I am planning to further my study in engineering. I am applying for a master’s degree next year and will emphasize on computer systems or communications and signal processing. I have just completed writing a statement of purpose. I have re-read it a couple of times. I think it still needs to be prove read. I would probably show it to a professor and also friends to be prove read before submission.
Leave a Comment August 2, 2006
Operational Amplifier or so called ‘op-amp’ is the famous solid-state IC that uses external feedbacks to contorl its functions. It has a very high gain with one inverting input (V-), one non-inverting input (V+), one output (Vout), positive and negative power supply (Vs+ and Vs-). Most of the time we look at op-amp as an ideal op-amp to simplify things. In real life applications, op-amp behave almost like an ideal op-amp usually in MOSFET type op-amp. In ideal op-amp, it has an infinite open-loop gain, infinite bandwidth, infinite input impedance and zero output impedance.
This is a picture of op-amps including the famous 741. These small ICs are cheap in the cents per piece. The DC behavior of such real op-amp for its open-loop gain usually in the 100k to millions. The real op-amp does not have infinite gain and bandwidth. When the two inputs are equal in voltages, then the output is zero volt. The current entering the two inputs are small or can be assume to be zero.
Op-amp is usually use for filter design. A simple sallen-key low pass filter is shown done on SPICE. It tooks less than 10 minutes to actually build the circuit using the computer aided design software and simulation shows almost everything than can be done hands on in laboratory. Simulation is a good way to check your work in laboratory.
The plot shown is the frequency response of the filter output. As we could see, this is a pretty simple low-pass filter that allow signals to be passed below the 5 kHz range and reject anything above 10 kHz. There are many other different filter techniques that can be used in filter design according to the specifications. Op-amp is widely used in analog signal processing systems and in many other applications.
Leave a Comment May 17, 2006
In analog designs, we deals with inputs and outputs that are continuous with values from the lowest potential Vss to the highest potential Vdd. There is so called the passive analog circuit which consumes no external power, and there is so called the active analog circuit which of course consumes external power to accomplish the designer’s task. The passive analog circuit involves the use of the basics devices such as resistors, capacitors, inductors and diodes. Whereas in active analog circuit involves the use of transistors and op-amps. Any of these circuits can be fabricated into analog IC chips. This brings us to the analog IC designs and also Mixed Analog and Digital VLSI circuits.
Leave a Comment May 16, 2006
Analog is not old fashioned. I think analog is interesting and fun. If you are into electrical technical knowledge, then understanding analog design is a good point to start. In today’s world, analog and digital designs comes hand-in-hand. So to be good in both is a plus. I personally have the passion for the digital designs a lot more than the analog designs. One thing to know is that in real world, signals are in analog then digitized into today’s digital trends. The analog signals is known to be continuous and we could take these continuous signals and convert them into discrete digital signals. Digital design techniques are easier to design, data storage is much easier, much accurate, less noise and can be easily fabricated into Integrated Circuit chips. Analog design has always been a much involved process in compare to the digital design. In analog designs there are extra specifications to be taken care of such as the gain, bandwidth, signal distortion and noise. It tooks longer to master analog domain than the digital domain. More in-depth about analog designs which includes analog IC designs and can be easily simulated using Computer Aided Design software such as SPICE (Simulation Program with Integrated Circuit Emphasis). Also, more in-depth about digital designs which means TTL Gates (Transistor-Transistor Logic Gates), flip-flops, processor, CMOS, etc.
Leave a Comment May 13, 2006
So I was sitting around today wondering what I know about impedance. I come across the term impedance a lot in analog circuit design. If you understand ohm’s law and the concept of resistance in DC circuit, then impedance is the generalization of the concent from DC to AC. In short, impedance is basically a measure of the total opposition to the current flow in an AC circuit. It is made up of two components, the resistance and the reactance. Impedance (Z) is expressed in complex number. Z=R+jX. Where R is the resistance and X is the reactance.
In AC we not only have the amplitude, we also have the frequency and phase, therefore impedance not only allow the current to flow but also changes the phase, as frequency changes, it also changes the ampltitudes and phases. In ideal resistor, which means ignoring all the parasitics, we should expect to see the same impedance for all frequencies. In ideal cap, we will have the impedance that goes down with increasing frequency. In an inductor, we will have the impedance that goes up with increasing frequency.
There is a linear relation between impedances for capacitor and inductor with respect to frequency. The phase for inductor’s voltage is always 90 degrees ahead of its current. The capacitor’s current leads the voltage.
Simple MATLAB Script to calculate impedance is shown below.
