electrical engineer lab2 dr. lars hansen - david sanchez engineer lab2 dr. lars hansen david sanchez...
TRANSCRIPT
Electrical Engineer
Lab2
Dr. Lars Hansen
David Sanchez
University of Texas at San Antonio
May 5th, 2009
Electrical Engineer Lab 2
David Sanchez Project 1 Page 2 of 15
Table of Contents Abstract ......................................................................................................................................................... 3
1.0 Introduction and Product Description .............................................................................................. 3
1.1 Problem Specifications ...................................................................................................................... 3
1.1.1 Project #1(A) Specifications ...................................................................................................... 3
1.1.2 Project #1(B) Specifications ...................................................................................................... 4
1.1.3 Project #1(C) Specifications ...................................................................................................... 5
1.2 Problem Description ......................................................................................................................... 5
1.2.1 Project 1 (A) Description ........................................................................................................... 5
1.2.2 Project 1 (B) Description ........................................................................................................... 5
1.2.3. Project 1 (C) Description ........................................................................................................... 6
2.0 Initial Design and PSpice Simulation ................................................................................................. 6
2.0.1 Project 1 (A) Design and PSpice Simulation .............................................................................. 6
2.0.2 Project 1 (B) Design and PSpice Simulation .............................................................................. 9
2.0.3 Project 1 (C) Design and PSpice Simulation ............................................................................ 10
3.0 Protoboard Circuit........................................................................................................................... 11
4.0 Printed Circuit Board (PCB) Design ................................................................................................. 13
5.0 Conclusion ....................................................................................................................................... 15
6.0 References ...................................................................................................................................... 16
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Abstract For Lab II, project 1 was split up into three different stages; from this stages one will
achieve a finished product on a PCB board. The first phase of the project was named 1(A), it
consisted of building an active unity gain low pass filter. Furthermore, this filter had to be
simulated on Pspice software and produce a prototype in a protoboard for demonstration
purposes. Secondly, project 1(B) was developed to achieve a volume control, pre amplifier, and
class AB power amplifier was developed. Similarly, this phase will have some of the aspects
that took place in project 1(A), one will simulate it in Pspice software and adding the final result
into a protoboard. Moreover, this phase will be connected directly after the low pass filter stage
1(A), which will be connected in the protoboard prototype also. Finally, project 1(C) included
generating the required files to fabricate a PCB board, containing all three parts of the project.
After the group received the protoboard they had to find any traces which were not well marked
by the fabrications, the group used the VMM to measure this. Additionally, the group members
had to start populating the PCB board and demonstrate it to illustrate the achievements of the
project.
1.0 Introduction and Product Description EE 4113 will introduce the students to real implementation topics and procedures that
will be helpful in the professional field. This course will work simultaneously with Senior
Design class which will give the student a clear way of presenting their ideas to the public. This
course will also guide the students in specific topics that are currently used in today’s
engineering society.
1.1 Problem Specifications
1.1.1 Project #1(A) Specifications 1. Use ±14V for DC power.
2. Use active-filter architecture based on the LF411-type (KF351).
3. The passband ripple should be less than or equal to 2dB.
4. High-frequency passband corner frequency fp,H = 14kHz.
5. High-frequency stopband corner frequency fS,H = 50kHz.
6. The circuit has a lowpass response and has gain within spec down to DC.
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7. The stopband must have an attenuation of at least 40dB below Ap,max over the stopband
frequency range f ≥ 50kHz.
8. Include 10μF electrolytic power-supply bypass capacitors where the two DC power lines
enter the circuit.
9. Include smaller 0.1 μF bypass capacitors close to the positive and negative power supply pins
of all op-amps in your circuit.
10. Use a 10kΩ load resistor for the output load of the filter.
1.1.2 Project #1(B) Specifications
1. Use ±14V for DC power.
2. Use an active-filter architecture based on the LF411-type (KF351)
3. The passband ripple should be less than or equal to 2dB.
4. High-frequency passband corner frequency fp,H = 14kHz.
5. High-frequency stopband corner frequency fS,H = 50kHz.
6. The circuit has a lowpass response and has gain within spec down to DC.
7. The stopband must have an attenuation of at least 40dB below Ap,max over the stopband
frequency range f ≥ 50kHz.
8. Include 10μF electrolytic power-supply bypass capacitors where the two DC power lines
enter the circuit.
9. Include smaller 0.1μF bypass capacitors close to the positive and negative power supply pins
of all op-amps in your circuit.
10. Include smaller 0.1μF bypass capacitors close to the drains of the two power MOSFETs.
11. Include even smaller 0.01μF bypass capacitors close to the drains of the two power
MOSFETs.
