Patent Grant
7929718
1. Field of the Invention
The invention relates generally to audio amplification systems, and more particularly to systems and methods for converting input data streams having a first sample rate to output data streams having a second data rate.
2. Related Art
Pulse Width Modulation (PWM) or Class D signal amplification technology has existed for a number of years. PWM technology has become more popular with the proliferation of Switched Mode Power Supplies (SMPS). Since this technology emerged, there has been an increased interest in applying PWM techniques in signal amplification applications as a result of the significant efficiency improvement that can be realized through the use of Class D power output topology instead of the legacy (linear Class AB) power output topology.
Early attempts to develop signal amplification applications utilized the same approach to amplification that was being used in the early SMPS. More particularly, these attempts utilized analog modulation schemes that resulted in low performance applications. These applications were complex and costly to implement. Consequently, these solutions were not widely accepted. Prior art analog implementations of Class D technology have therefore been unable to displace legacy Class AB amplifiers in mainstream amplifier applications.
Recently, digital PWM modulation schemes have surfaced. These schemes use Sigma-Delta modulation techniques to generate the PWM signals used in the newer digital Class D implementations. These digital PWM schemes, however, did little to offset the major barriers to integration of PWM modulators into the total amplifier solution. Class D technology has therefore continued to be unable to displace legacy Class AB amplifiers in mainstream applications.
There are a number of problems with existing digital PWM modulation schemes. One of the problems is that audio system implementations are requiring increasing numbers of channels, and increasing flexibility in routing signals through the different channels. For example, it may be desired to design a home audio system that provides audio to all of the rooms in the house. This system may need to be able to provide music to all of the rooms or selected ones of the rooms. The system may also need to be able to provide different audio signals to different rooms. For instance, audio from a home theater system may be provided to the speakers in a home theater room, while background music may be provided to all of the other rooms. It may also be desirable for the system to be able to mix audio signals that are provided to the different rooms. For instance, an intercom signal may be mixed with the background music or other audio signals. Similarly, a business application may require the ability to provide audio to many different speakers in a building. It may be desirable to have the capability of routing various different audio signals to the different speakers so that announcements can be directed to specific areas, so that music can be provided in different areas, and so on.
These and other such applications generally require more channels than are provided in a conventional system. Existing digital PWM amplification systems typically have only as many channels as can be implemented on a single chip (e.g., two or four channels). While it is possible to provide additional channels on a single chip, this typically is not a practical solution for several reasons. For example, there simply may not be enough space on the chip to implement the additional channels. It may also be possible that there are not enough resources (e.g., processor cycles) to process all of the channels on the same chip. Further, the complexity of the design may increase dramatically with the additional channels (which would also dramatically increase the cost). Still further, even if a few additional channels could be accommodated, such a solution would not address the next generation of system requirements in which still more channels would likely be required. Still further, there are difficulties that are associated with the interaction of multiple chips, such as the synchronization of the chips. It would be necessary to synchronize the chips in order to provide coherent control of all of the channels in the system and to allow switching and mixing of the audio signals among the different channels, as desired for the home and business applications described above.
One or more of the problems outlined above may be solved by the various embodiments of the invention. Broadly speaking, the invention comprises systems and methods for scaling the number of output channels that can be provided in an audio amplification system.
In one embodiment, a digital pulse width modulation (PWM) amplification system includes multiple four-channel PWM controller chips. The PWM controller chips are interconnected to enable them to be synchronized and to transfer digital audio data from one chip to another. In this embodiment, each channel has an input portion (an input channel) and an output portion (an output channel.) A different input audio signal can be received by each of the input channels on each of the PWM controller chips. These input audio signals can have different sample rates. Each input audio signal is processed by a sample rate converter to generate an internal audio signal that has a predetermined internal sample rate (e.g., 100 kHz). Each of the channels within a PWM controller chip is synchronized. Further, each PWM controller chip is synchronized with the other chips so that the internal audio signals of all of the channels are synchronized. The PWM controller chips are connected by a high-speed interconnect that enables the transfer of data between PWM controller chips. In this embodiment, the internal audio signal of each of the channels is made available to each of the other channels, so that each input of the system can be mapped to any of the outputs of the system. Further, two or more of the input signals can be mixed and provided at selected outputs of the system.
