Small Signal Model MOS FieldEffect Transistors (MOSFETs). 1. Quiz No 3 DE 27 (CE). 200307. R out. Draw small signal model (4) Find expression for R out (2) Prove v o /v sig = ( β 1 α 2 R C )/(R sig +r π ) (4).
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Small Signal Model
MOS FieldEffect Transistors (MOSFETs)
1
200307
Rout.
Figure 4.2 The enhancementtype NMOS transistor with a positive voltage applied to the gate. An n channel is induced at the top of the substrate beneath the gate.
Enhancementtype NMOS transistor:
iD = iS, iG = 0
Largesignal equivalentcircuit model of an nchannel MOSFET : Operating in the saturation region.
Largesignal equivalentcircuit model of an pchannel MOSFET : Operating in the saturation region.
Large Signal Model : MOSFET
Transfer characteristic of an amplifier
Conceptual circuit utilized to study the operation of the MOSFET as a smallsignal amplifier.
The DC BIAS POINT
To Ensure Saturationregion Operation
Signal Current in Drain Terminal
Total instantaneous voltages vGSand vD
Smallsignal ‘π’ models for the MOSFET
Common Source amplifier circuit
Example 410
Small Signal ‘T’ Model : NMOSFET
‘T’ Model
Single Stage MOS Amplifier
Amplifiers Configurations
Smallsignal analysis performed directly on the amplifier circuit with the MOSFET model implicitly utilized.
Commonsource amplifier
with a resistance RSin the source lead
Smallsignal equivalent circuit with ro neglected.
Smallsignal Analysis.
Voltage Gain : CS with RS
Smallsignal equivalent circuit directly on Circuit
A commongate amplifier based on the circuit
A smallsignal equivalent circuit
A smallsignal Analusis : CG
A smallsignal Analusis : CG
Small signal analysis directly on circuit
The commongate amplifier fed with a currentsignal input.
A commondrain or sourcefollower amplifier.
Smallsignal equivalentcircuit model
Smallsignal Analysis : CD
(a) A commondrain or sourcefollower amplifier :output resistance Rout of the source follower.
(a) A commondrain or sourcefollower amplifier. : Smallsignal analysis performed directly on the circuit.
Common Source Circuit (CS)
Common Source Circuit (CS) With RS
Common Gate Circuit (CG)
Current Follower
Common Drain Circuit (CD)
Source Follower
270307
Problem 544
SOLUTION : DC Analysis
SOLUTION : DC Analysis
IE
Check for Active Mode
IB
Solution Small Signal Analysis
Solution Small Signal Analysis
Solution Small Signal Analysis : Input Resistance
ib
+
vb

Rin
Itest
IE
IRC
IE/(1+ß)
Rout
Solution Small Signal Analysis : Voltage Gain
+
veb


Vo
+
+
vi

Solution Small Signal Analysis : Voltage gain
+
veb

+
vi

Solution Small Signal Analysis : Voltage Gain
+
vi

Solution Small Signal Analysis : Voltage Gain
Solution Small Signal Analysis : Voltage Gain

Vo
+
+
vi

Problem
Small Signal Model MOSFET : CD
Solution Small Signal Analysis
1/gm
D
gmvsg
Solution Small Signal Analysis : Input Resistance
1/gm
D
gmvsg
Ig=0
Rin
1/gm
D
gmvsg
Itest
ID
IRD
Vtest
IG=0
Rout
Solution Small Signal Analysis : Voltage Gain
1/gm
D
gmvsg
+
vsg


+
+
vi

Solution Small Signal Analysis : Voltage gain
1/gm
D
gmvsg
+
vsg

+
vi

Solution Small Signal Analysis : Voltage Gain
+
vi

Solution Small Signal Analysis : Voltage Gain
Solution Small Signal Analysis : Voltage Gain

+
+
vi

Solution Small Signal Analysis
Small Signal Model
Small Signal Model
Rin
Rout
Small Signal Model
Rin
Rout
+
vbe2

+
veb1

+
vbe2
+

+
vi
veb1


+
vgs2

+
vsg1

+
vgs2

+
vsg1

ig1=0
+
vi

VBE=0.7 V
β =200
K’n(W/L)=2mA/V2
Vt=1V
Figure P6.123
Figure P6.123
VBE=0.7 V
β =200
K’n(W/L)=2mA/V2
Vt1=1V
Vt2=25mV
DC Analysis
1mA
2V
IG=0
0.7V
I=0.7/6.8=0.1mA
ig=0
+
+
vi
vbe2


ii
ig=0
+
vi

Rin