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Real-World vs. Ideal Op-Amps: Developing Student Insight into Finite Gain-Bandwidth Limitations and Compensation

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Conference

2013 ASEE Annual Conference & Exposition

Location

Atlanta, Georgia

Publication Date

June 23, 2013

Start Date

June 23, 2013

End Date

June 26, 2013

ISSN

2153-5965

Conference Session

Laboratory Experiences in Electronics and Circuits

Tagged Division

Division Experimentation & Lab-Oriented Studies

Page Count

15

Page Numbers

23.1024.1 - 23.1024.15

Permanent URL

https://peer.asee.org/22409

Download Count

26

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Paper Authors

biography

Tooran Emami U.S. Coast Guard Academy

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Tooran Emami is an assistant professor in the Department of Engineering, Electrical Engineering Section, at the U. S. Coast Guard Academy. She received M.S. and Ph.D. degrees in Electrical Engineering from Wichita State University in 2006 and 2009, respectively. Dr. Emami was an adjunct faculty member of the Department of Electrical Engineering and Computer Science at Wichita State University for three semesters. Her research interests are Proportional Integral Derivative (PID) controllers, robust control, time delay, compensator design, and filter design applications, for continuous-time and discrete-time systems.

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biography

Richard J. Hartnett P.E. U.S. Coast Guard Academy

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Richard J. Hartnett is a professor of electrical engineering at the U.S. Coast Guard Academy in New London, CT. He received his B.S.E.E. degree from the U.S. Coast Guard Academy, the M.S.E.E. degree from Purdue University, and his Ph.D. in EE from the University of Rhode Island. He is a registered Professional Engineer in the State of Connecticut, and his research interests include efficient digital filtering methods, improved receiver signal processing techniques for electronic navigation systems, and autonomous vehicle design.

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Abstract

Real-World vs. Ideal Op-Amps: Developing Student Insight into Finite Gain-Bandwidth Limitations and CompensationAbstractIn learning circuit design using operational amplifiers, most EE students aretaught about inverting and non-inverting amplifier design, summing amplifierdesign, and simple filter design (first and second order), all assuming the use of anideal operational amplifier. While this is a great place to start a design discussion,students can be left with the lingering impression that a µA741 op-amp (whichworked fine for anything they needed to accomplish in their carefully scriptedlabs from sophomore or junior year) is a generic op-amp that will do anythingthey will ever need to do!This paper presents some successful design and compensation techniques fromone laboratory in a junior-level Linear Circuits class at the U.S. Coast GuardAcademy. In this lab, students are asked to design two Sallen-Key second orderlow pass sections, using the µA741 op-amp, in order to meet two specificresonant frequency ( f 0 ) and quality factor ( Q ) specifications. They typicallyachieve the first design specification (design #1, for f 0 = 7.23 KHz and Q = 2 ) onthe first try. However they typically fall short of the resonant frequency in theirsecond design specification (design #2, f 0 = 72.3 KHz and Q = 2 ) by 20% ormore. This creates a teachable moment, as students reflect on their success indesign #1, and their failure to meet specifications in design #2. We then remindstudents that they are dealing with a real-world µA741 op-amp, whose Gain-Bandwidth Product is approximately 1MHz, and they learn the theory thatpredicts the impact of that limitation.Recognizing that the real-world op-amp itself can be modeled as a first ordertransfer function, we present graphical techniques that can be used early in thedesign process to “pre-compensate” for gain-bandwidth product limitations.Using these techniques, students are then able to meet specifications for design #2with their µA741 op-amp. Finally, in the last part of this lab students use a moreexpensive (LM318) op-amp, with 15MHz gain-bandwidth product, to illustratethat minimal (if any) compensation is required to meet design specification #2.This paper presents typical measurement results, along with informal studentfeedback that suggests to us that this exercise does reinforce student learning withrespect to real-world characteristics of op-amps.

Emami, T., & Hartnett, R. J. (2013, June), Real-World vs. Ideal Op-Amps: Developing Student Insight into Finite Gain-Bandwidth Limitations and Compensation Paper presented at 2013 ASEE Annual Conference & Exposition, Atlanta, Georgia. https://peer.asee.org/22409

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