Abstract: A method and apparatus cancels an echo by using an echo replica generated such that a tap coefficient of an adaptive filter is sequentially updated, the echo being received from a transmitting end to a four-wire side through a two/four wire converter and being obtained such that a pulse signal having positive and negative polarities is fed into a receiving end, wherein a difference signal (error signal) between the echo replica and a reception signal is calculated; a correlation value between a signal representing a polarity of the error signal and a signal representing a polarity of the echo replica is calculated; when the correlation value is smaller than a predetermined value, a first of two types of tap coefficients which belong to each of a plurality of taps is updated based on at least the error signal and is set as the tap coefficient of the adaptive filter during a period in which the pulse signal is set in the positive polarity, and a second type of tap coefficient is updated based on at least the er

Abstract: Battery feed circuits function to supply a predetermined current to the communication pair and include circuitry to counteract the effects of balanced longitudinal signals which appear on the communication pair. Prior art battery feed circuits use either expensive matched power resistors or matched and tracking current sources to provide both the dc current and the necessary balance. The subject battery feed circuit separates the two functions: a pair of poorly matched inexpensive power resistors provide the basic dc current; and associated pair of low power electronic circuits supply compensation signals to provide the necessary balance. The compensation signals are applied to the power resistors in a manner to obtain precision resistor (.+-.0.1%) characteristics from the inexpensive (.+-.5%) power resistors.

Abstract: A voice-switched telephone circuit with center idle state improves bi-dirional gain control in loudspeaking telephones and thereby enhances the natural quality of interactive conversation. The voice-switched telephone includes: a transmit channel having a microphone and a three-state amplifier; a receiver channel having a three-state amplifier and a loudspeaker; and a hybrid circuit interconnecting the transmit and receive channels to a two-wire telephone line. The present invention is characterized by independent signal level detecting circuits for the transmit and receive channels. When the magnitude of the signal energy in the transmit channel exceeds a predetermined threshold, the transmit channel amplification is increased and the receive channel amplification is decreased by fixed equal amounts.

Abstract: A voice switched gain system is disclosed for loudspeaking telephone and hearing aid applications involving electret microphones. A voice switched gain circuit comprises an audio pre-conditioning circuit for providing a conditioned audio input referenced to an unconditioned audio input to a compandor circuit. A linear gain level reference generator circuit generates a level for comparison with the audio input level. A decision circuit then controls the compandor operation based on the result of the comparison. The decision circuit either maintains the audio output of the compandor in a compressed state or expands the audio input signal to a higher level expanded state for transmission. Two such circuits are provided in a loudspeaking telephone system, one circuit for maintaining a preemptive near end control through appropriate timing of the dual decision process. Far end control is provided by the other voice switched gain circuit.

Abstract: For the compensation of echo signals occuring in the course of the duplex transmission of digital signals by the dual channel system in signal transmission equipment provided with an echo compensator, the equipment is designed so that the clock pulses emitted by a timing generator for the transmission of the digital signals can be shifted in phase by predetermined phase grid steps. When a change in the phase position of the clock pulses takes place within one phase grid step, correction signals are generated, with the phase position that has been accurately set in each case being maintained. These correction signals are subtracted, together with the compensation signals emitted by the echo compensator for the compensation of the echo signals, from the digital signals received together with the echo signals.

Abstract: A two way telephone communication system includes a station having a signal transmitting channel for conveying a signal received at a microphone to another station, a signal receiving channel for conveying signals received from the other station to a speaker, and switches permitting the two signal channels to be selectively enabled or disabled. Two signal detection paths are associated with the transmitting and receiving channels, each containing circuitry which detects the presence of signals in one of the channels and responds by generating actuating signals. Control circuitry responds to the detection path which first generates an actuating signal by enabling its associated signal channel and simultaneously disabling the other signal channel, triggering the switches appropriately. Delay circuitry associated with each signal detection path can be selectively enabled to delay the generation of an actuating signal in the associated signal detection path.

