Abstract: The generally rectangular cross section of a telephone handset handle extends through a microphone portion of the handset. The microphone portion is angled about 38 degrees from the handle. The handle has a width of about 1.5 inches and a depth of about 0.7 inch to meet the requirements of 98% of the user population. A speaker portion, angled about 15 degrees from the handle, has a concave depression to be seated against a user's ear. The distance between the center of the speaker depression and the microphone cavity is about 5.8 inches. The microphone portion is about two inches long and has grooves extending to its end. Baffles extend across the hollow of the handle to acoustically isolate the speaker and microphone portions of the handset. To facilitate assembly, the connector and microphone are first fixed to a holder without the need for adhesive or additional fasteners. The speaker and holder are then positioned in a base section of the handset without the need for adhesive or additional fasteners.

Abstract: An improved offhook supervision circuit including an amplifier connected to a subscriber loop through the tip and ring conductors of a subscriber line circuit. The amplifier is arranged to develop and output a loop voltage signal representing the level of the DC signals applied to the subscriber loop circuit. A comparator device has a first input connected to the amplifier and is arranged to receive the loop voltage signal output by the amplifier. A second input of the comparator device is connected to a reference voltage device which outputs a predetermined reference signal voltage. Any significant reduction of the DC signal level on the loop circuit will cause the loop signal voltage output by the amplifier to fall below the reference signal voltage. An offhook signal is then output from the comparator device to a control device signaling an offhook condition.

Abstract: A wide band high voltage and high power amplifier is particularly useful for telephony applications. The amplifier employs a flyback converter with the capacitor storage element coupled across the line. The subscriber line is characterized in having a definite load impedance which impedance is in parallel with the storage capacitor of the flyback converter. The subscriber lines are monitored by a differential amplifier which provides a single-ended output indicative of the levels across the lines. This output is summed with the input signal to develop an error signal. The input signal to the line circuit is the particular signal of concern such as ringing, the voice signal and so on. The error signal is supplied as one input to a comparator having another input coupled to a triangular reference waveform. The output of the comparator provides a pulse width modulated waveform where the width of the pulses are indicative of the error signal.

Abstract: An echo canceller includes means for reducing correlation in a receiving side input signal based on a linear prediction model by regarding the receiving side input signal as an output signal of the linear prediction model. This means for reducing correlation is provided in a form suitable for hardware implementation, and thus, a convergence rate for the receiving side input signal having strong correlation as a speech signal can be improved without substantially increasing the number of calculations or the amount of memory.

Abstract: A telephone hanset is made with two elongate molded parts, a back part and a front part. The back part is arcuate in side view and is substantially rigid. The front part has a substantially flat central portion which is flexible, with a housing at each end for the transmitter and receiver. The two parts are assembled by flexing the front part to conform to the back part, the two parts being connected together. This avoids the need for complex molds for molding the front part as no re-entrant walls occur for the housings.

Abstract: A transistorized current amplifier based on a cascode stage feeding into a composite transistorized output stage. The amplifier employs a constant current source, decoupling (isolation) from the power source and a signal limiting network to lower distortion on high signal input conditions. A two-wire device, the amplifier derives signal and power from a telephone line. Surge protection is provided by a signal limiting network and the inclusion of relatively high value resistors in the circuit.

Abstract: For use in combination with a loudspeaker and at least one microphone, for example, by attendants in an auditorium, an echo cancelling circuit comprises a self-adaptive echo canceller responsive to a lower frequency component, such as below 1.7 kHz, of a receive-in signal for self-adatively cancelling a corresponding component of a reverberation signal included in a send-in signal during each interval during which an audio signal reaches the circuit from a remote party. For a higher frequency reverberation signal component, an echo suppressor or a voice switch may reduce a weaker one of two signals which are either the higher frequency send-in and receive-in signal components or a combination of a reverberation component cancelled signal with the higher frequency send-in signal component and the whole receive-in signal. Alternatively, a less expensive echo canceller non-adaptively cancels a part of the reverberation signal in response to the receive-in signal.

Abstract: The invention refers to a circuit for telephone systems for the transmission of alternating current signals such as voice signals from a subscriber telephone system to a central office, wherein a signal transformer is provided with a by-pass for the direct current running in both wires to the central office. According to the invention a current path is provided by an amplifier inserted between the two wires to the central office. The amplifier is controlled by the dc current from the central office and alternating current provided by the transformer. The resistance of the amplifier changes according to control signals in the form of current supplied. The application of an amplifier as a current path between the two wires of the central office enables maintenance of direct and alternating current in the central office and simultaneous transmission and amplification of voice signals. The transformer need only supply a small part of the analog transmission signal energy.

Abstract: An echo cancellation circuit is disclosed for use with full-duplex data transmission systems. The echo canceller can operate in spite of time invariant non-linearities in the echo channel or in the implementation of the echo canceller itself (such as in D/A converters). The echo canceller receives an echo signal having linear and non-linear components and includes N linear tap weights for cancelling the non-linear components of that echo signal where M is greater than N but less than 2.sup.N.

