5

Analog Building Blocks and

Operational Amplifiers

5.1 The Amplifier Block

5.2 Ideal Operational Amplifier

5.3 Practical Properties of Operational Amplifiers

5.4 Applications of Operational Amplifiers

5.5 Learning Objectives

5.6 Practical Application: A Case Study—Automotive Power-Assisted Steering System

Problems

Electronic systems usually process information in either analog or digital form. In order to process

the two different kinds of signals, analog circuits and digital circuits have been devised. While

almost all technology was of the analog type until around 1960, due to the advent of integrated

circuits (ICs), digital technology has grown tremendously.

In analog systems, a signal voltage or current is made proportional to some physical quantity.

Since voltages (or currents) can take on any values over a continuous range between some

minimum and some maximum, analog systems are also known ascontinuous-statesystems.

These are to be distinguished from digital ordiscrete-statesystems, in which only certain values

of voltage (or current) are allowed.

Most circuits found in analog systems are linear circuits in which one voltage (or current) is

meant to be linearly proportional to another.Linear active circuitsare also known asamplifiers,

which are the building blocks of linear systems with analog technology.

When describing and analyzing electric systems, which are often large and complex, it is very

helpful to consider such large systems as being built from smaller units, calledbuilding blocks.

These are then the subunits, which can be connected to form larger circuits or systems. More

importantly, the building blocks can be described adequately by their simpleterminal properties.

Thus, with the building block point of view, one is not concerned with the interiors of the blocks,

only with how they perform as seen from the outside.

The concept of amodel, which is a collection of ideal linear circuit elements simulating

approximately the behavior of a real circuit element or a building block under certain limitations,

223