8 Bit ALU

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8 Bit ALU

• Rahul Vyas
• Gyanesh Chhipa
• Jaimin Shah
• Advisor Dr.David W. Parent
• 05/08/2006

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Abstract

• The 8-bit ALU that our group designed can perform
  8 arithmatic function and 4 logic function
• The 8s-bit ALU is made up of 2 identical 4-bit
  ALU, and 25 DFFs.
• We designed an 8-bit carry look ahead adder that
  operated at 200 MHz

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Introduction

• An ALU is the fundamental unit of any computing
  system.
• Understanding how an ALU is designed and how it
  works is essential to building any advanced logic
  circuits.
• Using this knowledge and experience, we can move
  on to designing more complex integrated circuits.
• Design consists of different kinds of logic Look
  ahead carry generator, adder, Subtractor,
  Transfer Data, DFF, Multiplexer, Inv, and, Xor,
  etc

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Project Summary

• Created Schematic
• Tested the schematics logic by using NCVerilog.
• Finding longest path
• Sizing of Wn and Wp
• Layout of individual block
• Checked DRC and LVS for each block
• Integrated every block
• Checked DRC and LVS for final layout
• Verify the timing
• Measure power

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Block diagram of our project
ARITHMETIC CIRCUIT
DFFS
DFFS
MUX
LOGICAL CIRCUIT
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Project Details

1 AB8 Bit Inputs. S2 S1,S0,CIN-Selection
Lines
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Gate level schematic of our circuit
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Transistor Level Schematic
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NC VERILOG VERIFICATION
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Longest path in the circuit
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Longest Path Calculations
Note All widths are in Cm and capacitances in fF
Tphl 5ns/19 0.263ns
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Individual Block Layout
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Layout
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Verification
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Verification
LVS
The net lists matched
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Test Bench and Simulations
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Output Graphs
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Cost Analysis

• verifying logic 2 weeks
• verifying timing 1 week
• Layout 1weeks
• post extracted timing 5 days

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Lessons Learned

• Aspects of design processes
• Simulation and verification tools
• Optimize transistor size to meet specification
• Use instances
• See Dr. Parent more often to understand the
  concept fully.

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Summary

• Project
• Our 8-Bit ALU has 1520 transistors and 33
  terminals.
• The circuit can operate up to 250MHz.
• Designed a 8-Bit ALU that performs eight
  arithmetic and four logical functions at 200MHz
  frequency with setup and hold time 1ns, driving
  up to 30fF.
• This circuit can be used as a building block for
  16/32-bit ALU.
• The Logic design can be modified to perform more
  functions.

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Acknowledgements

• Thanks to Professor David Parent for his Guidance
  And Help
• Thanks to Cadence Design Systems for the VLSI lab