Op amp Amp - Lecture notes 12,13 PDF

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Lab Title

Inverting Amplifiers

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Objective  To construct inverting, non-inverting and voltage follower amplifiers.  To observe the gain of amplifiers.  To familiarize with operational amplifiers (op-amps) and basic opamp circuits: inverting, non-inverting, and voltage follower amplifiers.

Introduction Operational amplifiers (so called Op-Amps) are analog devices made in the form of integrated circuits containing tens of transistors with well-matched elements designed to achieve desired performance parameters. They come in a variety of packages, often in multiple units, and range in price from a fraction of a dollar to tens of dollars for special precision amplifiers. They are easy to use and very handy in many applications. If you need to process analog signals you will most likely use Op-Amps rather than discrete transistors. Analog op-amp circuits operate always with negative feedback accomplished by a connection between the output and the negative input. Output voltage is kept below saturation i.e. between a couple of volts below the positive supply voltage and a couple of volts above the negative (or zero) power supply voltage. First order analysis of op-amp circuits can be made with two simple rules: 1. The voltage between the negative and the positive inputs is zero. 2. The inputs draw no current.

pg. 2

Inverting Amplifier First Case Lab Work

a) Circuit Diagram

Figure 1: Inverting Amplifier

b) Components Used Components

Nominal Values

Measured Values

R1 R2

1K 1K

993 1.02 K ohm

 Op amp.  Power Supply  Oscilloscope

pg. 3

Theory An inverting-amplifier circuit is built by grounding the positive input of the operational amplifier and connecting resistors R1 and R2, called the feedback networks, between the inverting input and the signal source and amplifier output node, respectively.

Gain =

Vout Vin

R2

= - R1

Readings

Vin (v)

Vo (v)

Vo/Vin

Vo/Vin

Phase

(experiment

(Calculated)

Difference

) 0 1 2 3 4 5 6 7 8 9 10

Simulation

pg. 4

0 1 2 3 4 5 6 7 8 9 10

0 1 1 1 1 1 1 1 1 1 1

%Error

B/W Vo And 0 1 1 1 1 1 1 1 1 1 1

Vin 0 178 178 178 178 178 178 178 178 178 178

0 0 0 0 0 0 0 0 0 0 0

Second Case In this case R2 is greater than R1.

Components

pg. 5

Nominal Values

Measured Values

R1 R2

2K 10 K

1.93 K 9.98 K

 Op amp.  Power Supply  Oscilloscope

Readings

Vin (v)

Vo (v)

Vo/Vin

Vo/Vin

Phase

(experiment

(Calculated)

Difference

) 0 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5

Simulation

pg. 6

0 5.04 2 10.2 13 15.2 16.4 17.4 17.4 17.4 17.4

0 5.17 5.17 5.17 5.17 5.17 5.17 5.17 5.17 5.17 5.17

%Error

B/W Vo And 5 5 5 5 5 5 5 5 5 5 5

Vin 0 178 178 178 178 178 178 178 178 178 178

0 0.034 0.034 0.034 0.034 0.034 0.034 0.034 0.034 0.034 0.034

Analysis Q1: What is the phase difference with the input and output signals? Why does your phase difference act the way as you mentioned?

Ans: The phase difference is 180 degrees. Because in the circuit, we use the negative feedback. Due to this output voltage is negative.

Q2: How does the different values of R1 and R2 affects the results?

Ans: There is a little bit difference in R1 and R2 due to this ouput results become little bit different.

Q3: What is Random error? What is symmetric error?

Ans: Random error causes one measurement to differ slightly from the next. It comes from unpredictable changes during an experiment. Systematic error always affects measurements the same amount or by the same proportion, provided that a reading is taken the same way each time. It is predictable.

pg. 7

Q4: Draw your graph for Vin (experimental) Vs Vo (experimental)? Does the graph support our basic theory? If not comment errors?

Ans:

Yes the graph is supporting to the theory. Q5: In case 1 what is the maximum value of Vo? Up to what value of Vin is the Vin = Vout ? For what values of Vin the output is not equal to the input? Justify your answer with theory?

Ans: Maximum value of Vout = 10 volts. For all values of Vin the output Vo become equal.

Q6: In case 2 what is the maximum value of Vo? Up to what value of Vin is the Vin = Vout ? For what values of Vin the output is not equal to the input? Justify your answer with theory?

pg. 8

Ans: Maximum value of Vout = 5.14.

Q7: What can you deduce from case 1 and 2? Why are the values of Vo/vin are differenct in both cases?

Ans: In both the cases the values of R1 and R2 are different that’s why Vo/Vin in both cases are different.

Non-Inverting Amplifier First Case Lab Work

pg. 9

a) Circuit Diagram

Figure 2: Non-Inverting Amplifier

b) Components Used Components

Nominal Values

Measured Values

R1 R2

1K 1K

993 ohm 1.02 K

 Op amp.  Power Supply  Oscilloscope

pg. 10

Theory A non‐inverting amplifier is an amplifier in which we applied input on positive terminal and negative terminal grounded. The amplifier is non‐inverting with the feedback loop closed. The closed‐loop gain is solely determined by the feedback resistors R2and R1assuming that the loop gain of the circuit is very large. The positive input terminal now is connected to the input voltage source. The feedback path, however, is still connected around the output terminal and the negative input terminal. In this configuration, the input voltage signal, ( VIN ) is applied directly to the noninverting ( + ) input terminal which means that the output gain of the amplifier becomes “Positive” in value in contrast to the “Inverting Amplifier” circuit we saw in the last tutorial whose output gain is negative in value. The result of this is that the output signal is “in-phase” with the input signal. Feedback control of the non-inverting operational amplifier is achieved by applying a small part of the output voltage signal back to the inverting ( – ) input terminal via a Rƒ – R2 voltage divider network, again producing negative feedback. This closed-loop configuration produces a non-inverting amplifier circuit with very good stability, a very high input impedance, Rin approaching infinity, as no current flows into the positive input terminal, (ideal conditions) and a low output impedance

