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).