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

Tooran Emami; Richard J. Hartnett

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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
DOI: 10.18260/1-2--22409
Permanent URL: https://peer.asee.org/22409
Download Count: 812

Paper Authors

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Tooran Emami Ph. D. 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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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.

Citation
Format

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. 10.18260/1-2--22409

TY - CPAPER
AB - 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.
AU - Tooran Emami Ph. D.
AU - Richard J. Hartnett P.E.
CY - Atlanta, Georgia
DA - 2013/06/23
PB - ASEE Conferences
TI - Real-World vs. Ideal Op-Amps: Developing Student Insight into Finite Gain-Bandwidth Limitations and Compensation
UR - https://peer.asee.org/22409
DO - 10.18260/1-2--22409
ER -