ENGINEERING-43
The Operation Amplifier → NonInverting OpAmp
Lab-13
Lab Data Sheet – ENGR-43 Lab-13
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 NONinverting amplifier circuit.
Demonstrate the OpAmp’s ability to maintain constant gain over its operating range.
Inverting and NonInverting Circuits Compared
Lab-12 demonstrated the operating characteristics of the INVERTING OpAmp Circuit as
shown in Figure 1. The Inverting op-amp is connected using two resistors Ri and Rf such that
the input signal is applied in series with Ri and the output is connected back to the inverting
input through Rf. The noninverting (+) input is connected to the ground reference 1 . In
operation, as the input signal moves positive, the output will move negative and vise-versa.
The magnitude of the voltage change at the output relative to the input depends on the ratio of
the two resistors Ri and Rf as indicated in Figure 1. As the input moves in one direction, the
output will move in the opposite direction, so that the voltage at the inverting input remains at
very nearly zero volts in this case as the Large OpAmp gain forces the inverting input to a
virtual-GND condition.
1
In our case we have defined the center tap of the Tektronix PS280 dual-output power supply as the GROUND
Reference.
© Bruce Mayer, PE • Chabot College • 282235923 • Page 1
Rf
Ri
Rf
Ri
Vi
Vo
Vo
Vi
 Rf 
Vo    Vi
 Ri 
Figure 1 • The Inverting OpAmp Circuit
(Lab-11)
 Rf 
Vo  1 
Vi

 Ri 
Figure 2 • The NONInverting OpAmp
Circuit
Note that since the voltage at the inverting input is always zero by the virtual-GND, the input
signal will see a whole-circuit input-resistance equal to Ri. Thus to increase the circuit inputresistance while maintaining the same circuit-gain, BOTH resistor values can be increased.
This laboratory exercise modifies the inverting circuit to obtain the NONinverting form as
indicated in Figure 2. The NONinverting amplifier is connected so that the input signal goes
directly to the noninverting input (+) and the input resistor Ri is grounded. In this configuration,
the input impedance as seen by the signal is much greater since the input will be following the
applied signal and is not held constant by the feedback current. In this case the circuit inputresistance is equal to the OpAmp input-resistance (about 2 MΩ for the LM741). This is one of
the advantages of the NONinverting circuit.
As the signal moves in either direction, the output will follow to maintain the inverting input at
the same voltage as the input (+). The voltage gain is always greater than 1 as shown in
Figure 2. The fact that the circuit gain does not solely depend on the Rf:Ri ratio is one of the
DISadvantages of the NONinverting form.
Figure 3 displays the NONinverting amplifier circuit that will be characterized in this laboratory
exercise. As indicated in the figure the practical realization of the NONinverting amplifier is
based on the very popular and common general-purpose IC op-amp, the 741. See Appendix 2.
© Bruce Mayer, PE • Chabot College • 282235923 • Page 2
Figure 3 • NONinverting Amplifier circuit implemented using an LM741 Operational
Amplifier. Note that RT and RB form a Voltage Divider with which the NONinverting
Amp circuit input, Vi, may be varied. NC  No Connection.
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)
© Bruce Mayer, PE • Chabot College • 282235923 • Page 3

One each 1/4 Watt Resistors with 22 AWG2 Leads (Ø 0.0254” = Ø 0.64 mm Leads) with
Nominal Resistances
 Ri = 2.7-3.9 kΩ
 Rf = 10 kΩ (nominal)
2. 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
3. 4 each, Dual Alligator-Clip Lead-Wires
Directions
1. The PS280 Power Supplier will be configured as indicated in Figure 4. 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.
IN
OUT
-Vs
-
+
+Vs
-
+
Figure 4 • Power Supply SERIES configuration for OpAmp Supply Input.
2
AWG  American Wire Gage
© Bruce Mayer, PE • Chabot College • 282235923 • Page 4
2. Figure 5 contains the electrical schematic for the NONinverting Amplifier. Also the Diagram
in Figure 5 Indicates several voltage and current quantities such as V i and If. Study this
diagram carefully, and then construct the circuit per the schematics in Figure 3 and Figure
5.
3. Make the measurements, and perform the calculations needed to complete Table I, Table
II, Table III, and Table IV.
 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 Figure 5.
4. Next Test the affect of a LOAD by inserting a Resistor between Vo and GND as indicated in
Figure 6. Select the value of RB such that it has about 25% of the resistance of RT.
Complete Table V
5. Make the measurements, and perform the calculations needed to complete Table V and
Table VI.
 Always ASSUME that currents flow in the direction shown in Figure 6.
6. Return all lab hardware to the “as-found” condition
© Bruce Mayer, PE • Chabot College • 282235923 • Page 5
OUT
IN
-Vs
- +
+Vs
- +
14V
14V
IT
U1 = LM741
Ri
3.3k
RT
Vi
NC
NC
V-
+Vs
V+
Vo
Ii
Vo
RB
-Vs
IB
If
NC
Rf 10k
Figure 5 • Connection Diagram for the NONinverting OpAmp Circuit. Set BOTH
Voltage Supplies to 14.0 V. RT = 14-21 kΩ. RB = Per Data Table. NC  No Connection.
© Bruce Mayer, PE • Chabot College • 282235923 • Page 6
OUT
IN
-Vs
- +
+Vs
- +
14V
14V
IT
RL
U1 = LM741
Ri
3.3k
RT
Vi
NC
NC
V-
+Vs
V+
Vo
Ii
IL
Vo
RB
-Vs
IB
If
NC
Rf 10k
Figure 6 • LOADED NONinverting OpAmp. Note RL located between the output and
GND. RT same as in Figure 4. RB  RT/4. Values for RL per Table VI.
© Bruce Mayer, PE • Chabot College • 282235923 • Page 7
Table I – Fixed Actual-Values as Measured with the DMM
Value
+Vs
-Vs
Ri
Rf
RT
Nominal
14.00
14.00
3.3 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 – MEASURED & THEORETICAL Voltage Gain
RB No.
Gainmeas
Gaintheory
%
1
2
3
4
5
© Bruce Mayer, PE • Chabot College • 282235923 • Page 8
Ii
If
Note:
 Gmeas = Vo/Vi
 Gtheory = from Figure 2
 % = 100[Gmeas – Gtheory]/Gtheory

Table V – LOADING EFFECT Actual Values
+Vs =
-Vs =
RT =
RB =
Note:
 RT = Same as Previous Value
 RB  RT/4
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%
Run Notes/Comments
© Bruce Mayer, PE • Chabot College • 282235923 • Page 9
IL
Gain =
Vo/Vi
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 7 . 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 7 • Jameco JE25 BreadBoard
© Bruce Mayer, PE • Chabot College • 282235923 • Page 10
Appendix 2 – LM741 OpAmp Specifications
© Bruce Mayer, PE • Chabot College • 282235923 • Page 11
© Bruce Mayer, PE • Chabot College • 282235923 • Page 12
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