitor 322 through inductor 810. As current flows through inductor 810, a magnetic field is formed around it, thereby storing energy.

[0150] In the second stage of the charge transfer process, in response to an appropriate control signal transmitted by control circuit 850, fifth switch 830 closes, and second switch 824 and fourth switch 828 open. The magnetic field around inductor 810 collapses, thereby inducing a current flowing from inductor 810 to piezoelectric transducer 310, thereby increasing the charge on piezoelectric transducer 310.

[0151] When the variable voltage power supply circuit 800 needs to reduce the charge level on the piezoelectric transducer 310, the charge can be transferred from the piezoelectric transducer 310 to the storage capacitor 322, so that the charge is retained for future use rather than lost. This improves the efficiency of the primary driver circuit.

[0152] The process of transferring charge from the piezoelectric transducer 310 to the storage capacitor 322 occurs in two stages.

[0153] In the first stage, in response to an appropriate control signal transmitted by the control circuit 850, the third switching device 826 and the fifth switching device 830 are closed. This establishes a current path from the piezoelectric transducer 310 through the inductor 810. When current flows through the inductor 810, a magnetic field is formed around it, thereby storing energy.

[0154] In the second stage, in response to an appropriate control signal transmitted by the control circuit 850, the second switching device 824 and the fourth switching device 828 close, and the third switching device 826 and the fifth switching device 830 open. The magnetic field around the inductor 810 collapses, thereby inducing a current to flow to the storage capacitor 322, thereby charging the storage capacitor 322.

[0155] Therefore, in the variable voltage power supply circuit 800, the piezoelectric transducer 310 can be driven by transferring charge from the storage capacitor 322 to the piezoelectric transducer 310, and the charge can circulate between the piezoelectric transducer 310 and the storage capacitor 322 to improve power efficiency. The power supply circuit 840 provides an initial charge to the storage capacitor 322 during the charging process and occasionally or periodically fully charges or recharges the storage capacitor 322 when necessary.

[0156] Figure 9 is a schematic diagram of an example of a charge pump circuit 900 for use in driver circuits 300, 400, 500, and 600.

[0157] The charge pump circuit 900 includes: a flying capacitor 910, which can be a fixed capacitor or a variable capacitor (e.g., a group of capacitors coupled in parallel, each capacitor being selectable by one or more switching devices to implement a desired capacitance); and a switching network 920, which includes first to fourth controllable switching devices 922 to 928, said controllable switching devices being, for example, MOSFET devices. The output terminal 930 of the charge pump circuit 900 is coupled to a first terminal 312 of the piezoelectric transducer 310.

[0158] A first controllable switch 922 is coupled between the second positive power supply rail 360 and the first terminal of the flying capacitor 910. A second controllable switch 924 is coupled between the second terminal of the flying capacitor 910 and the negative power supply rail 940. A third controllable switch 926 is coupled between the first terminal of the flying capacitor 910 and the output terminal 930 of the charge pump circuit 900, and a fourth controllable switch 928 is coupled between the second terminal of the flying capacitor 910 and the output terminal 930.

[0159] The charge pump circuit 900 also includes a control circuit 950 operable to control controllable switching devices 922 to 928 to charge the flying capacitor 910 and to transfer charge to and from the piezoelectric transducer 310 in a manner readily apparent to those skilled in the art.

[0160] When the charge pump circuit 900 is used as the secondary driver circuit, the flying capacitor 910 can be relatively small because only a small output voltage needs to be provided by the secondary driver circuit to compensate for errors in the signal output by the primary driver circuit. However, when the charge pump circuit 900 is used as the primary driver circuit, the flying capacitor 910 is typically much larger because a relatively large output voltage needs to be provided by the primary driver circuit.

[0161] Figure 10 is a schematic diagram of an alternative example of a charge pump circuit 1000 for use in driver circuits 300, 400, 500, and 600.

[0162] The charge pump circuit 1000 includes: a flying capacitor 1010, which can also be a fixed capacitor or a variable capacitor (e.g., a group of capacitors coupled in parallel, each capacitor being selectable by one or more switching devices to implement a desired capacitance); and a switching network 1020, which includes a first controllable switching device 1022 and a second controllable switching device 1024, which can be, for example, MOSFET devices. The output terminal 1030 of the charge pump circuit 1000 is coupled to the first terminal 312 of the piezoelectric transducer 310.

