Preserving Polar Modulated Class-E Power Amplifier Linearity under Load Mismatch

Abstract

Power amplifiers (PAs) need digital predistortion (DPD) linearization to handle high-order complex modulation schemes in next-generation communication systems. While load variation is inevitable, DPD is generally designed considering only the nominal load impedance for PAs. This paper presents a polar class-E PA with an on-chip waveform characterizer enabling adaptive digital predistortion (ADPD) to preserve the linearity of the PA under load mismatch. The presented ADPD corrects both AM/AM and AM/PM distortions, which are prominent in the demonstrated PA, while simultaneously correcting for slow memory effects without the need for complex memory DPD algorithms. Load-pull measurements demonstrate that target error vector magnitude (EVM) and adjacent channel power ratio (ACPR) can be maintained in a significantly larger area on the Smith chart going from 50 Ω optimized static DPD to our ADPD for a 2 GHz 1024 QAM signal with 1 MSym/s symbol rate.

Integrated measurement techniques for RF-power amplifiers

“…Afterwards recommendations for future work to improve RF-PA performance are given. Chapters 4,6 and 7 are reformatted from published work in [74][75][76] and chapter 5 is reformatted from work that is currently accepted for publication in a future edition of the IEEE Transactions on Circuits and Systems I: Regular Papers.…”

“…The introduction of a technique to improve the save-operating-area of a class-E PA by measuring the peak drain voltage and adding or removing drain capacitance by means of a capacitor array [75,119] The design of a polar modulated class-E PA that utilizes the RF-waveform characterizer to tune DPD coefficients, achieving a significant improvement of EVM and ACPR for VSWR 9:1. [76] The development of an algorithm that can resolve frequency ambiguity and demodulate signals with an orthogonal frequency basis spanning multiple Nyquist zones by sampling at two distinct sample rates. It requires that the aggregate information-bearing bandwidth of the signals is less than half the cumulative data converter sampling rates.…”

“…This chapter consists of material previously published during the 2020 IEEE RadioFrequency Integrated Circuits Symposium[76] and it is reformatted to a thesis form.…”