AMPLIFIER HAVING A VIRTUAL GROUND AND METHOD THEREOF
An amplifier comprises first, second, and third modulators. The first modulator includes an input for receiving a first input signal, and an output for providing a first modulated output signal corresponding to the first input signal. The second modulator includes an input for receiving a second input signal, and an output for providing a second modulated output signal corresponding to the second input signal. The third modulator has an input for receiving a third input signal, and an output for providing a third modulated output signal corresponding to the third input signal and for providing a virtual ground. A first amplifier circuit is coupled to the outputs of the first and third modulators for driving a first load. A second amplifier circuit is coupled to the outputs of the second and third modulators for driving a second load.
1. Field
This disclosure relates generally to amplifiers, and more specifically, to an audio amplifier having a virtual ground.
2. Related Art
Traditional amplifiers, such as class D amplifiers used in audio applications use a system ground for coupling the amplifier to a load, such as a speaker, a headset, or an earphone. Use of the system ground requires the use of output coupling capacitors, which take up space. This poses problems for audio applications where space is limited, such as mobile devices. To address this problem, certain amplifiers use a differential output, which removes the need for a coupling capacitor. The use of differential output, however, results in two pins for coupling to the speaker, the headset, or the earphone. Moreover, stereo amplifiers need four pins for coupling to the speaker, the headset, or the earphone, when using differential output. This poses problems where there is a paucity of pins that can be used to couple to such loads. One way to reduce the number of pins in such amplifiers is to use a virtual ground. The stereo amplifiers that do use a virtual ground typically use a linear regulator to produce the virtual ground. The use of the linear regulator, however, results in lower efficiency. Moreover, in a class D audio amplifier, the linear regulator does not track changes in the supply voltage to the amplifier.
Accordingly, there is a need for an improved audio amplifier having a virtual ground.
The present invention is illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale.
In one aspect, an amplifier is provided. The amplifier includes a first modulation circuit having an input for receiving a first input signal, and an output for providing a first modulated output signal, the first modulated output signal corresponding to the first input signal. The amplifier further includes a second modulation circuit having an input for receiving a second input signal, and an output for providing a second modulated output signal, the second modulated output signal corresponding to the second input signal. The amplifier further includes a third modulation circuit having an input for receiving a third input signal, and an output for providing a third modulated output signal, the third modulated output signal corresponding to the third input signal and for providing a virtual ground. The amplifier further includes a first amplifier circuit coupled to the outputs of the first and third modulation circuits, the first amplifier circuit for driving a first load. The amplifier further includes a second amplifier circuit coupled to the outputs of the second and third modulation circuits, the second amplifier circuit for driving a second load.
In another aspect, an amplifier is provided. The amplifier includes a first sigma delta modulator having an input for receiving a first input signal, and an output for providing a first pulse density modulated output signal, the first pulse density modulated output signal corresponding to the first input signal. The amplifier further includes a second sigma delta modulator having an input for receiving a second input signal, and an output for providing a second pulse density modulated output signal, the second pulse density modulated output signal corresponding to the second input signal. The amplifier further includes a third sigma delta modulator having an input for receiving a third input signal, and an output for providing a third pulse density modulated output signal, the third pulse density modulated output signal corresponding to the third input signal and for providing a virtual ground. The amplifier further includes a first H-bridge circuit coupled to the outputs of the first and third sigma delta modulators, the first H-bridge circuit for driving a first load. The amplifier further includes a second H-bridge circuit coupled to the outputs of the second and third sigma delta modulators, the second H-bridge circuit for driving a second load.
In yet another aspect, method for amplifying first and second stereo audio signals is provided. The method includes modulating the first stereo audio signal to provide a first modulated stereo signal. The method further includes modulating the second stereo audio signal to provide a second modulated stereo signal. The method further includes modulating a third signal to provide a third modulated signal, the third modulated signal for providing a virtual ground. The method further includes amplifying the first modulated stereo signal to drive a first load, wherein the first load is coupled to receive the first modulated stereo signal and the virtual ground. The method further includes amplifying the second modulated stereo signal to drive a second load, wherein the second load is coupled to receive the second modulated stereo signal and the virtual ground.
As used herein the term “virtual ground” includes, but is not limited to, a point that has no real electrical connection to a system ground or a real ground, but instead is a point that is being held close to the amplifier's system ground or the real ground.
As used herein, the term “bus” is used to refer to a plurality of signals or conductors which may be used to transfer one or more various types of information, such as data, addresses, control, or status. The conductors as discussed herein may be illustrated or described in reference to being a single conductor, a plurality of conductors, unidirectional conductors, or bidirectional conductors. However, different embodiments may vary the implementation of the conductors. For example, separate unidirectional conductors may be used rather than bidirectional conductors and vice versa. Also, plurality of conductors may be replaced with a single conductor that transfers multiple signals serially or in a time multiplexed manner. Likewise, single conductors carrying multiple signals may be separated out into various different conductors carrying subsets of these signals. Therefore, many options exist for transferring signals.
