时分无线系统射频功放研究

发布时间：2018-12-22 07:59

【摘要】：随着无线通信的快速发展，TD-LTE标准已成为我国有自主知识产权的TD-SCDMA标准向第四代移动通信演进的新标准。 TD-SCDMA和TD-LTE系统属于时分系统，其工作模式是时分双工（TDD），其无线帧划分为不同的时隙，上下行数据通过时隙传输，同时可以灵活配置不同的上下行时隙比。对于时分系统，为了减少对接收通道的干扰和降低系统功耗，系统中耗能最大的射频功放仅在发射时隙才工作，在接收时隙将关断，因此时分无线系统射频功率放大器不同于频分系统射频功率放大器，需根据上下行信号分时工作，对时分无线系统射频功放的切换时间有严格限制，必须在规定的打开时间内启动射频功放并进入稳定工作状态，同时在规定的关断时间内彻底关断射频功放，停止发射信号输出，确保收发通道的隔离度，因此，本文将针对时分系统射频功放的开关切换特性进行研究，探索改善开关特性的方法，并进行功放偏置电路设计，以满足不同时分无线系统对射频功放切换特性的苛刻要求。本文参考3GPP R1-081181标准要求，TD-SCDMA信号上下行信道切换控制信号开启时间至少提前2μs，关断时间也需滞后2μs；TD-LTE从下行接收转换到上行发送为10-40us，从上行发送转换到下行接收为15-20us。根据切换时间要求，提出了在功放栅极偏置电路中添加切换控制电路，实现在时分系统下对功放工作状态的控制，并通过可控放电回路改善其切换性能，提高切换灵敏度。实验测试结果表明，未加可控加放电回路时，功放栅极电压切换的下降沿大约为50us；增加可控放电回路之后，下降沿缩短到20ns，切换速度完全可以满足TD-LTE系统对射频功放切换时间的要求。由于在TD-LTE系统中使用了正交频分复用(OFDM)的调制方式，而OFDM调制技术使信号产生高峰均比。为提高功放效率，射频功放采用了Doherty技术，以便在峰值功率有较大回退时仍能保持高效率特性。同时考虑到第三代移动通信（3G）能向第四代移动通信（4G）平滑演进，基站中射频功率放大器要求可以工作在TDS/TDL的双模状态中，以降低基站设计运营成本，避免重复性建设。因此，本文对双波段Doherty功率放大器进行了仿真研究。对于双波段Doherty功率放大器，其输入输出匹配电路和Doherty结构中的四分之一波长线和补偿线均需实现双波段特性，因此，本文提出运用双波段阻抗变换器和复合左右手传输线来实现其双波段传输特性。考虑到TD-SCDMA工作频段有2010-2025MHz，FuTURE4G TDD试验系统采用工作频率为3.45GHz，，频带宽度为20MHz，因此本文采用这两个频段设计双波段功放。设计仿真结果显示f=3.45GHz时，输出功率达到37.5dBm时，即Doherty功率放大器在6dB功率回退点时其功率附加效率PAE为50%，比平衡式功率放大器提高了19%；当f=2.017GHz时，输出功率为37dBm时，Doherty功率放大器到达6dB功率回退点，此时其功率附加效率PAE为50%，比平衡式功率放大器提高了24%。仿真结果显示证明了在输出饱和功率回退6dB范围时，功放在两个频段均获得了较高的效率。
[Abstract]:With the rapid development of the wireless communication, the TD-LTE standard has become the new standard for the evolution of the TD-SCDMA standard with the independent intellectual property in our country to the fourth-generation mobile communication. The TD-SCDMA and TD-LTE system belong to time division system, its working mode is time division duplex (TDD), its wireless frame is divided into different time slots, and the uplink and downlink data is transmitted through time slot, and different uplink and downlink time slot ratios can be flexibly configured. in the time-division system, in order to reduce the interference to the receiving channel and reduce the power consumption of the system, the radio-frequency power amplifier with the largest energy consumption in the system works only in the transmission time slot, and the radio-frequency power amplifier of the time-division wireless system is different from the radio-frequency power amplifier of the frequency subsystem, according to the uplink and downlink signals, the switching time of the radio frequency power amplifier of the time division wireless system is strictly limited, the radio frequency power amplifier is started to be started in a specified opening time and enters a stable working state, The output of the transmitting signal is stopped, and the isolation degree of the transmitting/ receiving channel is ensured. Therefore, the switching characteristic of the radio frequency power amplifier of the time division system is researched, the method for improving the switching characteristic is explored, and the circuit design of the bias circuit of the power amplifier is carried out, so as to meet the severe requirements of the radio frequency power amplifier switching characteristics of different time division wireless systems. According to the requirements of 3GPP R1-081181, the switching control signal of TD-SCDMA signal is at least 2. m in advance, and the turn-off time is 2. m according to the switching time requirement, a switching control circuit is added to the power amplifier grid bias circuit, the control of the power amplifier working state under the time division system is realized, the switching performance of the power amplifier is improved through a controllable discharge loop, and the switching sensitivity is improved The results of the experiment show that the falling edge of the voltage switching of the power amplifier is about 50us when the control and discharge loop is not applied; after the controllable discharging loop is increased, the falling edge is shortened to 20ns, and the switching speed can completely meet the requirement of the TD-LTE system to switch the radio frequency power amplifier An orthogonal frequency division multiplexing (OFDM) modulation scheme is used in a TD-LTE system, and an OFDM modulation technique causes a high signal to be generated. The peak-to-average ratio. In order to improve the efficiency of the power amplifier, the radio-frequency power amplifier adopts the Doherty technique, so that the high-efficiency can be maintained when the peak power has a large roll-off. rate characteristics. Considering that the third generation mobile communication (3G) can be smoothly evolved to the fourth generation mobile communication (4G), the requirements of the radio frequency power amplifier in the base station can be in the dual mode state of the TDS/ TDL to reduce the design and operation cost of the base station and avoid the repetition. In this paper, the double-band Doherty power amplifier is simulated. The dual-band Doherty power amplifier, the input-output matching circuit and the one-quarter wavelength line and the compensation line in the Doherty structure all need to realize the dual-band characteristic, therefore, the dual-band impedance transformer and the composite left-right-hand transmission line are used to realize the dual-wave band characteristic. The transmission characteristics of the section are considered. Considering that the TD-SCDMA working frequency band is 2010-2025MHz, the FuturE4G TDD test system adopts the operating frequency of 3.45GHz and the bandwidth of the frequency band is 20MHz, so the two frequency bands are designed in this paper Dual-band power amplifier. The simulation results show that when f = 3.45GHz, the power of Doherty power amplifier is 50% at 6dB power back-off point, which is 19% higher than that of balanced power amplifier. When f = 2.017GHz, the Doherty power amplifier reaches 6dB when the output power is 37dBm. The power back-off point, at which time its power-added efficiency PAE is 50%, is higher than the balanced power amplifier The simulation results show that the work is obtained in both frequency bands when the output saturation power is off the 6dB range.
【学位授予单位】：宁波大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TN722.75

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