Post on 01-Mar-2019
MOS transistor
Tranzystor MOS
27 stycznia 2014 Wojciech Kucewicz 3
n -
- -
-
-
-
-
- -
-
-
+
+
+
+
+
n + +
27 stycznia 2014 Wojciech Kucewicz 4
-
- -
-
-
-
-
- -
-
-
+
+
+
+
+
-
+
- - - - - - - - - -
Channel p
p - -
27 stycznia 2014 Wojciech Kucewicz 5
+
+ +
+
+ +
+
+
+
-
-
-
-
-
+
-
+ + + + + + + + + + +
Channel n
+
B.Razavi –Fundamentals of Microelectronics
6
B.Razavi –Fundamentals of Microelectronics
7
𝑉𝑜𝑢𝑡𝑉𝑖𝑛
=𝑅1
𝑅1 + 𝑅𝑀
B.Razavi –Fundamentals of Microelectronics
8
B.Razavi –Fundamentals of Microelectronics
9
B.Razavi –Fundamentals of Microelectronics
10
B.Razavi –Fundamentals of Microelectronics
11
B.Razavi –Fundamentals of Microelectronics
12
B.Razavi –Fundamentals of Microelectronics
13
B.Razavi –Fundamentals of Microelectronics
14
B.Razavi –Fundamentals of Microelectronics
15
)(THGSox
VVWCQ
B.Razavi –Fundamentals of Microelectronics
16
THGSox
VxVVWCxQ )()(
B.Razavi –Fundamentals of Microelectronics
17
vQI
B.Razavi –Fundamentals of Microelectronics
18
19
L
WC oxn
2)(
)(
)()(
2
0
)(
0)(
DSDSTHGSoxnD
THGS
Lx
x
VxV
xV oxnD
nTHGSoxD
nn
VVVV
L
WCI
dVVxVVWCdxI
dx
xdVVxVVWCI
dx
dVE
DS
B.Razavi –Fundamentals of Microelectronics
20
2
max, THGSDVVI
B.Razavi –Fundamentals of Microelectronics
21
Linear Resistance
At small VDS, the transistor can be viewed as a resistor, with the resistance depending on the gate voltage.
It finds application as an electronic switch.
THGSoxn
on
VVL
WC
R
1
B.Razavi –Fundamentals of Microelectronics
22
if VDS << 2(VGS − VTH)
2
)(2DS
DSTHGSoxnD
VVVV
L
WCI X
Application of Electronic Switches
In a cordless telephone system in which a single antenna is used for
both transmission and reception, a switch is used to connect either the
receiver or transmitter to the antenna.
B.Razavi –Fundamentals of Microelectronics
23
Effects of On-Resistance B.Razavi –Fundamentals of Microelectronics
24
In the cordless phone, the switch connecting the transmitter to the antenna must negligibly attenuate the signal, e.g., by no more than 10%. If VDD = 1.8V, μnCox = 100 μA/V2, and VTH = 0.4 V, determine the minimum required aspect ratio of the switch. Assume the antenna can be modeled as a 50W resistor.
Effects of On-Resistance
Assuming minimal lenght of the channel L = 90 nm, W = 115µm
B.Razavi –Fundamentals of Microelectronics
25
1276
1
6,59,0
W
L
W
VVL
WC
R
RRR
R
V
V
THGSoxn
on
on
onant
ant
in
out
Effects of On-Resistance
To minimize signal attenuation, Ron of the switch has to be as small as possible. This means larger W/L aspect ratio and greater VGS.
B.Razavi –Fundamentals of Microelectronics
26
B.Razavi –Fundamentals of Microelectronics
27
2
1
0
)(
0)(
)(2
1
)(1
THGSoxnD
THGS
Lx
x
VVxV
xV oxnD
VVL
WCI
dVVxVVWCdxITHGS
B.Razavi –Fundamentals of Microelectronics
28
B.Razavi –Fundamentals of Microelectronics
29
Triode or Saturation?
When the region of operation is not known, a region is assumed (with an
intelligent guess). Then, the final answer is checked against the
assumption.
B.Razavi –Fundamentals of Microelectronics
30
Triode or Saturation?
