DEPARTMENT OF ELECTRICAL ENGINEERING LAB WORK EE301 ELECTRONIC CIRCUITS EXPERIMENT : 5 TITLE : ACTIVE FILTERS OUTCOME : Upon completion of this unit, the student should be able to: 1. gain experience with design and construction of active filter circuits. 2. explore simple active low pass and high pass filter concepts and functional circuits. 3. develop skills with the laboratory equipment. MATERIALS REQUIRED: i. Resistors 2 x 1 kω, and 10 kω. ii. Integrated Circuit series 741 iii. DC Power Supply (13-15 Vdc) iv. Analogue / Digital Multimeter v. Oscilloscope vi. Laboratory Trainer
Part 1: THEORY ACTIVE LOW-PASS FILTER At low frequencies, the capacitor has an extremely high capacitive reactance. At higher frequencies, the capacitive reactance of Cf decreases. This causes the voltage gain to decrease due to the increased amount of negative feedback. When Xcf = Rf, the voltage gain equals 70.7% of its midband value. ACTIVE HIGH-PASS FILTER At high frequencies, Xc1 0 Ω and the voltage gain Av, equals Rf/R1. At very low frequencies, Xc1 Ω and the voltage gain Av approaches zero. Note: In the circuits below the pin numbers for the various op amp connections are shown. Pins not shown are to be left unconnected. Part 2: LABORATORY PROCEDURE PROCEDURE A: Part 1: ACTIVE LOW-PASS FILTER The op-amp circuits are the only type of active circuit that we will encounter in EE301. Active circuits require an external source of energy to operate properly. Figure below shows a picture of the LM741 op-amp that we will use, with the pin numbers conventionally labeled (for more detail, a copy of the LM741 data sheet is posted at the class web site - CIDOS). Most op-amps have the same pin configuration. Use the outputs of your bench power supply, adjusted appropriately, for the +/- 13 Vdc sources.
1. Assemble the non-inverting ACTIVE LOW-PASS FILTER circuit shown in figure 1 below. 2. Remember to shut off the +/-13 V supply before assembling a new circuit. 3. Add a capacitor of 1uF parallel with the Rf on your circuit. 4. Apply a 1 Volt amplitude, 1 khz sine wave at the input. 5. Display both input and output on the oscilloscope. Figure 1: Active Low Pass circuit 6. Make a plot of the input / output waveforms in your lab report. Note: In the circuits above change all resistor (1 kω to 2 kω) and (10 kω to 22 kω) also change the op-amp supply from +/- 15 to +/- 13Vdc.
PROCEDURE B: Part 2: ACTIVE HIGH-PASS FILTER 1. Assemble the non-inverting ACTIVE HIGH-PASS FILTER circuit shown in figure 2 below. 2. Remember to shut off the +/-13 V supply before assembling a new circuit. 3. Add a capacitor of 1uF before the R1 on your circuit. (series) 4. Apply a 1 Volt amplitude, 1 khz sine wave at the input. 5. Display both input and output on the oscilloscope. 6. Adjust the frequency generator until you get a stabile output waveform. 7. Make a plot of the input / output waveforms in your lab report. Figure 2: Active High Pass circuit Note: In the circuits above change all resistor (1 kω to 2 kω) and (10 kω to 22 kω) also change the op-amp supply from +/- 15 to +/- 13Vdc.
Part 3: RESULT (GRAPH SECTION) Part 1: ACTIVE LOW-PASS FILTER Be sure to note the scale Volt/div and Time/div settings. Graph 1.1: Input waveforms Graph 1.2: Output waveforms
Part 2: ACTIVE HIGH-PASS FILTER Be sure to note the scale Volt/div and Time/div settings. Graph 2.1: Input waveforms Graph 2.2: Output waveforms
Part 4: DISCUSSION Write discussion base for your result of the experiment and most importantly, what you learned from performing it. It is also encouraged to include personal statements and suggestions about the lab activities. Part 5: CONCLUSION Write conclusions base for your outcome of the experiment and most importantly, what you learned from performing it.