# lecture1 - Preliminaries Flow of current is due to flow of...

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Adaptive Integrated Microsystems Preliminaries - Flow of current is due to flow of charged particles (equivalently due to flow of electrons). - Current always flows from higher voltage (+) to lower voltage (-). - Electrons flow in the opposite direction to the flow of current. - Conductors (eg Aluminum, gold) can be assumed to be an infinite source of electrons. - Electric field cannot exist inside a good conductor ( static charge can not exist inside the body of the conductor)

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Adaptive Integrated Microsystems Current and voltage laws - The total current entering a node is equal to total current leaving a node (Kirchoff’s current law). 1 I 2 I 3 I 2 I 4 3 2 1 I I I I + = + - The total voltage drop across a loop is equal to zero. 1 V 2 V 3 V 4 V 0 4 3 2 1 = + + + V V V V
Adaptive Integrated Microsystems Ohms law - Current flowing through a linear resistor is proportional to the voltage drop across it. V I + - V I V R gV I = = Transconductance Resistance V I Slope is given by Transconductance

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Adaptive Integrated Microsystems Voltage and current sources - Ideal voltage source has zero internal resistance. - Ideal current source has infinite internal resistance. 0 V I + - V I V 0 I 0 V V I 0 I
Adaptive Integrated Microsystems Capacitance - Charge stored on a capacitor is directly proportional to voltage across the terminals. - Each terminal stores opposite charge. - Voltage across the capacitor can not change instantaneously. V Q + - V Q CV Q = Capacitance t V I C t V C t Q = = 1 Voltage change slowly proportional to charging current

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Adaptive Integrated Microsystems Measure of Capacitance - Capacitance is directly proportional to cross-sectional area. - Capacitance is inversely proportional to distance between opposite plates. Permittivity of free space d A K C d A C s 0 ε = d A Relative permittivity
Adaptive Integrated Microsystems Intrinsic silicon lattice - Silicon atom has 4 electrons in the outer shell. - In a silicon lattice each atom shares (bonds) all 4 electrons with 4 neighboring silicon atoms. - No electron is (conceptually) free. - For movement of electrons, bonds have to be broken to release electrons (semi-conductor). Bonded electrons

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Adaptive Integrated Microsystems N-doped silicon - Doping implies intentional replacement of silicon atoms in the lattice by foreign impurities. - eg. Phosphorous (P) has 5 electrons in its outer shell. - 4 of its electrons are used for bonding with silicon neighbors - 1 electron is free and leads to flow of current. - n+ semiconductor represents silicon with high concentration of electron rich dopants . 3 27 25 10 10 - - m
Adaptive Integrated Microsystems P-doped silicon - For P-type semiconductor, and electron deficient atom replaces the silicon atom.

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## This note was uploaded on 03/01/2010 for the course ECE 412 taught by Professor - during the Fall '08 term at Michigan State University.

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lecture1 - Preliminaries Flow of current is due to flow of...

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