[0163] A first controllable switch 1022 is coupled between the second positive power supply rail 360 and the first terminal of the flying capacitor 1010. A second controllable switch 1024 is coupled between the first terminal of the flying capacitor 1010 and the negative power supply voltage rail 1040.

[0164] The charge pump circuit 1000 also includes a control circuit 1050 operable to control the controllable switching devices 1022, 1024 to charge the flying capacitor 1010 and to transfer charge to and from the piezoelectric transducer 310 in a manner readily apparent to those skilled in the art.

[0165] Similarly, when the charge pump circuit 1000 is used as a secondary driver circuit, the flying capacitor 1010 can be relatively small because only a small output voltage needs to be provided by the secondary driver circuit to compensate for errors in the signal output by the primary driver circuit. However, when the charge pump circuit 1000 is used as a primary driver circuit, the flying capacitor 1010 is typically much larger because a relatively large output voltage needs to be provided by the primary driver circuit.

[0166] In the example described above with reference to Figures 3 through 6, each of the first terminal 312 and the second terminal 314 of the piezoelectric transducer 310 is permanently coupled to the output of the primary driver circuit 320 or the output of the secondary driver circuit 340 or a reference voltage (e.g., ground) rail.

[0167] In the series transducer arrangement shown in Figures 4, 5, and 7, it may be advantageous to be able to select, for example, which of the terminals 312 and 314 of the piezoelectric transducer 310 is coupled to the output of the primary driver circuit 320 and which is coupled to the output of the secondary driver circuit 340, based on the polarity of the input signal to the driver circuit. This can be achieved by using a commutator circuit 1100 coupled to the piezoelectric transducer 310, as will now be described with reference to Figure 11.

[0168] The commutator circuit 1100 includes a switching network, which in the illustrated example includes a first controllable switch 1112 through a fourth controllable switch 1118. The commutator circuit 1100 is coupled to a control circuit 1130 to receive control signals for controlling the operation of the first controllable switches 1112 through the fourth controllable switches 1118 based on input signals.

[0169] In an embodiment where the piezoelectric transducer 310 is coupled in series with the primary driver circuit 320 and the secondary driver circuit 340, and a commutator circuit 1100 is used, a first controllable switch 1112 is coupled between a first node 1120 of the switch network 1110 and a first terminal 312 of the piezoelectric transducer 310. The first node 1120 of the switch network 1110 is coupled to the output of the primary driver circuit 320.

[0170] The second controllable switch 1114 is coupled between the first terminal 312 of the piezoelectric transducer 310 and the second node 1140 of the switch network 1110. The second node 1140 of the switch network 1110 is coupled to the output of the secondary driver circuit 340.

[0171] The third controllable switch 1116 is coupled between the first node 1120 of the switch network 1110 and the second terminal 314 of the piezoelectric transducer 310.

[0172] The fourth controllable switch 1118 is coupled between the second terminal 314 of the piezoelectric transducer 310 and the second node 1140 of the switch network 1110.

[0173] By selectively opening and closing the first controllable switch 1112 to the fourth controllable switch 1118, one of the first terminal 312 and the second terminal 314 of the piezoelectric transducer 310 can be coupled to the output terminal of the primary driver circuit 320 or the secondary driver circuit 340, and the other of the first terminal 312 and the second terminal 314 of the piezoelectric transducer 310 can be coupled to the secondary driver circuit 340 or the primary driver circuit 320.

[0174] For example, closing the first controllable switch 1112 and the fourth controllable switch 1118 and opening the second controllable switch 1114 and the third controllable switch 1116 will cause the first terminal 312 of the piezoelectric transducer 310 to be coupled to the output of the primary driver circuit 320 and the second terminal 314 of the piezoelectric transducer 310 to be coupled to the output of the secondary driver circuit 340. Alternatively, opening the first controllable switch 1112 and the fourth controllable switch 1118 and closing the second controllable switch 1114 and the third controllable switch 1116 will cause the first terminal 312 of the piezoelectric transducer 310 to be coupled to the output of the secondary driver circuit 340 and the second terminal 314 of the piezoelectric transducer 310 to be coupled to the output of the primary driver circuit 320.

