全集成抗阻塞射频接收系统的设计方法及电路实现研究

With the development of wireless communication network, due to the spectrum resources limitation, the increasing number of communication standards and terminals leads to the wire-less channels more and more crowded and the blocker in the receiver, which may make the receiver system saturate in advance. Besides, the blocker may generate the regenerated spectrum when there is strong blocking signal, which will cover the desired signal and cause the loss of desired signal. The blocker is not usually filtered by LC filter because it is too close to target channels. High-Q SAW filter can provide effective suppression to blocker，but it is lack of tuning capability and can’t be fully integrated. For the past few years, the concept of fully integrated and anti-blocking idea based on blocker cancellation has been proposed and gets attention by this field. However，above-mentioned scheme cannot provide enough blocker rejection due to the restriction of structure and circuit matching. For that reason, this project proposes a high-Q RF band stop filter circuit based on impedance move of passive mixer, also proposes a RF front-end amplifier enabled through the feed-forward structure to suppress blocker. And comparing with traditional structure, this structure can offer better matching and blocker rejection ratio. In order to promote the blocker rejection ratio of the whole receiver system, this project expands the anti-blocking ability from RF front-end to the entire receiver link through the proposed RF front-end amplifier and the innovation of anti-blocker down-mixer and high-linearity IF circuit. The research result of this project will provide the theoretical guide for the research of anti-blocking RF receiver system and the circuit design.

随着无线通讯网络的发展，因频谱资源的有限性，不断增加的通信标准和用户终端使无线信道变得越来越拥挤,进而可能产生阻塞现象，接收系统可能发生提前饱和或产生再生频谱覆盖有用信号，造成接收信号丢失。阻塞信号通常因过于靠近目标信道而无法通过LC滤波器滤除。高Q值SAW滤波器虽可有效抑制阻塞信号，但其缺乏调谐能力并且无法实现全集成。近年来，基于阻塞信号抵消的全集成抗阻塞思路的提出得到了业界关注，然而受结构和电路匹配的限制，其阻塞抑制效果仍有提高的必要。鉴于此，本项目基于无源混频阻抗搬移特性，提出一种高Q值射频带阻滤波电路，并以此构造前馈结构射频前端放大器以实现对阻塞信号的抑制，相比传统结构可提供更好的匹配性和阻塞抑制比。结合抗阻塞下混频器以及高线性度的中频电路等的创新，将抗阻塞功能从射频前端延伸到整个接收链路以提高整个接收系统的阻塞抑制比。本项目研究成果将为抗阻塞射频接收系统及电路设计提供理论指导。

物联网的普及使得工作于同一频段的无线通讯终端数目迅速增多，环境中众多无线终端大大增加了信号阻塞的产生几率。强阻塞信号能改变接收系统电路的工作点，对接收系统的增益、噪声、带宽、线性度等性能造成不良影响。传统射频接收系统结构外加声表面波滤波器（SAW）来进滤除阻塞信号，这种方法增加了成本而且对带内阻塞信号无法进行有效抑制。全集成抗阻塞射频接收前端系统作为解决以上问题的一种有效途径成为近期学术研究的热点。项目以全集成抗阻塞射频接收系统的设计方法及电路实现为研究重点，在系统架构、关键电路模块方面开展了深入的研究。在系统层面，提出了一种全集成抗阻塞射频接收系统架构。该架构从射频放大器、下混频器和中频电路三个模块对阻塞信号进行逐级抑制。通过数字基带电路检测当前阻塞信号功率强度，当阻塞信号相对有用信号功率较小，则关闭前馈支路，降低功耗同时减少噪声源。在关键电路模块上，1、提出了一种高阻带抑制比和Q值射频带阻滤波器，该结构基于无源混频器的频谱搬移特性，将跨阻级的中频输入阻抗特性搬移到射频本振；2、提出了一种高相位和增益匹配的主支路和前馈支路，前馈结构射频前端放大器中的信号支路采用与前馈支路相同的结构，使得信号支路输出端的寄生电容和前馈支路相同，以实现两条支路的相位匹配；3、提出了一种利用电容交叉耦合技术设计的低噪声放大器；4、提出了一种抑制阻塞信号下混频器，该结构中跨阻放大器采用源极输入和跨导增强技术，实现了跨导级低阻抗宽带输入,减小了下混频跨导级输出端阻塞信号的摆幅。经仿真验证，整个前端的噪声系数小于5.3dB,带外抑制比大于42dB@20MHZ。