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Ideal 741 Operational Amplifier Lab

Objectives:

To become familiar with the use and characteristics of a
741 op‑amp , in an ideal amplifier configuration as an; inverting amplifier, noninverting amplifier, and voltage follower.

Materials:
1. 741 Op‑Amp
2. Assorted Resistors
3. Function Generator
4. Digital Multimeter
5. Dual Channel Oscilloscope

Procedure:

A. Inverting Amplifier

1. For each of the combinations of RF and R1 in Table 1 calculate and record Vo/Vi and Zin for the circuit shown in Figure 1. Assume an ideal op‑amp.

2. Construct the circuit shown in Figure 1, see Figure 2 for the pin‑out configuration of the 741 op‑amp. Adjust the voltage offset null potentiometer for Vo (DC) = OV for the circuit in Figure 1 with Vi (DC) = OV.

3. For each of the combinations of RF and R1 in Table 1 and f = 500Hz:
a. Measure and record Vo/Vin ; Compare with values calculated in Step 1.
b. Find the maximum peak‑to‑peak output voltage without distortion.
c. Measure and record Zin ; Compare with values calculated in Step 1.



Figure 1: Inverting Amplifier


Figure 2: Pinout Configuration of a 741 OpAmp



Table 1: Values of RF and R1 for the Inverting Amplifier


Table 2: Maximum Peak Voltage Limits for Vo




B. Non-Inverting Amplifier

1. For each of the combinations of RF and R1 in Table 3, calculate and record Vo/Vi and Zin for the circuit shown in Figure 3. Assume an ideal op‑amp.

2. Construct the circuit shown in Figure 3. Adjust for Vo (DC) = OV, for each of the combinations of RF and R1, in Table 3 and f = 500Hz:
a. Measure and record Vo/Vin ; compare with calculated values.
b. Find the maximum peak‑to‑peak output voltage without distortion.



Figure 3: Non-Inverting Amplifier

Table 3: Values for RF and R1
for the Non-Inverting Amplifier




C. Voltage Follower

1. Calculate Vo/Vi and Zin, for the circuit shown in Figure 4.

2. Construct the circuit shown in Figure 4. Adjust Vo (DC) = OV.

3. Measure and record Vo/Vi at f = 500Hz, and find the maximum peak‑to‑peak output voltage without distortion.


Figure 4: Voltage Follower

Procedure & Data:

Part A:

For the given experiment three configurations and there characteristics of the 741 op‑amp assuming ideal conditions where examined. First of the three was the inverting amplifier. Given combinations of RF and R1 (see Table 1) hand calculations were performed (E.1, E.2) to estimate the 741 op‑amp's behavior. Data was calculated and recorded for comparison (Table 1.A).


Vo/Vi = -RF/R1 (E.1)

Zin = R1 (E.2)

Table 1.A: Calculated Values for Ideal 741 Inverting Op‑Amp


Next the circuit was constructed (see Figure 1) and a potentiometer was used to adjust the voltage offset null to obtain Vo(DC) and Vi(DC) equal to zero. Frequency for the AC input sine wave signal was set to 500Hz with the DC biasing set to ±15V(DC). Measurements were then taken, recorded (Table 2.A), and compared to our calculated values. Do to the limiting factors of the test equipment some values for maximum peak‑to‑peak output voltage was unobtainable.

Table 2.A: Measured Values for Ideal 741 Inverting Op‑Amp


Part B.

In the second part of the given experiment the characteristics of a 741 non‑inverting op‑amp was examined. Again combinations of RF and R1 (see Table 3) were given. Data was then calculated (E.3), (E.2) to mathematically determine the behavior of the device and recorded (Table 1.B).

Vo/Vi = (RF/R1) +1 (E. 3)

Table 1.B: Calculated Values for Ideal 741 Non‑Inverting Op‑Amp


The circuit was constructed (see Figure 3) and a potentiometer was used to adjust the voltage offset null to obtain Vo(DC) and Vi(DC) equal to zero. Frequency for the AC input sine wave signal was set to 500Hz with the DC biasing set to 15V(DC). Measurements were then taken, recorded (Table 2.B), and compared to our calculated values.

Table 2.B: Measured Values for Ideal 741 Non‑Inverting Op‑Amp


Part C.

In the final step of examining the 741 op‑amp a voltage follower configuration was developed. Mathematical productions were then made to determine the behavior of the device (E.4), (E.5).

Vo/Vi = Av = 1 (E.4)

Zin = ∞ (E.5)

Next the voltage follower circuit was constructed (Figure 4) and its characteristics measured. Frequency for the input AC sine wave was set to 500Hz and the DC biasing set to plus or minus 15V(DC). However do to the previous problems of the equipment limiting the data gathering a second non­inverting op‑amp was constructed and used as the first stage of the device (Figure 5). The first stage, non‑inverting op‑amp was given a voltage gain of +11.0V and connected to the input of the second stage of the voltage follower. Data was then gathered on both individual stages and the over all characteristics of Figure 5 (Table 1.C).

Table 1.C: Measured Values for Ideal 741 Voltage Follower Op‑Amp, with a non‑inverting op‑amp first stage



Figure 5: Multi Stage Non‑Inverting / Voltage Follower Op‑Amp


Conclusion & Discoveries:

Measuring the input resistance of the op‑amp at both inverting and non‑inverting terminals confirmed a very high input resistance; allowing one to assume the input resistance approaches infinity.

In assuming an ideal op‑amp with infinite gain, the gain is only dependent on the ratio of the feed back resistor RF to the input resistance Rs. Therefore any load connected to the input terminals of the op‑amp vs. the feed back resistor will set the gain of the device given ideal conditions.


Using an op‑amp rather then a voltage divider configuration with resistors is a much better design. That is the op‑amp has a very high input resistance so almost any small load will not be affected by the op‑amp. Also one can also increase or decrease the voltage desired rather then just decrease the voltage as a voltage divider would do. However both an AC source and DC biasing source are needed for the op‑amp configuration.

It was discovered that by approaching the open loop differential voltage gain of the 741 op­amp device the gain became less then ideal. This was noted in tables 2.A, 2.B for the largest voltage gain attempted.

In closing the operation and characteristics of the 741 op‑amp in ideal conditions was better understood. Different configurations were constructed and tested to gain a better understanding of the device. Also several key points of the benefit of op‑amps were learned, such as the very high input resistance and its effect on other circuits connected to the device.


Lab Notes
Lab Notes Page 1 of 3
Lab Notes Page 2 of 3
Lab Notes Page 3 of 3

Electrical Engineering Research
Embedded Systems
Modeling and Simulation
Semiconductors and IC


Electrical Engineering lab key words: 741 Op-Amp, uA741, operational amplifier, ideal op-amp, inverting, non-inverting, voltage follower, null, voltage divider, infinite gain, multiple stages, potentiometer, characterization, peak to peak, peek output, P2P, distortion, clipping, saturation, amplifier effects, 741 pin out configuration, voltage limits, amplifier distortion, electronics engineering experiment.

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