Analog BiCMOS Design: Practices and Pitfalls

223 Pages·2000·2.483 MB·English

by  James C. Daly, Denis P. Galipeau

Analog
BiCMOS
DESIGN
Practices and Pitfalls
Analog
BiCMOS
DESIGN
Practices and Pitfalls
James C. Daly
Department of Electrical and Computer Engineering
University of Rhode Island
Denis P. Galipeau
Cherry Semiconductor Corp.
CRC Press
Boca Raton London New York Washington, D.C.

Foreword
This book presents practical methods and pitfalls encountered
in the design of biCMOS integrated circuits. It is intended as a
reference for design engineers and as a text for an introductory
course on analog integrated circuit design for engineering seniors
and graduate students. A broad range of topics are covered with
the intent of giving new designers the tools to complete a design
project. Most of the topics have been simplified so they can be
understood by students who have had a course in electronics.
The material has been used in a course open to seniors and
graduate students at the University of Rhode Island. In the
course, students were required to design an analog integrated cir-
cuit that was fabricated by Cherry Semiconductor Corporation.
In the process of assembling material for the book, we had dis-
cussions with many people who have been generous with informa-
tion, ideas and criticism. We are grateful to James Alvernez, Mark
Belch, Brad Benson, Mark Crowther, Vincenzo DiTommaso, Jeff
Dumas, Paul Ferrara, Godi Fischer, Justin Fisher, Robert Fugere,
Brian Harnedy, David Harrington, Ashish Kirtania, Seok-Bum
Ko, Shawn LaLiberte, Andreas Ladas, Sangmok Lee, Eric Lind-
berg, Jien-Chung Lo, Robert Maigret, Nadia Matchey, Andrew
McKinnon, Jay Moser, Ted Neira, Peter Rathfelder, Shelby Ray-
mond, Jon Rhan, Paul Sisson, Michael Tedeschi, Claudio Tuoz-
zolo, and Yingping Zheng.
Finally, we owe our thanks to the management and engineering
staff of Cherry Semiconductor Corporation. CSC has fabricated
scores of analog IC designs generated by the URI students enrolled
in the course that has been the basis for this book.
James C. Daly
Denis P. Galipeau
Contents
1 Devices
1.1 Introduction
1.2 Silicon Conductivity
1.2.1 Drift Current
1.2.2 Energy Bands
1.2.3 Sheet Resistance
1.2.4 Diffusion Current
1.3 Pn Junctions
1.3.1 Breakdown Voltage
1.3.2 Junction Capacitance
1.3.3 The Law of the Junction
1.3.4 Diffusion Capacitance
1.4 Diode Current
1.5 Bipolar Transistors
1.5.1 Collector Current
1.5.2 Base Current
1.5.3 Ebers-Moll Model
1.5.4 Breakdown
1.6 MOS Transistors
1.6.1 Simple MOS Model
1.7 DMOS Transistors
1.8 Zener Diodes
1.9 EpiFETs
1.10 Chapter Exercises
2 Device Models
2.1 Introduction
2.2 Bipolar Transistors
2.2.1 Early Effect
2.2.2 High Level Injection
2.2.3 Gummel-Poon Model
2.3 MOS Transistors
2.3.1 Bipolar SPICE Implementation
2.4 Simple Small Signal Models for Hand
Calculations
2.4.1 Bipolar Small Signal Model
2.4.2 Output Impedance
2.4.3 Simple MOS Small Signal Model
2.5 Chapter Exercises
3 Current Sources
3.1 Current Mirrors in Bipolar Technology
3.2 Current Mirrors in MOS Technology
3.3 Chapter Exercises
4 Voltage References
4.1 Simple Voltage References
4.2 Vbe Multiplier
4.3 Zener Voltage Reference
4.4 Temperature Characteristics of I and V
c be
4.5 Bandgap Voltage Reference
5 Amplifiers
5.1 The Common-Emitter Amplifier
5.2 The Common-Base Amplifier
5.3 Common-Collector Amplifiers (Emitter
Followers)
5.4 Two-Transistor Amplifiers
5.5 CC-CE and CC-CC Amplifiers
5.6 The Darlington Configuration
5.7 The CE-CB Amplifier, or Cascode
5.8 Emitter-Coupled Pairs
5.9 The MOS Case: The Common-Source
Amplifier
5.10 The CMOS Inverter
5.11 The Common-Source Amplifier with Source Degeneration
