Lucent Technologies Inc.

At&t Bell Laboratories

Bell Telephone Laboratories

Legerity, Inc.

Other

American Telephone and Telegraph, Co.

Dewayne Alan Spires

John C Gammel

Robert K Chen

Robert Kuo-Wei Chen

Donald Lars Duttweiler

Frode Larsen

Apurba Roy

Ian A Schorr

Joseph Elide Landry

Douglas G Marsh

Joseph H Havens

Dean Michael Umberger

Robert H Vaiden

Ronald Joseph Rees

Joseph F Carriere

Wilmer B Gaunt, Jr

Andrew J Marsh

Paul W Frazier

Lynn Emery Ditty

Randy Lee Hafer

Nuri Ruhi Dagedeviren

Christine Mary Gervesh

Gerard Joseph Pepenella

Denis W Aull

Kenneth A Houck

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

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

Quantization noise, introduced into data transmission when analog signals are translated into PCM code using the logarithmic conversion of &mgr;-law or A-law rules necessary to accommodate the transmission of voice signals, limits the maximum attainable speed of data transmission. However, when the PCM code signals represent data (rather than voice signals), linear conversion of analog data signals into the PCM code would avoid such logarithmic quantization noise. To signal the translating codec that a digital modem call is being made, the digital modem allocates one or more of the least significant bit positions of the code representing the 2100 Hz answer-tone-with-phase-reversal (specified in ITU-T Recommendation G. 165) to send a repetitive pattern &ldquo;P &rdquo; to signal to the associated codec that a digital modem connection has been made. When the codec detects the P pattern it will linearly convert analog data signals into PCM code, thereby reducing the introduction of logarithmic quantization noise.

Data optimized codec

The present invention is directed to an integrated circuit comprising a voltage source and a voltage sensing circuit having a switch circuit for sensing a switch voltage and a switch current; a voltage comparison circuit connected to the switch circuit for comparing the switch voltage to a limiting voltage; and a current limiting circuit connected to the switch circuit and the voltage comparison circuit, which is capable of limiting the switch current when the switch voltage reaches or exceeds the limiting voltage. In a preferred embodiment of the invention the switch circuit is a bi-directional switch circuit and the voltage comparison circuit incorporates a series of Zener diodes, wherein the current limiting circuit is a current foldback circuit.

Voltage sensing current foldback switch circuit

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 reference voltage source has at least one transistor having a base, emitter and collector electrode operating in an active state that has an inherent voltage drop between its base and emitter electrodes to generate a low noise core voltage which is applied to the input of an amplifier to set the amplifier operating point, and thereby the amplifier output, which is the reference voltage. The reference voltage is temperature compensated by providing the amplifier with a feedback loop, or by altering the core voltage applied to the amplifier, or by altering the gain of the amplifier. Several transistors can be connected in series and their base to emitter voltage drops added to change the core voltage value.

Partially temperature compensated low noise voltage reference

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.

Subscriber line interface and power circuit

Resistive circuits are provided at the tip and ring of the battery feed circuit as a method of alleviating the need for bulky DC transformers or complex integrated circuitry. The voltage is monitored through a set of comparators eliminating the expense of maintaining fused resistors. The voltages for voice or data transmission is amplified prior to being transmitted. Received signals are AC coupled, with proper biasing, onto the tip and ring lines. Any AC noise on the tip and ring line is shifted 180 degrees out of phase and re-inserted on the line to cancel the noise. As an enhancement to the battery feed circuit, another voltage comparator is added to check the line for DC current signifying an off hook condition.

Battery feed circuit

To accurately detect the short bursts of distinctive ringing signals within 100 milliseconds, a magnitude comparator produces a binary signal indicative of whether the instantaneous tip-ring voltage exceeds a predetermined magnitude. The binary signal is integrated over a predetermined period of time controlled by a timer. If the time integral is below a first predetermined value, the absence of ringing is detected; if above a second predetermined value, ringing is detected; if in between, the integrating interval is extended until the integral falls outside the two values.

Telephone ringing detector

To produce a high current carring inductor with a high inductance value in space normally too small, a transformer is chosen which meets space requirements and has a primary winding of sufficient current capacity, but too little inductance. A bidirectional current source drives the secondary winding under control of a feedback circuit in response to sensed primary winding current to effectively multiply the primary winding inductance.

Electronic inductor

A relay load is connected in the collector path of a first transistor (Q1) of high current carrying capacity. A second transistor (Q2) of similar conductivity type is effectively coupled across the first transistor. The bases of said first and second transistors are connected together. A current mirror circuit (Q3-Q6) is coupled from the collector of said second transistor to said bases to provide the additional base drive necessary to drive the first transistor towards saturation regardless of its Beta when maximum load current is required. The mirror circuit is designed so that the effects of transistor V.sub.be mismatches in the mirror are minimized.

Relay driver

A telephone line circuit comprises a transformer that has a primary (13) and a secondary (14) winding. A low resistance (15) is connected in series with the primary winding. An amplifier circuit (17) is coupled across the resistance and serves to develop a predetermined dc control voltage. This control voltage is used to establish a dc current flow in the secondary which is n times that of any dc current flow in the primary, where n is the transformer turns ratio. The dc current flow established in the secondary is in a direction opposite that of the dc current flow in the primary. A second amplifier circuit (31, 36, 23) is coupled across the primary winding and serves to generate an ac control signal which is also delivered to the secondary winding to create a predetermined ac termination impedance.

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Plaistow, NH, United States of America

Dewayne Alan Spires