EE 420L – Engineering Electronics II Lab – Lab 1
Email:
skellj1@unlv.nevada.edu
·
Simulation and implementation of various RC circuits.
Pre-Lab
·
Request a CMOSedu account from Dr. Baker
prior to the first day of lab.
·
Create a webpage for your EE 420L lab reports.
·
Read the lab write up prior to coming to lab.
Lab Tasks
·
Simulate (and verify simulation results with measurements) the
circuits seen in figures 1.21, 1.22, and
1.24 (using a 1 uF capacitor in place of the 1 pF
capacitor) of the book.
o
Circuit schematic
showing values and simulation parameters (snip the image from LTspice).
o
Hand calculations to
detail the circuit's operation.
o
Simulation results using
LTspice verifying hand calculations.
o
Scope waveforms
verifying simulation results and hand calculations.
o
Comments on any
differences or further potential testing that may be useful (don't just give
the results, discuss them).
·
For the AC response seen in Fig. 1.23 generate a table showing some representative
measurement results (frequency, magnitude, and phase).
------------------------------------------------------------------------------------------------------------
Experiment 1: Figure 1.21
AC Analysis
In this AC analysis, we see that the magnitude
begins to drop at -20db/dec starting at the cutoff
frequency,
which can be calculated in an RC circuit by
Figure 1.23, AC Magnitude and Phase Plots for RC
Circuit in Fig. 1.21
LTSPICE Cursor Data for AC Analysis
Calculating Magnitude (V) from Magnitude (dB)
For f = 200 Hz, Mag (dB) = -4.11
The table below was generated using values taken
from the LTSPICE simulation above.
|
Frequency |
Magnitude (V) |
Magnitude (dB) |
Phase (degrees) |
|
2 Hz |
0.999 |
-685.75e-6 |
-0.719 |
|
20 Hz |
0.992 |
-68.04e-3 |
-7.16 |
|
200 Hz |
0.623 |
-4.11 |
-51.5 |
|
2 kHz |
0.079 |
-22.01 |
-85.5 |
|
20 kHz |
0.008 |
-41.98 |
-89.54 |
Experimentally Measured Data for AC Analysis
f = 2 Hz
f = 20 Hz
f = 200 Hz
f = 2 kHz
f = 20 kHz
Calculating Magnitude (dB) from Magnitude (V)
For f = 200 Hz, Mag (V) = 0.660 V
The table below was generated using values taken
from the experimental measurements above.
|
Frequency |
Magnitude (V) |
Magnitude (dB) |
Phase (degrees) |
|
2 Hz |
1.080 |
0.69 |
0.36 |
|
20 Hz |
1.060 |
0.51 |
7.194 |
|
200 Hz |
0.660 |
-3.61 |
49.51 |
|
2 kHz |
0.120 |
-18.41 |
74.26 |
|
20 kHz |
0.050 |
-26.02 |
-134.7 |
The function generator, shown in the “Test Setup”
section of experiment 1 (below), is set to output
an input sine wave with an amplitude of 1V, which
should theoretically have a peak-to-peak voltage of
2 V. However, as we can see from the experimental
results, in more than one of the scope images, the
input waveform has a peak-to-peak voltage greater than
2, which causes our magnitude (|Vout/Vin|) to
be greater than 1 at lower frequencies. In the
future, we could adjust the function generator to output
a lower amplitude input signal at low frequencies
to accommodate for this overage, and get experimental
results closer to our simulation results.
Transient Analysis
Hand-Calculated Magnitude, Phase, and Time Delay
LTSPICE Schematic
Test Setup (Breadboard and Function Generator)
LTSPICE Simulation Waveform
Experimental Waveform
Our experimental waveform matches our simulation waveform
almost perfectly. Our hand calculated
phase angle is only 2 degrees off from our experimental
phase. In the future, we could use different
scope probes, test the phase using the different
probes, and take the average to bring our experimental
value closer to our simulated and hand calculated
value.
Experiment 2: Figure 1.22
AC Analysis
We see the phase make an inverted bell curve shape
in this circuit due to charge sharing between the
two capacitors. Due to the capacitor in parallel
with the 1k resistor, our cutoff frequency jumps down
the frequency axis to just around 10 Hz.
Transient Analysis
Hand-Calculated Magnitude, Phase, and Time Delay
LTSPICE Schematic
Test Setup (Breadboard and Function Generator)
LTSPICE Simulation Waveform
Experimental Waveform
Again, our experimental waveform matches our simulated
waveform almost perfectly. I accidentally
connected the channel 2 probe to the input instead
of the channel one probe, so the trace colors
are inverted in this image from others throughout
the lab report. However, we see from this transient
analysis of the waveforms that our experimental phase
angle only differs from our hand-calculated and
simulated phase angle by 0.3 degrees. Our calculated
magnitude differs from our experimental magnitude
by roughly 60 mV, reasonably accurate. In the
future, we could adjust the compensation of the scope
probe using a screwdriver and remeasure, or change
the output of the function generator such that the
peak-to-peak voltage of the input signal to our
circuit measures 2Vpp rather than 2.14Vpp.
Experiment 3: Figure 1.24
AC Analysis
The cutoff frequency of the RC circuit above
matches that from experiment one, 159 Hz, because the
same resistor and capacitor were used.
Transient Analysis
Hand-Calculated Plots for Charging and Discharging
the Load Capacitor
As is noted in the hand calculations, the capacitor
can never fully charge. For a capacitor to reach 99.7% of its
full capacity, it needs to be charging for 5 time constants. Because one time
constant is 1 ms, and our input source
only stays high for 3 ms,
the capacitor will never reach its full charge capacity. However, because the input
remains
low for 7 ms, the capacitor
does have time to fully discharge.
LTSPICE Schematic
Test Setup (Breadboard and Function Generator)
LTSPICE Simulation Waveform
Experimental Waveform
Our square wave input is not perfectly square.
This is because we did not correctly compensate our
scope probe. In the future, we could use a screwdriver
to adjust the input capacitance of the scope
probe to bring our rising edge up and our falling edge
down and correct these bizarre looking curves
in the yellow waveform above. Regardless of the
lack of compensation, our output waveform still matches
our simulations and hand calculations.