Lab 05_Passive_Filters

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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: Passive Filters Learning Outcomes: Students will be able to…  Identify different ceramic capacitors by reading their values.  Differentiate the frequency response of a 1 st order and 2 nd order filters.  Assemble different arrangement of filters: low pass filter and bandpass filter. Materials: 1. Solderless breadboard. 2. Wire box 3. Resistors – 2x 3.3 kΩ | 1x 1 kΩ 4. Capacitors – 2x 100 nF | 1x 10 nF 5. Oscilloscope a. Two gray lead BNC hook probes. 6. Function generator a. One black lead BNC connector with red/black alligator. Circuit Experiment #1: 1 st Order Low Pass Filter Figure 1: First Circuit 1. Select from the resistor pile one 3.3 kΩ. Review “How to read a resistor value”. 2. Select from the ceramic capacitor pile one 100 nF. Review “How to read a capacitor value”. 3. Connect function generator ( remember red is positive ) to the breadboard using a wire. Note : Connect one end of the wire to the alligator clip and the other end to the breadboard. This should be a shorter wire. 4. Complete the circuit in Figure 1 . 5. Compensate your two oscilloscope probes.

BIOMEDE 3702 Refer to the “Oscilloscope/Function Generator Tutorial” to remember how to do this. 6. Set a 10 Hz/ 2 Vpp signal in the function generator. 7. Connect your first oscilloscope probe across the function generator (Vin) (Ch 1) and your second oscilloscope probe across the capacitor (Vout) (Ch 2). 8. Measure the Vpp and Phase ( Meas>Ch1>Time>Phase (between 0 to 90, record as negative) between these signals for each frequency in Table 1 . Record in Post Lab. Note : You are measuring phase change between Ch1 and Ch2. You should measure Ch2 Vpp (Vout), but can measure Ch1 Vpp as well for consistency. Note : Make sure a clear signal is visible in the oscilloscope window so the phase measurement is accurate. Table 1: Frequencies to Test Frequencies 10 100 1,000 1,0000 20 200 2,000 2,0000 50 500 5,000 5,0000 9. Show your results to your TA and explain what is happening with your circuit. Circuit Experiment #2: 2 nd Order Low Pass Filter Figure 2: Second Circuit 1. Connect an additional 3.3 kΩ resistor and a 100 nF capacitor as shown in the image. Note: Notice both capacitors are going to ground. 2. Connect your first oscilloscope probe across the function generator (Vin) (Ch 1) and your second oscilloscope probe across the second capacitor (Vout) (Ch 2) as shown .

BIOMEDE 3702 3. Measure the Vpp and Phase ( Meas>Ch1>Time>Phase (between 0 to 180, record as negative) ) between these signals for each frequency in Table 2 . Record in Post Lab. 4. Show your results to your TA and explain what is happening with your circuit. Table 2: Frequencies to Test Frequencies 10 100 1,000 10,000 20 200 2,000 20,000 50 500 5,000 50,000 Circuit Experiment #3: Bandpass Circuit Figure 3: Third Circuit 1. Note: These component are slightly different, please note in the diagram. Remove the second resistor and the second capacitor (3.3 kΩ and 100 nF). Then connect an additional 1 kΩ resistor and a 10 nF capacitor as shown in the image. Rearrange the connected resistor and capacitor to match the image. Note: This time the first resistor and the second capacitor are connected to ground. 2. Connect your first oscilloscope probe across the function generator (Vin) (Ch 1) and your 3. oscilloscope probe across the second capacitor (Vout) (Ch 2) as shown . 4. Measure the Vpp (no need to measure phase) between these signals for each frequency in Table 3 . Record in Post Lab. Table 3: Frequencies to Test Frequencies 10 100 1,000 10,000 100,000 20 200 2,000 20,000 200,000 50 500 5,000 50,000 500,000 THE POINT In this lab, we were able to construct various passive filters with the objective of getting more familiar with analog frequency filtering. Similarly, as a Fourier Transform allows us to remove specific frequency

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BIOMEDE 3702 components, these passive circuits allow us to vary the relative proportion between a resistor and a capacitor to create an analog passive filter. These filters are simple to build and are highly useful to clean signals and record better data. They all work given that the capacitor reactance’s is dependent on a signal’s (or AC voltage’s) frequency. Learning Outcomes: Students will be able to…  Identify different ceramic capacitor by reading their values.  Differentiate the frequency response of a 1 st order and 2 nd order filters.  Assemble different arrangement of filters: low pass filter and bandpass filter.

BIOMEDE 3702 POST LAB: Passive Filters (20 points) Circuits Experiment #1 FILL THE TABLE WITH THE OBSERVED VALUES **Gain = Vout/Vin and dB = 20*log(Gain)** (2 Points) Table 4: First Circuit Table Frequency Vout Vin Phase Expect. Phase Gain dB 10 2 0 20 2 0 50 2 15 100 2 15 200 2 20 500 2 45 1,000 2 65 2,000 2 75 5,000 2 85 10,000 2 85 20,000 2 85 50,000 2 85 1. Explain briefly how this circuit works. What is causing the change in gain? (1 pts) 2. Calculate the cut-off frequency of this circuit. (1 pts) 3. At what phase angle should you expect to see the cutoff frequency? Look up online. (1 pts) 4. Using software (e.g. excel, matlab, etc) create a Bode magnitude plot (gain vs frequency) and a Bode phase plot (phase vs frequency). Use the in-class instructions. (1 pts) Circuits Experiment #2 FILL THE TABLE WITH THE OBSERVED VALUES **Gain = Vout/Vin and dB = 20*log(Gain)**

BIOMEDE 3702 (2 Points) Table 5: Second Circuit Table Frequency Vout Vin Phase Expec. Phase Gain dB 10 2 0 20 2 5 50 2 30 100 2 30 200 2 40 500 2 90 1,000 2 130 2,000 2 150 5,000 2 170 10,000 2 170 20,000 2 180 50,000 2 180 1. Calculate the cut-off frequency of this circuit. Reference the 2 nd Order Filter section here . (1 pts) 2. At what phase angle should you expect to see the cutoff frequency? Look up online. (1 pts) 3. Using software (e.g. excel, matlab, etc) create a Bode magnitude plot (gain vs frequency) and a Bode phase plot (phase vs frequency). Overlay each plot with the plot of the previous circuit. What stands out between these two bode plots? (1 pts) 4. What can you explain to be causing the phase change in each circuit? Refer to class or look up online. (1 pts) Circuits Experiment #3

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BIOMEDE 3702 FILL THE TABLE WITH THE OBSERVED VALUES **Gain = Vout/Vin and dB = 20*log(Gain)** (2 Points) Table 6: First Circuit Table Frequency Vout Vin Gain dB 10 2 20 2 50 2 100 2 200 2 500 2 1,000 2 2,000 2 5,000 2 10,000 2 20,000 2 50,000 2 100,000 2 200,000 2 500,000 2 1. Explain briefly how this circuit works. What is causing the change in gain? (1 pts) 2. Calculate the two cut-off frequencies of this circuit. (1 pts) 3. Using software (e.g. excel, matlab, etc) create the Bode Magnitude plot (gain vs frequency) of this circuit. (1 pts) 4. What kind of band (or cutoff frequencies) would you select for a bandpass filter filtering each biopotential signal: EKG, EEG, and EMG? Approximations are acceptable. (3 pts) Challenge Question 5: 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 in Tinkercad a passive band-stop filter (notch filter) for 50 Hz power-line noise (found in most European countries).