Transistor in General - Free Essay Example

Sample details Pages: 6 Words: 1879 Downloads: 7 Date added: 2017/09/14 Category Advertising Essay Did you like this example? Transistor A transistor is a semiconductor device used to amplify and switch electronic signals. It is made of a solid piece of semiconductor material, with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistors terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be much more than the controlling (input) power, the transistor provides amplification of a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits. The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems. Following its release in the early 1950s the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, amongst other things. Advantages The key advantages that have allowed transistors to replace their vacuum tube predecessors in most applications are * Small size and minimal weight, allowing the development of miniaturized electronic devices. Highly automated manufacturing processes, resulting in low per-unit cost. * Lower possible operating voltages, making transistors suitable for small, battery-powered applications. * No warm-up period for cathode heaters required after power application. * Lower power dissipation and generally greater energy efficiency. * Higher reliability and greater physical ruggedness. * Extremely long life. Some transistorized devices have been in service for mo re than 50 years. * Complementary devices available, facilitating the design of complementary-symmetry circuits, something not possible with vacuum tubes. Insensitivity to mechanical shock and vibration, thus avoiding the problem of microphonics in audio applications. Limitations * Silicon transistors do not operate at voltages higher than about 1,000 volts (SiC devices can be operated as high as 3,000 volts). In contrast, electron tubes have been developed that can be operated at tens of thousands of volts. * High power, high frequency operation, such as that used in over-the-air television broadcasting, is better achieved in electron tubes due to improved electron mobility in a vacuum. Silicon transistors are much more vulnerable than electron tubes to an electromagnetic pulse generated by a high-altitude nuclear explosion. Classification Transistors are categorized by * Semiconductor material: germanium, silicon, gallium arsenide, silicon carbide, etc. * Structure: BJT, JFET, IGF ET (MOSFET), IGBT, other types * Polarity: NPN, PNP (BJTs); N-channel, P-channel (FETs) * Maximum power rating: low, medium, high * Maximum operating frequency: low, medium, high, radio frequency (RF), microwave (The maximum effective frequency of a transistor is denoted by the term fT, an abbreviation for frequency of transition. Don’t waste time! Our writers will create an original "Transistor in General" essay for you Create order The frequency of transition is the frequency at which the transistor yields unity gain). * Application: switch, general purpose, audio, high voltage, super-beta, matched pair * Physical packaging: through hole metal, through hole plastic, surface mount, ball grid array, power modules * Amplification factor hfe (transistor beta) Thus, a particular transistor may be described as silicon, surface mount, BJT, NPN, low power, high frequency switch. Bipolar junction transistor Bipolar transistors are so named because they conduct by using both majority and minority carriers. The bipolar junction transistor (BJT) is a combination of two junction diodes, and is formed of either a thin layer of p-type semiconductor sandwiched between two n-type semiconductors (an n-p-n transistor), or a thin layer of n-type semiconductor sandwiched between two p-type semiconductors (a p-n-p transistor). This construction produces two p-n junctions: a base–emitter junction and a base–collector junction, separated by a thin region of semiconductor known as the base region (two junction diodes wired together without sharing an intervening semiconducting region will not make a transistor). The BJT has three terminals, corresponding to the three layers of semiconductor an emitter, a base, and a collector. It is useful in amplifiers because the currents at the emitter and collector are controllable by a relatively small base current. In an NPN transistor operating in the active region, the emitter-base junction is forward biased (electrons and holes recombine at the junction), and electrons are injected into the base region. Because the base is narrow, most of these electrons will diffuse into the reverse-biased (electrons and holes are formed at, and move away from the junction) base-collector junction and be swept into the collector; perhaps one-hundredth of the electrons will recombine in the base, which is the dominant mechanism in the base current. By controlling the number of electrons that can leave the base, the number of electrons entering the collector can be controlled. Collector current is approximately ? common-emitter current gain) times the base current. It is typically greater than 100 for small-signal transistors but can be smaller in transistors designed for high-power applications. The BJT is a low–input-impedance device. Also, as the base–emitter voltage (Vbe) is increased the base–emitter current and hence the collector–emitter current (Ice) increase exponentially according to the Shockley diode model and the Ebers-Moll model. Because of this exponential r elationship, the BJT has a good transconductance. Simple circuit to show the labels of a BJT As an electronic switch Amplifier circuit Bipolar transistors can be made to conduct by exposure to light, since absorption of photons in the base region generates a photocurrent that acts as a base current; the collector current is approximately ? times the photocurrent. Devices designed for this purpose have a transparent window in the package and are called phototransistors. Field-effect transistor The field-effect transistor (FET), sometimes called a unipolar transistor, uses either electrons (in N-channel FET) or holes (in P-channel FET) for conduction. The four terminals of the FET are named source, gate, drain, and body (substrate). On most FETs, the body