Combined plain old telephone system (POTS) and digital subscriber loop (DSL)
line card capable of suppressing low frequency transients. The line card includes
the following elements. A DSL receive path receives DSL data from a loop. A POTS
receive path receives POTS data from the loop. A combined POTS and DSL transmit
path transmits POTS and DSL data to the loop. An impedance generator is coupled
between the POTS receive path and the combined POTS and DSL transmit path for synthesizing
impedance for signals in the combined POTS and DSL transmit path. A low frequency
detector selectively applies a high pass filter to an output of the impedance generator
for filtering the low frequency transients. Further, a clipped signal detector
and a variable pole high pass filter are provided in the POTS receive path. The
clipped signal detector in the POTS receive path triggers a switch that discharges
stored transient energy in the receive path. The variable pole high pass filter
in the POTS receive path is modified during ringing and hook switch activity, by
the line card controller, in order to attenuate transient signals.
