Direct drive for a subscriber line differential ringing signal having a dc offset

Abstract

A method of generating a subscriber line differential ringing signal with a DC component includes providing a time-varying supply level, W(t), having a plurality of non-equidistantly spaced critical points along a folding line. W(t) is coupled to the tip line while coupling an alternate source to the ring line in response to a first critical point. W(t) is coupled to the ring line while coupling the alternate source to the tip line in response to a second critical point. An apparatus for generating the ringing signal includes a power supply providing a supply level W(t)=|f(t)−C|+C+D, wherein D is a power supply offset, wherein C≠0. When W(t)≦K a signal processor controls a linefeed driver to toggle between 1) coupling W(t) to the tip line while coupling the ring line to an alternate supply, V(t), and 2) coupling W(t) to the ring line while coupling the tip line to V(t), wherein K is a pre-determined switching threshold.