ENGINEERING-43
The Operation Amplifier  Inverting OpAmp
Lab-09
Lab Data Sheet – ENGR-43 Lab-09
Lab Logistics
Experimenter:
Recorder:
Date:
Equipment Used (maker, model, and serial no. if available)
Objectives


Validate the Ideal Operational Amplifier (OpAmp) Model through experimental
measurements of the OpAmp-based inverting amplifier circuit.
Demonstrate the OpAmp’s ability to maintain constant gain over its operating range.
Theory
This lab will demonstrate basic amplifier concepts. The first application is aimed at DC
DEPENDENT Sources. As noted in lecture batteries and power supplies are examples of
INdependent Sources, that is, their output (by definition) is not affected by anything going on in
their loads. Of course, real (not ideal) independent sources are affected to some extent by
their load, but not by design. On the other hand, Dependent Sources are intentionally
controlled by what is going on in the network to which they are connected. The dependent
source must therefore have two connections to its network: an input signal which represents
the control that the network will have over the dependent source, and an output which will in
some way be modified by the dependent source and then delivered to the connected network.
The two common modifications made by a dependent source to its input are an amplitude
increase, that is, the output is larger (or smaller) than the input by a factor called the GAIN, and
a change in polarity of the output called INVERSION. A dependent source may be
implemented by using an OpAmp.
© Bruce Mayer, PE • Chabot College • 282217820 • Page 1
Figure 1 • Inverting Amplifier circuit implemented using an LM741 Operational
Amplifier. Note that RT and RB form a Voltage Divider with which the Inverting Amp
circuit input, Vi, may be varied. NC  No Connection.
Recall from Lecture the list of the OpAmp’s strong points:
1. Very high open loop gain, Av
2. Closed loop gain as a function of resistor feedback network only
3. Very High input impedance, Ri
4. Very low output impedance, Ro
The first point means the bare components inside the device provide very high amplification –
sometimes as high as several hundred thousand. The second point means that the closed
loop gain is not a function of the semiconductor devices inside the op-amp, but only of the
external feedback resistors. The third point indicates that the input circuit of the op-amp will
not draw any current, and the last point means that the load will not affect the output. Of
course, all of this is very ideal and actual op-amps will fall short somewhere.
Figure 1 displays the inverting amplifier circuit that will be characterized in this laboratory
exercise. As indicated in the figure the practical realization of the inverting amplifier is based
on the very popular, and common general-purpose IC op-amp, the 741. See Appendix 2.
© Bruce Mayer, PE • Chabot College • 282217820 • Page 2
Standard Equipment






PS280 Power Supply
8050A DMM
Banana Leads, red & black, for use with the Power Supply and DMM
Plastic Grid-Plate BreadBoard for use with 1W Resistors
Various 1W resistors as stored in the Bins on the Rm1607 Components Counter
Resistor-Post Connecting wires as stored in the Bins on the Rm1607 Components
Counter
Special Equipment



