Download lab 1 – active filters

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