EE141 Microelectronic Circuits Chapter 10. Semiconductors, Diodes, and Power Supplies School of Computer Science and Engineering Pusan National University Jeong Goo Kim

10-1 Introduction Diode two-terminal electronic device forward bias; conducts current reverse bias; refuses to conduct current “check “ valves or “flapper” valves

10-2 p- and n-Type Semiconductors Elements surrounding silicon in periodic table group four elements covalent bonds form crystal lattice → poor conductor

Dopping n-Type silicon p-Type silicon intrinsic ; pure silicon 10-2 Semiconductors Dopping intrinsic ; pure silicon dopants ; impurities n-Type silicon donor Phosphorus free electron p-Type silicon acceptor Boron hole

n-type material p-type material Intrinsic material 10-2 Semiconductors n-type material free electron concentration, n, in electrons/cm3 n ≈ ND here ND is the donor atom dopping density in atoms/cm3 ND > NA and n>p p-type material free hole concentration, p, in holes/cm3 n ≈ NA here NA is the acceptor atom dopping density in atoms/cm3 NA > ND and p > n Intrinsic material Intrinsic carrier concentration, ni ni = n = p for silicon at 300°K, ni ≈ 1.6×1010 electrons/cm3

10-3 Current Conduction in Semiconductors Electric current electron and hole drift and diffusion current 10.3.1 Drift Electric field vector Electron drift velocity Hole drift velocity for silicon and

10-3 Current Conduction in Semiconductors Conductivity Resistivity Resistance Example 10.1 Current density Example 10.2

10-3 Current Conduction in Semiconductors 10.3.2 Diffusion Movement from a region of high concentration to a region of lower concentration. Diffusion current density dn/dx is the electron concentration gradient Dn is the diffusion constant for silicon at 300°K and Example 10.3

10-4 The p-n Junction Diode depletion region

10-4 The p-n Junction Diode Potential barrier Forward and reverse bias Forward bias Reverse bias

10-5 Diode Circuit Models Symbol and physical structure 10.5.1 The Ideal Diode V-I curve symbol switch model

10.5.2 Diode Equation and Model 10-5 Diode Circuit Models 10.5.2 Diode Equation and Model Diode equation ID : diode current Io : reverse saturation current q : electronic charge VD : voltage across the diode k: Boltzmann’s constant T: temperature V-I curve with equation and series resistance

10.5.3 The Piecewise Linear Diode Model 10-5 Diode Circuit Models 10.5.3 The Piecewise Linear Diode Model Turn-off voltage VF 1 μA as the threshold of conduction, for silicon VF=0.7V V-I curve for piecewise linear model and symbol Examples

10-6 Power Supply Circuits EE141 10-6 Power Supply Circuits Typical input section of a power supply Transformer is used to step down the voltage

10-6 Power Supply Circuits 10.6.1 Half-Wave Rectification Example 10.11 Average output voltage

10-6 Power Supply Circuits Example 10.13 Half-Wave Rectifier with PL Diode model

10-6 Power Supply Circuits EE141 10.6.2 Filter Circuits for Half-Wave Rectification filter : produce smooth dc from ac input ripple : small variation in voltage from filter output

10-6 Power Supply Circuits EE141 Calculation of ripple magnitude ripple factor, RF

10-6 Power Supply Circuits EE141 10.6.3 Full-Wave Rectification dc value of full-wave rectifier Alternation

10-7 Wave Shaping: Clippers and Clampers 10.7.1 Clipper Circuits are used to limit the voltage excursions of a signal at a positive value, at a negative value, or both. Example 10.14

10-7 Wave Shaping: Clippers and Clampers 10.7.2 Clamping Circuit is circuit that produces an output that appears just as input with one exception-the dc level or average voltage is shifted positively or negatively.

10-8 The Zener or Avalanche Diode Breakdown if reverse voltage increase high, a diode conducts a large current in the reverse direction. the reverse current remains extremely small until the reverse bias voltage reaches breakdown voltage, called avalanche or zener breakdown voltage, Vz.

10-9 Load Lines and Graphical Solutions current ID by diode equation loop equation

10-10 Photo Diode and Light Emitting Diode 10-10 Photo Diode and LED 10-10 Photo Diode and Light Emitting Diode Photo diode is used to convert incident radiation to electrical current Solar cell is a large p-n diode which creates electron-hole pairs in the depletion region from the sun’s radiation. are also used for light intensity meters. LED are p-n junction with Ga-As semiconductor. release energy in the form of light.

Chapter 11. Transistor Fundamentals Homework EE141 Homework Read textbook pp. 406-449 Solve problems 9, 16, 19, 24, 26, 34, 38, 40, 43, 47, 49, 52 Next Lecture Chapter 11. Transistor Fundamentals