Abstract: Systems and methods for wideband RF interference detection and suppression include an open-circuit stub, a first voltage peak detector, a second voltage peak detector, an analog-to-digital converter (ADC), and a controller. The open-circuit stub is configured to receive an input signal. The first voltage peak detector is coupled at the open end of the open-circuit stub and configured to output a first voltage signal based on a portion of the input signal. The second voltage peak detector is coupled a distance away from the open end of the open-circuit stub and configured to output a second voltage signal based on the portion of the input signal. The controller is configured to generate an output control signal operable to adjust a signal filter based on the first digital voltage signal and the second digital voltage signal to suppress the portion of the input signal.

Abstract: Disclosed herein are implementations of a hybrid network for use in a full duplex communication system. In one aspect, the hybrid network includes a first circuit coupled between an output of a communication channel and a shared output of a transmitter and the communication channel, a second circuit coupled between a first output of the transmitter and the shared output, a third circuit coupled between the shared output and an input of an amplifier, a fourth circuit coupled between the input of the amplifier and a second output of the transmitter, and a fifth circuit coupled between an output of the amplifier and the input of the amplifier. In some embodiments, the output of the amplifier is coupled to an input of a receiver.

Abstract: An electrical balance duplexer has multiple impedance gradients and multiple impedance tuners. The electrical balance duplexer transmits an outgoing signal from a transmitter during a transmission mode when a first set of impedance gradients of the multiple impedance gradients is operating in a first impedance state and a first set of impedance tuners of the multiple impedance tuners is operating in a second state. The electrical balance duplexer isolates the outgoing signal from a receiver during the transmission mode when a second set of impedance gradients of the multiple impedance gradients and a second set of impedance tuners of the multiple impedance tuners are operating in the second impedance state.

Abstract: An echo reducer includes: an obtainer configured to obtain frequency characteristics of a transmission system from a sound emitter of a sound emission and collection device to a sound collector of the sound emission and collection device; a determiner configured to determine whether or not both a transmission signal and a reception signal in the sound emission and collection device are in a state of including a sound; and an attenuator configured to attenuate the reception signal to be output to the sound emitter, by attenuation characteristics corresponding to the frequency characteristics of the transmission system that the obtainer obtains, when the determiner determines that both the transmission signal and the reception signal in the sound emission and collection device include a sound.

Abstract: A generator has a voltage regulator that includes a first control unit for lowering an output voltage of the generator when a first maximum value is exceeded and a second control unit for lowering the output voltage either when a first maximum value is exceeded or when a second maximum value that is different from the first maximum value is exceeded.

Abstract: A portable battery operated communication device provides a device interface formed of a plurality of exposed device contacts including a live voltage contact and a GND contact. Electronic circuitry associated with the interface is configured to operate in a non-linear mode using a low leakage path in response to electrolytic contamination across the two contacts. The interface is further configured to operate in a linear mode using a low current path during accessory attachment. Accessory detection is provided by a non-linear impedance device and sensor.

Abstract: A PHY is coupled across split primary windings of an isolation transformer for differential data transmission and reception between PHYs and for DC isolation. Positive and negative low impedance terminals of a DC power supply are coupled to first and second secondary windings of the transformer as split center taps of the transformer. Respective ends of the wires in the wire pair are coupled to the other ends of the secondary windings. Therefore, the power supply conducts DC current through the secondary windings, while the differential data signals also flow through the secondary windings, generating corresponding differential data signals at the inputs to the PHY. The transformer also attenuates common mode noise. Therefore, the circuit makes multi-use of the isolation transformer, allowing fewer components to be used for the DC coupling, wire termination, and common mode noise cancellation.

Abstract: An acoustic signal processing system and method. In accordance with an embodiment, the acoustic signal processing system includes an adaptive filter that filters a signal from a frequency band reservation module and generates a filter signal that is received by a subtractor. The subtractor generates an error signal that is used by a double-talk indicator module to generate a control signal that indicates the presence of double-talk.

