Lucent Technologies Inc.

American Telephone & Telegraph Co., At&t Bell Laboratories

Robert Frederick Lee

Milton L Embree

Donald Raymond Laturell

Jonathan Herman Fischer

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.

Interface devices providing electrical isolation

Embodiments of the invention include an amplifier having an enhanced feedforward arrangement. In a typical operational amplifier output stage of this type, conventional feedforward arrangements comprise one or more active electrical components coupled between the second stage amplifying transistor and the negative output driver. The enhanced feedforward arrangement includes a resistor connected between the second stage amplifying transistor and the negative voltage source and a second resistor connected between the second stage amplifying transistor and the negative output driver. Alternatively, a capacitor is connected in parallel with the second resistor. In this manner, feedforward arrangements according to embodiments of the invention advantageously provide stable, enhanced frequency response, including high frequency response, e.g., above approximately 10 kHz, using economically advantageous passive rather than active electrical components. Furthermore, feedforward arrangements according to embodiments of the invention typically require less components than conventional feedforward arrangements, making them further advantageous from an economic standpoint.

Amplifier feedforward arrangement and method for enhanced frequency

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. One transistor of the second pair having its collector connected to one side of the capacitor acts as a switch to provide charging current to the capacitor when the input voltage at the base of the first transistor of the differential pair is higher than the voltage across the capacitor, which is the same as the voltage at the base of the second transistor of the differential pair. The other transistor of the second pair acts as a voltage limiter for the collector voltage of the second transistor of the differential pair. It prevents saturation of that transistor and also reduces the voltage swing at the collector of the same transistor. This greatly improves circuit speed and prevents large errors which would occur for input voltage peaks of short duration.

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Wyomissing, PA, United States of America

Robert Frederick Lee