Lab 06_Amplifiers

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Pennsylvania State University *

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1110

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Electrical Engineering

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Apr 3, 2024

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BIOMEDE 3702 LAB PROCEDURE: Op-Amp Learning Outcomes: Students will be able to…  Understand the configuration of Integrated Circuits (ICs).  Build an amplification circuit using an operational amplifier (Op Amp).  Build an active filter by combining a passive filter low pass and an op amp. Lab Goals: The goal of this lab is the building of an operational amplifier circuit with a set gain, and convert that circuit into an active low pass filter (or an amplifying low pass filter). Materials: 1. Solderless breadboard 2. Multimeter 3. Wire box 4. Operational Amplifier IC (MCP 6002) 5. Resistors (detailed in procedure) - Review “ How to read a resistor values ” 6. Capacitors (detailed in procedure) - Review “ How to read a capacitor value ” 7. 3.3V/5V Power Module (for power supply) 8. Arduino (for -5 V power supply) 9. Oscilloscope a. Two gray lead BNC hook probes 10. Function generator a. One black lead BNC connector with red/black alligator clips. Circuit Experiment 1: Inverting Op-Amp Experiment 1. Compensate your two oscilloscope probes (Ch1 and Ch2). 2. Set the function generator to supply a V pp = 75 mV / 25 Hz sinusoidal signal. This will be the input into your operational amplifier. Note: Use the -20 dB bottom on the function generator. 3. You will be using a MCP6002 integrated circuit (specifically op- amp A ) to build an inverting amplifier circuit (Figure 1). 4. Build the circuit using the schematic on . DO NOT PLUG POWER JUST YET. LET US CHECK FIRST.

BIOMEDE 3702 Figure 1: Left – Op amp chip with pins labeled and orientation notch. Right - Description of the function for each pin, you will use op amp A. Figure 2: Schematic for lab op-amp circuit.

Setting up your Power Supply: The Power Module (Figure 3) will serve as your (+5 V/GND) for this lab. Simply connect it as seen in the figure. Make sure to match +/- symbols. To get a -5 V output you will be using the Arduino. Please follow these steps: 1. Option 1 : Power module connecting the two grounds; Arduino power goes directly to the op-amp. Option 2 : Grounds must be connected by a wire; Arduino power goes to the positive power rail on one side. The power module is on the opposite rail/side of the Arduino. Figure 3: Options for connecting the Arduino and power module. Important Step : It is good practice to always double check that your Power Module and Arduino is outputting +5V whenever you hook it up to your breadboard. Use a multimeter to verify the output. 5. Use the oscilloscope to simultaneously measure the waveforms from the inverting input of your amplifier (channel 1, V pp = 75 mV from your function generator) and the amp output (channel 2) Note: Set Channel #1 as your trigger channel (trig menu  select channel 1) Note: Set three measurements (meas botton): CH1 Vpp, CH2 Vpp, and Phase A – B) a. Answer the following questions: i. What is the experimental gain (in dB) of your inverting op-amp circuit? Is it what you theoretically expected? Record in Post Lab [Gain = 20 * log(Vout/Vin)] ii. What is the phase change for your inverting op-amp circuit? Record in Post Lab b. Take a picture with your phone of the wave. Record in Post Lab. Circuit Experiment 2. Low-Pass Filter Op-Amp 1. You will be modifying your inverting op-amp circuit to create an active low-pass filter.

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2. Use Figure 4 to build your sequential active filter. You will notice that the function generator signal will go through the operational amplifier first, then through the filter. 3. Your input will continue to be a Vpp = 75 mV from the function generator. Figure 4: Op amp with passive filter as input. 4. In your oscilloscope connect Channel 1 to the function generator, and Channel 2 across capacitor 1. 5. Use your oscilloscope to check that you are still getting Vpp = 75 mV. Adjust as necessary. 6. Set CH 1 as the trigger channel (Trig Menu  Ch1). Move the trigger threshold using the dial above the trigger menu key. 7. Using STEP 5 from the previous experiment save the waveform for your post-lab assignment. 8. Use what you have learned in previous labs and in class to calculate the theoretical cutoff frequency. Record in Post Lab 9. Write in Table 1: Active Filter GainTable 1 the Vouts obtained from your active filter. You will use these values to obtain the experimental Gain of your circuit, and create a bode plot. Record in Post Lab WARNING! Make sure you have all the data and/or images required for your Post-

Labs. Not doing so could lead you to re-doing the experiment. THE POINT In this lab, we finally were able to make a signal bigger through amplification. The process requires an operational amplifier, voltage fed to said op amp, and a special arrangement of resistors around the op amp. With the combination of these three elements, we were able to not only amplify the signal, but to control how much amplification we created using the relationship between feedback resistor (Rf) and input resistor (Ri). We also expanded our use of filters, by creating active filters that allow for a signal to be both filtered and amplified at the same time. This combination of operations are essential for the many biopotential applications out there in research and medicine. Learning Outcomes: Students will be able to…  Understand the construction of Integrated Circuits (ICs).  Build an amplification circuit using an operational amplifier (Op Amp).  Learn the basics on amplification through Op Amp integration.

POST LAB: Op-Amp Circuit Experiment 1. Inverting Op-Amp experiment 1. Show the saved oscilloscope image of your inverting op-amp input and output signals. Either include the Vpp measurement or label the peak-to-peak voltage values of the input and output signals. (2 points) 2. What was the experimental gain (in dB) of your inverting op-amp circuit? Was it what you theoretically expected? (2 points) 3. What was the phase change for your inverting op-amp circuit? (1 point) 4. What would be the output voltage of the inverting op-amp circuit if the resistance of R f were changed to ½ of its original value? (1 points) 5. What two ways could you add a resistor to the inverting op-amp circuit to increase the overall gain? Hint: Think back to class and how we derived gain differently. Show in the schematic below . (2 points)

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6. For the change in resistance involving Rf in the previous question, show the new resistance driven gain equation Vout = . (1 point) Circuit Experiment 2. Low-Pass Filter Op-Amp 1. Show the saved oscilloscope image of your two signals: input and active filter. Either include the Vpp measurement or label the peak-to-peak voltage values of the input and output signals. (2 points) 2. What is the cut-off frequency of the low-pass op-amp you built? Show your calculation (1 points) 3. Record your data from Part 2 in the table below. Calculate gain for each frequency (show what equation you used for the calculation) (2 points) Table 1: Active Filter Gain 4. Create a Bode Plot using the values in the previous table. Remember that your Bode plot is a log- log plot. Gain being in dB on the y-axis is already logarithmic, so do not forget to convert your x- axis (frequency) into logarithmic scale. Mark the cut-off frequency on the plot. No need to include phase (4 points) . Frequency (Hz) V out (mV) V in (mV) Gain (dB) 10 75 15 75 50 75 100 75 150 75 500 75 1000 75 1500 75

5. One of the problems that come with creating sequential active filters (filter – amp) is that it adds additional load (resistance) to our circuit. For this reason integrating the low pass filter into the op amp circuit is considered more efficient and practical. Where would you add a capacitor to create a low-pass filter in the following diagram? Hint: look up online inverting active low pass filters. Explain your reasoning. (2 points) Challenge Question 6: Note: Challenge questions in post-labs are bonus and optional. These questions are designed to be challenging. Please submit your attempts here on Carmen. 1. Build the following Band-Stop Filter in Tinkercad. Use three 741 op amps. What are the cutoff frequencies for both filters?