Using op amps as an alternative for driving PIN diodes (Part 1 of 2)

PIN diodes, which sandwich a lightly doped intrinsic (I) region between heavily doped P and N regions, are used extensively in RF and microwave applications. Common applications of PIN diodes are microwave switches, phase shifters, and attenuators, where high isolation and low loss are required. They can be found in test equipment, instrumentation, communications gear, radar, and a variety of military applications.

Every PIN diode in a switching circuit has an accompanying PIN diode driver or switch driver that provides a controlled forward bias current, a reverse bias voltage, and the activating interface between the control signal—typically a digital logic command—and one or more PIN diodes. This driver function can be rendered as a discrete design, or with specialized ICs to fit the application.

As an alternative, widely available op amps and specialty amplifiers, such as clamp amplifiers and differential amplifiers, can be used in place of discrete PIN-diode drive circuits and expensive PIN-diode driver ICs. Op amps in this class feature wide bandwidth, high slew rates, and more than enough steady-state current to drive PIN diodes.

This article discusses three different PIN-driver circuits that employ op amps or specialty amplifiers—the AD8037, AD8137, and ADA4858-3. The circuits are designed to work with single-pole double-throw (SPDT) PIN-diode switches, but they can be adapted for other circuit configurations as well. They will be described in detail following a discussion on the nature and use of PIN diodes.

It is presented in two parts, in pdf file format (no registration required), as follows:

Part 1 of this article examines and discusses PIN diodes, PIN-diode bias interface, and the traditional PIN-diode drivers, click here.

Part 2 examines and explains op amp-based PIN-diode drivers, using specific parts and circuits; it will go online on August 2, 2010.

About the author

John Ardizzoni is a senior applications engineer, High-Speed Amplifier Group, Analog Devices. John joined Analog Devices in 2002. Prior to that, he worked for IBM as an applications engineer and for M/A-COM as a design engineer. John graduated from Merrimack College in 1988 and has over 29 years of experience in the electronics industry.