On-chip inductor with audio headphone amplifier

A single integrated circuit may include a signal path configured to generate an output signal from an input signal, wherein the signal path includes an amplifier configured to drive the output signal, a direct-current-to-direct-current (DC-DC) power converter having a power inductor integrated in the single integrated circuit and configured to generate a supply voltage to the amplifier from a source voltage to the DC-DC power converter, and control circuitry for controlling operation of converter switches of the DC-DC power converter in order that the supply voltage tracks at least one among the input signal and the output signal.

FIELD OF DISCLOSURE

The present disclosure relates in general to circuits for audio devices, including without limitation personal audio devices, such as wireless telephones and media players, and more specifically, to systems and methods relating to an on-chip inductor with an audio headphone amplifier.

BACKGROUND

Mobile devices, including wireless telephones, such as mobile/cellular telephones, cordless telephones, mp3 players, and other consumer audio devices, are in widespread use. Such mobile devices may include circuitry for driving a transducer, including without limitation, a headphone, a speaker, a linear resonant actuator or other vibrational actuator, and/or any other suitable transducer.

In many audio systems, a linear amplifier may drive a transducer, and such linear amplifier may be powered from a variable supply voltage that tracks an envelope of the output signal driven by the linear amplifier to the transducer. For example, a power supply for implementing such variable supply voltage may include a buck converter or other switched-mode power converter, wherein such switched-mode power converter includes an off-chip power inductor. However, disadvantages of many implementations of such a topology is that the switched-mode power converter is unable to switch with sufficient bandwidth to effectively track the output signal driven by the linear amplifier over the full audio bandwidth.

SUMMARY

In accordance with the teachings of the present disclosure, one or more disadvantages and problems associated with existing approaches to implementing an output signal envelope tracking power supply may be reduced or eliminated.

In accordance with embodiments of the present disclosure, a single integrated circuit may include a signal path configured to generate an output signal from an input signal, wherein the signal path includes an amplifier configured to drive the output signal, a direct-current-to-direct-current (DC-DC) power converter having a power inductor integrated in the single integrated circuit and configured to generate a supply voltage to the amplifier from a source voltage to the DC-DC power converter, and control circuitry for controlling operation of converter switches of the DC-DC power converter in order that the supply voltage tracks at least one among the input signal and the output signal.

In accordance with embodiments of the present disclosure, a method may include, in a single integrated circuit generating an output signal from an input signal in a signal path, wherein the signal path includes an amplifier configured to drive the output signal, generating a supply voltage to the amplifier from a source voltage to a direct-current-to-direct-current (DC-DC) power converter, wherein the DC-DC power converter has a power inductor integrated in the single integrated circuit, and controlling operation of converter switches of the DC-DC power converter with control circuitry in order that the supply voltage tracks at least one among the input signal and the output signal.

DETAILED DESCRIPTION

FIG.1is an illustration of an example mobile device1, in accordance with embodiments of the present disclosure.FIG.1depicts mobile device1coupled to a headset3in the form of a pair of earbud speakers8A and8B. Headset3depicted inFIG.1is merely an example, and it is understood that mobile device1may be used in connection with a variety of audio transducers, including without limitation, headphones, earbuds, in-ear earphones, and external speakers. A plug4may provide for connection of headset3to an electrical terminal of mobile device1. Mobile device1may provide a display to a user and receive user input using a touch screen2, or alternatively, a standard liquid crystal display (LCD) may be combined with various buttons, sliders, and/or dials disposed on the face and/or sides of mobile device1. As also shown inFIG.1, mobile device1may include an audio integrated circuit (IC)9for generating an analog audio signal for transmission to headset3, a loudspeaker7, and/or another audio transducer.

FIG.2illustrates a block diagram of selected components of an example audio IC9of a personal audio device, in accordance with embodiments of the present disclosure. As shown inFIG.2, a microcontroller core18may supply a digital audio input signal DIG_IN to a digital-to-analog converter (DAC)14, which may convert the digital audio input signal to an analog signal VIN. DAC14may supply analog signal VINto an amplifier16which may amplify or attenuate audio input signal VINto provide a differential audio output signal VOUT, which may operate a speaker, a headphone transducer, a line level signal output, and/or other suitable output. In some embodiments, DAC14may be an integral component of amplifier16. A power supply10may provide the power supply rail inputs of microcontroller core18, DAC14, and/or other components of audio IC9. In some embodiments, power supply10may comprise a switched-mode power converter, as described in greater detail below. AlthoughFIGS.1and2contemplate that audio IC9resides in a personal audio device, systems and methods described herein may also be applied to electrical and electronic systems and devices other than a personal audio device, including audio systems for use in a computing device larger than a personal audio device, an automobile, a building, or other structure. Further, the systems and methods described herein are not limited to mobile audio devices, and may also be used in video game controllers, touchscreens, automobiles, and any other device for which audio and/or haptic output is desirable.

