射頻開關增加靈活性

　　標準機械開關不能正常工作。在高頻率時，信號耦合可能發生在機械接觸間隙上，在高通濾波器中它可以像電容器一樣。較長的間隙減少耦合，但執行大小問題。

　　半導體射頻開關是一類在有源時通過期望的頻帶，并在不活動時嚴重衰減的電路。互斥級聯開關允許射頻信號多路復用，從而允許現代設備共享天線或將RF路由到不同的階段。

　　此外，使用板載PCB天線或外部天線的能力需要在同一個板上的兩個開關之間切換。射頻開關增加了支持兩個主板的靈活性。

　　這篇文章著眼于射頻開關技術和可供多功能射頻設計工程師使用的部件，如藍牙和Wi-Fi。它將討論大小、功耗和包裝選項，以及當前可用產品所提供的限制。

　　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.