Class AB-D-G line driver for central office asymmetric digital subscriber line systems

This paper describes the design of a line driver that can be used for the downstream central office ADSL (asymmetric digital subscriber line) channel. The design uses a 0.35 μm/3.3 V CMOS process, and has a hybrid architecture that combines a class-AB stage in parallel with two class-D stages, each with different supply voltages. Due to the low power supply voltage, an alternative class-AB stage is used, that achieves a higher output voltage swing than the traditional class-AB stage. Simulations to estimate the power consumption of this design resulted in 1.3 W for the central office downstream channel; 83% of the power is dissipated in the switching transistors, and the buffers that drive them. The architecture is flexible to additional circuit enhancements.