PIN Diodes for Microwave Switch Designs

Rev. V2

AN3021

1

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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,

τ

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 per-

formance. Package capacitance, package inductance, package electrical resistance, and package thermal im-

pedance 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 ) manu-

facturing 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 considera-

tion.

The Decision Making Process for PIN Diode Selection for Microwave Switch Design

The following procedure outlines and Effective Process for PIN Diode Selection for Switch Design.

1. Determine the Preferred Type of Manufacturing for the PIN Diode in the Switch Design: Surface

Mount or Chip and Wire (Hybrid) Manufacturing.

2. Determine the Frequency of Operation and RF Power Handling of the Switch Design.

3. Use Table 1, “Relative Switch Performance and Design Evaluation Matrix” to determine the Type of

Switch Design that Best Satisfies the Particular Switch Specifications and Requirements.

4. Use Table 2, “Relative PIN Diode Performance Evaluation Matrix” to Determine the Type of PIN Di-

ode that Best Satisfies the Switch Design Selected from Table 1.

5. Use Table 3, “PIN Diode P/N Series Matrix” to Determine the PIN Diode P/N Series that Best Satis-

fies the Type of PIN Diode Selected from Table 2.