| 摘要 |
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 (&thetas;) and amplitude (R) components from envelope information in the input signal. A modulator (110) uses the phase component (&thetas;) 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).
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