is connected to the source inside the package, and this will be assumed for the following description. In FETs, the drain-to-source current flows via a conducting channel that connects the source region to the drain region. The conductivity is varied by the electric field that is produced when a voltage is applied between the gate and source terminals; hence the current flowing between the drain and source is controlled by the voltage applied between the gate and source. As the gate–source voltage (Vgs) is increased, the drain–source current (Ids) increases exponentially for Vgs below threshold, and then at a roughly quadratic rate () (where VT is the threshold voltage at which drain current begins) in the space-charge-limited region above threshold. A quadratic behavior is not observed in modern devices, for example, at the 65 nm technology node. For low noise at narrow bandwidth the higher input resistance of the FET is advantageous. FETs are divided into two families: junction FET (JFET) and insulated gate FET (IGFET). The IGFET is more commonly known as a metal–oxide–semiconductor FET (MOSFET), reflecting its original construction from layers of metal (the gate), oxide (the insulation), and semiconductor. Unlike IGFETs, the JFET gate forms a PN diode with the channel which lies between the source and drain. Functionally, this makes the N-channel JFET the solid state equivalent of the vacuum tube triode which, similarly, forms a diode between its grid and cathode. Also, both devices operate in the depletion mode, they both have a high input impedance, and they both conduct current under the control of an input voltage. Metal–semiconductor FETs (MESFETs) are JFETs in which the reverse biased PN junction is replaced by a metal–semiconductor Schottky-junction. These, and the HEMTs (high electron mobility transistors, or HFETs), in which a two-dimensional electron gas with very high carrier mobility is used for charge transport, are especially suitable for use at very high frequencies (microwave frequencies; several GHz). Unlike bipolar transistors, FETs do not inherently amplify a photocurrent. Nevertheless, there are ways to use them, especially JFETs, as light-sensitive devices, by exploiting the photocurrents in channel–gate or channel–body junctions. FETs are further divided into depletion-mode and enhancement-mode types, depending on whether the channel is turned on or off with zero gate-to-source voltage. For enhancement mode, the channel is off at zero bias, and a gate potential can enhance the conduction. For depletion mode, the channel is on at zero bias, and a gate potential (of the opposite polarity) can deplete the channel, reducing conduction. For either mode, a more positive gate voltage corresponds to a higher current for N-channel devices and a lower current for P-channel devices. Nearly all JFETs are depletion-mode as the diode junctions would forward bias and conduct if they were enhancement mode devices; most IGFETs are enhancement-mode types. Single-electron transistors Single Electron Transistor (SET) consists of a gate island between two tunnelling junctions. The tunnelling current is controlled by a voltage applied to the gate through a capacitor. In physics, a Coulomb blockade (abbreviated QB), named after Charles-Augustin de Coulombs electrical force, is the increased resistance at small bias voltages of an electronic device comprising at least one low-capacitance tunnel junction. Because of the QB, the resistances of devices are not constant at low bias voltages, but increase to infinity for zero bias (i. e. no current flows). Single electron transistor Schematic of a single electron transistor Energy levels of source, island and drain (from left to right) in a single electron transistor for both the blocking state (upper part) and the transmitting state (lower part). Single electron transistor with niobium leads and aluminium island The simplest device in which the effect of Coulomb blockade can be observed is the so-called single electron transistor. It consists of two tunnel junctions sharing one common electrode with a low self-capacitance, known as the island. The electrical potential of the island can be tuned by a third electrode (the gate), capacitively coupled to the island. In the blocking state no accessible energy levels are within tunneling range of the electron (red) on the source contact. All energy levels on the island electrode with lower energies are occupied. When a positive voltage is applied to the gate electrode the energy levels of the island electrode are lowered. The electron (green 1. ) can tunnel onto the island (2. ), occupying a previously vacant energy level. From there it can tunnel onto the drain electrode (3. ) where it inelastically scatters and reaches the drain electrode Fermi level (4. ). The energy levels of the island electrode are evenly spaced with a separation of ? E. ?E is the energy needed to each subsequent electron to the island, which acts as a self-capacitance C. The lower C the bigger ? E gets. To achieve the Coulomb blockade, three criteria have to be met: * the bias voltage cant exceed the charging energy divided by the capacitance Vbias = Â  ; * the thermal energy kBT must be below the charging energy EC = , or else the electron will be able to pass the QB via thermal excitation; and * the tunneling resistance (Rt) should be greater than , which is derived from Heisenbergs Uncertainty principle. Coulomb Blockade Thermometer A typical Coulomb Blockade Thermometer (CBT) is made from an array of metallic islands, connected to each other through a thin insulating layer. A tunnel junction forms between the islands, and as voltage is applied, electrons may tunnel across this junction. The tunneling rates and hence the conductance vary according to the charging energy of the islands as well as the thermal energy of the system. Coulomb Blockade Thermometer is a primary thermometer based on electric conductance characteristics of tunnel junction arrays. The parameter V? =5. 439NkBT/e, the full width at half minimum of the measured differential conductance dip over an array of N junctions together with the physical constants provide the absolute temperature.

