Abstract: Impulse response estimation is improved in an adaptive filter by compensating digital signals incoming to the filter to include a nonlinearity substantially identical to a nonlinearity included in a return signal path to the filter.

Abstract: The invention concerns a process and an apparatus to initiate the reversal of an inverter controlling the placement of a so-called hands-free telephone set in a reception mode or a transmission mode. According to the invention, the position of the inverter (8) is a function of the sign of the difference between the amplitudes of the integrated analog emitted signal and the integrated analog received signal. By preference, the received signal is drawn downstream (from the received-signal output) of the inverter, while the emitted signal is drawn upstream (from the emitted-signal input) of the inverter (8). A second received signal is drawn upstream of the inverter (from the received-signal input) so as to nullify the delay imparted to the change in position of the inverter if the amplitude of the corresponding integrated signal becomes significant.

Abstract: The circuit of the present invention detects variations of a current I.sub.L flowing in a telephone line LL. A low-value resistor r is connected in series with line LL. A constant voltage generator is connected across this resistor. The current Is applied to resistor r by the contant voltage generator varies as a function of I.sub.L. This being so, a measurement of the variations of Is will reflect variations of I.sub.L and, therefore, can be used to detect both amplitude and directional variations of I.sub.L.

Abstract: A tip-ring interface that utilizes a single detector to detect ringing, forward loop current, and reverse loop current. In one embodiment, forward or reverse battery state may be detected when on-hook.

Abstract: A SLIC includes controlled current circuits (CCCs) which simulate feed resistors for controlling d.c. feed to a two-wire telephone subscriber line which is coupled to two terminals, control being achieved via a feedback loop. A differential amplifier has an inverting input coupled to the tapping point of a potential divider connected between the terminals, and a non-inverting input connected to a reference potential of half of the supply battery voltage. For suppressing longitudinal currents on the line, the amplifier output is connected to each terminal via a d.c. blocking capacitor in series with a resistor, the resistors having closely matched resistances. For maintaining d.c. balance, the output of the amplifier is coupled via a low pass filter to control a current splitter included in the feedback loop, to control the relative proportions of control currents for the CCCs.

Abstract: A method for providing and for testing adaptive echo cancellation in an apparatus including transmission equipment for data communication. The apparatus includes a 2-wire to 4-wire hybrid circuit which receives a signal from a remote end which is cut off for purposes of the testing method. A signal consisting of randomly occurring ones and zeros is applied to the send end of the apparatus. Also included in the apparatus is an adaptive echo canceller which cooperates with the send end and with a filtered signal received from the hybrid circuit to produce a correction signal which is fed back to the adaptive echo canceller and which is also compared with threshold values for purposes of testing the function of the apparatus.

Abstract: In particular, there are provided in accordance with the invention a method and apparatus for adjusting a digital equalizing filter in a hybrid circuit in a telecommunication system for transmitting digital information in duplex on a single line pair with simultaneous adaptive echo elimination and adaptive elimination of noise caused by intersymbol interference, where a first and a second compensation signal (e(t), i(t)), which are respectively dependent on the stored parameters of a digital balance filter and an equalizing filter, are subtracted from a received signal (a(t)+e(t)+i(t)) to form a difference signal (r(t)) which is compensated for noise respectively caused by echoes and intersymbol interference, the balance filter parameters being corrected with the aid of a correction signal (.epsilon.B.sub..kappa.) dependent on the difference signal (r(t)). The equalizing filter parameters are adjusted with the aid of a further correction signal (.epsilon.U.sub..kappa.

Abstract: A circuit for reducing the effect of acoustic and electrical feedback in duplex "hands free" telephone sets. The circuit uses relatively simple and inexpensive gain control circuits and expanders to reduce the effects of feedback by controlling the gain of a transmitted signal in inverse relationship to the strength of a the received signal.

Abstract: A telephone terminal whose structure separates the high voltage and the low voltage functions in separate modules; the high voltage module being specific to the telephone network and the low-voltage module being in conformity with the service provided by the terminal.

Abstract: A constant current line circuit for connection to balanced tip and ring leads of a telephone line and unbalanced transmit and receive leads of a PABX. A differential amplifier receives and applies incoming audio signals carried by the tip and ring leads to the unbalanced transmit lead, and detects D.C. loop current flowing through the tip and ring leads and generates a D.C. signal in response thereto. A voltage controlled feed current supply, connected in a circuit to the differential amplifier, generates a constant current D.C. voltage to the tip and ring leads in response to receiving the D.C. signal, and an integrator circuit is connected in a feedback path from the output of the differential amplifier to a voltage control input of the supply, for filtering audio signals received by the differential amplifier and regulating the generated D.C. signal to a quiescent value of approximately zero volts. The line circuit provides simultaneous bidirectional signal translation and constant D.C.

Abstract: An animated telephone annunicator apparatus provides realistic movements so that a user of the apparatus appears to converse with the apparatus. The apparatus receives telephone signals, and in response to these received signals moves portions of the apparatus in synchronism with the signals. As a result, the apparatus appears to realistically speak the words of a calling party.

