WO2023081636A1

WO2023081636A1 - Systems and methods for maximizing amplifier linearity and minimizing noise in a single-ended amplifier

Info

Publication number: WO2023081636A1
Application number: PCT/US2022/079036
Authority: WO
Inventors: Chandra B. Prakash; Cory J. Peterson
Original assignee: Cirrus Logic International Semiconductor Ltd.
Priority date: 2021-11-08
Filing date: 2022-11-01
Publication date: 2023-05-11
Also published as: TW202326154A

Abstract

A system may include a driver configured to drive a load with a single-ended driving signal and a processing system configured to implement a function to minimize signal distortion within a signal path of the single-ended driving signal occurring for magnitudes of the single-ended driving signal within a threshold magnitude of a voltage rail of the driver.

Description

SYSTEMS AND METHODS FOR MAXIMIZING AMPLIFIER LINEARITY AND MINIMIZING NOISE IN A SINGLE-ENDED AMPLIFIER

RELATED APPLICATION The present application claims priority to United States Provisional Patent

Application No. 63/276,758, filed November 8, 2021, and United States Utility Application No. 17/545,378, filed December 8, 2021, both of which are incorporated by reference herein in their entireties. FIELD OF DISCLOSURE

The present disclosure relates in general to methods, apparatuses, or implementations for haptic devices. Embodiments set forth herein may disclose improvements relating to how a physical quantity, such as inductance or displacement, of a haptic actuator or other electromechanical load may be sensed.

BACKGROUND

Vibro-haptic transducers, for example linear resonant actuators (LRAs), are widely used in portable devices such as mobile phones to generate vibrational feedback to a user. Vibro-haptic feedback in various forms creates different feelings of touch to a user’s skin and may play increasing roles in human-machine interactions for modem devices.

An LRA may be modelled as a mass-spring electro-mechanical vibration system. When driven with appropriately designed or controlled driving signals, an LRA may generate certain desired forms of vibrations. For example, a sharp and clear- cut vibration pattern on a user’ s finger may be used to create a sensation that mimics a mechanical button click. This clear-cut vibration may then be used as a virtual switch to replace mechanical buttons.

FIGURE 1 illustrates an example of a vibro-haptic system in a device 100. Device 100 may comprise a controller 101 configured to control a signal applied to an amplifier 102. Amplifier 102 may then drive a vibrational actuator (e.g., haptic transducer) 103 based on the signal. Controller 101 may be triggered by a trigger to output to the signal. The trigger may, for example, comprise a pressure or force sensor on a screen or virtual button of device 100.

Among the various forms of vibro-haptic feedback, tonal vibrations of sustained duration may play an important role to notify the user of the device of certain predefined events, such as incoming calls or messages, emergency alerts, and timer warnings, etc. In order to generate tonal vibration notifications efficiently, it may be desirable to operate the haptic actuator at its resonance frequency.

The resonance frequency fo of a haptic transducer may be approximately estimated as:

where C is the compliance of the spring system, and M is the equivalent moving mass, which may be determined based on both the actual moving part in the haptic transducer and the mass of the portable device holding the haptic transducer.

Due to sample-to-sample variations in individual haptic transducers, mobile device assembly variations, temporal component changes caused by aging, and use conditions such as various different strengths of a user gripping of the device, the vibration resonance of the haptic transducer may vary from time to time.

FIGURE 2 illustrates an example of a linear resonant actuator (LRA) modelled as a linear system. LRAs are non-linear components that may behave differently depending on, for example, the voltage levels applied, the operating temperature, and the frequency of operation. However, these components may be modelled as linear components within certain conditions. In this example, the LRA is modelled as a third order system having electrical and mechanical elements. In particular, Re and Le are the DC resistance and coil inductance of the coil-magnet system, respectively; and Bl is the magnetic force factor of the coil. The driving amplifier outputs the voltage waveform F(t) with the output impedance Ro. The terminal voltage V_T(t) may be sensed across the terminals of the haptic transducer. The mass-spring system 201 moves with velocity u(t).

A haptic system may require precise control of movements of the haptic transducer. Such control may rely on the magnetic force factor Bl, which may also be known as the electromagnetic transfer function of the haptic transducer. In an ideal case, magnetic force factor Bl can be given by the product B ■ I, where B is magnetic flux density and I is a total length of electrical conductor within a magnetic field. Both magnetic flux density B and length I should remain constant in an ideal case with motion occurring along a single axis.

In generating haptic vibration, an LRA may undergo displacement. In order to protect an LRA from damage, such displacement may be limited. Accordingly, accurate measurement of displacement may be crucial in optimizing LRA

displacement protection algorithms. Accurate measurement of displacement may also enable increased drive levels of the LRA. While existing approaches measure displacement, such approaches have disadvantages. For example, displacement may be measured using a Hall sensor, but Hall sensors are often costly to implement.