The terms “assert” or “set” and “negate” (or “deassert” or “clear”) are used herein when referring to the rendering of a signal, status bit, or similar apparatus into its logically true or logically false state, respectively. If the logically true state is a logic level one, the logically false state is a logic level zero. And if the logically true state is a logic level zero, the logically false state is a logic level one.
Each signal described herein may be designed as positive or negative logic, where negative logic can be indicated by a bar over the signal name or an asterix (*) following the name. In the case of a negative logic signal, the signal is active low where the logically true state corresponds to a logic level zero. In the case of a positive logic signal, the signal is active high where the logically true state corresponds to a logic level one. Note that any of the signals described herein can be designed as either negative or positive logic signals. Therefore, in alternate embodiments, those signals described as positive logic signals may be implemented as negative logic signals, and those signals described as negative logic signals may be implemented as positive logic signals.
Brackets are used herein to indicate the conductors of a bus or the bit locations of a value. For example, “bus 60 [7:0]” or “conductors [7:0] of bus 60” indicates the eight lower order conductors of bus 60, and “address bits [7:0]” or “ADDRESS [7:0]” indicates the eight lower order bits of an address value. The symbol “$” preceding a number indicates that the number is represented in its hexadecimal or base sixteen form. The symbol “%” preceding a number indicates that the number is represented in its binary or base two form.
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Because the apparatus implementing the present invention is, for the most part, composed of electronic components and circuits known to those skilled in the art, circuit details will not be explained in any greater extent than that considered necessary as illustrated above, for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention.
Some of the above embodiments, as applicable, may be implemented using a variety of different processing systems. For example, although
Thus, it is to be understood that the architectures depicted herein are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In an abstract, but still definite sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality.
Furthermore, those skilled in the art will recognize that boundaries between the functionality of the above described operations merely illustrative. The functionality of multiple operations may be combined into a single operation, and/or the functionality of a single operation may be distributed in additional operations. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments.
Although the invention is described herein with reference to specific embodiments, various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention. Any benefits, advantages, or solutions to problems that are described herein with regard to specific embodiments are not intended to be construed as a critical, required, or essential feature or element of any or all the claims.
The term “coupled,” as used herein, is not intended to be limited to a direct coupling or a mechanical coupling.
Furthermore, the terms “a” or “an,” as used herein, are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an.” The same holds true for the use of definite articles.
Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements.
Claims
1. An amplifier comprising:
- a first modulation circuit having an input for receiving a first input signal, and an output for providing a first modulated output signal, the first modulated output signal corresponding to the first input signal;
- a second modulation circuit having an input for receiving a second input signal, and an output for providing a second modulated output signal, the second modulated output signal corresponding to the second input signal;
- a third modulation circuit having an input for receiving a third input signal, and an output for providing a third modulated output signal, the third modulated output signal corresponding to the third input signal and for providing a virtual ground;
- a first amplifier circuit coupled to the outputs of the first and third modulation circuits, the first amplifier circuit for driving a first load; and
- a second amplifier circuit coupled to the outputs of the second and third modulation circuits, the second amplifier circuit for driving a second load.
2. The amplifier of claim 1, wherein the first amplifier circuit comprises a first H-bridge circuit and the second amplifier circuit comprises a second H-bridge circuit.
3. The amplifier of claim 1, wherein the third input signal represents a common mode voltage.
4. The amplifier of claim 1, wherein the first, second, and third modulation circuits are characterized as being sigma delta modulation circuits.
5. The amplifier of claim 4, wherein each of the sigma delta modulation circuits comprises:
- a first summer having a first input for receiving the first input signal, a second input for receiving a feedback signal, and an output;
- a delay element having an input coupled to the output of the first summer, and an output for providing the feedback signal;
- a gain stage having an input coupled to the output of the delay element, and an output;
- a second summer having a first input coupled to the output of the gain stage, a second input for receiving a feed-forward signal from the output of the first summer, and an output; and
- a quantizer having an input coupled to the output of the second summer, and an output.
6. The amplifier of claim 5, wherein each of the sigma delta modulation circuits further comprises a scale factor generator having a first input coupled to the output of the quantizer, a second input coupled to receive a power supply voltage, and an output coupled to a third input of the first summer, wherein the scale factor generator adds a scale factor to the first summer to compensate for variations of the power supply voltage.
7. The amplifier of claim 1, wherein the amplifier is characterized as being a class D amplifier and the first, second, and third input signals are digital signals.