Abstract: An amplifier having properties of natural side tone balancing based on the utilization of a bridge arrangement, high efficiency with resulting high gain, high AC impedance and compatibility with electret microphones and electret microphone amplifiers. A matched pair of differential transistors arranged as part of a bridge circuit form a detector of the receive signal at one input versus a transmit signal which appears at both inputs in the same phase and therefore is rejected as a common mode signal. The resultant balancing of side tone and high gain finds particular application in telephone networks where the characteristics dictate the need for higher than usual receive gain or for use by auditorially handicapped users over a normal telephone network.

Abstract: One arm of a subscriber line battery feed circuit (Ra, Rb, B) contains a FET transistor (TrL) as a current limiting element which, when a limit value of feed current is reached, is operated in such manner that it limits the feed current. If the limiting operation exceeds a first time interval, the feed circuit is interrupted by the blockage of the transistor. The transistor cannot resume the conductive state until the elapse of a second, longer time interval which is sufficient for cooling the transistor. The threshold value is not rigid but changes in accordance with the amplitude and direction of interference longitudinal currents which are superimposed upon the feed current.

Abstract: A speakerphone control circuit is disclosed. The control circuit includes a first electronic switch coupled between the speakerphone microphone and a hybrid circuit coupled to the telephone line and a second electronic switch coupled between the speakerphone loudspeaker and the hybrid circuit coupled to the telephone line. A first sensing circuit for sensing the microphone signal and a second sensing circuit for sensing the received loudspeaker signal are provided. The outputs of the first and second sensing circuits are multiplexed and digitized and fed to a microprocessor controller. In response to the levels of the multiplexed signal, the microprocessor determines the state of the speakerphone from among four possible states, including a first talk state, low gain talk state, first listen state and low gain listen state.

Abstract: Improved speakerphones (120 and 130 in FIG. 1) for both radio (112) and landline (138) telephones are described. The improved speakerphones (120 and 130) each include a microphone (102 and 132), a speaker (104 and 134) and unique control circuitry (106 and 136). The control circuitry of the improved speakerphone (200 in FIG. 2) interfaces a microphone (250) to a transmit signal (220) and speaker (260) to a receive signal (222) of a duplex communication path, such as a radio channel or telephone line. Variable gain stages (212 and 202) amplify and attenuate the speaker and microphone audio paths, respectively, in response to a gain control signal (223) from control logic (230).

Abstract: An adaptive hybrid circuit is disclosed for adaptively cancelling a crosstalk component from a transmitter to a receiver in a local station of a local area network. In a preferred embodiment the adaptive hybrid circuit is coupled to a common two-wire transmission line in the network and also between the transmitter and the receiver of the local station. The adaptive hybrid circuit is comprised of a comparator, an integrator and an adjustment circuit. An output signal from the receiver is compared in the comparator with a transmit signal to develop a first signal which causes the integrator to develop a second signal having an amplitude which varies as a function of the states of the first signal. The second signal from the integrator, a transmitter signal, and a composite signal from the transmission line containing a crosstalk component from the transmitter and a received signal component transmitted from a remote station are applied to the adjustment circuit.

Abstract: The present invention is an improved subscriber line interface circuit which allows fast detection of an off-hook signal in the presence of a ringing signal during an answer mode while also permitting fast detection of dialing pulses during a calling mode. A programmable filter is used in the supervision circuit of the SLIC to allow the cutoff frequency of the filter to be varied so that the 20 Hz ringing signal will be attenuated during a ringing sequence and dialing pulse rates up to 20 Hz will be passed by the filter during the calling mode. A clamping amplifier is used to clamp the received signal to a maximum of 1.5 times the loop threshold current. This eliminates the large variations in the rise and fall times of the pulse dialing signal due to variations in the loop current caused by varying impedances of the telephone line. The filter is programmed by using an analog switch to bypass certain filter elements.

Abstract: An improved echo canceller control method utilizes two adaptive level detectors for controlling or inhibiting the updating of coefficients in the echo canceller. Updating is permitted only when an actual received signal is present and no transmit signal as measured by the adaptive level detector exists. During periods when no transmit or receive signals are present, update is inhibited and the adaptive level detector establishes a noise reference level. When transmission activity is present but no receive activity is present, inhibiting of the echo canceller updating allows the adaptive level detector to seek and establish the background noise reference level and avoids the disruption of the echo canceller coefficients that would occur from double talk if a receive signal were suddenly to become present. When actual double talk, i.e., both receive and transmit activities are present occurs, updating is also inhibited for the same reason.

Abstract: A teleconferencing system for connection to telephone lines or other communication links. Directionally gated microphones receive local speech for audio send signal transmission to the far end on the telephone line, and audio receive signals from the far end are output locally via a loudspeaker. The outgoing send signals and incoming receive signals are automatically suppressed in accordance with user and setup controls (volume and suppression) and in accordance with the strength of the incoming receive signal. When the system is in a send mode, the receive signals are suppressed to a lower audible level; when the system is in a receive mode, the send signals are suppressed. The mode of the system is switched during conversation. When simultaneous talking (speech from both ends) occurs, priority is given to the interrupting party.

Abstract: A subscriber telephone line interface circuit is provided with reduced power stand-by mode. For 90% of the time such circuits only have a function of monitoring the line. Means are described for considerably reducing the power consumption of the circuit during such monitoring periods. The reduction is provided essentially by modifying the construction of the output stages connected to the telephone line; these stages become generators of a fixed voltage for biasing the line when the circuit is in monitoring mode.