# 26-03-2024: Electronics 13#

Date: Tuesday, March 26 2024

Location: Chip

Time: 10:45 - 12:30

## Knowledge Test#

Press the button(s) below to test your knowledge and understanding of the topics covered this lecture.

## Frequency stability of negative-feedback amplifiers#

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

## Downloads#

The presentations are summarized on the poster: Frequency Compensation

## Root-locus technique#

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

## Demonstration frequency (in)stability and frequency compensation#

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

## Phantom-zero frequency compensation#

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.