Ikanos Communications, Inc.

Dale Smith

Behrooz Rezvani

Sam Heidari

John Zhongxuan Zhang

Sanjay Bhandari

Robert A Blauschild

Raminder Singh Bajwa

Rouben Toumani

Robert Ayrapetian

Ali K Al-Shamma

Jacky S Chow

Avadhani Shridhar

Peter Gunadisastra

John Gevargiz

Fernando Ramirez-Mireles

Homayoun Shahri

Saman Behtash

Prem Ramaswamy

Mong Yang

Caesar Seehoi Wong

Reuven Segev

Max Chien

A high efficiency line driver is disclosed. The line driver may be applied with equal advantage in wired and wireless communication media to amplify data signals with a minimum of power consumption. In an embodiment of the invention a line driver is disclosed which includes: at least one amplifier, a delay element, a control signal generator and a generator. The at least one amplifier includes at least one bias supply, a signal input and a signal output. The delay element accepts as an input the data signal and delays delivery of the data signal to the at least one line amplifier for amplification. The generator is responsive to a control signal to generate varying voltage levels corresponding thereto on the at least one bias supply of the at least one amplifier. The control signal generator is responsive to the input data signal to detect peaks therein and to generate the control signal corresponding thereto in advance of delivery of the data signal to the amplifier.

Method and apparatus for a high efficiency line driver

A transceiver for communicating a multi-tone modulated communication channel on a subscriber line. The transceiver includes: a digital signal processor (DSP) with a Fourier transform module and an analog front end (AFE). The DSP determines an available range of frequencies on the subscriber line and expands or contracts the tone spacing of each of a fixed number 'N' of tones accordingly by decreasing or increasing the processing interval associated with the Fourier transform of each tone set. The AFE performs digital-to-analog conversion of the multi-tone modulated communication channel at rates compatible with the processing interval of the Fourier transform module; whereby the range of frequencies spanned by the modulated tones on the subscriber line conforms to the available of frequencies on the subscriber line.

Method and apparatus for a variable bandwidth multi-protocol X-DSL transceiver

The apparatus for symbol boundary synchronization in one embodiment includes on the receive path of a multi-tone modem a window synchronizer, a converter and a symbol boundary component. The window synchronizer obtains windowed portions of the received datastream which includes symbols each expressed with a corresponding set of tones in a time domain. The windowed portions obtained in the training phase exhibit varying degrees of misalignment with the corresponding symbol boundaries. The window synchronizer is responsive to an alignment signal to obtain succeeding windowed portions of the incoming datastream aligned with the corresponding symbol boundaries therein. The converter couples to the window synchronizer to convert the set of tones from each windowed portion from the time domain to a frequency domain. The symbol boundary module couples to the converter to evaluate a phasor angle characteristic of selected tones from each windowed portion converted by the converter and to convert the phasor angle characteristic of the selected tones from a selected one of the windowed portions to the alignment signal to align the window synchronizer with the symbol boundaries in the received datastream. In an alternate embodiment of the invention the symbol boundary component couples to the window synchronizer to correlate sign values of the selected tones with a reference set and to output the alignment signal identifying the corresponding windowed portion which exhibits maximum correlation with the reference set to align the window synchronizer.

Method and apparatus for symbol boundary synchronization

A method and apparatus for communicating multi-tone modulated upstream and downstream channels of communication data between a pair of communication devices utilizing a common set of tones for the upstream and downstream channels. The pair of communication devices each include a digital stage configured to assign mutually orthogonal code sequences for encoding and decoding the upstream and downstream channel respectively. The transmit path of the digital stage of each communication device is configured to generate redundancy in the associated communication data in either the time or frequency domain and to encode the redundant communication data with the mutually orthogonal code sequence prior to transmission thereby allowing the communication devices to share a common frequency spectrum of a communication medium for the upstream and downstream communication channels.

