Abstract: A modem detects the received signal level at the start of communication and inserts an attenuator in the received input circuit if the level is too high. This arrangement extends the dynamic range of the modem without requiring a complex demodulating circuit.

Abstract: A power supply (ringer power supply) for a telephone exchange comprising a first switching circuit for receiving and subjecting direct current to high frequency switching by means of a switching element, a converter transformer connected to the switching circuit, a smoothing circuit connected to the secondary side of the converter transformer, a second switching circuit connected to the output stage of the smoothing circuit and used for switching the input current by means of a transistor bridge of a plurality of transistors for being alternately turned on, a direct-current bypassing diode connected between the input and output terminals of each transistor, a driving circuit for driving each of the transistors in accordance with a predetermined driving signal, and a driving signal generator circuit for generating the driving signal for setting timing to prevent the period during which a transistor is turned on from overlapping the one during which another transistor is subsequently turned on, permitting a red

Abstract: The invention is directed to a prower-supply transfer apparatus for a telephone wherein the power supply is fed from a telephone line by a power supply transferring circuit when the operation has been decided as a low speed operation by a speed deciding circuit, the power supply is fed from a separate power supply circuit by the power-supply transferring circuit when the operation has been decided as the high speed operation, so that the low-speed operation is performed through the speed control by the speed decision result not only when the processing may be performed even at the low speed operation in the common telephone or the like, but also when the high-speed processing is required in voice recognition or the like.

Abstract: A modem for a digital data transmission system in which binary-coded data at up to 9.6 Kbit/sec is transmitted over a telephone line pair circuit, as phase and amplitude modulation (QAM) of a carrier signal at a frequency of 1800 Hz, at a line symbol rate of 2400 bauds. The modem utilizes two data signal processors (4 and 5) and two gate arrays (6 and 7), controlled by a microprocessor (8), to carry out digitally all the processes required to convert binary coded data signals into PCM coded samples of the required carrier signal for transmission and to recover binary coded data signals from PCM coded samples of a received carrier signal.

Abstract: A method for gain control of telephone sets having an electronic speech circuit and an apparatus for carrying out the method include a modulation current source. Two line terminals connect the modulation current source to a telephone line. A microphone amplifier has an input connected to a microphone terminal and an output controlling the modulation current source for generating a line signal. Signals are derived from the modulation current source and converted into mutually associated measurement signals and threshold value signals. The mutually associated measurement and threshold value signals are compared with one another. The gain of the microphone amplifier is regulated as a function of the result of the comparison.

Abstract: A voice control circuit controls the volume range of the voice signals in a communication terminal, such as a video telephone having a hands-free facility. In a hands-free facility, the signal-to-noise ratio is lower than in telephones with handset. To avoid audible feedback, hands-free facility conventionally includes a volume control circuit which decreases or increases the gain in the receive path as the gain in the set path increases or decreases. The problem to be solved is to utilize the maximum possible loop gain without reducing the gain in the receive path. The idea is to place behind the microphone (50) a controllable compandor (52) in which the signal voltages from the microphone (50) are A. compressed if they lie above a predetermined level, B. expanded if they lie below the predetermined level, and C. imparted maximum gain if they have the predetermined level.

Abstract: A method and apparatus for disabling an echo canceller in a framed digital network from a remote terminal that is copuled to the network through an unframed data link. Control is effected by sending N different bit sequences from the remote terminal, where N is the number of different framing alignments that may be imposed on the unframed data by the network. The different sequences are chosen so that one will be framed by the network as the requisite control tone regardless of which framing alignment is actually imposed.

Abstract: An electronic hybrid circuit includes a differential amplifier having its non-inverting input coupled via a resistor to a four-wire input port and via a coupling transformer to a two-wire input/output port, its output coupled to a four-wire output port, and its inverting input coupled via a resistor to the input port and also coupled to an impedance network. The impedance network includes an inductive impedance which is coupled either to the amplifier output or to circuit ground, and which may be constituted by a gyrator or other electronic circuit which simulates an inductor.

Abstract: An apparatus is provided for programmably silencing a telephone ringer for one or more predetermined periods of time on a daily basis. In accordance with the time set by a user, the apparatus places the telephone ringer under the control of the data stored in the read only memory and the random access memory of the central processing unit, whereby the ringer can be automatically set at predetermined sounding condition.

Abstract: An electro-thermal isolator coupler including a pair of electrically isolated thermal receivers specifically spaced from an electrically isolated thermal transmitter such that their combined signals will produce a thermally compensated electrical output. A second pair of electrically thermal receivers is included in an error circuit which corrects the driver of the thermal transmitter for losses across the thermal coupler. Depending upon the use, the thermal coupler can be used in combination with RF capacitive coupling. Individual power terminals for the electrically isolated regions assure electric isolation.

Abstract: An analog echo suppression circuit is used with a telephony 2-wire circuit to 4-wire circuit interface. The 2-wire circuit carries a first signal and the 4-wire circuit carries a second signal. Each circuit has an input port and an output port. The interface produces an echo signal on the output of the 2-wire circuit when the second signal is received at the input port of the 2-wire circuit. A first communication channel connects the output of the 4-wire circuit to the input of the 2-wire circuit. A second communication channel connects the output of the 2-wire circuit to the input of the 4-wire circuit and series analog switches or transmission gates can interrupt the second channel. A comparator circuit receives the first and second signals from the first and second channels and has first and second outputs.

Abstract: 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.