SUMMARY

In accordance with the teachings of the present disclosure, the disadvantages and problems associated with existing approaches for sensing displacement of an electromagnetic transducer may be reduced or eliminated.

In accordance with embodiments of the present disclosure, a system may include a driver configured to drive a load with a single-ended driving signal and a processing system configured to implement a function to minimize signal distortion within a signal path of the single-ended driving signal occurring for magnitudes of the single-ended driving signal within a threshold magnitude of a voltage rail of the driver.

In accordance with these and other embodiments of the present disclosure, a method may include driving a load with a single-ended driving signal implementing a function to minimize signal distortion within a signal path of the single-ended driving signal occurring for magnitudes of the single-ended driving signal within a threshold magnitude of a voltage rail of a driver.

Technical advantages of the present disclosure may be readily apparent to one having ordinary skill in the art from the figures, description and claims included herein. The objects and advantages of the embodiments will be realized and achieved at least by the elements, features, and combinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description and the following detailed description are examples and explanatory and are not restrictive of the claims set forth in this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:

FIGURE 1 illustrates an example of a vibro-haptic system in a device, as is known in the art;

FIGURE 2 illustrates an example of a Linear Resonant Actuator (LRA) modelled as a linear system, as is known in the art;

FIGURE 3 illustrates selected components of an example host device, in accordance with embodiments of the present disclosure;

FIGURE 4 illustrates selected components of another example host device, in accordance with embodiments of the present disclosure;

FIGURE 5 illustrates selected components of yet another example host device, in accordance with embodiments of the present disclosure;

FIGURE 6 illustrates selected components of yet another example host device, in accordance with embodiments of the present disclosure;

FIGURE 7 illustrates selected components of yet another example host device, in accordance with embodiments of the present disclosure;

FIGURE 8 illustrates selected components of yet another example host device, in accordance with embodiments of the present disclosure;

FIGURE 9 illustrates selected components of yet another example host device, in accordance with embodiments of the present disclosure; and

FIGURE 10 illustrates selected components of yet another example host device, in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

The description below sets forth example embodiments according to this disclosure. Further example embodiments and implementations will be apparent to those having ordinary skill in the art. Further, those having ordinary skill in the art will recognize that various equivalent techniques may be applied in lieu of, or in conjunction with, the embodiment discussed below, and all such equivalents should be deemed as being encompassed by the present disclosure.

Various electronic devices or smart devices may have transducers, speakers, and acoustic output transducers, for example any transducer for converting a suitable electrical driving signal into an acoustic output such as a sonic pressure wave or mechanical vibration. For example, many electronic devices may include one or more speakers or loudspeakers for sound generation, for example, for playback of audio content, voice communications and/or for providing audible notifications.

Such speakers or loudspeakers may comprise an electromagnetic actuator, for example a voice coil motor, which is mechanically coupled to a flexible diaphragm, for example a conventional loudspeaker cone, or which is mechanically coupled to a surface of a device, for example the glass screen of a mobile device. Some electronic devices may also include acoustic output transducers capable of generating ultrasonic waves, for example for use in proximity detection-type applications and/or machine - to-machine communication.

Many electronic devices may additionally or alternatively include more specialized acoustic output transducers, for example, haptic transducers, tailored for generating vibrations for haptic control feedback or notifications to a user. Additionally or alternatively, an electronic device may have a connector, e.g., a socket, for making a removable mating connection with a corresponding connector of an accessory apparatus, and may be arranged to provide a driving signal to the connector so as to drive a transducer, of one or more of the types mentioned above, of the accessory apparatus when connected. Such an electronic device will thus comprise

driving circuitry for driving the transducer of the host device or connected accessory with a suitable driving signal. For acoustic or haptic transducers, the driving signal may generally be an analog time varying voltage signal, for example, a time varying waveform.

To accurately sense displacement of an electromagnetic load, methods and systems of the present disclosure may determine an inductance of the electromagnetic load, and then convert the inductance to a position signal, as described in greater detail below. Further, to measure inductance of an electromagnetic load, methods and systems of the present disclosure may utilize either a phase measurement approach and/or a high-frequency pilot-tone driven approach, as also described in greater detail below.

To illustrate, an electromagnetic load may be driven by a driving signal V (t) to generate a sensed terminal voltage V_T (t) across a coil of the electromagnetic load. Sensed terminal voltage V_T(t) may be given by:

wherein /(t) is a sensed current through the electromagnetic load, ZCOIL is an impedance of the electromagnetic load, and F_B(t) is the back-electromotive force (back-EMF) associated with the electromagnetic load.

As used herein, to “drive” an electromagnetic load means to generate and communicate a driving signal to the electromagnetic load to cause displacement of a movable mass of the electromagnetic load.

