Lab8 Tech Report (1)

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Bluegrass Community and Technical College *

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223

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Electrical Engineering

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Jan 9, 2024

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Laboratory Technical Report Title : Measurement of the frequency response of an operational amplifier Author: Elnoel Akwa Instructor: Dr. Caicheng Lu Experiment No: 8 Course: EE223

1. Objective Objectives of this laboratory are to: • Analyze and measuring the frequency response of an op-amp inverting amplifier circuit. • And Computing and measurement of the gain bandwidth product for this amplifier circuit. 2. Results Here are the following instruments that we used in this experiment: AD, 741 Op-Amp IC, various valued resistors and oscilloscope 2.1. Part A of the experiment from 1 to 4 We measured the frequency response by sweeping the generator frequency over the range necessary to determine the roll of the circuit gain (“roll off” = the 3dB frequency point). The data is given in the Table 1. Frequency Amplitude Log 10 frequency Gain 5,000 1 3.698 11 10,000 1 4 11 20,000 0.98 4.301 10 30,000 0.95 4.477 9.5 40,000 0.86 4.602 8.6 50,000 0.80 4.698 7.9 60,000 0.78 4.778 7.2 63,000 0.75 4.799 7.1 200,000 0.3 5.301 4.6 540,000 0.2 5.732 1 Table 1: Roll of Frequency at 63KHz Amplitude Gain

Figure 1: Roll off from the circuit gain The 3dB frequency (f H ) and unity gain crossover frequency is found from the Figure 2 Figure 2: 3dB frequency and unity gain crossover frequency 3dB = 63 KHz Unity gain crossover frequency = 540 KHz

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The dB versus log frequency graph is shown in Figure 3 Figure 3: dB VS log frequency 2.2 . Part B of the experiment from 1 to 9 In this next part of our experiment, we set the square wave frequency to f H / 2 = 63/2 = 31.5 KHz. We observed and captured the output wave from in Figure 4. 0 1 2 3 4 5 6 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 Gain log frequecy Hz db vs log frequency

Figure 4: Output waveform of square wave frequency 31.5 KHz From the waveform we measured the rise time. We measured t 10-90% = 5.91 microsecond. We can see that in Figure below (figure 5). Figure 5: Measuring the rise time t 10→90% Now we compare this with the pulse width (PW = ½ the period of square wave) Period = 31.75 micro sec P w = 31.75/2 = 15.88 micro sec t 10→90% ≈ PW/3 = 0.37 pw.

Now we adjust the wave frequency such that PW ≈ 6t 10→90% = 2 * 6 * 5.91 micro sec = 70.92 micro sec, so that we can observe and capture the waveform which is shown in Figure 6 Figure 6: Square waveform when PW ≈ 6t 10→90% Now again we adjust the square wave from such that PW ≈ t 10→90% = 2 * 5.91 = 11.82 micro sec and observe and sketch the waveform which is shown in Figure 7. Figure 7: Square wave form frequency PW ≈ t 10→90% Observing the 3 waveforms in Figures 5 to 7 we see that as frequency increases distortion increases.

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2.2.Part C of the experiment from 1 to 9 For part C of the experiment, we repeat what we have done in Part A and Part B. We measure the frequency response by sweeping the generator frequency over the range necessary to determine the roll of the circuit gain (“roll off” = the 3dB frequency point). The data is given in the Table 2 Frequency Amplitude log frequency Gain 20,000 0.5 4.301 5 50,000 0.48 4.698 4.9 100,000 0.45 5 4 127,000 0.4 5.103 3.1 Table 2: Roll of Frequency at 127KHz Amplitude Gain The dB versus Log frequency graph is shown in Figure 8 Figure 8: dB Versus Log Frequency We measure the frequency response by sweeping the generator frequency over the range necessary to determine the roll of the circuit gain (“roll off” = the 3dB frequency point). We find that when frequency is 460KHz amplitude is .1 V and unit gain crossover frequency is 460KHz. We captured the waveform in Figure 9. 0 1 2 3 4 5 6 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 Gain Log Frequency dB VS Log Freq

Figure 9: Roll off the circuit gain at 460KHz In this part of the experiment, we set the square wave frequency to f H / 2 = 127/2 = 63.5 KHz. We observed and captured the output wave from in Figure 10 Figure 10: Output waveform of square wave frequency 63.5KHz From the waveform we measure the rise time. We measured t 10-90% = 3.52 micro sec. We can see that in Figure 11

Figure 11: Measuring the rise time t 10→90% Now we compare this with the pulse width (PW = ½ the period of square wave) t 10→90% ≈ 3.52/7.87 = 0.45 PW Period = 2 * 6 * 3.52 = 42.24 microsec We can observe the waveform in Figure 12 which is captured Figure 12: Square waveform when PW ≈ 6t 10→90%

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Now again we adjust the square wave from such that PW ≈ t 10→90% = 2 * 3.52 = 7.04 micro sec and observe and sketch the waveform which is shown in Figure 13 Figure 13: Square wave form frequency PW ≈ t 10→90% at 7.04 mic sec By observing these Figures from 10 to 13 we see that as frequency increases distortion increases. 2.3. Part D of the experiment The gain is ½ with amplifier 2 versus amplifier 1. t 10→90% is also ½ with amplifier 2 versus amplifier 1. f H is 2 times with amplifier 2 versus amplifier 1. Waveform drawing looks similar.