Broadband analogue predistortion using a distortion generator based on two-stage RF mixer topology

ABSTRACTAn analogue predistorter using a distortion generator based on a two-stage radio frequency mixer topology is presented. The proposed distortion generator achieves fundamental signal cancellation without using a signal cancellation loop or a resonant circuit, thus it generates an error signal that predominantly consists of unwanted intermodulation distortion (IMD). Measurements are performed using multi-tones, WLAN- and Terrestrial Trunked Radio (TETRA)-modulated signals. Distortion generator provides high levels of IMD and achieves more than 40 dB fundamental signal cancellation across a bandwidth of 120 MHz. A proof-of-concept predistorter was constructed to validate the usefulness of the proposed distortion generator, which achieves up to 15 dB suppression of IMD and adjacent channel power ratio at the output of a power amplifier. Distortion generator and predistorter gave similar results at multiple frequencies between 920 MHz and 2 GHz, with different test signals having bandwidths ranging fro...