Circuit and method for reducing common mode interference in tele

Details Circuit and method for reducing common mode interference in tele Circuit and method for reducing common mode interference in tele

1996-02-07

1997-12-02

Kuntz, Curtis

Telephonic communications

Multi-line or key substation system with selective switching...

379398, 379416, H04M 160, H04M 900, H04M 704, H04M 176

Patent

active

056944608

ABSTRACT:
A circuit for, and method of, reducing cross-coupled interference between first and second telephone lines of a multi-line telephone instrument and a telephone instrument containing the same. The circuit includes: (1) a first differential input amplifier having first tip and ring inputs coupled to conductors of the first telephone line and first tip and ring shunt resistors coupling the first tip and ring inputs to a signal reference of the telephone instrument and (2) a second differential input amplifier having second tip and ring inputs coupled to conductors of the second telephone line and second tip and ring shunt resistors coupling the second tip and ring inputs to the signal reference, the first and second tip and ring shunt resistors decreasing a common mode input resistance of the first and second differential input amplifiers, thereby attenuating cross-coupled interference common to both of the first and second telephone lines. The circuit and method may further be suitably employed to reduce the effects of common mode interference in other telephone instruments, including, but not limited to, single-line telephone instruments.

REFERENCES:
patent: 4570034 (1986-02-01), Serrano
patent: 4803718 (1989-02-01), Neil et al.
patent: 5274702 (1993-12-01), Rosch et al.

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