Because back-EMF voltage F_B(t) may be proportional to velocity of the moving mass of the electromagnetic load, back-EMF voltage F_B(t) may in turn provide an estimate of such velocity. Thus, velocity of the moving mass may be recovered from sensed terminal voltage F_r(t) and sensed current /(t) provided that either: (a) sensed current /(t) is equal to zero, in which case F_B(t) = V_T(t); or (b) coil impedance ZCOIL is known or is accurately estimated.

Position of the moving mass may be related to a coil inductance LCOIL of the electromagnetic load. At high frequencies significantly above the bandwidth of the electromagnetic load, back- EMF voltage V_B (t) may become negligible and inductance may dominate the coil impedance Sensed terminal voltage at high

frequencies may be estimated by:

Hence, at high frequencies, the position of the moving mass of the electromagnetic load may be recovered from sensed terminal voltage V_T (t) and sensed current /(t) by: (a) estimating the coil impedance at high frequency as Z_C0IL@HF = where R@HF is the resistive part of the coil impedance at high

frequency, L@HF is the coil inductance at high frequency, and \ is the Laplace transform; and (b) converting the measured inductance to a position signal. Velocity and/or position may be used to control vibration of the moving mass of the electromagnetic load.

FIGURE 3 illustrates selected components of an example host device 300 having an electromagnetic load 301, in accordance with embodiments of the present disclosure. Host device 300 may include, without limitation, a mobile device, home application, vehicle, and/or any other system, device, or apparatus that includes a human-machine interface. Electromagnetic load 301 may include any suitable load with a complex impedance, including without limitation a haptic transducer, a loudspeaker, a microspeaker, a piezoelectric transducer, a voice-coil actuator, a solenoid, or other suitable transducer.

In operation, a signal generator 324 of a processing subsystem 305 of host device 300 may generate a raw transducer driving signal (which, in some

embodiments, may be a waveform signal, such as a haptic waveform signal or audio signal). Raw transducer driving signal x'(t) may be generated based on a desired playback waveform received by signal generator 324. In some embodiments, raw

transducer driving signal may comprise a differential pulse- width modulated

(PWM) signal.

Raw transducer driving signal may be received by waveform

preprocessor 326 which, as described in greater detail below, may modify or otherwise convert raw transducer driving signal

in order to generate processed transducer driving signal For example, waveform processor 326 may include a PWM

modulator 328 and non-overlap and slew controller 330. PWM modulator 328 may include any suitable device, system, or apparatus configured to generate a single-ended PWM signal from raw transducer driving signal x' (t) . For example, PWM modulator 328 may include a delta-sigma modulator comprising one or more integrator stages, a quantizer, and a conversion block configured to convert a differential signal into a single-ended signal. Accordingly, processed transducer driving signal %(t) may comprise a single-ended signal (e.g., a single-ended PWM signal) communicated to amplifier 306, which may also be referred to as a “driver.”

Processed transducer driving signal %(t) may in turn be amplified by amplifier 306 to generate a driving signal V (t) for driving electromagnetic load 301. Amplifier 306 may comprise a single-ended Class-D output stage (e.g., one half of an H-bridge). Responsive to driving signal V (t) , a sensed terminal voltage V_T (t) of electromagnetic load 301 may be sensed by a terminal voltage sensing block 307 of processing subsystem 305, for example a volt-meter, and converted to a digital representation by a first analog-to-digital converter (ADC) 303. As shown in FIGURE 3, a feedback resistor 316 coupled to a terminal of electromagnetic load 301 may provide closed- loop feedback to the generation of processed transducer driving signal %(t).

Similarly, sensed current /(t) may be converted to a digital representation by a second ADC 304. Current /(t) may be sensed across a shunt resistor 302 having resistance R_s coupled to a terminal of electromagnetic load 301. As shown in FIGURE 3, ADC 304 and shunt resistor 302 may be part of a current-sensing circuit including a ground return transistor 312 and a common-mode buffer 314. During a haptics mode,

when waveform preprocessor 326 drives a haptic waveform as processed transducer driving signal ground return transistor 312 may be enabled (e.g., on, closed,

activated) and common-mode buffer 314 may be disabled (e.g., off, deactivated), thus coupling a terminal of electromagnetic load 301 to ground. On the other hand, during a load sensing mode, ground return transistor 312 may be disabled and common- mode buffer 314 may be enabled, thus coupling the same terminal of electromagnetic load 301 to a common-mode voltage VCM. In the load sensing mode, waveform preprocessor 326 may drive a pilot tone or other signal suitable for measuring driving signal V (t) and sensed current /(t) in order to determine an impedance (e.g., resistance and inductance) of electromagnetic load 301, wherein a component of such impedance (e.g., inductance) may be representative of a displacement of electromagnetic load 301.

