2/27/2023
Lab 7 – Introduction to Operational
Amplifiers with Simple Circuit
YIN YU(SORA), CHAN A01088220 [B]
BIOMEDICAL ENGINEERING TECHNOLOGY
BMET 2200
Electronics Principles and Practice II: Laboratory Manual
Lab 7: Introduction to Operational Amplifiers with Simple Circuits
NAME: YIN YU(SORA), CHAN SET:
1.
B
Objectives
1.1. To examine the simple amplifier circuits built from Op-Amp 741. Including the noninverting amplifier, inverting amplifier, voltage follower, and integrator.
1.2. To measure the input impedance of non-inverting and inverting amplifier.
1.3. To investigate the effect of input impedance and output impedance.
1.4. To investigate the effect of output short circuit current of the Op-Amp 741.
Note: Operational amplifiers are electrostatically sensitive. It is recommended to wear a
grounded wrist strap while handling them.
2.
Equipment Used in the Laboratory
TYPE AND MAKE
3.
SERIAL #
Power supply
ANATEK 6030 & 1551
Function Generator
Model: BK PRECISION 4012A ;
SN:40121057405110160
Oscilloscope
Model: TDS 1002 ; SN:C016492
IC
741
Pre-Lab
3.1. Review the lecture notes and Datasheet of the 741 Op-amp posted to D2L, and then find the
value for the following specifications (including absolute value, typical value, and circuit
conditions if applicable).
Power supply range: ±22V
Input voltage range: ±15V
Output voltage swing: ±15V
Output short circuit current: 25mA
Input resistance: 2MΩ
Output resistance: 75Ω
Last Revised 08/23
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BMET 2200
Electronics Principles and Practice II: Laboratory Manual
3.2. Preview the lab manual including the questions session, and do all preparatory work.
3.3. Read the Appendix:
Measure input impedance and output impedance of an amplifier circuit.
3.4. In your own words, explain what is the output short circuit current and why it is critical to
know this specification with your design.
Output Short Circuit Current is the maximum current that a power supply can deliver
when its output terminals are shorted together.
It is important to know in power supply design because it determines the maximum
amount of current that can flow through the power supply in case of a fault or malfunction.
3.5. Due Power Supply Connection:
Prior to the lab session, draw below to show how you connect the dual power supply
output terminals to provide your circuit with the +15 [V], -15 [V], and one common. Label
the +15 [V], -15 [V], and the common on your drawing.
Instructor’s signature:
Last Revised 08/23
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4.
BMET 2200
Electronics Principles and Practice II: Laboratory Manual
Introduction: How to connect the dual power supply
It is critical that the dual power supplies be applied to the op-amp simultaneously. In the lab
follow the following procedures to setup and apply the power supply.
1) Turn on the power supply. Set both power supplies to 15 [V], check the actual output with DVM.
2) Turn off the power supply. Connect the power supplies output terminals as shown above in your
pre-lab, so the power supply provides +15 [V], -15 [V], and share one common
3) Turn on the power supply. Using DVM to check the outputs are as expected: +15 [V], -15 [V], and
one common
4) Turn off the power supply. Connect the power supply to the circuit.
5) Turn on the power supply after the circuit is completed.
Last Revised 08/23
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5.
Electronics Principles and Practice II: Laboratory Manual
Procedure: Part 1 – Inverting Amplifier
5.1. Pre-lab: design an inverting amplifier.
•
Voltage gain: 40 [dB] (Hint: what is the voltage gain in ratio?). Use R1 = 10 [k].
•
Draw the proper circuit schematic diagram below showing all component values.
Including the power supply connections on the schematic diagram. Label as NC for
pins not connected. Show your calculations below.
4
2
741
6
3
7
1
5
Figure 1: Inverting Amplifier with 40 [dB] Gain
5.2. Measure and record the voltage gain
Connect the circuit as Fig 1. Apply a 1 [kHz] sinusoidal input signal. To measure the voltage
gain, you will need to choose the proper input signal voltage level so the output voltage will
not saturate. At the same time, the input voltage level should not be too low to difficult to
work with. Measure the voltage gain with two different inputs.
