A 2-port 6T SRAM bitcell design with multi-port capabilities at reduced area overhead

Low power, minimum transistor count and fast access static random access memory (SRAM) is essential for embedded multimedia and communication applications realized using system on a chip (SoC) technology. Hence, simultaneous or parallel read/write (R/W) access multi-port SRAM bitcells are widely employed in such embedded systems. In this paper, we present a 2-port 6T SRAM bitcell with multi-port capabilities and a reduced area overhead compared to existing 2-port 7-transistor (7T) and 8T SRAM bitcells. The proposed 2-port bitcell has six transistors (6T) and single-ended read and write bitlines (RBL/WBL). We compare the stability, simultaneous read/write disturbance, SNM sensitivity and misread current from the read bitline with the 7T and 8T bitcells. The static noise margin (SNM) of the 6T bitcells around the write disturbed bitcell is 53% to 61% higher than that of the 7T bitcell. The average active power dissipation under the different read/write operations of the 6T bitcells is 28% lower than the 8T and equal to 7T bitcell. Hence, the proposed 2-port 6T-SRAM is a potential candidate in terms of process variability, stability, area, and power dissipation.

[1]  R. Engelbrecht,et al.  DIGEST of TECHNICAL PAPERS , 1959 .

[2]  Y. Nakagome,et al.  Trends in low-power RAM circuit technologies , 1994, Proceedings of 1994 IEEE Symposium on Low Power Electronics.

[3]  Y. Nakagome,et al.  Trends in low-power RAM circuit technologies , 1995 .

[4]  J. Meindl,et al.  The impact of intrinsic device fluctuations on CMOS SRAM cell stability , 2001, IEEE J. Solid State Circuits.

[5]  Anna W. Topol,et al.  Stable SRAM cell design for the 32 nm node and beyond , 2005, Digest of Technical Papers. 2005 Symposium on VLSI Technology, 2005..

[6]  A. Chandrakasan,et al.  A 180-mV subthreshold FFT processor using a minimum energy design methodology , 2005, IEEE Journal of Solid-State Circuits.

[7]  Kaushik Roy,et al.  Estimation of delay variations due to random-dopant fluctuations in nanoscale CMOS circuits , 2005 .

[8]  K. Takeda,et al.  A read-static-noise-margin-free SRAM cell for low-V/sub dd/ and high-speed applications , 2005, ISSCC. 2005 IEEE International Digest of Technical Papers. Solid-State Circuits Conference, 2005..

[9]  Masahiro Nomura,et al.  A read-static-noise-margin-free SRAM cell for low-VDD and high-speed applications , 2006, IEEE Journal of Solid-State Circuits.

[10]  K. Ishibashi,et al.  A 65 nm Ultra-High-Density Dual-Port SRAM with 0.71um/sup ~/ 8T-Cell for SoC , 2006, 2006 Symposium on VLSI Circuits, 2006. Digest of Technical Papers..

[11]  A.P. Chandrakasan,et al.  A 256-kb 65-nm Sub-threshold SRAM Design for Ultra-Low-Voltage Operation , 2007, IEEE Journal of Solid-State Circuits.

[12]  K. Ishibashi,et al.  A 65-nm SoC Embedded 6T-SRAM Designed for Manufacturability With Read and Write Operation Stabilizing Circuits , 2007, IEEE Journal of Solid-State Circuits.

[13]  T. Fukai,et al.  Understanding Random Threshold Voltage Fluctuation by Comparing Multiple Fabs and Technologies , 2007, 2007 IEEE International Electron Devices Meeting.

[14]  H. Yamauchi,et al.  A Stable 2-Port SRAM Cell Design Against Simultaneously Read/Write-Disturbed Accesses , 2008, IEEE Journal of Solid-State Circuits.

[15]  R.H. Dennard,et al.  An 8T-SRAM for Variability Tolerance and Low-Voltage Operation in High-Performance Caches , 2008, IEEE Journal of Solid-State Circuits.

[16]  Koji Nii,et al.  A 65 nm Embedded SRAM With Wafer Level Burn-In Mode, Leak-Bit Redundancy and Cu E-Trim Fuse for Known Good Die , 2008, IEEE Journal of Solid-State Circuits.

[17]  A.P. Chandrakasan,et al.  A 256 kb 65 nm 8T Subthreshold SRAM Employing Sense-Amplifier Redundancy , 2008, IEEE Journal of Solid-State Circuits.

[18]  Dhiraj K. Pradhan,et al.  Single ended 6T SRAM with isolated read-port for low-power embedded systems , 2009, 2009 Design, Automation & Test in Europe Conference & Exhibition.