Integrated Telecom Express, Inc.

Man Ho Ku

Ming-Kang Liu

Yukuang Wang

Po-Sheng Chou

Wai-Hung Leung

Ying-chang Chen

An analog front end (AFE) circuit used in a high-speed communications system is presented that includes multiple stages each including a bandpass filter, base band modulator, low pass filter and Sigma-Delta modulator. Each stage processes a fractional portion of the total frequency of a wide bandwidth analog signal. The number of such AFE stages is configurable in parallel to process the entire bandwidth of the received signal. The AFEs can be incorporated in a single integrated circuit or similar suitable manner so as to be modular, and easily replaceable/upgradeable. To achieve minimum quantization noise and reduce manufacturing costs, the Sigma-Delta modulators in each AFE are made to have identical characteristics. Because the wideband signal is broken down into smaller frequency portions, the sampling rate, and thus the complexity and cost associated with the AFEs, is reduced significantly. In a preferred embodiment, a number of such AFEs are used in an ADSL modem for processing separate but roughly equal portions of the wideband ADSL signal containing data carrying DMT sub-channels. The separated portions are re-combined in a DMT receiver logic circuit to reconstruct the original data stream.

Multiple low speed sigma-delta analog front ends for full implementation of high-speed data link protocol

A tone detector includes at least one circuit (hereinafter &ldquo;single phase reference matcher&rdquo;) that not only performs a convolution of an input signal with a reference signal, but also compares the result of convolution with a threshold to determine if there is a match, and if so drives a signal active indicating that tone is present. If there is no match, another circuit (hereinafter &ldquo;phase shifter&rdquo;) delays the reference signal by a fraction (e.g. &frac18;) of the measuring period, thereby to introduce a phase shift (e.g. &pgr;/8) between the input signal and the reference signal. The &ldquo;single phase reference matcher&rdquo; again performs the just-described operation, this time with a delayed reference signal, and repeats the operation as often as necessary (e.g. eight times) to cycle through the entire measuring period, thereby to ensure that tone (if present in the input signal) is detected irrespective of phase, during one of the operations. The smaller the phase shift, the greater the number of times the operation is repeated, and vice versa. A tone detector of the type described herein can include more than one &ldquo;single phase reference matcher,&rdquo; each of which performs one of the above-described operations in parallel, thereby to reduce the total time required to perform all operations. The number of samples over a measurement period is selected to minimize the noise, e.g. by selecting a number based on the input frequency and difference in frequency with the nearest adjacent frequency at which another tone may be present.

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Milpitas, CA, United States of America

Man Ho Ku