Common-Mode Compensation in a Multilevel Pulse Width Modulation System

Abstract

A system for sensing an electric quantity may include: a sensing stage configured to sense the electric quantity and generate a sensing signal indicative of the electric quantity, wherein the electric quantity indicates an electric signal generated by a class-DG amplifier configured to drive a load, and wherein the class-DG amplifier has multiple signal-level common modes; and a common-mode compensator configured to compensate for a change in a common-mode voltage of a differential supply voltage of the driver that occurs when switching between the signal-level common modes of the class-DG amplifier.

Description

Technical Field

[0001] The present disclosure generally relates to circuitry 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 common mode compensation in multilevel pulse width modulation systems. Background Art

[0002] Personal audio devices, including wireless telephones such as mobile / cellular telephones, cordless telephones, MP3 players, and other consumer audio devices, are being widely used. Such personal audio devices may include circuitry for driving a pair of headphones or one or more speakers. Such circuitry typically includes a power amplifier for driving an audio output signal to the headphones or speakers. Generally, the power amplifier amplifies the audio signal by obtaining energy from a power source and controlling the audio output signal to match the shape of the input signal but with a greater amplitude.

[0003] An example of an audio amplifier is a class-D amplifier. A class-D amplifier (also known as a "switching amplifier") may include an electronic amplifier in which the amplifying device (e.g., a transistor, typically a metal oxide semiconductor field effect transistor) operates as an electronic switch. In a class-D amplifier, the signal to be amplified may be converted into a series of pulses by pulse width modulation (PWM), pulse density modulation (PDM), or other modulation methods such that the signal is converted into a modulated signal, where the pulse characteristics (e.g., pulse width, pulse density, etc.) of the modulated signal are a function of the signal amplitude. After amplification using a class-D amplifier, the output pulse train may be converted into an unmodulated analog signal by passing through a passive low-pass filter, where such a low-pass filter may be inherent in the class-D amplifier and / or the load driven by the class-D amplifier. Class-D amplifiers are often used due to the fact that they are more energy efficient than linear analog amplifiers, as class-D amplifiers dissipate less power as heat in the active devices compared to linear analog amplifiers.

[0004] Some amplifier architectures provide at least two supply voltages to power a power amplifier in order to achieve greater energy efficiency over a single or constant supply voltage architecture. An example of a multi-supply voltage amplifier is a class-G amplifier. A class-G amplifier can provide two or more power supplies of different voltages and switch between them when the signal output approaches each level. Thus, a class-G amplifier can improve efficiency by reducing the wasted power at the output driver transistors of the amplifier. In some cases, a class-G amplifier can be combined with a class-D amplifier to create a class-DG amplifier. A class-DG amplifier can use pulse width modulation to generate a rail-to-rail digital output signal with a variable duty cycle as a pre-driver signal for the output driver, which is typical of class-D amplifiers. However, in contrast to class-D amplifiers, a class-DG amplifier can use a multi-level output stage that senses the amplitude of the audio output signal and switches between power supplies based on the output amplitude.

[0005] In some cases, a class-DG amplifier can be powered by both a positive supply rail and a negative supply rail, and each supply rail can have a variable supply voltage selected from two or more power supplies. For example, each of the positive supply rail and the negative supply rail can vary between -5V, 0V, 5V, and 10V, such that the fully differential output of the class-DG amplifier can vary between -15V, -10V, -5V, 0V, 5V, 10V, and 15V.

[0006] One disadvantage of such a class-DG architecture is that when a class-DG amplifier selects between different supply rail supply voltages, a step may occur in the common-mode voltage of the positive supply rail and the negative supply rail. If an output current or output voltage is delivered to the load of the class-DG amplifier, the varying common-mode voltage is replicated to the current or voltage sensing circuitry, resulting in inaccuracies in the sensor measurements. SUMMARY

[0007] In accordance with the teachings of the present disclosure, one or more disadvantages and problems associated with existing methods of measuring an output signal driven by an output stage can be reduced or eliminated.

