Microelectronics Circuits 1 Review
Prof. Y.Kwon
Electronic Circuits
• Static phenomenon only
• Simplified transistor model : MOSFET and BJT
회로이론
반도체 전자장 소자
Contents to Cover in this Course and Evaluation
• Chap 8 : Feedback Amplifier
• Chap 9 : Operational Amplifier
• Chap 12 : Filters and Tuned Amplifier (12.1 ~ 12.7)
• Chap 13 : Signal Generators and Waveform-Shaping Circuits (13.1~13.5)
• Chap 14 : Output Stage and Power Amplifiers (14.1 ~ 14.5)
• Chap 10 & 11 : Basics of Digital Circuits
• Evaluation
– Two mid terms and One final exam – Attendance
– Homework
Physical understanding of STC
Ærequires large I to reduce t Ærequires small R
Time Constant = RC
takes more charge to raise voltage level
s s
o
o o
V C t
Q V
t V
t V t
Q
C V Q
* )
( )
(
0 ) 0 (
0 ) 0 (
=
∞
=
→
=
∞
=
=
=
=
→
=
=
=
−
−
R V I V
d I t
Q
s t
I
−
=
= ∫
0( ) )
( τ τ
V s
Comparison of the MOSFET & the BJT
TABLE 6.3 Comparison of the MOSFET and the BJT
Circuit Symbol
NMOS npn
To Operate in the Active Mode, Two Conditions Have To Be Satisfied
( ) ( )
1 Induce a channel; (1)Forward-bias EBJ;
0 5 0 7 V 0 5
Let
2 Pinch-off channel at drain;
GS t t BE BE on BE on
GS t ov
V V ,V . . v V , V . V
V V v
≥ = − ≥ ≅
= +
(2)Reverse-bias CBJ;
0 4V or equivalently, or equ
GD t BC BCon BCon
V < V v < V ,V ≅ .
ivalently
v ≥ V ,V = v ≥
Comparison of the MOSFET & the BJT
Current-Voltage Characteristics in the
Active Region
( )
22
1 1 1
2
1 1 2
0
BE T A
DS v /V CE
D n ox GS t C S
A
DS
n ox ov
A G
v v
i C W v V i I e
L V V
W v
C v
L V
i
⎛ ⎞ ⎛ ⎞
= μ − ⎜ ⎜ ⎝ + ⎟ ⎟ ⎠ = ⎜ ⎝ + ⎟ ⎠
⎛ ⎞
= μ ⎜ + ⎟
⎝ ⎠
= i
B= i /β
CLow-Frequency Hybrid-π Model
Comparison of the MOSFET & the BJT
Transconductance gm
Output resistance
r0 0 0
0
is inversely proportional to the bias current.
A
A D A C
D
r V /I V' L r V /I I
r
= = =
⇒
D ox
n m
ov ox
n m
T C m
ov D
m
L I C W
g
L V C W
g
V I g
V I
g
⎟ ⎠
⎜ ⎞
⎝
= ⎛
⎟ ⎠
⎜ ⎞
⎝
= ⎛
=
=
) (
2 ) (
/ )
2 / /(
μ μ
Input Resistance with Source (Emitter)
Grounded
∞ r
π= β/g
mComparison of the MOSFET & the BJT
Intrinsic Gain A0=gmro
D ox n A
OV A
T A C
A T C o
m OV
A
I
WL C
A V
V L A V
V I V
V V r I
g A
V V A
μ 2 2
/ )
2 / /(
' 0
' 0
0 0
=
=
=
⋅
=
=
=
V
V
A
0= 1000 ~ 5000 /
( )
1
2 1
1
Transistor : Drain is shorted to its gate. Saturation mode 1
2
Since the gate currents are zero,
D n ox GS tn
Q
i C W V V
L
⇒
⎛ ⎞
= μ ⎜ ⎝ ⎟ ⎠ −
1
2
: In most cases, outside the IC chip Assuming in the satuaration mode,
DD GS
D REF
V -V I I
R R
Q
= =
( )
( ) ( )
2 2
2
2
1
= 1
2
=
/ is sole
O D n GS tn
O REF
O REF
I I k ' W V V
L
I W L
W
I L
I I
⎛ ⎞
= ⎜ ⎝ ⎟ ⎠ −
⇒
y determined by the geometries of the transistors.
Current Mirror Circuit
2
02 2
To ensure that is saturated, or equivalentely
At , .
As increases above , will increase according to
the incremental output resistance of .
O GS t O OV
O GS O REF
O GS
O
Q
V V V V V .
V V I I
V V
I
r Q
≥ − ≥
= =
Current Mirror Circuit
( )
( )
02 2
2 2
2
As is increases above , will increase according to the incremental output resistance of .