Abstract: In an adaptive crosstalk and/or echo compensation circuit which is arranged on the four-wire side parallel to a hybrid circuit and which has a variable filter and a compensation signal logic-linking element, the compensation signal is formed in dependence upon the, possibly averaged, difference between a decision device output signal formed following the signal compensation and following an adaptive signal equalization, and the decision device input signal. In the case of a greater, possibly averaged, difference between the decision device input and output signals, the filter coefficients are set in accordance with the compensated received signal, or only the sign thereof, and in the case of a smaller, possibly averaged, difference, the filter coefficients are set in accordance with this difference, or only the sign thereof. A compromise equalization of the received signal can take place prior to the crosstalk and/or echo compensation.

Abstract: A bidirectional transmission system with echo cancellation allows simultaneous interchange of digital information between an exchange and subscribers on a single transmission line. Data flows are transmitted by packets separated by short silence intervals within which clock signals are extracted and echo-cancellation adjustment is accomplished. Use of an adaptive equalizer and a single sampling operation per sampling period are possible.

Abstract: A signal transmission control apparatus connected between a telephone line and a terminal device controls signal transmission therebetween in no-ringing service. First DC and AC circuits of the apparatus become conductive in response to a DC control voltage from the telephone line. The first DC and AC circuits are connected to the telephone lines and the leads of a primary coil of the transformer of the apparatus. The secondary coil of the transformer is connected to the terminal device and an amplifier and first detection device of the apparatus. A subsequent AC calling signal from the telephone line, received on the first AC circuit, effects conduction in second DC and AC circuits through serial operation of the first detection circuit, a control circuit, a switching transistor and closure of relay contacts.

Abstract: An arrangement for supplying electrical power from a telecommunication central office to a remote network termination employs the wires of a two-wire digital subscriber loop in parallel using earth ground as a return path. At the central office, two power supplies separately provide power to the two wires of the loop in parallel and the current supplied by the two power supplies is added at the remote interface by means of a center-tapped transformer coil which is part of the transformer used for the transmission of digitally encoded voice and data signals. A DC-to-DC converter connected to the center tap provides the required power to the interface circuitry. The DC-to-DC converter is grounded to earth ground through a low-pass filter which is designed to block higher frequency noise signals.

Abstract: An improved loop current supply circuit including a first amplifier connected to a source of bias voltage. The first amplifier is further connected to a subscriber loop circuit through the tip and ring conductors. The first amplifier receives the bias voltage and supplies loop current to the loop circuit. A second amplifier connected to the tip and ring conductors outputs a voltage representative of the amount of current in the subscriber loop. When the output voltage of the second amplifier becomes greater than the bias voltage, a loop voltage network connected to the second amplifier and to the bias voltage source shunts the bias voltage from the first amplifier, decreasing the current in the loop circuit.

Abstract: Apparatus and a technique for echo cancellation is described in which the real and imaginary parts of an echo replica signal can evolve independently of each other. By removing the coupling heretofore found in cross coupled echo canceller structures, the echo replica obtained in conjunction with carrier-phase tracking circuitry can be a more exact duplicate of the real and imaginary components of a received echo containing signal. The echo canceller may include a plurality of subcancellers, each including at least four adaptive filters. Alternatively the filters within each subcanceller can be implemented by a suitably programmed digital signal processor.

Abstract: A transmit amplifier which also stabilizes the line direct voltage of the audio transmission circuit of a telephone set with respect to a reference voltage, the amplifier gain being adjustable to a high value by means of a resistor which does not affect the further properties of the audio transmission circuit. Variation of the line direct voltage by the offset current of the microphone pre-amplifier preceding the transmit amplifier, and by temperature fluctuations of the reference voltage, is greatly reduced by increasing the reference voltage and adding a temperature-dependent current source to a voltage divider which is comprised in the amplifier.

