AG314
Principles, Applications and Selection of Receiving Diodes
Rev. V1
INTRODUCTION
Many microwave and RF systems require the frequency of a signal to be translated to a higher or
lower frequency. Also, there are applications for the generation of a relatively low frequency volt-
age or current that is proportional to the amplitude of a higher frequency signal. The properties of
a Schottky diode can be exploited to perform these tasks.
This application note is a survey of the physical and electrical characteristics of Schottky mixer
and detector diodes. It reviews the semiconductor and electrical properties of these diodes and
illustrates how they are used in a number of receiving circuits. It also presents a number of tables
and criteria to select an appropriate Schottky diode depending on the requirement of the mixer or
receiving system.
This application note is divided into eight sections:
I.
A discussion of the fundamentals of Schottky diodes including the physics of Schottky junctions
and their characteristics such as resistance, capacitance and barrier heights. These properties
ultimately determine the performance of all mixer and detector diodes.
II.
A discussion of the principles of variable resistance mixer diodes and the diodes' RF properties
such as noise figure, conversion loss and impedance.
III.
A discussion of the principles of detector diodes and their RF properties such as sensitivity and
video resistance.
IV.
V.
A comparison of the differences in mixers and detectors when used in receivers.
A discussion of common mixer, modulator and multiplier circuits which use Schottky diodes.
Some of the advantages and disadvantages of different circuits are discussed.
VI.
A glossary containing definitions of the major terms used in discussing mixer and detector cir-
cuits and mixer and detector diodes.
VII.
VIII.
Tables and graphs to aid in the selection of an appropriate mixer circuit or diode for a circuit
based on the system's receiver requirements.
A Selection Guide to help select the most appropriate microwave diode.
This application note has been the standard Schottky diode reference since it was written in the
mid-1980’s. Since then, the fundamental principles of mixer technology and Schottky junction
physics have not changed, but many of the implementations of these technologies have evolved
and improved. This note has been extensively revised to reflect these advances in diode and
circuit design.
1
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