Op-Amps Applications

1

Abstract—This lab illustrates the function of an inverting,

differentiating, and integrating Op-Amp circuit.

I. INTRODUCTION

HIS lab demonstrates the operation characteristics of an

inverting, differentiating, and integrating Op-Amp circuit.

The frequency effects of these Op-Amps are also analyzed.

II. PROCEDURE

A. Equations

The equations used for the lab preparation were as follows:

1.

A

f

vR

RA −=

2.

21

1

CsRVo

−=

3. ∫−=1

021

')'(11

dttvCR

VV Co

These equations provided values to compare the simulation

and hands-on measurements to.

B. Inverting Op-Amp Circuit.

The circuit shown in Figure 1 was the circuit used to build

the inverting amplifier. The tool used to simulate the circuit

was National Instrument’s Multisim software package.

1kΩ

R1

100kΩ

R2

0.2 Vpk

500 Hz

0 °

Vsig

U1

741

3

2

4

7

6

51

R3

1kΩ

0 2

11 V212 V

3

4

1

12

0

Figure 1: Inverting Op-Amp

The inverting Op-Amp circuit in Figure 1 was designed and

tested with three different gains. The first gain was -1, the

second was -10, and the last was -100. The corner frequencies

for each circuit were calculated and recorded in Table 1. The

resistor values for each gain are also located in Table 1. A

plot of the gain for the -1, -10, and -100 are located in Figures,

2, 3, and 4 respectively. Bode plots for the -1, -10, and -100

gain circuits are located in Figures 5, 6, and 7. For Figures 2,

3, and 4 the input is shown in red and the output is shown in

green.

Figure 2: Gain of -1

Figure 3: Gain of -10

Figure 4: Gain of -100

Figure 5: Bode plot for gain of -1

Op-Amp Circuits Zack Phillips and Jenna Rock

T

Op-Amps Applications

2

Figure 6: Bode plot for gain of -10

Figure 7: Bode plot for gain of -100

Gain -1 -10 -100

Rf 1KΩ 1KΩ 1KΩ

Ra 1KΩ 10KΩ 100KΩ

Corner

Freq.

488.6KHz 1.273MHz 1.394MHz

Table 1: Inverting Op-Amp Values

The output plots of the physically built circuits are

contained in Figures 8, 9, and 10.

Figure 8: Gain of -1

Figure 9: Gain of -10

Figure 10: Gain of -100

As expected, the values for the computer simulation closely

followed the results of the physical circuit. In order to be able

to see all of the output for Figure 9, the setting had to be

altered slightly. The input was one volt per division, but the

output was set to five volts per division. Theses were the same

settings for Figure 10. To get a non clipped wave form on the -

100 gain circuit shown in Figure 10, the input voltage had to

be decreased 0.1 V.

C. Differentiating Op-Amp Circuit.

A differentiating Op-Amp was constructed that accepts a

triangular wave and outputs a square wave. The

differentiating Op-Amp circuit is located in Figure 11.

U1

741

3

2

4

7

6

51

R2

1kΩ

VCC

15V

VDD

-15V

VCC

VDD

30

XFG1

0

R1

1kΩ

C1

4.7nF

1

Vin

Vout

Figure 11: Differentiating Op-Amp.

The output plot generated by the simulation is located in

Figure 12, and the physical circuit output is located in figure

13. For Figure 12, the input is shown in red and the output is

shown in green.

Figure 12: Differentiator Simulation Output

Op-Amps Applications

3

Figure 13: Physical Differentiator Output.

D. Integrating Op-Amp.

An integrating Op-Amp was designed such that an input

square wave was converted to a triangular wave. The

integrating Op-Amp circuit is located in Figure 14.

C1

4.7nF

U1

741

3

2

4

7

6

51

R1

1kΩ

R2

1kΩ

VCC

15V

VDD

-15V

VCC

VDD

1

30

XFG1

0

Vout

Vin

Figure 14: Integrating Op-Amp circuit

The output from the computer simulation is located in

Figure 15, and the physical circuit output is located in Figure

16. For Figure 15, the input is shown in green and the output is

shown in red.

Figure 15: Integrator Circuit Simulation Results

Figure 16: Integrator Circuit Output

As shown in the results of the physical circuit, the given

parameters of a 10V peak to peak square wave causes a

distortion in the top of the output triangular wave. To fix this

problem, the input voltage was reduced to 1V peak to peak.

This drop in voltage resolved the distortion issue, and the new

output is shown in Figure 17.

Figure 17: Corrected circuit output.

III. CONCLUSION

This lab demonstrated how versatile the Op-Amp can be. It

also showed how accurately a computer simulation tool can

model the operation of real-world Op-Amp circuits.