Bell Telephone Laboratories

Storage Technology Corporation

Raychem Limited

Gte Lenkurt Incorporated

Call Management Products, Inc.

John Francis O'Neill

Milton L Embree

Peter G Ruether

Stephen Hunter Diaz

David C Goldthorp

Dennis Bryan James

James A Pinyan

Joseph M Carey

Patrick A Vachon

James Owen Dimmick

Theras Gordon Lewis

Charles Hamman Divine

J Mark Elder

Lawrence R Benko

Lucian Philip Fabiano, Jr

Howard Robert Popper

Thomas B Cannon

A low power, low cost distributed digital loop (DDL) carrier system that combines television and voice telephone signal transmission over coaxial cables. The DDL system employs a passive/active tap module (114) that controls the steering of the video and telephone signals. The high frequency down stream telephone signal is not processed until a routing terminator (110) converts it to lower frequency signal for transmission in the lower frequency subsplit channel. The telephone signal is then transmitted back up through the subsplit where the active circuitry of each tap intercepts the telephone signal, selects the needed signal and transmits it down to a network interface unit (120) located at the subscriber premises.

Distributed digital loop carriers system using coaxial cable

A call management system connected locally between a central office telephone company switching station (CO) and a conventional single telephone line having multiple extensions provides call paging and intercom capabilities between the multiple telephone extensions. An integrated voltage generator supplies a high voltage, local ringing voltage for ringing the local extensions independent from the CO and a low voltage talk or 'battery' feed to the local telephone when they are operated independently from the CO. Line splitting apparatus temporarily separates the CO from the local extensions when the local ringing voltage is generated by the integrated voltage generator and injected into the local telephone extensions. A hold device mimics an active local telephone off the hook, thereby keeping a call from the CO holding when the local telephones are being used in the paging or intercom modes. Detection devices detect touch tone or rotary dial inputs as well as off hook conditions of local telephones for initiating various local paging and intercom functions between the local extensions. Tone injector apparatus place a dial tone-like sound in the local telephones when they are separated from the CO. A central office ring detector detects a high voltage ring signal from the CO and signals the local users during intercom operation that a call is coming in from the CO and is waiting to be picked up.

Call management system

An improved adaptive echo cancelling system and method is disclosed. The system and method utilizes linear code spacing and is particularly well suited for echo cancellation of full scale signals. Echo cancellation is effected by use of digital-to-analog converters functioning as a multiplier receiving first digital signals representative of a received speech waveform signal and second digital signals representative of the termination network on the line, which termination network causes and defines an echo reflection of the received signal. The output of the multiplier is summed and the sum is then subtracted from the echo components of the received signal to thus achieve echo cancellation and to produce an error signal that is utilized to continuously reduce error between the actual and estimated echo waveforms. Provision is made to inhibit error indications due to circuit generated coding noise and/or predetermined small detected errors to thereby enhance system operation.

Adaptive echo cancelling system and method utilizing linear code spacing

Disclosed is a centralized circuit for determining whether input signals from a plurality of channels are speech which includes memory means in which digital amplitude samples from each of the input channels are stored in real time. A control means then periodically retrieves the samples from the memory in a time faster than real time and produces a series of time compressed input signals which are compared with a variable threshold derived from a stored level for each channel. Moreover, means are disclosed for setting a new threshold whenever the time compressed input signals differs from the old level for a predetermined time, the new level thereafter being stored in place of the previously stored old level.

Speech detector circuit for a TASI system

Disclosed is a circuit for determining whether an incoming signal is a speech signal or a data signal. In the preferred embodiment, means for separating the incoming signal into a low frequency component and a high frequency component are provided. The low frequency component consists of frequencies below a specified frequency, namely 1000 Hz. and the high frequency component consists of frequencies above 1000 Hz. Means are also provided for the comparison of the energy level of the high frequency components with a multiple of the energy level of the low frequency components. Also, means are provided for comparing a multiple of the energy level of the low frequency components with a maximum threshold and for comparing the energy level of the high frequency components with a minimum threshold. Further, means are provided for detecting whether the incoming signal has a slope. Data is determined to be present when the energy level of the high frequency components exceeds a multiple of the energy level of the low frequency components, and when the energy of the low frequency components is less than a maximum threshold and when the energy level of the high frequency components is greater than a minimum threshold and when the incoming wave has no slope all occurring simultaneously for a preselected period of time.

Data detection circuit for a TASI system

The disclosed signal limiting circuit is bridged on to a bidirectional communication path (T, R) and functions to selectively attenuate excessive signals (2V.sub.A) being transmitted in a predetermined direction on the bidirectional communication path. This is accomplished by a signal discriminator circuit (100) which separates the excessive signal (2V.sub.A) from the plurality of signals appearing on the communication path (T, R). The signal discriminator circuit (100) also inverts the isolated excessive signal, passes it through an attenuator (102) to a signal injection circuit (103) which injects a controlled amount of the 180 degrees out-of-phase isolated excessive signal back on the communication path (T, R) to cancel out a portion of the excessive signal, thereby providing selective attenuation of the excessive signal.

Signal limiting circuit

Circuitry useful in PCM coders for effectively shifting the idle channel noise signal to a level midway between the code state boundaries thereby significantly reducing the likelihood that noise signals will cross a boundary and be encoded.

PCM coder with shifting idle channel noise level

In a time assignment speech interpolation system, a fixed delay between the input speech channel and the transmission facility provides time to generate and transmit a symbol representing the speech channel to which the transmission facility has been assigned. At the remote location, a fixed delay between the transmission facility and the output speech channel provides time in which to detect the symbol and perform the necessary switching.