[0175] In the parallel transducer arrangement shown in Figures 3 and 6, it may be advantageous to be able to select, for example, which of the terminals 312, 314 of the piezoelectric transducer 310 is coupled to the output of the primary driver circuit 320 and the secondary driver circuit 340, and which is coupled to ground (or some other reference voltage), based on the polarity of the input signal to the driver circuit. The commutator circuit 1100 of Figure 11 can also be used for this purpose, as will now be described.

[0176] In an embodiment where the piezoelectric transducer 310 is coupled in parallel with the primary driver circuit 320 and the secondary driver circuit 340, and the commutator circuit 1100 is used, the first controllable switch 1112 is coupled between the first node 1120 of the switch network 1110 and the first terminal 312 of the piezoelectric transducer 310. The first node 1120 of the switch network 1110 is coupled to the output of the primary driver circuit 320 and the output of the secondary driver circuit 340.

[0177] A second controllable switch 1114 is coupled between a first terminal 312 of the piezoelectric transducer 310 and a second node 1140 of the switch network 1110. The second node 1140 of the switch network 1110 is coupled to ground or some other reference power supply (e.g., an auxiliary capacitor as described above with reference to FIG5).

[0178] The third controllable switch 1116 is coupled between the first node 1120 of the switch network 1110 and the second terminal 314 of the piezoelectric transducer 310.

[0179] The fourth controllable switch 1118 is coupled between the second terminal 314 of the piezoelectric transducer 310 and the second node 1140 of the switch network 1110.

[0180] By selectively opening and closing the first controllable switch 1112 to the fourth controllable switch 1118, one of the first terminal 312 and the second terminal 314 of the piezoelectric transducer 310 can be coupled to the output of the primary driver circuit 320 and the secondary driver circuit 340, and the other of the first terminal 312 and the second terminal 314 of the piezoelectric transducer 310 can be coupled to a reference voltage supply (e.g., ground).

[0181] For example, closing the first controllable switch 1112 and the fourth controllable switch 1118 and opening the second controllable switch 1114 and the third controllable switch 1116 will cause the first terminal 312 of the piezoelectric transducer 310 to be coupled to the output of the primary driver circuit 320 and the secondary driver circuit 340, and will cause the second terminal 314 of the piezoelectric transducer 310 to be coupled to the reference voltage supply. Alternatively, opening the first controllable switch 1112 and the fourth controllable switch 1118 and closing the second controllable switch 1114 and the third controllable switch 1116 will cause the first terminal 312 of the piezoelectric transducer 310 to be coupled to the reference voltage supply, and will cause the second terminal 314 of the piezoelectric transducer 310 to be coupled to the output of the primary driver circuit 320 and the secondary driver circuit 340.

[0182] In some examples of the driver circuits disclosed herein, a single storage capacitor 322 may be shared between the primary driver circuit 320 and the secondary driver circuit 340. For example, in cases where both the primary driver circuit 320 and the secondary driver circuit 340 include the variable voltage supply circuit 800 described above with reference to FIG8, a single storage capacitor 322 may be provided, which is shared by the primary driver circuit 320 and the secondary driver circuit 340 for charge recycling purposes. This avoids the need for the primary driver circuit 320 and the secondary driver circuit 340 to each have their own storage capacitor, thereby reducing the cost and area of ​​the driver circuit.

[0183] In other examples where both the primary driver circuit 320 and the secondary driver circuit 340 include the variable voltage power supply circuit 800 described above with reference to FIG8, only the primary driver circuit 320 may be provided with a storage capacitor 332. Again, this reduces the cost and area of ​​the driver circuitry, but at the cost of a slight decrease in efficiency because the charge cannot be recycled in the secondary driver circuit 340.

[0184] In an alternative embodiment where both the primary driver circuit 320 and the secondary driver circuit 340 include the variable voltage power supply circuit 800 described above with reference to FIG8, both the primary driver circuit 320 and the secondary driver circuit 340 may each be provided with a storage capacitor 332. Power efficiency is maximized by allowing charge recycling in both the primary driver circuit 320 and the secondary driver circuit 340, but at the cost of increased component count, cost, and circuit area.

