Design of a 4-Bit ALU

1
Design of a 4-Bit ALU
EE166 Project Presentation

• Presented by
• Preeti Chauhan, Aung Moe, Harsirat Mangat
• Advisor Professor David Parent
• 12/06/2004

2
Agenda

• Abstract
• Introduction Basic ALU Blocks
• -- Logic Unit
• -- Arithmetic Unit
• -- 2x1 Multiplexer
• -- D Flip-Flop
• 4-Bit ALU
• -- Schematic
• -- Size Calculations
• -- Layout
• -- Verification
• -- Simulation
• Conclusions

3
Abstract

• We designed a 4 Bit ALU that operated at 200 MHz
  and use 650mW of Power and occupied an area of
  649 x 240 mm2

4
Introduction

• Basic ALU Blocks
• 
  
• 
  

4-Bit ALU
Reference Digital Logic Circuit Analysis
Design by Nelson, Nagle, Irwin, and Carroll
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Logic Unit
Truth Table
Schematic
S1 S0 A B F
0 0 0 0 0 AND
0 0 0 1 0 AND
0 0 1 0 0 AND
0 0 1 1 1 AND
0 1 0 0 0 OR
0 1 0 1 1 OR
0 1 1 0 1 OR
0 1 1 1 1 OR
1 0 0 0 1 NOT
1 0 0 1 1 NOT
1 0 1 0 0 NOT
1 0 1 1 0 NOT
1 1 0 0 0 XOR
1 1 0 1 1 XOR
1 1 1 0 1 XOR
1 1 1 1 0 XOR
F S1ABS0ABS0ABS1S0A
Logic verification
6
Logic Unit
LVS

• Layout

7
Logic Unit

• Simulation

Delay
8
2X1 Multiplexer
9
D Flip-Flop
10
Full Adder
Cout ABACBC Y A xor B xor C ABC (ABC)
Cout
Wp 6 um Wn4.05um Worst Case Delay 0.627ns
11
Full Adder Wave_Form
Delay 677n 50n 627ns
12
Y-Gen Schematic
Wp 5.55um Wn 3.45um Delay 0.86 ns
13
Y-Gen and AU Logic Verification
Y S1S0B S0BS0 S1 S0 (S1B)
Cin S1 S0
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AU (Arithmetic Unit)
Cell Width 30 um Cell Length 125 um Delay
0.6270.860.4 1.887ns
Xor
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Longest Path Calculations
No of Logic Levels XOR 3 AND
2 INV 1 NAND 1 DFF
4
8
4
6
5
7
3
2
1
Delay 5ns/19 0.2ns
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Longest Path Calculations
Note All widths are in microns and capacitances
in fF
17
4 Bit_ALU Schematic
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4 Bit_ALU Test_Bench
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4 Bit ALU Wave_Form
20
Layout and LVS
21
Conclusions

• We are able to design a 4 Bit ALU which run at
  200mHz with 600mW of power
• Should work in the same account and consult with
  group member to get a good layouts
• More than 100 hrs of work

22
Acknowledgements

• Professor David Parent
• Thanks to Cadence Design Systems for the VLSI lab
• Thanks to Synopsys for Software donation
• Thanks to my wife/husband for putting up with me.