CN111869101B

CN111869101B - Method for limiting input current of amplifier to avoid low voltage condition

Info

Publication number: CN111869101B
Application number: CN201980018786.0A
Authority: CN
Inventors: 罗杰·史威; 杰森·W·劳伦斯; 菲拉斯·阿兹拉伊; 杰弗里·艾伦·梅; 苏洁
Original assignee: Cirrus Logic International Semiconductor Ltd
Current assignee: Cirrus Logic International Semiconductor Ltd
Priority date: 2018-03-12
Filing date: 2019-03-05
Publication date: 2023-07-28
Anticipated expiration: 2039-03-05
Also published as: GB202013376D0; KR102472738B1; KR20200129151A; CN111869101A; WO2019177806A1

Abstract

The predictive power loss prevention system may be configured to prevent power loss of the audio output signal. In particular, the power loss prevention system may be configured to: receiving information indicative of an adaptive estimate of a power supply condition, wherein the information indicative of the adaptive estimate of the power supply condition includes information about a voltage component and a resistance component received from an adaptive battery model of a battery used to provide power to a power supply to generate a power supply voltage; and adjusting the adaptive battery model based on the monitored battery voltage output by the battery and the load event of the signal path and excluding the load event of the components other than the signal path powered by the battery.

Description

Method for limiting input current of amplifier to avoid low voltage condition

Technical Field

The present disclosure relates generally to circuits for audio devices, including but not limited to personal audio devices such as wireless telephones and media players, and more particularly to systems and methods for predictively preventing power down conditions (brownout condition) in personal audio devices.

Background

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 circuits typically include a power amplifier for driving the audio output signal to headphones or speakers.

In general, the size of personal audio devices continues to decrease, but many users desire these personal audio devices to make louder sounds. This places physical size constraints on the battery used to power the components of the personal audio device while the audio subsystem of such personal audio device requires more output power. With the demand for higher audio volume and quality, a boosted supply voltage is typically generated that is higher than the battery voltage in order to power the audio amplifier and deliver more power to the speaker load. As more power is delivered to the speaker load, the battery of the personal audio device will be subjected to more stress.

The battery includes an output impedance and thus a heavy load condition on the battery may cause the output voltage of the battery to drop. This drop in output voltage may be more pronounced when the battery level is low. The sudden voltage drop created by such a load event may reduce the output voltage of the battery to the point where certain subsystems on the device are no longer able to function properly. When the battery is in a weakened or low-battery state and the personal audio device is unable to provide protection against such a weakened or low-battery state, the general end result is that the personal audio device resets itself due to the low-voltage condition. Such a self-resetting condition may be unsatisfactory for the user of the personal audio device and thus problematic for the provider of the personal audio device (e.g., manufacturer, supplier, distributor, or other provider in the commercial chain). Such a condition or conditions in which an unintentional voltage drop occurs are commonly referred to as a "power down" condition.

Conventional methods of mitigating power loss conditions in personal audio devices are reactive in nature in that reactive power loss reduction systems typically recognize that a condition occurs in which the battery voltage drops below a predetermined voltage threshold (e.g., configured by a user or provider of the personal audio device) and react in response to the battery voltage dropping below this threshold. One example of such a reaction is to reduce the volume in order to reduce the load of the audio amplifier on the battery.

The reactive approach is based on the following concept: the battery power source has occurred an undesirable event and, therefore, the personal audio device acts rapidly to reduce the load in order to prevent the personal audio device from powering down. Subsystems other than the audio subsystem and powered by the battery power source may also react independently to reduce the load on the battery power source and return it to a safe level to maintain the functionality of the more critical subsystems in the personal audio device. Such reactive approaches do little or nothing to prevent the audio subsystem, and in particular the audio amplifier, from being the cause of the battery power source falling to an undesirable level that may trigger a power down condition. Reactive power loss reduction systems typically do not know the audio content and, by extension, the actual power load caused by the audio signal path. Instead, such prior systems typically assume that the load of the output amplifier of the audio signal path is the source of the power supply droop and blindly reduce the load of the output amplifier even if it is not the primary source of the reduction power supply.

The reactive power down reduction system requires a certain amount of time to react before the audio signal to the audio amplifier decays. It takes an additional amount of time to attenuate the audio signal and return the battery power supply to the "safe" operating voltage once the battery's supply voltage drops. The accumulated initial reaction time, system response time, and battery power recovery time may cause the system to spend a significant amount of time below the preconfigured threshold voltage of the battery power supply.

If the audio system, in particular the audio amplifier, is the main cause of the battery power drop and the battery is in a weakened state, it is also possible for this reactive approach to enter such an operational state: the audio volume is repeatedly attenuated and then allowed to resume. From the user's perspective, this may create a "pumping" effect of the audio content, where the audio volume repeatedly becomes louder and softer, because the reactive power down reduction system may place the reactive power down response in successive cycles.

Disclosure of Invention

Certain disadvantages and problems associated with speaker electrical identification have been reduced or eliminated in accordance with the teachings of the present disclosure.

According to an embodiment of the present disclosure, an apparatus for providing an audio output signal to an audio transducer may include a signal path comprising: an audio input configured to receive an audio input signal; an audio output configured to provide an audio output signal; a power supply input configured to receive a power supply voltage; and an attenuation block, which may be configured to: receiving information indicative of an adaptive estimate of a power supply condition, wherein the information indicative of the adaptive estimate of the power supply condition includes information about a voltage component and a resistance component received from an adaptive battery model of a battery used to provide power to a power supply to generate the power supply voltage; adjusting the adaptive battery model based on monitored battery voltage output by the battery and load events of the signal path and excluding load events of components other than the signal path powered by the battery; and in response to determining that a portion of the audio input signal has reached a maximum power threshold, generating a selectable attenuation signal to reduce the amplitude of the audio output signal such that the signal path attenuates the audio input signal or a derivative thereof to prevent power loss prior to propagation to an audio output of the portion of the audio input signal.

In accordance with these and other embodiments of the present disclosure, a method for providing an audio output signal to an audio transducer may include: receiving information indicative of an amplitude of an audio input signal; receiving information indicative of a power condition of a signal path, the signal path having an audio input for receiving the audio input signal and an audio output for providing the audio output signal; receiving information indicative of an adaptive estimate of a power supply condition, wherein the information indicative of the adaptive estimate of the power supply condition includes information about a voltage component and a resistance component received from an adaptive battery model of a battery used to provide power to a power supply to generate the power supply voltage, adjusting the adaptive battery model based on monitored battery voltage output by the battery and load events of the signal path and excluding load events of components other than the signal path that are powered by the battery; and in response to determining that a portion of the audio input signal has reached a maximum power threshold, generating a selectable attenuation signal to reduce the amplitude of the audio output signal such that the signal path attenuates the audio input signal or a derivative thereof to prevent power loss prior to propagation to an audio output of the portion of the audio input signal.

