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  • 學位論文

應用於行動電話之高效率多頻帶CMOS功率放大器

Highly-efficient Multi-band CMOS Power Amplifier for Mobile Phone Applications

指導教授 : 陳怡然
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摘要


本論文主要針對現今及未來手機射頻功率放大器(RF PA)在使用易於整合之先進互補式金氧半(CMOS)製程,並具備可支援多個長期演進技術LTE操作頻帶(Multi-band)的性能及面積成本進行突破性的改良。 第一章簡介行動電話iPhone智慧型手機內部多顆商用射頻功率放大器模組配置情況及簡介砷化鎵(GaAs)射頻功率放大器模組演進趨勢,並介紹從第二代到第四代行動通訊標準的信號峰值平均功率比、通道頻寬、輸出動態範圍等各項挑戰,接著提出本論文的研究動機。 第二章考察近幾年利用CMOS製程開發射頻功率放大器之國際知名期刊及廠商的技術水平,探討利用奈米CMOS製程設計射頻功率放大器之難處與技術瓶頸。 第三章探討在CMOS製程設計射頻功率放大器所需之各類型功率結合變壓器,闡述各別優缺點,並針對擁有較佳功率結合能力之串聯結合變壓器(SCT)和並聯結合變壓器(PCT)進行分析與比較。 第四章提出圈數比1:n之同中心漩渦式變壓器(Concentric Vortical Transformer, CVT)架構,闡述其高轉換效率和寬比例頻寬的設計方法,和目前最普遍使用的圈數比1:1之分佈式主動變壓器(Distributed Active Transformer, DAT)架構皆使用條狀平板(slab)電感,但CVT擁有更好的各組輸入阻抗對稱性,故可均勻且有效率的結合多組相同之推挽式功率電晶體。透過整合被動元件(Integrated Passive Devices, IPD)製程利用雙差動背對背(Double-Differential Back-to-Back, DDBB)結構來驗證CVT和DAT,證實所提出的L型CVT擁有86.4%的轉換效率和177%的1-dB比例頻寬,且在具有幾乎相同之主線圈感值和兩組差動輸入結合的條件下,L型CVT擁有比L型DAT高2.2 %的轉換效率和高21 %的1-dB比例頻寬,而在1.72.7 GHz頻段內,直條型CVT每個主線圈輸入端之間的實部和虛部阻抗誤差約60210倍遠小於直條型DAT。 第五章剖析電流電阻壓降(IR-drop)效應對CMOS射頻功率放大器的效率影響,並提出耦合L型同中心漩渦式變壓器(Coupled L-shape CVT, CL-CVT)架構,可在正常2-mm以內晶片打線長度下仍維持足夠匹配頻寬,相較於DAT在四組差動輸入結合的條件下,CL-CVT僅需34 %的DAT外徑尺寸和12 %的DAT佈局面積就可達到跟DAT類似的特性和匹配頻寬,且CL-CVT提供可忽略的電流電阻壓降效應避免造成的效率退化情形。透過90-nm CMOS製程實現一個支援多個LTE頻帶7、38、40、41之高效率射頻功率放大器,並搭配所提出的8字型輸入平衡不平衡轉換器來縮小晶片面積至0.99 mm2,在僅1.2 V供應電壓下,單頻(CW)最大輸出功率在2.4 GHz可達27.3 dBm,此時最大汲極效率(DE)為47 %,最大功率附加效率(PAE)為35.7 %,而1-dB頻寬為630 MHz從2.13到2.76 GHz;在使用通道頻寬20-MHz之長期演進技術(Long Term Evolution, LTE) 16-QAM測試信號,可達到21.4–22.4 dBm之平均輸出功率和得到高達24.9 %的PAE,且未使用預失真或校正技術即符合LTE鄰近通道洩漏功率比(Adjacent Channel Leakage Ratio, ACLR)和頻譜遮罩(Spectrum Mask)規範;此為目前全球尺寸最小的低電壓奈米CMOS全積體化線性射頻功率放大器,相較於已發表最先進之低電壓CMOS全積體化線性射頻功率放大器約可節省其一半佈局面積,對使用昂貴奈米CMOS製程來系統單晶片(System-on-chip, SoC)整合射頻功率放大器來說是一個重大突破。 第六章總結本論文的具體貢獻,並加強說明在無需任何校正與預失真之高效率多頻帶射頻功率放大器的低成本及高競爭力優勢,並提出未來的展望。

