EE 403W SENIOR PROJECT DESIGN
Spring 2015
Experiment 1
“Applications of the Spectrum
Analyzer”
using a Linear/Non-linear Power
Amplifier with Filtering
Kamila Dagilova
The Pennsylvania State University
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Table of Contents
INTRODUCTION ........................................................................................................................................ 3
PART A – WAVEFORM ANALYSIS........................................................................................................ 3
PART-B – MEASUREMENT OF A LINEAR/NON-LINEAR POWER AMPLIFIER WITH
FILTERING .................................................................................................................................................. 5
PART B1 ....................................................................................................................................................................6
PART B2 ................................................................................................................................................................. 10
PART B3 ................................................................................................................................................................. 11
PART B4 ................................................................................................................................................................. 15
PART B5 ................................................................................................................................................................. 17
PART B6 ................................................................................................................................................................. 20
APPENDIX ................................................................................................................................................ 22
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INTRODUCTION
The purpose of this experiment is to become familiar with the use and
applications of the spectrum analyzer. Spectrum analyzer is a tool that
helps to observe and measure electrical signals in frequency domain. It
presents information (e.g. about distortions) that is sometimes
impossible to see in the time domain. In part A of the experiment we
need to capture amplitude spectra of two waveforms – the sine and
square waves. In part B we need to use a pre-built 1 watt Linear/NonLinear Power Amplifier with filtering to generate distortions in class AB
and Class B operation modes.
PART A – WAVEFORM ANALYSIS
Our first task was to produce amplitude spectra of the sine and square
waves outputs with the help of HP function generator. The range of
frequencies should include at least the tenth harmonic. After we set the
generator to produce a 1 Vp sine wave at a frequency 10 kHz, we then
measured the amplitude on the oscilloscope, which was 2.05 Vpp
because the function generator output was expecting a 50 Ohm load, but
our oscilloscope was in High z mode. After adjusting the generator to
produce a signal of 1 V peak at the oscilloscope input, we captured an
image (Figure 1) with a span of 10 harmonics. When we changed the
generator’s waveform to square wave the peaks on the spectrum
analyzer became more distinct (Figure 2.)
For the last steps of part A we used the Fourier series expansion for a
square wave that predicted the amplitude for each spectral component
in the square wave, noting that the amplitudes of even harmonics equal
zero. By normalizing the harmonic amplitudes to the amplitude of the
fundamental (then 3rd, 5th, etc.) we obtain relative amplitudes, which
can also be expressed in decibels, by using the relationship dB =
20log(1/n) (where n is odd). The results can be seen in Table 1.
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Figure 1
Figure 2
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n
F (kHz)
1
2
3
4
5
6
7
8
9
10
20
30
40
50
60
70
80
90
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Amplitude
(Vp)=Vrms
4A/pi
0
4A/3pi
0
4A/5pi
0
4A/7pi
0
4A/9pi
Relative
(Vp)
1
0
1/3
0
1/5
0
1/7
0
1/9
Amplitude
(dB)
0
-9.54
13.979
-16.90
-19.08
Table 1
PART-B – MEASUREMENT OF A LINEAR/NON-LINEAR POWER
AMPLIFIER WITH FILTERING
For this portion of the lab we use a Pre-built 1-Watt Linear/Non-linear
Amplifier with filtering and the Oscilloscope/Spectrum analyzer to
examine the distortions produced by this amplifier in both Class AB and
Class B operation modes. The amplifier’s schematic, board layout, to
which we referred to, as well as the bill of materials can be found in
Appendix.
The goal of the circuit is to deliver 1 watt to an 8 Ohm load, avoiding
excessive distortions.
Here are the requirements:
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We use the Stage 2 of the amplifier, which is Class AB/Class B
configuration, because Stage 1 (Broadband linear/non-linear inverting
amplifier or a tuned linear/non-linear inverting amplifier or an active
low pass filter inverting amplifier) cannot deliver enough output
current to drive the load directly. As we will observe later, a stage-2 in
the Class B mode configuration displays a phenomenon known as crossover distortion because of the non-conducting (dead) zone of 00.7 V of
the bipolar transistor.