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

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

Drawings

A more complete understanding of the examples, present embodiments, and certain 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 a diagram of an example personal audio device, according to an embodiment of the present disclosure;

FIG. 2 is a block diagram of selected components of an example audio integrated circuit of a personal audio device, according to an embodiment of the present disclosure;

FIG. 3 is a block diagram of selected components of a predictive power loss prevention system for use within the audio integrated circuit depicted in FIG. 2, in accordance with an embodiment of the present disclosure;

FIG. 4 is a circuit diagram of a model of an example battery according to an embodiment of the present disclosure;

FIG. 5 is a graph illustrating an example relationship between output impedance and battery charge voltage of the model of the example battery depicted in FIG. 4, in accordance with an embodiment of the present disclosure;

FIG. 6 is a graph of an example gain transfer function according to an embodiment of the present disclosure;

FIG. 7 is a graph of another example gain transfer function according to an embodiment of the present disclosure;

FIG. 8 is a graphical representation of various signals versus time that may occur when a predictive power down control system triggers attenuation of an audio signal to prevent power down, in accordance with an embodiment of the present disclosure;

FIG. 9 is a graphical representation of various signals versus time that may occur when a predictive power down control system does not trigger attenuation of an audio signal to prevent power down, in accordance with an embodiment of the present disclosure;

FIG. 10 is a block diagram of selected components of an example audio integrated circuit of a personal audio device, according to an embodiment of the present disclosure;

FIG. 11 is a plot of power versus time depicting the effect of bulk capacitance on linear frequency modulated signals (shirp signals) in accordance with an embodiment of the present disclosure;

FIG. 12 is a graphical representation of a bottom side envelope of a supply voltage according to an embodiment of the present disclosure;

FIG. 13 is a graphical representation of an upper side envelope of a supply voltage according to an embodiment of the present disclosure;

FIG. 14 is a block diagram of an adaptive battery model according to an embodiment of the present disclosure; and is also provided with

Fig. 15 is a block diagram of selected components of a personal audio device in accordance with an embodiment of the present disclosure.

Detailed Description

Fig. 1 is an illustration of an example personal audio device 1 in accordance with an embodiment of the present disclosure. The personal audio device 1 is an example of a device in which techniques according to embodiments of the present disclosure may be employed, but it should be understood that not all elements or configurations shown or embodied in circuitry depicted in the subsequent figures are required for practicing the subject matter recited in the claims. The personal audio device 1 may include a transducer, such as a speaker 5, which reproduces: long range speech received by the personal audio device 1 and other local audio events for providing balanced conversational awareness, such as ring tones, stored audio programming material, injection of near-end speech (i.e., speech of the user of the personal audio device 1), and other audio that needs to be reproduced by the personal audio device 1, such as sources from web pages or other network communications received by the personal audio device 1, and audio indications such as low battery indications and other system event notifications. Additionally or alternatively, the headphones 3 may be coupled to the personal audio device 1 to generate audio. As shown in fig. 1, the headset 3 may be in the form of a pair of ear bud speakers 8A and 8B. The plug 4 may provide a connection of the headset 3 to the electrical terminals of the personal audio device 1. The headphones 3 and speakers 5 depicted in fig. 1 are merely examples, and it should be understood that the personal audio device 1 may be used in conjunction with a variety of audio transducers, including but not limited to capturing or integrating speakers, headphones, ear buds, in-ear headphones, and external speakers.

The personal audio device 1 may provide a display to a user and receive user input using the touch screen 2, or alternatively, a standard LCD may be combined with various buttons, sliders and/or dials disposed on the front and/or sides of the personal audio device 1. As also shown in fig. 1, the personal audio device 1 may include an audio Integrated Circuit (IC) 9 for generating an analog audio signal for transmission to the headset 3, the speaker 5 and/or another audio transducer.

Fig. 2 is a block diagram of selected components of an example audio IC 9 of a personal audio device, according to an embodiment of the present disclosure. As shown IN fig. 2, a digital AUDIO source 18 (e.g., a processor, digital signal processor, microcontroller, test equipment, or other suitable digital AUDIO source) may supply a digital AUDIO input signal audio_in to a predictive power loss prevention system 20, which may process the digital AUDIO input signal audio_in and provide such processed signal to a digital-to-analog converter (DAC) 14, which DAC 14 may IN turn provide an analog signalAudio input signal V _IN Is supplied to a power amplifier stage A1, which power amplifier stage A1 can amplify or attenuate an audio input signal V _IN And provides an audio output signal V _OUT Which may operate a speaker, an earphone transducer, and/or a line level signal output. Although the amplifier A1 is depicted as generating a single-ended audio output signal V _OUT But in some embodiments the amplifier A1 may comprise a differential output and may thus provide a differential audio output signal V _OUT 。

The power supply 10 may supply a power supply voltage V _SUPPLY Is provided to the power rail input of the amplifier A1. The power supply 10 may include a charge pump power supply, a switching dc-dc converter, a linear regulator, or any other suitable power supply.

As discussed in more detail elsewhere in this disclosure, the predictive power loss prevention system 20 may be configured to prevent the audio output signal V _OUT Is powered down. As used herein, the term "power down" broadly refers to an unintentional drop in one or more supply voltages within the personal audio device 1, which may result in improper or undesired operation of one or more components receiving such one or more supply voltages. To perform this function, predictive power loss prevention system 20 may receive information indicative of the amplitude of digital AUDIO input signal audio_in (e.g., by monitoring characteristics indicative of the amplitude of digital AUDIO input signal audio_in). Although many of the embodiments disclosed herein contemplate such monitoring as being performed by directly extracting amplitude information from the digital AUDIO input signal audio_in or a buffered version thereof, IN other embodiments such monitoring may be any signal derivative of the digital AUDIO input signal audio_in (e.g., from the digital AUDIO input signal audio_in to the AUDIO output signal V _OUT Any signal in the signal path). Predictive power loss prevention system 20 may also receive information indicative of a condition of power supply 10. In some embodiments, the condition of the power supply 10 may be indicative of the audio output signal V that may be output by the amplifier A1 _OUT Or by triggering a power down condition (occurrence or violation of a user-defined or other indication of a power down condition)Type threshold value) of the power supply current consumed by the amplifier A1. As used throughout this disclosure, the term "power down condition" may refer broadly to a condition or situation in which power down may actually occur or a condition or situation in which power down may potentially occur, based on parameters measured by predictive power down prevention system 20, as described in more detail elsewhere in this disclosure. In these and other embodiments, the condition of the power supply 10 may be defined by a supply voltage V _SUPPLY At least one of a current of the power supply 10, an internal impedance of the power supply 10, an impedance external to the power supply 10, and a predicted behavior of the power supply 10 in response to a load condition of the power supply 10.

