IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES 1 A SiGe Envelope-Tracking Power Amplifier With an Integrated CMOS Envelope Modulator for Mobile WiMAX/3GPP LTE Transmitters Yan Li, Student Member, IEEE, Jerry Lopez, Student Member, IEEE, Po-Hsing Wu, Weibo Hu, Ruili Wu, Student Member, IEEE, and Donald Y. C. Lie, Senior Member, IEEE Abstract—This paper presents a SiGe envelope-tracking (ET) cascode power amplifier (PA) with an integrated CMOS envelope modulator for mobile WiMAX and 3GPP long-term evolution (LTE) transmitters (TXs). The entire ET-based RF PA system delivers the linear output power of 22.3/24.3 dBm with the overall power-added efficiency of 33%/42% at 2.4 GHz for the WiMAX 64 quadrature amplitude modulation (64QAM) and the 3GPP LTE 16 quadrature amplitude modulation, respectively. Additionally, it exhibits a highly efficient broadband characteristic for multiband applications. Compared to the conventional fixed-supply cascode PA, our ET-based cascode PA meets the WiMAX/LTE spectral mask and error vector magnitude spec at close to its com- pression without the need of predistortion. The SiGe PA and the CMOS envelope modulator are both designed and fabricated in the TSMC 0.35- m SiGe BiCMOS process on the same die. This study represents an essential integration step toward achieving a fully monolithic large-signal ET-based TX for wideband wireless applications. Index Terms—Differential cascode power amplifier (PA), en- velope tracking (ET), high efficiency, linear-assisted switching envelope modulator, long-term evolution (LTE), SiGe BiCMOS, WiMAX. I. INTRODUCTION T HIRD-GENERATION (3G) cellular services are being deployed on a worldwide basis, along with the higher data rate so-called fourth-generation (4G) wireless standards such as WiMAX/WiBro and 3GPP long-term evolution (LTE). The true 4G Advanced LTE service is expected to be offered in a few years, promising maximum download speed of 1 Gb/s. The IEEE 802.11n wireless local area network (WLAN) standard that utilizes the multiple input/multiple output (MIMO) antenna technology already achieves a maximum download speed of over 150 Mb/s in real-life Wi-Fi certified products today. These Manuscript received March 02, 2011; revised July 08, 2011; accepted July 28, 2011. This work was supported by the Industrial Technology Research Institute (ITRI), Taiwan. Y. Li, J. Lopez, W. Hu, R. Wu, and D. Y. C. Lie are with the Department of Electrical and Computer Engineering,Texas Tech University, Lubbock, TX 79409 USA (yan.li@ ttu.edu; yan.li.ttu@gmail.com; donald.lie@ttu.edu). P.-H. Wu was with the Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, TX 79409 USA. He is now with Diodes Taiwan Inc., Hsinchu 300, Taiwan. 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.2011.2164550 3G/4G/WLAN wireless services require wide bandwidths and spectrally efficient modulation schemes with larger peak-to-av- erage ratios (PARs) than their second-generation (2G)/2.5G counterparts. Therefore, it is becoming much more challenging to design highly efficient and linear transmitters (TXs) for portable wideband wireless applications. The RF power amplifier (PA) tends to be the most power- hungry block for a typical mobile TX (e.g., in [1], the PA con- sumes 78% power of the entire TX). The nonconstant-envelope modulated signals with the inherent high PAR and wide band- width require highly linear PAs having very low signal distor- tion. One way for the PA to satisfy the stringent linearity re- quirements is to back off from its compression region. This is a major bottleneck for realizing highly efficient mobile TXs, since the power-added efficiency (PAE) of the PA reduces dra- matically in back-off mode, as opposed to the PAE of saturated PAs operating at peak output power. For example, many com- mercially available PAs based on a III–V compound semicon- ductor can produce saturated output power over 30 dBm with peak PAEs greater than 45%, but they need 3–4-dB back-off from the compression points to meet the 3GPP LTE lin- earity specs, resulting in 35% PAE in the best case for the LTE quadrature phase-shift keying (QPSK) modulation (PAR of 6.5 dB). 1 Moreover, due to higher PAR of WiMAX over LTE, PAs would need more back-off (i.e., usually 6–8 dB) to meet the stringent WiMAX linearity specs, leading to even lower PAE (e.g., only 20% PAE 2 ). Likewise, in the recent liter- ature, CMOS PAs with on-chip transformers have successfully delivered over 30-dBm saturated power with the best PAE value of 50% [2]–[9], but they need a large back-off to meet the lin- earity specs for high PAR signals resulting in a greatly reduced PAE (e.g., only 10%–20% for WiMAX/WLAN [4], [8], [10]). A state-of-the-art linear SiGe dual-standard LTE/WiMAX PA has been recently reported with a saturated power of 30 dBm and a peak PAE of 30%, but again its PAE is less than 20% once backed off 5 dB to satisfy the WiMAX linearity require- ments [11]. To boost the PA efficiency for high PAR signals, enve- lope-tracking (ET) or envelope-elimination-and-restoration (EER) TX architectures can be very effective as the PA supply voltage is modulated according to the instantaneous output 1 For example: [Online]. Available: http://www.anadigics.com//prod- ucts/view/alt6713 2 For example: [Online]. 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