Method and apparatus for symmetrical DMT X-DSL communications

The current invention provides a method and apparatus for time domain equalization in an XDSL modem. A received communication channel is analyzed to determine the highest frequency component thereof. Typically, there is an inverse relationship between the length of a subscriber line and the highest frequency component over which communications can be supported. In response to the frequency determination, the sampling rate for the channel is reduced to the lowest sample rate consistent with maintaining signal integrity on the highest frequency component of the channel. The sampling rate reduction may accomplished in the analog portion of the receive path, e.g. the analog-to-digital converter (ADC) or in a digital decimator coupled thereto. Concurrently the demodulator complexity is also scaled back. Where the XDSL protocol is digital multi-tone (DMT) the input sample size to the discrete Fourier transform (DFT) engine is reduced accordingly. With these adjustments in place TEQ resources may be scaled inversely. Thus as line length increases and the available bandwidth on the subscriber line is reduced more TEQ resources are made available to deal with the increased delay interval over which intersymbol interference is evidenced. Scaling of TEQ resources may be accomplished using a TEQ architecture which allows either the length or the tap line or the delay between taps to be varied.

Method and apparatus for time domain equalization in an XDSL modem

An apparatus and method is disclosed for channel estimation in an X-DSL communication device. The communication device may include physical or logical modems. The modems may implement one or more of a group of X-DSL protocols including: G.Lite, ADSL, VDSL, and HDSL. The apparatus may be used for determining the location and magnitude of discontinuities or faults within the communication medium to which the X-DSL communication device is coupled. The information provided by the device may be used for line qualification or repair. No additional equipment is required for channel estimation. Instead the apparatus may be located within a single modem or shared between a group of modems. An N bit pseudo random codeword injected into the transmit path is used to generate both a leakage signal and a plurality of reflected signals on the receive path. No timing information is needed from the transmit path. Instead a unique correlator is utilized on the receive path to extract timing information for the reflected signals relative to the leakage signal. The broad bandwidth of the codeword and its relatively long duration allow channel estimation at significantly higher signal-to-noise ratios and with greater degrees of accuracy than heretofore possible.

Method and apparatus for channel estimation for X-DSL communications

An apparatus and method is provided for minimizing frequency distortion in the transmit path of an XDSL modem implementing digital multi-tone (DMT) line code. The current invention provides a means for both determining and correcting for distortion in the frequency domain. The apparatus may be incorporated in an existing X-DSL architecture without additional circuitry. In an embodiment of the invention the apparatus may include a calibration phase which may be implemented using the existing analog-to-digital (ADC) conversion and demodulation capabilities on the receive path of the modem. This calibration phase takes place before the training phase associated with establishing communications with a remote site. During the calibration phase a calibration sequence with known spectral characteristics in the frequency domain is injected digitally at the beginning of the transmit path into each of the tone bins of the inverse Fourier Transform engine (IFFT). The receive path is configured to receive feedback of a resultant analog output signal from the transmit path. A frequency analyzer is used to determine the spectral properties of the feedback from the analog output signal and a normalizer is used to compute a local gain table with gain factors for each tone bin which effect the required normalization.

Method and apparatus for pre-compensation of an XDSL modem

An X-DSL modem supporting multiple X-DSL line codes including discrete multi-tone (DMT) and carrierless phase and amplitude (CAP). The modem includes: components coupled to one another to form a transmit path and a receive path. The components include an encoder component and a Fourier transform component. The encoder component encodes data associated with a CAP communication channel into QAM symbols and encodes data associated with a DMT communication channel into DMT sub-symbols. The Fourier transform component couples to the encoder component on the transmit path for transforming DMT sub-symbols from a frequency-to-time domain and for transforming QAM symbols from the time-to-frequency domain followed by a filtering in the frequency domain and a subsequent transformation back from the frequency-to-time domain to effect a pulse shaping function without requiring a discrete pulse shaping component in the transmit path.