As shown in FIGURE 3, processing subsystem 305 may include an inductance measurement subsystem 308 that may estimate coil inductance LCOIL of electromagnetic load 301. From such estimated coil inductance LCOIL, inductance measurement subsystem 308 may determine a displacement associated with electromagnetic load 301. If such displacement exceeds a threshold, high-frequency pilot-tone driven inductance measurement subsystem 308 may communicate a limiting signal (indicated by “LIMIT” in FIGURE 3) to modify raw transducer driving signal x' (t) in a manner that prevents over-excursion in the displacement of electromagnetic load 301.

In operation, to estimate impedance ZCOIL, inductance measurement subsystem 308 may measure impedance in any suitable manner, including without limitation using the approaches set forth in U.S. Patent. Appl. No. 17/497,110 filed October 8, 2021, which is incorporated in its entirety by reference herein.

One disadvantage of the architecture shown in FIGURE 3 is that it may generate perceptible noise on driving signal V (t) even when raw transducer driving signal x' (t) is zero (known as “idle channel noise”) due to a deadzone in the transfer

function of waveform preprocessor 326. A noise gate could be used to reduce or eliminate such disadvantage, but the addition of a noise gate may negatively impact performance elsewhere in host device 300. Another possible solution may be to add a small direct-current offset within the signal path of raw transducer driving signal x' (t) and driving signal U(t), but such a solution does not generate a true idle channel condition.

Another disadvantage of the architecture shown in FIGURE 3 is that amplifier 306 may experience non-linearity, such that driving signal V (t) as a function of raw transducer driving signal x' (t) and as a function of processed transducer driving signal x(t) is non-linear when processed transducer driving signal x(t), and thus driving signal V (t), are at or near a supply voltage of amplifier 306.

Thus, the architecture shown in FIGURE 3 may have signal distortion (e.g., idle channel noise and/or non-linearity) when a single-ended signal x(t) or U(t) is near its rail voltages (e.g., near zero or ground voltage or near the supply voltage of amplifier 306). To overcome such disadvantages, further improvements may be made to the architecture shown in FIGURE 3, as illustrated in FIGURES 4-10 and described below.

FIGURE 4 illustrates selected components of another example host device 300A, in accordance with embodiments of the present disclosure. Host device 300A as shown in FIGURE 4 may be similar in many respects to host device 300 shown in FIGURE 3, so only certain differences between host device 300A and host device 300 may be set forth below. Further, processing subsystem 305A as shown in FIGURE 4 may be similar in many respects to processing subsystem 305 shown in FIGURE 3, so only certain differences between processing subsystem 305A and processing subsystem 305 may be set forth below. Moreover, waveform preprocessor 326A as shown in FIGURE 4 may be similar in many respects to waveform preprocessor 326 shown in FIGURE 3, so only certain differences between waveform preprocessor 326A and waveform preprocessor 326 may be set forth below. Additionally, PWM

modulator 328A as shown in FIGURE 4 may be similar in many respects to PWM modulator 328 shown in FIGURE 3, so only certain differences between PWM modulator 328A and PWM modulator 328A may be set forth below.

As is shown in FIGURE 4, PWM modulator 328 may include a loop filter 402, quantizer 404, and a differential to single-ended conversion block 406. Although not explicitly depicted in FIGURES 3, 5, or 6, PWM modulators 328 of host device 300, host device 300B (FIGURE 5), and host device 300C (FIGURE 6) may also include loop filter 402, quantizer 404, and a differential to single-ended conversion block 406. Loop filters, quantizers, and differential to single-ended conversion blocks are well- known in the art, and thus are not described here in detail.

As further shown in FIGURE 4, PWM modulator 328 may also include a bypass switch 408. In operation, when host device 300A enters a near-rail mode, which may occur when the magnitude of processed transducer driving signal x(t) is within a threshold magnitude of either of the voltage rails of amplifier 306 (e.g., within a threshold magnitude of either a supply voltage rail or a ground voltage rail of amplifier 306), bypass switch 408 may be activated (e.g., closed, on, enabled), thus bypassing the positive polarity of the differential output of quantizer 404 to nonoverlap and slew controller 330. The resulting bypassed signal may be use to generate processed transducer driving signal %(t) and driving signal F(t) for driving a first terminal of electromagnetic load 301.

In addition, a weak high-side transistor 410 (e.g., a p-type field-effect transistor) with a driver strength significantly weaker than a driver strength of a corresponding high-side transistor of amplifier 306 may be coupled to ground return transistor 312 and arranged such that high-side transistor 410 and ground return transistor 312 form a second driver, analogous to amplifier 306, for driving a second terminal of electromagnetic load 301. The driver formed by high-side transistor 410 and ground return transistor 312 may itself be driven by a non-overlap and slew controller 330 A which may be similar or identical to non-overlap and slew controller

330. Non-overlap and slew controller 330A may receive and process the negative polarity of the differential output of quantizer 404.

