ORTHOGONAL SIGNAL TRANSMITTER

摘要

A transmitter for transmitting orthogonal signals comprises a power amplifier (112) having a transfer characteristic in which gain is substantially independent of applied bias voltage. A digital signal for transmission is monitored by a level detector (116) which determines the peak output power required from the power amplifier (112). This information is used by a power supply controller (122) to control the DC bias voltage applied to the power amplifier (112) so that the applied voltage is reduced for low signal levels and increased for high signal levels, thereby increasing the efficiency with which supplied power is converted to radiated power. The applied voltage may be changed for each output symbol, or may be continuously adapted to track the peak envelope power. This method of controlling the amplifier (112) may be used in conjunction with coding schemes for reducing the peak to mean power ratio.