Circuit for suppressing noise influences in the evaluation of signal states on transmission lines

US4297531A · kind A · utility

Assignee

• Siemens Aktiengesellschaft · DE

Inventors

• Axel Dalhof · Puchheim, DE
• Robert Lechner · Otterfing, DE

Key dates

• Filing date: Oct 10, 1979
• Grant date: Oct 27, 1981
• Expiry date: Oct 10, 1999

Classification

• Technology area (CPC H): Electricity
• CPC primary: H04Q3/00
• WIPO field: Telecommunications
• WIPO sector: Electrical engineering

Abstract

A circuit arrangement is provided for suppressing periodic or non-periodic noise voltage components which are superimposed as an undesirable influence on the DC voltage signal to be evaluated on DC fed, two-conductor transmission lines, particularly for extension circuits in telephone systems which are fed in the subscriber circuit of the exchange location via symmetrical branches and evaluated with respect to the subscriber's loop state changes. By coupling to suitable circuit points of the subscriber circuit, the superimposed noise signal is separated by a differential amplifier and fed to a second differential amplifier. The original loop signals, superimposed with noise, is also fed to an input of the second differential amplifier so that a noise-free useful signal indicating the operational state arises at the output of the second differential amplifier.