Predictive power loss prevention system 20 may determine whether a power loss condition exists from a physical quantity indicative of the magnitude of digital AUDIO input signal audio_in and information indicative of the condition of power supply 10, where the power loss condition is present between digital AUDIO input signal audio_in and AUDIO output signal V _OUT Without attenuation in the signal path of (a), the audio output signal V _OUT Will be powered down IN response to the digital AUDIO input signal AUDIO IN. Responsive to determining that a power loss condition exists, predictive power loss prevention system 20 may generate a selectable attenuation signal to reduce audio output signal V _OUT Such that the signal path attenuates the digital AUDIO input signal AUDIO IN or its derivative to prevent power loss before propagating to the AUDIO output of amplifier A1 which is part of the digital AUDIO input signal AUDIO IN having a power loss condition. IN some embodiments, such attenuation may include reducing the AUDIO volume of the digital AUDIO input signal audio_in or its derivative within the signal path.

IN some embodiments, attenuating may include applying a nonlinear gain to the digital AUDIO input signal audio_in or its derivative IN the signal path. IN some embodiments, applying the nonlinear gain may include clipping (clipping) the digital AUDIO input signal audio_in or its derivative to a maximum amplitude. Such attenuation or clipping may occur, for example, in the digital path portion of the signal path (e.g., between digital audio source 18 and DAC 14). Alternatively or additionally, such attenuation (whether linear or non-linear) or clipping may occur in an analog path portion of the signal path (e.g., between DAC 14 and the output node), such as by applying a variable gain to the output stage of DAC 14 and/or to amplifier A1.

In these and other embodiments, as described in more detail below, attenuating may include soft clipping the audio input signal or its derivative with a gain transfer function (whose mathematical derivative is a continuous function). Soft clipping may be applied to the audio input signal or its derivative, for example, by an arctangent filter.

Fig. 3 is a block diagram of selected components of an example predictive power loss prevention system 20, according to an embodiment of the disclosure. In the embodiment represented by fig. 3, predictive power loss prevention system 20 may include an audio amplitude detection and volume adjustment block 110, a power supply monitoring block 120, and a predictive control state machine block 140.

User configurations including audio user configuration 102, power user configuration 106, and/or predictive control user configuration 108 may be applied to volume adjustment block 110, power monitor block 120, and predictive control state machine block 140, respectively. The audio user configuration 102 may include, but is not limited to, the ability to manipulate the audio amplitude detector 116. These user configurations may allow a user to set detection parameters including, but not limited to, peak level threshold, root mean square level threshold, frequency and/or duration of interest, and/or load impedance on the amplifier. The power supply user configuration 106 may include, but is not limited to, the ability of a user to set various voltage, impedance, current consumption and/or behavior thresholds of the battery power supply and/or power behavior characteristics of the audio IC 9. These thresholds may allow the user to customize when the battery is considered to be in a weak operating state that may create a voltage drop under load. Predictive control user configuration 108 may allow a user to manipulate the ability of the response of predictive power loss prevention system 20. These may include, but are not limited to, volume adjustment, control delay, masking or weighting of the provisioning information relative to the audio content, and the type and threshold of audio content to be predictively attenuated.

The user configurability of the predictive power loss prevention system 20 may be desirable because each different design of the portable audio device may have different parameters of interest, including but not limited to different battery output voltages, different battery characteristics, different audio amplifiers, and/or different audio loads. This variation in system requirements and parameters may dictate for different personal audio devices: the audio monitoring of the amplitude detection and volume adjustment block 110, the supply monitoring of the power supply monitoring block 120, and the control by the predictive control state machine block 140 should be flexible, adaptable, and user configurable so that predictive power down prevention can be optimized appropriately for each personal audio device. While in some cases it may be desirable for a user to flexibly "tune" the response of predictive power loss prevention system 20, in some embodiments some or all of the parameters associated with audio user configuration 102, power supply user configuration 106, and/or predictive control user configuration 108 may be fixed to a particular set of values (e.g., by the provider of the personal audio device).

As shown in fig. 3, the power supply monitoring module 120 may include a voltage monitor 122, a battery impedance monitor 124, and a power supply response predictor 126. The voltage monitor 122 may be configured to receive the power supply information 104 and perform a comparison of the battery voltage used to power the power supply 10 with a user-configurable threshold set in, for example, the power supply user configuration 106. The user may flexibly determine and adjust such voltage thresholds based on requirements of other components in the personal audio device. In some embodiments, multiple voltage thresholds may be set within the power supply user configuration 106, which will allow the predictive control state machine 140 to monitor and react to different levels of predictive audio load from the audio amplitude detector 116.

The battery impedance monitor 124 may be configured to receive the power supply information 104 and record recent load conditions and track the effects of changes in current consumption that may produce corresponding changes in battery impedance. When a battery becomes "weaker" via its charge level, discharge current, battery aging, and/or environmental impact, its output impedance may increase. At idle, the output impedance of the battery may have little effect on the output voltage of the battery. However, when current is being suppliedWhen the output impedance has a significant effect on the voltage generated at the output terminals of the battery. If the power supply 10 includes a DC-DC converter, such as a boost converter, a buck converter, a linear regulator, or a charge pump, to regulate V to the amplifier A1 _SUPPLY The voltage, the characteristics of the dc-dc converter may be included as part of the power supply information 104, the battery impedance monitor 124, or the power supply response predictor 126.

Fig. 4 is a circuit diagram of a model 40 of an example battery according to an embodiment of the present disclosure. As shown in fig. 4, the battery may be modeled as having an output voltage V _IDEAL And has a variable impedance Z and an ideal supply voltage 42 of (2) _OUT An output impedance 44 of (a) the variable impedance Z _OUT May vary due to battery charge level, discharge current, battery aging, and/or environmental impact. FIG. 5 is a graph illustrating an example relationship between output impedance of the model 40 depicted in FIG. 4 and battery charge voltage, showing a variable impedance Z, according to an embodiment of the present disclosure _OUT May vary due to changes in battery charge level. When the current I is delivered from the battery _LOAD When increasing, it generates an output voltage V _BATT (and which may be delivered to the power supply 10 to power the components of the audio IC 9) may be reduced. The battery impedance monitor 124 may monitor the variable impedance Z _OUT And if applicable, additional impedance external to the battery (e.g., present at the supply voltage V to the amplifier A1) _SUPPLY Those above).

