Chapter 1 Part 4 Introduction to Basic Filter

Chapter 1 Part 4 Introduction to Basic Filter 1

What is filter? Filter is a circuit that passes a specific range of frequencies while rejecting other frequencies. 2

Introduction to Filters Ø What is passive filter /active filter ? A passive filter consists of passive circuit elements such as capacitors, inductors and resistors. § An active filter uses active devices such as op-amps combined with passive elements. § 3

Introduction to Filters The passive elements provide frequency selectivity. Ø The active devices provide voltage gain, high input impedance and low output impedance. Ø 4

Types of filters Four basic types of filters: Ø 1. LOW PASS FILTER 3. BAND PASS FILTER Ø 2. HIGH PASS FILTER 4. BAND STOP 5

Types of filters Low Pass Filter (LPF) High Pass Filter (LPF) Pass all frequencies below cutoff frequency and reject all frequencies above cutoff frequency Pass all frequencies above the cutoff frequency and reject all frequencies below the cutoff frequency 6

Types of filters ØBand Pass Filter (BPF) Passes all frequencies within a band of frequencies and reject all other frequencies outside the band. Band Stop Filter ( Notch) Reject all frequencies within a band of frequencies and passes all other frequencies outside the band. 7

Ideal filters: LPF, HPF, BPF and BPF 8

Simple RC LPF Circuit 9

Simple RC LPF response curve or Bode Plot. 10

Typical LPF bode plot 11

Characteristics of Filters Ø The most common way to describe the frequency response characteristics of a filter is to plot the filter voltage gain (Vout/Vin) in d. B as a function of frequency (f). Ø What is cutoff Frequency? The frequency at which the output power gain drops to 50% of the maximum value is called cutoff frequency. 12

Characteristics of Filters (cont. . ) When the output power gain drops to 50%, the voltage gain drops 3 d. B (0. 707 of the maximum value. Ø The filter network voltage gain in d. B is calculated from the actual voltage gain (A) using the equation A(d. B) = 20 log A Where A=Vout/Vin Ø 13

BPF frequency response 14

END OF CHAPTER 1 15