Name:
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Section: _________________
Date:
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57:018 Laboratory Experiment 4
BASIC OP-AMP CIRCUITS
OBJECTIVES
 Become familiar with the operational amplifier
REQUIRED PARTS AND EQUIPMENT
 741 Op-amp
 10K, 6.2K, and 1K resistors
PRE-LAB
Noninverting op-amp amplifier
741 Op-Amp Pinout
For the op-amp circuit above suppose that the value of the resistance for each resistor may vary ±5%.
Calculate the worst-case maximum and minimum circuit gain 𝑣𝑂 𝑣𝑖 .
Maximum 𝑣𝑂 𝑣𝑖
Minimum 𝑣𝑂 𝑣𝑖
The voltage of the op-amp output 𝑣𝑂 , is limited by the ± 15 V power supplies. For the maximum worstcase gain, what is the largest amplitude for the input 𝑣𝑖 which will not be clipped?
Maximum 𝑣𝑖
If the op-amp has a unity-gain frequency of 1 MHz, what is the upper 3 dB frequency of the amplifier
circuit with nominal resistor values?
𝑓3dB
Search for the datasheet for the 741 op-amp on the Internet. Find the nominal slew-rate.
Slew rate
Show your work as Appendix A that you attach to the lab report.
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Lab Activities
Noninverting Amplifier
1. Using the multimeter, measure the value of the resistors you will use for the non-inverting amplifier.
𝑅1 =
𝑅2 =
2. Make sure the power is off. Construct the non-inverting op-amp amplifier.
3. An improperly wired circuit may destroy the op-amp or blow the power supply fuse, so have a T.A.
check your wiring before tuning on the power supply.
4. Use the signal generator to apply a 1 kHz since wave small enough that the output signal still looks
undistorted.
5. Measure the amplitudes of 𝑣𝑖 and 𝑣𝑂 and calculate the voltage gain.
𝑣𝑖 =
𝑣𝑂 =
Measured Gain =
Expected Gain (nominal) =
6. Increase the frequency of the input signal until the output is 0.707 times its value for the 1 kHz signal.
This is the upper 3 dB frequency, which also defines the bandwidth since there is no lower 3 dB
frequency.
Measured Bandwidth =
7. An important characteristic of an amplifier is its gain-bandwidth product. Find the gain-bandwidth
product
Gain× Bandwidth =
8. Change 𝑅2 to 10 kΩ, measure its actual value and recalculate the expected gain.
Measured 𝑅2 =
Measured Gain =
Expected Gain (nominal) =
9. Measure the new gain and bandwidth and compute the gain-bandwidth product.
Gain× Bandwidth =
10. Use the signal generator to apply a square wave. Increase the frequency and amplitude until the
output resembles a triangle wave. The inability of the op-amp to follow an abrupt, large signal
change is called “slewing”. Measure the maximum rate of change of the output in volts per 𝜇s, which
is the slew rate.
Slew rate =
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Voltage Follower
Constructing a signal generator with high
internal resistance
Voltage follower circuit
The voltage follower does not amplify voltage, however, it does amplify power. It has very high input
impedance and very low output impedance.
The internal resistance of the signal generator in the lab is 50 Ω. Add a 10 kΩ resistor in series with the
output to make a signal generator with an internal resistance of ~10 kΩ as shown above. Drive a 1 kΩ
load with this signal generator, and measure the no-load voltage.
No-load voltage =
Voltage with 1 kΩ load =
Note that the output voltage is considerably less than the no-load voltage
One can overcome this loss of signal power with a voltage follower. Use the op-amp and construct a
voltage follower. Measure the voltage follower input and output.
Follower input voltage =
Follower output voltage =
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DISCUSSION
Q1. For the noninverting amplifier, how does the measured maximum 𝑣𝑖 compare with what you
computed in the pre-lab? Give one possible explanation if the value is significantly different.
Q2. How close (in percent) is the measured gain to the predicted (from your prelab) for the noninverting
amplifier for 𝑅2 = 6.2K? Is this within the margins you computed during the pre-lab? If not, give one
possible explanation.
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Q3. How close (in percent) is the measured gain to the predicted (from your prelab) for the noninverting
amplifier for 𝑅2 = 10K? Is this within the margins you computed during the pre-lab? If not, give one
possible explanation.
Q4. How close (in percent) were the two gain-bandwidth products you measured for the non-inverting
amplifier? Since this parameter is essentially equal to the unity-gain bandwidth, it should not vary with
gain. Give at least two specific reasons why the measurements vary.
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Appendix A
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Grading
PRE-LAB
Are the five values (max, min, etc.) in the table? (0–5)
Are the supporting calculations in Appendix A? (0–2)
LAB ACTIVITIES: NONINVERTING AMPLIFIER
Rate the gain-bandwidth product measurement, including units. (0–3)
Rate the slew rate measurement, including units. (0–3)
DISCUSSION
Rate the answer to Q1, including neatness. Key points: as the output amplitude
grows, the op-amp will eventually clip its output. The 741 op-amp is not a railto-rail op-amp, so clipping will occur even before the power supply rail voltages
are reached. (0–5)
Rate the answer to Q2, including neatness. Key points: component tolerances
and measurement errors will cause the actual gain to be different from the
nominal gain. (0–2)
Rate the answer to Q3, including neatness. Key points: component tolerances
and measurement errors will cause the actual gain to be different from the
nominal gain. Also, this amplifier is slew-rate limited, so the measured gain
will be less that nominal. (0–5)
Rate the answer to Q4. (0–4)
GENERAL
Rate the overall presentation (neatness, spelling, …). (0–5)
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