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240-451 VLSI le Lecture 4 Lecture 4 MOS Circuits mputer Engineering, Prince of Songkla University by Wannarat
240-451 VLSI lecture, 2000
Lecture 4Lecture 4
MOS Circuits
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
Combination & Sequential
Logic
Circuit
Logic
CircuitOut
OutInIn
(a) Combinational (b) Sequential
State
Output = f(In) Output = f(In, Previous In)
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
Combination & Sequential
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
CMOS logic style
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
Example NAND gate
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
4-input NAND gate
Out
In1 In2 In3 In4
In3
In1
In2
In4
In1 In2 In3 In4
VDD
Out
GND
VDD
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
Example : NOR gate
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
Complex CMOS gate
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
Complex gate structures
A
C
B
A
B C
Vdd
Gnd
OutOut = A+(B*C) ...
ABC
And-Or-Invert (AOI)
How to add terms?
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
A
C
B
A
B C
Vdd
Gnd
OutOut = A+(B*C) ...
ABC
And-Or-Invert (AOI)
How to add terms?
OAI/AOI duality
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
Demorgan’s law in action
Out = A*(B+C) ...
ABC
Or-And-Invert (OAI)
A
C
B
A
B
C
Vdd
Gnd
Out
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
Demorgan’s law in action
Out = A*(B+C) ...
ABC
Or-And-Invert (OAI)
A
C B A
BC
Vd
dGn
d
Ou
t
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
Demorgan’s law in action
Out = A*(B+C) ...
ABC
Or-And-Invert (OAI)
A
C
B
A
B
C
Vdd
Gnd
Out
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
Demorgan’s law in action
Out = A*(B+C) ...
ABC
Or-And-Invert (OAI)
A
C
B
A
BC
Vdd
Gnd
Out
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
Demorgan’s law in action
Out = A*(B+C) ...
ABC
Or-And-Invert (OAI)
A
C
B
A
BC
Vdd
Gnd
Out
What is the Magic command to do this?
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
OAI/AOI duality
B
A
C
OUT
A
C
B
A
B C
Vdd
Gnd
Out
A
B
C
OUT
A
C
B
A
BC
Vdd
Gnd
Out
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
Step by step layout XNOR gate
• The equation for XNOR is:
– f = (a * b) + (a' * b')
• using DeMorgan's law on each of the two terms gives:
– f = (a'+ b')' + (a + b)'
• using DeMorgan's law on the two terms together gives:
– f = ((a'+ b') * (a + b))'
• This could be directly implemented with a single complementary CMOS gate: the equation is in a simple negated product of sums form. This form can be implemented with the standard Or-And-Invert (OAI) style gate.
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
Non-inverter input
• However, using DeMorgan's law one more time on the left term gives:
– f = ((a * b)' * (a + b))’
• This form uses no inverted inputs and can be implemented with two gates a NAND gate and an OAI gate.
ab f
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
Logic Graph
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
Example CMOS
240-451 VLSI lecture, 2000
Department of Computer Engineering, Prince of Songkla University by Wannarat Suntiamorntut
Complex CMOS graph
