Download Op Amp Amplifier

ECEN 313
The Operational Amplifier (Op Amp)
Objectives:
1. Familiarize yourself with the operation of a simple electronic amplifier
2. Familiarize yourself with simulations of an operation amplifier
3. Review the use of test equipment and test methods for performing basic amplifier
measurements
4. Examine the frequency response of an op-amp based inverting amplifier
Preliminary Work
Please complete the preliminary work before coming to lab. This will greatly reduce the
amount of time spent in the lab and will allow you to get more meaningful help from the TAs.
Part 1: Simple inverting amplifier
1. Figure 1 shows a simple inverting amplifier constructed using an operation amplifier (Op
Amp).
R2
C1
1mF
12V
50W
+
Rs
R1
V+
LF347/301/TI
V-
Vs
Vout
C2
1mF
-12V
Figure 1
IMPORTANT NOTE: Every time you use an op amp chip it should have the power
supply pins bypassed with a capacitor to ground. This is standard practice in industry.
Put capacitors located as close as possible to the IC from the positive supply pin to the
ground pin and from the negative supply pin to the ground pin. Typical values of
capacitance are 0.01 mF to 1 mF (non-electrolytic). Explain the purpose of these
capacitors.
2. Design a simple inverting amplifier to have a midband gain of A=Vout/Vin=12 V/V.
a. Make sure that you make the amplifier independent of the source resistance
(Rin>>50W).
b. Look up the gain-bandwidth product of the Op Amp available in your lab kit. You
should get the datasheet off of the internet.
c. Calculate the upper corner frequency.
Part 2: Frequency selective amplifier
1. Design a simple inverting amplifier to have the following specifications.
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Midband gain of 12 V/V. Make sure that you make the amplifier independent of the
source resistance (Rin>>50W). (This is the same as what you already did but you
might need to change the resistor values to meet the other requirement listed below.)
Lower corner frequency of fL=100Hz. (You should use a capacitor in series with
your source resistance. This is called a coupling capacitor.)
Upper frequency corner of fH=1kHz. (You should use a capacitor in parallel with
your feedback resistor to decrease your upper corner frequency. This is called a
feedback capacitor.)
Use the resistors and capacitors values available in your lab kit.
Laboratory Work
Part 1: Simple inverting amplifier
1. Simulate your design from the Preliminary section. This is the amplifier without coupling
and feedback capacitors.
a. Determine the upper corner frequency using an AC Sweep analysis. (Use a VAC
voltage source). This circuit should not have a lower corner frequency. (It is a low
pass filter.) Compare the simulated results to the values obtained during the
preliminary work.
b. Determine the midband gain using a Transient analysis (Use a VSIN voltage
source).
c. Determine the maximum undistorted output voltage and the corresponding input
voltage.
i. DC Sweep analysis.
1. Replace the source with a VDC part. You should be plotting the
output voltage versus the input voltage.
2. Perform a DC Sweep Analysis with a range from -2V < Vs < 2V.
3. The plot should be linear until it reaches the saturation point and then
the line should flatten out. The transition point where it is no long
linear is the maximum undistorted output voltage.
4. The maximum input voltage for non-distorted output is the
corresponding horizontal value.
ii. Transient Analysis
1. Replace the source with a VSIN part.
2. Set the amplitude of the source to the maximum for undistorted input
that you just found.
3. Perform a Transient analysis and verify that the output appears
sinusoidal.
4. Change the amplitude of the source to be 1.5 times larger and
perform the Transient analysis.
5. Describe the distortion in the output.
2. Construct your simple inverting amplifier
3. Characterize your circuit
a. Measure the midband gain and adjust the circuit if the midband gain is off by more
than 10%. Be sure to provide an oscilloscope plot with both the input and output
voltages and verify that the circuit is inverting and has the correct midband gain.
b. Measure the upper corner frequency.
c. Use the measured upper corner frequency.
d. Use the measured upper corner frequency to determine the GBW of your Op Amp.
e. Measure the maximum undistorted output voltage and the corresponding input
signal.
i. Apply a triangle wave to your amplifier. This is the measurement version of
the DC Sweep.
ii. The output should look like a clipped triangle wave. Be sure to be
measuring both the input and output voltage signals.
iii. Use the clipped triangle wave to determine the maximum input that will
produce an undistorted output signal.
iv. Now switch to a sinusoidal wave with amplitude that equals the maximum
undistorted value.
v. Now switch to a sinusoidal wave with amplitude that is 1.5 times the
maximum undistorted value. Be sure to describe any differences between
the actual measurement and the simulated output.
Part 2: Frequency selective amplifier
1. Simulate your design from the Preliminary section. This is the amplifier with coupling and
feedback capacitors.
a. Determine the upper and lower corner frequency using an AC Sweep analysis. (Use
a VAC voltage source). This circuit should not have a lower corner frequency. (It
is a low pass filter.) Compare the simulated results to the values obtained during
the preliminary work.
b. Determine the midband gain using a Transient analysis (Use a VSIN voltage
source).
c. Adjust your design to achieve the desired specifications within 10%.
2. Construct your circuit.
3. Characterize your circuit.
a. Measure the midband gain, lower corner frequency, and upper corner frequency.
b. Adjust your circuit until you are within 10% of the specifications
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Midband gain of 12 V/V.
Lower corner frequency of fL=100Hz
Upper frequency corner of fH=1kHz