One embodiment comprises a system that includes a plurality of audio amplifier channels, and a data transport medium coupled to each of the audio amplifier channels. Each of the audio amplifier channels has an input portion (input channel) and an output portion (output channel.) Each of the input channels is configured to receive a corresponding audio signal and to convert the corresponding audio signal to a predetermined digital data format. The data transport medium is configured to transmit audio signals in the predetermined digital data format from one or more of the audio amplifier channels to one or more others of the audio amplifier channels. The output channels can then select one or more of the audio signals and provide an output signal based on the selected audio signals. In one embodiment, each input signal can be mapped to any one of the outputs of the system, and multiple ones of the input signals can be mixed to form a composite signal that is provided at a selected output.
Another embodiment comprises a method that includes receiving audio signals in multiple audio amplifier channels, converting the received audio signals to a single, predetermined digital format, transmitting the converted audio signals from at least a first one of the audio amplifier channels to a second one of the audio amplifier channels, selecting at least one audio signal in the second one of the audio amplifier channels and processing the selected audio signals the second one of the audio amplifier channels to generate an output audio signal. In one embodiment, the various input audio signals are independently mapped to the outputs of the channels. In another embodiment, the various input audio signals are mixed and provided at selected outputs of the channels.
Numerous additional embodiments are also possible.
Other objects and advantages of the invention may become apparent upon reading the following detailed description and upon reference to the accompanying drawings.
While the invention is subject to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and the accompanying detailed description. It should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular embodiment which is described. This disclosure is instead intended to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims.
One or more embodiments of the invention are described below. It should be noted that these and any other embodiments described below are exemplary and are intended to be illustrative of the invention rather than limiting.
As described herein, various embodiments of the invention comprise systems and methods for scaling the number of output channels that can be provided in an audio amplification system.
In one embodiment, the invention is implemented in a digital pulse width modulation (PWM) amplification system. This system includes multiple four-channel PWM controller chips that provide PWM output signals to corresponding drivers and output stages, which in turn drive speakers. The PWM controller chips are interconnected to enable them to be synchronized and to transfer digital audio data from one chip to another.
In this embodiment, a different input audio signal can be received by each of the channels on each of the PWM controller chips. These input audio signals can have different sample rates. Each input audio signal is processed by a sample rate converter to generate an internal audio signal that has a predetermined internal sample rate (e.g., 100 kHz).
Each of the channels within a PWM controller chip is synchronized. Further, each PWM controller chip is synchronized with the other chips so that the internal audio signals of all of the channels are synchronized. The PWM controller chips are connected by a high-speed interconnect that enables the transfer of data between PWM controller chips. In one embodiment, the internal audio signal of each of the channels is made available to each of the other channels. One or more of the input signals can then be selected by each of the channels for processing and output to the corresponding output stage. Each input of this system can be mapped to any of the outputs of the system. Further, two or more of the input signals can be mixed and provided at selected outputs of the system.
Referring to
In the present systems and methods, sample rate converter 110 converts the input data stream from the sample rate at which it was received to a predetermined internal rate which is used within system 100. In one embodiment, this internal sample rate is 100 kHz. Thus, if data is received at a sample rate of 50 kHz, sample rate converter 110 will re-sample the data to produce a corresponding internal data stream at a sample rate of 100 kHz. This internal data stream is then provided to an audio effects subsystem 120. Audio effects subsystem 120 performs any desired processing on the internal data stream and provides the resulting processed data stream to PWM modulator 130.
The data stream received by PWM modulator 130 represents a pulse code modulated signal. PWM modulator 130 converts this data stream to a pulse width modulated signal. The pulse width modulated signal is then provided to output stage 140. In output stage 140 amplifies the pulse width modulated signal and may perform some filtering or further processing of the amplified signal. The resulting signal is then output to a speaker system 150, which converts the electrical signal to an audible signal which can be heard by a listener.
Channel 100 is implemented in a single chip. It is common for two or even four channels to be implemented in the same chip. Each additional channel typically replicates the components of the first channel. As mentioned above, however, if it is necessary or desirable to provide more channels (e.g., eight, sixteen, or even more), it may be necessary to use multiple chips, each having several channels. Further, it may be desirable to couple these chips in a way that allows various input audio signals to be switched to selected ones of the channels, and even to be combined for output on a single channel.
Referring to
The channels of system 200 differ from the channel of system 100, however, in that they incorporate a matrix switch 260 between the sample rate converters, 211-213, and the audio effects processors, 221-223. In this embodiment, matrix switch 260 comprises a single switch, although this structure could vary in other embodiments. In this embodiment, matrix switch 260 is an n×n switch. In other words, matrix switch 260 has n inputs and n outputs. Each of the n inputs of matrix switch 260 is coupled to a corresponding one of sample rate converters 211-213. Each of the n outputs of matrix switch 260 is coupled to a corresponding one of audio effects processors 221-223.