Accordingly, when host device 300A enters the near-rail mode, processing subsystem 305A may be configured to bypass differential to single-ended block 406 such that high-side transistor 410 and ground return transistor 312 may be driven as a second driver pair of a differential amplifier. As a result, quantizer 404 may generate a 50% duty cycle waveform during the near-rail mode, resulting in identical signals being driven to both terminals of electromagnetic load 301, thus reducing or eliminating signal distortion (e.g., idle channel noise, non-linearity, etc.).

FIGURE 5 illustrates selected components of another example host device 300B, in accordance with embodiments of the present disclosure. Host device 300B as shown in FIGURE 5 may be similar in many respects to host device 300 shown in FIGURE 3, so only certain differences between host device 300B and host device 300 may be set forth below. Further, processing subsystem 305B as shown in FIGURE 5 may be similar in many respects to processing subsystem 305 shown in FIGURE 3, so only certain differences between processing subsystem 305A and processing subsystem 305 may be set forth below.

As shown in FIGURE 5, processing subsystem 305B may implement a logical AND gate 502, such that ground return transistor 312 may be activated, and thus couples a terminal of electromagnetic load 301 to ground, when the haptics mode is enabled and when a near-rail mode is disabled (e.g., processed transducer driving signal x(t) is outside of a threshold magnitude of either of the voltage rails of amplifier 306). Otherwise, ground return transistor 312 may be deactivated. Further, during the near-rail mode (e.g., processed transducer driving signal %(t) is within a threshold magnitude of either of the voltage rails of amplifier 306) and during the load sensing mode, common- mode buffer 314 may be activated by way of a buffer enable control signal. During the near-rail mode, common-mode buffer 314 may set a common-mode

voltage at the terminals of electromagnetic load 301 which may act to reduce output noise during the near-rail mode.

Notably, in host device 300A and host device 300B, a voltage-mode driver in a return path of the signal path is used to create a signal offset when in the near-rail mode. In host device 300A, such voltage-mode driver is the driver formed by high- side transistor 410 and ground return transistor 312, while in host device 300B, such voltage-mode driver is formed by common-mode buffer 314. Such signal offset may minimize signal distortion (e.g., idle channel noise, non-linearity, etc.).

FIGURE 6 illustrates selected components of another example host device 300C, in accordance with embodiments of the present disclosure. Host device 300C as shown in FIGURE 6 may be similar in many respects to host device 300 shown in FIGURE 3, so only certain differences between host device 300C and host device 300 may be set forth below. Further, processing subsystem 305C as shown in FIGURE 6 may be similar in many respects to processing subsystem 305 shown in FIGURE 3, so only certain differences between processing subsystem 305C and processing subsystem 305 may be set forth below. Additionally, waveform preprocessor 326C as shown in FIGURE 6 may be similar in many respects to waveform preprocessor 326 shown in FIGURE 3, so only certain differences between waveform preprocessor 326C and waveform preprocessor 326 may be set forth below.

As shown in FIGURE 6, waveform preprocessor 326C may include a nonoverlap and bypassable slew controller 330C in lieu of non-overlap and slew controller 330 of FIGURE 3. As its name suggests, in a near-rail mode of host device 300C (e.g., processed transducer driving signal %(t) is within a threshold magnitude of either of the voltage rails of amplifier 306), non-overlap and bypassable slew controller 330C may be configured to bypass slew rate control logic (or alternatively, use a maximum slew rate setting) for controlling slew rates of amplifier 306. As a result, amplifier 306 may drive narrow pulses to electromagnetic load 301 which may be imperceptible to a user, and such narrow pulses may not have enough energy to cause the

electromagnetic radiation that non-overlap and bypassable slew controller 330C serves to avoid.

FIGURE 7 illustrates selected components of another example host device 300D, in accordance with embodiments of the present disclosure. Host device 300D as shown in FIGURE 7 may be similar in many respects to host device 300 shown in FIGURE 3, so only certain differences between host device 300D and host device 300 may be set forth below. Additionally, processing subsystem 305D as shown in FIGURE 7 may be similar in many respects to processing subsystem 305 shown in FIGURE 3, so only certain differences between processing subsystem 305D and processing subsystem 305 may be set forth below.

For example, as shown in FIGURE 7, processing subsystem 305D may include supply control circuitry 350 configured to modulate a supply voltage VDD of amplifier 306 generated by a programmable voltage supply 352 as a function of processed transducer driving signal %(t). Accordingly, in a near-rail mode of host device 300D (e.g., processed transducer driving signal x(t) is within a threshold magnitude of either of the voltage rails of amplifier 306), supply control circuitry 350 may cause supply voltage VDD to increase or decrease in magnitude in order to minimize signal distortion (e.g., idle channel noise, non-linearity, etc.).

