Lab 27 Op Amp Characteristics
4/22/19-4/27/19
Lab 27
Objectives:
· To verify experimentally that the gain of an op amp can be made dependent on on the external negative feedback loop from output to input
· To operate an op amp as a noninverting amplifier
· To operate an op amp as a inverting summer
Materials:
-10k resistor
-Dual power supply
-5k resistor
-3.33k resistor
-2.5k resistor
-20k resistor
-30k resistor
-741C op amp Data Sheet
-Multisim
-741C op amp
Procedure:
1. Connect the circuit of Figure 1 (27-9). RF = RR = 10K Ohms. Close S1 and S2 are open. Set each of the two supplies to 9 V. Set the sine wave generator at 1000 Hz, zero output. Connect the oscilloscope to the output of the op amp. External trigger / sync the oscilloscope with the output from the generator
2. Close S1 and S2
3. Gradually increase the output from the signal generator just below the point where the waveform distorts. Measure and record in Table 1 the peak to peak output signal for the feedback resistors in the circuit.
4. With the oscilloscope measure and record in Table 1 the input signal v in to the amplifier (output of signal generator).
5. Compute and then record the gain of the amplifier (v out / v in).
6. Compare the phase of the input and output signals and indicate
7. Reduce the output of the generator to 0.
8. Repeat steps 3-7 for each value of RR shown in Table 1. Use a resistor decade box to set up the required value of RR.
9. Open S1 and S2.
10. Modify the circuit to conform to that in Figure 2 (27-10). The power supplies remain connected as shown previously in Figure 1. Set each at 9 V. The generator output is at 1000 Hz.
11. Close S1 and S2. For each value of RF and RR shown, complete and record the data required in Table 2, following the same procedure as in Table 1.
12. Open S1 and S2. Keep the power supplies connected as in Figure 1, each at 9 V. Modify the experimental circuit as in Figure 3 (27-11). RF = R1 = R2 = 10,000.
13. Close S1, S2, and S3. S4 is open. Measure and record in Table 3 V1 and VOut.
14. Open S3. Close S4. Repeat step 13.
15. Close s2. Both S3 and S4 are now closed. Measure and record VOut and VIn.
16. Reverse the polarity of V1. Measure and record VOut and VIn with S3 and S4 closed
17. Modify the summer circuit so that with the two 1.5- V inputs in Figure 3, vOut = -4.5 V (approx). Show the values of all resistors and V1 and V2 polarities. Measure the output voltage and record it in a specially prepared table.
18. Modify the summer circuit so that with two 1.5-V inputs, the output voltage = + 1.5-V (approx). Show and record the values of all resistors and V1 and V2 polarities.
19. Experimentally determine if there is a practical limit on the undistorted gain of the inverting op amp. Record the maximum voltage and gain.
Discussion:
During this lab we ran into very few problems those problem were the lack of time we had this week as well as cole had issues setting up the breadboard because he configure the pins of the op amp incorrectly.
