Abstract:
In accordance with embodiments of the present disclosure, an apparatus may include a switched-mode power supply and a controller. The switched-mode power supply may include an inductor and a plurality of switches coupled to the inductor. The controller may be configured to control an inductor current of the inductor by controlling the plurality of switches to operate the switched-mode power supply in at least three phases, the at least three phases comprising: a first phase having a first period in which the inductor current increases; and a second phase having a second period in which the inductor current decreases; wherein, at least one of the first period and the second period is defined by a difference in time between switching of at least two switches of the plurality of switches.

Description:
RELATED APPLICATIONS 
       [0001]    The present disclosure claims priority to U.S. Provisional Patent Application Ser. No. 62/255,960, filed Nov. 16, 2015, which is incorporated by reference herein in its entirety. 
     
    
     FIELD OF DISCLOSURE 
       [0002]    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 a switched mode power supply for supplying a supply voltage to an amplifier or other load. 
       BACKGROUND 
       [0003]    Personal audio devices, including wireless telephones, such as mobile/cellular telephones, cordless telephones, mp3 players, and other consumer audio devices, are in widespread use. Such personal audio devices may include circuitry for driving a pair of headphones or one or more speakers. Such circuitry often includes a power amplifier for driving an audio output signal to headphones or speakers. Generally speaking, a power amplifier amplifies an audio signal by taking energy from a power supply and controlling an audio output signal to match an input signal shape but with a larger amplitude. Although many amplifier architectures (e.g., Class A, Class B, and Class AB amplifiers) provide for only a single power supply for a power amplifier, some architectures provide for at least two supply voltages for powering a power amplifier, in order to achieve greater power efficiency over single or constant power supply voltage architectures. 
         [0004]    One example of a multi-supply voltage amplifier is a Class H amplifier. A Class H amplifier may have an infinitely variable voltage supply rail that tracks an envelope of an output signal of the Class H amplifier. In order to provide such an infinitely variable voltage supply rail, the output supply rail may be modulated such that the rail is only slightly larger than a magnitude of the audio output signal at any given time. For example, switched-mode power supplies may be used to create the output signal-tracking voltage rails. Accordingly, a Class H amplifier may increase efficiency by reducing the wasted power at output driving transistors of the amplifier. 
         [0005]    Such amplifiers often utilize switched-mode power supplies for drawing a supply voltage. Switched-mode power supplies may include power converters for converting one direct-current voltage (e.g., provided by a battery or other power source) to another direct-current voltage. For example, buck converters are often used to generate voltages lower than the source (e.g., battery) voltage, and boost converters are often used to generate voltages higher than the source (e.g., battery) voltage. However, for both buck and boost converters, generating a voltage that is close to the power source voltage is challenging due to the extremely large or small duty cycles needed to do so. Realizing such small duty cycles using switches may require some of the switches to be activated (e.g., enabled, turned on, closed) for infinitesimally small periods of time. 
         [0006]    One solution to this challenge is to use a buck-boost converter when a voltage close to the power source voltage is desired. However, buck-boost converters are often power inefficient. Another solution is to use a multi-mode converter which operates in a buck mode at lower output voltages, a boost mode at higher output voltages, and a buck-boost mode at voltages near the power source voltage. However, transitions between the various modes are challenging, as the average inductor current in each of the modes is different, which may lead to large discontinuities when transitioning from one mode to another. Such transitioning can be especially difficult in certain applications such as Class H amplifiers in which accurate tracking supply rails are desired. 
       SUMMARY 
       [0007]    In accordance with the teachings of the present disclosure, one or more disadvantages and problems associated with existing approaches to driving an audio output signal to an audio transducer may be reduced or eliminated. 
         [0008]    In accordance with embodiments of the present disclosure, a method of controlling an inductor current in a switched-mode power supply having a plurality of switches may include controlling the plurality of switches to operate the switched-mode power supply in at least three phases, the at least three phases comprising: a first phase having a first period in which the inductor current increases; and a second phase having a second period in which the inductor current decreases; wherein, at least one of the first period and the second period is defined by a difference in time between switching of at least two switches of the plurality of switches. 
         [0009]    In accordance with these and other embodiments of the present disclosure, an apparatus may include a switched-mode power supply and a controller. The switched-mode power supply may include an inductor and a plurality of switches coupled to the inductor. The controller may be configured to control an inductor current of the inductor by controlling the plurality of switches to operate the switched-mode power supply in at least three phases, the at least three phases comprising: a first phase having a first period in which the inductor current increases; and a second phase having a second period in which the inductor current decreases; wherein, at least one of the first period and the second period is defined by a difference in time between switching of at least two switches of the plurality of switches. 
