Radio transmitters and methods of operation
A radio transmitter has a digital modulator 10 which modulates an incoming coded signal according to pi /4 DQPSK modulation. A signal 30 representative of the amplitude of the modulated signal is applied to a bias modulator 27 to modulate the magnitude of a bias voltage 26. The modulated bias voltage 26 is applied to a power amplifier 24 of the transmitter in order to improve the apparent linearity and adjacent channel performance of the power amplifier.