Conclusion:
· A signal applied to the minus terminal will be shifted in phase 180 degrees at the output
· Vout = 1 +(RF / RR) Vin
· Gain = RF / RR
· Vout = -(V1 + V2)
Tables:
Table 1- Gain of inverting Op-Amp
RF, Ohms
RR, Ohms
(V-p-p) Output
(V-p-p)
Input
Gain (V Out/V In)
Phase
10K
10K
16.1
16.1
1
180
10K
5K
7.9
15.8
2
180
10K
3,333
5.4
16.1
3
180
10K
2.5K
3.69
15.8
4
180
10K
20K
32.2
16.1
5
180
10K
30K
48.66
16.1
32
180
Table 2- Gain of non inverting Op-Amp
RF, Ohms
RR, Ohms
(V-p-p) Output
(V-p-p)
Input
Gain (V Out/V In)
Phase
10K
10K
16.1
8.2
2
0
10K
5K
16
5.4
3
0
10K
3,333
15.9
4
4
0
10K
20K
16.2
11.3
1.4
0
10K
30K
16.2
12.7
1.3
0
Table 3- Op Amp as a Summer
RF K Ohms
Condition
Condition
Input Polarity
Input Polarity
V IN, V
Vout, V
10
S3
S4
V1
V2
V1
V2
10
ON
OFF
+
X
1.5
X
-1.5
10
OFF
ON
X
+
X
1.5
-1.5
10
ON
ON
+
+
1.5
1.5
-3
10
ON
ON
-
+
-1.5
1.5
0
15
ON
ON
+
+
1.5
1.5
-4.5
Figure 1- Multisim Circuit
Figure 2- Datasheet pins
Lab 28
Cole Peterson
Derek Jordan
Dylan Huff
Objectives:
· To get data for input bias current
· To measure and null the output offset voltage
· To calculate the slew rate of a 741
· To observe the effect of power bandwidth
Procedure:
1. Construct the circuit in figure 28-9 to measure the dc voltage at the inverting and non inverting inputs and record the voltages in tables 28-1 and 28-5.
2. Then the remove the first 741 chip and repeat the first step twice with two different 741’s.
3. Next the input bias current was calculated based on the inverting and noninverting inputs using ohm's law. The current for each input was calculated and averaged together to find the input bias current, the input bias current of each 741 chip was record into tables 28-2 and 28-6.
4. After that figure 28-10 was constructed and the output voltage for each op-amp was measure and recorded in tables 28-3 and 28-7. Following those values the input voltage was calculated with the equation Vout/1000=Vin and the values for each 741 were recorded in tables 28-3 and 28-7 as well.
5. Next a 5Kᘯ potentiometer is added to the circuit to construct figure 28-11 in order to adjust the output voltage offset by adjusting the potentiometer.
6. The circuit in figure 28-12 was then constructed and the function generator was set to a frequency of 10KHz and the circuit was overdriven and the ΔV and ΔT was measure and recorded for the waveform in tables 28-8 and 28-4.
7. Once the values were found for ΔV and ΔT slew rate can be calculated using the equation SR =; the values for slew rate were recorded in tables 28-8 and 28-4.
8. After the slew rate is found the bandwidth is found by adjusting the function generator to 1 KHz and the output of the circuit to be 20 Vp-p. The frequency was adjusted past 10 KHz until the volts peak to peak began to decrease and or the wave became more triangular. For multisim that began at about 12 KHz and 19 KHz for the breadboard.
Tables:
Table 1- DC Return Voltage
Inverting
Non-Inverting
First 741C
-13.29
-11.18
Second 741C
N/A
N/A
Third 741C
N/A
N/A
Table 2- Calculated Bias Currents
Inverting (nA)
Non-Inverting
First 741C
-66.5
-0.01330V/200kΩ=-66.5nA
Second 741C
N/A
N/A
Third 741C
N/A
N/A
Table 3- Offset Voltages
VOut
VIn
First 741C
900
.90
Second 741C
460
.46
Third 741C
1360
1.36
Discussion- We couldn't do step 12 because multisim doesn't have all the components needed to complete this step but other then that we did not have any other issues in the lab.
Conclusion: The input bias current can be found by measuring the inverting and noninverting input voltage, using ohm's law to calculate the input current, and averaging the current values together. An operational amplifier can have an offset in the output voltage that can affect the output of a signal wave. In order to correct for this offset voltage, a potentiometer can be placed between pins 1 and 5, with the middle pin of the potentiometer being placed on the -Vcc pin or pin 4 of the LM741 op-amp. The slew rate of the LM741 op-amp was found by measuring the change in time and change in voltage and inputting the values into the equation: SR =. Power bandwidth controls the frequencies that a operational amplifier can amplify without a decreasing amplitude or distortion. When the input frequency of an operational amplifier is outside of the amplifier bandwidth, the output signal will distort into a sawtooth-like wave. Its amplitude will also decrease.