         [0010]    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. 
         [0011]    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 
         [0012]    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: 
           [0013]      FIG. 1  is an illustration of an example personal audio device, in accordance with embodiments of the present disclosure; 
           [0014]      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; 
           [0015]      FIG. 3  is a block diagram of selected components of an example buck converter, in accordance with embodiments of the present disclosure; 
           [0016]      FIG. 4A  illustrates possible connections among components of the buck converter of  FIG. 3  for each of three phases of operation and an equivalent circuit for each such phase, in accordance with embodiments of the present disclosure; 
           [0017]      FIG. 4B  illustrates additional possible connections among components of the buck converter of  FIG. 3  for each of three phases of operation and an equivalent circuit for each such phase, in accordance with embodiments of the present disclosure; 
           [0018]      FIG. 5  is a block diagram of selected components of an example boost converter, in accordance with embodiments of the present disclosure; 
           [0019]      FIG. 6  illustrates possible connections among components of the boost converter of  FIG. 5  for each of three phases of operation and an equivalent circuit for each such phase, in accordance with embodiments of the present disclosure; 
           [0020]      FIG. 7  is a block diagram of selected components of an example multi-phase power converter, in accordance with embodiments of the present disclosure; 
           [0021]      FIG. 8  illustrates possible connections among components of the multi-phase power converter of  FIG. 7  for each of four phases of operation and an equivalent circuit for each such phase, in accordance with embodiments of the present disclosure; 
           [0022]      FIG. 9A  illustrates a graph of an example inductor current for each of four phases of operation of the multi-phase power converter of  FIG. 7 , in accordance with embodiments of the present disclosure; and 
           [0023]      FIG. 9B  illustrates a another graph of an example inductor current for each of four phases of operation of the multi-phase power converter of  FIG. 7 , in accordance with embodiments of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]      FIG. 1  is an illustration of an example personal audio device  1 , in accordance with embodiments of the present disclosure.  FIG. 1  depicts personal audio 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 personal audio 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 personal audio device  1 . Personal audio 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 personal audio device  1 . As also shown in  FIG. 1 , personal audio device  1  may include an audio integrated circuit (IC)  9  for generating an analog audio signal for transmission to headset  3  and/or another audio transducer. 
         [0025]      FIG. 2  is 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. In some embodiments, example audio IC  9  may be used to implement audio IC  9  of  FIG. 1 . 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 stage  16  which may amplify or attenuate audio input signal V IN  to provide an audio output signal V OUT , which may operate a speaker, headphone transducer, a line level signal output, and/or other suitable output. A capacitor CO may be utilized to couple the output signal to the transducer or line level output, particularly if amplifier stage  16  is operated from a unipolar power supply having a quiescent voltage substantially differing from ground. Also, as shown in  FIG. 2 , audio IC  9  may include a control circuit  20  configured to, based on digital audio input signal DIG_IN, control a power supply voltage of amplifier stage  16  using one or more control signals (labeled as “VOLTAGE CONTROL” in  FIG. 2 ). 
         [0026]    As depicted in  FIG. 2 , amplifier stage  16  may include any suitable amplifier  26  which has an input for receiving analog signal V IN , an output for generating output signal V OUT  based on and indicative of analog signal V IN , and a power supply input for receiving a load voltage V LOAD  output by a power supply  28 , wherein power supply  28  outputs load voltage V LOAD  regulated by one or more control signals VOLTAGE CONTROL. In some embodiments, load voltage V LOAD  output by power supply  28  may be variable in that it is selected from a plurality of discrete voltages, or includes an infinite number of voltages between a minimum and maximum voltage. In some embodiments, power supply  28  may be implemented with a switched-mode power supply, such as, but not limited to, buck converter  30  depicted in  FIG. 3 , boost converter  50  depicted in  FIG. 5 , or multi-phase power converter  70  depicted in  FIG. 7 . 
         [0027]      FIG. 3  is a block diagram of selected components of an example buck converter  30 , in accordance with embodiments of the present disclosure. As shown in  FIG. 3 , buck converter  30  may include or may be coupled to a battery  38  or other voltage source configured to output a battery voltage V BAT . Battery  38  may comprise any suitable energy storage device, including without limitation one or more electrochemical cells configured to convert chemical energy into electrical energy at the terminals of battery  38 . As shown in  FIG. 3 , buck converter  30  may also include an output at which buck converter  30  may generate a single-ended load voltage V LOAD . 
