On the Design of a Switching xDSL Line-Driver

Since the xDSL specifications impose stringent linearity requirements to ensure the integrity of the data transferred, current line drivers use linear amplifiers. The downside of these solutions is their power consumption, as the xDSL modulation has a high peak to average ratio, forcing the amplifier to operate in its least efficient region. An alternative is the use of switching amplifiers, which theoretically have an efficiency of 100%. However, the nonlinear nature of these amplifiers complicates the design. To meet the linearity requirements, the switching frequency should be sufficiently high, but as this is limited by the technology used, additional techniques must be adopted. Therefor, a self-oscillating topology has been chosen and a mathematical model of the loop formulated to predict its behaviour. The model is then validated by numerical simulations on macro-blocks, yielding the values required for an implementation on silicon. Keywords—xDSL line-driver, nonlinear design, high voltage CMOS integrated circuits, asynchronous amplifiers, pulse width modulation, switching amplifiers, power amplifiers