Abstract: Systems and methods of the disclosed subject matter for converting light into electrical signals are provided including receiving light input and outputting electrical signals proportional to the light input with a sensor, increasing a transimpedance gain of an amplifier to amplify the electrical signals with a T-network of resistors coupled to the amplifier and the sensor, filtering the electrical signals with a filter circuit coupled to the amplifier and the T-network of resistors to increase noise rejection in a predetermined frequency range, and outputting the filtered electrical signals.

Abstract: A touch device and a sensing compensation method are provided. The touch device may include a touch panel, a sensing compensation circuit and a sensing circuit. The sensing compensation circuit may be coupled to the touch panel for providing a compensation-impedance according to features of the touch panel. The sensing circuit may be coupled to the sensing compensation circuit. The sensing circuit receives touch information compensated by the sensing compensation circuit.

Abstract: A cable signal detector for being provided at a connector at an end of a communication cable transmitting differential signals or at a relay connector to be connected to the connector to detect an existence of information communication. The cable signal detector includes an amplifier circuit that branches and extracts a portion of a signal transmitted through the communication cable, amplifies the extracted signal and outputs the amplified signal, and a display portion that display the existence of information communication based on the output of the amplifier circuit. The amplifier circuit is mounted on a detection device formed separately from the connector or the relay connector. The connector or the relay connector is configured to transmit the extracted signal to the detection device.

Abstract: A threshold control system for controlling a non-linear processor in an echo canceller, the non-linear processor being configured to remove any signal energy below a threshold that remains in a microphone signal after the echo canceller has subtracted an echo estimate from it, the threshold control system comprising a convergence unit configured to determine an indication of the stability of an adaptive filter, the adaptive filter being configured to continuously model an echo path so as to generate the echo estimate, and a threshold tuner configured to adjust the threshold of the non-linear processor in dependence on the indication.

Abstract: A combined sidetone and hybrid balance apparatus and method of operating same are disclosed. An embodiment of the present invention may provide both a hybrid balance mode of operation and a sidetone generation mode of operation within a single integrated circuit device. The functionality provided by an embodiment of the present invention may be used in both Internet protocol (IP)-based telephones and residential gateways, and may be incorporated within the IP telephone chip used in such devices. An embodiment of the present invention may be used to reduce processor demand and the cost of materials, permitting greater IP telephone or residential gateway functionality at lower cost.

Abstract: A differential transformer-free hybrid circuit includes a first amplifier configured to receive a first signal from a transmitter and output the first signal to a telephone loop, and a second amplifier configured to receive a second signal from the telephone loop and output the second signal to a receiver. Further, the differential transformer-free hybrid circuit also includes at least one balanced network element and a transformer-less interface configured to couple the first amplifier and the second amplifier to the telephone loop, wherein the transformer-less interface includes at least one current blocking device.

Abstract: A method of selecting an optimum impedance for a loop start trunk line, comprising successively applying respective ones of a plurality of impedance settings to the loop start trunk line, for each impedance setting measuring the impulse response of the trans-hybrid echo path by applying audio test signals to obtain a time-domain trans-hybrid transfer function and deriving a frequency-domain spectrum representative of trans-hybrid loss, and then calculating figure of merit of the transfer function based on the power spectrum. Once all impedance settings have been tested, the optimum impedance is selected as the impedance setting associated with the highest calculated figure of merit.

Abstract: A medium access control (MAC) entity first computes an achievable rate region based on a total transmit power limit and a channel gain of each of a plurality of WTRUs. Next, the MAC entity selects an order of DPC among the WTRUs. A rate set for use in transmitting to the WTRUs is then selected, said rate set being within the computed achievable rate region. Then, based on the selected DPC order and rate set, a DPC entity performs DPC on a plurality of data streams intended for the plurality of WTRUs. If nested lattice-based DPC is utilized, rate compatibility is achieved by selecting proper nesting ratios corresponding to a desired data rate set. Otherwise, if binary-code based DPC is utilized, rate compatibility is achieved via selecting appropriate message input sizes for input to point-to-point coding units prior to performing DPC.

