Department of Electronics and Mechanical Date:
ELEC 195 - Circuits Theory II
Experiment 10
RC Low-Pass
Objective:
1. To become familiar with the characteristics of passive Low-pass filters.
2. To analyze the frequency response of RC Low-pass filters.
3. To find the cutoff frequency experimentally and comparing the experimental value with the theoretical value.
Equipment Required:
Resistors: 1K W Jumpers
Capacitors: 0.1mF A breadboard
Leads BNC connectors
Resume of Theory:
Passive filters are constructed using resistors, capacitors and inductors, but no active devices such as transistors and operational amplifiers. A low-pass filter is an electronic device, which rejects high frequencies and passes lower frequencies. The figure shown below is a passive RC filter.
Procedure:
a) Construct the network shown below, and find the measured value of the resistor and the capacitor.
R measured = ______
C measured = ______
b) Write an equation for Vo in terms of Vi.
Vo = ______
Then establish the ratio V0/Vi in magnitude and phase form (polar form).
V0/Vi = ______
The condition R = Xc establishes the low cutoff frequency. Write an equation for frequency that establishes this condition. Show the derivation.
fc = ______
Using the measured resistor and capacitor values, calculate the cutoff frequency
fc = ______
c) Set the function generator to sinusoidal waveform 8 Vp-p, and complete the following table.
Frequency (KHz) / Vo(p-p) (volts) /0.1
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
3.0
4.0
5.0
6.0
8.0
10
12
14
16
18
20
40
60
100
d) Using Microsoft Excel or any other computer program of your choice Plot Av versus frequency.
e) Draw a horizontal dashed line at 0.707 level and determine the frequency at which the line intersects with the curve. Record the cutoff frequency.
fc = ______
How does it compare to the predicted level calculated in part b?
Using Pspice or Electronic Work Bench computer program, simulate the frequency response of the low-pass filter and compare them with experimental data.
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A. Khabari Wentworth Inst. of Tech.