The gain formula is

Gain = 1 +

pg. 11

R2 R1

Readings

Vin (v)

Vo (v)

Vo/Vin

Vo/Vin

Phase

(experiment

(Calculated)

Difference

) 0 1 2 3 4 5 6 7 8 9 10

Simulation

pg. 12

0 2 4 6 8 10 12 14 16 16.6 16.6

0 2 2 2 2 2 2 2 2 1.84 1.84

%Error

B/W Vo And 2 2.02 2.02 2.02 2.02 2.02 2.02 2.02 2.02 2.02 2.02

Vin 0 0 0 0 0 0 0 0 0 0 0

0 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99 9.782 9.782

Second Case In this case R2 is greater than R1.

pg. 13

Components

Nominal Values

Measured Values

R1 R2

2K 10 K

1.93 K 9.98 K

Readings

Vin (v)

Vo (v)

Vo/Vin

Vo/Vin

Phase

(experiment

(Calculated)

Difference

) 0 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5

Simulation

pg. 14

0 6.2 9.0 12 15 17.4 17.6 17.6 17.6 17.6 17.6

0 6.17 6.17 6.17 6.17 6.17 6.17 6.17 6.17 6.17 6.17

%Error

B/W Vo And 5.99 6.17 6.17 6.17 6.17 6.17 6.17 6.17 6.17 6.17 6.17

Vin 6.17 6.17 6.17 6.17 6.17 6.17 6.17 6.17 6.17 6.17 6.17

0 0 0 0 0 0 0 0 0 0 0

Analysis Q8: What is the phase difference with the input and output signals? Why does your phase difference act the way as you mentioned?

Ans: The phase difference is 0 degrees. Because in the circuit, we apply input at non inverting terminal.

Q9: How does the different values of R1 and R2 affects the results?

Ans: There is a little bit difference in R1 and R2 due to this ouput results become little bit different.

Q10: What is Random error? What is symmetric error?

Ans: Random error causes one measurement to differ slightly from the next. It comes from unpredictable changes during an experiment. Systematic error always affects measurements the same amount or by the same proportion, provided that a reading is taken the same way each time. It is predictable.

Q11: Draw your graph for Vin (experimental) Vs Vo (experimental)? Does the graph support our basic theory? If not comment errors?

Ans:

pg. 15

Yes the graph is supporting to the theory. Q12: In case 1 what is the maximum value of Vo? Up to what value of Vin is the Vin = Vout ? For what values of Vin the output is not equal to the input? Justify your answer with theory?

Ans: Maximum value of Vout = 16.6 volts. For all values of Vin the output Vo become equal.

Q13: In case 2 what is the maximum value of Vo? Up to what value of Vin is the Vin = Vout ? For what values of Vin the output is not equal to the input? Justify your answer with theory?

Ans: Maximum value of Vout = 17.6.

pg. 16

Q14: What can you deduce from case 1 and 2? Why are the values of Vo/vin are different in both cases?

Ans: In both the cases the values of R1 and R2 are different that’s why Vo/Vin in both cases are different.

Voltage Follower First Case Lab Work

pg. 17

c) Circuit Diagram

Figure 3: Unity Follower

d) Components Used  Op amp.  Power Supply  Oscilloscope

Theory Voltage follower is an Op-amp circuit whose output voltage straight away follows the input voltage. That is output voltage is equivalent to the input voltage. Op-amp circuit does not provide any amplification. Thus, voltage gain is equal to 1. They are similar to

pg. 18

discrete emitter follower. The other names of voltage follower are Isolation Amplifier, Buffer Amplifier, and Unity-Gain Amplifier. The voltage follower provides no attenuation or no amplification but only buffering. This circuit has an advantageous characteristic of very high input impedance.

Gain = 1

Readings

Vin (v)

0 1 2 3 4 5 6 7 8 9 10

Simulation

pg. 19

Vo (v)

0 1 2 3 4 5 6 7 8 9 10

Vo/Vin

Vo/Vin

Phase

(experiment

(Calculated)

Difference

)

B/W Vo And

1 1 1 1 1 1 1 1 1 1 1

Vin 0 0 0 0 0 0 0 0 0 0 0

0 1 1 1 1 1 1 1 1 1 1

%Error

0 0 0 0 0 0 0 0 0 0 0

Analysis Q14: What is the phase difference with the input and output signals? Why does your phase difference act the way as you mentioned?

pg. 20

Ans: The phase difference is 0 degrees. Because in the circuit, we apply input at non inverting terminal.

Q15: Draw your graph for Vin (experimental) Vs Vo (experimental)? Does the graph support our basic theory? If not comment errors?

Ans:

pg. 21

Yes the graph is supporting to the theory. Q12: Where do we use unity gain amplifier and why ? Ans: The use of voltage follower is that it has got very high input impedance and very low output impedance, which makes it a perfect circuit for impedance matching.

Conclusion In this we learn how to build Inverting amp, Non-Inverting and Unity gain Follower using operational amplifier, resistors and capacitors. In inverting amp, we apply

pg. 22

input at inverting terminal. In non-inverting amp, we apply input at non inverting terminal. First , I build all the circuits on breadboard. Then I calculate the all values. In the end I can say that, measured values are approximately the same as calculated values.

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