Abstract: A transceiver for a transmission and reception signal which can be transmitted via a signal line having a particular line impedance (ZLINE), having a line driver (6) for driving a transmission signal via the signal line and having an analog echo cancellation filter (15) for signal suppression for an echo signal brought about by the transmission signal, where the line driver (6) has a synthesized output impedance (RSYN), with the line driver (6) having a downstream hybrid circuit (11) for connecting an analog echo cancellation filter (15).

Abstract: An improved data access arrangement device for use in full-duplex two-wire communication systems having a transmission impedance characteristic. The DAA includes a transmit amplifier and a receive amplifier adapted for connection to a two-wire line, a codec connected to the transmit amplifier for generating a transmit signal, a summation device connected to the receive amplifier, an echo cancellation path including a variable gain amplifier, where the path extends between the codec and the summation device, and wherein the variable gain amplifier is adjusted in accordance with the transmission impedance characteristic. The variable gain amplifier may include a gain register that is programmed by a microprocessor, or may have the gain set by user-configurable switches. The summation device is preferably an operational amplifier.

Abstract: An analog electronic circuit is placed between the central office of a telecommunications provider and the customer premises equipment of a digital subscriber line system which uses unshielded twisted pair wires (“UTP”). The electronic circuit separates the downlink signals from the uplink signals with a first mixer. The voice signals, if present, are routed around the electronic circuit unmodified. The downlink signals are amplified, filtered, amplified again with a one or more peaking equalization amplifier, then amplified with drivers which provide the power to drive the downlink signal through a second mixer onto the UTP lines to the customer premises equipment. The electronic circuit separates the uplink signals from the downlink signals with the second mixer. The uplink signals are amplified, filtered, and amplified again, then driven onto the UTP connected with the central office through the first mixer.

Abstract: A central office modem (50) that includes the capability of single-ended loop testing (SELT) is disclosed. The modem (50) includes a digital signal processor (54), a codec (56), line driver and receiver circuitry (58), and a hybrid circuit (60), by way of which a subscriber loop (LOOP) can be driven and sensed. The line driver and receiver circuitry (58) may include a transformer (74a, 74b) for driving the loop (LOOP), or the output may be capacitively coupled. The line driver and receiver circuitry (58) includes active termination, by way of operational amplifiers (80a, 80b). Switches (82a, 82b; 84a, 84b) are provided to selectively enable and disable the active termination function, and to selectively bypass or include the hybrid circuit (60). This control of the line driver and receiver circuitry (58) provides the ability to calibrate out its own characteristics, providing high precision SELT measurements of the load impedance type, and of frequency domain reflectometry, and time domain reflectometry.

Abstract: An improved analog front end and methods for increasing the power efficiency of duplex signals on a transmission line are disclosed. The improved analog front end bifurcates a hybrid into a fixed portion and an adaptive portion. The adaptive portion combines a biquad and a summer to produce a filter transfer function suited to compensate for transmission line irregularities. A method for configuring a local transceiver to minimize power requirements at a remote transmitter is disclosed. Broadly the method entails, applying a transmit signal to a front end in the absence of a remote signal; optimizing the transmit signal power; recording the reflected transmit signal; applying an adaptive filter in response to transmission line irregularities; and controllably adjusting the adaptive filter to minimize the amplitude of the reflected version of the transmit signal in the receive path. A method for recovering a remotely generated signal is also disclosed.

Abstract: A communication system that permits the coexistence of a plurality of ultrawide band (UWB) radio communication networks that use different signal systems is achieved by using the same beacon signal and specifying the format of part of the control command among a plurality of UWB radio communication networks that use different signal systems, as defined, for example, by impulse period, impulse width, spreading ratio, and spreading code. When one UWB network receives a beacon signal from another UWB network, judging from the received beacon signal it grasps the transmission parameter that is used by another party and performs time-division on the transmission frame period for its own system.

Abstract: Echo return loss is analyzed to determine if the near end connection of a communication link has hybrid induced echo. If the echo return loss is above a threshold value for a predetermined period, than no echo or very little echo is present. The lack of echo is treated as a four wire connection and the near end signal is processed accordingly. If the foreground and background filter update relationship indicates the presence of a hybrid or if the echo return loss drops below a second threshold, the condition of the near end signal is treated as a two wire hybrid induced echo. The analysis of the near end signal continues and treatment of the signal may switch between four wire and two wire any number of times during a communication link.

