A 750 mW class G ADSL line driver with offset-controlled amplifier hand-over

This paper discusses the design of a high-efficiency ADSL line driver and reports some experimental results. The driver is a Class G power amplifier implementing a modified version of the architecture widely employed in hi-fi audio applications. The proposed architecture is based on two amplifiers operated in parallel and powered by different supply voltages (±5 V and ±12 V). The low-voltage amplifier operates on low-level input signals, whereas the high-voltage section processes the peaks of the ADSL signal. The hand-over between the low-voltage and the high-voltage amplifier is determined by a dead zone purposely introduced in the I/O characteristic of the high-voltage amplifier. This solution allows a smooth transition between lowand high-voltage operation, providing better distortion performances than the classical Class G scheme with series connected output devices. By this solution, low power consumption is achieved (750 mW with passive line impedance matching) with a distortion performance similar to the one achieved by conventional Class AB schemes. The circuit was designed in a 0.8 μm BCD technology.