Application Note
Selection Of M/A-COM PIN Diodes For Microwave Switch Designs
By Cobham Sensor Systems
Introduction
This Application Note is intended to provide practical guidance in the selection of PIN Diodes for switch control circuit functions. Switches, Digital and Analog Attenuators, and Limiters each have unique functions that require proper device selection. The design difficulty lies within the parametric translation from Diode Specifications, to the circuit designers' Microwave Specifications. Diode parametric language such as Vb, Vf, Ct, Rs, tL, ?, must convert into Insertion Loss, VSWR, Isolation, P1dB, Input IP3, RF Operating Power, RF Power Dissipation, and D.C. Power Consumption Specification Terminology.
In addition to actual diode parameters, package parasitics play a significant role in determining switch circuit performance. Package capacitance, package inductance, package electrical resistance, and package thermal impedance are extremely important considerations to determine the effective frequency bandwidth and maximum incident power for reliable switch operation.
The manufacturing methodology dictates the type of diode selection. Surface mount assembly will mandate the usage of either plastic, HMIC SURMOUNT, or MELF & HiPAX ceramic devices. Chip and Wire ( Hybrid ) manufacturing will determine the usage of Cermachips, Flip Chips, or Beam Lead Devices. Schematics for the most common switch designs: Series-Exclusive, Shunt-Exclusive, and Series-Shunt are outlined below for consideration.
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•Application Note: Selection Of M/A-COM PIN Diodes For Microwave Switch Designs