Abstract: An improved line driver-hybrid and method for increasing the power efficiency, signal accuracy, and stability of a transmit signal on a transmission line are disclosed. The improved line driver-hybrid uses a negative feedback control loop, thereby enhancing operational stability and suppressing both amplifier imperfections and discrete component manufacturing variances. Furthermore, the improved line driver-hybrid provides a power efficient full duplex solution for line driver applications. The present invention can also be viewed as providing a method for actively terminating a transmission line.

Abstract: In at least one embodiment, a current mode differential active hybrid circuit having an H-bridge output driver with a first output resistor coupled across a transmission medium output. Drive circuitry is coupled to the output H-bridge and constructed to supply data modulated signals to the output H-bridge. A second H-bridge is coupled to the drive circuitry in parallel with the output H-bridge to allow a second output across a second output resistor.

Abstract: An improved data access arrangement device for use in full-duplex two-wire communication systems having a transmission impedance characteristic. The DAA includes a transmit amplifier and a receive amplifier adapted for connection to a two-wire line, a codec connected to the transmit amplifier for generating a transmit signal, a summation device connected to the receive amplifier, an echo cancellation path including a variable gain amplifier, where the path extends between the codec and the summation device, and wherein the variable gain amplifier is adjusted in accordance with the transmission impedance characteristic. The variable gain amplifier may include a gain register that is programmed by a microprocessor, or may have the gain set by user-configurable switches. The summation device is preferably an operational amplifier.

Abstract: A hybrid circuit models a plurality of attributes of a communication system including a subscriber line coupled to a line interface circuit. The plurality of attributes includes subscriber line impedance, and impedance of a coupling transformer. The attributes are based on other factors, such as whether or not bridge taps exist at or near the line interface circuit on the subscriber line. The plurality of attributes are modeled by a specific arrangement of resistive and capacitive elements to substantially duplicate the collective transformative effects of the attributes on a transmission signal being sent out on the subscriber line. The transmission signal is transformed and provided to an output, where it is subtracted from a composite signal representing a combination of the actual transformed transmission signal and a receive signal. The subtraction yields an isolated receive signal, which is later processed to recover the full receive signal.

Abstract: Improved data communication for modems having digital identification information capability.

Abstract: A network interface circuit employs an extended feedback circuit topology for impedance matching across a high voltage boundary between a line side portion and low voltage portion of a network. The network interface circuit includes an operational amplifier-based circuit which is responsive to a signal applied from user equipment on the low voltage portion. Specifically, the present invention includes a transmit path having a first, second, and third amplifier circuit and an impedance element, and a receive path that includes a transfer function implemented as a second order low pass filter for correcting amplifier gain and phase effects in the complex feedback loop of the circuit. The output impedance is remotely set by multiplying the impedance element by a scale factor to match the network impedance. The feedback loop is extended across the high voltage boundary using high voltage interfaces such as linear optical coupling devices (LOCs).

Abstract: A signal matching apparatus for exchanging signals between a digital switching system and a two-wire long distance subscriber line signal switching system comprises a first PCM equipment for converting a 4-wire E1 signal of the digital switching system into a 4-wire analog signal, and for connecting a 4-wire analog signal of the long distance subscriber line signal switching system into a 4-wire digital signal transferred to the digital switching system, and a second PCM equipment for converting the 4-wire analog signal of the first PCM equipment into a 2-wire signal, and for converting the analog signal of the long distance subscriber line signal switching system into a 4-wire analog signal transferred to the first PCM equipment.

Abstract: An order wire accommodation system comprises four interface boxes each of which has the same order wire interface section as the others. The order wire interface section has a circuit which digitally adds order wire signals of the transmission lines from two ports and the order wire signals which interface with the other interface boxes or a telephone through the other two ports. Each output from the order wire interface section is a sum of all the order wire signals inputted except for those of the order wire interface section itself. Because of a provision of two ports which interface externally, the interface boxes can be cascaded connected to one another, by which order wire communications among all the transmission lines accommodated in the interface boxes become possible. Further, the order wire accommodation system can be minimized and be simplified.