The power response predictor 126 may be configured to receive the power information 104 and predict future behavior of the battery power under various load conditions based on monitoring of a recent behavior history of the battery power. The audio amplifier (e.g., amplifier A1) may not have sufficient system level visibility to determine the total absolute load on the battery power supply at any given time. However, the power supply response predictor 126 may be able to determine what the load contribution of the amplifier is on the battery power supply and monitor how the battery power supply responds to the load changes generated by the amplifier. Such information-enabled power supply response predictor 126 estimates that a certain amount of current may be drawn by amplifier A1What power supply voltage drop occurs. When the state of the power supply response predictor 126 is combined with the state of the voltage monitor 122, the state of the battery impedance monitor 124, and the state of the audio amplitude detector 116, the predictive control state machine 140 may determine how much of the audio output signal V the amplifier A1 may produce in the event that a sufficiently large voltage drop is not generated in the battery powered amplifier A1 to trigger a power down condition _OUT 。

As shown IN fig. 3, the AUDIO amplitude detection and volume adjustment block 110 may include an AUDIO buffer 112, a volume controller 114, and an AUDIO amplitude detector 116, and may be configured to monitor and manipulate the digital AUDIO input signal audio_in or its derivatives. Portions of the AUDIO amplitude detection and volume adjustment block 110 (e.g., AUDIO buffer 112, volume controller 114) may be integrated from the digital AUDIO input signal audio_in to the AUDIO output signal V _OUT Is provided. In some embodiments, all or part of the functionality of the audio amplitude detection and volume adjustment block 110 may be integrated into the amplifier A1. In these and other embodiments, all or part of the functionality of the audio amplitude detection and volume adjustment block 110 may be implemented in software or firmware. Accordingly, one or more features of the audio amplitude detection and volume adjustment block 110 may be implemented as software or firmware, one or more separate or integrated hardware blocks with respect to the amplifier A1, or any combination thereof.

The AUDIO buffer 112 may be any system, device, or apparatus that provides a delay to allow the AUDIO amplitude detector 116 and/or predictive control state machine 140 sufficient time to react before the digital AUDIO input signal AUDIO IN propagates through the signal path. For example, the audio buffer 112 may provide sufficient delay such that its delay plus the group delay of the signal path up to the volume controller 114 is greater than the processing time of the audio amplitude detector 116, predictive control state machine 140, and volume controller 114. In some embodiments, the audio buffer 112 may include memory. In these and other embodiments, the audio buffer 112 may include an inherent group delay of the audio path, a delay caused by audio processing, and/or other suitable delays.

In a more robust audio amplifier system, the audio data path storage buffer is typically available as part of another feature that may also require look-ahead or some time to pre-process. In this case, the same memory buffer may be used as audio buffer 112 for predictive power down prevention as long as it is large enough and has sufficient delay to allow for processing of other components of predictive power down prevention system 20.

In some embodiments, the total delay in the signal path may be large enough to allow processing by components of predictive power loss prevention system 20. In such an embodiment, the audio buffer 112 may not be present.

IN the embodiment represented by fig. 3, the AUDIO amplitude detector 116 may monitor the digital AUDIO input signal audio_in into the AUDIO buffer 112. In such embodiments, the audio amplitude detector 116 may evaluate such audio data against one or more thresholds (e.g., set within the audio user configuration 102) in order to identify any incoming audio signals that may generate load conditions that are large enough to stress the battery power supply that powers the power supply 10, generate voltage drops, and risk a power down condition if such audio signals are reproduced by the audio amplifier A1. The state determination generated by the audio amplitude detector 116 and provided to the predictive control state machine block 140 may be based on any number and type of parameters, including, but not limited to, physical quantities of the audio signal (e.g., frequency, peak amplitude, power, etc.), characteristics of the amplifier A1 (e.g., efficiency), and/or load impedance of the output of the amplifier A1.

Although fig. 3 depicts AUDIO amplitude detector 116 monitoring digital AUDIO input signal audio_in, IN other embodiments AUDIO amplitude detector 116 may detect the derivative of digital AUDIO input signal audio_in elsewhere within the signal path of AUDIO IC 9.

The volume controller 114 may comprise any system, device, or apparatus configured to control the volume of the audio signal buffered by the audio buffer 112 or to otherwise apply a selectable gain to the audio signal buffered by the audio buffer 112 (e.g., prior to transmitting the audio signal to the DAC 14) based on the volume control signal generated by the predictive control state machine 140. Thus, in the event that predictive control state machine 140 determines that a power down condition exists, it may transmit a volume control signal and in response thereto, volume controller 114 may attenuate the audio signal propagating through the audio signal path. In some embodiments, the volume controller 114 may attenuate the audio signal by reducing the audio volume of the audio signal. In these and other embodiments, the volume controller 114 may attenuate the audio signal in response to a power down condition by applying a nonlinear gain to the audio signal. For example, as shown IN fig. 6, the volume controller 114 may apply "hard clipping" to the AUDIO signal IN response to a power down condition such that the gain transfer function (e.g., f|vout (|audio_in|) |) of the AUDIO signal may be such that the mathematical derivative of the gain transfer function includes at least one discontinuity. As another example, as shown in fig. 7, the volume controller 114 may apply "soft clipping" to the audio signal in response to a power down condition such that the gain transfer function of the audio signal may be such that the mathematical derivative of the gain transfer function is a continuous function. Such a soft clipping gain transfer function may be implemented in any suitable manner, including by applying arctangent filtering to the audio signal.

As shown IN fig. 3, predictive control state machine 140 may receive state information from AUDIO amplitude detector 116, voltage monitor 122, battery impedance monitor 124, and power response predictor 126 and determine whether to attenuate (e.g., reduce the AUDIO volume via volume controller 114) digital AUDIO input signal audio_in (or its derivative) based on such state information IN order to prevent battery power supply voltage from dropping (if such signal may occur without attenuation). Additionally, once in a state where power loss prevention attenuation occurs, predictive control state machine 140 may determine whether to allow the audio signal amplitude to return to its non-attenuation level based on such state information.

If the states of the voltage monitor 122, the power response predictor 126, and the battery impedance monitor 124 indicate that the battery is in a weakened state, and the audio amplitude detector 116 indicates that a high load condition is imminent, the predictive control state machine 140 may react by transmitting an appropriate volume control signal to the volume controller 114 to cause the volume controller 114 to attenuate the audio signal. Thus, when an audio signal that potentially results in a power loss is passed to the amplifier A1, it may be attenuated to a level low enough to prevent the power loss.

Fig. 8 is a graphical representation of various signals versus time that may occur when a predictive power down control system triggers attenuation of an audio signal to prevent power down, in accordance with an embodiment of the present disclosure. IN fig. 8, the states of the voltage monitor 122, battery impedance monitor 124, and power response predictor 126 are shown to indicate that the battery powering the power supply 10 is IN a sufficiently weak state such that once the AUDIO signal propagates to the amplifier A1 and overburdenies the battery powering the power supply 10, it cannot support the incoming AUDIO signal audio_in without triggering a power down condition. This may result in predictive control state machine 140 generating an appropriate volume control signal to attenuate the audio signal in response to analyzing information received from audio amplitude detector 116 and power monitor 120 (e.g., in response to an indication that the audio amplitude is above a threshold level that may result in a power down condition). In some embodiments, for each time period t during which the audio amplitude of the audio signal monitored by the audio amplitude detector 116 remains above a threshold value _ATTACK The audio signal may be VOL _STEP1 Is a step-by-step attenuation of the amplitude of (a). Once the audio amplitude of the audio signal monitored by the audio amplitude detector 116 falls below a threshold (or another threshold), the decay may continue for a period of time t _WAIT Thereafter for each time period t _RELEASE The audio signal may be VOL _STEP2 Until returning to a normal operating state with little or no audio attenuation.

