Paradyne Corporation

Ramon B Hazen

Thomas Jeffrey Bingel

William Lewis Betts

Robert Earl Scott

Gordon F Bremer

A plain old telephone system (POTS) device, for example but not limited to, a telephone, facsimile machine, analog modem, caller identification (ID) system, speaker phone, cordless phone, etc., employs an on-board transistor-based linear polarity guard to enable decoupling of a POTS channel from one or more xDSL channels on a telephone connection (subscriber loop associated with a public service telephone network), while reducing undesirable interference, such as intermodulation distortion imposed upon the POTS and xDSL channels. Transistors associated with the polarity guard are operated in the ohmic region, or in a nonsaturated linear mode, to achieve a substantially linear transfer function through the transistors and through the overall linear polarity guard. Current that is input to the polarity guard and the voltage drop across the transistors that conduct the current in the polarity guard exhibit a substantially linear relationship, or linear VI transfer function. Hence, the VI relationship between the overall output voltage and overall input current of the polarity guard is substantially linear in the operating region of the polarity guard.

Linear polarity guard and method for DSL-ready pots devices

A plain old telephone system (POTS) device, for example but not limited to, a telephone, facsimile machine, analog modem, caller identification (ID) system, speaker phone, cordless phone, etc., employs an on-board POTS filter to enable reliable and efficient decoupling of a POTS channel from one or more xDSL channels on a telephone connection, while permitting and not interfering with the xDSL channels. The POTS device, which connects to a subscriber loop associated with the public service telephone system, includes a subscriber loop connection switch (for example, a hook switch), a POTS transmitter, receiver, or transceiver, and a low pass filter interconnecting the subscriber loop connection switch with the transmitter, receiver, or transceiver. The switch effectively isolates the POTS filter from the telephone line when the POTS device is disconnected, or is on hook, and interfaces the telephone line through the POTS filter to the POTS transceiver when the POTS device is connected, or is off hook. The arrangement enhances DSL device performance, network stability, sidetone, ringer load, and termination impedance and allows greater flexibility in the choice of filter elements, in that passive and active elements can be utilized and in that filters of higher order can be employed.

DSL-ready pots device and method

A central office (CO) filter system connects between a CO telephone switch and a telephone connection (subscriber loop) that can communicate voice and digital data channels. The CO filter system suppresses transients and harmonics on the connection caused by a telephone ring signal (typically, 90 to 150 Vrms at 15 to 68 Hz) generated by the switch in order to minimize adverse effects on the digital data channel on the connection. Architecturally, the CO filter system includes a first filter designed to implement a first low pass filter function to attenuate frequencies higher than a ring signal so that transients and harmonics produced from the ring signal are suppressed, a second filter designed to implement a second low pass filter function to attenuate frequencies higher than a voice channel, and a current detector designed to detect when a telephone is off-hook. The current detector implements the first filter when the telephone is on-hook, particularly, when the ring signal occurs, and implements the second filter when the telephone is off-hook.

Central office filter system and method

A filter system (and associated filtering method) is disclosed, the filter system being connected between a large-amplitude, high-frequency noise source and a frequency-division multiplexed communications channel. The large-amplitude, high-frequency noise commonly being a POTS (plain old telephone service) ring signal generated by a CO (central office) telephone switch. The frequency-division multiplexed communications channel generally used to carry digital signals at frequencies above the POTS baseband in order to implement a digital subscriber line (DSL). Large-amplitude, high-frequency signal components from the POTS ring signal impair the performance of frequency-division multiplexed channels on a transmission line such as a subscriber loop. The filter system of the present invention utilizes amplitude and also may utilize frequency to selectively suppress the transients and harmonics on the transmission line caused by a telephone ring signal. In addition, the present invention uses bidirectional current limiting filters to implement some of the amplitude-dependent filtering behavior.

Filter system and method to suppress interference imposed upon a frequency-division multiplexed channel

The present invention provides a method and apparatus for eliminating or reducing local area and broad area interference in a twisted pair transmission system. The apparatus of the present invention includes a detection device, such as an antenna, for example, for detecting electromagnetic interference coupled into a twisted pair line, a sampling/scaling device which samples and scales the detected signal, and a combiner device which combines a signal correction component with the signal received over the twisted pair by a differential receiver. The sampling/scaling device preferably includes an analog-to-digital converter (ADC) which converts the detected analog signal into a digital signal and a digital signal processor, which receives the digital signal from the ADC and processes the signal to generate a correction signal. The correction signal is then subtracted from the signal received by the differential receiver. The sampling/scaling device may be fixed or adaptive.

Method and apparatus for reducing interference in a twisted wire pair transmission system

The present invention provides a method and apparatus for eliminating or reducing local area and broad area interference in a twisted pair transmission system. The apparatus of the present invention comprises a detection device, such as an antenna, for example, for detecting electromagnetic interference coupled into a twisted pair line, a sampling/scaling device which samples and scales the detected signal, and a combiner device which combines a signal correction component with the signal received over the twisted pair by a differential receiver. The sampling/scaling device preferably comprises an analog-to-digital converter (ADC) which converts the detected analog signal into a digital signal and a digital signal processor which receives the digital signal from the ADC and processes the signal to generate a correction signal. The correction signal is then subtracted from the signal received by the differential receiver. The sampling/scaling device may be fixed or adaptive. If the interference is stationary in time, a fixed sampling/scaling device is suitable for use with the present invention. If the interference is non-stationary, preferably the sampling/scaling device will be adaptive such that the amount of scaling performed can be altered in accordance with changes in the interference signal detected by the detector.

A far-end modem transmits a 'pilot tone' during the time that a near-end modem is training its echo canceler. Correspondingly, the near-end modem is modified to notch, or filter, out this pilot tone from the received signal. The filtered received signal is then used by the near-end modem to train its echo canceler.

Half-duplex echo canceler training using a pilot signal

A processor of a cellular modem monitors for the presence of a residual echo signal during a full-duplex portion of a training sequence. In particular, the processor monitors an equalizer error signal during a full-duplex training phase that follows the half-duplex training phase for the echo canceler. If the processor detects a level of the error signal greater than a predefined threshold, the processor presumes the increase in the error signal is due to the presence of a residual echo signal and performs a predefined adjustment of the taps of the corresponding echo canceler of the cellular modem.

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Redington Beach, FL, United States of America

Ramon B Hazen