Understanding Analog Filters: Types, Designs, and Frequency Response Characteristics

Introduction

In this article, we explore the critical role of electronic filters in signal conditioning. Categorized into active and passive types, these filters serve as essential components in any electronic system. Their primary function is to permit useful signals to pass through with minimal attenuation, while effectively blocking or reflecting unwanted signals. Based on specific performance requirements, signal conditioning shapes the characteristics of these signals for optimized system performance. We will delve into the four fundamental types of filters and provide real-world examples to illustrate their applications 

Background

Filter Type

  |--- R ---|--- 

  |              |

  |            --- C

  |            ---

  |              |

  |---------|---


  |--- L ---|--- 

  |              |

  |             R

  |              

  |---------|---


  |--- R + L ---|--- 

  |                     |

  |                   --- C

  |                   ---

  |                     |

  |-------------|---


  |--- C ---|--- 

  |              |

  |             R

  |         

  |---------|---


  |--- R ---|--- 

  |              |

  |              L

  |         

  |---------|---


  |--- R + C ---|--- 

  |                     |

  |                    L

  |         

  |-------------|---


  |--- L + C ---|--- 

  |                     |

  |                    R

  |         

  |-------------|---



  |--- R ---|--- 

  |              |

  |          L || C

  |         

  |---------|---



  |--- R ---|--- 

  |               |

  |           L + C

  |         

  |---------|---


  |--- L || C ---|--- 

  |                     |

  |                    R

  |         

  |-------------|---


Filter Characteristics

First Order Filter Bode Plots

Second Order Filter Bode Plots

Here's how the key characteristics of a filter are represented in these plots:

Analog Filter

Digital Filter

Design Analysis

Digital Circuit

Power Circuit

RF Desense Circuit

Audio Processing

Q&A

What is the most commonly used filter for electronic system design for digital designers?

Low Pass filter!

Summary & Conclusion

Filter is widely used to conditioning signal transmissio within the electronic system. Understanding basic filter type and different real world filter components and application enables electronic system engineers to break down any filter design into its basics four types. We omitted more complex filter design used in RF world such as Chebychev, Butterworth, Ellipication,etc but provided link for anyone to play around with.

Further Reading/Practice

"Analog Filters", https://www.analog.com/media/en/training-seminars/design-handbooks/Basic-Linear-Design/Chapter8.pdf 

"Filter Design and Tool", http://sim.okawa-denshi.jp/en/Fkeisan.htm 

"RF LC RF Design Tool", https://rf-tools.com/lc-filter/