Abstract: A bedside control module is provided for healthcare stations and the like, of the type generally having a bed, and at least two control functions, such as bed adjustments, nurse call, telephone, television, radio, lights, and other such accessories. The control module includes a dual-sided control panel that is supported by an arm at a position adjacent to the bed for access by the user. Both sides of the control panel include manually-operable controllers for operating the various control functions. The control panel is rotatably mounted on the support arm for manual rotation about a normally, generally vertical axis that is oriented to selectively and sequentially present the opposite sides of the control panel to the user to regulate the various control functions.

Abstract: This arrangement is intended to control the operation of the coefficients adjusting circuit (12) of an echo canceller and of the operation of a center clipper (15) inserted in the send path (7) of a four-wire circuit at the output of the subtractor (13) of the echo canceller for suppressing there, when it is set to its active state, the signals whose amplitude is lower than or equal to a clipping threshold. The control arrangement operates on the basis of the signal in the receive path (2) of the four-wire circuit, the level N.sub.REC of this signal and the levels N.sub.AV and N.sub.AP of the signals before and after the subtractor (13). It comprises a controller (21) for comparing the level N.sub.AV to two fixed thresholds N.sub.AV0, N.sub.AV1 and for comparing the ratio N.sub.AP /N.sub.AV to a threshold a which is capable of varying as a function of N.sub.AV, the center clipper being only set to its active state when the level N.sub.AV is comprised between N.sub.AV0 and N.sub.AV1 and the ratio N.sub.AP /N.

Abstract: An apparatus for indicating to a central service unit of a telephone system having a central service unit coupled to a plurality of station sets whether a particular station set comprises a speakerphone and the type of speakerphone from among two types of speakerphone, is disclosed. The station set includes a microprocessor controller having an input line coupled to a selected one of a low or high logic level. The input line is connected to an electronic switch which receives interrogation signals from the central service unit. Depending on the logic level to which the input line is coupled and the state of the switch, the central service unit can determine whether the station set comprises a speakerphone and the type of speakerphone.

Abstract: When a floating battery feed circuit is used to power telephone lines, it is desirable to provide an anti-corrosion biasing circuit to keep the voltage on the tip and ring conductors from becoming positive. This can be done using an anit-corrosion circuit that sinks a dynamic amount of current from the tip conductor. A line circuit including such biasing is, however, incompatible with special lines such as PBX lines that rely on a grounded tip conductor in the talk state. In accordance with the present invention, a constant current is supplied from a ground reference circuit to the ring conductor of such special lines only when loop current is flowing. The magnitude of this supplied current is such that the anti-corrosion circuit holds the tip conductor sufficiently close to ground potential to allow the proper operation of circuits connected to the special lines.

Abstract: An improved AC impedance matching arrangement including a first amplifier connected to a subscriber loop through the tip and ring conductors of a subscriber line circuit. The first amplifier is arranged to supply loop current to the subscriber loop through first and second resistors. Each resistor having a set DC value. A second amplifier connected to the tip and ring conductors is arranged to develop and output a signal responsive to AC signals applied to the tip and ring conductors from the subscriber loop. A feedback circuit connected to the second amplifier is arranged to receive the second amplifier output signal and develop and output to the first amplifier an impedance matching signal. The impedance matching signal raises the impedance seen by the tip and ring conductors above the set DC value of the first and second resistors.

Abstract: An adaptive line hybrid for digital telecommunications including a bridge circuit for connection to the telecommunication line the bridge circuit having automatically adjustable components in two arms of the bridge to compensate for variations in the characteristics of the telecommunications line.

Abstract: A parametric echo canceller comprising two transversal filters is employed to recursively model the echo path. The first transversal filter receives the input signal, the fed-back echo residual signal and a first set of Kalman gain coefficients to produce a first intermediate result. The second transversal filter receives the echo signal, the fed-back echo residual signal and a second set of Kalman gain coefficients to produce a second intermediate result. The second intermediate result is subtracted from the first to yield an estimated echo replica. The estimated echo replica is then subtracted from the echo to yield an echo residual. The taps of the first and second transversal filters are weighted in accordance with first and second sets of weighting coefficients, which are generated in accordance with the Fast Kalman Algorithm.