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The NFET explained… in only a few confusing slides. Voltage-controlled Current Source. D rain. V ds. G ate. I DS. d. V gs. g. Vds > Vgs-Vt. S ource. s. l
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The NFET explained…
in only a few confusing slides.
Voltage-controlledCurrent Source
g
s
d
IDS = k ( ) ( Vgs - Vt )W
L
2
Drain
Source
GateIDS
Vgs
Vds
Vds > Vgs-Vt
Saturation Region:
(1 + Vds)
Early Effect
<< 1
Fig 4-13
Vt
Ids
Vgs
Drain
Source
GateIDS
Vgs
Vds
Vds > Vgs - Vt
Ohmic (Triode) Region:
IDS = k ( ) [ 2 (Vgs - Vt) Vds - Vds ]W
L
2
Vds < Vgs - Vt
Drain
Source
GateIDS
(Vds is small)
Vds
IdsFig 4-12
Drain
Source
GateIDS
dotted line iswhat the previousgraph plotted.
n+ n+
p-type
source = 0.0 v drain = 0.0 v
gate = 0.0 v
NFET - Operation
depletion regions
NFET - Operation
n+ n+
p-type
source = 0.0 v drain = 0.0 v
gate = 0.0 v
(subthreshold)
NFET - Operation
n+ n+
p-type
source = 0.0 v drain = 0.0 v
gate = 0.4 v
depletion region
(subthreshold)
NFET - Operation
n+ n+
p-type
source = 0.0 v drain = 0.0 v
gate = 0.6 v
(subthreshold)
NFET - Operation
n+ n+
p-type
source = 0.0 v drain = 0.0 v
gate = 0.75 v
inversion
A channel is formed….
Threshold Voltage, Vgs = 0.75 v
NFET - Operation
n+ n+
p-type
source = 0.0 v drain = 0.0 v
gate = 1.0 v
(above threshold)
Ids = 0.0 A
NFET - Operation
n+ n+
p-type
source = 0.0 v drain = .05 v
gate = 1.0 v
(above threshold)
Ids = 10 uA
NFET - Operation
n+ n+
p-type
source = 0.0 v drain = 0.1 v
gate = 1.0 v
(above threshold)
Ids = 20 uA
0.1v0.05v
NFET - Operation
n+ n+
p-type
source = 0.0 v drain = 0.2 v
gate = 1.0 v
(above threshold)
Ids = 40 uA
0.1v 0.2v.05v
NFET - Operation
n+ n+
p-type
source = 0.0 v drain = 0.25 v
gate = 1.0 v
(above threshold)
Ids = 59 uA
.05v 0.1v0.25v
Pinch-off
Vds > Vgs - Vt
NFET - Operation
n+ n+
p-type
source = 0.0 v drain = 0.3 v
gate = 1.0 v
(above threshold)
Ids = 60 uA
.05v 0.1v 0.25v
Vds > Vgs - Vt
NFET - Operation
n+ n+
p-type
source = 0.0 v drain = 0.4 v
gate = 1.0 v
(above threshold)
Ids = 61 uA
.05v 0.1v 0.25v
Vds > Vgs - Vt
= Vgs-Vt
NOTICE - thesaturation region isnow up where thecurrent is constant
for different VDS.
Vds
IdsFig 4-12
the arrows indicatewhat we showedin the previous figuresas Vds was increasedfor a fixed Vgs