It should be noted that, while the system of
Each of the n inputs of matrix switch 260 can be independently switched to any of the n outputs. As a result, the output of any one of sample rate converters 211-213 can be switched to any one of audio effects processors 221-223. The signal received by each of audio effects processors 221-223 is then processed by the remainder of the channel to generate a corresponding audio output signal. Thus, for example, a signal received by sample rate converter 211 can be converted and then switched to audio effects processor 222. The signal would then be processed by PWM modulator 232 and output stage 242, then provided to speaker 252.
The multi-channel digital amplification system of
Another characteristic of the channels of system 200 is that each of these channels is synchronized with the others. Because the channels are synchronized with each other, the data streams produced by each of the sample rate converters are also synchronized with each other. The data from the different data streams (in the different channels) can therefore be swapped between channels, distributed among the channels, combined in one or more channels, and so on.
Because the data output by each of the sample rate converters has a common format and is synchronous, it does not matter whether the data stream produced by any particular sample rate converter is processed by the remaining components (i.e., audio effects processor, PWM modulator and output stage) of the same channel, or the same components of a different channel. If the data stream can be physically redirected from one channel to another, it can be processed and output by any of the channels.
The matrix switch in the system of
It is contemplated that the matrix switch in a preferred embodiment will be dynamically reconfigurable. Although not shown separately in the diagram of
As pointed out above, one of the characteristics of the channels of multi-channel digital audio amplification system 200 is that the audio signals received by each of the channels are converted to a common, predetermined internal sample rate by the respective sample rate converters (211-213). Sample rate converters 211-213 employ polyphase filters to perform the up-sampling of the received audio data streams. Rather than up-sampling to a much higher sample rate than is ultimately desired and then decimating (removing unwanted samples), the use of a polyphase filter achieves the same result by interpolating the received audio data streams at points corresponding to the desired sample rate.
The use of a polyphase filter provides the number of advantages over the prior art, in which FIR-type filters were typically used to up-sample audio data to a very high sample rate and then decimate down to the desired sample rate. For instance, since it is not necessary to up-sample to a sample rate which is much higher than needed, it is not necessary to provide memory to store samples that will ultimately be discarded. Similarly, no processing power is used to generate these unneeded samples. Further, polyphase filtering can accommodate different sample rates, and variations between sample rates that are nominally the same, because this process is not constrained to up-sampling by an integer factor and then down-sampling by another integer factor.
An exemplary sample rate converter that is suitable for use in a system such as the one shown in
Frame sync signals associated with the audio data are received by rate estimator counter 320. Rate estimator counter 320 simply counts the numbers of clock cycles between received samples of the audio signal. The count from rate estimator counter 320 is filtered by low pass filter 340. The filtered sample rate count is forwarded to phase selection unit 350, and is used to interpolate the filter coefficients for the polyphase filter. The interpolated polyphase filter coefficients are then convolved with the data samples in convolution unit 310 to produce the re-sampled data.
The flow of data samples through FIFO 305 and FIFO 306 are managed by FIFO management unit 307. Based on the flow of data, FIFO management unit 307 provides feedback to feedback unit 370. This feedback is used to adjust low pass filter 340. This effectively adjusts the sample rate that is estimated and thereby adjusts the coefficient interpolation performed in the sample rate converter. The sample rate conversion is thereby also adjusted to more closely track the actual input sample rate and to prevent the overflow or underflow of FIFOs 305 and 306.
A sample rate converter of the type illustrated in
Another of the characteristics pointed out above with respect to audio amplification system 200 is that the channels are synchronized. While it is a relatively straightforward matter to synchronize the operation of channels on a single chip, it is a more complicated matter to synchronize channels that are on different chips. Because a chip will typically contain no more than four channels, an audio amplification system such as system 200 that needs to have more than four channels will likely have to be implemented using multiple chips. Consequently, the channels on these chips will need to be synchronized.
In one embodiment, the channels of the audio amplification system are implemented using multiple PWM controllers. In this embodiment, the PWM controller includes a sample rate converter, an audio effects processor and a PWM modulator. The output of the PWM controller is provided to an output stage (or to a driver for the output stage).