Input Voltage
[V]
Output Voltage
[V]
Voltage Gain [Ratio] Voltage Gain [dB]
0.204
5.60
27.45
28.77
0.292
8.00
27.40
28.75
5.3. Determine the maximum undistorted output voltage swing and the allowed input voltage
range for this amplifier circuit.
Slowly increase the amplitude of input voltage until the output voltage just start to be distorted.
The range of input voltage is the input voltage range[=200-296mV], and the range of output
voltage is the output voltage swing[=5.40-8.20V].
What is the relation between the input range, output swing, and the power supply?
The power supply refers to the voltage range that the op-amp could operate properly and allows
adjustment to determine the minimum and maximum limit (Range). Input range related to the
maximum and minimum voltage that the op-amp without causing output distortion (output
swing). In other words, when input voltage increases and exceed the maximum of its range, the
output voltage swing would start showing cap off peak.
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5.4.
Measure Inverting Amplifier’s input impedance.
Compare with the theoretical value and explain any discrepanc(ies).
Input Impedance [Ω]
Theoretical
10kΩ
5.5.
Electronics Principles and Practice II: Laboratory Manual
Output Impedance [Ω]
Measured
Theoretical
12.991k Ω
75Ω
Reduce the Rf by 10 times. Measure and complete the table below. Do the results agree
with your expectation? Rational your answer.
1.12
11.8
Av
[Ratio]
10.5
.152
34.8
228.9
Vi[Vpk] Vo[Vpk]
Av
[dB]
20.5
47.2
Output Voltage Swing
Input Voltage Range
±1.12
±11.8
±.152
±34.8
5.6. Output Short Circuit Current:
1) Keep the circuit used in procedure 5.5.
Set the input signal voltage level to Vin = 100 [mVPK]. Measure and record the output
voltage (in VPK) when RL is open circuit, RL = 200 [], 100 [], 47 [], 39 [], 22 [],
and 10 []. Calculate and record the output current.
Open
Circuit
1000[]
200 []
100 []
47 []
39 []
22 []
10 []
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.00
1.00
5.00
10.00
21.28
25.64
45.45
100.00
Open
Circuit
1000[]
200 []
100 []
47 []
39 []
22 []
10 []
Vout [VPK] Measured
1.10
1.10
1.40
1.80
0.96
0.56
0.40
0.22
Iout [mAPK] Measured
0.00
1.10
7.00
18.00
20.43
14.36
18.18
21.60
RL =
Vout [VPK] Theoretical
Iout [mAPK] Theoretical
RL =
Last Revised 08/23
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Electronics Principles and Practice II: Laboratory Manual
2) Are the outputs same for different load resistances? Why?
(Hint: What is the output short circuit current of this Op-Amp?)
Yes. Because for inverting op-amp, when the input voltage is applied to the inverting
input terminal and the output feed back to the inverting input through Rf. Since the load
resistance is way smaller than Rf, therefore most of the current would pass through the
load instead, ensure to maintain the same/majority voltage output. Therefore, the load
resistance is relatively no affected to Vo.
3) In procedure 5.4, you measured input impedance, but did not measure the output
impedance. Can you measure the output impedance using the techniques explained in
the Appendix? Why?
Yes. It is possible to measure in this method. Output Because the output impedance of
an inverting op-amp is determined by Rf and it in connected in between Vin and Vo.
Act as voltage divider, output impedance can be determined.
Last Revised 08/23
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6.
BMET 2200
Electronics Principles and Practice II: Laboratory Manual
Procedure: Part 2 – The Non-Inverting Amplifier
6.1. Pre-Lab, prior to the lab, design a non-inverting amplifier with voltage gain Av = 10, R1=10
[k], choose the appropriate standard/preferred resistance for the feedback resistor R f. Draw
the circuit schematic diagram below (label only connected pin numbers)
4
2
741
6
3
7
1
5
Figure 2: Non-Inverting Amplifier with Av = 10
6.2. Connect the Circuit. Apply a 1 [kHz] sinusoidal input signal. Set the input signal voltage
level properly. Measure and record the voltage gain.
