Laboratory Procedures

DeVry University

College of Engineering and Information Sciences

OBJECTIVES

To analyze a RC Low Pass Filter using simulation and circuit measurement

.To analyze a RC High Pass Filter using simulation and circuit measurement

.To analyze a LC Band Pass Filter using simulation and circuit measurement

.II

. PARTS LIST

Equipment:

IBM PC or Compatible

Function Generator

Dual Channel Oscilloscope

Parts:

1 - 50 ? Resistor 1 - 470 nF, 50 V Capacitor

1 - 330 ? Resistor 4 - 47 µF, 35 V Capacitor

4 - 4

.7 mH Inductor 2 - 100 µF, 25 V Capacitor

1 - 470 mH, Inductor

Software:

MultiSim 11

III

. PROCEDURE

Simulation of RC Low Pass Filter |

Enter the circuit shown in Figure 1 in MultiSim

.Figure 1 - Low Pass Filter

Set the function generator voltage, VIn = 1 VP

.Simulate the circuit shown for various frequencies indicated in Table 1 below

. Record the output voltage, VOut, for each frequency and calculate the gain using the formula: 20 log(VOut P-P / VIn P-P)

.Frequency, Hz VOut P-P GaindB Frequency, Hz VOut P-P GaindB

100 2000

200 4000

400 8000

800 10000

1000

Table 1 – Low Pass Filter Frequency Response Simulation Data

Low

Determine the voltage “Gain/Loss” in dB for the frequency response plot

. Plot the simulation data of on the semi-log graph sheet below

. The frequency must be on the X axis and the GaindB on the Y–axis

.What is the 3 dB cutoff frequency from the plot?

fC =___________________

Calculate the 3 dB Cutoff frequency using the formula: fC = 1/(2 ? R C)

fC =___________________

Does the simulated measurement agree with the theoretical calculation?

Yes ______ No ______

B

. Simulation of RC High Pass Filter

Enter the circuit shown in Figure 2 in MultiSim

.Figure 2 - High Pass Filter

Set the function generator voltage, VIn = 1 VP

Simulate the circuit shown for various frequencies indicated in Table 2 and record the output voltage and gain

.Frequency, Hz VOut P-P GaindB Frequency, Hz VOut P-P GaindB

100 2000

200 4000

400 8000

800 10000

1000

Table 2 - Low Pass Filter Frequency Response Simulation Data

Determine the voltage “Gain/Loss” in dB for the frequency response plot

. Plot the simulation data of on the semi-log graph sheet below

.What is the 3 dB cutoff frequency from the plot?

fC =___________________

Calculate the 3 dB Cutoff frequency using the formula: fC = 1/(2 ? R C)

fC =___________________

Does the simulated measurement agree with the theoretical calculation?

Yes ______ No ______

C

. Simulation of LC Band Pass Filter

Enter the circuit shown in Figure 3 in MultiSim

.Figure 3 - LC Band Pass Filter

Setup the function generator voltage, VIn = 1 VP

.Simulate the circuit shown for various frequencies indicated in Table 3 and record the output voltage and gain

.Frequency, Hz VOut P-P GaindB Frequency, Hz VOut P-P GaindB

200 340

250 344

280 348

290 355

300 352

320 356

324 360

330

Table 3 – Band Pass Filter Frequency Response Simulation Data

Determine the voltage “Gain/Loss” in dB for the frequency response plot

. Plot the simulation data of on the semi-log graph sheet below

.What are the 3 dB cutoff frequencies from the plot?

Upper fC =_____________ Low fC =_____________

The LC band pass filter is PI- Section filter which has been designed using the website:

http://www

.raltron

.com/cust/tools/band_pass_filters

.asp

The filter has been designed to operate at a center frequency, fo of 340 Hz and a 3dB Bandwidth of 10% of fo

.Log in to the above website; feed the data of center frequency and the bandwidth desired

. Verify if the design values chosen for the lab experiment are close enough

.What are the calculated 3 dB cutoff frequencies?

Upper fC =_____________ Low fC =_____________

Do the simulated measurements agree with the theoretical calculations?

Yes ______ No ______

Increase or decrease the center frequency by 5 and recalculate the element values

. Note and record the new design parameters

. What can you comment on the new design values when compared with the original values?

The filter can be reconfigured to a T–type using the transformation shown below:

Some useful formulas for the Constant K type band pass filter design:

fC = Filter Center Design frequency

R0 = Filter Design Impedance

f1 and f2 => 3 dB cutoff frequencies, Lower & Upper

..Also, f1 x f2 = fC2

Bandwidth = f2 – f1

L_1= R_0/(? (f_2- f_1))

L_2= (R_0 (f_2- f_1))/(4? f_C^2 )

C_1= ( (f_2- f_1))/(4? ?R_0 f?_C^2 )

C_2= 1/(? R_0 (f_2- f_1))

Source for the above formulas: “HANDBOOK OF LINE COMMUNICATIONS”, A Royal Signals Pub

., 1947

.Using the suggested transformation, change the original PI type filter to T-type and simulate to verify if it works as the original

. Include the new filter topology below here

.Did the filter work as the original? YES NO

D

. Breadboard Construction of the three Filters

Build the three filters simulated above on a breadboard, one at a time

Use a Function Generator to excite the filters and check for the pass band and the cut off frequencies

.Submit a photograph of each of your working circuits (online) or have your instructor sign-off each circuit (onsite)

.