A multi-mode radio transmitter for use in
mobile radio cellular standards, such as 2G, 2.5G and 3G, and a method of operating the
transmitter in which an input
signal is modulated independently of controlling the drive of a power
amplifier (PA) module (40). The
transmitter comprises circuitry (12, 60) for extracting the phase (θ) and amplitude (R) components from envelope information in the input
signal. A modulator (110) uses the phase component (θ) to produce a constant-envelope
signal comprising a phase modulated
real signal at the transmitter frequency. This signal is multiplied in a multiplier (72) with either a fixed bias
voltage (Vg1) to produce a
constant envelope signal or a low level
envelope tracking signal derived from an amplitude component (R) by a first
amplitude control circuit (78) to produce a signal modulated exactly by the amplitude component. An output from the multiplier is applied to the PA module (40) having a control input (41). The PA module is controllable in a plurality of manners dependent on the characteristics and the required output power of the signal being transmitted. These manners include applying a predetermined fixed
voltage to the control input or a less precise
envelope tracking signal which is derived by a second
amplitude control circuit (120) from the amplitude component (R).