EE3C11 2020 Electronics
Zoom Web Lectures
Please study the topics listed in the presentations section below.
Download the poster: “Modeling of negative feedback
Two-step design of negative-feedback amplifiers
The design of negative-feedback amplifiers can be performed in two steps:
This two-step design method requires that butgets for performance limitations of the amplifier are split into error budgets for the feedback networks and error budgets for the controller.
Presentation
The presentation “Two-step design of negative feedback amplifiers shows that a feedback model that supports the two-step design of negative feedback amplifiers will tell us in which way and to what extent performance limitations of the amplifier are affected by performance limitations of the controller(s).
Study
Chapter 10.1
Feedback model of Black
In 1927, Black built the first negative feedback amplifier. The feedback model of Black is commonly used to evaluate the dynamic performance of negative feedback systems. However, Black’s feedback model is not optimally suited for the analysis of dynamic behavior of electronic feedback amplifiers and providing meaningful design information from such analysis.
Presentation
The presentation “Feedback model of Black introduces the feedback model of Black and shows its limitations for the analysis of electronic feedback circuits.
Study
Chapter 10.2
Asymptotic-gain feedback model
The asymptotic-gain feedback model provides a solid base for relating controller imperfections such as:
to important performance limitations of the amplifier:
Presentation
The presentation “Asymptotic-gain model introduces the asymptotic-gain feedback model.
Study
Chapter 10.3.1, 10.3.2
Selection of the loop gain reference variable
The analysis of feedback circuits with the asymptotic-gain feedback model gives the same result as network analysis techniques. However, if the loop gain reference is selected in a proper way, the asymptotic-gain model provides much more design information and it facilitates two-step design of negative feedback circuits.
Presentation
The presentation “Selection of the loop gain reference illustrates the way in wich the loop gain reference should be selected such that the model provides meaningful design information.
Study
Chapter 10.3.3, 10.3.4
Port of impedance single-loop feedback amplifiers
The port impedance of single-loop feedback amplifiers can be expresses in tems of the asymptotic-gain feedback model.
Presentation
The presentation “Port impedance of single-loop feedback amplifiers shows the way in which this can be done.
Study
Chapter 10.3.6
Download the poster: “Derive Controller Requirements from Amplifier Specifications”
Bandwidth of a negative feedback amplifier
For design purposes it is convenient to decouple the definition of the bandwitdth of a negative feedback amplifier from its desired frequency characteristic. This can be achieved by defining the bandwidth of a negative feedback amplifier by that of its servo function.
Presentation
The presentation “Bandwidth of a negative feedback amplifier shows that the bandwidth of a negative feedback amplifier will be defined as that of its servo function.
Video
Bandwidth definition for negative feedback amplifiers (3:40)
Study
Chapter 11.4.1
Example: Bandwidth of a negative feedback transimpedance integrator
Presentation
The presentation “Bandwidth Transimpedance Integrator shows the bandwidth definition for a negative feedback transimpedance integrator.
Video
Example Bandwidth definition for an OpAmp Integrator Circuit (7:12)
study
Chapter 11.4
Butterworth or Maximally Flat Magnitude (MFM) responses
The -3dB cut-off frequency of systems with a Butterworth or MFM transfer equals the Nth root of the magnitude of the product of their N poles, where N is the order of the system.
In this course we will design the frequency response of a feedback amplifier in such a way that the servo function obtains an MFM or Butterworth filter characteristic over the frequency range of interest. Design procudures for other filter characteristics, such as, Bessel or Chebyshev do not differ. Only the numeric relation between the -3dB bandwidth and the gain-poles product of the loop gain will be different.
Presentation
The presentation “Butterworth or Maximally Flat Magnitude (MFM) responses shows the Laplace transfer functions, the pole patterns and the magnitude characteristics of first, second and third order Butterworth transfers.
Video
Butterworth frequency responses (4:07)
Study
Chapter 11.4.3
MFM bandwidth of an all-pole feedback amplifier
The product of the loop gain and the magnitude of the dominant poles of the loop gain is a design parameter for the -3dB MFM bandwidth of an all-pole negative feedback amplifier .
Presentation
The presentation “All-pole loop gain and servo bandwidth proofs the above.
Video
All-pole Loop Gain and Servo Bandwidth (5:13)
Study
Chapter 11.4.3
Determination of the dominant poles of the loop gain
Presentation
The presentation “Dominant and non-dominant poles in feedback systems illustrates the procedure for separating dominant poles and non-dominant poles on feedback systems.
Video
Dominant poles and non-dominant poles of the loop gain (8:53)
Study
Chapter 11.4.3
Determination of the requirement for the gain-bandwidth product of an operational amplifier
The requirement for the GB-product of an operational amplifier can be derived from the loop gain-poles product (for dominant poles only).
Presentation
The presentation “Determination of OpAmp GB-product requirement illustrates the procedure for deriving the requirement for the gain-bandwidth product of the operational amplifier from the expression of the loop gain.
Video
Determination of GB product requirements for operational amplifiers (5:35)
Study
Chapter 11.4.3
Frequency stability of negative feedback systems
A system is stable if its responses to bounded excitations are also bounded.
A lumped system is said to be stable if the solutions of its characteristic equation (the poles) all have a negative real part.
Presentation
The presentation “Frequency stability of feedback amplifiers presents three ways to determine the stability of feedback systems.
Study
Chapter 11.5