[0008] According to an embodiment of the present disclosure, a system for sensing an electrical quantity can include: a sensing stage configured to sense the electrical quantity and generate a sensing signal indicative of the electrical quantity, wherein the electrical quantity indicates an electrical signal generated by a class-DG amplifier configured to drive a load, wherein the class-DG amplifier has a multi-signal level common mode; and a common-mode compensator configured to compensate for a change in a common-mode voltage of a differential supply voltage of the driver that occurs when switching between the signal level common modes of the class-DG amplifier.

[0009] According to these and other embodiments of the present disclosure, a method for sensing an electrical quantity may include: generating a sensing signal indicative of the electrical quantity, where the electrical quantity indicates an electrical signal generated by a class-D amplifier configured to drive a load, and where the class-D amplifier has a plurality of signal-level common modes; and compensating for a change in a common-mode voltage of a differential supply voltage of the driver that occurs when switching between the signal-level common modes of the class-D amplifier.

[0010] The technical advantages of the present disclosure will be apparent to those skilled in the art from the accompanying drawings, the specification, and the claims included herein. The objectives and advantages of the embodiments will be achieved and attained at least by the elements, features, and combinations particularly pointed out in the claims.

[0011] It should be understood that the foregoing general description and the following detailed description are both exemplary and explanatory and do not limit the claims set forth in the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] A more complete understanding of the embodiments and their advantages may be obtained by reference to the following description in conjunction with the accompanying drawings, in which like reference numerals indicate like features and in which:

[0013] Figure 1 is a diagram of an example personal audio device in accordance with an embodiment of the present disclosure;

[0014] Figure 2 shows a block diagram of selected components of an example audio integrated circuit of a personal audio device in accordance with an embodiment of the present disclosure;

[0015] Figure 3 shows a block diagram of selected components of an example amplifier in accordance with an embodiment of the present disclosure;

[0016] Figures 4A - 4E shows an example graph of selected waveforms associated with an amplifier in accordance with an embodiment of the present disclosure;

[0017] Figure 5 shows a circuit diagram of selected components of an example current sensing circuit in accordance with an embodiment of the present disclosure. DETAILED DESCRIPTION

[0018] Figure 1 is a diagram of an example personal audio device 1 in accordance with an embodiment of the present disclosure. Figure 1 depicts a personal audio device 1 coupled to headphones 3 in the form of a pair of earbud speakers 8A and 8B. Figure 1The earphone 3 depicted is merely an example, and it should be understood that the personal audio device 1 can be used in combination with various audio transducers, including but not limited to over-ear headphones, earbuds, in-ear headphones, and external speakers. The plug 4 can provide a connection of the earphone 3 to the electrical terminals of the personal audio device 1. The personal audio device 1 can use the touch screen 2 to provide a display to the user and receive user input, or alternatively, a standard liquid crystal display (LCD) can be combined with various buttons, sliders, and / or dials arranged on the front and / or side of the personal audio device 1. Also as Figure 1 shown, the personal audio device 1 can include an audio integrated circuit (IC) 9 for generating an analog audio signal to be transmitted to the earphone 3 and / or another audio transducer.

[0019] Figure 2 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 is shown. In some embodiments, the example audio IC 9 can be used to implement Figure 1 the audio IC 9. As Figure 2 shown, the microcontroller core 18 can provide a digital audio input signal DIG_IN to the pulse width modulator 14, and the pulse width modulator 14 can convert the digital audio input signal into an equivalent differential pulse width modulation input signal V IN , such that the pulse width or duty cycle of the input signal V IN can indicate the value (e.g., amplitude and polarity) of the digital audio input signal DIG_IN. The pulse width modulator 14 can provide the analog input signal V IN to the amplifier 16, and the amplifier 16 can amplify or attenuate the analog input signal V IN to provide an audio output signal V OUT , and the audio output signal V OUT can operate a speaker, an over-ear headphone transducer, a line level signal output, and / or other suitable outputs. Also as Figure 2 shown, the example audio IC 9 can include a current sensing circuit 19 configured to sense an output current I OUT generated by the amplifier 16 and delivered to a load coupled to the output of the amplifier 16, which will be described in more detail below.

