Importance

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Abstract

An electronic telephone employing transmit and receive solid-state amplifiers having sufficiently low DC resistance to be biased by a DC signal over a pair of conductors with substantially less than four volts and having sufficiently high AC impedance for transmitting AC communication signals over and receiving AC communications from that pair of conductors. The amplifiers are directly coupled to the conductors, and the amplifiers include a transmitter section comprising a microphone and first solid state amplifier coupling the microphone to the pair of conductors, and a receiver section comprising a speaker and a solid state amplifier coupling the speaker to the pair of conductors. A shunt circuit is connected across the pair of conductors to adjust impedance characteristics of the telephone responsive to the available DC bias. A DC feedback circuit has an input coupled across the pair of conductors and an output coupled to the solid-state amplifiers, to provide a stable reference voltage to the solid-state amplifiers.

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First Claim