High efficiency line driver for high crest-factor signals such as dmt/adsl signals

Abstract

The present invention, generally speaking, achieves a highly efficient line driver for high crest-factor signals such as DMT/ADSL signals. In an exemplary embodiment, a digital signal produced by a digital signal processor or the like is processed by a sigma-delta modulator (SDM) to produce one or more binary signal pairs. The signals of a signal pair are low-pass filtered, if necessary, and applied across the winding of a transformer. The transformer has a single secondary winding connected to the line and may has as many primary windings as the number of signal pairs. The transformer may have a unity turns ratio or may have a turns ratio for accomplishing voltage step-up. For one signal pair, the number of possible resulting signals levels on the secondary side is three, for two signal pairs five, etc. Using more than two signal levels, it becomes possible to recreate from the digital signals the corresponding analog waveform with the required accuracy. The circuit requires only a single supply voltage, is inherently balanced and provides high-voltage DC isolation.