ENGINEERING-43
The Operation Amplifier NonInverting OpAmp
Lab-10 /

Lab Data Sheet – ENGR-43 Lab-10

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.

The weakness of the INVERTING circuit is 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 input-resistance while maintaining the same circuit-gain, BOTH resistor values can be increased. However this strategy does not produce an input resistance as great as the OpAmp input-Resistance itself.

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 resistance 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 input-resistance 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 asshown 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 3displays 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.

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 (seeAppendix 1)
  • One each 1/4 Watt Resistors with 22 AWG[2] Leads (Ø 0.0254” = Ø 0.64 mm Leads) with Nominal Resistances
  • Ri = 2.7-3.9kΩ
  • Rf = 10 kΩ (nominal)
  1. 22 AWG, bare-ended lead wires for use with the Jameco BreadBoard
  2. Seven total Wires, 2”-6” in Length
  3. Suggested Wire Colors

2 each, RED

2 each, BLACK

2 each, Color-1,

1 each, Color-2, NOT Red or Black or Color-1

  1. 4 each, Dual Alligator-Clip Lead-Wires

Directions

  1. The PS280 Power Supplier will be configured as indicated inFigure 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.

  1. Figure 5 contains the electrical schematic for the NONinverting Amplifier. Also the Diagramin Figure 5 Indicates several voltage and current quantities such as Vi and If. Study this diagram carefully, and then construct the circuit per the schematics in Figure 3 and Figure 5.
  1. Make the measurements, and perform the calculations needed to completeTable I,Table II, Table III, and Table IV.
  • Take care to use the Proper POLARITY When Measuring the voltages and, in particular, Currents.
  • Use the PASSIVE SIGN CONVENTION for consistent measurements
  • Always ASSUME that currents flow in the direction shown Figure 5.
  1. Next Test the affect of a LOAD by inserting a Resistor between Vo and GND as indicated inFigure 6. Select the value of RB such that it has about 25% of the resistance of RT. Complete Table V
  1. Make the measurements, and perform the calculations needed to completeTable V andTable VI.
  • Always ASSUME that currents flow in the direction shown in Figure 6.
  1. Return all lab hardware to the “as-found” condition

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 / RB Actual
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

Table III– MEASUREDCurrents and Potentials

RB No. / Vi / V- / V+ / Vo / Ii / If
1
2
3
4
5

Table IV– MEASURED & THEORETICAL Voltage Gain

RB No. / Gainmeas / Gaintheory / %
1
2
3
4
5

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 / IL / Gain =
Vo/Vi
22 kΩ ±50%
5.6 kΩ ±50%
1.2 kΩ ±50%
470 Ω ±50%
180 Ω ±50%

Run Notes/Comments

Print Date/Time = 19-Apr-19/10:08

Appendix 1 - Jameco JE25 BreadBoard

The JE25breadboard (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

Appendix 2 – LM741 OpAmp Specifications

Print Date/Time = 19-Apr-19/10:08

©Bruce Mayer, PE • ChabotCollege •ENGR-43_Lab_13_NonInv_OpAmp_090323.doc • Page 1

[1] In our case we have defined the center tap of the Tektronix PS280 dual-output power supply as the GROUND Reference.

[2] AWG American Wire Gage