BALUN基础介绍全解.ppt

* A variety of RF baluns have been developed in past decades. In this chapter, three types of baluns are emphasized: the transformer, LC , and micro strip line. 4. BALUN Types and Designs(1) 1) In the simulation stage of RF circuit design, the ideal transformer balun is a good candidate for a transformation block between single - ended and differential pair blocks. The greatest advantage of the transformer balun is its frequency response with an almost infinite bandwidth. In addition, the insertion loss of the balun can be set to zero since it is an ideal balun. * 2) In the testing stage, the LC and micro strip line baluns are recomm-ended. The greatest advantage of an LC balun is its simplicity: it can be implemented in a laboratory quickly and easily. Surprisingly, instead of a narrow - band response as might be expected, the LC balun behaves with a reasonably wide - band frequency response. (a) LC Splitter (b) LC Combiner * 3) Compared with the LC balun, the frequency response in a micro strip line balun is wider. In addition, its outstanding advantage is low cost, since its basic parts are micro strip lines. 微带线A的长度为0.5个波长，微带线B的长度为0.25个波长，波长为在实际基板上的信号波长，需要考虑基板的介电常数。 巴伦的性能和所用的节数有关系，节数越多，频宽越宽，不过节数越多，尺寸也越大. * LC Balun 最简单的LC巴伦仅有两个相同的电感和电容构成，如下图所示： L C元件值的计算公式如下： Rout和Rin为单端和输出端口的阻抗 4. BALUN Types and Designs(2) * 设计一个工作频率在100MHz巴伦，单端和差分阻抗为50欧姆. 按照上述公式计算得到 L=113nH，C=22.5pF. S参数仿真结果： 在100MHz频率上幅度和相位和设计值基本吻合，不过LC对工作频率较为敏感，因此，该balun的工作带宽不宽，基本只能工作在100MHz附近。 * Micro Strip Line Balun 在频率较高的情况下（大于1GHz），LC巴伦由于电感，电容的寄生效应，自谐振频率等影响，性能将变差，而在高频上，用微带线设计的巴伦在性能，尺寸上都比较理想. S参数仿真结果： * Radio and television In television, amateur radio, and other antenna installations and connections, baluns convert between 300 Ω ribbon cable or 450 Ω ladder line (balanced) and 75 Ω coaxial cable (unbalanced) or to directly connect a balanced antenna to (unbalanced) coaxial cable. To avoid feed line radiation, baluns are typically used as a form of common mode choke a