8. The amplifier of claim 1, wherein the first, second, and third modulated output signals are characterized as being pulse density modulated output signals.
9. The amplifier of claim 1, wherein the first amplifier circuit comprises a pair of series-connected transistors coupled between a power supply terminal and a ground terminal, the pair of series-connected transistors coupled to receive the first modulated output signal, and in response, to provide an amplified modulated output signal.
10. The amplifier of claim 1, wherein the first amplifier circuit comprises a first H-bridge circuit and the second amplifier circuit comprises a second H-bridge circuit, wherein:
- the first H-bridge circuit has a first input coupled to the output of the first modulation circuit and a second input coupled to the output of the third modulation circuit, the first H-bridge circuit having an output for driving the first load; and
- the second H-bridge circuit has a first input coupled to the output of the second modulation circuit and a second input coupled to the output of the third modulation circuit, the second H-bridge circuit having an output for driving the second load.
11. An amplifier comprising:
- a first sigma delta modulator having an input for receiving a first input signal, and an output for providing a first pulse density modulated output signal, the first pulse density modulated output signal corresponding to the first input signal;
- a second sigma delta modulator having an input for receiving a second input signal, and an output for providing a second pulse density modulated output signal, the second pulse density modulated output signal corresponding to the second input signal;
- a third sigma delta modulator having an input for receiving a third input signal, and an output for providing a third pulse density modulated output signal, the third pulse density modulated output signal corresponding to the third input signal and for providing a virtual ground;
- a first H-bridge circuit coupled to the outputs of the first and third sigma delta modulators, the first H-bridge circuit for driving a first load; and
- a second H-bridge circuit coupled to the outputs of the second and third sigma delta modulators, the second H-bridge circuit for driving a second load.
12. The amplifier of claim 11, wherein the third input signal represents a common mode voltage of the first and second input signals.
13. The amplifier of claim 11, wherein the first and second input signals are digital audio signals and each of the first and second loads is a speaker.
14. The amplifier of claim 11, wherein the each of the first, second, and third sigma delta modulators comprises:
- a first summer having a first input for receiving the first input signal, a second input for receiving a feedback signal, and an output;
- a delay element having an input coupled to the output of the first summer, and an output for providing the feedback signal;
- a gain stage having an input coupled to the output of the delay element, and an output;
- a second summer having a first input coupled to the output of the gain stage, a second input for receiving a feed-forward signal from the output of the first summer, and an output; and
- a quantizer having an input coupled to the output of the second summer, and an output.
15. The amplifier of claim 14, wherein each of the first, second, and third sigma delta modulators further comprises a scale factor generator having a first input coupled to the output of the quantizer, a second input coupled to receive a power supply voltage, and an output coupled to a third input of the first summer, wherein the scale factor generator adds a scale factor to the first summer to compensate for variations of the power supply voltage.
16. A method for amplifying first and second stereo audio signals, the method comprising:
- modulating the first stereo audio signal to provide a first modulated stereo signal;
- modulating the second stereo audio signal to provide a second modulated stereo signal;
- modulating a third signal to provide a third modulated signal, the third modulated signal for providing a virtual ground;
- amplifying the first modulated stereo signal to drive a first load, wherein the first load is coupled to receive the first modulated stereo signal and the virtual ground; and
- amplifying the second modulated stereo signal to drive a second load, wherein the second load is coupled to receive the second modulated stereo signal and the virtual ground.
17. The method of claim 16, wherein modulating the first stereo audio signal, modulating the second stereo audio signal, and modulating the third signal each further comprise pulse density modulating each of the first stereo audio signal, the second stereo audio signal, and the third signal.
18. The method of claim 16, wherein modulating the third signal further comprises providing a third signal that represents a common mode between the first and second stereo audio signals.
19. The method of claim 16, wherein modulating the first stereo audio signal further comprises:
- using a first summer, summing the first stereo audio signal input with a feedback signal to produce a summation signal;
- delaying the first summation signal to generate a delayed summation signal;
- feeding back the delayed summation signal to the first summer;
- amplifying the delayed summation signal;
- using a second summer, summing the delayed summation signal with a feed-forward signal from the first summer to produce a second summation signal; and
- quantizing the second summation signal to produce a quantized signal.
20. The method of claim 19, further comprising:
- coupling the quantized signal to an input of a scale factor generator; and
- feeding back an output of the scale factor generator to the first summer, wherein the scale factor generator adds a scale factor to the first summer to compensate for variations of the power supply voltage.
Type: Application
Filed: Jan 11, 2008
Publication Date: Jul 16, 2009
Inventors: Thomas J. Zuiss (Austin, TX), Kevin B. Traylor (Austin, TX)
Application Number: 12/013,070
International Classification: H03F 3/38 (20060101);