Abstract: A signal limiting amplifier includes interstage limiting devices to restrict the range of output voltage signals. The devices are base-emitter circuits of transistors, one of which operates in response to one polarity of signals and has its collector terminal unconnected, and the other of which operates in response to the other polarity of signals and has its collector circuit connected (when limiting) to operate an appropriate utilization circuit. In one embodiment, the limiting amplifier is applied as a common mode feedback amplifier in a telephone line feed circuit, and the limiter signal is used to limit large longitudinal signals on a customer line and to power down the line feed circuit in the event the limited signals persist beyond a certain interval.

Abstract: A subscriber line interface circuit described wherein a pair of line terminals are connected to a subscriber loop and a pair of output terminals are connected to a telecommunication exchange. A first amplifier is provided having a first pair of input terminals coupled to the line terminals and a second pair of input terminals. The first amplifier has a unity gain over a path from the input terminals of the first pair to said output terminals and a gain K over a path from the terminals of the second pair to said output terminals. A pair of reference resistors are cross-coupled from said output terminals to the line terminals, each of the reference resistors having a resistance Ro. A second amplifier is connected from the line terminals to the terminals of the second pair, the second amplifier having a transfer function -Ro/K.multidot.Zt, where Zt is an impedance to be synthesized across the line terminals.

Abstract: An integrated SLIC having input pins coupled to the wires of a two-wire telephone subscriber line is protected from excessive voltages on the line by reverse biassed 60 volt zener diodes connected between each input pin and ground, normally reverse biassed diodes within the integrated circuit connected between each input pin and the substrate of the integrated circuit, and a normally forward biassed diode connected between the substrate and a -48 volt (nominal) supply voltage.

Abstract: A telephone terminal box which is divided into two compartments so to provide a first compartment accessible only to the telephone operating company and a second compartment accessible to the subscriber. Each compartment has its own cover, and the covers may be individually locked by the subscriber and by the telephone company. The box is constructed so that if it becomes necessary, the telephone company can gain access to the subscriber compartment, however, the subscriber cannot gain access to the telephone company compartment. A terminal block is mounted in the subscriber compartment to provide connections to a predetermined number of subscriber telephones. A protector block is mounted in the telephone company compartment, the terminal block being wired at the factory to one side of the protector block.

Abstract: A receiver circuit uses switched capacitor circuits to couple signals received over a communication facility to connected apparatus. During a first time interval a capacitor is connected across each lead of a facility to sample the facility voltages. During a second time interval these capacitors are disconnected from the facility lines and reconnected in series as the input to a voltage regenerator circuit. The regenerator circuit reconstructs the received signals for output to connected apparatus.

Abstract: This invention relates to line circuits and, in particular, to the apparatus contained therein for switching the ringing signal on to the communication pair which connects the line circuit to the telephone station set which it serves.Electromechanical relays provide an ideal switching function but require a significant amount of space while semiconductor switches do not require much space but provide an imperfect switching function which adversely affects the performance characteristics of the line circuit.The subject ringing apparatus makes use of a semiconductor switch to provide the ring relay function and incorporates additional circuitry to eliminate the difficulties associated with semiconductor switches.

Abstract: The present invention relates to the D.C. supply for a subscriber control system, and consists essentially in supplying the control system from the exchange solely in response to a request, such request being emitted either by the exchange or by the control system, a preamble message being emitted in-line by the control system in order to initialize a communication in the latter case. The invention is applicable to the digitalization of the subscriber's telephone.

Abstract: A digital voice communication apparatus having improved echo suppression includes a transmission gain detection circuit for detecting a near talker signal and a receiver gain detection circuit for detecting a far talker signal. An echo detecting circuit detects which of the near talker and far talker signals has a lesser value and suppresses the gain of the one detected to have the lesser value. A far talker suppressing circuit detects whether the most recent peak gain in this near talker signal is greater than a threshold and is greater than the gain of the far talker signal. If this condition exists the far talker signal is suppressed. A near talker signal suppressing circuit detects whether the most recent gain of the far talker signal is greater than a threshold and is greater than the gain of the near talker signal. If so, the gain of the near talker signal is suppressed.

Abstract: A receiver circuit uses a switched capacitor circuit to couple either analog or digital signals received over a two lead communication facility to connected apparatus. During a first time interval, a capacitor is connected across a lead of a facility to sample the facility voltage. During a second time interval, this capacitor is disconnected from that lead and reconnected in series between the second facility lead and the input to a voltage regenerator circuit. An appropriate regenerator circuit is selected to reconstruct either the received analog or digital signals for output to connected apparatus.

Abstract: The telephone amplifier of an audio transmission circuit comprises a class-B output stage as a result of which the required supply current of this amplifier is considerably lower than with prior art telephone amplifiers. A distorting voltage produced by the current signal in the supply current of the glass-B output stage does not affect the output signal of the telephone amplifier because the input stage and the output stage each comprise their own setting circuits which produce mutually independent setting voltages.

Abstract: A voice-controlled hands-free facility contains a microphone, an internal and an external loudspeaker, and two series combinations of an input amplifier (EV), a variable attenuator (DR), and an output amplifier (AV), one for the send path and one for the receive path, and is controlled by a voice control unit (SS) connected to the output (E) of the input amplifier (EV), to the output (D) of the variable attenuator (DR), and, by a line (L), to an input of the variable attenuator (DR).To permit the hands-free facility to be switched from a single-part mode of operation to a two-part mode, the output (E) of the input amplifier (EV) in the send path and/or the receive path is connected to the output (A) of the output amplifiers (AV) through a bypass device (BP) and a switching unit (T).