The Real Cholly Breedlove - 900 Words

In Toni Morrison’s The Bluest Eye, one of the main characters, Cholly Breedlove, can be examined through a Freudian psychoanalytic lens, as he struggles with things like the structure of his personality and the Oedipal complex. Cholly is clearly a troubled man and throughout the story he experiences difficulty in trying to find a balance between his id and superego. Cholly also struggles with the Oedipal complex, raping his daughter, Pecola. This action ties in with his id, in that he acts impulsively to fulfill his wants. Cholly Breedlove, a main character from Morrison’s novel, can be examined using Freudian psychoanalysis as he struggles to maintain his ego and as he struggles with the Oedipal complex, raping his daughter Pecola.†¦show more content†¦Cholly’s id controls his life, and he is impulsive, carrying out many sick and twisted actions. Cholly has no ego or happy-medium between his id and superego. He lives a harsh reality that is of his own doings. Cholly is a drunk who lacks any sort of respect for women. He has physical fights with his wife, Pauline, on a regular basis. Cholly and Pauline Breedlove have always â€Å"fought each other with a darkly brutal formalism that is paralleled only by their lovemaking. Tacitly they have agreed not to kill each other† (43). Although sad, this is the Breedlove’s reality and it is all because of Cholly’s doings. Cholly is the one who drinks, has no respect for women, and has not attempted to change his family’s situation at all. Because of all of Cholly’s wrongdoings, his family has suffered alongside him, having no hope to become or do anything with their lives. In Morrison’s novel, The Bluest Eye, Cholly Breedlove can be examined through a Freudian psychoanalytic lense as he acts impulsively and faces the Oedipal complex. Cholly’s id is present throughout the majority of the story, and he does as he pleases. Because h is superego and ego are not in effect, Cholly does many awful things, such as rape his own daughter. Cholly has no respect for women, is violent, and does not care for anyone but himself. Cholly Breedlove is a twisted and terrible character and because his id is in effect, he is impulsive,Show MoreRelatedThe Price Of Persecution By Toni Morrison s The Bluest Eye1238 Words   |  5 Pagesthem. Geraldine’s obsession with pedantic distinctions between different groups of black residents in Lorain leads her son and the whole next generation to preserve the biases of their parents. The maltreatment practiced by those of mixed race has a real impact on those they perceive as inferior. Maureen Peal is a wealthy mixed race girl that moves to Pecola’s school. She enters Pecola’s narrative by holding some boys intent on harrassing Pecola at bay and starts a friendly conversation with her. SoonRead MoreThe Bluest Eye By Toni Morrison Essay931 Words   |  4 Pagesskinn ed blacks amongst other smaller issues that they thought made one superior over the other. This complex brought forth identity issues, especially women. In The bluest Eye by Toni Morrison the main character is a young girl named Pecola Breedlove, growing up in Lorain, Ohio, after the great depression. Nine year old Claudia MacTeer and her ten year old sister Frieda are also main characters. The MacTeers take in Pecola, and the young girls build a relationship with one another. Pecola hadRead MoreEssay about Fifty Shades of Skin Color2012 Words   |  9 Pagesdestructive than just the oppression from whites. Aunt Jimmy was the adoptive mother of Cholly Breedlove. His birth mother, Jimmy’s niece, thought that she could simply throw away baby Cholly. When Jimmy saw this, she went outside and picked up newborn Cholly out of the garbage heap and saved his life. She was always blatantly honest with Cholly, and she told him the truth when he questioned the truth about his real mother and father. â€Å"He wasn’t nowhere around when you was born. Your mama didn’t nameRead MoreThe Beauty Of Life Through The Colors Of Beauty1470 Words   |  6 Pagesstreak of green them june bugs made on the trees the night we left down home. All them colors was in me1. Pauline and Cholly left the colors of the South when they moved North to Ohio to begin their life together. Through Cholly, Pauline hoped to find those colors of beauty that she left down home. For a while she did find her colors, her beauty, in the eyes of Cholly. He released in her all the colors of life which were sealed down in her soul. Everything about their early marriedRead MorePerception Of Oneself Through The Eyes Of The White Culture1695 Words   |  7 Pagesliterature written by African American women about their experience as women of color. Inspired by a conversation Morrison had with one of her students who wished for blue eyes, the novel portrays the subconscious