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ECE 202 – Experiment 9 – Lab Report
RESONANT CIRCUITS
YOUR NAME______________________
GTA’S SIGNATURE_________________
LAB MEETING TIME______________
SELECTION OF CIRCUIT PARAMETERS
5. Assemble the resonant circuit of Part 1. Use the function generator for Vs and choose values of Rs
and Vs to provide Im = 0.1 mA while Rs >> R.
a) The instructor will provide a 1.0 mH inductor. Use the HP Impedance Analyzer to measure
and record the inductance and series resistance of this inductor.
L = ______________ (Experimental)
Rind = _______________ (Exp)
b) Knowing the measured value of L, select a capacitor which approximately yields fo = 50 kHz.
Use the Impedance Analyzer to measure and record the capacitance.
C = ______________ (Experimental)
c) Knowing the measured value of L and Rs, select the resistor R which approximately yields B =
5 kHz. Measure and record this resistance.
R = _______________ (Experimental)
d) Comment on the effect Rs had on the selection of R.
ECE 202 – Experiment 9 – Lab Report
VOLTAGE RESPONSE OF CIRCUIT WITHOUT LOADING
6. Note: Measured circuit element values (determined in part 5) should be used in the rest of the lab
to calculate theoretical parameters describing the circuit.
a) Measure the voltage response VR ( f ) of the parallel resonant circuit of Part 5 using the
DMM. Record a sufficient number of points (at least 12-15) to clearly determine the
resonance behavior of the RLC circuit. Also observe the waveforms at vS(t) and vR(t) on the
oscilloscope.
b) Plot VR ( f ) versus f for both the theoretical calculation and experimental data on the same
axes. Discuss the results.
c) Determine the resonant frequency fo of the circuit.
fo = _______________ (Exp)
_______________ (Theory)
d) Verify that the voltage measured across the resistance R is maximum at the resonant
frequency.
e) Determine the bandwidth of the circuit.
f1 = ______________
f2 = _______________
B = _______________ (Exp)
_______________ (Theory)
Is the bandwidth evenly distributed around the resonant frequency?
f) Determine the Q factor of the circuit.
Q = _______________ (Exp)
______________ (Theory)
g) From your observations with the oscilloscope, was there a phase shift between vS(t) and vR(t)?
Did vR lead or lag with respect to vS? Describe.
h) Explain the reasons for any discrepancies between theory and experiment.
Hint: Include the effect of the series resistance Rind of the inductor (see appendix to the
PreLab).
ECE 202 – Experiment 9 – Lab Report
VOLTAGE RESPONSE OF A CIRCUIT WITH THE LOAD
7. Choose a load resistor with nominal value of 3500 Ω and record the actual value:
RL = _______________ (Experimental)
a) Place this resistor across R and measure the voltage response Vo ( f ) of the resonant circuit
with the load. Plot Vo ( f ) versus f for both the theoretical result and experimental data on the
same graph. Discuss the results.
b) Determine the loaded resonant frequency f 0load of the circuit.
f 0load = _______________ (Exp)
_______________ (Theory)
c) Determine the bandwidth of the circuit.
f1load = _______________
Bload = _______________ (Exp)
f 2load = _______________
_______________ (Theory)
d) Determine the Q factor of the loaded circuit.
Qload = _______________ (Exp)
_______________ (Theory)
e) Compare results for circuits with and without the load.
ECE 202 – Experiment 9 – Lab Report
VOLTAGE RESPONSE WITH THE OPERATIONAL AMPLIFIER
8. Now construct the Op Amp circuit you designed in Part 3 and connect the Op Amp circuit to the
output of your circuit of Part 7 (i.e., input to the Op Amp circuit is across R and the output of the
Op Amp circuit is fed to RL). Use the LF412. Remember, MAXIMUM ratings for supply voltage
are +/- 18 V!
Pin-out diagram
a) Measure and plot Vo ( f ) versus f.
b) Determine the resonant frequency f 0OPAMP of the circuit.
f 0OPAMP = _______________ (Exp) _______________ (Theory)
c) Determine the bandwidth of the circuit.
f1OPAMP = _______________
f 2OPAMP = _______________
BOPAMP = _______________ (Exp) _______________ (Theory)
d) Determine the Q factor of the circuit.
QOPAMP = _______________ (Exp) _______________ (Theory)
e) Based on the values of fo, B, and Q that you measured in Parts 6, 7 and 8, discuss the
advantages of using an Op Amp with a parallel resonant circuit. Any disadvantages?
FILTER FREQUENCY RESPONSE
9. Now choose one of your team’s filter designs from Part 4 (you should each have done one in the
PreLab) and construct individually a chosen designed filter. Plot frequency response of the circuits
measuring the response at at least 20 different frequencies and compare measurements with the
theory and Cadence prediction. Under Display use Capture feature to plot multiple waveforms on
the same graph. Is there a difference in the frequency response and why? Attach paper with the
graphs.
Remember GTA’s signature!