# Filter Circuits

IN THIS CHAPTER

16.1 Introduction

16.2 The Electric Filter

16.3 Filters

16.4 Second-Order Filters

16.5 High-Order Filters

16.6 Simulating Filter Circuits Using PSpice

16.7 How Can We Check … ?

16.8 DESIGN EXAMPLE—Anti-Aliasing Filter

16.9 Summary

Problems

PSpice Problems

Design Problems

## 16.1 Introduction

Transfer functions are used to characterize linear circuits. In a previous chapter, we learned how to analyze a circuit so that we could determine its transfer function. In this chapter, we learn how to design a circuit to have a specified transfer function. This design problem does not have a unique solution. There are many ways to obtain a circuit from a specified transfer function. A popular strategy is to design the circuit to be a cascade connection of second-order filter stages. This is the strategy we will use in this chapter.

The problem of designing a circuit that will have a specified transfer function is called filter design. In this chapter we will learn the vocabulary of filter design and describe second-order filter stages. Finally, we will learn how to connect these filter stages to obtain a circuit that has a specified transfer function.

## 16.2 The Electric Filter

The concept of a filter was conceived early in human history. A paper filter was used to remove dirt and unwanted substances from water and wine. A porous material, such as paper, ...

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