[0185] Figure 12 schematically illustrates an alternative example of the driver circuit 1200 for driving the piezoelectric transducer 310. It should be understood that although the driver circuit 1200 in this example drives a piezoelectric transducer, it is also suitable for driving other capacitive transducers. For example, the driver circuit 1200 can be used to drive MEMS transducers or electrostatic transducers. The driver circuit 1200 is similar in some respects to the driver circuit 500 of Figure 5, and therefore, in Figures 5 and 12, the same elements are indicated by the same reference numerals. For clarity and brevity, some elements of the driver circuit 500 of Figure 5 are not shown in Figure 12.

[0186] The driver circuit 1200 includes a first "auxiliary" capacitor 1210 and a second "auxiliary" capacitor 1220. The first auxiliary capacitor 1210 is coupled in parallel with the piezoelectric transducer 310 between node 1212 and ground, the node being located between the output of the primary driver circuit 320 and the first terminal 312 of the piezoelectric transducer 310. The second auxiliary capacitor 1220 is coupled in parallel with the piezoelectric transducer 310 between node 1222 and ground, the node being located between the output of the secondary driver circuit 340 and the first terminal 312 of the piezoelectric transducer 310.

[0187] The first auxiliary capacitor 1210 can be selectively charged and discharged by the primary driver circuit 320 to adjust the voltage VH1 across the first auxiliary capacitor 1210 to facilitate the transfer of charge to or from the piezoelectric transducer 310 based on the primary drive signal output by the primary driver circuit 320.

[0188] The second auxiliary capacitor 1220 can be selectively charged and discharged by the secondary driver circuit 340 to adjust the voltage VH2 across the second auxiliary capacitor 1220 to facilitate the transfer of charge to or from the piezoelectric transducer 310, thereby correcting any errors in the primary drive signal output by the primary driver circuit 320.

[0189] As will be understood by those skilled in the art, circuit 1200 includes appropriate input, output, feedback, and error and filter signal paths of the kind described above with reference to FIG5, to provide the necessary control over primary driver circuit 320 and secondary driver circuit 340 in order to ensure that the displacement of piezoelectric transducer 310 is represented as accurately as possible to the input signal of circuit 1200.

[0190] Figure 13 schematically illustrates another alternative example of the driver circuit 1300 for driving the piezoelectric transducer 310. It should be understood that although the driver circuit 1300 in this example drives a piezoelectric transducer, it is also suitable for driving other capacitive transducers. For example, the driver circuit 1300 can be used to drive MEMS transducers or electrostatic transducers. The driver circuit 1300 is similar in some respects to the driver circuit 400 of Figure 4, and therefore, in Figures 4 and 13, the same elements are indicated by the same reference numerals. For clarity and brevity, some elements of the driver circuit 400 of Figure 4 are not shown in Figure 13.

[0191] The driver circuit 1300 includes an “auxiliary” capacitor 1310. The auxiliary capacitor 1310 is coupled in series between the output of the secondary driver circuit 340 and the first terminal 312 of the piezoelectric transducer 310.

[0192] The auxiliary capacitor 1310 can be selectively charged and discharged by the secondary driver circuit 340 to adjust the voltage VH across the auxiliary capacitor 1310 to facilitate the transfer of charge to or from the piezoelectric transducer 310, thereby correcting any errors in the primary drive signal output by the primary driver circuit 320.

[0193] Similarly, as those skilled in the art will understand, circuit 1300 includes appropriate input, output, feedback, and error and filter signal paths of the kind described above with reference to FIG5, to provide the necessary control over primary driver circuit 320 and secondary driver circuit 340 in order to ensure that the displacement of piezoelectric transducer 310 is represented as accurately as possible to the input signal of circuit 1300.

[0194] Figure 14 schematically illustrates another alternative example of the driver circuit 1400 for driving the piezoelectric transducer 310. It should be understood that although the driver circuit 1400 in this example drives a piezoelectric transducer, it is also suitable for driving other capacitive transducers. For example, the driver circuit 1400 can be used to drive MEMS transducers or electrostatic transducers. The driver circuit 1400 is similar in some respects to the driver circuit 1300 of Figure 13, and therefore, in Figures 13 and 14, the same elements are indicated by the same reference numerals.

[0195] The driver circuit 1400 includes a first “auxiliary” capacitor 1410, which is coupled in series between the output of the secondary driver circuit 340 and the first terminal 312 of the piezoelectric transducer 310 and ground.

