1. EE 5323 Project 16 Bit Sklansky Adder Phase 2 Report
Yuan Xu

2. Contents Summary Design Optimization & Changes Waveforms of test cases
Schematic & Layout
maximum operating frequency VS. VDD
Power consumption at the maximum operating frequency VS. VDD
Netlist
DRC,LVS results

3. Summary
The goal of this project is to realize 16bit Sklansky adder by using static CMOS devices.
Sklansky adder belongs to tree adder family.
The difference between Sklansky adder and other tree adders is prefix network.
Compare to other tree adders, Sklansky adder has minimum logic levels, wiring tracks, but maxinum fanout. Also, it has largest delay at the same condition.

4. Summary Structure of 16 bit Sklansky Adder
(Black square is dot operator
Grey square is empty dot operator
White triangle is buffer)

5. Reference List
D.Harris, “ A Taxonomy of Parallel Prefix Networks, Signals ”, Systems and Computers, Conference Record of the Thirty-Seventh Asilomar Conference on, 2, Vol.2,2003
J. Sklansky, “Conditional-sum addition logic,” IRE Trans. Electronic Computers, vol. EC-9, pp , June 1960.
J M. Rabaey, A. Chandrakasan, B. Nikolic, “ Digital Integrated Circuits-A Design Perspective (Second Edition)”, Prentice Hall, 2003
Wu,S.D.,Chun-Chi Tsai, Yang,M, “A VLSI Layout Legalization Technique Based on a Graph Fixing Algorithm”, VLSI Design, Automation and Test, 2006 International Symposium on, 2006, 1-4
Mason, J.S.B.; , "Layout tecbmques for mixed-signal VLSI design," Systems on a Chip (Ref. No. 1999/133), IEE Colloquium on , vol., no., pp.8/1-8/11, 1999

6. Design Optimization and changes
Sizing the gate to minimum size (90nm) reduces power
By using bubble shifting, we save totally 28 inverters, and 4 inverters on the critical path
Adding the buffer can effectively reduce delay. Setting stage=1, fanout=4
Minimizing each block to reduce area
Combining VDDs of different devices to reduce area

7. Design Optimization and changes
Combining Nwell and Pwell of different devices to simplify the layout
Using fewer metal layers (2 layers) to reduce complexity and capacitance
Changes: Fixing some flaws (body not connected to ground) in schematic

8. Waveforms of test cases
Worst case: For Sklansky adder, the worst case happens when inputs are 7FFF Since G will propagate from A_0 to S_15 which is the critical path.

9. Waveforms of test cases from layout
Worst case 7FFF+0001
A_0-A_ B_0-B_ Cout,S_0-S_15,

10. Waveforms of test cases from layout
Delay from A_0 to S_15 is 8.946E-10S

11. Waveforms of test cases from layout
FFFF+0002
A_0-A_ B_0-B_ Cout,S_0-S_15,

12. Waveforms of test cases from layout
Other cases( , , 11FF EDAB, , AABB 5432, AB,
FFFF FFEE, 1AB2 F182, 1BCD 2525, ,1278+AC00,FFFF+FFFF, , ,CC53+D126
A_0-A_ B_0-B_ Cout,S_0-S_15

13. Final schematic of adder

14. Final Layout Area: 37.4 μm×11.8μm

15. Maximum operating frequency for different VDD! from layout

16. Power consumption at the maximum operating frequency at different VDD

17. Circuit netlist from layout and modified runtestadder16b_xxx
Circuit netlist from layout and modified runtestadder16b_xxx.sp See attached files Netlist name is : new_16_bit_adder
Sizing
NMOS: L=50nm, W=90nm
PMOS: L=50nm, W=135nm
Temperature: 25°C

18. DRC Pass

19. LVS Pass