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Unformatted text preview: Logic Redesign for Low Power
ELEC 6970 Project Presentation
By Nitin Yogi
Nov. 29, 2005 ELEC6970001 Class Presentation 1 Outline Low Power Logic Synthesis Low Power Optimization Techniques Redundancy Insertion Logic Transformation Multiplier Cell Optimization Experimental Results Summary and Conclusion What I learnt !
ELEC6970001 Class Presentation 2 Nov. 29, 2005 Low Power Logic Synthesis Sources of Power Dynamic power Signal transitions Logic activity Glitches Shortcircuit Leakage Static Power Area Method : Area optimized logic synthesis Method : Optimized transistor level design for gates Method : Low Power Logic Synthesis
ELEC6970001 Class Presentation 3 Power Transistor Leakage and Shortcircuit current Power Signal Activity of Circuit Nov. 29, 2005 Low Power Optimization techniques Technology Independent Optimization Algebraic Logic Restructuring
Kernel and Cube Extraction Iterative extraction and resubstitution of subexpressions Post Mapping Structural Optimization Redundancy Insertion Logic Transformations Nov. 29, 2005 ELEC6970001 Class Presentation 4 Postmapping Structural Optimization Redundancy Insertion Redundancy is inserted into the circuit to minimize a cost function. 3 elements required in the process Suitable circuit location for redundancy insertion Candidate type of redundancy Cost function Identifying candidates for redundancy insertion at a suitable circuit location for minimum cost function. Applying logic transformation to insert redundancy Reducing the circuit by removing other generated redundancies by logic transformation.
ELEC6970001 Class Presentation 5 3 steps involved Nov. 29, 2005 Postmapping Structural Optimization Finding Circuit Locations for Redundancy Insertion Identify Source and Target locations using don't care implications
Possible target location x x A B x x x 0 0 Source location Y C D
Nov. 29, 2005 ELEC6970001 Class Presentation 6 Postmapping Structural Optimization Candidate Redundancy insertions Redundancy insertions to input of gates
x x 0 `0' implication don't care 1 `1' implication don't care Used to reduce signal activity at the output of a gate using another signal.
ELEC6970001 Class Presentation 7 Nov. 29, 2005 Gate Insertion: Postmapping Structural Optimization Nov. 29, 2005 ELEC6970001 Class Presentation 8 Postmapping Structural Optimization Circuit Reduction to eliminate unwanted redundancies Redundancy identification methods: ATPG based
Use of exhaustive ATPG to find redundant faults Redundant faults signify redundant logic Fault independent Controllability and Observability analysis
ELEC6970001 Class Presentation 9 Nov. 29, 2005 Postmapping Structural Optimization
Logic Transformations Permissible function: If all the network primary output functions do not change after the function realized at a signal line Li is replaced by a function f , then the function f is called a permissible function for the signal line Li . Gate Substitution Replace a target signal line with the candidate signal line having the same function. Replace a target signal line with the inverted candidate signal line having the same function.
ELEC6970001 Class Presentation 10 Inverter Insertion Nov. 29, 2005 Postmapping Structural Optimization Logic Transformations Eliminate inverters on signals with high activity Discourage the implementation of EXOR gates EXOR gate example: Y = AB + AB = (AB) + (AB) = (A + B) + AB Nov. 29, 2005 ELEC6970001 Class Presentation 11 Multiplier Cell
B3 0 B2 0 B1 0 B0 0 A0 0 Y0 0 A1 Y1 A2 0 Y2 A3 0 Y7 Y6 Y5 Y4 Y3 B Sum input A Carry out Full adder Carry in Sum output Array Cell Full Adder Nov. 29, 2005 ELEC6970001 Class Presentation 12 Multiplier Cell
EXOR EXOR Nov. 29, 2005 ELEC6970001 Class Presentation 13 Multiplier Cell
Modified
EXOR EXOR Nov. 29, 2005 ELEC6970001 Class Presentation 14 Multiplier Cell
Modified  2 Nov. 29, 2005 ELEC6970001 Class Presentation 15 Multiplier Cell Leonardo (delay optimized) Nov. 29, 2005 ELEC6970001 Class Presentation 16 Multiplier Cell
Leonardo (area optimized) Nov. 29, 2005 ELEC6970001 Class Presentation 17 Experimental Results
Multiplier Cell Design and simulation details Design Entry tool: Design Architect Simulation tool : Eldo (timing and power analysis) Technology library: tsmc 0.18um (VDD = 1.8V) Inputs: frequencies in multiples of 2 Output transitions generated: Input Vectors: Sum Out (Sout) : 25 Carry Out (Cout) : 12
ELEC6970001 Class Presentation 18 Nov. 29, 2005 Multiplier Cell Results
Unopt. Static Power Dyn. Power Tdelay
(A/B=>Sout) Opt. Leo_Area Leo_Delay 367.04 pW 201.93 pW 168.94 pW 194.28 pW 27.08 uW Avg. Peak Avg. Peak 276.13 ps 328.45 ps 226.08 ps 237.07 ps 17.39 uW 287.77 ps 345.74 ps 173.77 ps 177.02 ps 20.83 uW 225.85 ps 257.23 ps 80.59 ps 108.62 ps 21.28 uW 189.16 ps 255.17 ps 90.16 ps 96.60 ps
19 Tdelay
(A/B=>Cout)
Nov. 29, 2005 ELEC6970001 Class Presentation Summary and Conclusion Post Mapped Structural Optimization techniques for Low Power prove to be effective. Percentage reduction in power consumption of optimized Multiplier Cell as compared to: Unoptimized cell: ~35.7% Leonardo generated: ~15% Percentage increase in critical path delay of optimized Multiplier Cell as compared to: Unoptimized cell: ~35.7% Leonardo generated: ~50% Effective cost functions to include delay constraints will enhance the quality of the circuits. Effective algorithms for structural optimization. 32 x 32 bit Multiplier power optimization.