Abstract: The present invention provides a two-wire line conditioning apparatus having an improved calibration and cancellation circuit and provides an improved calibration method using a multitone calibration signal. The output is monitored by an AGC circuit which controls the output, and prevents hard clipping. This is particularly important for DTMF receivers. Additionally, the apparatus automatically adjusts an electronic hybrid as part of a calibration procedure so as to eliminate undesirable echo effects when calls are placed along the line. The electronic hybrid balancing process and echo cancellation circuitry may also be utilized in a circuit for converting four-wire communications systems to two-wire communications systems. The line conditioning device of the present invention utilizes a multitone signal to simulate the voice frequency spectrum between approximately 500 Hz and 3500 Hz to probe the line side with a plurality of tones (e.g., 500, 1500 and 3500 Hz; or 500, 1000, 1500, 2000, 2500, 3000, 3500 Hz).

Abstract: The present invention provides a two-wire line conditioning apparatus having an improved calibration and cancellation circuit and provides an improved calibration method using a multitone calibration signal. The apparatus automatically adjusts an electronic hybrid as part of a calibration procedure so as to eliminate undesirable echo effects when calls are placed along the line. The hybrid has capacitors and resistors which can be switched into and out of the circuit by using simple transistor devices. The electronic hybrid balancing process and echo cancellation circuitry may also be utilized in a circuit for converting four-wire communications systems to two-wire communications systems. The line conditioning device of the present invention utilizes a multitone signal to simulate the voice frequency spectrum between approximately 500 Hz and 3500 Hz to probe the line side with a plurality of tones (e.g., 500, 1500 and 3500 Hz; or 500, 1000, 1500, 2000, 2500, 3000, 3500 Hz).

Abstract: An adaptive handset interface for interfacing a two-wire analog telephone instrument to a telephone set having a base unit connected to a handset via a four-wire handset cable. The interface is suitable for use with a variety of telephone sets produced by different manufacturers despite differences in the signalling between the telephone base and the handset. This is because, upon initiation of a learning technique, the interface automatically adapts to variations in signalling between the telephone base and handset among the different telephone manufacturers. To use the interface, the handset is unplugged from the handset jack of the telephone base and plugged into a handset jack of the interface. In addition, a four-wire cable is plugged into a telephone base jack of the interface and into the handset jack of telephone base. The interface includes a modular jack for coupling the interface device to the two-wire telephone instrument.

Abstract: A repeater apparatus includes a first trunk circuit for receiving and sending data input from and to a first section of the communication link and a second trunk circuit for receiving and sending data input from and to a second section of the communication link. An Isolating circuit is connected to the first trunk circuit for electrically isolating the first section from the second section. For protecting against an overvoltage condition from the communication network, a protection circuit is operatively connected to the first and second trunk circuits. A controller has a first receiver/transmitter circuit for transmitting data from the first trunk circuit to the second trunk circuit, and a second receiver/transmitter circuit for transmitting data from the second trunk circuit to the first trunk circuit. The controller also produces a signal for indicating the completion of data transmission by the first and second receiver/transmitter.

Abstract: An artificial echo signal generator generates an artificial echo signal from received voice signal data stored in a first data memory and a presumed impulse response outputted from a tap coefficient updater. The artificial echo signal is subtracted from an echo signal from a four-wire/two-wire converter by a subtractor, which then outputs a remainder signal that is stored in a second data memory. An updating time controller determines and outputs an updating time based on the data stored in the second data memory. An updating element selector selects one time element of the updating time from the updating time controller. The tap coefficient updater updates the presumed impulse response so as to approach the impulse response of a true echo path at the selected time element, and outputs the updated presumed impulse response to the artificial echo signal generator.

Abstract: In a subband acoustic echo canceller, FG/BG filters are provided in M ones of N subbands into which the received signal is divided, and adaptive filters are provided in the other remaining subbands. In the respective FG/BG filters, during the detection of a non-double-talk state their transfer logic parts output state signals GD-j, GD-k, . . . and their adaptive operation control parts each apply an adaptation condition signal ADP to the adaptive filter in each of the above-mentioned other remaining subbands when a predetermined number or more of the FG/BG filters output the state signals GD-j, GD-k, . . . The adaptive filter updates the subband estimated echo path coefficient only when it is supplied with the signal ADP.

