数字集成电路设计 第三章 ppt

Mostly occurring as parasitic element in Digital ICs
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Depletion Region
hole diffusion electron diffusion p hole drift electron drift Charge Density + x Distance (b) Charge density. n (a) Current flow.
2.5 x 10
-4
Early Saturation
2
VGS= 2.5 V
VGS= 2.0 V
1.5
ID (A)
1
VGS= 1.5 V
Linear Relationship
0.5
VGS= 1.0 V
0
0
0.5
1 VDS (V)
1.5
2
2.5
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-0.8
VGS = -2.5V
-1 -2.5
-2
-1.5
VDS (V)
-1
-0.5
0
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Devices
Transistor Model for Manual Analysis
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Devices
The Body Effect
0.9 0.85 0.8 0.75 0.7
VT (V)
0.65 0.6 0.55 0.5 0.45 0.4 -2.5 -2 -1.5 -1 -0.5 0
V
BS
(V)
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Devices
Current-Voltage Relations A good ol’ transistor
Digital Integrated Circuits
A Design Perspective
Jan M. Rabaey Anantha Chandrakasan Borivoje Nikolic
The Devices
July 30, 2002
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7 x 10
5
6 5
Req (Ohm)
4
电阻反比于器件的（W/L）
3
2 1
0 0.5
1
1.5
2
2.5
V
DD
(V)
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Devices
The Transistor as a Switch
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Saturated
1 1.5 2 2.5
VDS (V)
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Devices
A PMOS Transistor
0
x 10
-4
VGS = -1.0V -0.2 VGS = -1.5V -0.4
ID (A)
-0.6
VGS = -2.0V
Assume all variables negative!
-4
quadratic
linear
1.5
ID (A)
3
1
2
1 0 0 0.5
quadratic
0.5 1
VGS(V)
1.5
2
2.5
0 0
0.5
1
VGS(V)
1.5
2
2.5
Long Channel
Short Channel
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Devices
ID versus VDS
Diffusion Capacitance
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Devices
Secondary Effects
0.1
ID (A)
0
–0.1 –25.0
–15.0 VD (V)
–5.0
0
5.0
Avalanche Breakdown
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pn0
np0
p-region
-W1 0
W2
n-region diffusion
x
The Dominant Operation Mode
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Models for Manual Analysis
ID = IS(eV D/T – 1) VD – – ID + + – VDon
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-submicron effects Future trends
Transistor in Saturation
VGS G S n+
-
VDS > VGS - VT D
+
VGS - VT
n+
Pinch-off
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Devices
Current-Voltage Relations Long-Channel Device
Devices
Transistor in Linear
VGS S G n+ – VDS D n+ L x ID
V (x )
+
p-substrate B
MOS transistor and its bias conditions
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Devices

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The Diode
B Al p n Cross-section of pn -junction in an IC process A p n B One-dimensional representation B diode symbol Al A A SiO2
G
S
D
B
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Simple Model versus SPICE
2.5 x 10
-4
VDS=VDSAT
2
1.5
Velocity Saturated Linear
ID (A)
1
VDSAT=VGT
0.5
VDS=VGT
0 0 0.5
Devices
Forward Bias
pn (W2)
pn0 Lp np0
p-region
-W1 0
W2
n-region
x
diffusion
Typically avoided in Digital ICs
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Reverse Bias
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Devices
A model for manual analysis
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Devices
Current-Voltage Relations The Deep-Submicron Era
Electrical Field

x
(c) Electric field.
Potential -W 1
V W2 x (d) Electrostatic potential.
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Devices
Diode Current
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6 5 4 x 10
-4
VGS= 2.5 V
x 10 2.5
-4
VGS= 2.5 V
2
Resistive Saturation VDS = VGS - VT
VGS= 1.5 V
0.5
ID (A)
3 2 1 0 0
ID (A)
VGS= 2.0 V
VGS= 2.0 V
1.5
1
VGS= 1.5 V
VGS= 1.0 V
VGS V T Ron S D
An MOS Transistor
|VGS|
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Devices
The MOS Transistor
Polysilicon
Aluminum
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MOS Transistors Types and Symbols
D
D G S G
S
NMOS Enhancement NMOS Depletion
D D
G
G S S
B
PMOS Enhancement
NMOS with Bulk Contact Devices
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Devices
The Transistor as a Switch
VGS V T Ron S
ID V GS = VD D Rmid R0 V DS VDD/2 VDD
D
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The Transistor as a Switch
Diode Model
RS + VD ID CD
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Leabharlann Baidu
SPICE Parameters
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What is a Transistor?
A Switch!
ID
Long-channel device VGS = VDD Short-channel device
V DSAT
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VGS - V T
VDS
Devices
ID versus VGS
6 5 2 4
I D (A)
x 10
-4
x 10 2.5
Devices
Velocity Saturation
u n (m/s)
usat = 105
Constant velocity
Constant mobility (slope = µ)
c = 1.5
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(V/µm)
Devices
Perspective
0.5 1 VDS(V) 1.5 2 2.5 0 0 0.5 1 VDS(V) 1.5
VGS= 1.0 V
2 2.5
Long Channel © Digital Integrated Circuits2nd
Short Channel Devices
A unified model for manual analysis
Threshold Voltage: Concept
S + VGS G D
n+
n+
n-channel p-substrate B
Depletion Region
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The Threshold Voltage
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+ VD
(a) Ideal diode model
(b) First-order diode model
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Junction Capacitance
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Devices
MOS Capacitances Dynamic Behavior
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Dynamic Behavior of MOS Transistor
G
CGS S
CGD D
CSB
CGB
CDB
6 x 10
-4
VGS= 2.5 V
5
Resistive
4
Saturation
VGS= 2.0 V
ID (A)
3
VDS = VGS - VT
VGS= 1.5 V
Quadratic Relationship
2
1
VGS= 1.0 V
0
0
0.5
1 VDS (V)
1.5
2
2.5
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