Analysis and Design of Doherty Power Amplifiers for Digital Pre-distortion Linearizer

• Published in: 2007 Asia-Pacific Microwave Conference pp. 1 - 4
• Main Authors: Jaewoo Sim, Jaeyoung Choic, Kwon Kim, Myoungkyu Park, Wonwoo Kang, SeungGon Kim
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.12.2007
• Subjects: 3-carriers; 6.5dB PAR; Design optimization; Digital Pre-distortion; Distributed parameter circuits; Doherty Amplifier; Frequency; Impedance matching; Microstrip; Microwave amplifiers; Multiaccess communication; Power amplifiers; Power transmission lines; Radiofrequency amplifiers; WCDMA signal(34DPCH
• ISBN: 9781424407484; 1424407486
• ISSN: 2165-4727; 2165-4743
• DOI: 10.1109/APMC.2007.4555140

In this paper, we propose the optimum design of microwave Doherty power amplifier for digital pre-distortion system. The design concept for the load modulation matching and its experimental optimization procedure were presented. The output matching circuit consists of a short lambda/4 microstrip line located between the carrier and peaking amplifier offset transmission lines and a 35 Omega transmission line for broad power matching. Two 2.14GHz Doherty amplifiers have been implemented using silicon LDMOS FETs. The RF performance of the Doherty amplifier-AB (a combination of a class AB carrier amplifier and a bias-tuned class C peaking amplifier) has been compared with the Doherty amplifier-B(a combination of a class B carrier amplifier and a bias-tuned class C peaking amplifier). The input signal applied in both case was WCDMA signal (34DPCH, 3-carrier, 6.5dB PAR). A combination of digital pre-distortion along with highly linear Doherty amplifier achieved an ACLR of -55 dBc at plusmn5 MHz offset frequency and -57 dBc at plusmn10 MHz offset frequency for a 3-carriers WCDMA signal. Thus the Doherty amplifier with digital pre-distortion gives an increased linearity as well as efficiency.