Download Lab 5: Frequency Response of an Op Amp Circuit

ECE 2055 Sec 100
cmck
Spring 09
LAB 5: Frequency Response of an Op-Amp Circuit
Lab Objectives
1) To investigate the frequency response of a simple op-amp amplifier circuit.
2) To reinforce the concepts of gain, phase angle, decibels and the Bode diagram.
Exercise 1: Preliminary Calculations
The circuit to be analyzed is given in Figure 1. The circuit input is at terminals 1 – 1 and the
output is at terminals 2 – 2. The circuit is an inverting amplifier with capacitance feedback.
C
R2
1
R1
-
U1
2
OUT
Vin
+
Vout
OPAMP
1'
2'
0
Figure 1
Compute the gain function Gv(jω) = Vout / Vin in terms of R1, R2, C and ω. Note that Gv(jω) is a
complex quantity; put your result in polar form.
Sketch (and label) the expected | Gv(jω) | vs ω, and the expected angle of Gv(jω) vs ω in your
notebook.
Show the results to the lab instructor.
Exercise 2: Measuring Gain and Phase
Suggested values are:
R1 = in the range of 2 k to 5 k
R2 = in the range of 5 k to 10 k
C in the range of 0.07 μF to 0.5 μF.
Collect the required components; measure and record their values. Build the circuit and connect it
to a sinusoidal source (FG).
Test the circuit for ω ranging from 0.1 krad/s to 30 krad/s. Note: Keep the input voltage constant
and measure the output voltage magnitude and phase.
Plot gain magnitude versus radian frequency, and phase versus radian frequency (all axes should
be linear).
Exercise 3: Bode Diagrams
Use your data to produce Bode diagrams: plot decibel gain (on a linear axis) versus ω (on a log
axis), and phase (on a linear axis) versus ω (on a log axis).
Print a copy of both plots for your instructor and annote the plots as follows:
* include component values of R1, R2 and C.
* include hand drawn low frequency and high frequency asymptotes
* mark off the frequency where the asymptotes meet.
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Exercise 4: Bode Diagrams
In your report, write a MATLAB script to produce two Bode plots (magnitude versus frequency
and phase versus frequency) for the gain function derived in Exercise 1.
For comparison, write a MATLAB script to produce two Bode plots using the data measured in
Exercise 2.
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