Part B1
For Configuration #1 (Broad band power amplifier) shown in Figure 3,
we need to determine the following:
a) The circuit’s natural -3dB (Gain = 0.707 of the Maximum Value)
Cutoff frequency (Fc) with the gain adjust knob of RP1 set in the
Full Clockwise 0 Ohm Position (R = R3+RP1=1 kOhm + 0 kOhm =
1 kOhm)
b) The circuit’s natural -3dB (Gain = 0.707 of the Maximum Value)
Cutoff frequency (Fc) with the gain adjust knob of RP1 set in the
Full Counter-clockwise 10 kOhm Position (R = R3+RP1=1 kOhm +
10 kOhm = 11 kOhm)
c) The FFT spectrum plot using the Oscilloscope’s FFt function under
the conditions described above.
Figure 3
Following the steps 1-18 we have recorded the results to the
engineering notebook. Step 6 determines the circuits natural -3dB
(Gain = 0.707 of the Maximum Value) Cutoff frequency (Fc) with the
gain adjust knob of RP1 set in the Full Clockwise 0 Ohm Position (R =
R3+RP1=1 kOhm + 0 kOhm = 1 kOhm), which is 3.67 MHz under which
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the output sine wave (channel 2) is distorted (amplifier’s limit) (Figure
4.)
Figure 4
In step 8, we get the frequency value, which is 2.69 MHz - the circuits
natural -3dB (Gain = 0.707 of the Maximum Value) Cutoff frequency (Fc)
with the gain adjust knob of RP1 set in the Full Counter-clockwise 10
kOhm Position (R = R3+RP1=1 kOhm + 10 kOhm = 11 kOhm) (Figure 5.)
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Figure 5
After completing the adjustments in steps 12-14 (WaveTek set up) we
reconnected HP generator (Figure 6), switched the Oscilloscope to FFT
mode and adjusted the Frequency and Amplitude settings to display as
many harmonics as possible (Figure 7). Figures 8 and 9 show the plots
of the output wave due to HP/WaveTek generator alone, after we
remove the BNC cable connected to J2/J1 of the Power Amplifier.
Figure 6
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Figure 7
Figure 8
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Figure 9
Part B2
For Configuration #2 (Broad band power amplifier) shown in Figure 10,
we need to repeat steps 15-18 of Part B1, the images of the results of
steps 15, 16, 17, 18 are shown in Figures 11, 12, 13, 14 accordingly.
Figure 10
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Figure 11
Figure 12
Figure 13
Figure 14
Part B3
For Configuration #3 (Active Low-Pass Filter power amplifier) shown in
Figure 15, we need to determine the following:
a) The circuit’s natural -3dB (Gain = 0.707 of the Maximum Value)
Cutoff frequency (Fc) with the gain adjust knob of RP1 set in the
Full Clockwise 0 Ohm Position (R = R3+RP1=1 kOhm + 0 kOhm =
1 kOhm)
b) The circuit’s natural -3dB (Gain = 0.707 of the Maximum Value)
Cutoff frequency (Fc) with the gain adjust knob of RP1 set in the
Full Counter-clockwise 10 kOhm Position (R = R3+RP1=1 kOhm +
10 kOhm = 11 kOhm)
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c) The FFT spectrum plot using the Oscilloscope’s FFt function under
the conditions described above.
d) The calculated value of Fc for this Amplifier in Engineering
notebook.
Figure 15
The results of steps 1-18 were recorded to the engineering notebook.
Step 6 determines the circuits natural -3dB (Gain = 0.707 of the
Maximum Value) Cutoff frequency (Fc) with the gain adjust knob of RP1
set in the Full Clockwise 0 Ohm Position (R = R3+RP1=1 kOhm + 0
kOhm = 1 kOhm), which is approximately 180 kHz with the output V
~5.6 V (Figure 16.) The result is not much different from the calculated
value, which was 160 kHz by formula Fc = 1/(2pi*R*Ct) (with Ct=1e-9F,
R = 1 KOhm).