LM741CN Operational Amplifier (See Appendix 2)
Jameco Proto Board JE25 (see Appendix 1)
One each 1/4 Watt Resistors with 22 AWG1 Leads (Ø 0.0254” = Ø 0.64 mm Leads) with
Nominal Resistances
 Ri = 2.7-3.6 kΩ
 Rf = 10 kΩ (nominal)
5. 22 AWG, bare-ended lead wires for use with the Jameco BreadBoard
 Seven total Wires, 2”-6” in Length
o Suggested Wire Colors
 2 each, RED
 2 each, BLACK
 2 each, Color-1,
 1 each, Color-2, NOT Red or Black or Color-1
6. 4 each, Dual Alligator-Clip Lead-Wires
Directions
1. The PS280 Power Supply will be configured as indicated in Figure 2. Set the two
TRACKING push-buttons in the SERIES configuration as shown. Note that with the
buttons in these positions the GND connection is made INTERNALLY by the power supply;
NO external wire is needed between the two inner-most terminals. In addition with the
buttons in the SERIES configuration the RIGHT-most VOLTAGE dial on the PS280 controls
the output level for BOTH of the voltage supplies; +Vs and –Vs.
1
AWG  American Wire Gage
© Bruce Mayer, PE • Chabot College • 282217820 • Page 3
IN
OUT
-Vs
-
+
+Vs
-
+
Figure 2 • Power Supply SERIES configuration for OpAmp Supply Input.
2. Figure 3 contains the electrical schematic for the Inverting Amplifier. Also the Diagram in
Figure 3 Indicates several voltage and current quantities such as V i and If. Study this
diagram carefully, and then construct the circuit per the schematic. Refer to these Figures
when building the circuit:
 Figure 4
 Figure 5
 Figure 6
 Figure 7
 Figure 8
3. Make the measurements, and perform the calculations needed to complete Table I, Table
II, Table III, Table IV, and Table V.
 Take care to use the Proper POLARITY When Measuring the voltages and, in
particular, Currents.
o Use the PASSIVE SIGN CONVENTION for consistent measurements
 Always ASSUME that currents flow in the direction shown in Figure 3.
4. Next Test the affect of a load by inserting a Resistor between Vo and GND as indicated in
Figure 9.
5. Make the measurements, and perform the calculations needed to complete Table VI.
 Always ASSUME that currents flow in the direction shown in Figure 9.
6.
© Bruce Mayer, PE • Chabot College • 282217820 • Page 4
7. Return all lab hardware to the “as-found” condition
OUT
IN
-Vs
- +
+Vs
- +
14V
14V
IT
U1 = LM741
RT
Ri
Vi
Ii
NC
V-
+Vs
V+
Vo
3k
Vo
RB
IB
NC
-Vs
If
NC
Rf
10k
Figure 3 • Connection Diagram for the Inverting OpAmp Circuit. Set BOTH Voltage
Supplies to 14.0 V. RT = 14-21 kΩ. RB = Per Data Table I. NC  No Connection.
© Bruce Mayer, PE • Chabot College • 282217820 • Page 5
+Vs
-Vs
Ri
Rf
+Vs
Vo
Vi
G
N
D
-Vs
U1
Figure 4 • OpAmp BreadBoard Wiring Connections. Note that the SemiCircular
Notch at the Pin-1 end of the U1 OpAmp defines its Polarity.
© Bruce Mayer, PE • Chabot College • 282217820 • Page 6
Vo
+Vs
+Vs
U1
Rf
-Vs
Ri
GND
-Vs
Figure 5 • OpAmp Bread Board Wiring.
© Bruce Mayer, PE • Chabot College • 282217820 • Page 7
-Vs
GND
+Vs
Figure 6 • Power Supply Wiring Connections.
© Bruce Mayer, PE • Chabot College • 282217820 • Page 8
Vi
+Vs
RT
RB
GND
Vi
Figure 7 • 1W Resistor Wiring Connections. Note that RB is the physical variable in
this experiment.
© Bruce Mayer, PE • Chabot College • 282217820 • Page 9
DMM-V
RB’s
DMM-COM
GND
Figure 8 • Overall System wiring connections for the Inverting OpAmp Experiment.
© Bruce Mayer, PE • Chabot College • 282217820 • Page 10
OUT
IN
-Vs
- +
+Vs
- +
14V
14V
IT
RL
U1 = LM741
RT
Ri
Vi
Ii
NC
V-
+Vs
V+
Vo
3k
IL
Vo
RB
IB
NC
-Vs
If
NC
Rf
10k
Figure 9 • LOADED Inverting OpAmp. Note RL located between the output and GND.
RT same as in Figure 3. RB = 10-19 kΩ. Values for RL per Table VI.
© Bruce Mayer, PE • Chabot College • 282217820 • Page 11
Table I – Fixed Actual-Values as Measured with the DMM
Value
+Vs
-Vs
Ri
Rf
RT
Nominal
14.00
14.00
3 kΩ
10 kΩ
14-21 kΩ
Measured
Table II – Parametric Quantity, RB, as DMM Measured
RB No.
RB Range
1
1.6-2.4 kΩ
2
2.6-3.5 kΩ
3
3.7-4.9 kΩ
4
5.2-7.5 kΩ
5
10-20 kΩ
RB Actual
Table III – MEASURED Currents and Potentials
RB No.
Vi
V-
V+
Vo
1
2
3
4
5
Table IV – CALCULATED2 From Values in Table III
RB No.
Virtual GND
I-
1
2
3
4
5
2
Think about Av
→ , R- → 
© Bruce Mayer, PE • Chabot College • 282217820 • Page 12
Ii
If
Note:
 Virtual GND = V- - V+
 I- = I f - Ii
Table V – MEASURED & THEORETICAL Voltage Gain
RB No.
Gainmeas
Gaintheory
%
1
2
3
4
5
Note:
 Gmeas = Vo/Vi
 Gtheory = -Rf/Ri
 % = 100[Gmeas – Gtheory]/Gtheory
 LOADING EFFECT Actual Values
+Vs =
-Vs =
RB =
Table VI – LOADING EFFECT Measured Currents and Potentials
RL
Nominal
RL
Actual
Vi
Vo
22 kΩ ±50%
5.6 kΩ ±50%
1.2 kΩ ±50%
470 Ω ±50%
180 Ω ±50%
© Bruce Mayer, PE • Chabot College • 282217820 • Page 13
IL
Gain =
Vo/Vi
Run Notes/Comments
Print Date/Time = 29-May-16/04:00
© Bruce Mayer, PE • Chabot College • 282217820 • Page 14
Appendix 1 - Jameco JE25 BreadBoard
The JE25 breadboard (Jameco p/n 207773) has two terminal strips, four bus strips, and three
binding posts as shown in Figure 10 . Each bus strip has two rows of contacts. Each of the two
rows of contacts on the bus strips are a node. That is, every contact along a row on a bus strip
is connected together, inside the breadboard. Bus strips are used primarily for power supply
connections but are also used for any node requiring a large number of connections. Each
terminal strip has 60 rows and 5 columns of contacts on each side of the center gap. Each row
of 5 contacts is a node. You will build your circuits on the terminal strips by inserting the leads
of circuit components into the contact receptacles and making connections with 22 AWG
(American Wire Gauge) wire with a diameter of 0.0254” (0.65 mm).
Figure 10 • Jameco JE25 BreadBoard
© Bruce Mayer, PE • Chabot College • 282217820 • Page 15
Appendix 2 – LM741 OpAmp Specifications
© Bruce Mayer, PE • Chabot College • 282217820 • Page 16
© Bruce Mayer, PE • Chabot College • 282217820 • Page 17
© Bruce Mayer, PE • Chabot College • 282217820 • Page 18
Print Date/Time = 29-May-16/04:00
© Bruce Mayer, PE • Chabot College • 282217820 • Page 19