FIG.3is a circuit diagram of selected components of an example switched-mode power supply10, in accordance with embodiments of the present disclosure. In some embodiments, switched-mode power supply10shown inFIG.3may be used to implement switched-mode power supply10ofFIG.2.

As shown inFIG.3, switched-mode power supply10may be implemented as a buck power converter comprising a battery72, a power inductor78, converter switches74and76, a buck capacitor80, a level detector84, a bypass switch90, and a switch control circuit86. In operation, level detector84may receive digital audio input signal DIG_IN, audio output signal VOUT, and/or another signal indicative of audio output signal VOUT, and based on a detected signal level and/or time-rate-of-change of such detected signal level (e.g., slope of such detected signal level), switch control circuit86may cyclically commutate converter switches74and76to generate supply voltage VSUPPLYacross buck capacitor80smaller than battery voltage VBATof battery72, such supply voltage VSUPPLYbeing a minimal magnitude that is of sufficient headroom to ensure linear and accurate operation of current DAC14(e.g., a Class-H amplifier). For example, switch control circuit86may vary one or both of a switching frequency and a duty cycle of switched-mode power supply10in order to generate supply voltage VSUPPLY.

A current source integral to DAC14may require a sufficient voltage drop across it to operate accurately, wherein such sufficient voltage drop may also be referred to as a voltage headroom. To create sufficient voltage headroom while minimizing power consumption, switched-mode power supply10may track output signal VOUT(e.g., by tracking digital audio input signal DIG_IN, which may be indicative of output signal VOUT) to generate a supply voltage VSUPPLYsufficient to allow for linear and accurate operation of current-mode DAC14, while maintaining a supply voltage VSUPPLYas small in magnitude as possible. The amount of headroom generated by switched-mode power supply10may be optimized for efficiency or audio accuracy, and such optimization may be varied dynamically, for example, based on program material, volume control setting, environmental noise, and/or a noise cancellation setting.

In implementation, some or all components of audio IC9, including power inductor78, other components of switched-mode power supply10, and amplifier16, may be formed on a single integrated circuit die. Having power inductor78integrated on a single integrated circuit die with other components of switched-mode power supply10and amplifier16may enable a fast switching frequency for switched-mode power supply10, which may enable supply voltage VSUPPLYto track audio output signal VOUTover full audio bandwidth. For an even faster loop response for control of supply voltage VSUPPLY, switch control circuit86may be configured to operate switched-mode power supply10in a discontinuous conduction mode (e.g., in a mode in which electrical current through power inductor78is zero for a period of a switching cycle of switched-mode power supply10).

Forming some or all of audio IC9on a single integrated circuit die, including power inductor78, other components of switched-mode power supply10, and amplifier16, may have one or more advantages. For example, using a single integrated circuit die, switched-mode power supply10may operate at switching frequencies of 10 megahertz and above, including 20 megahertz or more. With a 20-megahertz switching frequency, switched-mode power supply10may effectively track 20-kilohertz audio signals amplified by amplifier16, enabling a high level of power efficiency and enabling adequate headroom and low audio distortion.

As shown inFIG.3, in some embodiments, switch control circuit86may activate (e.g., turn on, enable, close) bypass switch90to bypass battery voltage VBATto supply voltage VSUPPLY. For example, such bypass may occur when the switching frequency of switched-mode power supply10is insufficient to track the signal frequency of audio output signal VOUT. As another example, if audio output signal VOUTis close in magnitude to battery voltage VBAT, switch control circuit86may activate bypass switch90in order to maximize converter efficiency.

As shown inFIG.3, switch control circuit86may control switching frequency and/or duty cycle of converter switches74and76and operation of bypass switch90in a feedforward operation (e.g., based on digital audio input signal DIG_IN), a feedback operation (e.g., based on output signal VOUT), or a combination thereof. For example, in some embodiments, a hybrid approach may be used in which feedforward operation may be used to determine switching frequency of converter switches74and76based on signal power estimation, and the feedback operation may be used to control duty cycle based on comparison of supply voltage VSUPPLYto a reference. As another example, in other embodiments, feedback operation may be used to control duty cycle until a duty cycle limit is used, and then the feedforward operation may be used to control switching frequency of converter switches74and76once such duty cycle limit is reached.