Found this really cool tutorial on Operational Amplifiers by Dr. Holbert, Arizona State University. It includes the Op-Amp basics, a few op-amp circuits including the differentiator and integrator circuits and a few examples. Its flash-based and easy to understand. Here’s the link-http://holbert.faculty.asu.edu/ece201/opamp.html
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Any subject you learn, you first start with the fundamentals of the subject and later use them to make bigger concepts-a cluster of fundamentals. The concepts grow in size until you completely master the subject. Any subject can hence be divided into a set of layers of abstraction.
The most basic concepts form the lowest layers of abstraction and the resulting devices form the higher layers of abstraction. The lower levels require the maximum effort and time while the higher levels are easy-depending only upon how well you understand the lower ones.
Electronics Engineering begins with Basic Physics all the way to the Microprocessor. Like any other subject, it can be summarized and over-viewed using such a set of abstraction layers.
The Atom
Electronics emerges from the basics of electricity-the flow of electrons & the fact that charge exists on the electron. We then take a look at the atomic view-the nature of the atom. This includes the study of energy levels and energy radiation from the atom. Once we know that elements can conduct-we can make use of the knowledge. As you may notice-this abstraction layer can further be divided into sub-levels(the electron, the atom & conducting elements)
Once we start noticing and studying the various elements-we come across the “gifted” elements of Group 4. The gift they have is a unique energy gap-one that lies between the conductors & the insulators. They appear harmless at 0K-but do wonders under room temperature or when doped with another element from the 3rd or the 5th group. This classifies the semiconductors as Extrinsic & Intrinsic.
a)conductor b)insulator c)semiconductor
Once we learn about doping & the extrinsic semiconductors, we make use of the fact. The p-n Junction results. Here, we introduce a concept called “recombination”. We expand the concepts of electricity to incorporate the conduction by holes-which are considered as physical positive charges. We play around with the junction-we bias it with an external voltage. It allows current only through a particular direct-it has directionality!
The P-N Junction
The device resulting from the p-n junction is the Diode. It shows certain characteristics-that of conduction with directionality-and that of breakdown when reverse biased. There are a number of types of diodes-with slight variations in structure-but a greater variation in functionality. The diode emerges as a rectifier with many other applications including clipping & clamping & peak detection.
The Transistor
Putting two diodes back to back give us the transistor. A device used for amplification & switching. It can be seen as a combination of two p-n junctions. This device has the directionality-but in addition -has gain. It is hence, an active device.
Consider the layers of abstraction as layers of sand piled over each other. You are still aware of the deeper & more fundamental layers-but you are now looking at the higher ones. Here, we look at the transistor and how it performs amplification/switching but we do not consider how doping results in p & n type semiconductors-that is the essence of abstraction.
The NAND Gate
The transistors-alone-or combined with the diode and other passive devices lead to what are called-the logic families. They are used to realize the logic gates-devices which perform simple operations on digital signals. Amongst the logic gates-the NAND and NOR are the universal gates & form the basis of most of the further levels of abstraction.
A Counter
A MUX
Logic gates are then combined to form circuits that establish certain logic functions-they are called the combinational circuits. These include multiplexers, demultiplex, encoders, decoders and all the logic circuits you can think of that do not use a circular logic path(no feedback).
A Flip Flop
The sequential circuits are combinational circuits with storage. They add a state to the combinational circuit-and they store it. They use feedback to store this state. The basic sequential device is a flip-flop and other devices include counters and shift registers.
An Integrated Circuit
The Digital Circuits allow us to build Integrated Circuits. Our building blocks still being the NAND & NOR gates. We now have functionality(combinational circuits) and storage(sequential circuit)-and those are the two things a CPU does. So, we now have the CPU. We may further have all the CPU functionality on a single chip-called the Microprocessor. The digital circuits also make way for Computer Architecture which builds the Operating System-The Computer is complete. All electronic devices we see and use everyday use a microprocessor CPU-the highest level of Electronics Abstraction.
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Communication is simply, the process of transferring information from one entity(the source) to another(the destination). This is the process involved when you talk to someone face to face or on the phone, when you listen to music on your iPod, when you use the internet, when you listen to your favorite show on TV or the radio.
Consider two people standing and talking on the street. Suppose that they keep moving away from each other. After a certain time, they are not able to communication. In technical terms, the amplitude of their speech signals die out-they get mixed with noise-noise from the environment.
Here, we are just dealing with the speech signal which is an em wave, but not really what you would call an electrical signal. Now consider the two using a wire for communication. Now, they might be able to communicate for a longer distance with better clarity. But the signal(now an electric signal) eventually dies out.
Now there are two things to consider here-
1)The signal being “transmitted” now is electric in nature. So we must use a device that converts from speech to electric signal at the senders end and something that does the inverse operation at the receivers end.
These are called the input and output transducers respectively. The best transducers you can think of are the microphone(input transducer) and the speaker/headphones(output transducer).
