| 摘要 |
An interface circuit is provided for a telephone answering machine which does not require a transformer and which provides the proper direct current and alternating current terminating impedance for the telephone line. The direct current terminating impedance is provided by connecting a resistor of a selected resistance value across the telephone line, and the alternating current terminating impedance is achieved by multiplying the effective impedance of the resistor for alternating current audio signals by providing an amplifier for the outgoing audio signals with positive feedback of amounts sufficient to provide the desired impedance multiplication effect but which is insufficient to sustain oscillation.
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