An impedance blocking filter circuit is provided for use in
telecommunication systems for interconnecting between incoming telephone
lines and customer's terminal equipment so as to unconditionally block
impedances above 20 KHz due to the customer's terminal equipment from an
ADSL network unit and/or home networking interface unit. The filter
circuit includes first, second, and third inductors connected in series
between a first input terminal and a first common point. A first resistor
has its one end connected also to the first common point and its other
end connected to a first output terminal. Fourth, fifth and sixth
inductors are connected in series between a second input terminal and a
second common point. A second resistor has its one end also connected to
the second common point and its other end connected to a second output
terminal. A capacitor has its ends connected across the first and second
common points. In other aspects, the filter circuit also includes
switching means for eliminating shunt additive capacitance and/or
correction circuit means reducing significantly return loss. An impedance
blocking filter circuit is provided for use in telecommunication systems
for interconnecting between incoming telephone lines and customer's
terminal equipment so as to block impedances above a desired frequency
range due to the customer's terminal equipment from a DSL network unit
and/or home networking interface unit. In one exemplary embodiment, the
filter circuit includes first, second, and third inductors connected in
series between a first input terminal and a first common point. A first
resistor has its one end connected also to the first common point and its
other end connected to a first output terminal. Fourth, fifth and sixth
inductors are connected in series between a second input terminal and a
second common point. A second resistor has its one end also connected to
the second common point and its other end connected to a second output
terminal. A capacitor has its ends connected across the first and second
common points. In other configurations, the filter circuit also includes
switching means for eliminating shunt additive capacitance and/or
correction circuit means reducing significantly return loss.