Design and Analysis of A Novel 8T SRAM Cell December 14, 2010 Department of Microelectronic Engineering & Centre for Efficiency Oriented Languages University College Cork, Ireland & Synopsys, Ireland Jiaoyan Chen, Dilip Vasudevan, Emanuel Popovici, Michel Schellekens, Peter Gillen
Contents Motivation Architectures of 6T SRAM, 9T SRAM and our 8T SRAM Adiabatic and Non-Adiabatic Operations SNM Comparison Dynamic Power Static Power Conclusion
Motivation Roadmap –Cell Area Trend(ITRS 2008) Consumer Portable Power Consumption Trend (ITRS 2008 update) SOC Consumer Stationary Power Consumption (2008) SRAM consumes a lot of power and area in chips. Our aim is to built an efficient SRAM.
Conventional 6T SRAM 4 Technology: 90nm,65nm,45nm, 28nm… Stability: Static Noise Margin (SNM) is getting Down. Leakage Power: a) Subthreshold leakage current b) Gate oxide leakage current
9T SRAM 9T SRAM 5 Features: a) 2 sub-circuits: Upper : Writing Lower: Reading b) Minimal Sizing for the upper part c) SNM is much better d) Lower leakage Power (in super cut-off mode) Z. Liu and V. Kursun, “Characterization of a novel nine-transistor sram cell,” IEEE Trans. Very Large Scale Integr. Syst., vol. 16, no. 4, pp. 488–492, 2008
Proposed 8T SRAM 6 Features: a) 2 sub-circuits: Upper :1. No GND Connection 2. Add One Sharing transistor Lower: Using PMOS b) Half swing BL and BL’ return to VDD/2 after writing or reading.
Adiabatic Operations: Writing PMOS P3 is used to meet the Adiabatic Principle: No voltage difference before the transistor turns on
Adiabatic Operations: Reading
Simulation Waveforms
SNM Comparison (45nm) Proposed 8T SRAM Conventional 6T SRAM
Dynamic Power Comparison (1) Dynamic Power Comparison (1) 8*8 Array 1 Bit Cell
Dynamic Power Comparison (2) 62% 67%
Leakage Power Analysis
Temperature Variation >90%
Process Variation (65nm) – TOX, VTH, U0 >90%
Process Variation (45nm) – TOX, VTH, U0 90%
Conclusion Summary Efficient 8T SRAM architecture Improved SNM compared with 6T SRAM Very Low Dynamic and Leakage power Future work Use 36nm, 28nm…Check performance particularly for leakeage Further Enhance the Stability Fabricate and validate the proposed architecture
Thank You Questions?