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Development of a Spice op-amp macro-model for current-feedback amplifiers (Part 1 of 2)

Current-feedback amplifiers (CFAs) are the high-speed relatives of more common voltage-feedback amplifiers (VFAs). CFAs have wider bandwidths and faster slew rates. Applications like DSL rely on their fast and strong output drives. Models are important because they allow engineers to test designs before they go through the time-intensive and costly process of building a working prototype.

In this article, we introduce you to a circuit model for a current-feedback amplifier. Since it would take far too long to simulate every nuance of a complete design, this macromodel simulates the most common effects such as transient response, frequency response, voltage noise and output slew rate limiting. Detailed descriptions of each stage in the model will be presented with examples of model performance and correlation to actual device behavior.

The article is presented in two parts, as pdf files (no registration required), as follows:

· Part 1 discusses the overall approach, the input stage, gain stage, frequency-shaping stages, noise module, and output stage, click here.

· Part 2 discusses the simulation results and includes a net list; it will be posted on August 5, 2010.

About the authors

Jian Wang was born in China in 1975 and has served as an applications engineer with Intersil since 2005, focusing on high speed amplifiers and drivers. He received a Ph.D. from the University of California at Davis in 2006.
Tamara Schmitz holds BS, MS, and PhD degrees in electrical engineering. She taught analog circuits and test development engineering as an assistant professor at San Jose State University. With eight years of part-time experience in applications engineering, she joined Intersil in August 2007 as a principal applications engineer.

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