Abstract: The device comprises an echo cancelling circuit receiving a first signal and a second signal and a real echo between channels for producing a third signal containing the second signal and a difference between the real echo and the estimated echo. Detectors detect the echo difference and the second signal in the third signal when the level of the third signal exceeds a predetermined threshold. Circuits gain-control the adaptation in the adaptive filtration of the echo cancelling circuit in such a way as to modify the adaptation gain when the second signal is not detected and to prohibit all filtration modifications as long as the second signal is detected. For instance, for an acoustic echo in a telephone set, the echo is not processed when the third signal contains a local speech signal as second signal.

Abstract: In order to back up by an ISDN line two analog lines connected to MODEM of a four wire full duplex type for data transmission and reception, a terminal adapter is connected to a pair of back-up ports. Dial pulse signals delivered through the back-up ports are detected and converted into an ISDN telephone number. A D-channel processor performs the call connection by use of the D-channel signal having the ISDN telephone number and an identifier of a particular one of B-channels. An outgoing analog data from the MODEM through one of the back-up ports is A/D converted and then transmitted on the particular B-channel to the ISDN line. An incoming digital data on the particular B-channel signal received at the terminal adapter is D/A converted and is supplied to the MODEM through the other of the back-up ports. Thus, the back-up is performed by use of a single B-channel on the ISDN line.

Abstract: A circuit is described which comprises an operational amplifier, two resistors connected between the telephone line and the inputs of the amplifier, a capacitor which is charged via a first bipolar transistor controlled by the amplifier via a first FET transistor, a second bipolar transistor in parallel to the connection of the first transistor and the capacitor, a second FET transistor, identical to the first and having its source and gate terminals connected to the corresponding terminals of the first, and two current generators connected to the drain terminals respectively of the first and the second FET transistor and to the bases, respectively, of the first and second bipolar transistor.

Abstract: A portable telephone set having a ringing circuit for producing different ringing tones depending upon the use mode of the portable telephone set, a portable mode or a mobile mode. The ringing circuit comprises a mode detecting circuit for detecting the use mode, an internal loudspeaker housed in a housing of the portable telephone set for producing a first ringing signal when the portable telephone set is in the portable mode, an external loudspeaker connected externally of the housing for producing a second ringing signal when it is in the mobile mode and a ringing tone generator for generating a first and a second ringing tones for driving the respective loudspeakers producing first and second ringings. The first and second ringing tones have frequency spectra compatible with frequency characteristics of these loudspeakers to produce the respective ringings efficiently.

Abstract: A ring trip detection circuit detects an OFF-hooked state of a telephone receiver during ringing of a telephone set by detecting a change in a voltage across two terminals of a transmission resistor through which a ringing signal is supplied to the telephone set from a ringing signal source.

Abstract: A current limiting circuit in a battery feed arrangement provides a variable DC resistance for limiting subscriber loop current to a threshold value. The current limiting circuit also presents a low AC impedance so that no imbalance is introduced between tip and ring leads of the subscriber loop. The current limiting component is a low ON resistance power MOSFET in the ring side of the battery feed arrangement. The current limiting circuit is self protecting in the event of lightning strikes and AC power signals either induced or short-circuited.

Abstract: A communication terminal adaptor, or an automatic dialer, for connecting a communication terminal such as a facsimile apparatus and a telephone line network, is capable of handling both the push button signal and the dial pulse signal in mixed manner, and transmitting the identification information of the communication terminal, stored in advance in the adaptor, upon receiving the tone prompt signal from the destination station without referring to the communication terminal. Thus the telephone connection can be made in simpler and more prompt manner.

Abstract: An information retrieving system in which information arranged by a series of more than one character is inputted and data corresponding to said input information is read out from a disk-shaped recording medium, such that every time the characters of the input information are successively inputted, a head is seeked for a direction of a recording position of the data on the disk-shaped recording medium, corresponding to the input information, and also the head is located at the recording position of the data upon completion of the entry operation of the input information.

Abstract: A subband adaptive filter is disclosed that retains the computational and convergence speed advantages of subband processing while eliminating delay in the signal path. The technique has applications in active noise control where delay seriously limits cancellation performance and in acoustic echo cancellation where transmission delay specifications may limit the use of conventional subband designs. A reference signal and a residual error signal are each decomposed into a plurality of subband signals, and a set of adaptive weighting coefficients is generated for each of these subbands by a conventional complex LMS (least-mean-squared) technique. These sets of subband weighting coefficients are then transformed into the frequency domain, appropriately stacked and inverse transformed back into the time domain to obtain wideband filter coefficients for a programmable filter.

Abstract: An echo canceler (10) is controlled and operated during hangover time between a double talk condition and a single talk condition for a more natural residual echo cancellation. The adaptive gain and the residual suppression threshold necessary for controlling an adaptive filter and a residual echo suppressor, respectively, are computed such that their respective values increase gradually and smoothly from predetermined minimum values to predetermined maximum values during the hangover time.