[0196] The driver circuit 1400 also includes a second “auxiliary” capacitor 1420, which is coupled in parallel with the piezoelectric transducer 310 between the output of the secondary driver circuit 340 and ground.

[0197] The first auxiliary capacitor 1410 and the second auxiliary capacitor 1420 can be selectively charged and discharged by the secondary driver circuit 340 to adjust the voltages VH1 and VH2 across the first auxiliary capacitor 1410 and the second auxiliary capacitor 1420 respectively, so as to facilitate the transfer of charge to or from the piezoelectric transducer 310, thereby correcting any errors in the primary drive signal output by the primary driver circuit 320.

[0198] Similarly, as those skilled in the art will understand, circuit 1400 includes appropriate input, output, feedback, and error and filter signal paths of the kind described above with reference to FIG5, to provide the necessary control over primary driver circuit 320 and secondary driver circuit 340 in order to ensure that the displacement of piezoelectric transducer 310 is represented as accurately as possible to the input signal of circuit 1400.

[0199] Figure 15 schematically illustrates another alternative example of the driver circuit 1500 for driving the piezoelectric transducer 310. Again, it should be understood that although the driver circuit 1500 in this example drives a piezoelectric transducer, it is also suitable for driving other capacitive transducers. For example, the driver circuit 1500 can be used to drive MEMS transducers or electrostatic transducers. The driver circuit 1500 is similar in some respects to the driver circuit 1200 of Figure 12, and therefore, in Figures 12 and 15, the same elements are indicated by the same reference numerals.

[0200] The driver circuit 1500 includes an “auxiliary” capacitor 1510, which is coupled in parallel with the piezoelectric transducer 310 between node 1512 and ground, the node being located between the output of the primary driver circuit 320 and the first terminal 312 of the piezoelectric transducer 310.

[0201] The auxiliary capacitor 1510 can be selectively charged and discharged by the primary driver circuit 320 to adjust the voltage VH across the auxiliary capacitor 1510 to facilitate the transfer of charge to or from the piezoelectric transducer 310 based on the primary drive signal output by the primary driver circuit 320.

[0202] As will be understood by those skilled in the art, circuit 1500 includes appropriate input, output, feedback, and error and filter signal paths of the kind described above with reference to FIG5, to provide the necessary control over primary driver circuit 320 and secondary driver circuit 340 in order to ensure that the displacement of piezoelectric transducer 310 is represented as accurately as possible to the input signal of circuit 1500.

[0203] Figure 16 schematically illustrates another alternative example of the driver circuit 1600 for driving the piezoelectric transducer 310. It should be understood that although the driver circuit 1600 in this example drives a piezoelectric transducer, it is also suitable for driving other capacitive transducers. For example, the driver circuit 1600 can be used to drive MEMS transducers or electrostatic transducers. The driver circuit 1600 is similar in some respects to the driver circuit 1200 of Figure 12, and therefore, in Figures 12 and 16, the same elements are indicated by the same reference numerals.

[0204] The driver circuit 1600 includes an “auxiliary” capacitor 1610, which is coupled in parallel with the piezoelectric transducer 310 between node 1612 and ground, said node being located between the output of the secondary driver circuit 340 and the first terminal 312 of the piezoelectric transducer 310.

[0205] The auxiliary capacitor 1610 can be selectively charged and discharged by the secondary driver circuit 340 to adjust the voltage VH across the auxiliary capacitor 1610 to facilitate the transfer of charge to or from the piezoelectric transducer 310 in order to correct any errors in the primary drive signal output by the primary driver circuit 320.

[0206] As will be understood by those skilled in the art, circuit 1600 includes appropriate input, output, feedback, and error and filter signal paths of the kind described above with reference to FIG5, to provide the necessary control over primary driver circuit 320 and secondary driver circuit 340 in order to ensure that the displacement of piezoelectric transducer 310 is represented as accurately as possible to the input signal of circuit 1600.

[0207] As is apparent from the foregoing discussion, the circuit of this disclosure provides a driver circuit for driving a piezoelectric transducer, the driver circuit comprising: a power-efficient primary driver circuit for providing most of the power required to drive the piezoelectric transducer; and an accurate secondary driver circuit for providing a small secondary drive signal (relative to the primary drive signal provided by the primary driver circuit) to at least partially correct or compensate for errors in the primary drive signal, thereby providing accurate and power-efficient driving of the piezoelectric transducer.