[0020] Figure 3 A block diagram of selected components of an example amplifier 16 according to an embodiment of the present disclosure is shown. In some embodiments, the amplifier 16 can be used to implement Figure 2 all or a part of the amplifier 16. As Figure 3 shown, Figure 2 the amplifier 16 can be implemented using a class-DG amplifier 18 that has a for receiving an analog signal V INInput for generating and indicating an analog signal V IN Output signal V OUT Output, and a power input for receiving a plurality of power supply voltages (e.g., V SUP1 、V SUP2 、V SUP3 、V SUP4 ) at each of its positive and negative power supply terminals based on one or more control signals for selectively activating (e.g., enabling, closing, turning on) and deactivating (e.g., disabling, opening, turning off) switches 21 (e.g., switches 21A, 21B, 21C, and 21D) and 22 (e.g., switches 22A, 22B, 22C, and 22D), where each switch 21 will have its positive power supply terminal voltage V SUPPLY + Positive power supply terminal coupled to a corresponding power supply voltage (e.g., V SUP1 、V SUP2 、V SUP3 、V SUP4 ), and each switch 22 will have its negative power supply terminal voltage V SUPPLY - Negative power supply terminal coupled to a corresponding power supply voltage (e.g., V SUP1 、V SUP2 、V SUP3 、V SUP4 ). For purposes of clarity and illustration, Figure 3 Amplifier 16 is depicted as having four selectable power supply voltages. However, amplifier 16 may have any suitable number of selectable power supply voltages.

[0021] To further illustrate the operation of amplifier 16, in some embodiments, the power supply voltages may be configured such that V SUP1 = -5V, V SUP2 = 0V, V SUP3 = 5V, V SUP4 = 10V, and switches 21 and 22 may be controlled such that the full-swing differential power supply voltage V SUPPLY = V SUPPLY + -V SUPPLY - Can vary between -15V, -10V, -5V, 0V, 5V, 10V, and 15V. Figures 4A - 4E Shows an example graph of selected waveforms associated with amplifier 16 according to an embodiment of the present disclosure, and uses the example power supply voltages listed in the previous sentence.

[0022] As Figures 4A - 4E Shown, amplifier 16 may be based on a desired full-swing differential power supply voltage V SUPPLYOperate in multiple regions. For example, in region A of the operation, as Figure 4A shown, the full-swing differential supply voltage V SUPPLY can vary between 10V and 15V, which results in the common-mode voltage V OUT of the output signal V CM (e.g., V CM =(V SUPPLY + +V SUPPLY - ) / 2) to vary between 0V, 2.5V, and 5V. As another example, in region B of the operation, as Figure 4B shown, the full-swing differential supply voltage V SUPPLY can vary between -10V, -5V, and 0V, which results in the common-mode voltage V CM to vary between -2.5V, 0V, and 2.5V. As a further example, in region C of the operation, as Figure 4C shown, the full-swing differential supply voltage V SUPPLY can vary between -5V, 0V, and 5V, which results in the common-mode voltage V CM to vary between 0V, 2.5V, and 5V. As yet another example, in region D of the operation, as Figure 4D shown, the full-swing differential supply voltage V SUPPLY can vary between -10V, -5V, and 0V, which results in the common-mode voltage V CM to vary between -2.5V, 0V, and 2.5V. As still another example, in region E of the operation, as Figure 4E shown, the full-swing differential supply voltage V SUPPLY can vary between 10V and 15V, which results in the common-mode voltage V CM to vary between 0V, 2.5V, and 5V.

