Improvement on linearity with iterative calibration technique for multilevel LINC transmitters

This paper proposes an iterative calibration technique to enhance the linearity for multilevel LINC transmitters. With this approach, the precision of characterising AM/AM and AM/PM behaviours for discrete levels can be improved, which results in better adjacent channel leakage ratio (ACLR) and error vector magnitude (EVM) performance. An ML-LINC transmitter is built with two PAs in GaN technology, which delivers 40.8 dBm output power with 68% drain efficiency at 2.05 GHz. Up to 5 dB ACLR improvement can be observed by iterative calibration using S1/S2 for a 5 MHz LTE signals. The configuration with 16 levels can give satisfying linearity performance to meet the standard specification, while keep the complexity reasonable. Measurement results show an ACLR of -46 dBc, EVM of 1.9% (QPSK) and 4.2% (64-QAM) at average output power of 35.7 dBm with 51.1% drain efficiency for a 10 MHz LTE signals with a PAPR of 7.9 dB. The performance of the built ML-LINC tranmitter is compared to the state-of-the-art. Both the linearity and drain efficiency are quite competitive.