Fig. 9 is a graphical representation of various signals versus time that may occur when a predictive power down control system does not trigger attenuation of an audio signal to prevent power down, in accordance with an embodiment of the present disclosure. As shown in fig. 9, the audio amplitude detector 116 indicates that the audio amplitude is below a threshold level that may result in a power down condition. However, in the scenario represented in fig. 9, large audio amplitudes may only occur when the voltage monitor 122, the battery impedance monitor 124, and/or the power response predictor 126 report that the power supply 10 is capable of handling loads caused by such audio amplitudes. Such large audio amplitudes may not occur when the battery powering the power supply 10 is in a weakened state, as indicated by the state of the voltage monitor 122, the battery impedance monitor 124, and/or the power supply response predictor 126. Thus, in this set of cases, predictive control state machine 140 may not cause audio signal attenuation.

Fig. 10 is a block diagram of selected components of an example audio IC 1300 of a personal audio device, according to an embodiment of the disclosure. The apparatus includes a signal path having: an AUDIO input configured to receive an AUDIO input signal audio_in; an audio output configured to provide an audio output signal V _OUT The method comprises the steps of carrying out a first treatment on the surface of the A power input terminal configured to receive a power voltage V _SUPPLY The method comprises the steps of carrying out a first treatment on the surface of the And an attenuation block 1302. The attenuation block 1302 is configured to receive information indicative of one or more of: 1) Adaptive estimation of power supply conditions; 2) The expected effect of the power supply capacitance; and 3) at least one condition of the complex load impedance. In response to determining from the received information that a portion of the audio output signal may reach a maximum power threshold, the attenuation block 1302 may generate a selectable attenuation signal to reduce an amplitude of at least a portion of the audio output signal such that the signal path attenuates the audio input signal or a derivative thereof to prevent power loss before propagating to an audio output of the portion of the audio input signal. The information indicative of the adaptive estimation of the power supply condition may include information about the voltage component and the resistance component received from the adaptive battery model as described in fig. 14. Such voltage and resistance components may be used to calculate a maximum power threshold. Similar to fig. 2 and as shown IN fig. 10, a digital AUDIO source 1301 (e.g., a processor, digital signal processor, microcontroller, test equipment, or other suitable digital AUDIO source) may supply a digital AUDIO input signal audio_in to an attenuation block 1302, which may Processing a digital AUDIO input signal audio_in and providing such processed signal to a digital-to-analog converter (DAC) 1303, which DAC 1303 may IN turn provide an analog AUDIO input signal V _IN Is supplied to a power amplifier stage A2, which power amplifier stage A2 can amplify or attenuate an audio input signal V _IN And provides an audio output signal V _OUT Which may operate a speaker, an earphone transducer, and/or a line level signal output. Although the amplifier A2 is depicted as generating a single-ended audio output signal V _OUT But in some embodiments, the amplifier A2 may comprise a differential output and may thus provide a differential audio output signal V _OUT . The power supply 1304 may supply a power supply voltage V _SUPPLY To the power rail input of amplifier A2. The power supply 1304 may include a charge pump power supply, a switching DC-DC converter, a linear regulator, or any other suitable power supply.

It will be appreciated that IC 1300 may also include a predictive power loss prevention system as previously described with reference to fig. 2 and 3.

In some embodiments, some or all of the functions of the attenuation block may be integrated into the amplifier A2.

In fig. 10, an amplifier A2 may receive an audio input signal V _IN And a gain may be applied to increase the signal amplitude, typically in the form of a voltage. For audio and haptic amplifiers, high currents may be generated. When considered as a voltage amplifier, the amplifier A2 may typically appear as a scaling of the AUDIO input signal audio_in and may have a frequency influence, such as high-pass or low-pass filtering. Without loss of generality, the amplifier A2 may receive an input voltage V _IN And may provide gain to provide an amplified output voltage V _OUT . By knowing the load impedance, the current output of the amplifier A2 can be known by ohm's law (which also applies to complex impedance by convolution). In the case where both voltage and current are known, the attenuation block 1302 may calculate the required power of the amplifier as the product of the voltage and current.

The amplifier A2 may be regarded as a power converter, in fact its power conversion ratioIs not perfect. The attenuation block 1302 may estimate the required power of the amplifier A2 and the efficiency of the amplifier A2 and calculate the amplifier input V from the estimate _IN Supply voltage V _SUPPLY And electrical characteristics at the power supply input current. Inserting the estimated amplifier required power into a battery model with capacitive elements will mimic the behavior of many practical amplifier circuit configurations. In this example, a simple battery model is utilized; however, an adaptive battery model may be used, as described with reference to fig. 14. The AUDIO input signal audio_in can then be used to pair the supply voltage V _SUPPLY Modeling the impact of (c) is performed. The AUDIO input signal AUDIO IN may need to be attenuated to ensure the supply voltage V _SUPPLY Is kept at the threshold V _THRESH The above. The attenuation may be calculated by attenuation block 1302.

For resistive loads, the current and voltage may be in phase. However, for loads with reactance (such as speakers), the actual power required for a particular frequency may be less than the product of root mean square voltage and current. This lower power requirement means less attenuation is required to ensure that the voltage (or current) threshold is met but not exceeded, and for example, allows more power to be delivered to the load, resulting in a higher sound pressure level of the speaker and vibration intensity of the haptic system.

For a given AUDIO input signal audio_in, the attenuation block 1302 may utilize a complex load impedance (Z _LOAD ) Is modulated to V by pulse code and estimation value of (2) _IN The estimated value of the transfer function (typically the scaling constant H) is used to calculate the required power (P) of the amplifier A2 required to amplify the AUDIO input signal audio_in using the following equation _LOAD )：

P _LOAD =voltage current (1)

Where voltage=audio_in×h, and current=voltage/Z _LOAD . Because of the inefficiency of the amplifier A2, the source power required by the amplifier A2 to amplify the signal may be greater than the required power P _LOAD . Source power P _SRC Set to the source power required by the amplifier A2. Source power P _SRC By an efficiency parameter n and P _LOAD In relation, the efficiency parameter n is between 0 and 1:

P _SRC ＝P _LOAD /n (2)

an estimate of the power required by the amplifier A2 and the voltage component (V _BATT ) Resistor component (R _BATT ) And power supply capacitance (C) _BULK ) To predict the supply voltage. In particular, for a given battery model, the voltage at which the voltage threshold V is maintained above can be calculated by solving a system of associated equations (simultaneous system of equations) that relate the battery model to the power required by the amplifier _THRESH Maximum power that can be obtained at the same time.

