A CMOS direct access arrangement using digital capacitive isolation

A Direct Access Arrangement (DAA) provides a customer interface to the public switched telephone network (PSTN). In addition to DC and AC termination and ring detect functions, the DAA must also provide high voltage isolation (>1500 V) between the phone network and system side devices while passing control information and a high integrity audio signal. This solution uses a capacitive isolation technique with a pair of 5 V 0.5 mm triple-metal CMOS devices in 16-pin SOIC packages that provides a digital communication link between the telephone line circuitry (isolated side) and the system side of the barrier. A few low-cost, high-voltage discrete components are added to interface the isolated-side device to the high-voltage telephone network.