Chapter03 - Chapter 3 Solid-State Diodes and Diode Circuits...

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Jaeger/Blalock 4/30/07 Microelectronic Circuit Design, 3E McGraw-Hill Chapter 3 Solid-State Diodes and Diode Circuits Microelectronic Circuit Design Richard C. Jaeger Travis N. Blalock Chap 3 -1
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Jaeger/Blalock 4/30/07 Microelectronic Circuit Design, 3E McGraw-Hill Chapter Goals Understand diode structure and basic layout Develop electrostatics of the pn junction Explore various diode models including the mathematical model, the ideal diode model, and the constant voltage drop model Understand the SPICE representation and model parameters for the diode Define regions of operation of the diode (forward bias, reverse bias, and reverse breakdown) Apply the various types of models in circuit analysis Explore different types of diodes Discuss the dynamic switching behavior of the pn junction diode Explore diode applications Practice simulating diode circuits using SPICE Chap 3 -2
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Jaeger/Blalock 4/30/07 Microelectronic Circuit Design, 3E McGraw-Hill Diode Introduction A diode is formed by joining an n -type semiconductor with a p -type semiconductor. A pn junction is the interface between n and p regions. Diode symbol Chap 3 -3
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Jaeger/Blalock 4/30/07 Microelectronic Circuit Design, 3E McGraw-Hill pn Junction Electrostatics Donor and acceptor concentration on either side of the junction. Concentration gradients give rise to diffusion currents. Chap 3 -4
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Jaeger/Blalock 4/30/07 Microelectronic Circuit Design, 3E McGraw-Hill Drift Currents Diffusion currents lead to localized charge density variations near the pn junction. Gauss’ law predicts an electric field due to the charge distribution: Assuming constant permittivity, Resulting electric field gives rise to a drift current. With no external circuit connections, drift and diffusion currents cancel. There is no actual current, since this would imply power dissipation, rather the electric field cancels the diffusion current ‘tendency.’ ∇⋅ E = ρ c ε s E ( x ) = 1 ε s ρ ( x ) dx Chap 3 -5
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Jaeger/Blalock 4/30/07 Microelectronic Circuit Design, 3E McGraw-Hill Space-Charge Region Formation at the pn Junction Chap 3 -6
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Jaeger/Blalock 4/30/07 Microelectronic Circuit Design, 3E McGraw-Hill Potential Across the Junction Charge Density Electric Field Potential φ j = E ( x ) dx = V T ln N A N D n i 2 Λি Νয় Μ৏ Ξ৯ Πਏ Ο৿ , V T = kT q Chap 3 -7
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Jaeger/Blalock 4/30/07 Microelectronic Circuit Design, 3E McGraw-Hill Width of Depletion Region w d 0 = ( x n + x p ) = 2 ε s q 1 N A + 1 N D Λি Νয় Μ৏ Ξ৯ Πਏ Ο৿ φ j Combining the previous expressions, we can form an expression for the width of the space-charge region, or depletion region. It is called the depletion region since the excess holes and electrons are depleted from the dopant atoms on either side of the junction.
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