V _SUPPLY ＝(V _BATT +SQRT(V _BATT ^2-4*P _SRC *R _BATT ))/2 (3)

Wherein V is _BATT Is the battery model voltage, is and R _BATT Battery model resistance. Using this equation, for the supply voltage V _SUPPLY The influence of (2) can be predicted as the source power P required by the amplifier _SRC Is a function of (2). If the power supply voltage V _SUPPLY To remain above the threshold, the source power P may be determined _SRC Maximum power allowed. With the known maximum allowed power and the ability to estimate the power demand from the AUDIO input signal audio_in, the AUDIO input signal audio_in can now be attenuated to meet the maximum power allowed condition.

In a physical system, the capacitor will supply current instantaneously rather than a battery, so the capacitor effect will make the power supply voltage V _SUPPLY Is complicated by the prediction of (a). A simple approximation of the capacitive effect is the estimated power required to apply a low pass filter to the amplifier instead, and the time constant of the low pass filter is approximately R _BATT *C _BULK Wherein R is _BATT Is the resistance of the battery model, and C _BULK Is a large capacity capacitor connected in parallel with the power supply. Thus, the indication power supply capacitance (C _BULK ) Can be used to optionally apply a linear filter operation to the predicted supply voltage.

To ensure that the gain applied to the input audio signal actually protects the system from power loss, the gain may be applied earlier than necessary (i.e., above a voltage threshold at which power loss actually occurs) and maintained. IN order to maintain causality, the AUDIO input signal audio_in and its gain calculation must be delayed IN order to look ahead and apply the required gain signal as early as possible.

With known power requirements, V can be estimated using parameters of the battery model _SUPPLY Replaced by V _THRESH And rearranged to give the following equation, while the maximum allowable power, i.e., the maximum power threshold P of the audio input signal, is calculated from equation (3) _MAX ：

P _MAX ＝(V _THRESH *V _BATT –V _THRESH ^2)/R _BATT (4)

Wherein V is _THRESH Is the allowable supply voltage V _SUPPLY Is set to a target minimum voltage value of (a). Using maximum allowable power P _MAX And an amplifier power requirement P _SRC Satisfies the estimated value of the power supply voltage V _SUPPLY Must remain greater than V _THRESH The gain G required for the condition of (2) is:

with known gain values, the protected signal amplitude is now known. The gain may be applied by the attenuation block to the wideband signal or to the sum of the bandpass filtered signals comprising the wideband signal. For bandpass filtered signals, the gain value for each band can be adjusted as long as the sum remains the same, which allows for multiband compression capability.

The concept of attack time and release time refers to the rate at which the applied gain approaches the gain required to prevent power loss. These attack and release rates may be configured, typically in dB/second.

To avoid low voltage conditions caused by excessive current demand from the battery, a capacitor may be added in parallel to the power supply 1304 in order to buffer transient current spikes. These capacitors can act as a pair of supply voltages V _SUPPLY Is provided. In a physical system, due to its input capacitanceWiring topology, etc., parasitic effects connecting multiple components to the power supply 1304 may also increase this capacitance.

In the presence of this bulk capacitance, the amplifier A2 may draw current from the capacitor and battery, which means that the voltage drop may be less compared to a system without bulk capacitance. By taking into account the effects of this large capacitance, the power demand on the battery power supply can be more accurately calculated by the attenuation block, and less attenuation can be applied to the AUDIO input signal audio_in while still ensuring that no power down conditions are present.

Fig. 11 is a plot of power versus time showing the effect of bulk capacitance on a chirp signal, according to an embodiment of the present disclosure. Fig. 11 shows the frequency of a chirp signal increasing with time. At higher frequencies, large capacity capacitances can result in less power requirements.

As described previously, fig. 4 shows an example battery model. For example, as shown in FIG. 4, a battery model (e.g., and may be used as the power supply 10 in FIG. 2) includes a battery having an output impedance Z _OUT Is set to be the battery voltage V of _BATT Or as output impedance Z _OUT Series cell resistance R of a subset of (2) _BATT Is a Thevenin circuit. As the system current demand increases, the available voltage is due to the series battery resistance R _BATT And decrease, wherein V _SUPPLY ＝V _BATT –R _BATT *I _SUPPLY . Using only V _SUPPLY Signals, can be directed to changing I _SUPPLY The signal (i.e. the current demand based on the change in load impedance) infers the battery voltage V _BATT And battery resistance R _BATT In the case of the amplifier A1, the signal requires a current I _SUPPLY The input current I to be the amplifier _SUPPLY 。

If there is no signal to be amplified, it is converted into a zero input current (I _SUPPLY =0), then the power supply voltage V _SUPPLY Will reveal the effective battery voltage V _BATT . If other parts of the system, separate from the amplifier A2, draw current, such as a radio or a Light Emitting Diode (LED), there may be a supply voltage drop. From the slaveFrom the point of view of the battery model of the amplifier A2, this supply voltage drop corresponds to a reduced effective battery voltage V _BATT 。

When there is a signal generating the current-consuming amplifier A2, the supply voltage V _SUPPLY May drop. The power supply voltage drop may be related to the battery resistance R _BATT Proportional to the ratio. By using the supply voltage V of a given amplifier AUDIO input signal AUDIO_IN _SUPPLY Can be compared between the actual signal and the predicted signal to adjust the battery resistance R _BATT Is used for the estimation of the estimated value of (a). This may improve the accuracy of the battery model and may thus result in reduced unnecessary attenuation of the audio signal.

Due to capacitive effects, relative to the estimated supply voltage V _SUPPLY The signal, group delay, can be introduced into the actual supply voltage V _SUPPLY Is a kind of medium. The compensation may require accurate knowledge of group delay effects and slight phase errors may amplify or attenuate the supply voltage V _SUPPLY And predicted or estimated supply voltage V _{EST_SUPPLY} Differences between them. To avoid these phase effects, envelope prediction or estimation may be used.

If the battery model matches the actual system, the actual supply voltage V _SUPPLY And predicted or estimated supply voltage V _SUPPLY The envelope of the signal may be nearly identical. However, the bias may reveal a mismatch between the reality and the model and require correction of the response.

In fig. 12, the power supply voltage V _SUPPLY The bottom side or bottom envelope of the signal may provide information about the cell resistance R _BATT Is a function of the value of (a). Suppose that if the battery resistance R _BATT Zero, the power supply voltage V _SUPPLY Will be the same as the bottom envelope and the top envelope of (c). However, due to the battery resistance R _BATT Is not zero, as by the corresponding broken line V _SUPPLY And V _{EST_SUPPLY} The bottom envelope will be lower than the upper envelope, as shown.

