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Digital Integrated Circuits A Design Perspective

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x 10. I. D (A) VGS= 2.5 V. VGS= 2.0 V. VGS= 1.5 V. VGS= 1.0 V. Early Saturation ... x 10 -4. V. GS (V) I. D (A) quadratic. quadratic. linear. Long Channel ... – PowerPoint PPT presentation

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Title: Digital Integrated Circuits A Design Perspective


1
Digital Integrated Circuits A Design Perspective
Jan M. Rabaey Anantha Chandrakasan Borivoje
Nikolic
The Devices
July 30, 2002
2
Goal of this chapter
  • Present intuitive understanding of device
    operation
  • Introduction of basic device equations
  • Introduction of models for manual analysis
  • Introduction of models for SPICE simulation
  • Analysis of secondary and deep-sub-micron effects
  • Future trends

3
The Diode
Mostly occurring as parasitic element in Digital
ICs
4
Depletion Region
5
Diode Current
6
Models for Manual Analysis
7
Diode Model
8
SPICE Parameters
9
What is a Transistor?
10
The MOS Transistor
Polysilicon
Aluminum
11
MOS Transistors - Types and Symbols
D
D
G
G
S
S
Depletion
NMOS
Enhancement
NMOS
D
D
G
G
B
S
S
NMOS with
PMOS
Enhancement
Bulk Contact
12
Threshold Voltage Concept
13
The Threshold Voltage
14
The Body Effect
15
Current-Voltage Relations A good ol transistor
16
Transistor in Linear
17
Transistor in Saturation
18
Current-Voltage Relations Long-Channel Device
19
A model for manual analysis
20
Current-Voltage Relations The Deep-Submicron Era
21
Velocity Saturation
Constant velocity
Constant mobility (slope µ)
22
Perspective
I
D
Long-channel device
V
V
GS
DD
Short-channel device
V
V
V
- V
DSAT
DS
GS
T
23
ID versus VGS
linear
quadratic
quadratic
Long Channel
Short Channel
24
ID versus VDS
Long Channel
Short Channel
25
A unified model for manual analysis
NB For PMOS, use Vmaxmax() instead of Vmin
26
Simple Model versus SPICE
(A)
D
I
V
(V)
DS
27
A PMOS Transistor
VGS -1.0V
VGS -1.5V
VGS -2.0V
Assume all variables negative!
VGS -2.5V
28
Transistor Model for Manual Analysis
29
The Transistor as a Switch
30
The Transistor as a Switch
31
The Transistor as a Switch
32
Unified Model Examples
33
MOS Capacitances Dynamic Behavior
34
Dynamic Behavior of MOS Transistor
35
The Gate Capacitance
36
Gate Capacitance
Cut-off
Resistive
Saturation
Most important regions in digital design
saturation and cut-off
37
Gate Capacitance
Capacitance as a function of VGS (with VDS 0)
Capacitance as a function of the degree of
saturation
38
Measuring the Gate Cap
39
Diffusion Capacitance
Channel-stop implant
N
1
A
Side wall
Source
W
N
D
Bottom
x
Side wall
j
Channel
L
Substrate
N
S
A
40
Junction Capacitance
41
Linearizing the Junction Capacitance
Replace non-linear capacitance by large-signal
equivalent linear capacitance which displaces
equal charge over voltage swing of interest
42
Capacitances in 0.25 mm CMOS process
43
Sub-Threshold Conduction
The Slope Factor
S is DVGS for ID2/ID1 10
Typical values for S 60 .. 100 mV/decade
44
Sub-Threshold ID vs VGS
VDS from 0 to 0.5V
45
Sub-Threshold ID vs VDS
VGS from 0 to 0.3V
46
Summary of MOSFET Operating Regions
  • Strong Inversion VGS gt VT
  • Linear (Resistive) VDS lt VDSAT
  • Saturated (Constant Current) VDS ? VDSAT
  • Weak Inversion (Sub-Threshold) VGS ? VT
  • Exponential in VGS with linear VDS dependence

47
Parasitic Resistances
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