Legerity, Inc.

Lucent Technologies Inc.

Other

John C Gammel

Dewayne Alan Spires

Robert K Chen

Robert Kuo-Wei Chen

Apurba Roy

Joseph H Havens

Robert H Vaiden

Ronald Joseph Rees

David Paul Chabinec

Andrew J Marsh

Paul W Frazier

Randy Lee Hafer

Dean Umberger

Christine Mary Gervesh

A capacitor cancellation method and apparatus for use in an interface circuit having a transformer blocking capacitor. The method includes sensing a voltage across the transformer blocking capacitor and generating a cancellation signal to compensate for the effect of the transformer blocking capacitor. The apparatus includes a sensor to sense a differential voltage across the transformer blocking capacitor to develop a capacitor signal and an amplifier to amplify the capacitor signal to obtain a cancellation signal.

Capacitor cancellation method and apparatus

A subscriber-line interface circuit (SLIC) has tip and ring amplifiers connected to the tip and ring lines, respectively, of customer premises equipment (CPE). The SLIC returns the ringing signal (provided to the CPE from a power supply connected to the CPE's ring line), to ground or to battery, through the SLIC's tip amplifier. In one embodiment, the SLIC has three switches: S1 connecting the power supply to the ring line, S2 connecting the ring amp to the ring line, and S3 connecting the tip amp to the tip line. During ringing, S1 and S3 are closed to return the ringing signal to ground through the tip amp, which is preferably driven to saturation during ringing to reduce power consumption. By eliminating the fourth switch that appears in prior-art SLICs (e.g., connecting the tip line to ground), SLICs of the present invention can be smaller and therefore less expensive to implement.

Returning ringing signals through the tip amplifier of subscriber-line interface circuitry

An impedance warping circuit (IWC) and technique for compensating the effect of a blocking capacitor within a transformer of an interface circuit for passing plain old telephone service (POTS) band and asynchronous digital subscriber line (ADSL) band signals on signals having frequencies in the POTS band. The IWC does not significantly affect the performance of the interface circuit in the ADSL band. The IWC synthesizes impedance to compensate the frequency-dependent deviation in the termination impedance across the tip/ring lines. The resulting termination impedance may be designed to conform to the Telcordia Standard of 900 &#x3a9;+2.16 &#x3bc;F or other telecommunication standards throughout the entire POTS band.

Frequency-dependent impedance synthesis for DSL interface circuits

An amplifier having an improved output current drive capability includes an input stage and an output stage. An input of the output stage is operatively coupled to an output of the input stage. The amplifier further includes a current regeneration circuit operatively coupled to the input of the output stage in a feedback arrangement, the current regeneration circuit feeding back a current to the output circuit in accordance with a predetermined scale factor, the fed back current being proportional to an input current supplied to the output stage. The input current supplied to the output stage is dynamically adjustable by the current regeneration circuit in response to an input current requirement at the output stage.

Amplifier circuit with regenerative biasing

Automatic testing a group of line circuits on a smart line card served by a central switch over a PCM bus is localized by using the microprocessor/DSP that provides codec functions for the group of line circuits. Tests such as DC overhead that are not performable by the central switch over the PCM bus are performed by the microprocessor/DSP when informed by the central switch that at least one of the channels is not processing voice signals. The microprocessor/DSP controls test switches on the line card to set-up various test terminations for the idle circuit as well as to selectively control the gain of the idle channel's amplifiers. The microprocessor/DSP synthesizes test tones and executes test tone detection processes within the time slot intervals accorded by the central switch to the idle channel. Among the tests performed are Forward Loop Gain with different resistance terminations, cable and fuse tests, DC overhead, and idle channel noise utilizing a limited number of test routines such as tone generation, DC generation, discrete Fourier transform, peak detection and variance from acceptable limits. The pass/fail condition of the idle channel under test is reported to the central switch.

Self-testing of smart line cards

A line circuit whose circuit components are selectively controllable by a microprocessor/DSP to provide normal BORSCHT functions or to be selectively tested without need for an electromechanical relay to isolate the line circuit from the loop conductors. The conventional line transformer is advantageously replaced by a loop current feed resistor network and either a high voltage or a lower voltage battery may be connected to provide loop current to the resistor network through a current regulator circuit and battery switch circuit. In normal operation, an ac feedback path, which includes the line receive amplifier, increases the terminating impedance above the dc value of the feed resistors so the loop termination resistor network may match the characteristic impedance of the loop at the audio frequencies employed. In the testing mode, the microprocessor/DSP selectively applies or denies power to the line driving and receive amplifiers as well as to a level shifting circuit interposed between the codec analog output and the input to isolate or include these components or to provide a codec loop-back path. The condition of the dc feed resistors and protective fuses, the condition of the loop closure detector and of the ringing generator are reported to the microprocessor/DSP over the same terminal normally used for reporting the on-hook and off-hook status of the loop.

Self-monitoring line interface circuit

A line circuit provides BORSCHT functions and supplies the customer loop through a feed resistor network and current limiter either from a high voltage battery to provide for maximum signaling range or from a lower voltage battery to conserve power. The current limiter operates under the control of a microprocessor/DSP which selectively applies or denies power to isolate or include components for testing and controls the switching in and out of transistors to control the scaling factor between the channel width-to-length ratios of the current mirror's input and output FET transistors according to the type of test or operating condition dictated by the microprocessor while the input reference current to the current mirror is maintained constant.

Dual voltage, self-monitoring line circuit

A subscriber line circuit which truly implements all of the BORSCHT functions and which does not rely on an external ringing generator to provide the ringing voltage when needed is disclosed. This implementation is achieved by recognizing that supervisory and ringing signals occur in some sort of sequence and, therefore, do not have to be generated simultaneously. Based on this recognition, we provide a circuit which truly implements all of the BORSCHT functions and includes a power section that generates each of the supervisory signals, e.g., -48 volts and -24 volts, and alerting signal, e.g., ringing signal, in turn and as required.

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Birdsboro, PA, United States of America

John C Gammel