Patent ID: 6181777
Filing Date: 2001-01-30
Classification: H03G,H03H,H04M

Abstract:
An impedance blocking filter circuit used in telecommunication systems for interconnecting between incoming telephone lines and customer's terminal equipment so as to unconditionally block impedances from above 20 KHz due to the customer's terminal equipment from an ADSL network unit and/or home networking interface unit, said filter circuit comprising:first, second, and third inductors connected in series between a first input terminal and a first common point;said first inductor having its one end connected to said first input terminal and its other end connected to one end of said second inductor, said second inductor having its other end connected to one end of said third inductor, said third inductor having its other end connected to said first common point;fourth, fifth, and sixth inductors connected in series between a second input terminal and a second common point;said fourth inductor having its one end connected to said second input terminal and its other end connected to one end of said fifth inductor, said fifth inductor having its other end connected to one end of said sixth inductor, said sixth inductor having its other end connected to said second common point;first switching means having a first end and a second end and being responsive to DC loop current for electrically connecting said first end to said second end;a capacitor having a first end connected to said first common point and a second end connected to said first end of said switching means, said second end of said switching means being connected to said second common point; andcorrection circuit means interconnected between said common points and said output terminals for significantly reducing return loss caused by inductive impedance when the customer's terminal equipment goes off-hook.