Linearization and Imbalance Correction Techniques for Broadband Outphasing Power Amplifiers

This paper presents adaptive phase-only memory digital pre-distortion (DPD) and gain/phase/delay imbalance correction techniques for outphasing power amplifiers (PAs). Least squares adaptation is used for the phase-only DPD and imbalance correction techniques. The performance of these techniques is verified by co-simulations and measurements of an outphasing PA implemented with two identical class-F PAs and a Chireix combiner. The Chireix combiner with compensating stubs added to achieve high efficiency introduces nonlinearity. The proposed adaptive phase-only memory DPD corrects for the nonlinearity due to the Chireix combiner. The proposed gain/phase/delay imbalance correction technique achieves total lower/upper adjacent channel power ratio (ACPR) improvements of 43.8/37.6 dB for 5-MHz and 46.2/38.3 dB for 10-MHz long-term-evolution signals in measurements. The fractional-sample delay imbalance correction reduces distortion at low input amplitudes and demonstrates on the order of a 10-dB ACPR improvement compared to full-sample delay imbalance correction.