2)The signal dies out after traversing a certain distance. Consider the old times when the kings used to send their messengers to other kingdoms to deliver messages. Walking those distances would tire the men-so, they started using horses. Similarly, we sent our signals “on” a high frequency carrier wave.(not exactly “superimposed on” but “modulated on”). We would then need to demodulate the signal(get the guy down from the horse to deliver the message).
So, we can now start forming our communication system-The modulation process takes place in the transmitter and the demodulation is performed in the receiver. We shall be only dealing with black boxes and not going into the circuits and glass boxes.
Now, between the transmitter and the receiver lies the channel which is the most susceptible to any noise signals or interferences. You will find that all communication system block diagrams are a mirror image about the channel. The channel may be wired or wireless/broadcast. Every channel has a limited capacity called the information capacity. The noise is unwanted energy that interferes with the message signal in the form of amplitude variations. Noise may be external(created outside the receiver) or internal(created inside the receiver).
The Process Of Modulation-Modulation is the process by which we vary a property of a high frequency carrier wave with respect to the modulating signal(message signal).
Hence, we are transmitting the high frequency signal giving it some property of out message signal in such a way that the message signal can be retrieved from the transmitted carrier using this transmitted property.
This property may be the amplitude, frequency or phase of the signal leading to the three types of modulation-Amplitude Modulation(AM), Frequency Modulation(FM) & Phase Modulation(PM). FM & PM are sometimes colletively referred to as forms of angle modulation.
The three forms are illustrated below(images by Ivan Akira)
Amplitude Modulation(AM)
Frequency Modulation(FM)
Phase Modulation(PM)
It can be seen in the above illustrations that the type of modulation depends on the property of the carrier wave that varies. For instance, in case of amplitude modulation, the amplitude of the carrier varies with the amplitude of the modulation signal. Now there is one thing to understand carefully-
Even in case of angle modulation the frequency or phase of the carrier varies with the AMPLITUDE of the message signal and not with its freq/phase.
In other words, in case of FM, the frequency(carrier) varies with the amplitude(message) and in case of PM, the phase(carrier) varies with the amplitude(message). Hence, we always consider the amplitude of the modulation/msg signal.
We must then, also demodulate the signal at the receiver to generate the information signal back to the destination. This is the basic principle all communication systems follow.
Lets go back to the concept of noise being introduced in the channel as amplitude variations. For all analysis, study and design, we consider noise to be additive in nature. Which is to say, that the noise signal just adds to the transmitted signal like usual superposition.
Such a communication channel is called an additive noise channel. We also classified noise as external and internal noise. Further, External noise includes noise from the atmosphere, from industries, noise from space and solar radiations while internal noise includes shot noise, transit time noise and thermal agitation/white/Johnson noise.
Our basic aim as engineers is to design communication systems with very low noise or if possible, no noise at all. The basic idea is to get an exact replica of the information at the source to the destination.
Now, for all the right brained people like mi-self, lets take a look at a particular communication system. Consider two people talking over a certain distance using a walkie-talkie. Now, the microphone on the walkie-talkie of the person speaking is the input transducer.
It converts his speech signal into an electric signal which gets modulated by the modulator in the walkie-talkie circuit. This signal is sent by the antenna through the wireless channel to the antenna at the other person’s walkie-talkie whose receiver circuit comes into the action.
The signal, once demodulated by the receiver is then converted back to speech signal by the output transducer which is the speaker.
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Simply put-every device that has the ability to control electron flow-electrically-is an active device. Controlling it electrically would require a control current/control voltage. All transistors and vacuum tubes fall into the category of active devices.
And making use of the controlled electron motion is what electronics is all about. All active components have Gain & Directionality, And since there’s no free lunch-they’re all powered by some external energy source.
On the other hand-stuff like R,C & L’s are passive-incapable of controlling electron flow electrically-no gain-IF you’re under the impression that electronics is all about active devices-Passive devices include the DIODE-which is also the most important semiconductor device.
Random Insight-Passive components have much better drift characteristics than active components-hence, it would be great if somehow the amplifier operation/gain depended on passive components rather than active components-this was the basic idea that built the Op-Amp which has its gain depending only on the passive components in the feedback network.
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The diode’s we’ve been talking about all this time do have some really cool applications in signal processing, power supply & a lot of other places.
And yes, the AOD stands for “Applications of Diodes” & we’re gonna use that for the rest of the apps as well.
Diodes are used in rectifiers which are devices that convert an AC to a DC signal, not a pure dc signal though… And as a matter of fact, the only source of pure DC is a battery.
And this process of converting AC to DC is called rectification. Consider a simply sine wave as the input from an AC source. Then the following summarizes the overall process of rectification…
So, there is no output for the negative half as the diode is in the reverse bias condition(considered OFF). Also, the circuit we use here is just what the half wave rectifier really is.
Now, considering the two halves collectively, we get an output signal like so…
Notice here that the peaks of the positive cycle appear at equal distances, and this distance is same for the input & the output signal. Hence, the frequency of the signal does not change.
(fin=fout)
Getting into the mathematical view of things, we can now calculate the RMS & Average values of the voltage for our new output signal.
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