Download impedance.m
% Matlab script to calculate impedance for series and parallel circuits
% Author: Ridwan Chendarma Chin
mode=input(‘Select 1 for series and 2 for parallel: ‘);
C=input(‘C= ‘);
R=input(‘R= ‘);
L=input(‘L= ‘);
f=input(‘f= ‘);
X_C=1/(2*pi*f*C);
X_L=2*pi*f*L;
Z_C=(0-j*X_C);
Z_L=(0+j*X_L);
Z_R=(R+j*0);
if (mode == 2)
Z_T=1/((1/Z_C)+(1/Z_L)+(1/Z_R));
else
Z_T=Z_C+Z_L+Z_R;
end
Z_mag=abs(Z_T) % magnitude
Z_angle=angle(Z_T)*(180/pi) % angle in degrees
1 Comment May 12, 2006
My graduation ceremony is set on Sunday, June 11, 2006. I have not yet purchased my cap, gown and tassel as they are available for purchse starting April 27. The engineering grads stole is orange in color. I am planning to purchase the honor stole and cord as well. I am probably allowed to only wear 1 stole and maybe several cords during the commencement. Therefore I am still considering on which to purchase. If I am to get from TBP, they look like below:
When I looked at the TBP stole, it looks a little funny or maybe not. It is white and triangular in shape. Maybe I will not wear that stole and wear the stole shown below from HKN instead. The other set will be from HKN, and they look like below:
I like the looks of the cord from TBP and both the stole and cord from HKN. I have to make my decision really soon to place an order for the stoles and cords. Because I am adviced that if I am to order early, they will arrive in time. I am considering to order all of them and just wore the ones that I like. I am also considering the GoldenKey Medallion and Ribbon. Oh.. is this too much of a graduation accessories 
2 Comments April 6, 2006
I am now in the process of becoming a member of Eta Kappa Nu Electrical and Computer Engineering Honor Society. Induction ceremony will be held on Friday, May 26, 2006. I am also a member of Golden Key International Honour Society. One of the requirements to be a member of HKN is to complete the soldering of the Wheatstone Bridge and get fifteen HKN members to verify the completion. I have completed this and have submitted my Bridge to the chapter members. I certainly did not have a lot of fun soldering the Bridge 
Leave a Comment April 5, 2006
Progress!…Progress!…Progress!… I have spend a couple of hours each day to polish the Bent and I have some progress to report 
This is the picture taken during the first few strokes using the filer. It is not that fun filing the old way using your hand. I could probably make use of a machine to do this job, but as people said the old way works as well as the new way. Everything done the old way by filing, sandpapering and polishing using both of my hands. I spend approximately two hours each day for several days to get the results shown later.
I have decided to start from the bottom handle since it seems to be easier. Then, after a few hours of experimental filing at the bottom portion as well as applying sandpaper from the roughest to medium roughness to the finest, it appears that it works as I expected. I tried to apply some polish as well to see the shine result. So all is good and I continued doing the same thing for the rest of the surface.
I have not been keeping track on the number of hours I have been working on the Bent itself. But hey look at this shiny thing… I did it. The Bent shown won 2nd best Bent. I did not expect to be congratulated and win a price for the second best Bent because I have seen some other really nice Bents from other initiates as well. But overall I could have done better to at least get the 1st 
Leave a Comment November 14, 2005
I have been eager to join in as a member of the prestigious Tau Beta Pi Engineering Honor Society. This quater is the time that I will put my effort to get myself admitted
There are certainly requirements to be met before being initiated as a member. One of them is the BENT casting and polishing. At this point in time, I have the casted BENT in my possession. A picture of the BENT is shown in the picture below.
As you could see, the casted BENT that I got has a rough finish. The BENT was casted from a molten brass into a sand form during the manufacturing process. It would be nice if it comes in polished form from the manufacturer 
To be admitted as a member, I am required to polish the BENT until it shines. In other words, I should be able see a reflection on the surface of the BENT itself. It is said that the BENT represents my character and therefore polishing the bent represents my character 
I would have to get down to the tools store one of these days to get a filer and the necessary polishing equipment that I needed to get this done. I have never expected myself to learn how to polish a chunk of brass. This should be an experience I would hardly forget. I would post more information about this soon.
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Leave a Comment October 21, 2005
A few weeks ago, I have received letters of congrats again. This time is for my accomplishment in the previous academic year. I made it to the president list again and I am happy with my academic progress. Here are the two letters I received. One is personally hand signed by the president.
Leave a Comment September 17, 2005
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