Patent Publication Number: US-2021175322-A1

Title: On-chip inductor with audio headphone amplifier

Description:
RELATED APPLICATION 
     The present disclosure claims priority to U.S. Provisional Patent Application Ser. No. 62/944,820, filed Dec. 6, 2019, which is incorporated by reference herein in its entirety. 
    
    
     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. 
     Technical advantages of the present disclosure may be readily apparent to one skilled 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: 
         FIG. 1  is an illustration of an example personal audio device, in accordance with embodiments of the present disclosure; 
         FIG. 2  is a block diagram of selected components of an example audio integrated circuit of a personal audio device, in accordance with embodiments of the present disclosure; and 
         FIG. 3  is a circuit diagram of selected components of an example switched-mode power supply, in accordance with embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is an illustration of an example mobile device  1 , in accordance with embodiments of the present disclosure.  FIG. 1  depicts mobile device  1  coupled to a headset  3  in the form of a pair of earbud speakers  8 A and  8 B. Headset  3  depicted in  FIG. 1  is merely an example, and it is understood that mobile device  1  may be used in connection with a variety of audio transducers, including without limitation, headphones, earbuds, in-ear earphones, and external speakers. A plug  4  may provide for connection of headset  3  to an electrical terminal of mobile device  1 . Mobile device  1  may provide a display to a user and receive user input using a touch screen  2 , 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 device  1 . As also shown in  FIG. 1 , mobile device  1  may include an audio integrated circuit (IC)  9  for generating an analog audio signal for transmission to headset  3 , a loudspeaker  7 , and/or another audio transducer. 
       FIG. 2  illustrates a block diagram of selected components of an example audio IC  9  of a personal audio device, in accordance with embodiments of the present disclosure. As shown in  FIG. 2 , a microcontroller core  18  may 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 V IN . DAC  14  may supply analog signal V IN  to an amplifier  16  which may amplify or attenuate audio input signal V IN  to provide a differential audio output signal V OUT , which may operate a speaker, a headphone transducer, a line level signal output, and/or other suitable output. In some embodiments, DAC  14  may be an integral component of amplifier  16 . A power supply  10  may provide the power supply rail inputs of microcontroller core  18 , DAC  14 , and/or other components of audio IC  9 . In some embodiments, power supply  10  may comprise a switched-mode power converter, as described in greater detail below. Although  FIGS. 1 and 2  contemplate that audio IC  9  resides 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. 3  is a circuit diagram of selected components of an example switched-mode power supply  10 , in accordance with embodiments of the present disclosure. In some embodiments, switched-mode power supply  10  shown in  FIG. 3  may be used to implement switched-mode power supply  10  of  FIG. 2 . 
     As shown in  FIG. 3 , switched-mode power supply  10  may be implemented as a buck power converter comprising a battery  72 , a power inductor  78 , converter switches  74  and  76 , a buck capacitor  80 , a level detector  84 , a bypass switch  90 , and a switch control circuit  86 . In operation, level detector  84  may receive digital audio input signal DIG_IN, audio output signal V OUT , and/or another signal indicative of audio output signal V OUT , 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 circuit  86  may cyclically commutate converter switches  74  and  76  to generate supply voltage V SUPPLY  across buck capacitor  80  smaller than battery voltage V BAT  of battery  72 , such supply voltage V SUPPLY  being a minimal magnitude that is of sufficient headroom to ensure linear and accurate operation of current DAC  14  (e.g., a Class-H amplifier). For example, switch control circuit  86  may vary one or both of a switching frequency and a duty cycle of switched-mode power supply  10  in order to generate supply voltage V SUPPLY . 
     A current source integral to DAC  14  may 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 supply  10  may track output signal V OUT  (e.g., by tracking digital audio input signal DIG_IN, which may be indicative of output signal V OUT ) to generate a supply voltage V SUPPLY  sufficient to allow for linear and accurate operation of current-mode DAC  14 , while maintaining a supply voltage V SUPPLY  as small in magnitude as possible. The amount of headroom generated by switched-mode power supply  10  may 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 IC  9 , including power inductor  78 , other components of switched-mode power supply  10 , and amplifier  16 , may be formed on a single integrated circuit die. Having power inductor  78  integrated on a single integrated circuit die with other components of switched-mode power supply  10  and amplifier  16  may enable a fast switching frequency for switched-mode power supply  10 , which may enable supply voltage V SUPPLY  to track audio output signal V OUT  over full audio bandwidth. For an even faster loop response for control of supply voltage V SUPPLY , switch control circuit  86  may be configured to operate switched-mode power supply  10  in a discontinuous conduction mode (e.g., in a mode in which electrical current through power inductor  78  is zero for a period of a switching cycle of switched-mode power supply  10 ). 
     Forming some or all of audio IC  9  on a single integrated circuit die, including power inductor  78 , other components of switched-mode power supply  10 , and amplifier  16 , may have one or more advantages. For example, using a single integrated circuit die, switched-mode power supply  10  may operate at switching frequencies of 10 megahertz and above, including 20 megahertz or more. With a 20-megahertz switching frequency, switched-mode power supply  10  may effectively track 20-kilohertz audio signals amplified by amplifier  16 , enabling a high level of power efficiency and enabling adequate headroom and low audio distortion. 
     As shown in  FIG. 3 , in some embodiments, switch control circuit  86  may activate (e.g., turn on, enable, close) bypass switch  90  to bypass battery voltage V BAT  to supply voltage V SUPPLY . For example, such bypass may occur when the switching frequency of switched-mode power supply  10  is insufficient to track the signal frequency of audio output signal V OUT . As another example, if audio output signal V OUT  is close in magnitude to battery voltage V BAT , switch control circuit  86  may activate bypass switch  90  in order to maximize converter efficiency. 
     As shown in  FIG. 3 , switch control circuit  86  may control switching frequency and/or duty cycle of converter switches  74  and  76  and operation of bypass switch  90  in a feedforward operation (e.g., based on digital audio input signal DIG_IN), a feedback operation (e.g., based on output signal V OUT ), 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 switches  74  and  76  based on signal power estimation, and the feedback operation may be used to control duty cycle based on comparison of supply voltage V SUPPLY  to 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 switches  74  and  76  once such duty cycle limit is reached. 
     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.