Figure 16
In step 8, we get the frequency value, which is ~17 kHz - the circuits
natural -3dB (Gain = 0.707 of the Maximum Value) Cutoff frequency (Fc)
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with the gain adjust knob of RP1 set in the Full Counter-clockwise 10
kOhm Position (R = R3+RP1=1 kOhm + 10 kOhm = 11 kOhm) (Figure
17.) The result is not much different from the calculated value, which
was 14.476 kHz by formula Fc = 1/(2pi*R*Ct) (with Ct=1e-9F, R = 11
KOhm).
Figure 17
After completing the adjustments in steps 12-14 (WaveTek set up) we
reconnected HP generator (Figure 18), switched the Oscilloscope to FFT
mode and adjusted the Frequency and Amplitude settings to display as
many harmonics as possible (Figure 19). Figures 20 shows the plot of
the output wave due to WaveTek generator alone, after we remove the
BNC cable connected to J1 of the Power Amplifier. (Due to incorrect
brightness settings some of our waveforms are not bright, and we
noticed that later.)
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Figure 18
Figure 19
Figure 20
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Part B4
For Configuration #4 (Active Low-Pass Filter power amplifier) shown in
Figure 21, we need to repeat steps 15-18 of Part B3, the images of the
results of steps 15, 16, 17, 18 are shown in Figures 22, 23, 24, 25
accordingly.
Figure 21
Figure 22
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Figure 23
Figure 24
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Figure 25
Part B5
For Configuration #5 (Tuned power amplifier) shown in Figure 26, we
need to determine the following:
a) The second order circuit’s 2 natural -3dB (Gain = 0.707 of the
Maximum Value) Cutoff frequencies (FCL and FCU) with the gain
adjust knob of RP1 set in the Full Clockwise 0 Ohm Position (R =
R3+RP1=1 kOhm + 0 kOhm = 1 kOhm)
b) The second order circuit’s 2 natural -3dB (Gain = 0.707 of the
Maximum Value) Cutoff frequency (Fc) with the gain adjust knob
of RP1 set in the Full Counter-clockwise 10 kOhm Position (R =
R3+RP1=1 kOhm + 10 kOhm = 11 kOhm)
c) The FFT spectrum plot using the Oscilloscope’s FFt function under
the conditions described above.
d) The calculated value of Resonant frequency for this Amplifier in
Engineering notebook.
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Figure 26
The results of steps 1-18 were recorded to the engineering notebook.
Step 6 determines the second order circuit’s 2 natural -3dB (Gain =
0.707 of the Maximum Value) Cutoff frequencies (FCL and FCU) with the
gain adjust knob of RP1 set in the Full Clockwise 0 Ohm Position (R =
R3+RP1=1 kOhm + 0 kOhm = 1 kOhm) which are approximately
0.93MHz and 1.13 MHz (Figure 27.) In step 8, we get the second order
circuit’s 2 natural -3dB (Gain = 0.707 of the Maximum Value) Cutoff
frequency (Fc) with the gain adjust knob of RP1 set in the Full Counterclockwise 10 kOhm Position (R = R3+RP1=1 kOhm + 10 kOhm = 11
kOhm, the range of which is 0.903 kHz – 1.064 kHz (Figure 28.)
After completing the adjustments in steps 12-14 (WaveTek set up) we
reconnected HP generator (Figure 29), switched the Oscilloscope to FFT
mode and adjusted the Frequency and Amplitude settings to display as
many harmonics as possible (Figure 30). Figures 31 and 32 show the
plots of the output wave due to HP/WaveTek generator alone, after we
remove the BNC cable connected to J2/J1 of the Power Amplifier.
The calculated value for resonant frequency is 1.007 MHz – obtained by
formula Fr = 1/(2pi*sqrt(LtCt)) with Ct = 1e-9 F, and Lt = 25e6 Henrys.
Kamila Dagilova EE403W Experiment 1
Figure 27
Figure 28
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Figure 29
Figure 30
Figure 31
Figure 32
Part B6
For Configuration #6 (Tuned power amplifier) shown in Figure 33, we
need to repeat steps 15-18 of Part B5, the images of the results of steps
15, 16, 17, 18 are shown in Figures 34, 35, 36, 37 accordingly.
All necessary calculations are recorded in the lab notebook.
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Figure 33
Figure 34
Figure 35
Figure 36
Figure 37
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APPENDIX
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