If the predicted supply voltage V _{EST_SUPPLY} Not falling so far as to measure the supply voltage V _SUPPLY As far as the signal is, then it is necessaryIncreasing the battery resistance R _BATT And vice versa to correct the battery resistance R _BATT Is an overestimation of (a).

In FIG. 13, the supply voltage V _SUPPLY The upper or top envelope of the signal may be used to adjust the battery voltage V _BATT And (5) estimating a value. Supply voltage V _SUPPLY Can provide the peak value of the voltage V with the actual battery voltage _BATT The value closest to the value. If the predicted peak value and the actual peak value are different, the battery voltage V _BATT Correction may be required.

The presence of large capacity capacitance confuses the battery voltage V _BATT And battery resistance R _BATT Adaptability, the high capacity capacitance for a specific frequency can be regarded as the battery voltage V at the same time _BATT And battery resistance R _BATT Is reduced. By including a large capacitance in the power estimation, the battery voltage V _BATT And battery resistance R _BATT The estimation may become more accurate, thereby further reducing any unnecessary attenuation of the audio signal.

Fig. 14 shows an example of an adaptive battery model 1600 that may be included within or separate from the attenuation block 1302 and/or amplifier A2. The battery model 1600 may include an envelope tracker 1601, which may be configured to receive a supply voltage V _SUPPLY And an estimated value V of the power supply voltage _{EST_SUPPLY} . The envelope tracker 1601 may track the supply voltage V in a first tracking block 1602 _SUPPLY And compares the peak of the resulting envelope with the upper envelope of the predicted supply voltage upper envelope from the second tracking block 1603. The comparison may be used to update V in update block 1604 _BATT Values. The third tracking block 1605 may track the supply voltage V _SUPPLY And compares the local minimum of the resulting envelope with the bottom envelope of the predicted supply voltage from the fourth tracking block 1606. The comparison is used to update R in update block 1607 _BATT Values. R is R _BATT And V _BATT The updated value of (c) may be provided to the attenuation block 1302 to calculate the maximum power threshold.

As the amplitude of the AUDIO input signal AUDIO IN increases, more supply current is required to provide amplification. Excessive supply current may lead to a power down condition. The amplitude of the AUDIO input signal AUDIO IN must be attenuated to avoid power loss. The dynamic range compressor and limiter may attenuate and limit the supply current.

Embodiments of the present disclosure also provide: 1) Providing an adaptive estimate of battery condition; 2) Predicting the influence of power supply capacitance; and 3) determining the required power using a complex impedance model of the load (rather than a resistor) because the load reactance may reduce the required power (e.g., the condition of the load impedance).

As an example of an application of predictive power loss prevention system 20, reference is made to fig. 15. Fig. 15 is a block diagram of selected components of the personal audio device 1 in accordance with an embodiment of the present disclosure. As shown in fig. 15, the personal audio device 1 may include an audio IC 9 similar to that depicted in fig. 2, wherein the power supply 10 of fig. 2 may be implemented with a power converter 11 and a battery for providing electrical energy to the audio IC 9 and other components 14. As shown in fig. 15, the battery 12 is modeled as having an ideal voltage V according to the battery model 40 of fig. 4 _IDEAL And output impedance Z _OUT 。

The power converter 11 may comprise a suitable dc-dc converter for generating the output voltage V as a battery _BATT Is a multiple of the supply voltage V _SUPPLY . The power converter 11 may comprise a boost converter, a charge pump, a buck converter, or any other suitable type of power converter. In some embodiments, power converter 11 may not be present and amplifier A1 may draw power directly from battery 12.

Depending on the current drawn from the battery 12, the battery 12 generates an output voltage V _BATT . Applying ohm's law:

V _BATT ＝V _IDEAL –(I _OTHER +I _AMP )*Z _OUT

wherein I is _AMP Equal to the current delivered from the battery 12 to the power converter 11, and I _OTHER Representing the residual current delivered from the battery 12 to the other components 14. The above equation is rewritten:

V _BATT ＝V _IDEAL –I _OTHER *Z _OUT –I _AMP *Z _OUT

According to the above equation, the apparent ideal voltage (apparent ideal voltage) V _IDEAL’ The definition is as follows:

V _IDEAL’ ＝V _IDEAL –I _OTHER *Z _OUT

such that:

V _BATT ＝V _IDEAL’ –I _AMP *Z _OUT

as shown in fig. 15, the predictive power loss prevention system 20 may be able to easily measure or sense the output voltage V _BATT And current I _AMP But may not be able to easily measure the current I _OTHER . However, predictive power loss prevention system 20 may prevent a power loss by taking into account a load event of power source 10 on battery 12 (e.g., current I delivered to power source 10 _AMP And an output voltage V available to the power supply 10 _BATT ) But ignores the load event of other components 14 on the battery 12 to prevent power loss. To this end, predictive power loss prevention system 20 may ignore current I _OTHER And instead assume that the power supply 10 is modeled as having a substitute ideal voltage V _IDEAL Apparent ideal voltage V of (2) _IDEAL’ Variable output impedance Z _OUT And adaptively updates the apparent ideal voltage V of the battery model based on various measured parameters of the audio IC 9 _IDEAL’ And variable output impedance Z of battery model _OUT As explained in more detail above.

Thus, when the current I _OTHER When increasing, the apparent ideal voltage V _IDEAL’ May be reduced and predictive power loss prevention system 20 may reduce current I _AMP And when the current I is _OTHER When decreasing, the apparent ideal voltage V _IDEAL' Current I may be increased and predictive power loss prevention system 20 may increase _AMP Is set to the maximum current draw of (2).

To further illustrate, predictive power loss prevention system 20 may directly measure current I _AMP And measuring the output voltage V _BATT And based on the measured current I _AMP And/or measuring output voltage V _BATT Is to refine the impedance Z of the battery model _OUT And an apparent ideal voltage V _IDEAL’ Thus providing the accuracy of the battery model and the current I _OTHER Robustness of the relevant loading event.

The present disclosure includes all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that one of ordinary skill in the art would understand. Similarly, where appropriate, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person of ordinary skill in the art would understand. Furthermore, references in the appended claims to an apparatus, system, or component of an apparatus or system being adapted, arranged, capable, configured, enabled, operable, or operative to perform a particular function, include the apparatus, system, or component whether or not it or that particular function is activated, or unlocked, so long as the apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative.

All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the concepts contributed by the disclosure and the inventor to furthering the art, and are to be 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 can be made hereto without departing from the spirit and scope of the present disclosure.

