A 2.5-GHz asymmetric multilevel outphasing power amplifier in 65-nm CMOS

Abstract

Abstract-We present a high-efficiency transmitter based on asymmetric multilevel outphasing (AMO). AMO transmitters improve their efficiency over LINC (linear amplification using nonlinear components) transmitters by switching the output envelopes of the power amplifiers among a discrete set of levels. This minimizes the occurrence of large outphasing angles, reducing the energy lost in the power combiner. We demonstrate this concept with a 2.5-GHz, 20-dBm peak output power transmitter using 2-level AMO designed in a 65-nm CMOS process. To the authors' knowledge, this IC is the first integrated implementation of the AMO concept. At peak output power, the measured power-added efficiency is 27.8%. For a 16-QAM signal with 6.1dB peak-to-average power ratio, the AMO prototype improves the average efficiency from 4.7% to 10.0% compared to the standard LINC system.Index Terms-power amplifier (PA), outphasing, LINC, asymmetric power combining, asymmetric multilevel outphasing (AMO), digital predistortion Recently, asymmetric multilevel outphasing (AMO) has been proposed for high-efficiency wideband RF transmission [6], [7], [8]. This paper presents the first IC implementation of this technique. AMO improves the classical outphasing power efficiency by switching the output amplitudes of the PAs among a discrete set of levels. In this work, the discrete amplitude changes are accomplished by switching the supply voltages of the PAs. This discrete amplitude modulation reduces the amount of outphasing required, thereby reducing the power lost in the combiner. A block diagram of the AMO system with supply voltage switching is shown in Fig. 1.

A 1.5–5-GHz Integrated RF Transmitter Front End for Active Matching of an Antenna Cluster

“…By scaling the supply voltage, one can tune the amplitude or power of the respective antenna feed. Nevertheless, this amplitude scaling could also be embedded on an actual transmitter, such as polar [37]- [39] and multilevel outphasing architectures, which tolerate PA nonlinearity and inherently support high-power switching PA's [40] and wideband phase modulation [26] and provide means for amplitude control [36], [41], [42].…”

Digital transmitter design for mobile devices

“…One issue related to linear amplification using nonlinear components (LINC) is the efficiency degradation due to wasted power at the power combiner when phase difference is large. One variation of LINC, called asymmetric multilevel outphasing (AMO), is proposed to minimize the energy loss due to large outphasing angles [8]. Another DSP-assisted technique is also proposed to enable dynamic reactive termination for combiner-loss reduction [9].…”

A low power all-digital signal component separator for uneven multi-level LINC systems

“…Accordingly, uneven multi-level LINC (UMLINC) [3] have been suggested to improve the combining efficiency by reducing the possibility of large outphasing angles. To apply these techniques, the PA implementations with two gain modes have been proposed [4], [5]. However, a low power SCS design to separate signal into two constant-envelope signals and give corresponding gain mode controls is still required for these high-efficiency systems.…”