ECE_1_Prelim.pdf

ECE 1: Prelim WEEK 01 CATHODE - It is the electrode that emits electrons when heated in a vacuum tube HEATER - radiates heat when an electric current flows through it PLATE (ANODE) - the electrode that draws/ attracts electrons...

ECE 1: Prelim WEEK 01 CATHODE - It is the electrode that emits electrons when heated in a vacuum tube HEATER - radiates heat when an electric current flows through it PLATE (ANODE) - the electrode that draws/ attracts electrons emitted by the cathode THERMIONIC EMISSION - the process of emitting electrons as the filament or heater is heated or applied with heat ELECTRONICS - the science dealing with the development and application of devices and systems involving the flow of electrons or other carrier of electric charge, in a vacuum, in gaseous media, in plasma, in semiconductors, in solid state and/or in similar devices, including but not limited to, applications involving optical, electromagnetic and other energy forms when transduced or converted into electronic signals. My own: Electronics is the study of how to use electricity to create and control devices that process information. It involves working with things like semiconductors, vacuum tubes, and other electronic components. DEVICE - It is a component for controlling the flow of electrical currents for the purpose of information processing and system control. Example: vacuum tube, diode, transistor, capacitor CIRCUIT – It is consists of electronic devices interconnected together to performs a specific task or purpose. Example: power supply, voltage regulator, clipper, etc. SOLID STATE - It refers to the material electronic devices are formed or made in which electricity flows through solid semiconductor crystals rather than through vacuum tubes. refers to electronic devices that use solid materials like semiconductors instead of vacuum tubes. These devices are typically smaller, more efficient, and more reliable than those based on vacuum tubes. ECE 1: Prelim 1  BRIEF HISTORY OF ELECTRONICS 1873 - The principle of operation of thermionic diode was discovered by Frederick Guthrie 1880 - Thermionic diode principles were rediscovered by Thomas Edison on February 13 and took out a patent in 1883 1897 - Sir Joseph Thomson discovered electron: Qe = - 1.602 x 10 -19 C ; me = 9.109 x 10 -31 kg 1904 - The first thermionic diode was patented in Britain by John Ambrose Fleming on November 16 1906 - Lee de Forest added a third element called the control grid to the vacuum tube diode resulting in the first amplifier, the TRIODE 1913 - In this year, William Henry Eccles coined the term diode from Greek roots: “di” means two and “ode” means path - In the same year, Ernest Rutherford discovered proton: Qp = 1.602 x 10 -19 C ; mp = 1.67x10-27 kg 1932 - Sir James Chadwick discovered neutron: Qn = 0 C ; mn = 1.6749 x 10 -27 kg 1947 - December 23, Walter H. Brattain and John Bardeen demonstrated the amplifying action of the first transistor at the Bell Telephone Laboratories. 1958 - Jack Kilby produces a microcircuit with both active and passive components fabricated from semiconductor material. This circuit is what we know today as INTEGRATED CIRCUIT (IC) 1971 - Microprocessor Integrates CPU Function onto a Single Chip (Central Processing on a Chip) WEEK 2 Definition of Terms Feedback - A path that provides energy transferred from the output to the input ECE 1: Prelim 2  Heater - It radiates heat when an electric current flows through it Interelectrode Capacitance - It refers to the capacitance between two electrodes of a vacuum tube Plate - It is the electrode that draws/ attracts electrons emitted by the cathode Space Charge - It is the repelling force exerted by electrons remained in space to the other electrons given off by the cathode, thus impeding their flow to the plate TUBE FAMILIES VACUUM TUBE - is a device used to amplify, switch, otherwise modify, or create an electrical signal by controlling the movement of electrons in a low-pressure space - It consists of electrodes in a vacuums in an insulating heat resistant envelope. - it operates in the principle of “ Thermionic Emission” - also known as Fleming valve Vacuum Tubes, Schematic Symbols, and Characteristics Diode - Terminals: anode (plate) and cathode When plate or anode is positive, conducts current one direction only, electron flows from cathode to anode. Its problem is space charge Triode - Terminals: anode (plate), cathode and control grid Negative grid controls plate current. The higher the negative grid bias, the lower the plate current. It minimizes space charge. However, it has ECE 1: Prelim 3  interelectrode capacitance. CGA is the most troublesome because of feedback. Tetrode - Terminals: anode (plate), cathode, control grid and screen grid Screen grid reduces miller effect (interelectrode capacitance) because it acts as an electrostatic shield between the anode and control grid. Screen grid must have positive dc voltage. Problem is secondary emission. Pentode - Terminals: anode (plate), cathode, control grid, screen grid and suppressor grid Suppressor grid is connected directly to the cathode. It prevents the secondary electrons from travelling to the screen grid. It eliminates secondary emission. It should