demolition of a young black girl, Pecola Breedlove, who searches for love and acceptance in a world that underrates people of her own race. Pecola hopelessly longs to possess the traditional American standards of feminine beauty—white skin, blonde hair, and blue eyes—as presented to her by the popularRead MoreAnalysis Of The Book The Bluest Eye 1484 Words   |  6 PagesWithin The Bluest Eye, as in real life, black people, no matter their wealth or education, are const antly faced with the assumptions and demands of a Eurocentric dominated world. Some of these involve encounters with actual people, as when white furniture movers refuse to take back the Breedlove’s torn couch, or when a white candy store owner displays his contemptuous indifference towards Pecola because she’s black. In the novel,Morrison looks deeply into the personality of her characters, exploringRead MoreEssay about Racism and Sexism in the Bluest Eye1798 Words   |  8 Pagescertain characters do or say certain things. Morrison provides the reader with a light-skinned black character whose racist attitudes affect the poorer, darker blacks in the community, especially the main characters, Claudia MacTeer and Pecola Breedlove. Maureen Peal comes from a rich black family and triggers admiration along with envy in every child at school, including Claudia. Although Maureen is light-skinned, she embodies everything that is considered white, at least by Claudias standards:Read MoreAnalysis Of Tony Morrison s The Bluest Eye 1263 Words   |  6 Pagesstandard of beauty which distorts blacks everywhere. Pauline and Pecola have troubles with the whites. The Bluest Eyes. is one of the most prevalent concerns role appearance novel in society, Pecola Breedlove is described herself as ugly not because she necessarily is, but because all the Breedloves see themselves as ugly; this is the role they see themselves playing in society because they have darker skin. Toni Morrison describes outraged and desperate life during the Great Depression in LorainRead MoreStruggling through the Great Depression in Toni Morrisons The Bluest Eye1347 Words   |  5 PagesSuddenly, we get a series of paragraphs from Paulines viewpoint. One minute were reading a lyrical line about how Pauline, saw the Kentucky sun drenching the yellow, heavy-lidded eyes of Cholly Breedlove. The next minute were deep in Paulines own Southern language as she says, When I first seed Cholly...it was like all the bits of color from that time down home when all us chilren went berry picking after a funeral†. This makes the narrative more complete, giving rural, less-educated charactersRead MoreThemes Of The Bluest Eye1871 Words   |  8 Pagesher by her father, Cholly. One day when Pecola is washing dishes Cholly comes up to her and begins to interact with her in the same sexual way he interacted with Mrs. Breedlove when they first met, by tickling her foot. He begins to fee l the desire to rape her, and he does, so violently that she ends up fainting and â€Å"the gigantic thrust he made into her then provoked the only sound she made—a hollow suck of air in the back of her throat† (Morrison 163). This violence by Cholly is one of the most

A Jest of God by Margaret Laurence free essay sample

Laurence, the reader is introduced to a small town school teacher, Rachel. Rachel is 34 years old and a single female taking care of her mother after her fathers death. Through Earaches eyes the reader is shown her thoughts, desires and struggles. One side of Rachel that Is seen in this novel Is the struggle with death and her father; Rachel approaches death as way out of her life, an escape from the claustrophobic life (214) trapping herself from being the person she wants to be.Before the novel even begins we are shown a glimpse of how Rachel approaches ere spiritual life and how death is an integral part of the way she thinks: l was swallowed one time deep in the dark (5). This quote from Carl Sandburg Losers foreshadows the struggle which haunts Rachel from a child to the point in her life when she finally gets a grasp on death. Her life through her eyes seems boring almost unbearable at times and her fantasy of escape comes in the form of dieing: Rachel Cameron says shell die (7).Her thoughts turn reality into a dream world seeing the children In the playground growing old finally die[inning], the last dried shell f them painted and prettified for decent burial by mortal men like Animal Cameron, my father. Stupid thought, Morbid. I mustnt give houseroom In my skull to that sort of thing (8). Rachel knows [l]its dangerous (8) to let herself think these Immature thoughts; She is a grown woman not a child. Her thoughts at the beginning seem to get the best of her; Conforming to be someone she is not happy with. Death started with her father and his business at the