Patent ID: 7006623

Claim:
A DC driver circuit coupled to a tip/ring line, said DC driver circuit comprising: a first capacitor coupled to a first switch, said first switch coupled to an amplification circuit, said amplification circuit being coupled to said tip/ring line; an RC circuit coupled to a second switch, said second switch coupled to said amplification circuit, said RC circuit comprising a second capacitor and at least one resistor; said first switch being closed and said second switch being closed during a make state to cause said amplification circuit to draw current from said tip/ring line; said first switch being open and said second switch being open during a break state to prevent said amplification circuit from drawing current from said tip/ring line; a third switch having a first terminal coupled to a voltage source and a second terminal coupled to said first capacitor, said third switch being closed during said break state to precharge said first capacitor to enable said first capacitor to transfer charge onto said second capacitor at initiation of said make state; wherein said RC circuit, said first switch, and said amplification circuit share a common node such that a rate of discharge of a voltage at said common node is controlled by changing at least one value of said second capacitor and said at least one resistor, thereby changing a rate at which a DC loop current at said tip/ring line changes; wherein said amplification circuit comprises an op amp coupled to a first transistor.