Transcript Electronic Circuit Analysis and Design Second Edition

Introduction
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Labs and Course
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Multiple experiments
Prerequisites- Administrative drop
General Approach
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FETs and BJTs
Analytical approach
First Mid-Term
Syllabus
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Semiconductor fundamentals. Diodes and diode circuits.
Field Effect Transistor (FET), FET Amplifiers and circuits.
Bipolar Junction Transistor (BJT), BJT Amplifiers and circuits
Exam 1
Frequency response.
Output Stages and Power Amplifiers
Ideal Operational Amplifier
Integrated Circuit Biasing and Active Loads.
Differential and Multistage Amplifiers.
Operational Amplifier Circuits
Exam 2
Nonideal Effects in Operational Amplifier Circuits
Design of Integrated Circuits
Feedback and Stability
Introduction to Semiconductors
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Metals, Insulators, Semiconductors
In SC we have 2 ‘types’ of carriers present.
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Electrons
Holes- Absence of electrons
Separated in different energy bands
The separation between these bands is the band gap of
the SC
Three types of solids, classified according to atomic arrangement:
(a) crystalline and (b) amorphous materials are illustrated by
microscopic views of the atoms, whereas (c) polycrystalline structure
is illustrated by a more macroscopic view of adjacent singlecrystalline regions, such as (a).
Unit cells for three types of cubic lattice structures.
Semiconductor Structure
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The fundamental property that distinguishes SC
from other materials is bonding.
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Ionic Bonding- Coulombic Interaction (localized
carriers)
Metallic- Plenty of electrons that move around ‘freely’
Covalent [SC]- Electrons shared by atoms, rather
localized, but can be ‘freed’ to move around the lattice.
The limited number of available carriers in SC
compared to metals is key to their behavior.
Different types of chemical bonding in solids (a) an example of ionic bonding in
NaCl; (b) covalent bonding in the Si crystal, viewed along a <100> direction
(see also Figs. 1–8 and 1–9).
Diamond lattice unit cell, showing the four nearest neighbor structure. (From Electrons and
Holes in Semiconductors by W. Shockley, © 1950 by Litton Educational Publishing Co.,
Inc.; by permission of Van Nostrand Reinhold Co., Inc.)
Electronic structure and energy levels in a Si atom: (a) The orbital model of a Si atom showing the
10 core electrons (n = 1 and 2), and the 4 valence electrons (n = 3); (b) energy levels in the
coulombic potential of the nucleus are also shown schematically.
Linear combinations of atomic orbitals (LCAO): The LCAO when 2 atoms are brought together leads to 2
distinct “normal” modes—a higher energy anti-bonding orbital, and a lower energy bonding orbital. Note
that the electron probability density is high in the region between the ion cores (covalent “bond”), leading
to lowering of the bonding energy level and the cohesion of the crystal. If instead of 2 atoms, one brings
together N atoms, there will be N distinct LCAO, and N closely-spaced energy levels in a band.
Energy levels in Si as a function of inter-atomic spacing. The core levels (n = 1,2) in Si are
completely filled with electrons. At the actual atomic spacing of the crystal, the 2 N electrons in
the 3 s sub-shell and the 2 Nelectrons in the 3 p sub-shell undergo sp 3 hybridization, and all end
up in the lower 4 Nstates (valence band), while the higher lying 4 Nstates (conduction band) are
empty, separated by a bandgap.
Typical band structures at 0 K.
Relationship between band gap and lattice constant for alloys in the InGaAsP and AlGaAsSb systems. The dashed
vertical lines show the lattice constants for the commer-cially available binary substrates GaAs and InP. For the marked
example of InxGa1—xAs, the ternary composition x ~ 0.53 can be grown lattice-matched on InP, since the lattice
constants are the same. For quaternary alloys, the compositions on both the III and V sub-lattices can be varied to grow
lattice-matched epitaxial layers along the dashed vertical lines between curves. For example, In x Ga 1— x As y P 1— y can
be grown on InP substrates, with resulting band gaps ranging from 0.75 eV to 1.35 eV. In using this figure, assume the
lattice constant a of a ternary alloy varies linearly with the composition x.
Electron-hole pairs in a semiconductor.
Energy band model and chemical bond model of dopants in semiconductors: (a) donation of
electrons from donor level to conduction band; (b) acceptance of valence band electrons by an
acceptor level, and the resulting creation of holes; (c) donor and acceptor atoms in the covalent
bonding model of a Si crystal.
Electron–hole pairs in the covalent bonding model of the Si crystal.
