Optimized Current of the Peaking Amplifier for Two-Stage Doherty Power Amplifier

• Published in: IEEE transactions on microwave theory and techniques 2017-01, Vol.65 (1), p.209-217
• Main Authors: Lee, Hwiseob, Kwon, Jinhee, Lim, Wonseob, Lee, Wooseok, Kang, Hyunuk, Hwang, Keum Cheol, Lee, Kang-Yoon, Park, Cheon-seok, Yang, Youngoo
• Format: Article
• Language: English
• Subjects: Amplification; Bias; Carrier amplifier; Doherty power amplifier (DPA); Efficiency; Gain; Leakage; Logic gates; long-term evolution (LTE); Modulation; Peak to average power ratio; peaking amplifier; Power amplifiers; Power gain; Power generation; Transconductance; Transistors; two stage
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2016.2613050

This paper presents a method of improving efficiency for the two-stage Doherty power amplifier (DPA) using the optimized current of the peaking amplifier. The DPA has a two-stage structure for both the carrier and peaking amplifiers. The first stage of the peaking amplifier has an adjusted bias condition for a near Class-B operation, while the first stage of the carrier amplifier has a higher Class-AB operation. The gain expansion of the first stage due to its lower gate bias helps the second stage of the peaking amplifier to be biased for light Class-C operation and to have steeper turn-ON characteristics, which leads higher peak output power and higher back-off efficiency. The two-stage DPA was designed for the 2.655-GHz band. Using a downlink long-term evolution signal with a signal bandwidth of 10 MHz and a peak-to-average power ratio of 6.5 dB, the overall power gain of 25 dB and a peak output power of 54.2 dBm are experimentally obtained. Using an optimized shape of the peaking amplifier's current, a drain efficiency (DE) of 53% and an adjacent channel leakage power ratio of -30 dBc were obtained at an average output power of 47.8 dBm. A DE of 56.8% and an adjacent channel leakage power ratio of -25 dBc were also obtained at an average output power of 49.5 dBm.