Laboratory 9: Laboratory 9: Electronic FiltersElectronic Filters

OverviewOverview

• Objectives• Background• Materials• Procedure• Report / Presentation• Closing

ObjectivesObjectives

• Learn about electrical filters– Different types – Uses

• What is a -3dB point?• Create filters using multiple circuit

elements• Identify filters based on generated

graphs

Frequency Response GraphFrequency Response Graph• Gain

– Measured of power produced by circuit

– 20*log (Vout/Vin)

– In terms of decibels (dB)– Always negative value

• -3dB Point – 3dB drop of signal power from highest point on gain– Signal power is half of original value

• Cutoff Frequency– Frequency at -3dB Point– Units of Hertz (Hz)

Frequency Response GraphFrequency Response Graph

• Plot of Gain versus Frequency of electrical signal

• Semi-logarithmic scale– Linear Y-axis, logarithmic X-axis

Cutoff Frequency

3 dB

f (kHz) (log scale)

Gain (dB)(linear scale)

Gain vs. Frequency

Max Gain (dB)

Gain is 3 dB lower than the max

Bandwidth

What are Filters?What are Filters?

• Eliminate unwanted frequencies

– High-pass or low-pass

• Favor desired frequencies

– Band-pass• Bandwidth: frequency range filter allows to pass

– Example• Radio tunes in to particular station

Basic Filter TypesBasic Filter Types

• Low-Pass Filter– Low frequencies pass

•Low-Pass

•High-Pass

•Band-Pass3dB Point:-3dB

Cutoff Frequency:1590 Hz

Bandwidth:0 - 1590 Hz

Basic Filter TypesBasic Filter Types

• High-Pass Filter– High frequencies pass

•Low-Pass

•High-Pass

•Band-Pass

3dB Point: -3dB

Cutoff Frequency:160 Hz

Bandwidth:160 - ∞ Hz

Basic Filter TypesBasic Filter Types

• Band-Pass Filter– Limited frequency range

passes

•Low-Pass

•High-Pass

•Band-Pass3dB Point: -3dB

Cutoff Frequencies:400 and 600 Hz

Bandwidth:400 - 600 Hz

Resonant Frequency (High Response Point):500 Hz

Electrical TerminologyElectrical Terminology

• Voltage (V) [unit = V for Volts]– Difference in electrical potential

energy

• Current (I) [unit = A for Amperes]– Charge flow rate– Can be positive or negative

•Terms

•Elements

•Wiring

Electrical TerminologyElectrical Terminology

• Resistor (R) [unit = Ω for Ohms]– Resists flow of electrical current– Dissipates electrical energy as heat– Often used to alter voltages in

circuits– Characterized by Ohm’s Law: V = I*R– Not sensitive to frequency– Uses a poor conductor

• Example: Carbon

•Terms

•Elements

•Wiring

Symbol

Electrical TerminologyElectrical Terminology

• Capacitor (C)[unit = F for Farads]– Stores and delivers electrical energy– Affected by voltage and frequency– Uses metal plates that are

separated by material that does not conduct electricity• Example: Air

– Electrical charge accumulates on plates

•Terms

•Elements

•Wiring

Symbol

Electrical TerminologyElectrical Terminology

• Inductor (L)[unit = H for Henries]– Stores and delivers energy in a

magnetic field– Affected by current and

frequency– Uses a coil of wire– Allow current through wire to

form magnetic field

•Terms

•Elements

•Wiring

Symbol

Electrical TerminologyElectrical Terminology

• SeriesSame current through

all elementsVin = VA + VB + VC

• ParallelSame voltage across

all branchesVin = VD = VE = VF + VG

•Terms

•Elements

•Wiring

Materials for LabMaterials for Lab

• Resistors Brown, black, yellow = 100KΩBrown, black, green = 1MΩ

• Capacitors 103 = 0.01 µF102 = 0.001 µF100 µF

• Inductor 1 mH

Materials for Lab Materials for Lab (continued)(continued)

• Function generator• Coax cable• Alligator clips• Breadboard• PC

Virtual Bench OscilloscopeDAC Board

ProcedureProcedure• Calibrate Function Generator

– Insert coaxial end of connecting cable into 50Ω output on function generator

– Connect alligator clips• Red to pin 3 wire of DAC board• Black to pin 4 wire of DAC board

– Set function generator range to 1 kHz– Set mode to Sine Wave (~)– Tune output frequency to 1kHz

• Display must read 1.000 kHz

ProcedureProcedure

• Circuit 1 configurationConnect the 100kΩ resistor and .001

µF capacitor in series

ProcedureProcedure

• Circuit 2 configurationConnect 0.001 µF capacitor to 1

MΩ resistor in series

ProcedureProcedure

• Circuit 3 configurationConnect 1 mH inductor in parallel

with 100 µF capacitor

ProcedureProcedure

• Circuit Testing1. Connect function generator to circuit in test

(function generator is VIN in schematics)2. Set function generator to 10 Hz3. Record Vp-p reading on Virtual Bench Scope

• One whole sine wave must be visible on screen

4. Repeat steps 1-3 for frequencies of 20, 50, 100, 200, 500, 1000, 2000, 5000, 10000 Hz

DataData

• For each circuit, generate a graphPlot of 20*log(Vout/Vin) vs. FrequencySemi-log scale

Y-axis must be linearX-axis must be log scale

Properly label each graph and all axes

• TA must sign lab notes to verify data

Assignment: ReportAssignment: Report

• Individual Report (one report per student)• Title page• Discussion topics in the manual• For each circuit

– Include Excel tables and Gain vs. Frequency graphs– Determine filter type– Label each graph with determined filter type

• Have TA scan in signed lab notes• OPTIONAL- Include photos of circuits and

setup

Assignment: PresentationAssignment: Presentation

• Team presentation

• Include tables and plots (as in report)

• Refer to “Creating PowerPoint Presentations” found on EG website

• OPTIONAL – Include photos of circuits and setup

ClosingClosing

• Have all original data signed by your TA

• All team members must actively participate in experiment

• Submit all work electronically

• Return all materials to your TA