[0023] It should be noted that regions B and D, which may be near the zero-crossing point of the output signal V OUT , have different (e.g., lower) common-mode voltages V CM than those that appear within regions A, C, and E. This drift in the common-mode voltage may be replicated at the input of the current sensing circuit 19, thereby affecting the measurement result of the output current I OUT , unless measures are taken to account for this variation in the common-mode voltage V CM .

[0024] Figure 5 Shows a circuit diagram of selected components of an example current sensing circuit 19 according to an embodiment of the present disclosure. As Figure 5 shown, the current detection circuit 19 can be implemented by using a resistor R SNSimplemented by the sense resistor 32 such that the output current I flowing through the sense resistor 32 OUT causes a sense voltage V proportional to the output current I to be formed across the terminals of the sense resistor 32 OUT (e.g., V SNS = I SNS R OUT ). An amplifier stage including an amplifier 34, an input resistor 36, a feedback resistor 38, and a feedback capacitor 40 can amplify the sense voltage V SNS to generate an analog amplified signal proportional to the output current I SNS . Further, an analog-to-digital converter (ADC) 42 can generate a digital output signal I equivalent to the analog amplified signal generated by the amplifier 34 OUT such that the digital output signal I SNS indicates the output current I SNS . OUT .

[0025] Also as Figure 5 shown, changes in the common-mode voltage V OUT that affect the measurement results of the output signal V SNS and the sense voltage V CM can be corrected using an analog common-mode compensator 44 and / or a digital common-mode compensator 46.

[0026] The analog common-mode compensator 44 can include any such system, apparatus, or device that is configured to generate a correction signal applied at the summing node of the amplifier 34 in response to a mode change signal MODE CHANGE and a correction factor FACTOR to compensate for changes in the common-mode voltage V OUT that affect the measurement results of the output signal V SNS and the sense voltage V CM . For example, when the mode change signal MODE CHANGE is non-zero, the analog common-mode compensator 44 can be configured to apply a correction signal to the summing node of the amplifier 34 in an amount indicated by the correction factor FACTOR. On the other hand, when the mode change signal MODE CHANGE is zero, the analog common-mode compensator 44 does not apply a correction to the summing node of the amplifier 34.

[0027] The mode change signal MODE CHANGE can indicate the timing at which changes in the common-mode voltage V CM occur and can be scaled using an analog and / or digital scale factor to indicate the amount of change in the common-mode voltage V CM . In these and other embodiments, the mode change signal MODE CHANGE can be generated by the microcontroller core 18 based on the value of the digital audio input signal DIG_IN. For example, in connection with Figures 4A - 4EIn a specific example described, when DIG_IN is below the threshold amplitude, the microcontroller core 18 can cause the mode change signal MODE CHANGE to have a non - zero value (e.g., 2.5V), which may indicate operation in region B or D (where the common - mode voltage VCM may drop relative to regions A, C, and E).

[0028] The correction factor FACTOR can include an estimate of the value required to correct for changes in the common - mode voltage V CM For example, in some embodiments, the difference in the common - mode voltage V CM between the operating regions of the amplifier 16 can be known (e.g., 2.5V in the example of Figures 4A - 4E ). In other embodiments, the correction factor FACTOR can be generated by the digital common - mode compensator 46, as described below.

[0029] The digital common - mode compensator 46 can include any such system, device, or apparatus that is configured to generate the correction factor FACTOR in response to the mode change signal MODE CHANGE and the digital output signal I SNS and apply the correction factor FACTOR to the digital output signal I SNS in order to generate a corrected digital output signal I SNS ’. As Figure 5 shown, the digital common - mode compensator 46 can include an adder 50, a high - pass filter (HPF) 52, HPF 54, a correlation block 56, a low - pass filter (LPF) 58, and a gain element 60.