Direct and indirect electron transitions in semiconductors: (a)
direct transition with accompanying photon emission; (b) indirect
transition via a defect level.
Saturation of electron drift velocity at high electric
fields for Si.
Properties of an equilibrium p-n junction: (a) isolated, neutral regions of p-type
and n-type material and energy bands for the isolated regions; (b) junction,
showing space charge in the transition region W, the resulting electric field % and
contact potential V0, and the separation of the energy bands; (c) directions of the
four components of particle flow within the transition region, and the resulting
current directions.
Space charge and electric field distribution within the transition region of a p-n junction
with Nd > Na: (a) the transition region, with x = 0 defined at the metallurgical junction; (b)
charge density within the transition region, neglecting the free carriers; (c) the electric
field distribution, where the reference direction for % is arbitrarily taken as the +xdirection.
Examples of contact potential for a heavily doped p-n
junction: (a) at equilibrium; (b) approaching the
maximum forward bias V = V0
Effects of a bias at a p-n junction; transition region width and electric
field, electrostatic potential, energy band diagram, and particle flow and
current directions within W for (a) equilibrium, (b) forward bias, and (c)
reverse bias.
I–V characteristic of a p-n junction.
The Zener effect: (a) heavily doped junction at equilibrium; (b)
reverse bias with electron tunneling from p to n; (c) I–V
characteristic.
Reverse breakdown in a p-n junction.
Saturation of electron drift velocity at high electric
fields for Si.
Forward and reverse current-voltage characteristics plotted on semi-log scales, with current normalized with
respect to saturation current, I0; (a) the ideal forward characteristic is an exponential with an ideality factor, n = 1
(dashed straight line on log-linear plot). The actual forward characteristics of a typical diode (colored line) have
four regimes of operation; (b) ideal reverse characteristic (dashed line) is a voltage-independent current = 2 I0.
Actual leakage characteristics (colored line) are higher due to generation in the depletion region, and also show
breakdown at high voltages.
Ideal forward-biased I-V characteristics of pn junction diode, with the
current plotted on a log scale for Is = 10-14 A and n = 1
The ideal diode: (a) I-V characteristics, (b) equivalent circuit under
reverse bias, and (c) equivalent circuit in the conducting state
I–V characteristics of heavily doped p-n junction diodes at 77 K,
illustrating the effects of contact potential on the forward current:
(a) Ge, Eg . 0.7 eV; (b) Si, Eg . 1.4 eV; (c) GaAs, Eg . 1.4 eV; (d)
GaAsP, Eg . 1.9 eV.
Piecewise-linear approximations of junction diode characteristics:
(a) the ideal diode; (b) ideal diode with an offset voltage; (c) ideal
diode with an offset voltage and a resistance to account for slope
in the forward characteristic.
AC circuit analysis: (a) circuit with combined dc and sinusoidal input voltages, (b) sinusoidal
diode current superimposed on the quiescent current, (c) sinusoidal diode voltage
superimposed on the quiescent value, and (d) forward-biased diode I-V characteristics with a
sinusoidal current and voltage superimposed on the quiescent values
The diode and load line characteristics for the circuit shown in
Figure 1.24
The diode rectifier: (a) circuit, (b) sinusoidal input signal,
(c) equivalent circuit for vI> 0, (d) equivalent circuit for vI < 0, and
(e) rectified output signal
The diode equivalent circuit (a) in the “on” condition when VD  Vy,
(b) in the “off” condition when VD < Vy, and (c) piecewise linear
approximation when rf = 0
A breakdown diode: (a) I–V characteristic;
(b) application as a voltage regulator.
Space charge and electric field distribution within the transition region of a p-n junction with Nd > Na:
(a) the transition region, with x = 0 defined at the metallurgical junction; (b) charge density within the
transition region, neglecting the free carriers; (c) the electric field distribution, where the reference
direction for % is arbitrarily taken as the +x-direction.
Effects of a step turn-off transient in a p+-n diode: (a) current
through the diode; (b) decay of stored charge in the n-region;
(c) excess hole distribution in the n-region as a function of time
during the transient.
Effects of storage delay time on switching
signal: (a) switching voltage; (b) diode current.
A Schottky barrier formed by contacting an n-type semiconductor with a
metal having a larger work function: (a) band diagrams for the metal and
the semiconductor before joining; (b) equilibrium band diagram for the
junction.
Ohmic metal–semiconductor contacts: (a) Fm < Fs for an n-type
semiconductor, and (b) the equilibrium band diagram for the junction; (c) F m <
Fs for a p-type semiconductor, and (d) the junction at equilibrium.