Design Technologies
Put them in series - both must be on to
complete the circuit. Put them in parallel - either can be on to
complete the circuit.Generate all sorts of Switching Functions.NOT the same as Boolean Functions.... Its.RELAY logic - pin ball machines
Design Technologies
Introduction to VLSI Design Introduction © Steven P. Levitan 1998
Views / Abstractions / Hierarchies
Structural
Behavioral
device
Circuit
Logic
Architectural
Physical
D.Gajski, Silicon Compilation, Addison Wesley, 1988
Introduction to VLSI Design Introduction © Steven P. Levitan 1998
N-Channel Enhancement
mode MOS FET
– Four Terminal Device - substrate bias
–The “self aligned gate” - key to CMOS
Introduction to VLSI Design Introduction © Steven P. Levitan 1998
The MOS Transistor
Gate Oxyde
Gate
Polysilicon Field-Oxyde
Source Drain
(SiO2)
n+ n+
p+ stopper
p-substrate
Bulk Contact
CROSS-SECTION of NMOS Transistor
Digital Integrated Circuits Introduction © Prentice Hall 1995
MOS transistors
Types and Symbols
D D
G G
S S
NMOS Enhancement NMOS Depletion
D D
G G B
S S
PMOS Enhancement NMOS with
Bulk Contact
Digital Integrated Circuits Introduction © Prentice Hall 1995
The Basic Idea…
» Voltage on the Gate controls the current through
the source/drain path
» N-Channel - N-Switches are ON when the Gate
is HIGH and OFF when the Gate is LOW
» P-Channel - P-Switches are OFF when the Gate
is HIGH and ON when the Gate is LOW
» (ON == Circuit between Source and Drain)
Introduction to VLSI Design Introduction © Steven P. Levitan 1998
Transistors as Switches
N Switch
D
0 1
G Passes “good zeros”
S
P Switch
D
0
G 1 Passes “good ones”
S
Introduction to VLSI Design Introduction © Steven P. Levitan 1998
….The Rest of the Story...
» Put them in series - both must be on to
complete the circuit
» Put them in parallel - either can be on to
complete the circuit
» Generate all sorts of Switching Functions
» NOT the same as Boolean Functions.... Its
RELAY logic - pin ball machines
Introduction to VLSI Design Introduction © Steven P. Levitan 1998
Series Parallel Structures
D
1 G
S D D
D
1 G G 1
S S
1 G
S
N Channel: on=closed when gate is high
Introduction to VLSI Design Introduction © Steven P. Levitan 1998
NMOS Transistors in Series/Parallel
Connection
Transistors can be thought as a switch controlled by its gate signal
NMOS switch closes when switch control input is high
A B
X Y Y = X if A and B
A
X B Y = X if A OR B
Y
NMOS Transistors pass a “strong” 0 but a “weak” 1
Digital Integrated Circuits Introduction © Prentice Hall 1995
Series Parallel Structures(2)
D
0 G
S D D
D
0 G G 0
S S
0 G
S
P Channel: on=closed when gate is low
Introduction to VLSI Design Introduction © Steven P. Levitan 1998
PMOS Transistors in Series/Parallel
Connection
PMOS switch closes when switch control input is low
A B
X Y Y = X if A AND B = A + B
A
X B Y = X if A OR B = AB
Y
PMOS Transistors pass a “strong” 1 but a “weak” 0
Digital Integrated Circuits Introduction © Prentice Hall 1995
Series Parallel Structures (3)
N Switch
0
S 1
G
Passes “good zeros”
D
S
D
S
Passes “good ones”
G
S’ 0
1
P Switch
Open Circuit, High Z
Bidirectional Switch
Introduction to VLSI Design Introduction © Steven P. Levitan 1998
From Switches to Boolean
Functions...
q Use the Switching Functions to provide paths
to Vdd or GND
» Vdd is the source of all Truth (Vdd = = 1)
» GND is the source of all Falsehood (GND == 0)
Pchannel Nchannel 0
0 1
1
Introduction to VLSI Design Introduction © Steven P. Levitan 1998
The Inverter
q True to False / False to True Converter
1/0 0/1
Introduction to VLSI Design Introduction © Steven P. Levitan 1998
…That’s it!
q This is Non-Trivial: it defines the basis
for the logic abstraction which is
essential for all Boolean functions.
» Provide a path to VDD for 1
» Provide a path to GND for 0
» For complex functions - provide complex
paths
Introduction to VLSI Design Introduction © Steven P. Levitan 1998
Four Views
Logic Transistor Layout Physical
Introduction to VLSI Design Introduction © Steven P. Levitan 1998
Cross-Section of CMOS
Technology
Digital Integrated Circuits Introduction © Prentice Hall 1995
Magic Layout of Inverter
Introduction to VLSI Design Introduction © Steven P. Levitan 1998
Magic “Palette” of Layers
Introduction to VLSI Design Introduction © Steven P. Levitan 1998