FIGURE 8 illustrates selected components of another example host device 300E, in accordance with embodiments of the present disclosure. Host device 300E as shown in FIGURE 8 may be similar in many respects to host device 300 shown in FIGURE 3, so only certain differences between host device 300E and host device 300 may be set forth below. Additionally, processing subsystem 305E as shown in FIGURE 8 may be similar in many respects to processing subsystem 305 shown in FIGURE 3, so only certain differences between processing subsystem 305E and processing subsystem 305 may be set forth below.

For example, as shown in FIGURE 8, processing subsystem 305E may include frequency control circuitry 354 configured to modulate a switching frequency f_s (e.g.,

a Class-D switching frequency) of amplifier 306 as a function of processed transducer driving signal %(t). Accordingly, in a near-rail mode of host device 300E (e.g., processed transducer driving signal x(t) is within a threshold magnitude of either of the voltage rails of amplifier 306), frequency control circuitry 354 may cause switching frequency f_s of amplifier 306 to increase or decrease in magnitude in order to minimize signal distortion (e.g., idle channel noise, non-linearity, etc.).

FIGURE 9 illustrates selected components of another example host device 300F, in accordance with embodiments of the present disclosure. Host device 300F as shown in FIGURE 9 may be similar in many respects to host device 300 shown in FIGURE 3, so only certain differences between host device 300F and host device 300 may be set forth below. Additionally, processing subsystem 305F as shown in FIGURE 9 may be similar in many respects to processing subsystem 305 shown in FIGURE 3, so only certain differences between processing subsystem 305F and processing subsystem 305 may be set forth below.

For example, in lieu of a single amplifier 306 as shown in FIGURE 3, host device 300F may include a first amplifier 306-1 (e.g., a Class-D amplifier) and a second amplifier 306-2 (e.g., a Class-AB amplifier). Further, processing subsystem 305F may include mode control circuitry 356 configured to generate a control signal for selectively enabling one of either first amplifier 306-1 or second amplifier 306-2 as a function of processed transducer driving signal x(t). Accordingly, when operating outside a near-rail mode of host device 300F (e.g., processed transducer driving signal x(t) is outside of a threshold magnitude of either of the voltage rails of amplifier 306), mode control circuitry 356 may select first amplifier 306-1 for generating driving signal V (t) . However, when operating in the near-rail mode of host device 300F (e.g., processed transducer driving signal x(t) is within a threshold magnitude of either of the voltage rails of amplifier 306), mode control circuitry 356 may select second amplifier 306-2 for generating driving signal U(t) in order to minimize signal distortion (e.g., idle channel noise, non-linearity, etc.).

FIGURE 10 illustrates selected components of another example host device 300G, in accordance with embodiments of the present disclosure. Host device 300G as shown in FIGURE 10 may be similar in many respects to host device 300 shown in FIGURE 3, so only certain differences between host device 300G and host device 300 may be set forth below. Additionally, processing subsystem 305G as shown in FIGURE 10 may be similar in many respects to processing subsystem 305 shown in FIGURE 3, so only certain differences between processing subsystem 305G and processing subsystem 305 may be set forth below.

For example, as shown in FIGURE 10, processing subsystem 305G may include noise shaping control circuitry 358 configured to modulate characteristics (e.g., filter coefficients, poles, zeroes, corner frequencies, etc.) of a noise-shaping filter 360 of amplifier 306 as a function of processed transducer driving signal x(t). Accordingly, in a near-rail mode of host device 300G (e.g., processed transducer driving signal x(t) is within a threshold magnitude of either of the voltage rails of amplifier 306), noise shaping control circuitry 358 modify one or more characteristics of noise shaping control circuitry in order to minimize signal distortion (e.g., idle channel noise, non-linearity, etc.).

For purposes of clarity and exposition, various features of the embodiments represented by FIGURES 4-10 are depicted as being used alone. However, those of skill in the art will recognize that either of various techniques for creating and modifying a signal return path offset shown in FIGURES 4 and 5 may be combined with one or more of the techniques for bypassing slew rate control shown in and described with respect to FIGURE 6, modulating amplifier supply voltage shown in and described with respect to FIGURE 7, modulating amplifier switching frequency shown in and described with respect to FIGURE 8, selection of output driver shown in and described with respect to FIGURE 9, and/or modification of noise shaping filter characteristics shown in and described with respect to FIGURE 10.