12. The passband voltage gain must be adjustable over the range -10dB ≤Ap,max ≤ +20dB.
13. Use a class-AB push-pull final output stage constructed from an IRF510 and IRF9510 power
MOSFET pair. Use appropriate biasing and possibly negative feedback with an op-amp in
order to minimize cross-over distortion.
14. The circuit must be capable of generating an output voltage of at least 20Vpp into a 20Ω load
when driven by a 1000Hz input sine wave of amplitude 2.0 Vpp. The output sine wave should
have at Total Harmonic Distortion (THD) less than 1%.
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1.1.3 Project #1(C) Specifications 1. The maximum allowable board size is 4.5" x 3.25" = 4500 x 3250 mils.
2. The BOTTOM layer should be the routing layer. This facilitates soldering since parts with
radial leads are difficult to solder when the traces are on the same side as the part. It also
makes for an easier connection to the BNC connectors whose center pins exit on the
BOTTOM side of the board.
3. The TOP layer and any unused area on the BOTTOM layer should be used for ground plane.
Be sure and place dynamic copper over these areas and make sure to attach to net 0.
4. DC ±14V power and ground will come into the board via wires and be soldered to the board.
5. Input and output signals will enter and leave the board via BNC connectors.
1.2 Problem Description
1.2.1 Project 1 (A) Description The first stage of the entire project was to build an active unity gain low pass filter that
will meet the specifications listed above. To achieve this low pass filter design the group used a
program developed by Texas Instruments called Filter Pro. The group decided to develop a
Butterworth filter to achieve the given specifications. Furthermore, a low noise junction gate
field-effect transistor dual amplifier was used. Moreover, the DIP utilized in this phase of the
project was ST’s TL072 which has small harmonic distortion. The main specifications were that
the high frequency passband corner frequency had to be equal to 14 kHz. Additionally, the
stopband corner frequency had to be equal to 50 kHz. Along with these requirements the project
also required a passband ripple had to be less than or equal to 2dB. Finally, the stopband should
have an attenuation of at least 40db/decade below Ap, max over the stopband frequency range
greater or equal to 50 kHz. After all this specifications where met, the group started simulating
in Pspice for the required waveforms. Lastly, the schematic was built in the protoboard for real
value testing.
1.2.2 Project 1 (B) Description This stage of the project consisted on designing and developing a volume control, pre
amplifier, and a class AB amplifier. The specifications for this phase where: The volume
control had to attenuate between the passband voltage gain which was -10dB and +20dB, it also
had to achieve a voltage output of 20 volts peak to peak with no visible Total Harmonic
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Distortion (THD). Furthermore, this output voltage had to be driven by an input sine wave with
amplitude 2 volts peak to peak and with frequency of 1 kHz. After simulating this circuit in
Pspice and looking at its final results it was implemented to the protoboard (Remember that the
first phase is already on the protoboard, the second phase comes directly after the first phase).
1.2.3. Project 1 (C) Description The third stage for this project was to develop the files needed to fabricate a printed
circuit board (PCB). Prior to developing these files the students had to read and fulfill all the
examples that were given in the PCB Tutorial provided by Dr. Hansen. This tutorial will be a
clear guide on how to develop this specific PCB. Moreover, the PCB will have the available
space to populate the board with the specific components discussed in parts A and B. After the
PCB is fabricated the group started testing the board for any shorts. Finally, the group began
populating process on the board. The PCB board then was tested for previous specifications.
2.0 Initial Design and PSpice Simulation Initial design for this project requires basic understanding of the components that where
going to be utilize in this project. Afterwards, the components where simulated in Pspice to have
a clear understanding of how the system will work. This will help the group know how each
phase of the circuit will react; it will also help achieve the specifications of each stage. It also
will benefit the group to quickly simulate any changes in the real circuit and simulate in Pspice
to see if there was any improvement on the system.
2.0.1 Project 1 (A) Design and PSpice Simulation For the first stage of the project the group had to design an active unity gain low pass
filter. Furthermore, the group members started their research on how the lowpass filters worked
and their main components. Afterwards, the group decided to design a Butterworth low pass
filter to achieve the specifications for the given project. The group started simulating on the
“Filter Pro simulation from Texas Instruments” (Texas Instruments), this will give the required
frequency and right attenuation. The filter will consist of two LF 411 operational amplifiers,
four capacitors, five resistors (including the load resistor which will be removed to unify project
1 (B) to this phase).
