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A Method For Obtaining The Transfer Function Of Inverting And Non Inverting Op Amp Circuits Based On Classical Feedback Theory

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2001 Annual Conference


Albuquerque, New Mexico

Publication Date

June 24, 2001

Start Date

June 24, 2001

End Date

June 27, 2001



Page Count


Page Numbers

6.49.1 - 6.49.9

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Paper Authors

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Vernon Blackledge

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Narciso Macia

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NOTE: The first page of text has been automatically extracted and included below in lieu of an abstract

A Method for Obtaining the Transfer Function of Inverting and Non-inverting Op-amp Circuits Based on Classical Feedback Theory

N.F. Macia, V. O. Blackledge Arizona State University

Abstract This paper presents an alternate approach for deriving the transfer function (gain, bandwidth) for both inverting and non-inverting Op-amp circuits. The approach uses classical feedback theory, in which the Op-amp circuit is represented in terms of its corresponding closed-loop, (feedback) block diagram. The characteristics of the Op-amp (open-loop), together with the equivalent transfer function of the accompanying circuit components, are incorporated into the classical, general feedback block diagram. The equivalent transfer functions (pre-filter and feedback) are obtained by means of superposition. Then, all the blocks are reduced into a single transfer function by means of the simplification formula: P(s)G(s)/(1+G(s)H(s)). The resulting transfer function shows the gain for each configuration (-RF/RA for the inverting Op-amp and 1+RF/RA for the non-inverting configuration) and bandwidth. It also shows that the Gain*Bandwidth product is constant for the non-inverting configuration, but not so for the inverting configuration. This approach is straightforward and insightful, specially for those students who have previously been exposed to feedback theory and who have backgrounds in fields other than electronics.

I. Introduction Often non-electrical engineers and technologists find themselves using Operational amplifiers (Op-amps). This occurs because electronic instrumentation has become very pervasive, specially with the proliferation of the PC. The approach presented in this paper is helpful to someone who is attempting to understand the Op-amp’s transfer characteristics. It is assumed that the individual has had a basic electrical science course and an understanding of feedback control. This approach has some advantages over the classical method used in electronic classes, aimed at electrical engineering/engineering technology students. Further, it is also insightful to students with an electronics background, even though they have the skills to understand the material as presented from an electronic presentation approach. We will derive the equivalent transfer function for both the inverting and non-inverting amplifiers. This transfer function will convey the DC gain and the bandwidth, which allows the relationship between gain and bandwidth to be observed. The approach assumes that the input signal source has low input impedance and that the load has relative high impedance. This approach does not produce information about input nor output impedance.

Proceedings of the 2001 American Society for Engineering Education Annual Conference & Exposition Copyright @2001, American Society for Engineering Education

Blackledge, V., & Macia, N. (2001, June), A Method For Obtaining The Transfer Function Of Inverting And Non Inverting Op Amp Circuits Based On Classical Feedback Theory Paper presented at 2001 Annual Conference, Albuquerque, New Mexico.

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