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OBJECTIVES After performing this experiment, students should be able to: 1

Electrical Engineering

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OBJECTIVES

After performing this experiment, students should be able to:

1. Construct a simulated circuit that uses 741 operational amplifiers.

2. Demonstrate the practical limitations of operational amplifiers

3. Conduct a simulation to experiment using operational amplifiers to amplify voltage signals.

EQUIPMENT AND MATERIAL LIST

1. Power supply

2. Multimeter

3. Function generator

4. Operational Amplifiers

5. Resistors

6. Breadboard

7. Jumper wires

* All the above are simulation-based components.

PROCEDURE

1. Select resistor values for R] and R2 such that the following conditions are met:

a. R1>R2

b. R1<R2

C. R1=R2

2. Calculate the gain using the values of the resistors chosen, insert into table.

3. Configure the circuit shown in Figure 1 (Inverting configuration) using a suitable software.

4. Set the DC supply to +/-12V. Connect to the +/-V_cc pins of the op-amp.

5. Set up a function generator to provide a sine wave with amplitude of 0.50V (1.0V peak-to-peak) at 50 Hz. Connect the function generator to the input of the op-amp circuit. (This signal remains constant throughout the experiment).

6. Connect the oscilloscope (OSC) to display the input and output waveforms.

7. Calculate the gain of the circuit (V_s /V_in) using the output and input values on the OSC display.

8. Record the amplitude of the input and output signal. Note the characteristics of the waveforms obtained.

9. Repeat steps 7 — 8 for all three R1 and R2 conditions.

10. Repeat steps 1 — 9 for Figure 2 (Non-inverting configuration).

11. Tabulate all results for the calculated and measured values using the format given in Table 1.

Input    R1   R2   -     V_o = - (R2/R1)V_in

        0V             +

   Figure 1

Input       +   Opt          V₀ = (1 + R2/R1)V_in

R1    R2    -

0V

Figure 2

         V_s+

V₊                             V_out

V_-     V_s-

Offset null 1    8 pin not used

Inverting input V_- 2     7 positive voltage V_s+

Non-inverting input V₊  3      6 output V_out

Negative voltage V_s-  4            5 offset null

Figure 3 (a) Symbol for an op-amp; (b) the 741 op-amp package; (c) top view of an

LM741 dual inline package (DIL), showing internal configuration and pin connections.

NOTE:

How do outputs of the inverting and non-inverting op-amps differ? If shown just the output waveforms from the oscilloscope screens, how would you differentiate between the two configurations? What is the effect on the output for both amplifier configurations if R1 is larger than R2 or vice versa, and if they are equal? Effect of having supply voltage supplied at pins 4 and 7 on the output? What limits the output? Cut-off voltage?

Results

Table 1a for Inverting Opamp

Resistor values (W)		Input amplitude from OSC (Vin)	Output amplitude from OSC (Vo)	Measured gain from OSC display (Vo/Vin)	Calculated gain (R2/R1)
R1	R2

 

                      Table 1b for Non-Inverting Opamp

Resistor values (W)		Input amplitude from OSC (Vin)	Output amplitude from OSC (Vo)	Measured gain from OSC display (Vo/Vin)	Calculated gain 1 + (R2/R1)
R1	R2