Abstract: Embodiments of the present invention are directed to interface devices that provide an interface between a first device and a second device, where the interface device provides electrical isolation between the first device and the second device, and where codec processing is distributed between the first-device side and the second-device side of the interface device. In a preferred embodiment, the second device has a transmission line, the interface device is a modem, and the electrical isolation is provided by one or more digital couplers that transmit sigma-delta signals that are coded and decoded in both the first-device-side and second-device-side circuitries of the modem.

Abstract: A device for providing a balanced input over a photoelectric cell used in a motion picture film projector and for providing an unbalanced output audio signal for driving subsequent elements in an audio reproduction unit connected to the motion picture film projector, wherein the reproduced output audio signal has an improved quality over that of a previously known transformer output signal. The circuit supplies an unbalanced voltage signal in response to a current generated by a photoelectric cell having at least a first and second terminal. The circuit includes: a current to voltage converter for receiving the current from the first terminal of the photoelectric cell and providing a first output voltage and a current return unit connected to the current to voltage converter for receiving the first output voltage and for providing a second output voltage and for providing a return current along the second terminal of the photoelectric cell.

Abstract: A high voltage operational amplifier includes a first differential stage whose output is supplied to a current mirror amplifier (CMA) comprised of bipolar transistors, for driving a high voltage MOS output transistor. The bipolar CMA is selected and configured to provide low equivalent input noise and low input voltage offset.

Abstract: A high voltage capacitor structure for integrated circuits or the like. The capacitor includes a provision for equalizing charge when multiple capacitors are series coupled. Charge is equalized by a SiN layer overlaying, and in contact with one terminal of, the capacitor. A ground ring surrounds the capacitor structure and is also overlayed by, and in contact with, the SiN layer.

Abstract: A peak catcher circuit comprises an input differential amplifying circuit consisting of a pair of transistors. An input signal in the form of an electrical wave or pulse is applied between the base of the first transistor of the pair and a point of fixed potential, while a capacitor is connected between the base of the second transistor of the pair and the fixed potential. A first fixed current source is connected between the coupled emitters of the differential pair and the fixed potential, and a second smaller fixed current source is connected between the collector of the second transistor and a second fixed potential. A second pair of oppositely poled emitter-coupled, common base connected transistors is connected between the base of the second transistor of the differential pair and the second fixed potential, and there is a connection from the coupled emitters of the second pair to the collector of the second transistor of the differential pair.

Abstract: An origination scan circuit for detecting circuit closure state in a loop circuit has a much lower impedance than does the typical loop circuit. Its source impedance is split into separate resistive parts for connecting opposite terminals of an office battery to the tip and ring leads of the loop. Currents in the separate resistive parts are sensed and summed for comparison against a threshold current to indicate whether or not a subscriber station on the loop is off hook. Threshold current magnitude is variable to accommodate loop start and ground start applications. When the off-hook state is detected, the origination scan circuit is disabled by switching open the resistive part connections, and loop current is thereafter provided by other suitable means. Automatic current limiting arrangements are included for converting the switching functions to high impedance circuit elements.

Abstract: The present invention relates to a circuit capable of providing a negative temperature coefficient greater than that provided by discrete silicon integrated circuit components. A constant current source and a resistor divider network are added to a bipolar junction transistor, where the resistors and the constant current source function to increase the negative temperature coefficient of a bipolar junction transistor. The negative temperature compensation circuit formed in accordance with the present invention provides a sufficient negative temperature coefficient to offset the large positive temperature coefficient associated with high voltage avalanche breakdown diodes without requiring a high voltage integrated circuit.

Abstract: There is disclosed a precision linear comparator for a speakerphone circuit having two rectifying constant voltage nodes for separately summing two groups of signals derived from a speakerphone transmit channel and receive channel and supplying at an output terminal a signal representative of the difference between two unblocked summed signals. Each node blocks its summed signal if the signal is not representative of a true voice signal. A null signal is supplied at the output terminal during the absence of unblocked summed signals.

Abstract: There is disclosed a circuit, using integrated techniques, for dividing the AC component of an input signal by the DC component of that signal and then muitiplying the signal by a fixed DC current. This circuit is useful in opto-coupled gain control devices where the output AC signal must be gain adjusted for the light transfer characteristics of the opto-couplers.

