Gain or loss compensation circuit for telephone lines

Claim 1

A gain or loss compensation circuit, interconnected between a digital carrier transmission line and a customer loop telephone line, said telephone line defining a length, comprising, in combination: a converter, interconnected to said transmission line, for accepting a receive digital data signal and converting said receive digital data signal to a receive intermediate analog signal and for accepting a transmit intermediate analog signal and converting said transmit intermediate analog signal to a transmit digital data signal, said converter changing said analog signals with a variable gain in response to a compensation signal; an interface circuit, interconnected between said converter and said telephone line, for accepting said receive intermediate analog signal and providing a receive analog telephone signal to said telephone line and for accepting a transmit analog telephone signal from said telephone line and providing a transmit intermediate analog signal to said converter, said interface circuit including a pulse width modulated power converter defining a pulse width, said pulse width being correlated to said length of said telephone line, and said interface circuit providing a direct current to said telephone line related to said pulse width; a gate array for sensing said pulse width of said power converter and responsively providing a measured signal representative of said pulse width; and a controller for receiving said measured signal and responsively providing said compensation signal to said converter to vary said variable gain of said converter relative to said pulse width of said power converter and said length of said telephone line.