Lab 6 for First Order RC Circuits | EE 271, Assignments of Microelectronic Circuits

Download Lab 6 for First Order RC Circuits | EE 271 and more Assignments Microelectronic Circuits in PDF only on Docsity! - p. 1 of 6 - UNIVERSITY ☺F P☺RTLAND Sch☺☺l ☺f Engineering EE271-Electrical Circuits Laboratory Spring 2004 Dr. Aziz S. Inan & Dr. Joseph P. Hoffbeck Lab Experiment #6: First-Order RC Circuits - p. 2 of 6 - First-Order RC Circuits I. Objective In this experiment, the students will make measurements and observations on the step and sinusoidal steady-state responses of simple first-order RC circuits. II. Procedure PART 1: Step Excitation of First-Order RC Circuits Pre-lab Assignment 1.a: A first-order capacitive circuit is excited by a periodic rectangular pulse train as shown in Fig. 1. The elements values of the circuit are given by R1=10 kΩ and C1=10 nF respectively. Calculate the following: • The time constant τ of this circuit. • Approximate time it takes for the capacitor to fully charge or discharge. (The time for the capacitor to fully charge or discharge corresponds to the time it takes for the capacitor voltage to reach approximately 99% of its final value.) VC1 VS R1= 10 kΩ C1= 10 nF 2.5 V −2.5 V Scope Channel 2 Output Signal Scope Channel 1 Input Signal LPF Fig. 1. First-order RC circuit connected like a Low-Pass Filter (LPF). Lab Experiment 1.a: Construct the first-order RC circuit shown in Fig. 1 using R1=10 kΩ and C1=10 nF. Measure and record the actual values of the resistor and the capacitor used in your circuit. Use the function generator available on your bench to supply the periodic rectangular pulse train to the circuit. Set the function generator to provide the rectangular pulse train represented with source voltage VS(t) which oscillates between −2.5 V and 2.5 V (i.e., 5 V peak-to-peak) with frequency of oscillation 5001 == Tf Hertz (Hz). (Note that T=f −1 is the period of the periodic pulse train). Use the oscilloscope to monitor the source voltage VS(t) and the capacitor voltage VC1(t) simultaneously. - p. 5 of 6 - Lab Experiment 1.e: Construct the first-order RC circuit shown in Fig. 4. Measure and record the actual value of the 100 nF capacitor used. Set the source frequency to 50 Hz. Observe both VS(t) and VC12(t) waveforms on the scope simultaneously. Measure the new time constant from the VC12(t) waveform. PART 2: Sinusoidal Excitation of First-Order RC Circuits Pre-lab Assignment 2: Replace the rectangular pulse source in the RC circuit in Fig. 1 with a sinusoidal source as shown in Fig. 5. Note that the cutoff frequency of this first-order LPF circuit is defined as the frequency at which the peak value of the output signal is ( )21 (or ~0.707) times the peak value of the input signal and is given by ( ) ( )πτπ 2121 == RCfc (in Hz). This means that a sinusoidal input signal VS with an oscillation frequency below this cutoff frequency yields an output signal which is very close to the input signal (that is the input signal VS applied at the input port of the circuit results in an output signal at the output port of the circuit which is almost identical to the input signal) whereas a sinusoidal input signal VS with frequency above this cutoff frequency yields an output signal which has a much smaller peak value compared to the peak value of the input signal. Calculate the cutoff frequency of this LPF from the element values provided in the Fig. 5 using ( )RCfc π21= . Lab Experiment 2.a: Construct the circuit shown in Fig. 5. Observe both voltages VS(t) and VC1(t) on the scope simultaneously for 500 Hz, 5 kHz, and 50 kHz. Comment on your observations based on the cutoff frequency calculated in the pre-lab assignment. V C1 VS R1= 10 kΩ C 1= 10 nF 2.5 V − 2.5 V Scope Channel 2 Output Signal Scope Channel 1 Input Signal LPF Fig. 5. First-order LPF RC circuit excited by a sinusoidal source. Lab Experiment 2.b: Construct the circuit shown in Fig. 6. Observe both voltages VS(t) and VR1(t) on the scope simultaneously for 500 Hz, 5 kHz, and 50 - p. 6 of 6 - kHz. Comment on your observations based on the cutoff frequency calculated in the pre-lab assignment.. VR1 VS C 1= 10 nF R1= 10 kΩ 2.5 V − 2.5 V Scope Channel 1 Scope Channel 2 HPF Fig. 6. First-order HPF RC circuit excited by a sinusoidal source. III. Discussions & Conclusion 1. In this section, discuss the various aspects of Experiment # 6 and make some conclusions. In your write-up, you should at least address the following questions: 2. What was the objective of this experiment and was the objective achieved? 3. Did any of your measurements have more than 5% error? What was your maximum % error? 4. What sources of error may have contributed to the differences between the theoretical values and the measured values? 5. Other comments relevant to this experiment.