A signal coupler is provided which decreases the number of discreet elements required to provide low pass filtering for the plain old telephone service (POTS). The low pass filtering is shifted to areas of the signal coupler circuit which do not operate with the high battery voltage present on telephone...http://www.google.com/patents/US6418221?utm_source=gb-gplus-sharePatent US6418221 - Signal coupler using low voltage filtering
