A novel modulated rapid load pull system with digital pre-distortion capabilities

This paper investigates the concurrent operation of a commercially available, modulated impedance synthesis and measurement system with digital pre-distortion (DPD) for industry standard modulated signals. The system was used to characterize a 10W GaN HEMT device, and provide impedance control over signal and distortion bandwidths, in response to a 10 MHz LTE signal centred at 2 GHz, and was able to rapidly achieve target reflection coefficients with an error less than −40dB (1%). A National Instruments (NI) PXi based characterisation system was used to apply a commercially available memory-based DPD algorithm. The transistor was biased in class-AB and was successfully linearised to better than −47.95 dBc ACPR when delivering at 2.5W average output power into an optimum load. Interestingly, the analysis showed that the DPD corrected ACPR contours aligned closely with the P 1dB contours, confirming the relevance of targeting peak-power for DPD, rather than raw ACPR. Also, and importantly, a level of linearity performance was achieved that meets for example, the 3GPP linearity specifications (45dBc) for commercial deployment, and demonstrates how this modulated load-pull system and DPD can be combined to de-risk an amplifier design at a very early stage in the design process