Day 5¶

Two-step design of negative-feedback amplifiers

The design of negative-feedback amplifiers can be performed in two steps:

1. The design of the ideal gain of the amplifier. This comprises the design of the structure of the amplifier with feedback networks and nullors as ideal controllers.
2. The design of the controller(s) (also error amplifiers)

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:

1. Static (DC) gain limitation
2. Bandwidth limitation
3. Weak nonlinearity (differential gain)

to important performance limitations of the amplifier:

1. Gain inaccuracy
2. Frequency response
3. Differential gain

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