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.

Level 1 – The Physics/The Electron

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)

Level 2 – The Semiconductor/The Holes

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.

Level 3-The P-N Junction/The Diode/Rectifiers

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 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.

Level 4-The Transistor/Amplifiers/Filters

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.

Level 5-The Logic Gates

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.

Level 6-Digital Circuits/Combinational & Sequential Circuits

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).

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.

Level 7-The Microprocessor/CPU/Integrated Circuits/Micro Chip

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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All of us use the Pen Drive to store data everyday. We use it like an external storage device, much like an external hard drive. A Pen drive or Flash drive or USB drive has two basic elements-

• Flash Memory (NAND Flash with a crystal oscillator)
• USB (USB Male & a Microcontroller)

The USB(or Universal Serial Bus) just allows the pen drive to communicate with the computer or any other device. Based on their construction, the USB has various versions. The ones which are at work in pen drives are USB 1.1 & 2.

The heart of the “flash” drive is the Flash Memory. This is where digital electronics comes in. There are three kinds of storage media.

• Volatile(info stored does not survive system crashes)
• Non-Volatile(info usually survives crashes)
• Stable(info is never lost-not practically possible-but can be approximated by RAID, etc)

Our flash memory falls into the category of non-volatile devices. It can be implemented by using both NOR & NAND logic circuits. In flash drives, NAND gates are used.

Digital circuits can be classified into Combinational & Sequential Circuits. A combinational circuit is a combination of a number of logic gates. A sequential circuit is a combination of gates which has a state or memory associated to it. So, a sequential circuit is a combinational circuit with memory.

Latches and flip-flops are sequential circuits which can store 1-bit of information(either 0 or 1). Further, n flip-flops could store n bits of information.

We could further use an assembly of flip-flops to store data. Such an assembly of NAND flip-flops is used as flash memory.

The crystal oscillator acts as a clock to trigger the sequential circuit. Sequential circuits that use a clock/trigger are called Synchronous Sequential Circuits.

The sequential logic used in the flash memory are realized using floating gate transistors. These are transistors(MOSFET’s) whose gate is electrically isolated-and hence, acts as a floating node.

We have a floating gate(represented by the bold line) and three inputs for the transistor shown.

The use of floating gate transistors makes the flash memory electrically erasable & programmable. It is hence a type of EEPROM. It is a read-only memory that can be erased and rewritten(reprogrammed) electrically-by means of voltage/current.

However, the number of times it can be reprogrammed is limited. We always loose some bit when we format our jump drives.

Put together, our flash memory and the USB configuration forms the USB Flash drive.

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