This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES 1 Highly Linear mm-Wave CMOS Power Amplifier Byungjoon Park, Sangsu Jin, Daechul Jeong, Jooseung Kim, Yunsung Cho, Kyunghoon Moon, and Bumman Kim, Fellow, IEEE Abstract—A Ka-band highly linear power amplifier (PA) is implemented in 28-nm bulk CMOS technology. Using a deep class-AB PA topology with appropriate harmonic control circuit, highly linear and efficient PAs are designed at millimeter-wave band. This PA architecture provides a linear PA operation close to the saturated power. Also elaborated harmonic tuning and neu- tralization techniques are used to further improve the transistor gain and stability. A two-stack PA is designed for higher gain and output power than a common source (CS) PA. Additionally, average power tracking (APT) is applied to further reduce the power consumption at a low power operation and, hence, extend battery life. Both the PAs are tested with two different signals at 28.5 GHz; they are fully loaded long-term evolution (LTE) signal with 16-quadrature amplitude modulation (QAM), a 7.5-dB peak- to-average power ratio (PAPR), and a 20-MHz bandwidth (BW), and a wireless LAN (WLAN) signal with 64-QAM, a 10.8-dB PAPR, and an 80-MHz BW. The CS/two-stack PAs achieve power-added efficiency (PAE) of 27%/25%, error vector magni- tude (EVM) of 5.17%/3.19%, and adjacent channel leakage ratio (ACLR E-UTRA ) of -33/-33 dBc, respectively, with an average output power of 11/14.6 dBm for the LTE signal. For the WLAN signal, the CS/2-stack PAs achieve the PAE of 16.5%/17.3%, and an EVM of 4.27%/4.21%, respectively, at an average output power of 6.8/11 dBm. Index Terms— Average power tracking (APT), CMOS, efficiency, 5G wirless communcation, linear, long-term evolution (LTE), power amplifier (PA), wireless LAN (WLAN). I. I NTRODUCTION W ITH the trend toward 5G wireless communications, millimeter-wave (mm-wave) power amplifiers (PAs) are being spot lighted. Although the 5G’s system architecture is not determined yet, to support the 5G requirements, such as 1000 times more capacity and less latency than 4G systems, 5G will need to provide higher spectral efficiency, the ability to support large and fragmented spectrum, dynamic spectrum access, and short packet transmissions with loose synchro- nization requirements. Since the modulation schemes used in the current 4G systems, such as orthogonal frequency division multiplexing (OFDM), do not fulfill all of these requirements, Manuscript received June 30, 2016; revised September 23, 2016; accepted October 25, 2016. An earlier version of this paper was presented at the IEEE MTT-S International Microwave Symposium, San Francisco, CA, USA, May 22–27, 2016. B. Park and Y. Cho are with the Division of IT Convergence Engineering, Pohang University of Science and Technology, Pohang 790-784, South Korea. S. Jin is with Qualcomm, San Diego, CA 92121 USA. D. Jeong, J. Kim, K. Moon, and B. Kim are with the Department of Electrical Engineering, Pohang University of Science and Technology, Pohang 790-784, South Korea (e-mail: bmkim@postech.ac.kr). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMTT.2016.2623706 new modulation schemes, such as filter-bank multicarrier, uni- versal filtered multicarrier, and generalized frequency division multiplexing, have been proposed for 5G [1]–[7]. All of these waveforms have in common that they reduce the adjacent channel leakage ratio (ACLR) and the peak-to-average power ratio (PAPR) compared with an OFDM system to increase the operating output power and efficiency [8], [9]. Although the 5G modulation schemes target for a reduced ACLR and PAPR, linearity of the PA is still one of the most important issue. Hence, the linearity should be considered in designing mm-wave PAs, which can be prevented from the operation in a large back-off region with poor efficiency. Since the first fully integrated mm-wave IC was reported in 1986 [10], the ampli- fiers are usually gain limited, and are operated in class-A mode for a high gain with high power-added efficiency (PAE). The PAs are aimed at military applications or point-to-point communications, where highly modulated signals are not used, resulting in less importance in linearity. But as the mm-wave band is a strong candidate for the 5G wireless communication system, the PAs require not only the high PAE (PAE MAX ), saturated output power ( P Sat ), and gain, but also the high linearity close to the saturated power. As designed for the PAs in 3G and 4G wireless communication systems, the PAs in 5G should also be designed in deep class-AB mode for high efficiency and linearity up to the near saturation region. To achieve a high gain at the mm-wave band in the deep class-AB mode, a nano-scaled CMOS process with high gain is essential. This paper is the expansion of [11]. Detailed description of the key techniques to achieve high efficiency and linearity are included. We propose a deep class-AB PA operation, which provides the proper sweet-spot for linear operation close to the saturated power [12]. In this biasing, a large second harmonic is produced and should be controlled properly. The class-AB PA with the harmonic control is a popular structure at a low frequency band operation (around 2 GHz) [13]–[17], but needs some modifications to use the architecture in the mm-wave band, especially due to the low gain, large current loss, and increased harmonics. Extensive harmonic suppression methods have been studied to get a high-performance PA. The linearity analysis of a class-AB PA is introduced based on paper [12]. We further show the relation with the PAE, gain, and linearity. For realization of the linear class-AB PA, proper harmonic control method and circuit topology are proposed. Additional linearization can be made by adding linearizing techniques reported in mm-wave band, such as [18] and [19]. As mentioned, the low gain at the mm-wave band is a big limiting factor to get a good performance PA, and our 0018-9480 © 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. 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