1

4-bit ALU

Cailan ShenTing-Lu Yang

Advisor: Dr. ParentMay 11, 2005

2

Agenda

• Introduction• Project (Experimental) Details

– ALU design in Cadence– DFF, MUX and Adder

• Summary– Project result– Lesson learned

3

Introduction• The 4-bit ALU that our group designed can

perform following functions:– Add, Subtract, NOR, OR, and AND.

• The 4-bit ALU operates at 200 MHz with an area of 300 um x 320 um and use 1.3 mW power.

• The 4-bit ALU is made up of 4 identical 1-bit ALU, and DFFs ensure the 4-bit ALU to obtain the correct inputs and send out correct outputs.

• This project is worthwhile because this ALU has all the logic blocks that we learned in class.

4

Project Description and ALU Schematic

- 1-bit Adder- Four 2 to 1 MUXs- 1 AND and 1 OR gates- Four control inputs, two

data inputs.

1 B A B -A

B and A Bnor A

5

Longest Path Calculations

• Note: All widths are in microns and capacitances in fF

nsns

PHL 313.16

5

6

4-bit ALU Layout and LVS

7

SimulationALU Control Lines Function

A_inv B_inv OP1 OP0  

0 0 0 0 AND

0 0 0 1 OR

0 0 1 0 ADD

0 1 1 0 SUBTRACT

1 1 0 0 NOR

Inputs

A B

1010 1010

1010 1011

A – B = 1010 -1011 =1111Cout = 0 (Borrowed)

8

Verification of Final Output

9

Power = 1.3 mW

10

Summary

• After this project, we became familiar with Cadence tool and the fundamental concepts of IC design.

• The total area is = 300um x 320um• The power = 1.3mW• Lessons learned

• How to fix the LVS error• Learn how to work in a team• Learn how to make trade offs

11

Acknowledgements

• Thanks to Cadence Design Systems for the VLSI lab

• Thanks to Synopsys for Software donation.

• Thanks to Professor David Parent.