Lecture

Feedback Amplifiers: Stability Analysis

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In course

MICRO-211: Analog circuits and systems

This course introduces the analysis and design of linear analog circuits based on operational amplifiers. A Laplace early approach is chosen to treat important concepts such as time and frequency responses, convolution, and filter design. The course is com ...

Description

This lecture covers the stability analysis of feedback amplifiers, focusing on the frequency dependence of loop gain and the impact on amplifier stability. It discusses the stability criteria based on loop gain magnitude and phase, as well as gain and phase margins. The lecture also explores the effects of phase margin on closed-loop response and alternative approaches for stability investigation. Various amplifier types, such as voltage and current feedback amplifiers, are analyzed in terms of stability. The Butterworth and Chebyshev approximations for filter design are presented, emphasizing ripple in passbands and stopbands. The lecture concludes with detailed examples of Butterworth and Chebyshev transfer functions and their frequency responses.

Instructor

Christian Enz

Christian C. Enz (M84, S'12) received the M.S. and Ph.D. degrees in Electrical Engineering from the EPFL in 1984 and 1989 respectively. From 1984 to 1989 he was research assistant at the EPFL, working in the field of micro-power analog IC design. In 1989 he was one of the founders of Smart Silicon Systems S.A. (S3), where he developed several low-noise and low-power ICs, mainly for high energy physics applications. From 1992 to 1997, he was an Assistant Professor at EPFL, working in the field of low-power analog CMOS and BiCMOS IC design and device modeling. From 1997 to 1999, he was Principal Senior Engineer at Conexant (formerly Rockwell Semiconductor Systems), Newport Beach, CA, where he was responsible for the modeling and characterization of MOS transistors for the design of RF CMOS circuits. In 1999, he joined the Swiss Center for Electronics and Microtechnology (CSEM) where he launched and lead the RF and Analog IC Design group. In 2000, he was promoted Vice President, heading the Microelectronics Department, which became the Integrated and Wireless Systems Division in 2009. He joined the EPFL as full professor in 2013, where he is currently the director of the Institute of Microengineering (IMT) and head of the Integrated Circuits Laboratory (ICLAB).He is lecturing and supervising undergraduate and graduate students in the field of Analog and RF IC Design at EPFL. His technical interests and expertise are in the field of very low-power analog and RF IC design, semiconductor device modeling, and inexact and error tolerant circuits and systems.He has published more than 200 scientific papers and has contributed to numerous conference presentations and advanced engineering courses. Together with E. Vittoz and F. Krummenacher he is one of the developer of the EKV MOS transistor model and the author of the book "Charge-Based MOS Transistor Modeling - The EKV Model for Low-Power and RF IC Design" (Wiley, 2006). He has been member of several technical program committees, including the International Solid-State Circuits Conference (ISSCC) and European Solid-State Circuits Conference (ESSCIRC). He has served as a vice-chair for the 2000 International Symposium on Low Power Electronics and Design (ISLPED), exhibit chair for the 2000 International Symposium on Circuits and Systems (ISCAS) and chair of the technical program committee for the 2006 European Solid-State Circuits Conference (ESSCIRC). Since 2012 he has been elected as member of the IEEE Solid-State Circuits Society (SSCS) Administrative Commmittee (AdCom). He is also Chair of the IEEE SSCS Chapter of Switzerland.

Official source

Ontological neighbourhood

Information engineering

Signal processing: Filtering theory

Physics

Electromagnetism: Electrical networks

Related concepts (32)

Negative-feedback amplifier

A negative-feedback amplifier (or feedback amplifier) is an electronic amplifier that subtracts a fraction of its output from its input, so that negative feedback opposes the original signal. The applied negative feedback can improve its performance (gain stability, linearity, frequency response, step response) and reduces sensitivity to parameter variations due to manufacturing or environment. Because of these advantages, many amplifiers and control systems use negative feedback.

System

A system is a group of interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its environment, is described by its boundaries, structure and purpose and is expressed in its functioning. Systems are the subjects of study of systems theory and other systems sciences. Systems have several common properties and characteristics, including structure, function(s), behavior and interconnectivity.

Amplifier

An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It is a two-port electronic circuit that uses electric power from a power supply to increase the amplitude (magnitude of the voltage or current) of a signal applied to its input terminals, producing a proportionally greater amplitude signal at its output. The amount of amplification provided by an amplifier is measured by its gain: the ratio of output voltage, current, or power to input.

Negative feedback

Negative feedback (or balancing feedback) occurs when some function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by other disturbances. Whereas positive feedback tends to lead to instability via exponential growth, oscillation or chaotic behavior, negative feedback generally promotes stability. Negative feedback tends to promote a settling to equilibrium, and reduces the effects of perturbations.

Analogue filter

Analogue filters are a basic building block of signal processing much used in electronics. Amongst their many applications are the separation of an audio signal before application to bass, mid-range, and tweeter loudspeakers; the combining and later separation of multiple telephone conversations onto a single channel; the selection of a chosen radio station in a radio receiver and rejection of others.

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