With the increasing popularity of ADSL-modems, there is a stringent need to develop highly efficient line-drivers. Currently most line-drivers use linear amplifiers, such as class AB. Due to the nature of the DMT-encoded signal, the efficiency of such amplifiers is limited. Another issue is the transformer turns ratio and the resulting supply voltage of the amplifier. In general, a high-voltage supply is needed. In this paper, a high-voltage switching differential amplifier using a 50 V supply is described. The maximum efficiency into a matched load yields over 40%, with an efficiency of 13.1% for a full downstream signal while maintaining a minimum MTPR of 40 dB. The circuit is processed in a 100 V 0.7 mu m technology. (C) 2005 Elsevier Ltd. All rights reserved.