Method and apparatus for an X-DSL modem supporting multiple X-DSL line codes

An apparatus and method is provided for minimizing in channel distortion in an X-DSL line driver is disclosed. The apparatus may be incorporated in an existing X-DSL architecture without additional circuitry. Out of band monitoring of a channel is implemented to adaptively minimize out of band interference and in band distortion. A unique training sequence, suitable for DMT line codes is set forth. The training sequence allows a full spectral characterization of the downstream signal space with a single upstream monitoring tone. The invention may be used with multi-channel X-DSL line drivers interfacing with any of a number of multi-channel supply architectures. The apparatus may be applied with equal advantage to communication protocols other than X-DSL. The apparatus may be applied with equal advantage in wired and wireless media.

Method and apparatus for pre-distortion of an X-DSL line driver

An apparatus and method is disclosed for minimizing in band distortion in the transmit path of an XDSL modem. The transmit path of an XDSL modem introduces various non-linearities into transmissions in both the frequency and time domains. The current invention provides a means for both determining and correcting for distortion in the time domain. In an embodiment of the invention the apparatus may include a calibrator which may be implemented using the existing analog-to-digital (ADC) conversion and demodulation capabilities on the receive path of the modem or alternately, a dedicated module. During a calibration phase a training signal is injected digitally into the digital-to-analog converter of the transmit path. The analog portion of the transmit path is coupled to a calibrator which measures the corresponding analog response. The correlation between input and response is stored in an analog model. During subsequent training and run-time phases of modem operation an oversampled digital input stream is subject to digital Delta Sigma Modulation (&Dgr;&Sgr;M) with the analog model injected into the feedback path from the quantizer. The injection of the analog model into the feedback improves the noise transfer function (NTF) associated with the &Dgr;&Sgr;M.

Method and apparatus for digital to analog conversion with distortion calibration

An apparatus and method for reducing power requirements in X-DSL and other communication protocols is disclosed. The apparatus may be applied with equal advantage in wired and wireless media Power is supplied selectively to input lines in which input signals exceed selected threshold levels. The apparatus is configured to support statistical multiplexing of the input signal lines across a plurality of amplification means which support amplification at up to either of at least two power levels. This reduces overall power requirements for the combined input lines. In an embodiment of the invention an apparatus for providing amplification of input signals on corresponding ones of a plurality of input signal lines is disclosed. The apparatus includes primary amplifiers and at least one secondary amplifier with higher output levels than the primary amplifier which can be statistical multiplexed to whichever of the input signal lines requires additional amplification. In an alternate embodiment of the invention each input signal line is coupled to a corresponding amplifier which can be statistically multiplexed to a power supplies of varying output levels depending on the amplification requirements of each of the input signal lines.

Method and apparatus for multi-channel X-DSL line driver

An apparatus and method is disclosed for a digital-to-analog converter (DAC) system with both uniform and non-uniform sampling rates. The system includes a digital portion in which samples of a set of &ldquo;N&rdquo; digital samples are obtained from a digital input stream. Each set of samples is evaluated with various test decimations which may include various combinations of uniform and non-uniform timing intervals between the selected members of each decimation. Each test decimation includes substantially the same number &ldquo;M&rdquo; of digital samples where &ldquo;M&rdquo; is less than the number of samples &ldquo;N&rdquo; in each sample set. Each test decimation is digitally evaluated to determine which is the optimum test decimation. The optimum test decimation exhibits the best fit with the original set of &ldquo;N&rdquo; samples using a reduced set of &ldquo;M&rdquo; digital samples. This optimum test decimation along with the appropriate timing information is subject to an digital-to-analog conversion, with the corresponding analog output signal retaining a high degree of fidelity with the digital input signal albeit at a reduced average sampling rate. The reduction in sampling rate for the DAC simplifies circuit design and reduces power requirements.

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Fremont, CA, United States of America

Dale Smith