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The implementation stage started after the team knew which components where going to
be taken into consideration for the design. The group started simulating the lowpass filter with
resistor values with tolerances of 5% and capacitor values of 10%. After this values where
inserted into Pspice, the group decided to simulate it using the Monte Carlo method which will
give the user the various outputs one can achieve with the given inputs. “Monte Carlo methods
are a class of computational algorithms that rely on repeated random sampling to compute their
results. Monte Carlo methods are often used when simulating physical and mathematical
systems. Because of their reliance on repeated computation and random or pseudo-random
numbers, Monte Carlo methods are most suited to calculation by a computer” (Monte Carlo
Method). Monte Carlo plot verifies that passband ripple < 2dB also shows all possibilities using
resistor and cap values with tolerance. This plot will be illustrated in figure 1.0.
After modeling the schematic in Pspice with the Monte Carlo method the group was
ready to implement the real values into the design. The parts where tested with the Digital
measurement equipment available in Lab 1. Figure 2 shows the PSpice schematic of the lowpass
filter and all the values of the components and the power supplied to the circuit.
Figure 1 Monte Carlo Simulation
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After inserting the schematic into Pspice the group decided to run the simulation to verify
that the circuit will meet the specifications listed for the project. By looking at Figure 3 one can
see that the specifications for this project still meet, less than 2dB ripple and at 50 kHz less than
40 dB.
Figure 2 Real Values used for the Lowpass Filter
Figure 3 Simulation for Real Values in Lowpass Filter
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2.0.2 Project 1 (B) Design and PSpice Simulation Stage of two of this project consisted of creating the volume control, pre amplifier, and a
class AB amplifier. The basic schematic for this stage was provided by Dr. Hansen, but the
group had to figure out the values for each of the components. The components that where
implemented into this stage are: one LF411 operational amplifier, seven resistors, one
potentiometer, and two power MOSFETS. First the group should be aware that the more
efficient the amplifier becomes, the more power consumption it requires. The group used the
recommended potentiometers to set the DC bias on the MOSFET; they had to adjust the pots so
that the gate to source voltage of the two MOSFETS have no voltage. This stage should be
added to part 1(A) (remember the resistor load from stage 1(A) should be removed), the
schematic illustrating both stages added is shown in Figure 4.
Figure 4 Schematic for Stages 1(A) and 1(B)
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Just as stage 1(A) this phase should also be simulated to make sure that this stage meets
all the specifications. Figure 5 will illustrate the output for this stage which will already
integrate the lowpass filter from phase 1(A).
Figure 5 Output stage from part 1(B) added to stage 1(A)
2.0.3 Project 1 (C) Design and PSpice Simulation In phase three the group will create the files to manufacture the PCB which will be
populated with the components that where design in stages 1(A) and 1(B). As mentioned before
the group had to understand how the PCB creator works and to learn this the team had to go
through a tutorial provided by Dr. Hansen. Before these files are created the users have to
change the footprints for each of the components on the Pspice file. Moreover, the group also
added some connections to be used as the power supplies. Additionally, the team had to add
some BNC’s to represent the incoming input signal. The BNC’s will also be utilized to output
the signal to the oscilloscope. Bypass capacitors where added to the schematic to be used as
bypass capacitors. Electrolytic capacitors where also added to the design to reduce the noise
incoming from the power rails in the system. After all this components where properly added
and modified to the schematic the final result will be illustrated in Figure 6.
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3.0 Protoboard Circuit In stage one; the lowpass filter was prototype with no extreme changes in the
components. Different from stage one the rest of the design had several changes to make the
specifications meet. Prototyping for phases one and two was done after the design was created
and tested on Pspice.
Phase two was really challenging for the group, since no one in the group understood
how the potentiometers work and how they are measured with the VMM. These potentiometers
had to be adjusted to have zero voltage through them to protect the MOSFETS. As power
consumption increase, current starts flowing through the circuit and the MOSFETS might burn
out. The group encountered many challenges in this stage, but solved it the only way electrical
engineers can, by starting from scratch.
Figure 6 Final Schematic to be send into the PCB creator
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After resolving all the problems that were presented in stage 1(B) the group started to
take screenshots of the output for the final output from the circuit. Figure 6 will illustrate the
desired output voltage of 20 volts peak to peak.
Since the group already had the assemble part 1(B) into the breadboard it was only
logical to take the Oscilloscope screenshot of the FFT of the 1000 Hz 10 Vpp sine wave across
the 20 Ohm load. Figure 8 will illustrate this output with a frequency input of 3 kHz. Figure 9
Figure 7 Output for stage 1(B)
Figure 8 THD of output for stage 1(B) @ 3 kHz
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will illustrate this same output with a 5kHz frequency input.