[0208] The implementation scheme can be implemented as an integrated circuit, which in some examples may be a codec or an audio DSP, etc. The implementation scheme can be incorporated into electronic devices, which may be, for example, portable devices and / or devices capable of operating on battery power. The device may be a communication device, such as a mobile phone or smartphone. The device may be a computing device, such as a laptop computer, notebook computer, or tablet computer. 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 cases, the device may be an accessory to be used with other products, such as a headset kit, headphones, in-ear headphones, earbuds, etc.

[0209] 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, for example, on non-volatile media such as disks, CD-ROMs, or DVD-ROMs, or on data carriers such as read-only memory (firmware) or optical or electrical signal carriers. For many applications, implementations will be 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 (such as reprogrammable gate arrays). Similarly, the code can include code for hardware description languages ​​(such as Verilog). TM Alternatively, VHDL (Very High Speed ​​Integrated Circuit Hardware Description Language) code may be used. Those skilled in the art will understand that this code can be distributed among multiple coupled components that communicate with each other. Where appropriate, the implementation scheme may also be implemented using code that runs on a field-programmable analog array or similar device to configure the analog hardware.

[0210] 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, "a (or an)" does not exclude a plurality, and a single feature or other unit may perform the function of several units recited 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 capacitive transducer based on an input signal, the circuit comprising: A primary driver circuit is configured to receive the input signal and output a primary drive signal to the capacitive transducer based on the input signal. as well as The secondary driver circuit is configured to receive an error signal indicating the error between the input signal and the primary drive signal, and to output a secondary drive signal to the capacitive transducer based on the error signal. Both the primary driver circuit and the secondary driver circuit include a switch converter circuit.

2. The circuit of claim 1, wherein the primary driver circuit includes a variable voltage power supply circuit, and the secondary driver circuit includes a charge pump circuit.

3. The circuit according to claim 2, wherein the variable voltage power supply circuit includes a switching network, an inductor, and a storage capacitor.

4. The circuit according to claim 2 or claim 3, wherein the charge pump circuit includes a switching network and a flying capacitor.

5. The circuit of claim 4, wherein the flying capacitor is variable.

6. The circuit of claim 4, wherein the charge pump circuit is configured to receive a power supply that varies based on parameters of the input signal.

7. The circuit of claim 6, wherein the variable voltage power supply circuit is configured to provide the power supply to the charge pump circuit.

8. The circuit of claim 7, wherein the variable voltage power supply circuit includes a detector circuit configured to detect the level, envelope, or other parameters of the input signal and control the power supply voltage supplied to the charge pump circuit based on the detected level, envelope, or other parameters.

9. The circuit of claim 3, wherein the charge pump circuit includes one or more supply capacitors, and wherein the switching network is operable to transfer charge between the storage capacitor and the one or more supply capacitors.

10. The circuit of claim 1, wherein the primary driver circuit includes a first variable voltage power supply circuit, and the secondary driver circuit includes a second variable voltage power supply circuit.

11. The circuit of claim 10, wherein the primary driver circuit and the secondary driver circuit each include a switching network and an inductor, wherein the inductor of the secondary driver circuit is smaller than the inductor of the primary driver circuit.

12. The circuit of claim 11, wherein the inductor of the secondary driver circuit is embedded in an integrated circuit implementing the circuit.

13. The circuit of claim 10, wherein the first variable voltage power supply circuit includes a first storage capacitor for storing charge.

14. The circuit of claim 13, wherein the first storage capacitor is shared by the first variable voltage power supply circuit and the second variable voltage power supply circuit.

15. The circuit of claim 13, wherein the second variable voltage power supply circuit includes a second storage capacitor for storing charge.

16. The circuit according to any one of claims 1 to 3, further comprising an auxiliary capacitor configured to receive charge from the primary driver circuit or the secondary driver circuit in order to adjust the voltage across the auxiliary capacitor.

17. The circuit of claim 16, wherein the auxiliary capacitor: Series coupling between the capacitive transducer and ground; or The secondary driver circuit is coupled in series between its output and the first terminal of the capacitive transducer; or The capacitor transducer is coupled in parallel between the output of the secondary driver circuit and ground; or It is coupled in parallel with the capacitor transducer between the output of the primary driver circuit and ground.

