| 摘要 |
Alternating current signals are differentially coupled between a two wire communications line and a telecommunications facility by a line interface circuit. The line interface circuit differentially drives signals destined for the two wire communications line, with a predetermined source impedance, via tip and ring amplifiers and tip and ring feed resistors. An amplifier circuit differentially receives signal voltages being developed by currents traversing the tip and ring feed resistors, and detects signals destined for the telecommunications facility by subtracting a representation of the signals destined for the two wire communications from a representation of the differentially received signals. A notch filter connected in series with the tip and ring feed resistors impedes any longitudinal signals of about a predetermined frequency which would otherwise traverse the tip and ring feed resistors, whereby a routinely available industry standard common mode rejection performance characteristic of a differential input of the amplifier circuit consistently yields telephony standard performance in the presence of reactively coupled longitudinal power line signals of about said predetermined frequency.
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