SOPA: A high-efficiency line driver in 0.35 /spl mu/m CMOS using a self-oscillating power amplifier

Recently, with development of xDSL technologies, design of line drivers regains attention since the thermal limitation at the central office side (CO) demands high-efficiency line drivers. This specification becomes more severe since for the ADSL standard Discrete Multi Tone (DMT) modulation is chosen. DMT signals have a high crest factor (CF=V/sub max//V/sub min/) and demand a highly-linear line driver. Since efficiency of a class AB line driver ideally is inverse proportional to the CF, the efficiency of this type of line driver is low in DMT-based applications. When implementing a line driver in a mainstream CMOS technology, decreasing supply voltage increases this problem, since a higher quiescent current is necessary to maintain the same distortion levels. This paper depicts the principle of the differential self-oscillating power amplifier (SOPA).