         [0028]    Buck converter  30  may comprise a power inductor  36  and a plurality of switches  31 - 35 . Power inductor  36  may comprise any passive two-terminal electrical component which resists changes in electrical current passing through it and such that when electrical current flowing through it changes, a time-varying magnetic field induces a voltage in power inductor  36 , in accordance with Faraday&#39;s law of electromagnetic induction, which opposes the change in current that created the magnetic field. 
         [0029]    Each switch  31 - 35  may comprise any suitable device, system, or apparatus for making a connection in an electric circuit when the switch is enabled (e.g., activated, closed, or on) and breaking the connection when the switch is disabled (e.g., deactivated, open, or off) in response to a control signal received by the switch. For purposes of clarity and exposition, control signals for switches  31 - 35  (e.g., control signals communicated from control circuit  20 ) are not depicted although such control signals would be present to selectively enable and disable switches  31 - 35 . In some embodiments, a switch  31 - 35  may comprise an n-type metal-oxide-semiconductor field-effect transistor. 
         [0030]    Switch  31  may be coupled between a positive input terminal of battery  38  and a first terminal of power inductor  36 . Switch  32  may be coupled between a negative input terminal of battery  38  (e.g., a ground voltage) and the first terminal of power inductor  36 . Switch  33  may be coupled between the positive input terminal of battery  38  and a second terminal of power inductor  36 . Switch  34  may be coupled between the negative input terminal of battery  38  and the second terminal of power inductor  36 . Switch  55  may be coupled between the second terminal of power inductor  36  and an output terminal of buck converter  30 . 
         [0031]    In operation, switches  31 - 35  may be controlled by control circuit  20  such that buck converter  30  sequentially operates in a plurality of phases as shown in either of  FIG. 4A  or  FIG. 4B , the length of each phase controlled in order to regulate a desired load voltage V LOAD  less than battery voltage V BAT . As shown in  FIG. 4A , buck converter  30  may operate in a repeating sequence of a charging phase T 1 , a discharge phase T 2 , and a hold phase T 3 . In charging phase T 1 , switches  31  and  35  may be activated (e.g., enabled, turned on, closed) and switches  32 ,  33 , and  34  may be deactivated (e.g., disabled, turned off, opened). In discharging phase T 2 , switches  32  and  35  may be activated and switches  31 ,  33 , and  34  may be deactivated. In hold phase T 3 , switches  31  and  33  may be activated and switches  32 ,  34 , and  35  may be deactivated. Accordingly, an inductor current I L  flowing through power inductor  36  may increase during charging phase T 1 , decrease during discharging phase T 2 , and remain substantially constant during hold phase T 3 . 
         [0032]    Thus, when a duration of hold phase T 3  is sufficiently large, a duration of charging phase T 1  may be made infinitesimally small, because as buck converter  30  sequences from hold phase T 3  to charging phase T 1  to discharging phase T 2 , switches on opposite sides of inductor  36  need to be toggled between activated and deactivated, or vice versa. The ability to realize infinitesimally small durations of charging phase T 1  may enable buck converter  30  to generate arbitrary small voltages (e.g., near zero) for load voltage V LOAD , which is often difficult using traditional approaches. 
         [0033]    Similarly, as shown in  FIG. 4B , buck converter  30  may operate in a repeating sequence of a charging phase T 1 , a discharge phase T 2 , and a hold phase T 3 . In charging phase T 1 , switches  31  and  35  may be activated (e.g., enabled, turned on, closed) and switches  32 ,  33 , and  34  may be deactivated (e.g., disabled, turned off, opened). In discharging phase T 2 , switches  32  and  35  may be activated and switches  31 ,  33 , and  34  may be deactivated. In hold phase T 3 , switches  32  and  34  may be activated and switches  31 ,  33 , and  35  may be deactivated. Accordingly, an inductor current I L  flowing through power inductor  36  may increase during charging phase T 1 , decrease during discharging phase T 2 , and remain substantially constant during hold phase T 3 . 
         [0034]    Thus, when a duration of hold phase T 3  is sufficiently large, a duration of discharge phase T 2  may be made infinitesimally small, because as buck converter  30  sequences from charging phase T 1  to discharge phase T 2  to hold phase T 3 , switches on opposite sides of inductor  36  need to be toggled between activated and deactivated, or vice versa. The ability to realize infinitesimally small durations of discharge phase T 2  may enable buck converter  30  to generate voltages near that of battery voltage V BAT  for load voltage V LOAD , which is often difficult using traditional approaches. 