local funeral home.It was a business for her father and Rachel was never part of it: This is no place for you, Rachel. Run along now, theres a good girl. This is no place for you (124). Rachel was sheltered as [t]he sign on the door says Private (124), shutting out a child not really understanding death and reality. To Rachel death is not something to be brought out in the open but rather kept Inside hidden from everyone: All that remains Is for someone to delete the word funeral. A nasty word, smacking of mortality. No one In Mackinaw ever dies, at least not on this side of the tracks. We are a gathering of immortals.We pass on C] but we do not die. Death is rude, unmannerly, not to be spoken to in the street. (19, 20) Seeing the word funeral everyday in neon lights on the front of her house was always n, keeping it fresh in her mind as a reminder of death. It also reminds her that it is a part of life and reading it on the sign only makes it public; Something Rachel struggles with and tries to keep hiding it inside. After breaking the barriers put up by her father in the funeral home she goes looking for answers. Hector Jonas welcomes her Into the basement, something her father would never do, and she begins to ask questions.Earaches first question, Deaths unmentionable? (128) seems Like she Is trying to get Jonas to answer a question that she had been wanting to ask her father but couldnt. Jonas then gives n undesirable answer almost repeating the question. Rachel tries to get more of an a full explanation. Sonars answer, [I]its simply nicer not to have to think about all that stuff (128) shows Rachel that her father was the one who took the burden for other people; He was only trying to let her grow up with out knowing or understanding this pressure so that she would not have to deal with it.After realizing being sheltered not only from death itself but everything that comes with it, Rachel has to deal with a tumor which could be benign or malignant, death or life. Rachel begins to think of something and her father said: I looked down once through the at the lake, and it trembled and changed, and still I could see, far below, the thousand minute creatures spinning in a finned dance, and my father said Fishes, only Just spawned, and there were thousands of them, thousands.The waters are in front of my eyes. (187) To Rachel this is time for rebirth, a coming out of who she was and finally being an adult and standing up for herself. Rach el sees that her father was trying to do the right thing. Death and the pressures it brings are not for a child but an adult and with Rachel accepting responsibly, she can now cope by herself. Well, in the end 0 in the end 0 its in others hands (201) shows how Rachel knows she can only do so much and to let things happen is the only way to be happy.At the end Rachel accepts her father for who he was and not who she wanted him to be. Her and Hector talk about the night she came to visit and Rachel expresses how she now understands who her father was: He probably did do what he wanted most, even though he might not have know it (206). His love for Rachel was not expressed outwardly but through what he done she now understands. The new found freedom inside herself boils over when she sees Hector had changed the unreal home sign: Cacophonic Chapel (208).She realizes that funeral was gone in not only the sign but also herself: Its a change, Hector. Its 0 evolution (208). For Rachel it was setting her free for who she wanted to be. Rachel overcame her struggle with death and her father to become the person she wants to be. Her realization in being independent and letting go of the past only made the traumatic experience of tumor a life changing event. With Rachel accepting her father for who he was she can now be the person she wanted to be: And came out alive after all

Kadeejah Johnson Essays - Economy, Economic History, Money

Kadeejah Johnson Professor Dr. G. Sochan American History Opening Due: 11 April, 2016 The Great Depression and African Americans In American history there had been many drawbacks that caused major obstructions within the country and primarily amongst its people. The most notorious of those drawbacks was none other than the Great Depression. This was a time period in American history where more than $10 billion in market value had vanished within hours, and the United States had begun to find itself in the waking of the greatest economic disaster in history. Although the stock market crashed, it was not by itself the cause of the Great Depression. Much of America during 1929 had experienced signs of economic trouble. Banks failed, land undeveloped, mortgages foreclosed, and many Americans began to question the government and its spending. Amongst those who were affected were African Americans, much of whom