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Lecture

Feedback and Stability

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 principles of feedback in analog circuits, focusing on negative feedback. It explains how negative feedback is used in amplifiers to desensitize gain, reduce distortion, control noise, and extend bandwidth. The lecture also delves into the general feedback structure, closed-loop gain, loop gain, and the impact of feedback on amplifier stability. Various feedback amplifier configurations are discussed, such as the series-shunt feedback topology. The systematic analysis of feedback voltage amplifiers is presented, including the calculation of loop gain, input/output resistances, and closed-loop gain. Examples of noninverting and inverting amplifiers are provided to illustrate the application of feedback in circuit design.

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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

Physics

Electromagnetism: Electrical networks

Mechanical engineering

Acoustical engineering: Audio engineering

Related concepts (32)

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.

Operational amplifier

An operational amplifier (often op amp or opamp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. In this configuration, an op amp produces an output potential (relative to circuit ground) that is typically 100,000 times larger than the potential difference between its input terminals. The operational amplifier traces its origin and name to analog computers, where they were used to perform mathematical operations in linear, non-linear, and frequency-dependent circuits.

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.

Feedback

Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to feed back into itself. The notion of cause-and-effect has to be handled carefully when applied to feedback systems: Simple causal reasoning about a feedback system is difficult because the first system influences the second and second system influences the first, leading to a circular argument.

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.

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