The application of digital signal processing to transmitter linearisation

A description is given of three prototype transmitters, using digital signal processing in different ways to achieve linear RF amplification. The Cartesian feedback technique, the adaptive predistortion technique, and the LINC (linear amplification with nonlinear components) technique, are all shown to provide a good degree of intermodulation product suppression (>50 dB), with the LINC amplifier approach potentially the most power-efficient (>70%). Both the LINC and predistortion systems can operate in a wideband mode. The Cartesian approach, because of the inherent feedback control system, is limited to a bandwidth of about 10% of the operating frequency. The implementation costs are considerably reduced over conventional analog realizations of such systems for all three techniques