MOSFET CIRCUITS AT DC
Example 4.2
Triode region :
1 2 ⎤
W⎡
(
)
v
V
v
vDS ⎥
−
−
GS
t DS
⎢
2
L⎣
⎦
Saturation region
1 W
(vGS − Vt )2 , kn' = μ nCox
iD = k n'
2
L
iD = k n'
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Solution for Ex. 4.2
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Example 4.4
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Solution to 4.4
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Example 4.5
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Example 4.5
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Solution for Example 4.5
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Solution for Example 4.5
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THE MOSFET AS AN
AMPLIFIER OR AS A SWITCH
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THE MOSFET AS AN AMPLIFIER
OR AS A SWITCH
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Example 4.8
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Solution to Example 4.8
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Solution to Example 4.8
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Solution to Example 4.8
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SMALL-SIGNAL OPERATION
AND MODELS
Figure 4.34 Conceptual circuit utilized to study the operation of the MOSFET as a
small-signal amplifier.
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Small-signal operation
Figure 4.35 Small-signal operation of the enhancement MOSFET amplifier.
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Voltage Gain
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Voltage Gain
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Voltage Gain
Figure 4.36 Total instantaneous voltages vGS and vD for the circuit in Fig.
4.34.
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Small-signal Equivalent Circuit
Figure 4.37 Small-signal models for the MOSFET: (a) neglecting the dependence of iD
on vDS in saturation (the channel-length modulation effect); and (b) including the effect
of channel-length modulation, modeled by output resistance ro = |VA| /ID.
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Small-signal Equivalent Circuit
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T-Model of the MOSFET
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Effect of The Body on the Model
Figure 4.41 Small-signal equivalent-circuit model of a MOSFET in which
the source is not connected to the body.
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The Common-Source (CS)
Amplifier
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CS Amplifier
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CS Amplifier with a Source
Resistance
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CS Amplifier with a Source
Resistance
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The Common-Gate (CG) Amplifier
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The Common-Gate (CG) Amplifier
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The Common-Gate (CG) Amplifier
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The Common-Gate (CG) Amplifier
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The Common-Drain or SourceFollower Amplifier
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CD Amplifier
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CD Amplifier
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THE DEPLETION-TYPE
MOSFET
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N-Channel Depletion-Type
MOSFET
Figure 4.59 (a) Circuit symbol for the n-channel depletion-type MOSFET. (b)
Simplified circuit symbol applicable for the case the substrate (B) is connected to
the source (S).
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Depletion Mode
I-V Characteristics
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The iD–vGS Characteristics For
MOSFETs
Figure 4.62 Sketches of the iD–vGS characteristics for MOSFETs of enhancement and depletion types, of both polarities
(operating in saturation). Note that the characteristic curves intersect the vGS axis at Vt. Also note that for generality
somewhat different values of |Vt| are shown for n-channel and p-channel devices.
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Home work: 4.2, 4.15, 4.35,4.39, 4.54
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