This paper presents the design of a high-efficiency line driver for central-office ADSL modems. This driveris a modification of the conventional class-G architecture already in use for hi-fi audio applications and it isbased on two amplifiers operating in parallel and powered by different power supplies (±5 V and±12 V). The low-voltage amplifier is active with low-level input signal, while the high-voltageamplifier is used for processing the peaks of the DMT signal. By means of this solution and by properly interfacingthe two amplifiers, high efficiency is achieved while maintaining a harmonic distortion similar to the one achievedby conventional class-AB schemes and compatible with the ADSL requirements. The circuit was designed in a 0.8-mBCD technology.