2166 IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 41, NO. 9, SEPTEMBER 2006 Adaptive Multi-Band Multi-Mode Power Ampliﬁer Using Integrated Varactor-Based Tunable Matching Networks W. C. Edmund Neo, Student Member, IEEE, Yu Lin, Xiao-dong Liu, Leo C. N. de Vreede, Senior Member, IEEE, Lawrence E. Larson, Fellow, IEEE, Marco Spirito, Student Member, IEEE, Marco J. Pelk, Koen Buisman, Student Member, IEEE, Atef Akhnoukh, Anton de Graauw, and Lis K. Nanver, Member, IEEE Abstract—This paper presents a multi-band multi-mode class-AB power ampliﬁer, which utilizes continuously tunable input and output matching networks integrated in a low-loss silicon-on-glass technology. The tunable matching networks make use of very high varactor diodes ( @ GHz) in a low distortion anti-series conﬁguration to achieve the de- sired source and load impedance tunability. A QUBIC4G (SiGe, GHz) high voltage breakdown transistor ( V, V) is used as active device. The realized adaptive ampliﬁer provides 13 dB gain, 27–28 dBm output power at the 900, 1800, 1900 and 2100 MHz bands. For the communication bands above 1 GHz optimum load adaptation is facilitated resulting in efﬁciencies between 30%–55% over a 10 dB output power control range. The total chip area (including matching networks) of the ampliﬁer is 8 mm . Index Terms—Adaptive matching network, dynamic loadline, high efﬁciency, multi-band, multi-mode, power ampliﬁer, RF adaptivity. I. INTRODUCTION I N ORDER TO fulﬁll the multi-band, multi-mode demands of today’s cellular market, current handset implementations are based on parallel line-ups for the transmit and receive paths [Fig. 1(a)] with antenna duplexers and switches to meet the speciﬁc requirements of each communication standard. Next-generation wireless systems aim for size and cost reduc- tion by utilizing only one or two adaptive transmit/receive paths to replace the parallel path concept [Fig. 1(b)]. Although con- ceptually simple, practical design considerations place severe design constraints and technology challenges on the adaptive circuit blocks required. For most of the circuit functions in the receive path, acceptable implementations have already been demonstrated [1]–[3]. Major challenges remain, however, in creating the tunable ﬁlters and adaptive power ampliﬁers (PAs) [4], [5]. To address these challenges we focus in this paper on Manuscript received January 6, 2006; revised May 10, 2006. This work was supported in part by Philips Semiconductors, Philips Research, and the Dutch Technology Foundation (STW). W. C. E. Neo, Y. Lin, X.-D. Liu, L. C. N. de Vreede, M. Spirito, M. J. Pelk, K. Buisman, A. Akhnoukh, and L. K. Nanver are with the DIMES Institute, Delft University of Technology, 2628 CT, Delft, The Netherlands. L. E. Larson is with the University of California at San Diego, La Jolla, CA 92093 USA. A. de Graauw is with Philips Semiconductors, 6534 AE Nijmegen, The Netherlands. Digital Object Identiﬁer 10.1109/JSSC.2006.880586 the implementation of an adaptive PA. Our aim is to improve the power-added efﬁciency (PAE) and provide adaptation of the operating frequency. A. PA Requirements The power ampliﬁer stage in a mobile handset is considered to be one of the most power hungry components. As a result, the talk-time of a typical handset is restricted to several hours by the limited PA efﬁciency and battery performance. There are two basic constraints for a mobile system that are responsible for this limitation: • the maximum output power required, related to transmitted power, when the handset is operated at a large distance from the base-station; • the high linearity requirement of a modern wireless com- munication system, which translates to a power back-off condition of several dB for the output stage. In traditional ampliﬁer implementations, the linearity require- ment typically results in the use of class-AB operation for the output stage [6], which provides a workable compromise be- tween linearity and efﬁciency. When considering linearity, the class-AB output stage must be dimensioned in such a way that it can provide its peak output power without saturation. As a re- sult, for a given peak output power ( ) and battery voltage ( ), the load impedance for a class-AB stage at the funda- mental frequency is ﬁxed to . Unfortunately, class-AB operation provides its highest efﬁ- ciency only under maximum drive conditions. When operated at the required back-off level, due to linearity reasons for a given communication standard like (W)CDMA, a rather dramatic loss in efﬁciency occurs [7]. It is for these reasons that improving ampliﬁer efﬁciency, while maintaining linearity, is currently a major research topic in wireless communications. In linearity-focused research, the circuit is designed so that the resulting overall linearity performance of the PA module is improved. In this way, the active device can be operated closer to its peak-power capabilities and still be able to meet the lin- earity requirements. Pre-distortion is one technique that falls in this category. In pre-distortion (analog or digital) [8], the input signal is adjusted such that it compensates for the nonlinear- ities of the PA stage. Another increasingly utilized lineariza- tion technique is that of out-of-band termination [9]; here the impedances at baseband and second harmonic frequencies are 0018-9200/$20.00 © 2006 IEEE