1
O GS O
O A
o o
O O
O GS
O REF
V V I
r Q
ΔV V
R r
ΔI I
W/L V V
I I
W/L V
≡ = =
⎛ − ⎞
= ⎜ + ⎟
⎝ ⎠
Current Mirror Circuit
Once a constant current is generated, it can be replicated to provide dc bias currents for various amplifier stages in an IC.
Current Steering Circuit
F H Estimation : Open-circuit time constant Method
• High Frequency Gain Function :
• Practical Bandwidth is determined by 3dB roll-off point ( )
• When dominant pole exists, &
• Gray and Searle Æ
• IF there is dominant pole,
Pn P
P
n n
n n Pn
P P
Zn Z
Z H
b
s b s
b s b
s a s
a s a s
s s
s s
s s F
ω ω
ω
ω ω
ω
ω ω
ω
1 1
1
1 1 ) / 1 ( ) / 1 )(
/ 1 (
) / 1 ( ) / 1 )(
/ 1 ) ( (
2 1
1
2 2 1
2 2 1
2 1
2 1
+
⋅⋅
⋅ + +
=
+
⋅⋅
⋅ + +
+
+
⋅⋅
⋅ + +
= + +
⋅⋅
⋅ +
+
+
⋅⋅
⋅ +
= +
ω
H/
11 ) 1 (
P
H
s s
F ≅ + ω ω
H≅ ω
P1∑
=
i
io i
R C b
1=
∑
≈
≈
→
≅
i
io i P
H
P
b C R
b
1 1 11 1 1
1
ω ω
ω
) ( )
( s A F s
A =
M HA
M: Midband Gain
Miller’s Theorem
• When the circuit conditions remain to make
• Proof : derive the same I/V relationship at both ports
• Æ Miller multiplication (“Miller Effect”) for conductance or susceptance
) 1 ( −K 2
1
KV
V =
) 1
( − K
The MOSFET internal capacitances and high- frequency model
gs gd gb sb db
Five capacitance
C , C , C , C and C
• The gate capacitive effect – Triode region
• Cgs= Cgd = 1/2WLCox
– Saturation region
• Cgs= 2/3WLCox
• Cgd = 0
– Cutoff
• Cgs= Cgd = 0
• Cgb = WLCox
• The junction capacitances
,
1 1
sbo dbo
sb db
SB DB
o o
C C
C C
V V
V V
= =
+ +
The MOSFET internal capacitances and high-
frequency model
• The high-frequency MOSFET model
(a) High-frequency equivalent circuit model for the MOSFET.
(b) The equivalent circuit for the case in which the source is connected to the substrate (body).
(c) The equivalent circuit model of (b) with Cdbneglected (to simplify analysis).
The MOSFET internal capacitances and high-
frequency model
• The MOSFET unity-gain frequency (f
T)
Determining the short-circuit current gain Io /Ii.
The frequency at which the short-circuit curent-gain of the common-source configuration becomes unity.
/ ( )
o m gs gd gs
o m gs
gs i gs gd
I g V sC V I g V
V I s C C
= −
≅
= +
( )
For physical frequencies
/( )
2 ( )
o m
i gs gd
T m gs gd
m T
gs gd
I g
I s C C
s j
g C C
f g
C C
ω ω
π
= +
=
= +
= +
The MOSFET internal capacitances and high-
frequency model
(1) The current source can be
implemented using a PMOS transistor.
Î Active load
(2) Obviously, Q
1is biased at I
D=I.
But what are V
DSand V
GS?
Î We just assume that the MOSFET is biased to operate in the saturation region throughout this chapter.
CS Amplifier
i i
i RL
o
vo m o
i RL
R v i
A v g r
v
=∞
=∞
= = ∞
= = −
CS Amplifier
( )
2 32 2
The value of is set by passing the reference bias current through
When exceeds operates in satuaration.
When operates in satuaration, behaves as a current source.
Wh
SG R EF
SD SG tp
V I Q .
v v V - V , Q
Q Q
=
2
2 2
en is in satuaration, it exhibits a finite incremental resistance :
oV
AQ r
= I
CS Amplifier
1
When the amplifier is biased at a point in region III,
small signal voltage gain can be determined
by replacing Q with its
CS Amplifier
0
vo m o
x
o o
x vi
A g r
R v r
i
== −
= =
CS Amplifier
( )
( ) ( )
( ) ( )
1 1 1 2
2
1 1 1 1 2
2 1
1 1 2
, and in this case , , and
Or from the other circuit,
VO VO
o L
v m o O o L o
i L O
o
v m o m o o
o o
o m i o o