Calculate the bias current of M1. Assume μnCox = 100 μA/V2 and VTH =
0.4 V. If the gate voltage increases by 10 mV, what is the change in the
drain voltage?
B.Razavi –Fundamentals of Microelectronics
31
B.Razavi –Fundamentals of Microelectronics
32
VIRVV
AVVL
WCI
DDDDx
THGSoxnD
8,0
200)(2
1 2
VV
AI
x
D
766,0
7,206
DSTHGSoxnD VVVL
WCI 1
2
1 2
B.Razavi –Fundamentals of Microelectronics
33
and L
The channel length modulation factor can be controlled by the circuit designer.
For long L, the channel-length modulation effect is less than that of short L.
B.Razavi –Fundamentals of Microelectronics
34
How drain voltage afects drain current?
A MOSFET carries a drain current of 1 mA with VDS = 0.5 V in saturation. Determine the change in ID if VDS rises to 1V and λ = 0.1V−1.
What is the device output impedance?
mAV
VII
VVVL
WCI
VVVL
WCI
DS
DSDD
DSTHGSoxnD
DSTHGSoxnD
048,11
1
12
1
12
1
1
212
2
2
2
1
2
1
B.Razavi –Fundamentals of Microelectronics
35
The change in ID is 48 µA (<5%). The device output impedance:
W
k
I
Vr
D
DSo 42,10
000048,0
5,0
Transconductance
As a voltage-controlled current source, a MOS transistor can be characterized by its transconductance:
GS
Dm
V
Ig
B.Razavi –Fundamentals of Microelectronics
36
This quantity serves as a measure of the “strength” of the device: a higher value corresponds to a greater change in the drain current for a given change in VGS.
For saturation region:
1) Derivative 2) VGS – VTH = f(ID) 3) gm/ID
2)(2
1THGSoxnD VV
L
WCI
THGSoxnm VVL
WCg Doxnm I
L
WCg 2
THGS
Dm
VV
Ig
2
Transconductance
1)
2)
3)
These dependencies prove critical in understanding performance trends of MOS devices.
THGS
mDDmTHGS
THGS
Dm
mDDm
Doxnm
mTHGSTHGSm
THGSoxnm
VVgconstIIgconstVV
VV
Ig
L
WgconstIIgconst
L
W
IL
WCg
L
WgconstVVVVgconst
L
W
VVL
WCg
1;
2
;
2
;
37
Doubling of gm due to doubling W/L
If W/L is doubled, effectively two equivalent transistors are added in parallel, thus doubling the current (if VGS-VTH is constant) and hence gm.
B.Razavi –Fundamentals of Microelectronics
38
B.Razavi –Fundamentals of Microelectronics
39
B.Razavi –Fundamentals of Microelectronics
40
2
12
1THDDoxnD
VVVL
WCI
B.Razavi –Fundamentals of Microelectronics
41
2
1
2
1
1
THGSoxnDS
Do
VVL
WCV
Ir
B.Razavi –Fundamentals of Microelectronics
42
D
oI
r
1
PMOS Transistor
B.Razavi –Fundamentals of Microelectronics
43
2,
2
,
22
1
12
1
DSDSTHGSoxptriD
DSTHGSoxpsatD
VVVVL
WCI
VVVL
WCI
B.Razavi –Fundamentals of Microelectronics
44
Small-Signal Model of PMOS Device
The small-signal model of PMOS device is identical to that of NMOS
transistor; therefore, RX equals RY and hence (1/gm)||ro.
B.Razavi –Fundamentals of Microelectronics
45
46
D
G
S
D
G
S
B
D
G
S
B
D
G
S
B
D
G
S
D
G
S
B
D
G
S
B
D
G
S
B
D
G
S
D
G
S
NMOS
47
DSTHGSoxnD
THGSDS
DSDSTHGSoxnD
THGSDS
VVVL
WCI
VVV
VVVV
L
WCI
VVV
12
1
2)(
2
2
D
oI
r
1 THGSoxnm VV
L
WCg
PMOS
48
DSTHGSoxpD
THGSDS
DS
DSTHGSoxpD
THGSDS
VVVL
WCI
VVV
VVVV
L
WCI
VVV
12
1
2)(
2
2
B.Razavi –Fundamentals of Microelectronics
49