Lab 2 - Operational Amplifiers

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ENGR-240

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Feb 20, 2024

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ELEE 3101 Electronics I Lab Lab : Operational Amplifiers Circuits I Page 1 of 5 Lab 2: Operational Amplifiers Circuits 2 Student name: ________________________________ Student ID: ____________ I. Introduction This laboratory assignment is a continuation of the previous assignment, where operational amplifiers are implemented in circuits for different purposes, with the idea that the learner can observe and analyze different applications of this electronic components. II. Objectives • Identify the different types of circuits implemented with OpAmps. • Develop the ability to design and construct a circuit with operational amplifiers. • Run circuits simulations to perform DC and Frequency sweep analysis. III. Equipment Required • Multimeter • Dual Trace Oscilloscope • Function Generator • Breadboard • Miscellaneous cables IV. Material Required • (1) Operational Amplifier LM741 Integrated Circuit • Resistors of different values • Jumper wires

ELEE 3101 Electronics I Lab Lab : Operational Amplifiers Circuits I Page 2 of 5 V. Before the Lab 5.1 Frequency Response a. A frequency response measurement determines how a given quantity in a linear circuit behaves as the frequency of its input changes. b. Since the circuit is assumed to be linear, the response of a circuit will always be at the same frequency as the input signal. c. Different quantities can be measured, for example, an impedance response, or a phase response. However, if nothing else is specified, one is normally measuring the amplitude of the gain versus frequency. d. Frequency response must always be measured using a sinusoidal input and sinusoidal response. If the output is not sinusoidal, the measurement is wrong. e. Since the circuit is assumed to be linear, in theory the input amplitude should not matter. Gain in this lab is defined at 𝑉 ??? /𝑉 𝑖? , and if one halves the input, the output should reduce by half as well. However, in practice, it is important to have the input large enough to get an accurate measurement, but small enough so that the op-amp does not distort the output. You may need to use different amplitudes at different frequencies. f. Normally we plot gain in a Bode Plot format, with the gain in decibels on the vertical axis and the frequency on a log scale on the horizontal axis. g. For voltage gain, decibels are defined as 20 log 10 |𝑉 ??? /𝑉 𝑖? | h. The 3dB point is defined as the frequency where the gain drops to 3 dB less than its maximum value.

ELEE 3101 Electronics I Lab Lab : Operational Amplifiers Circuits I Page 3 of 5 VI. In the Lab Now it is time to put some hands on to build some of the circuits showed before, so that you can physically analyze each of them. 6.1 Voltage Follower 1) Build a voltage follower using a LM741 type op-amp. For the power supply use +15 and -15 Volts (if you are working at the lab) or +5 and 0 Volts (if you are working remotely). Note that the chip does not have a ground pin. Leave the "Null Offset" pins unconnected. For the input use a potentiometer configured as a voltage divider. (Figure 4.1). Figure 4.1.- Voltage follower schematic NOTE: The potentiometer is not considered part of the voltage follower, we are simply using it as a variable voltage source to test the follower without using an extra power supply. 2) Vary the potentiometer to get voltages every three volts from -15 Volts to +15 Volts, or every 0.5 volts from 0 to +5 Volts. Do not waste too much time adjusting to exactly the specified voltage as long as you record the actual value accurately. Record both the input and corresponding output voltages. It is preferable to use the same voltmeter for all measurements. Table 1.- Input/Output voltage ratio 𝑣 𝑖? 𝑣 ??? 𝑣 𝑖? 𝑣 ???

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ELEE 3101 Electronics I Lab Lab : Operational Amplifiers Circuits I Page 4 of 5 3) The data above should show that the voltage follower cannot "follow" all the way out to +15 and -15 or 0 to +5. Vary the potentiometer to find the exact points where the 𝑣 ??? = 𝑣 𝑖? relationship starts to fail, on both the positive and negative sides. The advantage of using the voltage follower is that its output has a low (almost zero) output impedance; thus, it looks like an ideal voltage source. The potentiometer by itself would have a nonzero output impedance. 6.2 Slew Rate 1) Using an LM741 type op-amp, construct a non-inverting amplifier with a gain as given by Table 2 below. Set up the function generator to produce a 2V pk-pk, 10 kHz square wave, and connect this as the input to the non-inverting amp. The op-amp output will show a finite rise/fall time. Capture a screen shot of the output. Sketch and measure the slope of the rising and falling edges; this is the slew rate. Include proper units. Figure 4.2.- Non-Inverting amplifier schematic Gain (Step 1, 2) Gain (Step 4) A 30 3 B 40 4 C 50 5 D 60 6 2) Change the function generator to produce a sine wave at 100 Hz. Using the same amplifier as in Step 1 of this section. Adjust the generator to get an undistorted sine wave signal at both the input and output of the op-amp. Check the ratio of the input and output signals and make sure it is close to your specified gain. 3) Then measure the amplitude of the frequency response from 100 Hz to 1 MHz. As you change frequency, you may need to adjust the input voltage to maintain a clean 2 V pk-pk / 10 kHz

ELEE 3101 Electronics I Lab Lab : Operational Amplifiers Circuits I Page 5 of 5 sine wave at the output. Take enough points to accurately get the shape of the curve and to determine the 3 dB down point. NOTE For the frequency response measurement, it is important to ensure that the output amplitude is controlled by the small signal frequency response rather than the slew rate. For this reason, you should take care to have an input small enough so that the output sine wave is not clipped or showing slew rate effects, but large enough so that you can get a reasonably accurate measurement. You will need to use your own judgement here to pick the correct amplitude, which may change with frequency. 4) Change the amplifier to have a gain one-tenth as large as in Step 1. You should be using the same operational amplifier as in Step 1. Then repeat the frequency response measurement. VII. After the lab 1) Plot the frequency responses from steps 6.2 (2) and 6.2 (3) and try to determine the gain bandwidth product for the 741 op-amp. The gain bandwidth product is the gain at DC multiplied by the 3dB corner frequency. It should be roughly the same for both responses. 2) Record all information in your lab report, remember to not include pictures of handwriting work, everything must be developed in computer.