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LAB 1 – ACTIVE FILTERS 1. Materials Required Equipment 11111- protoboard dual dc power supply (+15 V dc and -15 V dc) medium frequency function generator (1 MHz) standard oscilloscope (10 MHz) assortment of test leads and hookup wire Parts List 112- op amp (741 or equivalent) 1-k resistors 10-k resistor 222- 22-k resistor 0.001-F capacitor 0.01-F capacitor 2. Pre-lab Print the LM741 and LM148 data sheets and the note, “Plotting Frequency Response”. Review these and bring them to the lab. Hand-sketch the theoretical straight-line gain plot and mark on it the cutoff frequency for each of the five filters. 3. Procedure For this lab you will be using type 741 operational amplifiers, either a single LM741 or an LM148, which has four such circuits. Connect +15 Volts to the V+ pin and -15 Volts to the V- pin, as shown in Figure 1. The individual experiments don’t specify pin numbers, so you will have to refer to the appropriate data sheet for these. + V+ Gnd Circuit Ground V- - Dual Power Supply Protoboard Figure 1. Power Supply Connections. LAB 1 – ACTIVE FILTERS Follow these steps for each of the five active filters. 1. Make a theoretical straight-line Bode plot of the filter response by using Excel as described in the memo, “Plotting Frequency Response”. 2. Construct the circuit. 3. Have the wiring checked by someone other than the person who connected it. 4. Apply the power and measure the Voltages at the two amplifier inputs and its output; all should be at 0 Volts. Correct the circuit if necessary. 5. Set the signal generator amplitude to 1 V peak-to-peak. (Note: the generator output level meter is calibrated only when the unit is driving 50 . The actual Voltage will be about twice the indicated one. Measure the input Voltage with the same device that you use to measure the output Voltage.) 6. Measure the gain from 1 decade below the breakpoint to 1 decade above it. Use 5 points per decade at frequencies that are equally spaced on a log scale. (For example, choose multiples of 1, 1.6, 2.5, 4, 6.3, and 10). Enter Vin and Vout on the spreadsheet you created in step 1. 7. Program Excel to calculate the Voltage gains in dB = 20∙log10(Vout/Vin), and use Excel to plot these and the theoretical straight-line plot on the same chart. (Plot just the gain, not the phase.) 8. For each filter circuit, compare the theoretical and measured responses, including the cutoff frequency, the flat gain, and the gain slope. Explain any significant differences. 5. Circuits R1 10 k - Vout 741C + Signal Generator R2 1 k C1 0.001 F Figure 2. Non-inverting, Single-pole Low-pass Filter. 2 LAB 1 – ACTIVE FILTERS R2 10 k C1 0.001 F R1 10 k Vout 741C + Signal Generator R3 1 k Figure 3. Inverting, Single-pole Low-pass Filter. C1 0.01 F Signal Generator R1 22 k R2 22 k - Vout 741C + C2 0.01 F R3 1 k Figure 4. Non-inverting, Two-pole Low-pass Filter. C1 0.001 F - Vout 741C + Signal Generator R1 10 k Figure 5. Non-inverting, Single-pole High-pass Filter. 3 LAB 1 – ACTIVE FILTERS R2 22 k C1 0.01 F C2 0.01 F - Vout 741C + Signal Generator R1 22 k Figure 6. Non-inverting, Two-pole High-pass Filter. 6. Discussion Questions 1. 2. 3. 4. How closely did your results match the theoretical ones? Are the differences consistent with the component tolerances? If not, what are likely error sources? Which, if any, properties of the op amp significantly affect the frequency response of these circuits? 7. Lab Report Each group will submit a lab report, using the Lab Report Template and following Sample Lab Report and the guidelines in Professor Rockland’s Quick Guide to Writing Laboratory Reports (all on the ECET-324 CD-ROM). These will include a cover sheet, table of contents, and sections on your pre-lab work, the objectives of the lab, descriptions of the experiments, and discussion of the results. The descriptions and discussion will cover each of the five active filters. 4