Input Voltage
.098V
.288
Output Voltage
.182
Voltage Gain (Ratio) Voltage Gain [dB]
1.86
5.38
.544
1.89
5.52
6.3. Determine the maximum undistorted output voltage swing and the allowed input
voltage range for this amplifier circuit.
Slowly increase the amplitude of input voltage until the output voltage just starts to be distorted.
The range of allowable input voltages is the input voltage range[.088-1.12V], and the range of
output voltage is the output voltage swing[.40-2.08V] for this circuit configuration.
For this circuit configuration, what is the relationship between the input range, output swing, and
the power supply?
Same as 5.3. The power supply refers to the voltage range that the op-amp could operate properly
and allows adjustment to determine the minimum and maximum limit (Range). Input range related
to the maximum and minimum voltage that the op-amp without causing output distortion (output
swing). In other words, when input voltage increases and exceed the maximum of its range, the
output voltage swing would start showing cap off peak.
Last Revised 08/23
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6.4.
BMET 2200
Electronics Principles and Practice II: Laboratory Manual
Measure and record the input impedance.
Input Impedance [Ω]
Output Impedance [Ω]
Theoretical
Measured
Theoretical
2M Ω
1.26M Ω
75Ω
1. Compare your measured Input Impedance with the theoretical value. Explain any
discrepancy.
It is about 37% less than expected theoretical value.
It might cause by
1) Input bias current that is not negligible, resulting some voltage drop across the
input resistor and lower the input impedance.
2) Parasitic capacitance occurs between pins and component inside the op-amp and
lower the input impedance.
2. In procedure 6.4, you measured input impedance, but did not measure the output
impedance. Can you measure the output impedance using the techniques explained
in the Appendix? Why?
No. Because Vo direct connected to the input source in this configuration.
Last Revised 08/23
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7.
BMET 2200
Electronics Principles and Practice II: Laboratory Manual
Procedure: Part 3 – The Unity Gain Voltage Follower/ Buffer
7.1. Pre-lab: Examine the circuit 3a.and 3b. Inside the dotted box, it is a simulated system made of
a function generator and a resistor. RS simulates the source resistor (or output resistance); the
function generator simulates the signal source voltage, and RL simulates the load to the
simulated system (also known as the input resistance of the following stage in a multistage/cascaded system).
In the given space below, calculate the voltage on the load resistor R L, when RL is open
circuit, and RL =1 [kΩ], for both circuit 3a and 3b. Enter your calculated results in the table.
Set the output from the function generator to a 1 [VPK] sine wave.
Note: For the voltage follower, the input impedance is ideally infinity, and the output
impedance is ideally zero.
U1
4
Rs
1kΩ
XFG1
2
Rs
RL
1kΩ
741
7
XFG1
(a)
6
3
1kΩ
1
5
RL
1kΩ
(b)
Figure 3: Voltage Follower buffer circuits
Calculate VRL, assuming VIN = 1 [Vpk] for circuits a) and b) here
Construct the circuit 3a and 3b side by side. Measure and record the voltage on RL, when
RL is open circuit, and RL =1 [k]. Record the results in the table below.
Vin =1 [Vpk]
sine wave
RL is open
Theoretical
RL is open
Measured
RL =1 [k]
Theoretical
RL =1 [k]
Measured
Circuit 3a: Vout[Vpk] =
1.0
1.0
0.5
.48
Circuit 3b: Vout [Vpk] =
1.0
1.0
1.0
1.0
Question: What do these results tell you about the advantages of a voltage follower/buffer?
(Hint: What is the input impedance and output impedance of a voltage buffer?) In what
circumstances will you need a voltage buffer?
It tells me a voltage buffer could help maintain output voltage peak across the load resistor
as close as input voltage peak.