ELEC6970001 Class Presentation 20 Nov. 29, 2005 What I learnt ! Low Power Logic Synthesis Logic synthesis Logic optimization Redundancy insertion, identification and elimination Use of EDA tools for timing and power analysis Start your projects early! (wish I would have) Large patience required with EDA tools!
ELEC6970001 Class Presentation 21 Nov. 29, 2005 References
1. 2. 3. 4. 5. 6. S. Devadas, S. Malik, "A Survey of Optimization Techniques Targeting Low Power VLSI Circuits," Annual ACM IEEE Design Automation Conference, Proceedings of the 32nd ACM/IEEE conference on Design automation, San Francisco, California, United States, pp. 242 247, 1995 Pradhan D.K., Chatterjee M., Swarna M.V., Kunz W, "Gatelevel synthesis for lowpower using new transformations," Low Power Electronics and Design, 1996, International Symposium on, pp 297300, Aug 1996 Wang Q., Vrudhula S.B.K., "Multilevel logic optimization for low power using local logic transformations," ComputerAided Design, 1996. ICCAD96., 1996 IEEE/ACM International Conference on 1014 Nov. 1996 Page(s):270 277 ShihChieh Chang, MarekSadowska M, "Perturb And Simplify: Multilevel Boolean Network Optimizer," ComputerAided Design, 1994., IEEE/ACM International Conference on November 610, 1994 Page(s):2  5 R. V. Menon, S. Chennupati, N. K. Samala, D. Radhakrishnan and B. Izadi, "Power Optimized Combinational Logic Design," Proceedings of the International Conference on Embedded Systems and Applications, pp. 223  227, June 2003. W. Kunz, "Multilevel Logic Optimization By Implication Analysis," ComputerAided Design, 1994., IEEE/ACM International Conference on November 610, 1994 Page(s):6  13
ELEC6970001 Class Presentation 22 Nov. 29, 2005 References
1. 2. 3. 4. 5. Roy K., Prasad S.C., "Circuit activity based logic synthesis for low power reliable operations," Very Large Scale Integration (VLSI) Systems, IEEE Transactions on Volume 1, Issue 4, Dec. 1993, pp 503 513 KiWook Kim, Ting Ting Hwang, Liu C.L., SungMo Kang, "Logic transformation for low power synthesis," Design, Automation and Test in Europe Conference and Exhibition 1999. Proceedings, pp158 162, March 1999 Brzozowski I., Kos A., "Minimisation of power consumption in digital integrated circuits by reduction of switching activity," EUROMICRO Conference, 1999. Proceedings. 25th Volume 1, 810 Sept. 1999 Page(s):376  380 vol.1 M. A. Iyer and M. Abramovici, "LowCost Redundancy Identification for Combinational Circuits," in Proc. 7th International Conf. on VLSI design, pp. 315317, January 1994. V.D. Agrawal; M.L. Bushnell, Qing Lin, "Redundancy identification using transitive closure," Test Symposium, 1996., Proceedings of the Fifth Asian 2022 Nov. 1996 Page(s):4 9 Abramovici M., Iyer M.A., "OnePass Redundancy Identification and Removal," Test Conference, 1992. Proceedings., International Sept. 2024 1992 Page(s):807
ELEC6970001 Class Presentation 23 Nov. 29, 2005 Thank You!
Questions ??? Nov. 29, 2005 ELEC6970001 Class Presentation 24 ...
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This note was uploaded on 09/17/2011 for the course ELEC 6970 taught by Professor Staff during the Spring '08 term at Auburn University.
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