Transcript
Outline
• NMOS Operation in
Cut off ,Linear and Saturation mode
Related Equations
1/27/2015 EEE C424/ECE C313
Outline
Cut off ,Linear and Saturation mode
EEE C424/ECE C313 1
Recap
• Physics of MOSFET
• NMOS
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Recap
EEE C424/ECE C313 2
CMOS DESIGN
•The operation of PMOSto the NMOS transistor,that the majority carriersvoltages are negative with
substrate.
MOSFET
CMOS DESIGN
PMOS transistor is analogoustransistor, with the exception
carriers are holes and thewith respect to the
MOSFET
MOS Transistors
• Silicon, forms the basic starting material
• MOS structure is created by superimposing several layers of conducting,insulating and transistor forming materials
• CMOS technology provides two types of transistorsNegatively (-ve) diffused silicon that is rich in electrons :
Positively (+ve) doped silicon that is rich in holes :
CMOS DESIGN
MOS Transistors
Silicon, forms the basic starting material
structure is created by superimposing several layers of conducting,insulating and transistor forming materials
technology provides two types of
ve) diffused silicon that is rich in electrons : NMOS
Positively (+ve) doped silicon that is rich in holes : PMOS
CMOS DESIGN
MOSFET
Perspective View
MOSFET
Cross sectional View
Operation of nmos with no gate voltage applied
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Channel Formation In NMOS
Operation of nmos with no gate voltage applied
6
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Accumulation mode [ 0 < V
7
Accumulation mode [ 0 < Vg ]
Vg = Vgs = Gate Voltage
Operation of nmos with gate voltage applied
Operation of nmos with gate voltage applied
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What happens if Gate Voltage V
EEE C424/ECE C313 9
What happens if Gate Voltage Vg = Vgs is increased ?
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Depletion Mode [ 0<V
10
Depletion Mode [ 0<Vg<Vt ]
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Inversion mode [V
Enhacement NMOS
11
Inversion mode [Vg >Vt ]
Enhacement NMOS
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MOSFET
NMOS PMOS
Enhacement NMOS Depletion NMOS
13
MOSFET
NMOS PMOS
Depletion NMOS
Enhacement PMOS Depletion PMOS
Applying a small VApplying a small VDS
ID Vs Vds Characterstics when Vsmall (Linear Region)
Characterstics when Vds
small (Linear Region)
Chapter 4 MOS field-Effect Transistors (MOSFETs)
Figure 4.5Operation as VEffect Transistors (MOSFETs)
Figure 4.5Operation as VDS increased
Applying a small VApplying a small VDS
ID Vs Vds Characterstics when Vsmall (Linear Region)
Conductance of channel propotional to V(Vov,overdrive voltage
Characterstics when Vds
small (Linear Region)
Conductance of channel propotional to VGS-Vt
,overdrive voltage)
Chapter 4 MOS field-Effect Transistors (MOSFETs)
Figure 4.5Operation as V
VGS
•The voltage between the gate and points along the channel decreases from VGS
VGS – VDS at the drain end
Effect Transistors (MOSFETs)
Figure 4.5Operation as VDS increased
VGS - VDS
The voltage between the gate and points along the at the source end to
ID Vs VDS Characterstics
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Characterstics
EEE C424/ECE C313 20
Channel isPinched off point
Effect on Channel as V
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Effect on Channel as VDS increased
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Chapter 4 MOS field-Effect Transistors (MOSFETs)
Figure 4.15Channel Length ModulationEffect Transistors (MOSFETs)
Figure 4.15Channel Length Modulation
iD Vs VDS relationship
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relationship
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Current Equation in Linear/Triode region
• Linear Region :
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saturation
Current Equation in Linear/Triode region
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• Linear Region :
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Substituting VGS – Vt = V
Current Equation in saturation region
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VDS
saturation
Current Equation in saturation region
I-V Characteristics of MOSFETV Characteristics of MOSFET
HomeWork
• Derive Current equation in linear and saturation mode for NMOS
(Ref: Page 243 Sedra Smith)
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HomeWork
Derive Current equation in linear and saturation mode for NMOS
(Ref: Page 243 Sedra Smith)
EEE C424/ECE C313 27
Drain Current
• ID α W/L (Aspect Ratio)
α
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Drain Current
W/L (Aspect Ratio)
EEE C424/ECE C313 28
NMOS Transistor
CMOS DESIGN
NMOS Transistor
CMOS DESIGN
NMOS Transistor - Symbolic RepresentationSymbolic Representation
NMOS Transistor with vNMOS Transistor with vGS and vDS applied
iD - vDS Characterstics
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Triode Region Saturation Region
Channel isPinched off
Characterstics
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Saturation Region
vGS= vt+ 0.5
vGS= vt+ 1.0
vGS= vt+ 1.5
vGS= vt+ 2.0Channel isPinched off
iD - vDS CharactersticsCharacterstics
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