Further, those of skill in the art will recognize that the techniques for bypassing slew rate control shown in and described with respect to FIGURE 6 may be combined with one or more of the techniques for modulating amplifier supply voltage shown in and described with respect to FIGURE 7, modulating amplifier switching frequency shown in and described with respect to FIGURE 8, selection of output driver shown in and described with respect to FIGURE 9, and/or modification of noise shaping filter characteristics shown in and described with respect to FIGURE 10.

Moreover, those of skill in the art will recognize that the techniques for modulating amplifier supply voltage shown in and described with respect to FIGURE 7 may be combined with one or more of the techniques for modulating amplifier switching frequency shown in and described with respect to FIGURE 8, selection of output driver shown in and described with respect to FIGURE 9, and/or modification of noise shaping filter characteristics shown in and described with respect to FIGURE 10.

In addition, those of skill in the art will recognize that the techniques for modulating amplifier switching frequency shown in and described with respect to FIGURE 8 may be combined with one or more of the techniques for selection of output driver shown in and described with respect to FIGURE 9, and/or modification of noise shaping filter characteristics shown in and described with respect to FIGURE 10.

Additionally, those of skill in the art will recognize that the techniques for modulating amplifier switching frequency shown in and described with respect to FIGURE 9 may be combined with one or more of the techniques for modification of noise shaping filter characteristics shown in and described with respect to FIGURE 10.

In accordance with the systems and methods described above, the present disclosuree may enable a system comprising a driver configured to drive a load with a single-ended driving signal and a processing system configured to implement a function to minimize signal distortion within a signal path of the single-ended driving

signal occurring for magnitudes of the single-ended driving signal within a threshold magnitude of a voltage rail (e.g., supply voltage rail or ground voltage rail) of the driver. Such function may include one or more of: (a) modifying a signal return path offset of the system (e.g., FIGURES 4 and 5), bypassing slew rate control for the single-ended driving signal (e.g., FIGURE 6), modulating a supply voltage of the driver (e.g., FIGURE 7), modulating a switching frequency of the driver (e.g., FIGURE 8), selection between the driver and an alternate driver for driving the single- ended driving signal (e.g., FIGURE 9), and/or modification of noise shaping filter characteristics associated with the driver (e.g., FIGURE 10).

As used herein, when two or more elements are referred to as “coupled” to one another, such term indicates that such two or more elements are in electronic communication or mechanical communication, as applicable, whether connected indirectly or directly, with or without intervening elements.

This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Similarly, where appropriate, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. Accordingly, modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the disclosure. For example, the components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses

disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, “each” refers to each member of a set or each member of a subset of a set.

Although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described above.

Unless otherwise specifically noted, articles depicted in the drawings are not necessarily drawn to scale.

All examples and conditional language recited herein are intended for pedagogical objects to aid the reader in understanding the disclosure and the concepts contributed by the inventor to furthering the art, and are construed as being without limitation to such specifically recited examples and conditions. Although embodiments of the present disclosure have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the disclosure.

Although specific advantages have been enumerated above, various embodiments may include some, none, or all of the enumerated advantages. Additionally, other technical advantages may become readily apparent to one of ordinary skill in the art after review of the foregoing figures and description.

To aid the Patent Office and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims or claim elements to invoke 35 U.S.C. § 112(f) unless the words “means for” or “step for” are explicitly used in the particular claim.

Claims

WHAT IS CLAIMED IS:

1. A system comprising: a driver configured to drive a load with a single-ended driving signal; and a processing system configured to implement a function to minimize signal distortion within a signal path of the single-ended driving signal occurring for magnitudes of the single-ended driving signal within a threshold magnitude of a voltage rail of the driver.

2. The system of Claim 1, wherein the voltage rail comprises one of either a supply voltage rail or a ground voltage rail.

3. The system of Claim 1 or 2, wherein the function comprises one or more of the following: modifying a signal offset of a signal return path of the single-ended driving signal; modifying a slew rate for the single-ended driving signal; modulating a supply voltage for the driver; modulating a switching frequency of the driver; selecting an alternate driver in lieu of the driver for driving the single-ended driving signal; and modification of noise shaping filter characteristics of a noise shaping filter associated with the driver.

4. The system of Claim 3, wherein modifying the slew rate for the single- ended driving signal comprises: for magnitudes of the single-ended driving signal outside of the threshold magnitude of the voltage rail of the driver, causing the single-ended driving signal to have a first slew rate; and for magnitudes of the single-ended driving signal outside of the threshold magnitude of the voltage rail of the driver, causing the single-ended driving signal to have a second slew rate higher than the first slew rate.

5. The system of Claim 4, wherein the processing system is configured to cause the single-ended driving signal to have a second slew rate higher than the first slew rate by bypassing slew rate controls in a signal path of the driver.