5.12 The MOS Cascode Amplifier
5.13 The Common-Drain (Source Follower)
Amplifier
5.14 Source-Coupled Pairs
5.15 Chapter Exercises
6 Comparators
6.1 Hysteresis
6.1.1 Hysteresis with a Resistor Divider
6.1.2 Hysteresis from Transistor Current Density
6.1.3 Comparator with V -Dependent Hysteresis
be
6.2 The Bandgap Reference Comparator
6.3 Operational Amplifiers
6.4 A Programmable Current Reference
6.5 A Triangle-Wave Oscillator
6.6 A Four-Bit Current Summing DAC
6.7 The MOS Case
6.8 Chapter Exercises
7 Amplifier Output Stages
7.1 The Emitter Follower: a Class A Output Stage
7.2 The Common-Emitter Class A Output Stage
7.3 The Class B (Push-Pull) Output
7.4 The Class AB Output Stage
7.5 CMOS Output Stages
7.6 Overcurrent Protection
7.7 Chapter Exercises
8 Pitfalls
8.1 IR Drops
8.1.1 The Effect of IR Drops on Current Mirrors
8.2 Lateral pnp
8.2.1 The Saturation of Lateral pnp Transistors
8.2.2 Low Beta in Large Area Lateral pnps
8.3 npn Transistors
8.3.1 Saturating npn Steals Base Current
8.3.2 Temperature Turns On Transistors
8.4 Comparators
8.4.1 Headroom Failure
8.4.2 Comparator Fails When Its Low Input Limit Is
Exceeded
8.4.3 Premature Switching
8.5 Latchup
8.5.1 Resistor ISO EPI Latchup
8.6 Floating Tubs
8.7 Parasitic MOS Transistors
8.7.1 Examples of Parasitic MOSFETs
8.7.2 OSFETs
8.7.3 Examples of Parasitic OSFETs
8.8 Metal Over Implant Resistors
9 Design Practices
9.1 Matching
9.1.1 Component Size
9.1.2 Orientation
9.1.3 Temperature
9.1.4 Stress
9.1.5 Contact Placement for Matching
9.1.6 Buried Layer Shift
9.1.7 Resistor Placement
9.1.8 Ion Implant Resistor Conductivity Modulation
9.1.9 Tub Bias Affects Resistor Match
9.1.10 Contact Resistance Upsets Matching
9.1.11 The Cross Coupled Quad Improves Matching
9.1.12 Matching Calculations
9.2 Electrostatic Discharge Protection (ESD)
9.3 ESD Protection Circuit Analysis
9.4 Chapter Exercises
chapter 1
Devices
1.1 Introduction
The properties and performance of analog biCMOS integrated circuits
are dependent on the devices used to construct them. This chapter is
a review of the operation of silicon devices. It begins with a discus-
sion of conductivity and resistance. Simple physical models for bipolar
transistors,MOStransistors,andjunctionanddiffusioncapacitanceare
developed.
1.2 Silicon Conductivity
The conductivity of silicon can be controlled and made to vary over
several orders of magnitude by adding small amounts of impurities. Sil-
icon belongs to group four in the periodic table of elements. It has four
valence electrons in its outer shell. A silicon atom in a silicon crystal
has four nearest neighbors. Silicon forms covalent bonds where each
atom shares its valence electrons with its four nearest neighbors. Each
atom has its four original valence electrons plus the four belonging to
its neighbors. That gives it eight valence electrons. The eight valence
electronscompletetheshellproducingastablestateforthesiliconatom.
Electrical conductivity requires current consisting of moving electrons.
The valence electrons are attached to an atom and are not free to move
far from it. Some valence electrons will receive enough thermal energy
tofreethemselvesfromthesiliconatom. Theseelectronsmovetoenergy
levelsinabandofenergycalledtheconductionband. Conductionband
electrons are not attached to a particular atom and are free to move
about the crystal.
When an electron leaves a silicon atom, the atom becomes a posi-
tively charged silicon ion. The situation is represented schematically in
Figure 1.1. The vacant valence state, previously occupied by the elec-
tron, is called a hole. Each hole has a positive charge equal to one