Referring to
Each of PWM controller chips 411 and 412 receives four input signals. Each of the input signals is processed by a corresponding sample rate converter to produce an internal signal in an identical format. Each of the internal signals within the chip is generated in such a manner that the signals are synchronized. The channels of the PWM controller chips are interconnected, however, so that the signal generated by the sample rate converter of a particular channel need not be processed by the audio effects processor and PWM modulator of that channel. Each of the signals produced by the four sample rate converters is made available to each of the four audio effects processor/PWM modulator pairs. Any one of the signals can then be selected (via provided control logic) to be processed by the respective audio effects processor/PWM modulator pairs.
In addition to having the four locally generated internal signals available for processing by the audio effects processor/PWM modulator pairs, the internal signals generated by the sample rate converters of the other chip are made available via a high-speed data interconnect 420 coupled between PWM controller chips 411 and 412. High-speed data interconnect 420 may, for example, be an ESSI (Enhanced Synchronous Serial Interface) interconnect. PWM controller chips 411 and 412 are synchronized via control signals that are communicated between them (as will be described in more detail below), so no additional processing of the signals is necessary to synchronize them before they can be used by other channels' audio effects processors and PWM modulators. It may, however, be necessary to add a delay to the locally generated data in order to match delays that may be incurred in transferring data from other chips.
Once a signal is selected for processing by a channel's audio effects processor and PWM modulator, the signal is processed to generate a PWM output signal that is provided to a corresponding one of output stages 431-438. The output stage generates an output signal that drives a corresponding one of speakers 441-448. While a single signal can be processed and output on each of the channels, it should be noted that each channel may also be configured to combine signals from multiple sample rate converters or otherwise manipulate the signals before generating a corresponding output signal.
Referring to
One wire, 540, which is connected to each of the chips is used for synchronization. (Although the interconnect between the different chips is referred to herein as a “wire”, it should be noted that any suitable type of interconnect can be used.) In this embodiment, the wire can be in one of two states: active or passive. The actual encoding (high/low) will depend on the particular implementation. Within the master chip, synchronization wire 540 is coupled to a transmit unit 511 and a receive unit 512 via corresponding drivers 513 and 514. Each of slave chips 520 is coupled to synchronization wire 530 in the same manner. The transmit units are identified as items 521 and 531, and receive units are identified as items 522 and 532, respectively in the slave controller chips. The corresponding drivers are labeled as items 523, 524, 533 and 534.
When it is necessary for master controller chip 510 to communicate with slave chips 520 and 530, the appropriate signal is generated by transmit unit 511. The signal is driven onto synchronization wire 540 by driver 513. At each of the slave chips, the signal is amplified by the corresponding driver and forwarded to the corresponding receive unit 522, from which it is passed to the PWM engine of the controller chip. If it is necessary for one of slaves 520 or 530 to communicate with the master, it can do so by causing all of the controller chips to lose synchronization. In other words, a signal is generated by the corresponding transmit unit and driven onto synchronization wire 540 by the corresponding driver. The signal is then received by the driver and receive unit of each of the controller chips.
It should be noted that, with respect to the synchronization of the controller chips, the transition signal indicating that the chips should start operating is received by all of the chips, including the master, in one embodiment. Thus, both the master and the slaves watch the synchronization wire for the transition. When the master sees the transition, it begins operation, just as the slaves do. The master and slaves may therefore be identically configured with respect to the way each begins synchronous operation.
In one embodiment, after initialization, the master assumes control of the wire and drives it into its passive state. All the chips (both master and slaves) then set up and prepare to run (generate audio). All chips (master and slaves) monitor the wire for a transition to the active state. The fact that all chips are ready to run can be ensured in one embodiment by waiting for a known time to start up. In another embodiment, the readiness of the chips can be communicated by other shared communication channels. In still other embodiments, other alternative mechanisms may be used. When all of the chips are ready, the master generates a transition to the active state on the wire. All of the chips then start up simultaneously when they detect the transition.
As shown in
Referring to
High-speed interconnect 650 is configured to connect the respective ESSI ports of PWM controller chips 610, 620 and 630 to enable the transfer of this data between the PWM controllers. More specifically, interconnect 650 consists of three sub-interconnects, 651-653. Sub-interconnect 651 couples ESSI port 0 of PWM controller 610 to ESSI port 0 of PWM controller 630, sub-interconnect 652 couples ESSI port 1 of PWM controller 610 to ESSI port 0 of PWM controller 620, and sub-interconnect 653 couples ESSI port 1 of PWM controller 620 to ESSI port 1 of PWM controller 630. Sub-interconnect 651 is used to transfer input signals from PWM controller 610 to PWM controller 630 and to transfer input signals from PWM controller 630 to PWM controller 610. Similarly, sub-interconnect 652 is used to transfer input signals between PWM controller 610 and PWM controller 620, and sub-interconnect 653 is used to transfer input signals between PWM controller 620 and PWM controller 630.