Abstract: A processor controlled test set for testing special service circuits of a telecommunication system. A microprocessor controls the overall operation of the test set, while a digital signal processor provides high speed timing signals to the various test circuits for generating the wave forms used in testing, as well as analyzes the test result signals that are converted into digital signals. A calibration of the test generator signals as well as the signal measuring path is carried out prior to the test sequence. The digital signal processor also provides gain control over a talking path to maintain stability thereof. An I/O circuit of the test set provides plural communication paths between remote equipment and the test set to initiate and carry out various tests. Processors in the I/O module are effective to convert the various protocols of the serial data, by way of software, to digital bit streams usable by the test set.

Abstract: A method and apparatus for providing a telephone hybrid function is provided. The present invention maximizes dynamic range while providing a receive signal without interference from a transmit signal. The present invention also provides single-ended to differential conversion. The present invention may be practiced with an integrated circuit powered by a telephone line and coupled to the telephone line without the need for a high voltage isolation barrier between the integrated circuit and the telephone line.

Abstract: A communications station (10) couples a bidirectional input-output signal path (16') to two unidirectional signal paths; a transmit signal path (12') and a receive signal path (14'), using a controllable hybrid (20). A feedback control system in the station minimizes the amount of transmit signal appearing at the receive output port (24) of the hybrid (20). The control system spreads the spectrum of a pilot signal (40) by means of a biphase modulator (46) and a pseudorandom generator (42) to produce a spread-spectrum pilot, which is added, in a summer 30, to the transmit signal. The spread-spectrum pilot signal covers the bandwidth of the information signal, and is reflected in an amount and with a phase which depends upon the relative impedance presented to the hybrid (20) by the bidirectional signal path (16').

Abstract: A hybrid circuit for coupling a modem to an external telephone line substantially compensates for and thereby cancels reflected echo. The hybrid includes a transformer coupled between the telephone line and the modem transceiver, which includes a transmitter and a receiver. A matching resistor connected between the transceiver transmitter and the transformer at a hybrid point presents a matching impedance to the telephone line impedance. A feedback network is implemented between the transceiver receiver and transmitter to feed back sufficient voltage into the receive line to cancel echo produced at the hybrid point.

Abstract: Method and apparatus for temperature compensation of transhybrid loss in a data access arrangement (DAA) is provided. A thermal compensation device is situated in proximity to a thermally sensitive device. If devices which dissipate substantial power cause heating of the thermally sensitive device and change its characteristics, the thermal compensation device is also heated and compensates for the changes. Thus, a DAA that is unaffected by temperature changes and self-heating is provided. The DAA is suitable for use with data communications equipment utilizing echo cancelling circuitry, such as CCITT V.32 and V.32 bis modems. When used with such modems, the present invention avoids the need to perform retraining and equalization during changes in DAA operating temperature.

Abstract: An enhanced amplifier for interconnecting a two-wire, bidirectional cable side transmission path and a two-wire bidirectional equipment side transmission path in a communication system includes a first splitter and a second splitter. The first splitter is formed of a cable-to-equipment voltage sense amplifier, a shunt current driver, and a series current compensator for generating a first simulated terminating impedance. The second splitter is formed of an equipment-to-cable voltage sense amplifier, the shunt current driver and the series current compensator for generating a second simulated terminating impedance. Other features disclosed include manual balancing circuitry for manually adjusting the cable side balance networks. Further, a loopback circuit is provided form facilitating remote testing and alignment of the amplifier from the cable side.

