Patent Application
20070286266
Other aspects, features, and advantages of the present invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which like reference numerals identify similar or identical elements.
In most real-world implementations, medium 220 will be substantially symmetrical, i.e., the same or at least a similar degree of impairment occurs in a transmission from transmitter 202-1 to receiver 203-2 as in a transmission from transmitter 202-2 to receiver 203-1. Even if medium 220 is not symmetrical, the impairment in a transmission from transmitter 202-1 to receiver 203-2 will at least be correlated or closely correlated to the impairment in a transmission from transmitter 202-2 to receiver 203-1. Accordingly, transceiver 201-1 is adapted to exploit this symmetry or correlation to permit coefficients, which are generated by a coefficient calculator 213-1 of receiver 203-1 based on step-response characteristics extrapolated or derived from the digital signal provided by an analog-to-digital (A/D) converter 210-1 of receiver 203-1, to be used by a coefficient register 208-1 of transmitter 202-1 to set the coefficients for a finite-impulse response (FIR) filter 205-1 of transmitter 202-1.
Transmitter 202-1 includes an encoder 204-1, FIR filter 205-1, coefficient register 208-1, a Digital-to-Analog (D/A) converter 206-1, and an amplifier 207-1. Encoder 204-1 receives and encodes digital information and provides the encoded digital information to FIR filter 205-1. FIR filter 205-1 receives coefficients from coefficient register 208-1, which FIR filter 205-1 uses in filtering and pre-distorting the encoded digital information. These coefficients may be statically or dynamically fed to FIR filter 205-1 based upon, e.g., empirical rules or bit-error checking, to modify the characteristics of the signal to permit eventual recovery of the encoded information with the least amount of error. As will be explained in further detail below, the coefficients are generated, at least in part, using coefficient calculator 213-1 of receiver 203-1. Other methods of generating coefficients may be used in conjunction with coefficient calculator 213-1. For example, the coefficients may be determined, e.g., based on prior knowledge of the channel, e.g., component location, type of media, or transmission distance. In certain complex systems, a handshake might occur with second transceiver 201-2 through impaired medium 220 to determine the best setting for the coefficients to provide to FIR filter 205-1. In some embodiments, preamplifier 209-1 might include a conventional analog filter (not shown), whereby coefficient calculator 213-1 alternatively or additionally uses signals from the conventional analog filter to generate and supply coefficients to DFE 211-1 and/or coefficient register 208-1.
FIR filter 205-1 provides the filtered, pre-distorted encoded information to D/A converter 206-1, which information D/A converter 206-1 converts to an analog signal, providing the analog signal to amplifier 207-1. Amplifier 207-1 amplifies the analog signal to permit travel of the analog signal through impaired medium 220, to be received by receiver 203-2.
In the embodiment shown, transmitter 202-2 is configured similarly to transmitter 202-1, with the amplified analog signal from amplifier 207-2 traveling through impaired medium 220 for receipt by receiver 203-1.
Receiver 203-1 includes a preamplifier 209-1, A/D converter 210-1, a decision-feedback equalizer (DFE) 211-1, coefficient calculator 213-1, and a decoder 212-1. Preamplifier 209-1 receives the analog signal from amplifier 207-2 via impaired medium 220 and provides an amplified analog signal to A/D converter 210-1, which provides a digital signal to both DFE 211-1 and coefficient calculator 213-1. In this embodiment, based on step-response characteristics (or alternatively, impulse-response or frequency-response) extrapolated or derived from the digital signal received from A/D converter 210-1, coefficient calculator 213-1 generates and provides to DFE 211-1 coefficients that DFE 211-1 uses in equalizing the digital signal.
In this embodiment, the received data is non-return-to-zero (NRZ) and approximates a step response for long run-length data, i.e., lengthened periods of a high or low state. Accordingly, A/D converter 210-1 includes a quantizer (or comparator or “slicer”) to permit digitization of the step response, so that overshoot, frequency, waveform-ringing, and other step-response characteristics may be captured either over a single event or over a period of time. Capturing this step response numerically permits the computation of a transfer function within receiver 203-1 that restores the step response to a more ideal step. This transfer function may also include known impairment differences, such as the presence (or absence) of vias, connectors, stubs, or other impairments in the transmit direction. These computed coefficients, however obtained, are used not only to set the DFE of receiver 203-1, but also to set the FIR of transmitter 202-1, as will be explained below, thereby optimizing the bit-error rate at the receiver 203-2 corresponding to transmitter 202-1.
In other embodiments, the coefficients may also be derived in other ways (not shown), just as with the coefficients for FIR filter 205-1 of transmitter 202-1. For example, the coefficients may be statically or dynamically fed to DFE 211-1 based upon, e.g., empirical rules or bit-error checking, to modify the characteristics of the signal to permit recovery of the encoded information with the least amount of error. The coefficients may be determined based on prior knowledge of the channel, e.g., component location, type of media, or transmission distance. In certain complex systems, a handshake might occur with second transceiver 201-2 through impaired medium 220 to determine the best setting for the coefficients to provide to DFE 211-1. Information during the encoding process typically includes an encoding, error-correction, and/or parity-checking scheme, such that errors may be detected in the receiver. The task of DFE 211-1 is to minimize errors, and the error check is sometimes sufficient to determine the optimum coefficients for DFE 211-1. The equalized output of DFE 211-1 is provided to decoder 212-1, which decodes the equalized output and provides decoded digital information.
