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Digital Integrated Circuits A Design Perspective

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Combinational Circuits. Class Information. Makeup Quiz is on Thu. 4/8/04. Worth 10 points. ... Combinational Circuits. Complementary Pass Transistor Logic. EE141. 13 ... – PowerPoint PPT presentation

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Title: Digital Integrated Circuits A Design Perspective


1
Digital Integrated CircuitsA Design Perspective
Jan M. Rabaey Anantha Chandrakasan Borivoje
Nikolic
Designing CombinationalLogic Circuits
April 6, 2004
2
Pass-TransistorLogic
3
Class Information
  • Makeup Quiz is on Thu. 4/8/04. Worth 10
    points.Purpose to make-up for test1 loss of 10
    pts.Any test1 like question is fair
    game10-15 minute duration
  • Project part 1 is due next week!
  • Anyone looking for a partner?

4
Schedule
QUIZ
5
Pass-Transistor Logic
6
Example AND Gate
7
NMOS-Only Logic
3.0
In
Out
2.0
V
x

e
g
a
t
l
o
V
1.0
0.0
0
0.5
1
1.5
2
Time ns
8
NMOS-only Switch
V
C
2.5 V
C
2.5

M
2
A
2.5 V
B
A
2.5 V
M
n
B
M
C
1
L
does not pull up to 2.5V, but 2.5V -
V
V
TN
B
Threshold voltage loss causes
static power consumption
NMOS has higher threshold than PMOS (body effect)
9
NMOS Only Logic Level Restoring Transistor
V
DD
V
DD
Level Restorer
M
r
B
M
2
X
M
A
Out
n
M
1
Advantage Full Swing
Restorer adds capacitance, takes away pull down
current at X
Ratio problem
10
Restorer Sizing
3.0
  • Upper limit on restorer size
  • Pass-transistor pull-downcan have several
    transistors in stack

W
/
L
1.75/0.25
V
r
e
W
/
L
1.50/0.25
g
r
a
t
l
o
V
W
/
L
1.25/0.25
W
/
L
1.0/0.25
r
r
Time ps
11
Solution 2 Single Transistor Pass Gate with VT0
V
DD
V
DD
0V
2.5V
Out
0V
V
DD
2.5V
WATCH OUT FOR LEAKAGE CURRENTS
12
Complementary Pass Transistor Logic
13
Solution 3 Transmission Gate
C
C
A
A
B
B
C
C
C
2.5 V
A
2.5 V
B
C
L
C

0 V
14
Resistance of Transmission Gate
15
Pass-Transistor Based Multiplexer
S
VDD
GND
In1
In2
S
16
Transmission Gate XOR
B
B
M2
A
A
F
M1
M3/M4
B
B
17
Delay in Transmission Gate Networks
m
R
R
R
eq
eq
eq
In
C
C
C
C
(c)
18
Delay Optimization
19
Transmission Gate Full Adder
Similar delays for sum and carry
20
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