be negative with respect to the plate and because it is close to the plate, it will repel the secondary electrons and drive them back into the plate Note: First Law of Electrostatics ECE 1: Prelim 4  “two charged particles of same charge (positive or negative) will repel each other and two charged particles of opposite charges (one positive and one negative) will attract each other.” SEMICONDUCTOR THEORY Advantages of Solid State Semiconductor over Vacuum Tubes 1. Small and lightweight 2. No heater requirement 3. Rugged construction 4. More efficient 5. Faster in speed CONDUCTOR - any material that will support generous flow of charge when a voltage source of limited magnitude is applied across its terminals - a material which has a very low electrical resistance - a material with less than four valence electrons examples: gold, silver, aluminum, copper INSULATOR - a material that offers a very low level of conductivity under pressure from an applied voltage source - a material with more than four valence electrons examples: mica, paper, porcelain SEMICONDUCTOR - a material that has a conductivity level somewhere between the extremes of an insulator and a conductor - a material with exactly four valence electrons examples: Silicon, Germanium, Gallium Arsenide, Cadmium Sulfide RECOMBINATION - It is a process where a free electron is captured by a hole ECE 1: Prelim 5  VALENCE ELECTRONS - It refers to the electrons found at the outermost shell of an atom Resistivity – measure of materials resistance to current flow Typical Resistivity Values ρCu ≈ 10 -6 Ω-cm ρGe ≈ 50 Ω-cm ρSi ≈ 50 x 10 3Ω-cm COVALENT BONDING - bonding of atoms, strengthened by the sharing of valence electrons - the shared electrons are attracted simultaneously by two atoms resulting in a force that holds them together POSITIVE TEMPERATURE COEFFICIENT - It is the increase in resistance with the increase in temperature NEGATIVE TEMPERATURE COEFFICIENT - It is the decrease in resistance with the increase in temperature ENERGY LEVELS - The more distant the electron from the nucleus, the higher the energy state, and any electron that has left its parent atom has a higher energy state than any electron in the atomic structure. Energy band - also known as energy levels Energy gap (Eg) ECE 1: Prelim 6  - it refers to the distance between the conduction band and valence band - required energy in electron volt (eV) for a valence electron to leave the valence band and enter conduction band to become free electron - also known as forbidden band Energy gap for each type of material IONIZATION is the process whereby an electron can absorb sufficient energy to break away from the atomic structure and enter conduction band eV = 1.6 x 10 -19 J SEMICONDUCTOR MATERIALS Classes: 1. Single-Crystal - have a repetitive crystal structure e.g. silicon and germanium 2. Compound – constructed of two or more semiconductor materials of different atomic structures. e.g. Gallium Arsenide (GaAs), Cadmium Sulfide (CdS), Gallium Nitride (GaN), Gallium Arsenide Phosphide (GaAsP ) Types: 1. INTRINSIC - a material that has been carefully refined to reduce the number of impurities to a very low level e.g. Silicon and Germanium Intrinsic Carriers ECE 1: Prelim 7  Semiconductor ( per cubic centimeter ) GaAs 1.7 x 106 Si 1.5 x 1010 Ge 2.5 x 1013 Relative Mobility Factor (μn ) Semiconductor μn ( cm2 / V.s ) Si 1500 Ge 3900 GeAs 8500 RELATIVE MOBILITY - the ability of the free carriers to move throughout the material HOLE - is defined as an absence or vacancy of an electron - limited current/ carrier flow - need to alter the electrical characteristic to increase conductivity As the temperature rises above 0 K, an increasing number of valence electrons absorb sufficient thermal energy to break the covalent bond and contribute to the number of charge carriers (electrons 2. EXTRINSIC - a material that has been subjected to the doping process DOPING - is the process of adding impurities to the relatively pure semiconductor material to increase conductivity ECE 1: Prelim 8  Types: 1. N-TYPE uses pentavalent elements as impurities excess of electron also known as donor atoms/ impurities examples of pentavalent elements include Phosphorus, Arsenic, Antimony majority carrier: electron minority carries: hole positive ion (cation) is created 2. P-TYPE uses trivalent elements as impurities excess of hole also known as acceptor atoms/ impurities examples of trivalent elements include Boron, Indium, Gallium, Aluminum majority carrier: hole minority carries: electron negative ion (anion) is created Inside a silicon crystal Some free electrons and holes are created by thermal energy. Other free electrons and holes are recombining. Some free electrons and holes exist temporarily, awaiting recombination. note: Recombination varies from a few nanoseconds to several microseconds ECE 1: Prelim 9  Summary: ¨most popular material is silicon. ¨Pure crystals are intrinsic semiconductors. ¨Doped crystals are extrinsic semiconductors. ¨Crystals are doped to be n type or p type. ¨An N TYPE semiconductor will have a few hole carriers (minority). ¨A p type semiconductor will have a few electron carriers (minority). Week 4 Depletion region - It is an area void of carriers. It