基于WCDMA的线性功放研究
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摘要
以WCDMA为代表的第三代移动通信技术,为实现宽带调制、多载波应用,同时减小邻信道干扰以满足通信系统的误码率要求,对基站发射机功放的线性指标要求苛刻。前馈技术因宽带、稳定等优点被广泛的运用于线性功放。
本文根据3GPP对WCDMA发射机功率放大器的射频指标要求,在对功率放大器的非线性特性和前馈技术的特性进行详细理论分析的基础上,结合EDA仿真工具,设计了基于自适应前馈的功放系统,并完成了系统的调试和测试。与传统前馈法相比,本文加入了基于最小功率检测算法的自适应控制电路,对输入功率变化、温漂和器件老化等导致系统性能下降的扰动进行自适应调整,使功放的非线性失真在很大程度上得到改善。
测试结果表明,自适应前馈功放系统在双音输出功率20W时三阶交调系数小于-50dBc,邻信道泄漏抑制比(ACLR)的估算结果大于53dB,在理论上满足3GPP对WCDMA基站发射机的指标要求。同时,通过自适应控制电路对系统参数的调整,该系统在射频输入功率变化的条件下实现了对三阶交调分量稳定的抑制度。
For implement of wide band modulation, multi-carries and elimination of adjacent channel interference to satisfy BER requirement in WCDMA system,which is most popular in 3G technology, the linearity requirement of the base station power amplifier becomes tighter. Feedforward is generally known as the best performing linearization technique for its advantages, such as broadband, stability, etc.
This paper introduces the theories of power amplifier nonlinear characters and feedforward technique. According to the RF specifications in 3GPP for WCDMA transmitter power amplifier, an adaptive feedforward amplifier system is completed including EDA simulation, circuits layout and main mechanical structure design. Compared with traditional feedforward, this paper presents an adaptive control method based on power detection minimization. With strong and fast digital signal processing ability, the adaptive system can control feedforward amplifier parameters exactly and suppress non-linear products at last by detecting changes of signals and environments.
Test results show that under 2-tone test in 5MHz tone spacing, the power amplifier system achieves -50dBc IMD3 with 20w output power, improved 20dB in IMD3 compared with the one without linearity. Estimated value of ACLR comes to 53dB,which satisfies the 3GPP requirement for WCDMA base-station transistor. Further tests with alterative input power indicate a steady suppression to the IMD3 controlled by the adaptive system.
本文根据3GPP对WCDMA发射机功率放大器的射频指标要求,在对功率放大器的非线性特性和前馈技术的特性进行详细理论分析的基础上,结合EDA仿真工具,设计了基于自适应前馈的功放系统,并完成了系统的调试和测试。与传统前馈法相比,本文加入了基于最小功率检测算法的自适应控制电路,对输入功率变化、温漂和器件老化等导致系统性能下降的扰动进行自适应调整,使功放的非线性失真在很大程度上得到改善。
测试结果表明,自适应前馈功放系统在双音输出功率20W时三阶交调系数小于-50dBc,邻信道泄漏抑制比(ACLR)的估算结果大于53dB,在理论上满足3GPP对WCDMA基站发射机的指标要求。同时,通过自适应控制电路对系统参数的调整,该系统在射频输入功率变化的条件下实现了对三阶交调分量稳定的抑制度。
For implement of wide band modulation, multi-carries and elimination of adjacent channel interference to satisfy BER requirement in WCDMA system,which is most popular in 3G technology, the linearity requirement of the base station power amplifier becomes tighter. Feedforward is generally known as the best performing linearization technique for its advantages, such as broadband, stability, etc.
This paper introduces the theories of power amplifier nonlinear characters and feedforward technique. According to the RF specifications in 3GPP for WCDMA transmitter power amplifier, an adaptive feedforward amplifier system is completed including EDA simulation, circuits layout and main mechanical structure design. Compared with traditional feedforward, this paper presents an adaptive control method based on power detection minimization. With strong and fast digital signal processing ability, the adaptive system can control feedforward amplifier parameters exactly and suppress non-linear products at last by detecting changes of signals and environments.
Test results show that under 2-tone test in 5MHz tone spacing, the power amplifier system achieves -50dBc IMD3 with 20w output power, improved 20dB in IMD3 compared with the one without linearity. Estimated value of ACLR comes to 53dB,which satisfies the 3GPP requirement for WCDMA base-station transistor. Further tests with alterative input power indicate a steady suppression to the IMD3 controlled by the adaptive system.
引文
[1] 彭林.第三代移动通信技术.北京:电子工业出版社,2001.1,12-14
[2] 于澄.WCDMA 系统物理层设计.北京:人民邮电出版社,2003.2,18-21
[3] 郭梯云.移动通信.西安:西安电子科技大学出版社,1999.10,
[4] A.Katz.TWTA Linearization.Microwave Journal.,Vol.39, No.4. April 1996 pp:78-90
[5] 苏华鸿.蜂窝移动通信射频工程.北京:人民邮电出版社,2004.8,291-321
[6] Stephen A.Maas.Nonlinear Microwave and RF Circuits.second Edition
[7] Joel Vuolevi. Distortion in Rf Power Amplifiers. Artech House,2003.2
[8] Wu Q, Xiao H, Lif. Understanding ACPR measurements. MICROWAVE&RF. May 2001:91～95
[9] Kenington P.B.High-linearity RF Amplifier Design[M].Boston:Artech House,2000.
