Transformerless line interface solution for baseband modems

In a conventional modem front end, the digital PCM data generated by the data pump is converted by a codec into analog signals. These signals are then transferred via hybrid, transformer, and DAA (data access arrangement) to the telephone line. The transformer is used for the mandatory potential decoupling between the line and the modem itself. This article presents a two-chip solution, which replaces the transformer and integrates all needed functions of a modem front end like AC and DC characteristics, ring impedance and ring detection. This integration gives the opportunity to cover different country specifications with a unique board by just programming software coefficients.