| 摘要 |
TELECOMMUNICATION LINE CIRCUIT Each line wire is separately biassed by DC potentials feeding inputs of the respective line wire driver amplifiers, the first potential (BA) being nearer ground and the second at an equal distance from the negative supply used to power the amplifiers so as to allow a suitable AC swing for the speech and metering signals also feeding the inputs of the amplifiers. The second potential (BB) is obtained from a DC synthesizing loop voltage and to which is added (OA6) the first potential, both potentials being also combined (OA5) to control a switched mode DC/DC converter delivering the negative power supply. In addition to both Potentials being filtered with reference to ground, another measure reducing noise relies on AC signals push-Pull outputs driving the amplifier inputs, also in push-pull, through four resistances.
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