A high-voltage, 765mW switching ADSL line-driver

To satisfy the high linearity requirements of ADSL line-drivers, most solutions to date use linear amplifiers, such as class AB. However their efficiency remains limited because of the modulation scheme used. As such alternative classes of amplifiers are necessary to lower dissipation, increasing the capacity of central offices. In addition the transformer turns ratio and the resulting supply voltage of the amplifier require a high-voltage supply. In this paper a switching differential amplifier is described. The circuit is processed in a 100V extension of a standard 0.7μm CMOS technology, using a supply voltage of 50V. A full downstream signal maintains a minimum MTPR of 40dB with an efficiency of 13.1%, while the maximum efficiency into a matched load is more than 40%.