Passive Filters I

Dr. Mohamed Refky Amin

Electronics and Electrical Communications Engineering Department (EECE)

Cairo University

elc.n112.eng@gmail.com

http://scholar.cu.edu.eg/refky/ 1

OUTLINE

• Introduction

• Low-pass Filters

• High-pass Filters

• Band-pass and Band-stop Filters

• Double tune filter

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Introduction

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• A lowpass filter passes low frequencies and stops high

frequencies.

• A highpass filter passes high frequencies and rejects low

frequencies.

• A bandpass filter passes frequencies within a frequency band

and blocks or attenuates frequencies outside the band.

• A bandstop filter passes frequencies outside a frequency band

and blocks or attenuates frequencies within the band.

Type of the filter

Low pass 0

High pass 0

Band-pass 0 0

Band-Stop

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Introduction

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• A filter is a passive filter if it consists of only passive elements

R, L, and C. It is said to be an active filter if it consists of

active elements (such as transistors and op amps) in addition to

passive elements R, L, and C.

• For a passive filter, the maximum output amplitude is equal to

the input amplitude

• For an active filter, the output amplitude can be greater than the

input amplitude

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Passive Filters

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Low-pass RC Filter

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Passive Filters

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Low-pass RC Filter

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Passive Filters

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Low-pass RC Filter

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Low-pass RC Filter

Negative angle means that

the circuit is a Lag Network

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Example 1

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Example 2

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High-pass RC Filter

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High-pass RC Filter

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High-pass RC Filter

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High-pass RC Filter

Positive angle means that the

circuit is a Lead Network

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Example 3

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Example 4

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Band-pass Filter

0

0

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Band-pass Filter

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Band-pass Filter

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Passive Filters

Band-pass Filter

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Passive Filters

Band-stop Filter

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Passive Filters

Band-stop Filter

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Band-stop Filter

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What is the Bandwidth?

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Band-stop Filter

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Band-stop and Band-pass Filters

Always valid

Valid only at resonance

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Example 5

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Example 6

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