         [0035]      FIG. 5  is a block diagram of selected components of an example boost converter  50 , in accordance with embodiments of the present disclosure. As shown in  FIG. 5 , boost converter  50  may include or may be coupled to a battery  58  or other voltage source configured to output a battery voltage V BAT . Battery  58  may comprise any suitable energy storage device, including without limitation one or more electrochemical cells configured to convert chemical energy into electrical energy at the terminals of battery  58 . As shown in  FIG. 5 , boost converter  50  may also include an output at which boost converter  50  may generate a single-ended load voltage V LOAD . 
         [0036]    Boost converter  50  may comprise a power inductor  56  and a plurality of switches  51 - 54 . Power inductor  56  may comprise any passive two-terminal electrical component which resists changes in electrical current passing through it and such that when electrical current flowing through it changes, a time-varying magnetic field induces a voltage in power inductor  56 , in accordance with Faraday&#39;s law of electromagnetic induction, which opposes the change in current that created the magnetic field. 
         [0037]    Each switch  51 - 54  may comprise any suitable device, system, or apparatus for making a connection in an electric circuit when the switch is enabled (e.g., activated, closed, or on) and breaking the connection when the switch is disabled (e.g., deactivated, open, or off) in response to a control signal received by the switch. For purposes of clarity and exposition, control signals for switches  51 - 54  (e.g., control signals communicated from control circuit  20 ) are not depicted although such control signals would be present to selectively enable and disable switches  51 - 54 . In some embodiments, a switch  51 - 54  may comprise an n-type metal-oxide-semiconductor field-effect transistor. 
         [0038]    Switch  51  may be coupled between a positive input terminal of battery  58  and a first terminal of power inductor  56 . Switch  52  may be coupled between a negative input terminal of battery  58  (e.g., a ground voltage) and the first terminal of power inductor  56 . Switch  53  may be coupled between a second terminal of power inductor  56  and the output terminal of boost converter  50 . Switch  54  may be coupled between the negative input terminal of battery  58  and the second terminal of power inductor  56 . 
         [0039]    In operation, switches  51 - 54  may be controlled by control circuit  20  such that boost converter  50  sequentially operates in a plurality of phases as shown in  FIG. 6 , the length of each phase controlled in order to regulate a desired load voltage V LOAD  greater than battery voltage V BAT . As shown in  FIG. 6 , boost converter  50  may operate in a repeating sequence of a charging phase T 1 , a transfer phase T 2 , and a hold phase T 3 . In charging phase T 1 , switches  51  and  54  may be activated and switches  52  and  53  may be deactivated. In transfer phase T 2 , switches  51  and  53  may be activated and switches  52  and  54  may be deactivated. In hold phase T 3 , switches  52  and  54  may be activated and switches  51  and  53  may be deactivated. Accordingly, an inductor current I L  flowing through power inductor  56  may increase during charging phase T 1 , decrease during transfer phase T 2 , and remain substantially constant during hold phase T 3 . 
         [0040]    Accordingly, when a duration of hold phase T 3  is sufficiently large, a duration of charging phase T 1  may be made infinitesimally small, because as boost converter  50  sequences from hold phase T 3  to charging phase T 1  to transfer phase T 2 , switches on opposite sides of inductor  56  need to be toggled between activated and deactivated, or vice versa. The ability to realize infinitesimally small durations of charging phase T 1  may enable boost converter  50  to generate voltages for load voltage V LOAD  which are arbitrary close to battery voltage V BAT , which is often difficult using traditional approaches. 
         [0041]      FIG. 7  is a block diagram of selected components of an example multi-phase power converter  70 , in accordance with embodiments of the present disclosure. As shown in  FIG. 7 , multi-phase power converter  70  may include or may be coupled to a battery  78  or other voltage source configured to output a battery voltage V BAT . Battery  78  may comprise any suitable energy storage device, including without limitation one or more electrochemical cells configured to convert chemical energy into electrical energy at the terminals of battery  78 . As shown in  FIG. 7 , multi-phase power converter  70  may also include an output at which multi-phase power converter  70  may generate a single-ended load voltage V LOAD . 