Fixed speech buffer memories for signalling without an order wire

A circuit for converting an input analog signal into a digital representation and a remainder signal is disclosed. The digital representation is generated by a coder that counts an integral number of clock cycles during an interval in which the magnitude of the input analog signal is compared with the magnitude of a ramp signal. The remainder signal is generated by duration-to-amplitude conversion of a pulse whose duration is the fractional remainder of the final uncounted clock cycle.

Cascadable analog to digital converter

A local battery feed circuit for telephone station sets comprises two half circuit portions substantially symmetric about an imaginary line midway between the TIP and RING telephone lines. Each half circuit includes a current drive amplifier including a pair of up-down emitter follower transistors and a driver transistor. A coupling capacitor and matched resistors provide common mode interference reduction without degrading differential mode signals. Power supply noise is substantially eliminated by transistors in each half circuit arranged to produce an a.c. current equal and opposite to that generated from the power source.

Circuit for supplying direct current to telephone station sets

A line transformer circuit in which the DC component of magnetization produced in the tip and ring windings by the battery supplying loop current to the telephone set microphone may be neutralized by an oppositely-poled, serially-connected balancing winding is disclosed. One end of the balancing winding is connected to the supply battery and is, therefore, at AC ground. The other end is kept at a point of high AC impedance to ground by the collector of a transistor so that audio frequency voltages induced in the balancing winding cannot load the transformer. The AC currents in the tip and ring windings are provided with a virtual ground return path by means of a differential amplifier controlled Darlington pair in circuit between the tip and ring windings and the balancing winding. The AC components of the Darlington pair collector current are bypassed to ground by a shunt capacitor at the junction of the Darlington pair collector terminal and the third winding. The differential amplifier senses voltage changes at the virtual ground so that the Darlington pair is driven to suppress these changes. Advantageously, the differential amplifier may be powered from the voltage drop appearing across the Darlington pair thereby facilitating circuit integration.

Integrable line circuit for use with miniature line transformer

A line circuit is disclosed employing a transformer having tip and ring windings and a third balancing winding designed to be serially connected in circuit with the tip and ring windings and poled so as to balance out their DC magnetization. The AC components of longitudinal current flowing through the tip and ring windings are prevented from flowing through the balancing winding by a capacitor bypass which offers a low impedance path compared to that of the balancing winding. This capacitor is prevented from short circuiting the AC voice frequency voltages induced by transformer action in the balancing winding by driving the balancing winding from the collector terminal of a transistor biased to remain out of saturation and which, therefore, exhibits a high impedance to changes in collector voltage. The resistance in the emitter circuit of this transistor determines the level of DC current delivered through the balancing winding to the tip and ring windings and the telephone line. The transistor base is supplied with current drive by a Darlington pair which avoids longitudinal unbalance in the tip and ring conductors. By effectively preventing the effects of DC magnetization a smaller and lighter weight transformer core is obtained.

Line circuit using miniature line transformer

A time-sampled port circuit is shown in which the charges impressed by the telephone set on the shunt capacitor of a low-pass filter associated with the port are passively sampled for transmission to the other port circuits, but which capacitor is impulse driven at a repetition rate equal to twice the cut off frequency of the filter with speech samples received from the other port circuits. By employing passive sampling in the transmitting leg instead of actual charge transfer, as in conventional resonant transfer design, the series inductor normally required in resonant transfer circuits may be omitted with the result that the port circuit switches may be integrated on one chip together with the digital circuitry for encoding and decoding the amplitude samples. Further, all need for amplifier gain adjustment in the port circuit is eliminated by applying different amplitude send and receive ramp signals to the encoder and decoder circuits. Transmission delay in a time division system employing the port circuit is compensated by delaying the onset of the receive ramp waveform.

Four-wire integrable hybrid

A read only memory (ROM) patching arrangement is disclosed for providing valid output information whenever ROM word locations containing invalid information are addressed. The disclosed arrangement uses a plurality of small capacity PROMs as a decoder to detect the receipt of each address word representing a defective ROM locaton. Upon each detection of a defective address, the decoder temporarily inhibits the output of the ROM and causes a small auxiliary memory to output valid program information as a substitute for that in the defective ROM location. A counter is used as a supplemental addressing source for both the decoder and the auxiliary memory. This increases the patching capability by subdividing the decoder and the auxiliary memory into 2.sup.n segments where n is the number of bits supplied by the counter.

Memory patching circuit with counter

A conference port for permitting simultaneous voice communication among a plurality of local stations and an external or central office line is shown. The stations may be part of a time division PBX or may be arranged as a time-sampled key telephone system having access to the same line. The conference port includes a first operational amplifier for summing the station port voltages on a capacitor during an interval that is a predetermined fraction of the resonant transfer interval. This first, or quasi-resonant, interval is sufficient to reduce the initial voltage on each of the station port sampling capacitors to a predetermined fraction of their initial level. At the conclusion of this interval the voltage on the summing capacitor in the conference port is multiplied by an appropriate factor in a second operational amplifier and is applied back simultaneously to all of the conference ports together with the signal incoming over the external or central office line. The voltage impulse, so applied, causes the signal contributed by each station port to appear at each other station port attenuated by a suitable factor, illustratively 6dB, while the incoming signal appears full strength at each station port. Accordingly, good return loss is provided at each station port and contrast between signals from stations and the incoming line is reduced via the controllable station-to-station loss.

Growing community of inventors

Boulder, CO, United States of America

John Francis O'Neill