mobile studio activity 3 report

8/9/2019 Mobile Studio Activity 3 Report

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Mobile Studio Activity #3

Adam Steinberger

1

Introduction

The Operational Amplifier (Op Amp) is an electronic device that can be used to

manipulate signals by changing their voltages. In this lab, we use negative feedback loops in Op

Amp circuits to control how voltages of input signals change inside of the amplifiers.

Procedure

The protoboard at right was designed for this

lab. The Op Amps used on the protoboard are

powered by two 9V batteries. Two potentiometers at

the bottom are used to control the voltages going into

each Op Amp. These potentiometers are also

connected in negative feedback loops back to the Op

Amp inputs, which give the Op Amps the ability to amplify the signals going into them. In order

to produce an input voltage source of 0.1V in the circuit, the Mobile Studio function generator

had to be connected to the two negative input leads of the Op Amps.

Analysis

After configuring the protoboard, the Mobile Studio Desktop oscilloscope and function

generator were used to take voltage readings of both Op Amp outputs over a period of 500s.

For the first reading, both potentiometers were set to maximum (approx. 10k). A screenshot

of the resulting graph (see page 5) was taken, including cursor readings of the high and low

peak voltage values for each curve. Readings were taken for potentiometer values of 5k and

0k as well. The voltage readings taken from the Mobile Studio Desktop oscilloscope were used

to calculate the gain of the Op Amps for different input voltages. The gain values calculated

were then compared to the ideal gain values for each resistance of the potentiometer.

Differences between these two sets are due to the %5 tolerance of the resistors used in the

circuit, as well as static electricity from the dry winter air causing the Op Amps to get electrical

noise.


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Adam Steinberger

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Conclusion

The two configurations for negative feedback loop Op Amps used in the lab amplified

their input signals in different ways. The Inverting Amplifier took an input voltage source and

produced an inverted output voltage amplified by the ratio of the two resistors connected. The

Non-Inverting Amplifier, however, produced an output voltage amplified by the ratio of the

sum of both resistors connected to the value of only one of those resistors. Potentiometers

were used to verify that the Op Amps abide by the Linearity Properties that govern Linear

Circuits.


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Adam Steinberger

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Questions:

1. When varying the resistance of the potentiometers, the output of the Op Amps in thecircuit is always a linear version of the inputs. This is evident in the results obtained

from our measurements using the Mobile Studio Desktop software. There are three

separate graphs taken from this measuring software that show the output voltages from

the Op Amps in the circuit in the form of sinusoidal waves. The vertical distance

between peaks of each sinusoidal curve on these graphs represent the absolute output

voltage produced when a sine wave at 1.000 kHz of 0.1 V peak to peak from the Mobile

Studio function generator is connected to the circuit at VIN. As seen in these graphs, as

the resistance of the potentiometers decreases, the absolute output voltage decreases

as well. The cursor readings from the graphs show that this decrease is linear. For

example, the top peak of the inverting amplifier for 10 k reads 543.86 mV; for 5 k it

reads 280.70 mV; and for 0 k it reads 000.00 mV.

2. Output voltages and gains are listed in the table below. Voltages are readings from thegraph, and gains are calculated as .

Operational

Amplifier

Voltage at

10k

Gain at

10k

Voltage at

5k

Gain at

5k

Voltage at

0k

Gain at

0k

Inverting -991.23 mV -9.9123 -508.77 mV -5.0877 0.000 mV 0

Non-Inverting 1149.13 mV 11.4913 640.35 mV 6.4035 100.00 mV 1

3. Gains for the two Op Amps in the circuit are calculated using the output voltageformulas for the two unique types of Op Amps, Inverting and Non-Inverting Amplifiers.


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Adam Steinberger

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Inverting Amplifier:

= 2

1

= 1

0.1

Non-Inverting Amplifier:

= 1 + 2

2

= + 1

1

0.1

Operational

Amplifier

Voltage at

10k

Gain at

10k

Voltage at

5k

Gain at 5k Voltage at

0k

Gain at 0k

Inverting -1.0 V -10 -0.5 V -5 0.0 V 0

Non-Inverting 1.1 V 11 0.6 V 6 0.1 V 1

4. The true resistance of the potentiometer in the Non-Inverting Op Amp Circuit when thepotentiometer is at maximum resistance is 10491.3.

1.14913 = + 10001000 0.1

= 10491.3

5. The following circuit will result in an output of = .51 + .22. The circuit is aSumming Amplifier connected to an Inverting Amplifier.


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Adam Steinberger

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Output Voltages of OpAmp Circuits at 10k



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