6. The system of any of Claims 1-5, further comprising: a signal return path for the load, wherein the signal return path comprises a voltage-mode driver configured to create a signal offset, and wherein implementing the function comprises creating the signal offset for magnitudes of the single-ended driving signal within a threshold magnitude of a voltage rail of the driver.

7. The system of Claim 6, wherein the voltage-mode driver comprises a second driver that includes a ground-return transistor of load sensing circuitry for sensing one or more parameters associated with the load.

8. The system of Claim 6, wherein the voltage-mode driver comprises a common-mode voltage buffer of load sensing circuitry for sensing one or more parameters associated with the load.

9. The system of any of Claims 1-8, wherein the load is an electromagnetic load.

10. The system of any of Claims 1-9, wherein the load is a haptic actuator.

11. The system of any of Claims 1-10, further comprising: a current-sensing circuit having a sense resistor coupled between a first terminal of the load and an electrical node driven to a common-mode voltage; and a control circuit configured to: during a haptic mode of the system, couple a first terminal of the load to a ground voltage; and during a load sensing mode of the system, the load sensing mode for sensing a current associated with the load, couple the first terminal to the current- sensing circuit; wherein the current-sensing circuit is further configured to implement the function by creating the signal offset for magnitudes of the single-ended driving signal within a threshold magnitude of a voltage rail of the driver.

12. The system of Claim 11, wherein the current- sensing circuit comprises a voltage-mode driver configured to create the signal offset for magnitudes of the single-ended driving signal within a threshold magnitude of a voltage rail of the driver.

13. The system of Claim 12, wherein the voltage-mode driver comprises a second driver that includes a ground-return transistor of the current-sensing circuit.

14. The system of Claim 12, wherein the voltage-mode driver comprises a common-mode voltage buffer of the current-sensing circuit.

15. A method comprising: driving a load with a single-ended driving signal; and implementing a function to minimize signal distortion within a signal path of the single-ended driving signal occurring for magnitudes of the single-ended driving signal within a threshold magnitude of a voltage rail of a driver.

16. The method of Claim 15, wherein the voltage rail comprises one of either a supply voltage rail or a ground voltage rail.

17. The method of Claim 15 or 16, wherein the function comprises one or more of the following: modifying a signal offset of a signal return path of the single-ended driving signal; modifying a slew rate for the single-ended driving signal; modulating a supply voltage for the driver; modulating a switching frequency of the driver; selecting an alternate driver in lieu of the driver for driving the single-ended driving signal; and modification of noise shaping filter characteristics of a noise shaping filter associated with the driver.

18. The method of Claim 17, wherein modifying the slew rate for the single-ended driving signal comprises: for magnitudes of the single-ended driving signal outside of the threshold magnitude of the voltage rail of the driver, causing the single-ended driving signal to have a first slew rate; and for magnitudes of the single-ended driving signal outside of the threshold magnitude of the voltage rail of the driver, causing the single-ended driving signal to have a second slew rate higher than the first slew rate.

19. The method of Claim 18, further comprising causing the single-ended driving signal to have a second slew rate higher than the first slew rate by bypassing slew rate controls in a signal path of the driver.

20. The method of any of Claim 15-19, further comprising creating a signal offset with a voltage-mode driver of a signal return path for the load, wherein implementing the function comprises creating the signal offset for magnitudes of the single-ended driving signal within a threshold magnitude of a voltage rail of the driver.

21. The method of Claim 20, wherein the voltage-mode driver comprises a second driver that includes a ground-return transistor of load sensing circuitry for sensing one or more parameters associated with the load.

22. The method of Claim 20, wherein the voltage-mode driver comprises a common-mode voltage buffer of load sensing circuitry for sensing one or more parameters associated with the load.

23. The method of any of Claims 15-22, wherein the load is an electromagnetic load.

24. The method of any of Claims 15-23, wherein the load is a haptic actuator.

25. The method of any of Claims 15-24, further comprising: during a haptic mode of a system comprising the load, coupling a first terminal of the load to a ground voltage; and during a load sensing mode of the system, the load sensing mode for sensing a current associated with the load, couple the first terminal to a current-sensing circuit having a sense resistor coupled between a first terminal of the electromagnetic load and an electrical node driven to a common-mode voltage; and implementing the function with the current- sensing circuit by creating the signal offset for magnitudes of the single-ended driving signal within a threshold magnitude of a voltage rail of the driver.

26. The method of Claim 25, wherein the current- sensing circuit comprises a voltage-mode driver configured to create the signal offset for magnitudes of the single-ended driving signal within a threshold magnitude of a voltage rail of the driver.

27. The method of Claim 26, wherein the voltage-mode driver comprises a second driver that includes a ground-return transistor of the current-sensing circuit.

28. The method of Claim 26, wherein the voltage-mode driver comprises a common-mode voltage buffer of the current-sensing circuit.