Last Revised 08/23
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8.
Electronics Principles and Practice II: Laboratory Manual
Procedure: Part 4 – The Integrator Circuit
8.1. Bonus Pre-lab Before the lab, design an integrator circuit that uses a capacitance of 0.0l
[F]. Calculate the Rin value such that Vout is 2 [VPP] when the input voltage Vin is a 2
[VPP] sine wave at a frequency of 1 [kHz]. Remember that  sin tdt = − 1 cos t . Predict the

voltage gain of the circuit for input sine waves of 100 [Hz], 1 [kHz], and 10 [kHz] and
record your predictions in the table below.
Note: It will be necessary to place a resistor of value 500 [k] to 10 [M] across the
integrating capacitor to prevent the buildup of DC voltage due to offset voltage and bias
currents. Use the DC OFFSET adjustment on the function generator to zero this offset if a
DC offset is observed.
C1
Rf
Vin
U1
4
R1
Vout
2
741
6
3
7
1
5
Figure 4: Integrator Circuit
8.2.
Construct the circuit. Measure and record the results in the table.
Input Signal frequency
100 [Hz]
1[kHz]
10[kHz]
Predicted Voltage Gain
25.3[V]
2.53[V]
0.25[V]
Measured Voltage Gain
13.6[V]
2.38[V]
0.272[V]
Last Revised 08/23
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8.3.
BMET 2200
Electronics Principles and Practice II: Laboratory Manual
Draw the waveforms for both of the input and output sine wave signals (1 [kHz] only), time
synchronized.
Change input voltage to a 1 [kHz] Square Wave. Monitor and draw the waveforms for input
and output voltage time synchronized.
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Electronics Principles and Practice II: Laboratory Manual
Calculation:
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9.
BMET 2200
Electronics Principles and Practice II: Laboratory Manual
Conclusions:
•
•
•
•
•
•
Inverting op-amp appeared to have higher gain than non-inverting op-amp.
There is a range of input voltage level that an op-amp can handle, when it reaches to the
maximum level the output peak would start to cap off.
Measuring the output impedance of an inverting op-amp can be performed by the method
listed in appendix; but not possible to perform with non-inverting op-amp.
The load resistance is relatively no affected to Vo in inverting op-amp.
A buffer can maintain the voltage level across a circuit to its output level.
Integrator would be able to function accurately in high input frequency but not in low
frequency.
Last Revised 08/23
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BMET 2200
Electronics Principles and Practice II: Laboratory Manual
10. Appendix: How to measure the input and output impedances of an amplifier circuit.
How to measure the input impedance of the amplifier:
•
Set the decade-resistance box to 0 [Ω].
•
Insert the decade-box in series with the input.
•
Apply a sine wave input to the amplifier. Monitor the output voltage on the oscilloscope.
•
Adjust the input voltage level and the vertical scale on the oscilloscope, so the output
voltage has a reasonable amplitude level (for example fill 8 divisions peak to peak on the
oscilloscope).
•
Increase the resistance of the decade box until the output voltage falls to half of the initial
value.
•
Remove the decade box. Measure and record the resistance of the decade box. This is the
input impedance of the amplifier.
How to measure the output impedance of the amplifier:
•
Set the decade-resistance box to ∞ [Ω].
•
Connect the decade-box in parallel with the output.
•
Apply a sine wave input to the amplifier. Monitor the output voltage on the oscilloscope.
•
Adjust the input voltage level and the vertical scale on the oscilloscope, so the output
voltage has a reasonable amplitude level (for example fill 8 divisions peak to peak on the
oscilloscope).
•
Decrease the resistance of the decade box until the output voltage falls to half of the initial
value.
•
Remove the decade box. Measure and record the resistance of the decade box. This is the
output impedance of the amplifer.
Note: Remember to calculate the power dissipations on the decade box resistor. Consider the
resistor in the decade box is 0.5 [W] resistor. Determine the input voltage level
accordingly.
Last Revised 08/23
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