Patent ID: 6940969
Filing Date: 2005-09-06
Classification: H04M

Abstract:
1. An interface circuit for interfacing between a pair of subscribe tip/ring lines and a central office of a telecommunications network, the interface circuit comprising: (a) filter circuitry configured to separate low-frequency and high-frequency signals appearing on the tip/ring lines, wherein the filter circuitry comprises a blocking capacitor that affects the impedance of the tip/ring lines; (b) high-frequency interface circuitry configured to process the high-frequency signals; (c) low-frequency interface circuitry configured to process the low-frequency signals, wherein the low-frequency interface circuitry comprises: (d) a capacitor cancellation circuit (CCC) coupled across the blocking capacitor and adapted to generate a first single-ended signal, which is applied to the SLIC and coupled via the SLIC and the filter circuitry to the tip/ring lines to cancel a portion of the effect of the blocking capacitor on the impedance of the tip/ring lines.