608 IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 49, NO. 3, MARCH 2014 A 2.4-GHz CMOS Power Ampliﬁer With an Integrated Antenna Impedance Mismatch Correction System Youngchang Yoon, Member, IEEE, Hyoungsoo Kim, Member, IEEE, Hyungwook Kim, Member, IEEE, Kun-Seok Lee, Member, IEEE, Chang-Ho Lee, Senior Member, IEEE, and James S. Kenney, Fellow, IEEE Abstract—To prevent the performance degradation of a power ampliﬁer (PA) from an antenna impedance mismatch, we pro- pose a fully integrated PA with an automatic antenna-mismatch correction system. Using only voltage amplitude information, this method reduces the complexity of the system while compensating impedance mismatch at all mismatched impedance angles. The proposed PA is implemented in 0.18- m CMOS technology and the measurement results show it maintains its 1-dB gain variation point as well as power-added efﬁciency under the mismatched condition close to that of a well-matched condition. To the best of our knowledge, this is the ﬁrst fully integrated CMOS PA that is capable of automatically recovering antenna-mismatch conditions without any help from the off-chip components. Index Terms—Antenna mismatch, CMOS, impedance matching, power ampliﬁer (PA). I. INTRODUCTION I N recent years, wireless communication has been growing explosively, and mobile devices have become an essential part of daily life. One of the most noticeable trends in wireless communication is the increased data rate. Nowadays, a cellular phone is used for not only making phone calls, but also for video streaming and e-mailing. This high-data-rate characteristic re- quires a power ampliﬁer (PA) with both stringent linearity and high efﬁciency. The stringent linearity is necessary because of the high peak-to-average-power ratio (PAPR) of 3G/4G mobile communication systems. The high efﬁciency is also required be- cause a PA consumes a large part of the battery current. These requirements focus attention on the antenna mismatch effect. Typically, a radio-frequency (RF) PA is designed under a 50- antenna impedance condition. All of the critical performances, Manuscript received May 02, 2013; accepted December 13, 2013. Date of publication January 16, 2014; date of current version March 05, 2014. This paper was approved by Associate Editor Brian A. Floyd. Y. Yoon was with the Georgia Institute of Technology, Atlanta, GA 30308 USA. He is now with Qualcomm Technologies Inc., San Diego, CA 92121 USA (e-mail: youngcha@qti.qualcomm.com). H. Kim is with the Department of Electrical Engineering, College of Engi- neering, University of North Texas, Denton, TX 76207-7102 USA. H. Kim is with Qualcomm Atheros Inc., Santa Clara, CA 95051 USA. K.-S. Lee is with Marvell Semiconductor Inc., Santa Clara, CA 95054 USA. C.-H. Lee is with Qualcomm Technologies Inc., San Diego, CA 92121 USA. J. S. Kenney is with the School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30308 USA. 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/JSSC.2013.2297414 such as output power, efﬁciency, and linearity, are optimized under the 50- condition. As a result, the varied load impedance critically degrades the performances of a PA. Recently, much re- search has been conducted to show how the performance of RF front-ends is degraded due to the mismatched impedance [1], [2] and to resolve the antenna mismatch problems [3]–[12]. The requirements and types of automatic antenna tuning units are well presented in [9], yet it may be helpful here to restate the requirements of the detection and control circuits. First, since environmental ﬂuctuations for antennas occur on a time scale of milliseconds, the speed of the control loop needs to be within milliseconds. Next, the detection and control circuits must be simple to implement to minimize their power consumption and area. These requirements should be considered when designing an automatic antenna impedance mismatch correction circuit. Many approaches [3], [6], [8], [11] are based on the measure- ment of reﬂection coefﬁcient by utilizing a directional coupler or quarter-wave transmission line, which are difﬁcult to be inte- grated into the PA itself on a single chip. These approaches have relative shortcomings in terms of cost and area. The presented work in [5] does not require those kinds of off-chip components, but the method is able to recover only imaginary impedance variation. In addition, it is required to have information on both the amplitude and phase of a signal at the RF frequency. How- ever, obtaining phase information of the voltage or current at RF frequencies demands relatively complicated detection cir- cuitry. Therefore, a detection method which uses only the RF signal’s amplitude is highly desirable. One such method, which is presented in [9], adjusts the distorted antenna impedance to 50 , as shown in Fig. 1(a). However, the antenna tuning unit in Fig. 1(a) is added as an extra component on the transmission path, which inevitably introduces extra loss, thereby increasing the total cost of the transmitter system. In addition, the tunable matching network described in [9] is hard to be integrated on a single-chip solution with low loss. The presented work in [12] demonstrates that an integrated tunable output-matching network can be used for an antenna impedance mismatch tuning system. However, the proper matching network condition under mismatch is searched for manually in [12]. The proposed technique in this paper presents a more complete design, including an automatic impedance tuning system. Fig. 1(b) represents a diagram of the proposed PA with an automatic antenna mismatch impedance tuning system. We propose the new method as a way to maintain 0018-9200 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.