Date: Tuesday, March 29 2022
Location: Chip
Time: 10:45 - 12:30
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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.
Presentation in parts
Frequency stability of feedback amplifiers (parts)
Video
EE3C11 lecture 14: The Root locus technique
Study
Chapter 11.5
The presentations are summarized on the poster: “Derive Controller Requirements from Amplifier Specifications”
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.
Presentation in parts
Frequency stability of feedback amplifiers (parts)
Video
EE3C11 lecture 14: The Root locus technique
Study
Chapter 11.5
Capacitively loaded Common Collector Stage
The common collector stage (CC stage) is a nonenergic unity-gain negative feedback voltage amplifier that has a CE (common-emitter) stage as controller. Under ideal drive and load conditions, the loopgain in a CC stage is usually larger than the loop gain of its MOS equivalent: the CD stage. As a result, a capacitively loaded CC stage easily becomes instable.
A demonstration of the step response a capacitively loaded CC stage with a 2N3904 BJT shows this effect.
Presentation
The presentation “Capacitively loaded CC stage” discusses the analysis of the frequency response of the demonstrated stage with the aid of the asymptotic gain feedback model and elucidates frequency compensation with the aid of a phantom zero at the input and at the output of the stage.
Download the LTspice files
Download the SLiCAP files
Introduction to Frequency Compensation
After the bandwidth of a negative feedback amplifier has been designed, the poles of the transfer are not necessarily in the desired positions.
Presentation
The presentation “Introduction to Frequency Compensation defines the term frequency compensation and presents strategies and methods for frequency compensation.
Presentation in parts
Video
Introduction to frequency compensation (9:01)
Study
Chapter 12.1
The Phantom Zero
Phantom zero frequency compensation is the most powerful frequency compensation technique.
Presentation
The presentation Frequency Compensation: the Phantom Zero introduces the concept of the phantom zero.
Presentation in parts
Frequency Compensation: the Phantom Zero (parts)
Video
Study
Chapter 12.2.1
Phantom Zero Compensation of a 2nd-order System
Presentation
The presentation Frequency Compensation: the Phantom Zero Compensation of a 2nd-order System applies the concept of phantom zero frequency compensation to the compensation of a second order system.
Presentation in parts
Frequency Compensation: the Phantom Zero Compensation of a 2nd-order System (parts)
Video
Study
Chapter 12.2.2
Implementation of Phantom Zeros
Practical implementation of phantom zeros can be accomplishes in two ways:
Active phantom zeros
Passive phantom zeros
Active implementation requires the use of active differetiating circuits in the feedback loop of the amplifier.
Passive compensation requires the insertion of loop gain zeros in:
The feedback network
Coupling networks between the signal source and the input of the amplifier
Coupling networks between the output of the amplifier and the load.
Such passive zeros are called effective if:
They do not significantly affect the initial pole positions (before compensation) of the loop gain
They do not introduce new dominant poles
This is usually the case if, before compensation, these feedback networks or coupling networks introduce a large attenuation in the loop gain at the phantom zero frequency.
Presentation
The presentation Implementation of Phantom Zeros presents passive implementation techniques for phantom zeros and discusses the effectiveness of the frequency compensation.
Presentation in parts
Implementation of Phantom Zeros (parts)
Study
Chapter 12.2.4, 12.2.5, 12.2.6
Examples Phantom Zero Frequency Compensation
Presentation
The presentation Examples Phantom Zero Compensation presents Examples 11.8, 12.8 and 12.9.
Presentation in parts
Examples Phantom Zero Compensation (parts)
Video
Examples of implementation of phantom zeros (15:23)
Study
Examples 11.8, 12.8 and 12.9
Phantom zero compensation and interaction with other performance aspects
Presentation
The presentation Phantom zero compensation and interaction with other performance aspects briefly discusses the interaction between frequency compensation with phantom zeros and other performance aspects, such as, noise, bandwidth, weak distortion, energy storage, power dissipation and overdrive recovery.
Presentation in parts
Phantom zero compensation and interaction with other performance aspects (parts)
Video
EE3C11 lecture 14: Phantom Zero Interaction with other Design Aspects.
Study
Chapter 12.2.8.
Set up the requirement specification for the operational amplifier to be used as controller in the active antenna. Use the amplifier configuration from assignment 5. The following spects should be discussed:
The show-stopper values for the equivalent input noise sources of the OpAmp.
The gain-bandwidth product of the OpAmp.
The input capacitance of the OpAmp.
The output resistance of the OpAmp.
The composition of the groups for this assignment must be the same as for the previous assignment.
The results should be presented in a SLiCAP HTML report (Zipped html sub directory of your SLiCAP project).