[10] 张玉兴.射频模拟电路.北京:电子工业出版社,2003.5,121-128
[11] W. Woo,M.D.Marvin,,J.S Kenney, A hybrid digital/RF envelope predistortion linearization system for power amplifiers.IEEE Trans.MTT,vol.53,pp229-236,Jan.2005.
[12] J.K.Cavers.Amplifier linearization using a digital predistorter with fast adaption and low memory requirements.IEEE Trans.Veh.Technol,vol.39,pp.374-382,Nov.1990.
[13] P.B. Kenington and D.W. Bennett.Linear distortion correction using a feedforward system.IEEE Transactions on Vehicular Technology, vol. 45, no.1,pp.74-81, February 1996
[14] Cavers J K.Adaptation behavior of a feedforward amplifier linearizer[J].IEEE Transactions on Vehicular Technology, vol.44, no.1, pp. 31~40, February 1995.
[15] Gadringer.Loop controller for a feedforward amplifier minimizing the measured power signal.Radio and Wireless Conference, 2003. RAWCON '03. Proceedings , Aug. 10-13, 2003 Pages:281 – 284.
[16] Paulo S. R. Diniz.自适应滤波算法与实现(刘郁林,景晓军,谭刚兵等译).北京:电子工业出版社,2004.3
[17] Guillermo Gonzalez.Microwave Transistor Amplifers Analysis and Design.Second Edition.
[18] 微波晶体管功率放大器.人民邮电出版社,1988
[19] A Simple and effective Load-pull system for RF power Transistor large signal measurements for wirless communication power amplifier design. IEEE.Trans. instrumentation andmeasurement vol46,NO.5,Oct 1997
[20] 清华大学微带电路编写组.微带电路.北京:人民邮电出版社,1975.1
[21] 顾其铮.微波集成电路设计.人民教育出版社.1978
[22] Application Note 1355, Agilent, Designing and test 3GPP WCDMA base transceiver stations
[2] 于澄.WCDMA 系统物理层设计.北京:人民邮电出版社,2003.2,18-21
[3] 郭梯云.移动通信.西安:西安电子科技大学出版社,1999.10,
[4] A.Katz.TWTA Linearization.Microwave Journal.,Vol.39, No.4. April 1996 pp:78-90
[5] 苏华鸿.蜂窝移动通信射频工程.北京:人民邮电出版社,2004.8,291-321
[6] Stephen A.Maas.Nonlinear Microwave and RF Circuits.second Edition
[7] Joel Vuolevi. Distortion in Rf Power Amplifiers. Artech House,2003.2
[8] Wu Q, Xiao H, Lif. Understanding ACPR measurements. MICROWAVE&RF. May 2001:91～95
[9] Kenington P.B.High-linearity RF Amplifier Design[M].Boston:Artech House,2000.
[10] 张玉兴.射频模拟电路.北京:电子工业出版社,2003.5,121-128
[11] W. Woo,M.D.Marvin,,J.S Kenney, A hybrid digital/RF envelope predistortion linearization system for power amplifiers.IEEE Trans.MTT,vol.53,pp229-236,Jan.2005.
[12] J.K.Cavers.Amplifier linearization using a digital predistorter with fast adaption and low memory requirements.IEEE Trans.Veh.Technol,vol.39,pp.374-382,Nov.1990.
[13] P.B. Kenington and D.W. Bennett.Linear distortion correction using a feedforward system.IEEE Transactions on Vehicular Technology, vol. 45, no.1,pp.74-81, February 1996
[14] Cavers J K.Adaptation behavior of a feedforward amplifier linearizer[J].IEEE Transactions on Vehicular Technology, vol.44, no.1, pp. 31~40, February 1995.
[15] Gadringer.Loop controller for a feedforward amplifier minimizing the measured power signal.Radio and Wireless Conference, 2003. RAWCON '03. Proceedings , Aug. 10-13, 2003 Pages:281 – 284.
[16] Paulo S. R. Diniz.自适应滤波算法与实现(刘郁林,景晓军,谭刚兵等译).北京:电子工业出版社,2004.3
[17] Guillermo Gonzalez.Microwave Transistor Amplifers Analysis and Design.Second Edition.
[18] 微波晶体管功率放大器.人民邮电出版社,1988
[19] A Simple and effective Load-pull system for RF power Transistor large signal measurements for wirless communication power amplifier design. IEEE.Trans. instrumentation andmeasurement vol46,NO.5,Oct 1997
[20] 清华大学微带电路编写组.微带电路.北京:人民邮电出版社,1975.1
[21] 顾其铮.微波集成电路设计.人民教育出版社.1978
[22] Application Note 1355, Agilent, Designing and test 3GPP WCDMA base transceiver stations