SRAM- Ultra low voltage operation

DESIGN OF A NOVEL SINGLE-ENDED, ROBUST 8T

SRAM CELL FOR ULTRA LOW-VOLTAGE, APPLICATIONS

Presented By:Rajesh Yadav

12ECP01P- M.Tech.(VLSI Design)

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Thesis Phase - I

7th December 2013

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Contents

•Objective•Literature Survey•Analysis of conventional 6T SRAM Cell•Analysis of proposed 8T SRAM Cell•References

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Thesis Phase - I

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•To overcome the bottleneck of 6T SRAM cell in terms of low voltage operation.

•Design a single ended 8T SRAM cell with following characteristics: Ultra Low Voltage operation Low power consumption Increased Write and Read Margin

Objective

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Objective Literature Survey 6T SRAM Cell

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• Most of the area of any SoC is consumed by memory.• Minimum operating voltage of SRAM cell is 0.45V

reported till now as per my best Knowledge.• Power dissipation will reduce, if we reduce its

operating voltage.• As scale down the device (technology lower down)

leakage current is the major issue which causes great power dissipation

Literature Survey

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Objective Literature Survey 6T SRAM Cell

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Analysis of 6T SRAM Cell

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Literature survey Current Scenario Requirements

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Operating Voltage = 1.8V

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Analysis of Proposed 8T SRAM Cell

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Response of Single ended 8T cell at operating Voltage = 900mV

Operation Hold Write 0 Write 1 read

WL 1 0 0 0

WWL/WBL 0/0 1/0 1/1 0/0RWL/RBL 0/1 0/1 0/1 1/1

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WL 1 0 0 0

WWL/WBL 0/0 1/0 1/1 0/0RWL/RBL 0/1 0/1 0/1 1/1

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WL 1 0 0 0

WWL/WBL 0/0 1/0 1/1 0/0RWL/RBL 0/1 0/1 0/1 1/1

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WL 1 0 0 0

WWL/WBL 0/0 1/0 1/1 0/0RWL/RBL 0/1 0/1 0/1 1/1

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Butterfly curve of proposed 8T SRAM Cell (Hold State) – HSNM =130mV

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

qb (Volt)

q (

Volt

)

HSNM of 8T SRAM

HSNM =130mV

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ncurve of proposed 8T SRAM Cell

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

-0.00000001

-0.000000005

0

0.000000005

0.00000001

0.000000015

0.00000002

q (Volt)

I (A

)

SVNMWTI

WTV

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[1] Koichi Takeda et al, “A Read Static Noise Margin Free SRAM cell for Low Vdd and High Speed Applications”, Solid-State Circuits, IEEE Journal vol. 41, Jan.2006, Issue 1 , pp.113-121

[2] M.F. Chang et al., A Differential Data Aware Power-supplied (D2AP) 8T SRAM Cell with Expanded Write / Read Stabilities for Lower VDDmin Applications. Symposium on VLSI Circuits Digest of Technical Papers, pp. 156–157 (2009a)

[3] M. Yabuuchi et al., A 45 nm 0.6 V Cross-Point 8T SRAM with Negative Biased Read/Write Assist, Symposium on VLSI Circuits Digest of Technical Papers, pp. 158–159 (2009) 30 2 SRAM Bit Cell Optimization

[4] L. Chang et al., An 8T-SRAM for variability tolerance and low-voltage operation in high performances caches. IEEE J. Solid-State Circuits, 43, 4, April (2008)

[5] B.H. Calhoun et al., A 256 k Sub threshold SRAM Using 65 nm CMOS. Proceedings of IEEE International Solid-State Circuits Conference (ISSCC), pp. 628–629, Feb 2006

[6] T.H. Kim et al., A High-Density Sub threshold SRAM with Data–Independent Bitline Leakage and Virtual Ground Replica Scheme. Proceedings of IEEE International Solid-State Circuits Conference (ISSCC), pp. 330–331, Feb 2007

[7] I.J. Chang et al., A 32 kb 10T sub-threshold SRAM array with bit-interleaving and differential Read scheme in 90 nm CMOS. IEEE J. Solid-State Circuits 44(2), 650–658 (2009b)

[8] J. Wu et al., A Large rVTH/VDD Tolerant Zigzag 8T SRAM with Area-Efficient Decoupled Differential Technical Papers, pp. 101–102 (2010)

[9] T. Suzuki et al., 0.5 V, 150 MHz, Bulk-CMOS SRAM with Suspended Bit-Line Read Scheme, Proceedings of Sensing and Fast Write-Back Scheme. Symposium on VLSI Circuits Digest of IEEE European Solid-State Circuits Conference (ESSCIRC), pp. 354–357, Sept 2010

[10] V. Sharma et al., A 4.4 pJ/Access 80 MHz, 128 kbit variability resilient SRAM with multi-sized sense amplifier redundancy. IEEE J. Solid-State Circuits, 46, 10 (2011a)

[11] H.Pilo,J.Barwin,G.Braceras,etal.,AnSRAMdesignin65-nmand45-nm technology nodes featuring read and write-assist circuits to expand operating voltage, Symposiumon VLSI Circuits, Digest of Technical Papers, 2006, pp.15-16.