18. The circuit of claim 16, wherein the circuit comprises: A first auxiliary capacitor is coupled in parallel with the capacitive transducer between the output terminal of the secondary driver circuit and ground. as well as The second auxiliary capacitor is coupled in parallel with the capacitive transducer between the output of the primary driver circuit and ground.

19. The circuit of claim 16, wherein the circuit comprises: A first auxiliary capacitor is coupled in parallel with the capacitive transducer between the output terminal of the secondary driver circuit and ground. as well as A second auxiliary capacitor is coupled in series between the output of the secondary driver circuit and the first terminal of the capacitive transducer.

20. The circuit of claim 1, wherein the primary driver circuit is configured to be coupled to a terminal of the capacitive transducer, and the secondary driver circuit is configured to be coupled to the same terminal of the capacitive transducer.

21. The circuit of claim 1, wherein the primary driver circuit is configured to be coupled to a first terminal of the capacitive transducer, and the secondary driver circuit is configured to be coupled to a second terminal of the capacitive transducer.

22. The circuit of claim 16, further comprising a commutation circuit configured to selectively couple one of a first terminal and a second terminal of the capacitive transducer to the primary driver circuit and the secondary driver circuit, and to couple the other of the first terminal and the second terminal of the capacitive transducer to a reference voltage supply.

23. The circuit of claim 22, wherein the commutation circuit is configured to selectively couple one of the first terminal and the second terminal of the capacitive transducer to the primary driver circuit and the secondary driver circuit based on the polarity of the input signal, and to couple the other of the first terminal and the second terminal of the capacitive transducer to a reference voltage supply.

24. The circuit of claim 22, wherein the commutation circuit is configured to selectively couple one of the primary driver circuit and the secondary driver circuit to a first terminal of the capacitive transducer, and to couple the other of the primary driver circuit and the secondary driver circuit to a second terminal of the capacitive transducer.

25. The circuit of claim 24, wherein the commutation circuit is configured to selectively couple one of the primary driver circuit and the secondary driver circuit to the first terminal of the capacitive transducer based on the polarity of the input signal, and to couple the other of the primary driver circuit and the secondary driver circuit to the second terminal of the capacitive transducer.

26. The circuit according to any one of claims 1 to 3, further comprising a first control circuit for regulating the operation of the primary driver and a second control circuit for regulating the operation of the secondary driver circuit, wherein the bandwidth of the second control circuit is greater than the bandwidth of the first control circuit.

27. The circuit according to any one of claims 1 to 3, wherein the secondary driver circuit is capable of selectively operating based on parameters of the input signal.

28. The circuit of claim 27, wherein the parameters of the input signal include one or more of the signal level, envelope, and frequency of the input signal.

29. The circuit according to any one of claims 1 to 3, wherein the primary driver circuit is capable of selectively operating based on the signal level or envelope of the input signal.

30. The circuit according to any one of claims 1 to 3, wherein the primary driver circuit and / or the secondary driver circuit are capable of selectively operating based on the operating mode of the circuit.

31. The circuit of claim 30, wherein the secondary driver circuit is enabled in a first mode in which the input signal includes an audio signal, and wherein the secondary driver circuit is disabled in a second mode in which the input signal includes a tactile signal or a waveform.

32. The circuit according to any one of claims 1 to 3, wherein both the primary driver circuit and the secondary driver circuit include a charge pump circuit.

33. The circuit according to any one of claims 1 to 3, wherein the primary driver circuit includes a charge pump circuit, and the secondary driver circuit includes a variable voltage power supply circuit.

34. The circuit according to any one of claims 1 to 3, wherein the capacitive transducer is a piezoelectric transducer, a MEMS transducer, or an electrostatic transducer.

35. An integrated circuit comprising the circuit of any one of the preceding claims.

36. An apparatus comprising the circuit of any one of the preceding claims.

37. The device of claim 36, wherein the device is a mobile phone, tablet computer or laptop computer, smart speaker or accessory.

38. The device of claim 37, wherein the accessory is a headset.

39. The device of claim 37, wherein the accessory is an in-ear headphone.

40. The device of claim 37, wherein the accessory is an earbud-type headphone.

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