Characterization of Half-Select Free Write Assist 9T SRAM Cell

Abstract

Modern biomedical applications have created a high demand for low power static random access memory (SRAM). In this article, a reliable low power half-select free-write assist 9T (HFWA9T) cell has been proposed. To analyze the impact of process variations on different design metrics, the proposed cell has been compared with other contemporary designs such as feedback-cutting 7T (7T), fully differential 8T (FD8T), and single-ended disturb free 9T (SEDF9T) cells. The HFWA9T cell exhibits 2.87×/3.37× higher read stability or read static noise margin (RSNM) than that of 7T/FD8T and 1.40×/6.55× higher write ability or write static noise margin (WSNM) than that of FD8T/SEDF9T,2.90×/2.67× and 1.06×/1.01×/5.05× narrower spread in RSNM and WSNM than that of 7T/FD8T and 7T/FD8T/ SEDF9T cells, respectively. In addition, it shows 1.11×/1.03× narrower spread in read delay (TRA) than that of FD8T/SEDF9T and 1.33× shorter TRA than that of SEDF9T cell. Furthermore, it consumes only 0.67×/0.31×/0.48× of the write power and 0.262×/0.605×/0.90× of the read power, respectively, consumed by 7T/FD8T/SEDF9T, while consuming 0.34×/0.96× of static power consumed by 7T/FD8T cell. For all these improvements, it incurs a penalty of 1.62×/1.78× in write delay (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">WA</sub> ) compared to 7T/SEDF9T and 1.58×/1.58× in T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RA</sub> compared to 7T/FD8T cell at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DD</sub> = 700 mV.