並列摘要


This dissertation is mainly focused on making a breakthrough improvement in the performance and chip area of radio-frequency power amplifiers (RF PAs) in modern and future mobile phones by using the advanced standard CMOS process for easy integration and supporting LTE multi-band operation. Chapter 1 is the brief introduction about the arrangement of multiple commercial RF PA modules inside the mobile phones such as the iphones and the evolution of GaAs RF PA modules. In addition, the challenge to wireless communication systems from 2G to 4G and the requirement of peak-to-average power ratio (PAPR), channel bandwidth, and output dynamic range are also introduced. The performance and technique levels of CMOS RF PAs from the best-known international journal papers and commercial products in recent years were surveyed in the chapter 2. Moreover, the difficulties and bottleneck of designing RF PAs in nanometer CMOS processes are also discussed. The different kinds of power combining transformers used in CMOS RF PAs are discussed in the chapter 3, and their advantage and disadvantage are also elaborated. Besides, the comparison between the series combining transformer (SCT) and the parallel combining transformer (PCT) both with better power-combining ability is also analyzed in this chapter. The architecture of the concentric vortical transformer (CVT) with 1:n turn ratio is proposed in the chapter 4, and the design methodology about the high transformation efficiency and wide fractional bandwidth for the CVT is also illustrated. The 1:n CVT uses the slab inductors as the most widely used 1:1 distributed active transformer (DAT), but the CVT has more symmetric input impedances than the DAT and therefore has the ability to uniformly and efficiently combine the power of multiple identical differential power transistors. By using the double-differential back-to-back architecture in the integrated passive device (IPD) process, the L-shape CVT was demonstrated with 86.4% of transformation efficiency and 177% of 1-dB fractional bandwidth. Both are 2.2% higher and 21% wider than that of the L-shape DAT respectively under almost the same primary inductance with two differential inputs. Moreover, the mismatch in the real and imaginary parts of input impedances among each primary input terminal of the slab CVT over 1.72.7 GHz is about 60210 times less than that of the slab DAT. The IR-drop impact on the efficiency of CMOS RF PAs is analyzed in the chapter 5, and the architecture of coupled L-shape concentric vortical transformer (CL-CVT) is proposed. The CL-CVT is capable of sufficient matching bandwidth while keeping all essential bonding wires within a feasible length, namely less than 2 mm. As compared to the DAT with four differential inputs, the CL-CVT can achieve similar performance and matching bandwidth with only 34% of outer diameter (OD) needed and 12% of area occupied. Moreover, the CL-CVT provides negligible IR-drop impacts to avoid a serious deterioration on the efficiency of PAs. A highly-efficient multi-band CMOS RF PA supporting LTE band-7, 38, 40, and 41 was implemented in the 90-nm CMOS process. The proposed CL-CVT and 8-shape input balun were used to achieve a compact chip area of 0.99 mm2. Under the supply voltage of 1.2V, the PA achieves 27.3-dBm maximum output power with a peak drain efficiency and power-added efficiency (PAE) of 47% and 35.7% respectively at 2.4 GHz. The 1-dB bandwidth of PA is 630 MHz from 2.13 GHz to 2.76 GHz. Using a 20-MHz channel bandwidth Long Term Evolution (LTE) 16-QAM test signal, the PA achieves up to 24.9% PAE at output power level of 21.422.4 dBm and passes the adjacent channel leakage ratios (ACLRs) and spectral requirements defined by the LTE standard without using any pre-distortion or calibration techniques. This low supply-voltage PA is the world’s smallest fully-integrated nanometer-CMOS linear PA with the ability of saving about half of chip area as compared to the state-of-the-art CMOS PAs. It is a key breakthrough for system-on-a-chip (SoC) integration with the RF PAs in an expensive nanometer CMOS process. The contributions of this dissertation are summarized in the chapter 6, and the advantage of low cost and high competition for multi-band RF PAs without the use of any calibration or pre-distortion is highlighted. In the end, the future prospect and work are posed.

參考文獻


[1] “iPhone5 Technical Specifications,” Apple Product, Sep. 25, 2013. [Online]. Available: http://support.apple.com/kb/sp655
[2] “iPhone5s Technical Specifications,” Apple Product, Feb. 19, 2014. [Online]. Available: http://support.apple.com/kb/SP685
[3] “iPhone5c Technical Specifications,” Apple Product, Feb. 19, 2014. [Online]. Available: http://support.apple.com/kb/SP684
[4] “iPhone5 Teardown,” IFIXIT website, Sep. 2012. [Online]. Available: http://www.ifixit.com/Teardown/iPhone+5+Teardown/10525
[5] “Power amplifier module,” Skyworks, Woburn, MA, SKY77336 Data Sheet, Mar. 2, 2009. [Online]. Available: http://www.skyworksinc.com

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