Summary
International Symposium on Antennas and Propagation
2010
Session Number:4FD1
Session:
Number:4FD1-4
Doherty Power Amplifier integrating a novel adaptive biasing network
Shichang Chen, Quan Xue,
pp.-
Publication Date:2010/11/23
Online ISSN:2188-5079
Summary:
The efficiency improvement of microwave power amplifiers has been attracting continuous interests because power amplifiers consume most of energy in transceivers for modern wireless communication. High efficiency usually means low power consumption, and extended battery operating endurance [1],[2]. Besides, modern wireless communication systems always require high data rate and large channel capacity, which inevitably leads to large high peak-to-average power ratio (PAPR). To meet the stringent linearity requirement of suppressing in-band distortion and out-of-band spectrum emission, PAs have to operate at large back off region from saturation where efficiency is quite low. Doherty power amplifier (DPA) is an effective solution for efficiency enhancement at reduced power region, which relies on the concept of active load-pull [3],[4]. Fig. 1 shows the typical schematic of the Doherty power amplifier which consisting two parallel connected power amplifiers (carrier and peaking PAs) and an λ / 4 impedance transformer. At low power region, only the carrier power amplifier operates and the impedance represented to it is 2Zopt . When the input power increases, the peaking starts to turn on, and the impedance reduces to Zopt at full power. However, peaking PA can not give identical current with the carrier one at maximum power and immediately open up at half the maximum input voltage that are pre-assumed for optimal performance of Doherty power amplifier [4]. Uneven power division [5] or larger-sized transistor for peaking PA [6] provides an effective solution to the first problem. For the second problem which is mainly caused by the detrimental soft turn-on effect, adaptive biasing schemes can be helpful. Nevertheless, conventional approaches are complicated and bulky [7],[8]. This paper presents a simple and cost-effective self-adaptive biasing circuit which is integrated into the gate bias network of the peaking PA to solve the above two problems simultaneously. As a result, significant efficiency improvement is achieved at back-off power.