4.0 Printed Circuit Board (PCB) Design In this stage the group gathered all the files necessary to fabricate their final PCB which
was then populated with all the components design in previous sections. The group became
familiar with the PCB editor to layout all of the components required. Furthermore, the
components had to be edited on Pspice with their respective footprints. While the group was
grouping the components in the PCB editor they had to make sure that the wires would not cross
each other this wiring crossing is commonly known as ratsnest, “Ratsnest command cleans up
the un routed wires. A ratsnet reports the number of air wires remaining” (Build your own
circuit board). This nest would become more complicated as time went one and it took several
hours to reduce it to where no wire would cross.
The PCB editor had the option of auto routing the components, this is highly
recommended since it will achieve the cohesive wiring for the components. Moreover, the group
had to make sure that long wiring loops where not created to decrease any induction in the
Figure 9 THD of output for stage 1(B) @ 5 kHz
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circuit. The group had many difficulties with the auto routing option since they were unfamiliar
with PCB editor program. Once again the group had to start from scratch the design.
After the routing took place with the correct distance that was required for all the
components sizes group started creating the files for manufacturing. Furthermore, the group
received the final PCB. The group was then required to check for any shorts in the board. If all
the traces where check then the population process would begin.
The population process required concentration and steady hands for the soldering to
begin. The group started soldering the main components, such as the power amplifier.
Afterwards, these amplifiers where tested to verify that they worked correctly. Since the ground
plane was on both the top and bottom; the components that required both sides grounded where
soldered on both sides. After all the testing for the amplifiers was verified by the team the pre
amplifier and lowpass filter where soldered into the PCB board. Similarly to previous stages the
team had some trouble, try to find different solutions to the problem but did not know what was
wrong with the board. After Dr. Hansen took a look into the board we figure out that the board
was correctly assembled and manufactured, the group then notices that one of the probes used for
testing the board was not in the right setting.
After the PCB was populated with all the components and was tested to meet
specifications it was presented to the instructor to see if it met specifications. The results
achieved by the group where: The passband voltage gain must be adjustable over the range -
10dB to 20dB, the group had 380mv to 20 Vpp. The screenshot for this result will be shown in
Figure 10. The passband ripple should be less than or equal to 2dB, the circuit has a lowpass
response and has a gain that will meet with the specifications, the group achieve Ap,max = 11.69
and (.79)*(Ap,max)=9.23. The high frequency stopband corner should be 50kHz, the stopband
attenuation had to be at least 40dB, the team obtain (Ap,max)*(.01) = 117mV. Finally the team
had to find if there were any visible THD, Figure 11 will demonstrate that no visible THD was in
the circuit. All of this specifications where achieved by the group; they were proud of how their
design concluded.
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5.0 Conclusion After achieving a successful project I was satisfied with all the knowledge achieved from
all the different stages in the project. It was really a gratifying experience to build a PCB, since
this was my first time designing and working with an actual one. I learned a lot of how the
Figure 10 PCB output with input 1KHz 20Vpp across 20ohm load
Figure 11 Screenshot of FFT, PCB output with input of 1KHz
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design process for these boards are brought into real life components. This project will also be
helpful for our Senior Design course. It was good to encounter some of the problems we as a
team arrived, since this will help foresee any problems we will have in future projects.
Furthermore, testing each stage worked concurrently with the given specifications was also
challenging but all verified to achieve a great final result. When populating the PCB one as a
student wants to do it all at once, but this is not the correct way since each stage was designed to
meet specifications. Overall, I think this was a great experience on how PCBs are design and
manufacture. I personally enjoyed this project and will do it all over again.
6.0 References "Low-pass Filters." All About Circuits. Feb. 2006. 15 Mar. 2009.
"Capacitor Types and Colors." Elecraft. 20 Feb. 2009
<http://www.elecraft.com/Apps/caps.htm>.
Hansen, Lars. Electrical Engineer Lab 2. University of Texas At San Antonio, San
Antonio. Spring 2008.
Horowitz, Paul, and Hill Winfield. The Art of Electronics. New York: Cambridge UP, 1989.
“Monte Carlo Method” Wikipedia, The Free Encyclopedia. 15 Apr 2009, 14:27 UTC. 1 Mar.
2009.
<http//en.wikipedia.org/w/index.php?title=Monte_Carlo_method%oldid=287056722>
“Texas Instruments Filter Pro Simulation”
<http://www-s.ti.com/sc/techzip/slvc003.zip>
Williams, Al. Build Your Own Circuit Board. New York: New York, 2004