射频开关增加灵活性

　　射频开关增加灵活性

　　标准机械开关不能正常工作。在高频率时，信号耦合可能发生在机械接触间隙上，在高通滤波器中它可以像电容器一样。较长的间隙减少耦合，但执行大小问题。

　　半导体射频开关是一类在有源时通过期望的频带，并在不活动时严重衰减的电路。互斥级联开关允许射频信号多路复用，从而允许现代设备共享天线或将RF路由到不同的阶段。

　　此外，使用板载PCB天线或外部天线的能力需要在同一个板上的两个开关之间切换。射频开关增加了支持两个主板的灵活性。

　　这篇文章着眼于射频开关技术和可供多功能射频设计工程师使用的部件，如蓝牙和Wi-Fi。它将讨论大小、功耗和包装选项，以及当前可用产品所提供的限制。

　　Pin diode switches

　　Semiconductor switches for RF low power applications are widely used and a well understood technology. It is important to note the low power caveat， as high power switches will use specialty materials. Older ham radios， for example， still use mercury switches， admittedly not the most environmentally friendly material， but very effective at switching high power and completely safe when used properly.

　　For the vast majority of designs， power levels are in the range of micro-Watts to Watts， meaning semiconductor technology can easily perform well here – and it does. Two main technologies used for RF switching are PIN diode and transistor-based RF switches.

　　The PIN diode switch takes advantage of a ‘near intrinsic’ （lightly doped） semiconductor layer between highly doped P and N type semiconductor junctions （Figure 1）。 The high doping preserves low Ohmic resistance， since these are contact points for the switch.