Abstract: An enhanced subscriber line interface circuit for a digital switching system which includes a line configuration and protection circuit connection tot he subscriber line and to a thick-film hybrid module. The thick-film hybrid module comprises a high voltage interface circuit and a PCM conversion circuit. The high voltage interface circuit provides power to the subscriber line, converts received analog voice signals transmitted from the subscriber instrument into differential voltage voice signals and detects the subscriber lines status. The PCM conversion circuit is connected to the high voltage interface circuit and is disposed to convert received differential voice signals into PCM digital signals.

Abstract: A two-wire telephone line interface circuit comprises a driver circuit for supplying direct current on the line, a controlled voltage generator, a sensing circuit for monitoring the line current, a control circuit for controlling an output voltage of the voltage generator, and a switching circuit. The control circuit controls the switching circuit to supply, as a supply voltage for the driver circuit, a battery voltage in an on-hook state of the line or the controlled output voltage of the voltage generator in an off-hook state of the line, this output voltage being controlled to provide off-hook current limiting. The control circuit also controls the switching circuit to selectively supply the controlled output voltage of the voltage generator as a signalling voltage to at least one wire of the line for high voltage signalling, e.g. ringing, on the line. Desirable forms of the switching circuit are described.

Abstract: A telephone circuit subset arrangement in which the base/emitter junction of a switching transistor (TR1) coupling an internal battery (B1) to the dialler chip's power terminals (VDD, VSS) is shunted by hook-switch signal contacts (HS) when the subset is brought into the off-hook mode, thereby turning the switching transistor off and disconnecting the battery. The circuit is so arranged that upon the switching transistor turning off, three auxiliary switching transistors (TR3, TR4 and TR5) turn on and operate the subset's line switch to connect line current to the dialler chip's power terminals. A network of resistors (R1, R2 and R3) associated with the switching transistor (TR1) ensure that on the one hand sufficient current is available to turn on the auxiliary switching transistors, and on the other hand limit the current to a magnitude which dose not cause excessive battery discharge while the subset is off-hook.

Abstract: An electronic interface circuit between a telephone subscriber line and a telephone main exchange is disclosed which forms, with the main exchange battery, a supply bridge for the telephone line, with limitation of the line current to a predetermined threshold value. The voltage/current characteristic of the supply bridge is balanced for lower values of the line current than the threshold current and is unbalanced whenever the line current attains said threshold current.

Abstract: A communication apparatus, which is able to receive a peculiar information of other station and a voice message from the another station, records the peculiar information and the voice message in connection with each other.

Abstract: A low frequency high voltage AC power for a telephone system is provided by a ring signal generator, which produces a ring signal from a DC power supply using a pair of switches controlled by pulse width modulation (PWM) circuit. The ring signal generator includes a PWM circuit driving a pair of MOSFET transistors via a respective pair of opto-isolators. The output of the MOSFET transistor switches is commonly connected to a low pass filter network. The ring signal generator of the present invention advantageously produces a 65 VRMS ring signal at very high efficiency.

Abstract: An echo canceller and method for cancelling in a return channel signal an echoed receive channel signal where the echoed receive channel signal is combined by an echo channel with an input return channel signal. The echo canceller has a first filter which generates first filter coefficients, generates a first echo estimate signal with the first filter coefficients, and updates the first filter coefficients in response to a first filter control signal. A first summer subtracts the first echo estimate signal from a combined return channel and echo receive channel signal to generate a first echo residual signal. A second filter generates second filter coefficients, generates a second echo estimate signal with the second filter coefficients, and updates the second filter coefficients in response to a second filter control signal.

Abstract: In an ISDN communications system, a remote station power detector circuit comprises a capacitor connected between center taps of transformers on the receive and transmit pairs of conductors. The capacitor stores energy delivered from a central DC power source. Two serially-connected opto-couplers form a discharge path for the capacitor. The first opto-coupler is periodically driven on to partially complete the discharge path. If the capacitor charge exceeds a predetermined minimum, the second opto-coupler will then be driven on, providing a logic level output usable by the remote station. Power consumption is minimized by the use of large resistors in series with the capacitor while reliable power detection is achieved by detecting accumulated charge on the capacitor. Dielectric isolation is provided through the use of opto-coupler circuits.

Abstract: A sending data buffer for holding sending data temporarily and transmitting the data to an echo canceler section is installed between a sending section and an echo canceler section of an echo canceler integrated circuit included in a subscriber line circuit of an integrated service digital network. The sending data buffer is operated in a shift register mode during a sending training mode, and operated in FIFO (first in-first out) mode during a sending/receiving training mode. Also, an adjustment function of the delay amount corresponding to the use setting is added.

Abstract: In an optical fiber telecommunications network, an optical network unit is provided in the subscriber neighborhood for terminating the optical fiber transmission line and for providing electrical signals over metallic lines to the subscribers. The unit functions to convert the optical signal to an electrical signal and demultiplex the electrical signal to divide out baseband telephony signals from broadband video channels. The electrical signals are further demultiplexed and distributed to line cards serving each subscriber, while the broadband video channels are demultiplexed and provided to subscribers that have requested specific video channels. The system includes a test unit for performing metallic tests and also a means to gather subscriber channel requests to form a video control channel which is transmitted to a remote terminal via a baseband telephony channel.