Title: AC Circuits II (RL)
Richard Madison Haynie
Partner: Joseph Gilgen
(All graphs are attached to back)
Objective:
In this lab the goal is to observe lowpass and high passfilters, how
they function and why they function as they do. Once this is done learn
how these filters can be used as either a garbage detector and filtering
out noise when added to an input signal.
Lowpass Filter:
Here the circuit shown in figure1 was constructed.
From theory the reactance of a capacitor is
given by
1
2
C
X
fC
π
=
which means when f is small X
C
is large and when f is large X
C
is small.
For this circuit this means when f is small enough
in
out
V
V
X
and when f is infinitely large
0
out
V
X
. Since
in
out
V
V
X
for small frequencies the circuit earns its name, lowpass filter. A low pass filter
is a voltage divider and the equation is
(
29
2
2
2
2
1
1
1
2
1
out
in
V
C
V
fRC
R
C
ϖ
π
ϖ
=
=
+
+
. The phase angle
can be found using
1
1
tan
90
2
fRC
φ
π

�
�
=

�
�
�
�
o
. To find the values of f that are small or large
enough for our expected results we compute a f
3dB
. From theory
3
1
2
dB
f
RC
π
=
and with this
circuit f
3dB
=1061Hz. The circuit was then driven with a frequency of 1065Hz and is shown in
graph1 with
.676
out
in
V
V
=
from theory
.706
out
in
V
V
=
differing by 4.2% from the experimental value.
Next f
3dB
is calculated experimentally by finding the frequency for which V
out
is 70.7% of V
in
.
The value found experimentally was f
3dB
=969Hz with
.716
out
in
V
V
=
(graph2), so f
3dB
from theory
and experimentally are approximately equal differing by 8.7%. The circuit was then driven with
96.98Hz which is much smaller then f
3dB
(our small frequency) shown in graph3. Indeed
0
out
V
V
X
which expected, from theory
.021
out
in
V
V
=
. The circuit was then driven with 49.36kHz
which is much greater then f
3dB
(our large frequency) shown in graph4. For this frequency V
out
is
greatly attenuated because V
out
approaches zero as f approaches infinity which was expected. The
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '08
 Tsong
 Highpass filter, Bandpass filter, Lowpass filter, Bandstop filter, Vin Vin Vout, Richard Madison Haynie

Click to edit the document details