[0030] The adder 50 can combine the difference between the digital output signals I SNS with the correction factor FACTOR to generate the corrected digital output signal I SNS ’. Since the desired common - mode compensation may only be for content outside the audio spectrum, the HPF 52 can filter out the audio - frequency components of the corrected digital output signal I SNS ’. Similarly, the HPF 54 can perform high - pass filtering of the mode change signal MODE CHANGE such that the resulting output signals of the HPF 52 and HPF 54 can be correlated by the correlation block 56. The correlation between the resulting output signals of the HPF 52 and HPF 54 can indicate whether large changes in the corrected digital output signal I SNS ’ are caused by changes in the operating region of the amplifier 16 that result in changes in the common - mode voltage V CM . In other words, when the changes in the corrected digital output signal I SNS ’ are not correlated with the mode change signal MODE CHANGE, the corrected digital output signal ISNS The change in OUT may occur in response to an actual change in the output current I CM rather than due to a change in the common-mode voltage V

[0031] The output of the correlation block 56 can be low-pass filtered by the LPF 58 to smooth the correlation signal generated by the correlation block 56 (e.g., removing noise). The gain element 66 can apply a gain K to the signal generated by the LPF 58, resulting in a correction factor FACTOR that will be applied by the adder 50 to the digital output signal I SNS and / or applied by the analog common-mode compensator 44 to the summing node of the amplifier 34.

[0032] Although the foregoing systems and methods have been described for applications involving audio signals, it should be understood that the same systems and methods or similar systems and methods can be applied to other signal processing systems employing a multilevel pulse-width modulation system.

[0033] Although the foregoing systems and methods have been described for applications involving sensing of the output current I OUT it should be understood that the same systems and methods or similar systems and methods can be applied to sensing and measurement of other electrical quantities in a multilevel pulse-width modulation system, including but not limited to the output voltage (e.g., the output signal V OUT ).

[0034] As used herein, when two or more elements are referred to as being "coupled" to each other, such terminology indicates that such two or more elements are in electrical communication or mechanical communication, as applicable, whether directly or indirectly connected, with or without intermediate elements.

[0035] This disclosure covers all variations, substitutions, permutations, alterations, and modifications of the example embodiments herein that would be understood by a person of ordinary skill in the art. Similarly, where appropriate, the appended claims cover all variations, substitutions, permutations, alterations, and modifications of the example embodiments herein that would be understood by a person of ordinary skill in the art. Additionally, in the appended claims, a reference to a device or system or a component of a device or system that is adapted to, configured to, capable of, configured to be, enabled to be, operable to, or operable to perform a particular function covers that device, system, or component, whether or not the particular function of the device, system, or component or the device, system, or component itself is activated, turned on, or unlocked, so long as the device, system, or component is so adapted, configured, capable, configured, enabled, operable, or operative. Accordingly, the systems, devices, and methods described herein may be modified, added to, or omitted without departing from the scope of this disclosure. For example, components of the systems and devices may be integrated or separated. Additionally, the operations of the systems and devices disclosed herein may be performed by more, fewer, or other components, and the methods described may include more, fewer, or other steps. Further, the steps may be performed in any suitable order. As used in this document, "each" refers to each member of a set or each member of a subset of a set.

[0036] Although example embodiments are shown in the drawings and described below, any number of techniques may be used to implement the principles of this disclosure, whether currently known or not. This disclosure should not in any way be limited to the example embodiments and techniques shown in the drawings and described above.

[0037] Unless otherwise specifically noted, the items shown in the drawings need not be drawn to scale.

[0038] All of the examples and conditional language recited herein are intended for pedagogical purposes to assist the reader in understanding the disclosure and the concepts contributed by the inventor to further the art, and are to be construed as not being limited to such specifically recited examples and conditions. Although the embodiments of this disclosure have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of this disclosure.

[0039] Although specific advantages have been enumerated above, various embodiments may include some, all, or none of the enumerated advantages. Additionally, other technical advantages will become apparent to those of ordinary skill in the art upon review of the foregoing drawings and description.