         [0042]    Multi-phase power converter  70  may comprise a power inductor  76  and a plurality of switches  71 - 74 . Power inductor  76  may comprise any passive two-terminal electrical component which resists changes in electrical current passing through it and such that when electrical current flowing through it changes, a time-varying magnetic field induces a voltage in power inductor  76 , in accordance with Faraday&#39;s law of electromagnetic induction, which opposes the change in current that created the magnetic field. 
         [0043]    Each switch  71 - 74  may comprise any suitable device, system, or apparatus for making a connection in an electric circuit when the switch is enabled (e.g., activated, closed, or on) and breaking the connection when the switch is disabled (e.g., deactivated, open, or off) in response to a control signal received by the switch. For purposes of clarity and exposition, control signals for switches  71 - 74  (e.g., control signals communicated from control circuit  20 ) are not depicted although such control signals would be present to selectively enable and disable switches  71 - 74 . In some embodiments, a switch  71 - 74  may comprise an n-type metal-oxide-semiconductor field-effect transistor. 
         [0044]    Switch  71  may be coupled between a positive input terminal of battery  78  and a first terminal of power inductor  76 . Switch  72  may be coupled between a negative input terminal of battery  78  (e.g., a ground voltage) and the first terminal of power inductor  76 . Switch  73  may be coupled between a second terminal of power inductor  76  and the output terminal of multi-phase power converter  70 . Switch  74  may be coupled between the negative input terminal of battery  78  and the second terminal of power inductor  76 . 
         [0045]    In operation, switches  71 - 74  may be controlled by control circuit  20  such that multi-phase power converter  70  sequentially operates in a plurality of phases as shown in  FIG. 8 , the length of each phase controlled in order to regulate a desired load voltage V LOAD . As shown in  FIG. 8 , multi-phase power converter  70  may operate in a repeating sequence of a charging phase T 1 , a bridge phase T 2 , a discharging phase T 3 , and a hold phase T 4 . In charging phase T 1 , switches  71  and  74  may be activated and switches  72  and  73  may be deactivated. In bridge phase T 2 , switches  71  and  73  may be activated and switches  72  and  74  may be deactivated. In discharging phase T 3  switches  72  and  73  may be activated and switches  71  and  74  may be deactivated. In hold phase T 4 , switches  72  and  74  may be activated and switches  71  and  73  may be deactivated. Accordingly, as shown in  FIG. 9A , an inductor current I L  flowing through power inductor  76  may increase during charging phase T 1 , increase during bridge phase T 2  (e.g., if battery voltage V BAT  is greater than load voltage V LOAD ), decrease during discharge phase T 3 , and remain substantially constant during hold phase T 4 . Alternatively, as shown in  FIG. 9B , an inductor current I L  flowing through power inductor  76  may increase during charging phase T 1 , decrease during bridge phase T 2  (e.g., if battery voltage V BAT  is lesser than load voltage V LOAD ), decrease during discharge phase T 3 , and remain substantially constant during hold phase T 4 . 
         [0046]    Thus, successive phase transitions have switches toggling on opposite sides of power inductor  76 . For example, when transitioning from phase T 1  to phase T 2  phase, switches  74  and  73  on the second terminal of power inductor  76  toggle. When transitioning from phase T 2  to phase T 3 , switches  71  and  72  on the first terminal of power inductor  76  toggle. Similar patterns are observed when transitioning from phase T 3  to phase T 4  and from phase T 4  to phase T 1 . Thus, each pair of successive transitions involves toggling switches on opposite terminals of power inductor  76 . Thus, in successive transitions, the same switch does not have to toggle. Now, as long as a duration of phase T 4  phase is sufficiently large, the durations of any of phase T 1 , phase T 2 , or phase T 3  may be infinitesimally small. This is because the same switch does not have to toggle when going from one phase to another. 
         [0047]    Although the foregoing contemplates one of buck converter  30 , boost converter  50 , or multi-phase power converter  70  used to implement power supply  28 , power supply  28  may be implemented using any suitable switched-mode power supply (including a multi-mode switched-mode power supply capable of operating in a plurality of modes including a buck mode, a boost mode, and/or a buck-boost mode). 
         [0048]    In addition, although the foregoing describes a hold phase in which an inductor current remains constant, in some embodiments, such hold phase may result in an increase or decrease in inductor current. 
         [0049]    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. 
         [0050]    This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the exemplary 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 exemplary 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. 
         [0051]    All examples and conditional language recited herein are intended for pedagogical objects to aid the reader in understanding the invention 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 inventions 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.