Abstract: A method and apparatus for communicating a modulated signal across an isolation barrier using capacitors is provided. The present invention allows low distortion communication of an audio signal across an isolation barrier without the need for a large and bulky isolation transformer. The present invention may be used to provide telephone line isolation for modem applications compliant with governmental regulations. A line interface integrated circuit (IC) may be connected directly to a telephone line and powered by the telephone line. The line interface IC may include a sigma delta modulator to communicate the receive signal across a capacitor over an isolation barrier and a digital-to-analog (D/A) converter to provide an analog transmit signal from a sigma delta bit stream communicated across a capacitor over an isolation barrier. Circuitry on the opposite side of the isolation barrier includes similar components to process the transmit and receive signals.

Abstract: A method and apparatus for providing a telephone hybrid function is provided. The present invention maximizes dynamic range while providing a receive signal without interference from a transmit signal. The present invention also provides single-ended to differential conversion. The present invention may be practiced with an integrated circuit powered by a telephone line and coupled to the telephone line without the need for a high voltage isolation barrier between the integrated circuit and the telephone line.

Abstract: A method and apparatus for passing a high frequency signal across an isolation barrier while rejecting low frequency common mode interference is provided. A high frequency signal is coupled across an isolation barrier. A circuit comprising an element having an impedance that is a function of frequency rejects low frequency common mode interference. The high frequency signal is provided as an output. The present invention is useful, for example, for isolating telephone apparatus, such as a telephone modem, from a telephone line.

Abstract: A method and apparatus for providing a telephone line interface having selectable termination characteristics, such as impedance parameters, is provided using AC and DC transconductance loops. The present invention may be used with modem apparatus to provide regulatory compliance of line termination characteristics in multiple countries having different, even conflicting, standards or regulations. The preferred embodiment of the present invention uses a programmable switched capacitor filter to drive a transconductance driver that drives the telephone line. An AC transconductance loop controls AC transconductance characteristics, while a DC transconductance loop controls DC transconductance characteristics.

Abstract: The present invention relates to the field of capacitor layout schemes for integrated circuits. A method comprising nine specific layout criteria is disclosed that eliminates or greatly suppresses problems of prior art capacitance matching.

Abstract: An optical communication system includes two optical modems (12) and (14) which are disposed at either end of an optical fiber data link (10). The optical modems (12) and (14) communicate through LEDs (16) and (18), respectively, with the fiber data link (10). Each of the optical modems (12) and (14) on start-up are peerless and do not operate in either a master or a slave configuration. A ping-pong transmission format is utilized with transmitted packets of data. When one of the optical modems (12) or (14) detects a transmitted packet from the other, it locks up to the transmitted packet with a phase lock loop and takes on slave status. This slave status is transmitted back to the fiber data link (10) in another transmitted packet. The transmitted packet from the slave device is then adjusted time relative to the machine cycle of the slave device until the packet is received by the other optical modem.