Abstract: Analog signals representing individual digital values (+3, +1, -1, -3) of data pass through a telephone line to a receiver. These signals may first be provided in a pseudo random sequence. A linear echo canceller and a first adder at the receiver simultaneously eliminate, to some extent, echo signals resulting from second analog signals transmitted through the telephone line by the receiver. A non-linear echo canceller and a second adder further significantly reduce the echo signals and specifically reduce non-linear components in the echo signals. Adjustable signal delays achieve optimal performance of the linear and non-linear echo cancellers. In one inventive embodiment, each echo canceller includes a memory which stores, for each terminal in such echo canceller, data representing (a) the pseudo random sequence and (b) coefficients for adjusting the signals in such sequence. Such data for each terminal in such echo canceller is recorded in the memory for introduction to the next terminal in the memory.

Abstract: A switching device is presented for the transmission of telecommunication signals between a telephone network exchange and at least one subscriber connected thereto, where the exchange is able to transmit metering pulses, in addition to the voice signal. The signals are transmitted as digital signals between the exchange and the subscriber via a two-wire line, Which is connected with the exchange through a hybrid switching unit. To prevent the metering pulses from interfering with the voice signals, a parallel resonant circuit consisting of an inductance and a capacitor is connected to the two-wire system of the hybrid switching unit, and the receiving branch of the hybrid switching unit has an active and a passive filter connected in series. The passive filter is adjusted for the metering pulse frequency, and a filter that is tuned to the passive filter is used as the active filter, which compensates for a decrease in the NF (low frequency) level caused by the passive filter, with a corresponding increase.

Abstract: A hybrid circuit applies a data sending signal and an inverted data sending signal to the ends of a primary coil, so that the primary coil receives voltages based on the sum of the voltages of the two signals. As a result, the gains of internal amplifiers can be small, thereby maintaining low level voltages in the hybrid circuit. In addition, because the hybrid circuit is balanced, grounding is unnecessary and noise is kept at a low level.

Abstract: A circuit for comparing transmitted and received data frames containing appropriate stuff symbols to detect when a channel is disconnected. Transmit data symbols consisting of frames of user data, each with a constant number of symbols, are separated by a sequence of symbols known as the frame pattern. At the end of each data frame, just before the next frame pattern, a small number of stuff symbols are added into the frame. The stuff symbols injected in the transmit signal are chosen to be identical to the last scrambled data symbol in the frame of user data. Stuff symbols in a recovered receive signal are chosen to look identical to data symbols which were scrambled at the remote transceiver. A frame-by-frame comparison between the transmit stuff symbols and the next received stuff symbols is carried out on a continual basis.

Abstract: A channel unit network for interconnecting a two-wire, bidirectional signal transmitting means with a four-wire digital transmitting means in a communication system to create a precision bidirectional simulated two-wire cable pair over a transmission medium includes tip and ring switch mode drivers, a signal processing circuit, a decoupling circuit, and tip and ring balance amplifiers. The decoupling circuit is used for splitting off "voice band" frequency signals from incoming tip and ring "DC band" signals from the two-wire means. The signal processing circuit performs both analog-to-digital conversions and digital-to-analog conversions.

Abstract: A subscriber line interface circuit, coupled between a telephone unit terminal and a switching system, includes a coding and decoding circuit for controlling analog voltages inputted thereinto and outputted therefrom, using a direct current bias voltage, and an interface circuit. The interface circuit has an amplifier for detecting the analog voltage output, a unit for detecting a direct current bias voltage of the analog voltage output, a subtracting unit for determining the difference between the detected analog voltage output and the detected bias voltage, and resistors for driving the telephone unit terminal on the two-wire side. The analog voltage and the direct current bias voltage output terminals of the encoding and decoding circuit are directly connected with the input terminal of the amplifier for detecting the outputted analog voltage and the interface circuit, respectively, so that only a desired alternating current signal is outputted to the telephone unit terminal on its two-wire side.

Abstract: An echo cancellation device usable in telephone connections affected by phase-roll is described. The canceller calculates the echo path propagation delay and produces an estimate of the echo signal by digitally filtering the signal originated by the far-end talker. The echo estimate is then subtracted from the actual echo to eliminate listening disturbances. The filter used is of the FIR type with adaptive coefficients updated iteratively by adding algebraically, to the values which they had upon the preceding iteration, a correction term proportional to the estimate error. The frequency of the coefficient updating iterations is a multiple of the rate f.sub.c of acquisition of the voice and echo samples by the canceller.