is the area of uncovered positive and negative ions Biasing - It is the application of DC voltage source across the device to achieve the desired region of operation Breakdown Region - It is the region where a high avalanche current due to the movement of minority carrier is produced from increasing the reverse bias voltage, VR, greater than the breakdown voltage, VBR. Unidirectional - Allows current to pass in one direction only Semiconductor Diode - is a unidirectional device. It is an exponential non- linear device. A P-N junction diode is formed when a P-type semiconductor and an N- type semiconductor are joined together. At the junction, a region called the depletion region forms, where there are no free electrons or holes. This creates a potential barrier that prevents most electrons and holes from crossing the junction. However, some electrons and holes with enough energy can still cross the barrier. This creates a balance, known as thermal equilibrium, where the number of electrons and holes crossing the junction in one direction is equal to the number crossing in the other direction. This balance is important for the diode's function, which is to allow current to flow in one direction but not the other. Physical Appearance of Rectifier Diode ECE 1: Prelim 10  Types of biasing Forward Bias (VS > 0) It is established by connecting the negative source terminal is connected to the ntype material or the cathode side, and the positive terminal is connected to the p-type material or the anode side (Figure 4.3). This biasing indicates a very low resistance called forward resistance. This will results in the reduction in width of the depletion region Reverse Bias (VS < 0) Established by connecting the negative source terminal is connected to the p-type material or the anode terminal, and the positive terminal is connected to the n-type material or the cathode terminal Diode Characteristic Curve To the left of the reverse bias region is the breakdown region. It is also known as Avalanche Region or Zener Region. This region is employed in some special purpose diode like zener diode. Shockley’s Equation: ECE 1: Prelim 11  Progress Check: ECE 1: Prelim 12  Draw the schematic symbol of the following vacuum tubes: I. Multiple Choice. Encircle the letter of the BEST answer. 1. Every known element has (a) the same type of atoms (b) the same number of atoms (c) a unique type of atom (d) several different types of atoms 2. An atom consists of (a) one nucleus and only one electron (b) one nucleus and one or more electrons (c) protons, electrons, and neutrons (d) answers (b) and (c) 3. The nucleus of an atom is made up of (a) protons and neutrons (b) electron (c) electrons and protons (d) electrons and neutrons 4. Valence electrons are (a) in the closest orbit to the nucleus (b) in the most distant orbit from the nucleus (c) in various orbits around the nucleus(d) not associated with a particular atom 5. _____ is an example of an insulator. (a) Copper (b) Gold (c) Mica (d) Boron 6. The difference between an insulator and a semiconductor is (a) a wider energy gap between the (b) the number of free electrons valence band and the conduction band (c) the atomic structure (d) answers (a), (b), and (c) ECE 1: Prelim 13  7. ______ is an example of single element semiconductor. (a) Silver (b) Gold (c) Mica (d) Arsenic 8. In a semiconductor crystal, the atoms are held together by (a) the interaction of valence electrons(b) forces of attraction (c) covalent bonds (d) answers (a), (b), and (c) 9. The atomic number of silicon is (a) 8 (b) 14 (c) 28 (d) 32 10. The valence shell in a carbon atom has ______ electrons. (a) 0 (b) 1 (c) 3 (d) 4 11. Each atom in a silicon crystal has (a) four valence electrons (b) four conduction electrons (c) eight valence electrons, four of its (d) no valence electrons because all own and four shared are shared with other atoms 12. Electron-hole pairs are produced by (a) recombination (b) thermal energy (c) ionization (d) doping 13. The current in a semiconductor is produced by (a) electrons only (b) holes only (c) negative ions (d) both electrons and holes 14. In an intrinsic semiconductor, (a) there are no free electrons (b) the free electrons are thermally produced (c) there are only holes (d) there are as many electrons as there are holes (e) answers (b) and (d) 15. A p-type semiconductor has impurity atoms with ______ valence electrons. (a) 3 (b) 5 (c) 0 (d) 1 III. True or False. Write your answer on the space provided before each number. __________1. Each element has a unique atomic structure. __________2. A proton is a negatively charged particle. __________3. In their normal (or neutral) state, all atoms of a given element have the same number of electrons as protons. ECE 1: Prelim 14  __________4. Valence electrons contribute to chemical reactions. __________5. Most metals are bad conductors. __________6. An insulator is a material that does not conduct electrical current under normal conditions. __________7. Doping increases the number of current carriers. __________8. A boron atom removes a hole when it bonds with silicon atoms. __________9. An intrinsic crystal is one that has no impurities. __________10. Silicon is a tetravalent element. ECE 1: Prelim 15