[0040] To assist the Patent Office and any readers of any patent issued on this application in interpreting the appended claims, the Applicants wish to note that they do not intend to invoke 35 U.S.C. § 112(f) with respect to the appended claims or claim elements, unless the recitations "means for" or "step for" are expressly used in a particular claim.

Claims

1. A system for sensing electric quantity, comprising: A sensing stage configured to sense the electric quantity and generate a sensing signal indicative of the electric quantity, wherein the electric quantity indicates an electric signal generated by a class-DG amplifier configured to drive a load, and wherein the class-DG amplifier has multiple signal-level common modes; And A common-mode compensator configured to compensate for a change in a common-mode voltage of a differential power supply voltage of the class-DG amplifier that occurs when switching between the signal-level common modes of the class-DG amplifier.

2. The system according to claim 1, wherein the electric quantity includes current.

3. The system according to claim 1, wherein the electric quantity includes voltage.

4. The system according to claim 1, wherein the sensing stage includes a sensing resistor configured to generate a sensing voltage indicative of the electric quantity.

5. The system according to claim 4, wherein the sensing stage includes a sensing-stage amplifier configured to amplify the sensing voltage.

6. The system according to claim 5, wherein the sensing stage includes an analog-to-digital converter configured to convert the sensing voltage amplified by the sensing-stage amplifier into an equivalent digital signal indicative of the electric quantity.

7. The system according to claim 6, wherein the common-mode compensator includes a digital compensator configured to apply a correction factor to the equivalent digital signal.

8. The system according to claim 7, wherein, The digital compensator is further configured to apply the correction factor to the equivalent digital signal based on a correlation between a change in the equivalent digital signal and a change between operating regions of the differential power supply voltage that caused the change in the common-mode voltage of the differential power supply voltage.

9. The system according to claim 8, further comprising a second common-mode compensator configured to apply the correction factor to an input summing mode of the sensing-stage amplifier.

10. The system according to claim 5, wherein the common-mode compensator includes an analog compensator configured to apply a correction factor to an input summing mode of the sensing-stage amplifier.

11. The system according to claim 1, wherein the common-mode compensator is configured to enable compensation in response to a change in an operating region of the differential power supply voltage that caused the change in the common-mode voltage.

12. A method for sensing electric quantity, comprising: Generating a sensing signal indicative of the electric quantity, wherein the electric quantity indicates an electric signal generated by a class-DG amplifier configured to drive a load, and wherein the class-DG amplifier has multiple signal-level common modes; And Compensating for a change in a common-mode voltage of a differential power supply voltage of the class-DG amplifier that occurs when switching between the signal-level common modes of the class-DG amplifier.

13. The method according to claim 12, wherein the electric quantity includes current.

14. The method according to claim 12, wherein the electric quantity includes voltage.

15. The method according to claim 12, wherein the sensing signal is a sensing voltage across a sensing resistor, and wherein the sensing voltage indicates the electric quantity.

16. The method according to claim 15, wherein generating the sense signal includes being configured to amplify the sense voltage using a sense stage amplifier.

17. The method according to claim 16, further comprising converting the sense voltage amplified by the sense stage amplifier into an equivalent digital signal indicative of the amount of electricity using an analog-to-digital converter.

18. The method according to claim 17, further comprising applying a correction factor to the equivalent digital signal using a digital compensator.

19. The method according to claim 18, wherein the digital compensator is further configured to apply the correction factor to the equivalent digital signal based on a correlation between a change in the equivalent digital signal and a change in an operating region of the differential supply voltage that causes a change in a common-mode voltage of the differential supply voltage.

20. The method according to claim 19, further comprising applying the correction factor to an input summing mode of the sense stage amplifier using a second common-mode compensator.

21. The method according to claim 16, further comprising applying a correction factor to an input summing mode of the sense stage amplifier using an analog compensator.

22. The method according to claim 12, further comprising enabling compensation in response to a change in an operating region of the differential supply voltage that causes a change in the common-mode voltage.

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