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In this paper, the effect of the fundamental current provided by a peaking cell consisting of a Doherty amplifier is analyzed using a new closed-current model. The proposed current model can be used as a foundation to accurately explain and optimize previous compensation methods such as uneven, asymmetric, and gate envelope cases. Based on the proposed analysis, and in conjunction with the envelope tracking scheme, two-point envelope modulation simultaneously supplying the carrier and peaking cells is introduced to improve the overall efficiency. For further verification, the Doherty amplifier, targeting a third-generation long-term evolution base station at 2.6 GHz has been fabricated utilizing a commercially available 120-W gallium nitride device, which provides a drain efficiency of 53.1% at an average output power of 45.8 dBm with an 8.5-dB peak-to-average power ratio signal maintaining an adjacent channel leakage power ratio of - 48.6 dBc using digital pre-distortion functionality.
Microwave Theory and Techniques, IEEE Transactions on (Volume:60 , Issue: 5 )
Date of Publication: May 2012