Abstract: The subject switchhook status detector is part of a battery feed circuit and functions to sense the magnitude of the current flowing on both the tip and ring conductors. The detector also generates a sum signal which represents the total metallic current flowing in the loop. The subject detector maintains the battery feed circuit in the off state until the sum signal exceeds a first predetermined threshold and, concurrently, both the tip and ring currents individually exceed another predetermined threshold. This combination of requirements prevents the generation of erroneous off-hook indications.

Abstract: The battery feed circuit of the present invention does not rely principally on balanced current generation circuitry but, instead, uses a feedback circuit to ensure the production of the required currents on the communication pair. The subject feedback circuit automatically and instantaneously compensates for longitudinal currents by precisely sensing the currents appearing on each lead of the communication pair. These sensed currents are summed to remove the balanced longitudinal component and the resultant signal represents the actual metallic current on the communication pair. This actual metallic current is subtracted from a predetermined reference current and the difference between these two signals constitutes an error signal which is amplified to provide the current drive supplied to the communication pair.

Abstract: The subject precision isolation amplifier adds error correction circuitry to a basic isolation amplifier circuit to thereby produce an error-free output signal comprising only the metallic component of the monitored voltages. The error correction circuit consists of a pair of up/down emitter followers and a current mirror circuit which function to eliminate both the longitudinal components of the monitored voltage signals and the voltage offset generated by the basic isolation amplifier. A second error-free ouput signal comprising only the longitudinal component of the monitored voltage signals is also provided.

Abstract: In situations where it is desired to provide an extremely accurate output current generated from an input voltage, errors occur in the conversion. Conventional solutions depend upon operational amplifiers and rely upon the availability of both positive and negative reference voltages. When attempting to design an integrated circuit having accurate output currents using only integrated circuit technology the circuit components introduce undesirable errors. These problems have been overcome by an arrangement which includes a current mirror (104, 105) for providing the output current and also for providing a feedback current (101, 102) for use in modifying the current flowing in an input emitter follower (103). Using this approach, the base emitter voltages of the emitter follower transistor and the input transistor of the current mirror are forced to cancel each other. By adjusting the current densities of the two transistors, substantially perfect error compensation is achieved.

Abstract: The subject circuit is a converter/isolation circuit which employs only a few components yet functions to monitor a particular signal and produce an output signal which is identical to or proportional to (to a high degree of accuracy) to the monitored input signal. The subject circuit monitors a voltage and generates both a current and a voltage as output signals.

Abstract: A circuit is provided in which the output current is the inverse, that is, the reciprocal, of the input current.The circuit comprises an input current branch and an output current branch, each branch including the emitter-collector electrodes of one of matching transistors, and a reference current branch containing a pair of serially connected, like poled, diode-connected transistors. The base electrode of the input branch transistor is connected to a node in the reference branch on one side of both diode-connected transistors, and the emitter of the output branch transistor is connected to a node in the reference branch on the other side of both diode-connected transistors. The base of the output branch transistor is connected to a node in the input branch on the emitter side of the input branch transistor.The circuit thus represents sums and differences of various voltages across the PN junctions in the several branches.

Abstract: In an oscillatory signal generator circuit exceptional frequency stability is insured by the use of interrelated constant current sources (520, 521, 522) that provide an insensitivity to supply voltage variations over a wide range. Two of the current sources determine the duty cycle by controlling the charge and discharge current of a capacitor (C) in the circuit. A third current source determines the voltage swing on the capacitor. By varying the current output from the third current source, the generator circuit provides a variable frequency signal.

Abstract: An electronic tone ringer responds to ringing signals on a telephone line while being unresponsive to dialing pulses or other signals on the line. Powered directly from the telephone line the ringer uses current sources (223-226) to provide a high impedance to the ringer circuitry and an insensitivity to line voltage variations so that reliable operation of the ringer is maintained on long loops and with multiple ringers terminated on the line. A multitone signal for activating an electroacoustic transducer (300) is provided by frequency modulating a single oscillator (500) within the tone ringer.