Claims

1. An apparatus for providing an audio output signal to an audio transducer, comprising a signal path comprising:

an audio input configured to receive an audio input signal;

an audio output configured to provide an audio output signal;

a power supply input configured to receive a power supply voltage; and

an attenuation block configured to:

receiving information indicative of an adaptive estimate of a power supply condition, wherein the information indicative of an adaptive estimate of a power supply condition comprises: information about a voltage component and a resistance component received from an adaptive battery model of a battery used to provide power to a power source to generate the power source voltage; and is also provided with

Adjusting the adaptive battery model based on monitored battery voltage output by the battery and load events of the signal path and excluding load events of components other than the signal path powered by the battery; and is also provided with

In response to determining that a portion of the audio input signal has reached a maximum power threshold, generating a selectable attenuation signal to reduce the amplitude of the audio output signal such that the signal path attenuates the audio input signal or a derivative thereof to prevent power loss before the portion of the audio input signal propagates to an audio output.

2. The apparatus of claim 1, further comprising:

a predictive power loss prevention system configured to prevent power loss of the audio output signal, wherein the predictive power loss prevention system is configured to:

receiving information indicative of an amplitude of the audio input signal;

receiving information indicative of the power supply condition;

determining from the received information whether a power down condition exists; and is also provided with

In response to determining that a power down condition exists, the attenuation block is instructed to generate the selectable attenuation signal.

3. The apparatus of claim 1, wherein the audio input is one or more audio inputs and the audio output is one or more audio outputs.

4. The apparatus of claim 1, wherein the load event of the signal path comprises a first current drawn from the battery by the signal path and the load event of a component other than the signal path comprises a second current drawn from the battery by another component.

5. The apparatus of claim 1, wherein the adaptive battery model is to generate a predicted supply voltage.

6. The apparatus of claim 5, wherein the voltage component and the resistance component are used to calculate the maximum power threshold.

7. The apparatus of claim 6, wherein the adaptive battery model comprises: a Thevenin circuit having a voltage component and a resistor component, wherein a supply voltage signal generated by the adaptive battery model, an amplifier input to an amplifier, an estimate of a supply capacitance, and an estimate of a load impedance of the amplifier are used to identify the voltage component and the resistor component.

8. The apparatus of claim 7, wherein the adaptive battery model is configured to provide an estimate of the power required by the amplifier, wherein the estimate of the power required by the amplifier is calculated from an output of the amplifier and a load impedance of the amplifier to derive a product of voltage and current.

9. The apparatus of claim 8, wherein the estimated value of the power required by the amplifier and the estimated values of the voltage component, the resistor component, and the supply capacitance are used to predict the supply voltage.

10. The apparatus of claim 5, wherein the information indicative of the expected effect of the supply capacitance is used to apply a linear filter operation to the predicted supply voltage.

11. The apparatus of claim 7, wherein a first envelope detector that detects a first envelope is applied to the supply voltage signal and a second envelope detector that detects a second envelope is applied to the predicted supply voltage to track local maxima.

12. The device of claim 11, wherein a difference between the first envelope and the second envelope is used to adjust an estimate of the voltage component.

13. The apparatus of claim 7, wherein a first envelope detector that detects a first envelope is applied to a negative pole of the supply voltage signal and a second envelope detector that detects a second envelope is applied to a negative pole of the predicted supply voltage to track a local minimum.

14. The apparatus of claim 13, wherein a difference between the first envelope and the second envelope is used to adjust an estimate of the resistor component.

15. The apparatus of claim 2, wherein the signal path further comprises a buffer configured to delay propagation of the audio input signal to the audio output by one of the following durations: which is sufficient to allow the predictive power loss prevention system to generate the selectable attenuation signal such that the signal path is capable of receiving and processing the selectable attenuation signal in response to the portion of the audio input signal having a power loss condition before such portion of the audio input signal propagates to the audio output.

16. A method for providing an audio output signal to an audio transducer, comprising:

receiving information indicative of an amplitude of an audio input signal;

receiving information indicative of a power condition of a signal path, the signal path having an audio input for receiving the audio input signal and an audio output for providing the audio output signal;

receiving information indicative of an adaptive estimate of a power supply condition, wherein the information indicative of an adaptive estimate of a power supply condition comprises: information about a voltage component and a resistance component received from an adaptive battery model of a battery used to provide power to a power source to generate the power source voltage;

17. The method of claim 16, further comprising preventing power down of the audio output signal by:

receiving information indicative of an amplitude of the audio input signal;

receiving information indicative of the power supply condition;

determining from information indicative of an amplitude of the audio input signal and information indicative of a condition of a power source whether a power down condition exists; and is also provided with

In response to determining that a power down condition exists, attenuation of a portion of the audio input signal is caused.

18. The method of claim 16, wherein the audio input signal is one or more audio inputs and the audio output signal is one or more audio outputs.

19. The method of claim 16, wherein the load event of the signal path comprises a first current drawn from the battery by the signal path and the load event of a component other than the signal path comprises a second current drawn from the battery by other components.

20. The method of claim 19, further comprising generating a predicted supply voltage using the adaptive battery model.

21. The method of claim 20, wherein the voltage component and resistance component are used to calculate the maximum power threshold.

22. The method of claim 21, wherein the adaptive battery model comprises a Thevenin circuit having a voltage component and a resistor component, wherein a supply voltage signal generated by the adaptive battery model, an amplifier input to an amplifier, an estimate of a supply capacitance, and an estimate of a load impedance of the amplifier are used to identify the voltage component and the resistor component.

23. The method of claim 22, further comprising:

calculating, from the adaptive battery model, an estimate of the power required by the amplifier from the output of the amplifier and the load impedance of the amplifier to derive a product of voltage and current; and is also provided with

An estimate of the power required by the amplifier is provided by the adaptive battery model.

24. The method of claim 23, further comprising: the power supply voltage is predicted using an estimate of the power required by the amplifier and estimates of the voltage component, the resistor component, and the power supply capacitance.

25. The method of claim 20, wherein the information indicative of the expected effect of the supply capacitance is usable to apply a linear filter operation to the predicted supply voltage.

26. The method of claim 22, further comprising:

applying a first envelope detector to the supply voltage and a second envelope detector to the predicted supply voltage;

outputting a first envelope from the first envelope detector to track a local maximum of a supply voltage; and is also provided with

A second envelope is output from the second envelope detector to track a local maximum in the predicted supply voltage.

27. The method of claim 26, wherein a difference between the first envelope and the second envelope is used to adjust an estimate of the voltage component.

28. The method of claim 22, further comprising:

applying a first envelope detector to a negative pole of the supply voltage signal and a second envelope detector to a negative pole of the predicted supply voltage;

outputting a first envelope from the first envelope detector to track a valley and a local minimum in a negative pole of the supply voltage; and is also provided with

A second envelope is output from the second envelope detector to track a minimum value of the predicted supply voltage.

29. The method of claim 28, wherein a difference between the first envelope and the second envelope is used to adjust an estimate of the resistance component.

30. The method of claim 17, further comprising: the propagation of the audio input signal to the audio output is delayed for a duration sufficient to allow the audio input signal or derivative thereof to attenuate before the portion of the audio input signal having the power down condition propagates to the audio output.