EE 5323 Project
16 Bit Sklansky Adder
Phase 2 Report
Yuan Xu
4139225
xuxxx488@umn.edu
Contents
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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
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.
Summary
Structure of 16 bit Sklansky Adder
(Black square is dot operator
Grey square is empty dot operator
White triangle is buffer)
15 14 13 12 11 10
15:14
13:12
11:10
15:12 14:12
15:8
14:8
11:8 10:8
13:8
9
9:8
8
7
6
7:6
7:4
5
5:4
6:4
4
3
2
3:2
3:0
1
0
1:0
2:0
12:8
15:0 14:0 13:0 12:0 11:0 10:0 9:0 8:0 7:0 6:0 5:0 4:0 3:0 2:0 1:0 0:0
Reference List
• D.Harris, “ A Taxonomy of Parallel Prefix Networks, Signals ”,
Systems and Computers, 2003. Conference Record of the ThirtySeventh Asilomar Conference on, 2, 2213-2217 Vol.2,2003
• J. Sklansky, “Conditional-sum addition logic,” IRE Trans. Electronic
Computers, vol. EC-9, pp. 226-231, 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
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
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
Waveforms of test cases
• Worst case: For Sklansky adder, the worst case
happens when inputs are 7FFF+0001. Since G
will propagate from A_0 to S_15 which is the
critical path.
Waveforms of test cases from layout
• Worst case 7FFF+0001
• A_0-A_15
B_0-B_15
Cout,S_0-S_15,
Waveforms of test cases from layout
• Delay from A_0 to S_15 is 8.946E-10S
Waveforms of test cases from layout
• FFFF+0002
• A_0-A_15
B_0-B_15
Cout,S_0-S_15,
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Waveforms of test cases from layout
Other cases(1111 0000, 0011 0045, 11FF EDAB, 9782 1234, AABB 5432, 1543 78AB,
FFFF FFEE, 1AB2 F182, 1BCD 2525,2312+4567,1278+AC00,FFFF+FFFF,4444+7777,
1894+2636,CC53+D126
A_0-A_15
B_0-B_15
Cout,S_0-S_15
Final schematic of adder
Final Layout
Area: 37.4 μm×11.8μm
Maximum operating frequency for
different VDD! from layout
Frequency VS. VDD
T=25C, 1.1, 1.13
Frequency (GHz)
T=25C, 0.9, 0.759
T=100C, 1.1, 0.691
T=25C
T=100C
T=100C, 0.9, 0.4689
T=25C, 0.7, 0.3795
T=100C, 0.7, 0.24
VDD! (v)
Power consumption at the
maximum operating frequency at
different VDD
Power VS. VDD
T=25C, 1.1, 0.931
Power (mW)
T=100C, 1.1, 0.61588
T=25C
T=100C
T=25C, 0.9, 0.41989
T=100C, 0.9, 0.27835
T=25C, 0.7, 0.12988
T=100C, 0.7, 0.087154
VDD (v)
Circuit netlist from layout
and
modified runtestadder16b_xxx.sp
See attached files
Netlist name is : new_16_bit_adder
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Sizing
NMOS: L=50nm, W=90nm
PMOS: L=50nm, W=135nm
Temperature: 25°C
DRC Pass
LVS Pass