In one embodiment, the data is transferred over interconnect 650 using time division multiplexing (TDM). In other words, there are time-based slots that are assigned to the different PWM controller's data. Each of the controllers is aware of the correspondence between particular slots and the data that should be transmitted in those slots, so they can drive their data onto the interconnects at the appropriate times and read other controllers' data from the interconnects at the appropriate times. In one embodiment, interconnect 650 is configured to operate in a four-slot network mode, with 24 bits per slot. PWM controllers 610, 620 and 630 are designed to operate using an internal sample rate of 100 kHz, so interconnect 650 must support a data transfer rate of 9.6 megabits per second.
Another alternative embodiment of a multi-channel audio amplifier system is shown in
While the present invention has been described with reference to particular embodiments, it should be understood that the embodiments are illustrative and that the scope of the invention is not limited to these embodiments. Many variations, modifications, additions and improvements to the embodiments described above are possible. It is contemplated that these variations, modifications, additions and improvements fall within the scope of the invention as detailed within the claims below.
Those of skill in the art will understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. The information and signals may be communicated between components of the disclosed systems using any suitable transport media, including wires, metallic traces, vias, optical fibers, and the like.
Those of skill will further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Those of skill in the art may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with general purpose processors, digital signal processors (DSPs) or other logic devices, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete gates or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be any conventional processor, controller, microcontroller, state machine or the like. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
The steps of the methods or algorithms described in connection with the embodiments disclosed herein may be embodied directly in hardware, in software or firmware modules executed by a processor, or in a combination thereof. A software product may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
The benefits and advantages which may be provided by the present invention have been described above with regard to specific embodiments. These benefits and advantages, and any elements or limitations that may cause them to occur or to become more pronounced are not to be construed as critical, required, or essential features of any or all of the claims. As used herein, the terms “comprises,” “comprising,” or any other variations thereof, are intended to be interpreted as non-exclusively including the elements or limitations which follow those terms. Accordingly, a system, method, or other embodiment that comprises a set of elements is not limited to only those elements, and may include other elements not expressly listed or inherent to the claimed embodiment.
This application claims priority to: U.S. Provisional Patent Application No. 60/469,733, entitled “Matrix Mixing methods for Four-Channel Intelligent Amplifier,” by Douglas D. Gephardt, filed May 12, 2003; U.S. patent application Ser. No. 10/805,569, entitled “Systems and Methods for Implementing a Sample Rate Converter Using Hardware and Software to Maximize Speed and Flexibility,” by Andersen, et al., filed Mar. 20, 2004; and U.S. patent application Ser. No. 10/805,593, entitled “Multi-Chip PWM Synchronization and Communication,” by Andersen, et al., filed Mar. 19, 2004, which in turn claims priority to U.S. Provisional Patent Application No. 60/469,734, entitled “Multi-chip PWM with Staggered Outputs,” by Jack B. Andersen, et al., filed May 12, 2003 U.S. Provisional Patent Application No. 60/456,414, entitled “Adaptive Anti-Clipping Protection,” by Taylor, et al., filed Mar. 21, 2003 U.S. Provisional Patent Application No. 60/456,430, entitled “Frequency Response Correction,” by Taylor, et al., filed Mar. 21, 2003 U.S. Provisional Patent Application No. 60/456,429, entitled “High-Efficiency, High-Performance Sample Rate Converter,” by Andersen, et al., filed Mar. 21, 2003 U.S. Provisional Patent Application No. 60/456,421, entitled “Output Device Switch Timing Correction,” by Taylor, et al., filed Mar. 21, 2003 U.S. Provisional Patent Application No. 60/456,422, entitled “Output Filter, Phase/Timing Correction,” by Taylor, et al., filed Mar. 21, 2003 U.S. Provisional Patent Application No. 60/456,428, entitled “Output Filter Speaker/Load Compensation,” by Taylor, et al., filed Mar. 21, 2003 U.S. Provisional Patent Application No. 60/456,420, entitled “Output Stage Channel Timing Calibration,” by Taylor, et al., filed Mar. 21, 2003 U.S. Provisional Patent Application No. 60/456,427, entitled “Intelligent Over-Current, Over-Load Protection,” by Hand, et al., filed Mar. 21, 2003; each of which is fully incorporated by reference as if set forth herein in its entirety.
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