Pre-Charged Local Bit-Line Sharing SRAM Architecture for Near-Threshold Operation

Abstract

In this paper, a pre-charged local bit-line sharing (PCLBS) static random access memory (SRAM) for near-threshold operation is proposed. In previous local bit-line sharing SRAMs, such as average-8T and full-swing local bit-line (FSLB) SRAMs, multiple bit-cells share a local bit-line pair with a small capacitance for high read stability. However, the average-8T SRAM has a considerably large delay because the full development of the local bit-line cannot be achieved. On the other hand, the FSLB SRAM reduces the delay but requires a timing constraint of control signals to achieve sufficient read sensing margin. The proposed PCLBS SRAM achieves high read speed by fully developing local bit-line pair without a timing constraint. Furthermore, the proposed PCLBS SRAM enhances the read stability and the write ability by, respectively, applying a pre-charged local bit-line scheme and transmission gates in write paths. Based on a 22-nm FinFET technology, the FSLB and proposed PCLBS SRAM have the minimum operating voltages of 0.44 and 0.4 V, respectively, while achieving the $5\sigma$ target read stability and write ability yields. Compared with the FSLB SRAM, the proposed PCLBS SRAM consumes 21% less energy at each minimum operating voltage and has 57% smaller read delay at the operating voltage of 0.4 V.