[12] A. Bhavn agarwala, S. Kosonocky, C. Radens, etal., Fluctuation limits and scaling opportunities for CMOS SRAM cells, in: Proceedings of International Electron Devices Meeting (IEDM) Technical Digest, 2005, pp.659-662.

References

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Trade off Expected Outcomes

References

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[13] A. Bhavn agarwala, S. Kosonocky, Y. Chan, etal., Asub-600mV fluctuation tolerant 65nm CMOS SRAM array with dynamic cell biasing, Symposium on VLSI Circuits Digest of Technical Papers, 2007, pp. 78–79.

[14] M. Yamaoka, N. Maeda, Y. Shinozaki, etal., Low-power embedded SRAM modules with expanded margins forwriting, IEEE International Solid-State Circuits Conference, Digest of Technical Papers, 2005, pp. 480–611.

[15] K. Zhang, U. Bhattacharya, Z. Chen, etal. A 3-GHz 70-MBSR AM in 65-nm CMOS technology with integrated column-based dynamic power supply, IEEE J. Solid-State Circuits 41(1)(2006)146–151.

[16] S. Ohbayashi ,M. Yabuuchi, K.Nii ,etal., A 65-nm SoC embedded 6T-SRAM designed for manufactur ability with read and write operation stabilizing circuits, IEEE J.Solid-State Circuits 42 (4) (2007) 820–829.

[17] K.Sohn,Y.H.Suh,Y.J.Son,etal.,A100-nmdouble-stacked500-MHz72-MB separate I/O synchronous SRAM with automatic cell-bias scheme and adaptive block redundancy, IEEE International Solid-State Circuits Conference, Digest of Technical Papers, 2008, pp.386–622.

[18] O .Hirabayashi ,A. Katayama, A. Suzuki, etal., Aprocess-variation-tolerant dual-power-supply SRAM with 0.179-mm 2 cell in 40-nm CMOS using level-programmable wordline driver, IEEE International Solid-State Circuits Conference, Digest of Technical Papers, 2009, pp. 458–459.

[19] Y.H.Chen, W.M.Chan, S.Y.Chou, etal., A 0.6-V 45-nm adaptive dual-rail SRAM compiler circuit design for lower VDDmin VLSIs, Symposiumon VLSI Circuits Digest of Technical Papers, 2008, pp. 210–211.

[20] M. Khellah, N. S. Kim, J. Howard, etal., A 4.2-GHz 0.3-mm 2 256 KB dual-Vcc SRAM building blockin65-nmCMOS,IEEEInternationalSolid-StateCircuits Conference, DigestofTechnicalPapers,2006,pp.2572–2581.

[21] [13]J.Davis,D.Plass,P.Bunce,etal.,A5.6GHz64-KBdual-readdatacacheforthe POWER6TM processor,IEEEInternationalSolid-StateCircuitsConference, Digest ofTechnicalPapers,2006,pp.2564–2571.

[22] [14]J.Pille,C.Adams,T.Christensen,etal.,ImplementationoftheCELLbroadband engine ina65-nmSOItechnologyfeaturingdual-supplySRAMarrays supporting 6GHzat1.3V,IEEEInternationalSolid-StateCircuitsConference, Digest ofTechnicalPapers,2007,pp.322–606.

[23] [15] M. Yamaoka,K.Osada,K.Ishibashi,0.4-Vlogic–library-friendlySRAMarray using rectangular-diffusioncellanddelta-boosted-arrayvoltagescheme,IEEE J. Solid-StateCircuits39(6)(2004)934–940.

[24] [16] F.S.Lai,C.F.Lee,On-chipvoltagedownconvertertoimproveSRAMread/write margin andstaticpowerforsub-nanoCMOStechnology,IEEEJ.Solid-State Circuits 42(9)(2007)2061–2070.

References

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Trade off Expected Outcomes

References

Thesis Phase - I

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Thank You For Your Kind Attention

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Open For Discussion

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Pre-Thesis Presentation , Phase - I

Date post:	06-May-2015
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SRAM- Ultra low voltage operation

Engineering