Signal coupler using high voltage and low voltage filtering

Abstract

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 lines. The low voltage filtering reduces the need for components, which are capable of operating in the high voltage environment and therefore reduces the space on the circuit board, which is occupied by each of the signal couplers. In this way, the number of individual subscriber lines that a given circuit board can accommodate can be increased.

What is claimed is:  
     
         1 . A signal coupler comprises: 
 high-voltage low pass filter operably coupled to low pass filter an analog signal to produce a partially filtered Plain Old Telephone System (POTS) signal;    subscriber loop interface circuit operably coupled to provide a two-wire to four-wire interface conversion between a PTIP line and PRING line carrying the filtered POTS signal, a transmit line pair, and a receive line pair,    wherein an incoming portion of the partially filtered POTS signal is provided on the transmit line pair; and    low-voltage low pass filter operably coupled to low pass filter the incoming portion of the partially filtered POTS signal to produce a filtered incoming POTS signal.    
     
     
         2 . The signal coupler of  claim 1 , wherein the high-voltage low pass filter further comprises: 
 a pair of resistors;    a pair of inductors; and    a capacitor operably coupled to the pair of resistors and to the pair of inductors to provide a single stage-second order low pass filter.    
     
     
         3 . The signal coupler of  claim 2 , wherein the low-voltage low pass filter further comprises: 
 continuous time low pass filter stage operably coupled to provide second order filtering of the incoming portion of the partially filtered POTS signal to produce the filtered incoming POTS signal.    
     
     
         4 . The signal coupler of  claim 2 , wherein the low-voltage low pass filter further comprises: 
 first continuous time low pass filter stage operably coupled to provide second order filtering of the incoming portion of the partially filtered POTS signal to produce a first filtered incoming POTS signal;    second continuous time low pass filter stage operably coupled to provide second order filtering of the first filtered incoming POTS signal to produce a second filtered incoming POTS signal; and    third continuous time low pass filter stage operably coupled to provide second order filtering of the second filtered incoming POTS signal to produce the filtered incoming POTS signal.    
     
     
         5 . The signal coupler of  claim 1  further comprises: 
 coding/decoding circuit operably coupled to the filtered incoming POTS signal into a digital POTS signal; and  
 digital low pass filter operably coupled to digitally low pass filter the digital POTS signal to produce a filtered POTS signal.  
 
     
     
         6 . The signal coupler of  claim 1  further comprises: 
 high pass filter operably coupled to high pass filter the analog signal to produce data signals; and  
 hybrid operably coupled to provide a two-wire to four-wire interface between a line carrying the data signals and a transmit line and a receive line.