June 22, 2003
June 22, 2003
June 25, 2003
8.1222.1 - 8.1222.9
Understanding Loading in Feedback Ampliﬁer Analysis Manuel Toledo-Quiñones Electrical and Computer Engineering Department University of Puerto Rico Mayagüez, Puerto Rico
Introduction The application of negative feedback concepts to the analysis and design of electronic ampliﬁers is widely recognized as one of the most important subjects in electrical engineering curricula. Most electrical engineering students are exposed to feedback theory in courses primarily focused on systems and automatic controls. However, instructors teaching analog electronic circuits courses still devote considerable time explaining how to analyze feedback ampliﬁers because many practical aspects, such as the consideration loading effects, do not show up in other courses.
This paper presents some examples that illustrate some aspects of feedback ampliﬁer analysis related to the correct use of input and output impedances. It is the author´s experience that the relevant material normally found in undergraduate textbooks on microelectronics does not illustrate how to properly use these quantities. The objective of this paper is to provide educators with an additional tool to clarify these aspects of the subject.
Overview of the Feedback Method An ideal feedback ampliﬁer can be represented by the block diagram shown in ﬁgure 1. The quantities ωs , ωi , ωo and ωf represent the source, ampliﬁer input, ampliﬁer output and feedback signal, and can be voltages or currents. Ampliﬁers are classiﬁed according to the type of signal (voltage or current) being sampled at the output and mixed at the input. The four feedback conﬁgurations are shown in ﬁgure 2. The naming convention used in this article is summarized in table 1.
amplifier ωS ωi ωo A ωF
β feedback network
Figure 1: Ideal feedback ampliﬁer, composed of a non-feedback ampliﬁer and a feedback network.
Proceedings of the 2003 American Society for Engineering Education Annual Conference & Exposition Copyright c 2003, American Society for Engineering Education
Toledo-Quinones, M. (2003, June), Understanding Loading In Feedback Amplifier Analysis Paper presented at 2003 Annual Conference, Nashville, Tennessee. 10.18260/1-2--12516
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