Laboratory 9 Electronic Filters Overview Objectives Background Materials

Laboratory 9: Electronic Filters

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

Objectives • Learn about electrical filters – Different types – Uses • What is a -3 d. B point? • Create filters using multiple circuit elements • Identify filters based on generated graphs

Frequency Response Graph • Gain – – Measured of power produced by circuit 20*log (Vout/Vin) In terms of decibels (d. B) Always negative value • -3 d. B Point – 3 d. B drop of signal power from highest point on gain – Signal power is half of original value • Cutoff Frequency – Frequency at -3 d. B Point – Units of Hertz (Hz)

Frequency Response Graph • Plot of Gain versus Frequency of electrical signal • Semi-logarithmic scale – Linear Y-axis, logarithmic X-axis Gain (d. B) (linear scale) Max Gain (d. B) Gain is 3 d. B lower than the max 3 d. B Bandwidth Cutoff Frequency f (k. Hz) (log scale) Gain vs. Frequency

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 Types • Low-Pass Filter • High-Pass • Band-Pass 3 d. B Point: -3 d. B Cutoff Frequency: 1590 Hz Bandwidth: 0 - 1590 Hz – Low frequencies pass

Basic Filter Types • Low-Pass • High-Pass Filter • High-Pass • Band-Pass 3 d. B Point: -3 d. B Cutoff Frequency: 160 Hz Bandwidth: 160 - ∞ Hz – High frequencies pass

Basic Filter Types • Low-Pass • Band-Pass Filter • High-Pass – Limited frequency range passes • Band-Pass 3 d. B Point: -3 d. B Cutoff Frequencies: 400 and 600 Hz Bandwidth: 400 - 600 Hz Resonant Frequency (High Response Point): 500 Hz

Electrical Terminology • Terms • Elements • Wiring • 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

Electrical Terminology • Terms • Elements • Wiring • Resistor (R) [unit = Ω for Ohms] Symbol – 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

Electrical Terminology • Terms • Elements • Wiring • Capacitor (C) [unit = F for Farads] Symbol – 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

Electrical Terminology • Terms • Elements • Wiring • Inductor (L) [unit = H for Henries] Symbol – 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

Electrical Terminology • Terms • Elements • Wiring • Series Ø Same current through all elements Ø Vin = VA + VB + VC • Parallel Ø Same voltage across all branches Ø Vin = VD = VE = VF + VG

Materials for Lab • Resistors ØBrown, black, yellow = 100 KΩ ØBrown, black, green = 1 MΩ • Capacitors Ø 103 = 0. 01 µF Ø 102 = 0. 001 µF Ø 100 µF • Inductor Ø 1 m. H

Materials for Lab (continued) • Function generator • Coax cable • Alligator clips • Breadboard • PC ØVirtual Bench Oscilloscope ØDAC Board

Procedure • 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 k. Hz – Set mode to Sine Wave (~) – Tune output frequency to 1 k. Hz • Display must read 1. 000 k. Hz

Procedure • Circuit 1 configuration ØConnect the 100 kΩ resistor and. 001 µF capacitor in series

Procedure • Circuit 2 configuration ØConnect 0. 001 µF capacitor to 1 MΩ resistor in series

Procedure • Circuit 3 configuration ØConnect 1 m. H inductor in parallel with 100 µF capacitor

Procedure • Circuit Testing 1. Connect function generator to circuit in test (function generator is VIN in schematics) 2. Set function generator to 10 Hz 3. 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

Data • For each circuit, generate a graph ØPlot of 20*log(Vout/Vin) vs. Frequency ØSemi-log scale ØY-axis must be linear ØX-axis must be log scale ØProperly label each graph and all axes • TA must sign lab notes to verify data

Assignment: 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: Presentation • Team presentation • Include tables and plots (as in report) • Refer to “Creating Power. Point Presentations” found on EG website • OPTIONAL – Include photos of circuits and setup

Closing • 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