In the embodiment shown, receiver 203-2 is configured similarly to receiver 203-1, with preamplifier 209-2 receiving the amplified analog signal from amplifier 207-1 of transmitter 202-1.
As mentioned above, within transceiver 201-1, transmitter 202-1 is “sideways-fed,” i.e., coefficient register 208-1 is coupled to receive coefficients for FIR filter 205-1 from coefficient calculator 213-1 of receiver 203-1, so as to create a control from receiver 203-1 to transmitter 202-1. This control permits transceiver 201-1 to use a signal received by its own receiver 203-1 to determine the response of medium 220 and to set the coefficients of its own transmitter 202-1 to compensate for the response. It is desirable that medium 220 be substantially symmetrical, i.e., that channel characteristics be substantially the same in the transmit and receive directions. It is also desirable that the characteristics of transmitter 202-2 be known, so that channel characteristics of the transmission medium can be determined independent of the characteristics of transmitter 202-2.
Conversely, within transceiver 201-2, coefficient register 208-2 is coupled to coefficient calculator 213-2, so as to create a control between transmitter 202-2 and receiver 203-2. Even if medium 220 is not symmetrical, the impairment in a transmission from transmitter 202-2 to receiver 203-1 will at least be correlated to the impairment in a transmission from transmitter 202-1 to receiver 203-2. Accordingly, transceiver 201-2 is adapted to exploit this symmetry or correlation to permit coefficients generated by coefficient calculator 213-2 based on step-response characteristics extrapolated or derived from the digital signal provided by A/D converter 210-2 to be used by coefficient register 208-2 to set the coefficients for FIR filter 205-2.
The foregoing configuration eliminates the need for a dedicated training sequence (although, in other embodiments, a training sequence could still be used in addition to the sideways-fed equalization) and further permits each of the transceivers to be self-adjusting, i.e., to have its respective transmitter and receiver function at optimal conditions independent of any channel characteristics that might be detected at the transmitter and receiver of the other transceiver.
While the embodiments herein are described with respect to wired (e.g., copper) communications, the present invention may have utility with other types of communications, including radio, electrical, and optical communications.
Although each transceiver described herein is shown as a single integrated device, each comprising a transmitter and a receiver, in other embodiments, a transceiver could alternatively comprise a separate transmitter and receiver that are co-located, i.e., at the same site or in proximity to one another, so long as there is a control or other means for providing to the transmitter channel characteristics generated by the receiver. In certain embodiments of the present invention, it is not necessary that the local transceiver transmit data to and receive data from a single remote transceiver, nor that a remote transmitter and receiver with which the local transceiver communicates be a single, integrated transceiver.
The stages or processing blocks in a transceiver (e.g., encoder, FIR filter, D/A converter, amplifier, decoder, DFE, A/D converter, and preamplifier) consistent with the present invention could be ordered in a number of different ways and are not limited to the order shown or described herein. Some stages or blocks might be omitted in various embodiments, and other stages not described herein could be added.
It should further be recognized that a system consistent with the present invention may include a control, from a local receiver to a local transmitter (i.e., either at the same site or in the same transceiver), for sharing processing parameters, step-response characteristics, transmission medium characteristics, or other data between the receiver and transmitter, without relying on a remote transceiver to generate such parameters or characteristics. It should be understood that processing parameters other than channel coefficients could alternatively or additionally be provided to the transmitter by the receiver in a system consistent with certain embodiments of the present invention. Even raw digital signal information could be provided (e.g., from A/D converter 210-1) to the transmitter by the receiver, for processing within the transmitter, in a system consistent with certain embodiments of the present invention.
The present invention may be implemented as circuit-based processes, including possible implementation as a single integrated circuit (such as an ASIC or an FPGA), a multi-chip module, a single card, or a multi-card circuit pack. As would be apparent to one skilled in the art, various functions of circuit elements may also be implemented as processing blocks in a software program. Such software may be employed in, for example, a digital signal processor, micro-controller, or general-purpose computer. The present invention may further be implemented as part of a simulator or electronic-design automation (EDA) tool.
The present invention can be embodied in the form of methods and apparatuses for practicing those methods. The present invention can also be embodied in the form of program code embodied in tangible media, such as magnetic recording media, optical recording media, solid state memory, floppy diskettes, CD-ROMs, hard drives, or any other machine-readable storage medium, wherein, when the program code is loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention. The present invention can also be embodied in the form of program code, for example, whether stored in a storage medium, loaded into and/or executed by a machine, or transmitted over some transmission medium or carrier, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the program code is loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention. When implemented on a general-purpose processor, the program code segments combine with the processor to provide a unique device that operates analogously to specific logic circuits.
It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this invention may be made by those skilled in the art without departing from the scope of the invention as expressed in the following claims.
It should be understood that the steps of the exemplary methods set forth herein are not necessarily required to be performed in the order described, and the order of the steps of such methods should be understood to be merely exemplary. Likewise, additional steps may be included in such methods, and certain steps may be omitted or combined, in methods consistent with various embodiments of the present invention.
Although the elements in the following method claims, if any, are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.
Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.”
