A Pipeline Replica Bitline Technique for Suppressing Timing Variation of SRAM Sense Amplifiers in a 28-nm CMOS Process

Abstract

With advances in semiconductor technology, the threshold voltage variation has worsened, which has a great impact on the speed and stability of static random access memory (SRAM). This paper proposes a pipeline replica bitline (RBL) delay technique designed to reduce the timing variation of SRAM sense amplifiers. This design takes full advantage of all cells in the RBL as replica cells (RCs). A tunable pipeline structure is applied to control the discharge of groups of RCs. The structure is designed based on theoretical analysis and fabricated using an SMIC 28-nm CMOS process. The measurement results show that the delay variation can be reduced by approximately 43% and 32% compared with the conventional RBL and multistage RBL, respectively. Furthermore, with slight tuning of the normal 28-nm foundry process, four wafers were obtained under extreme conditions to comprehensively test the proposed technique. The results show that the proposed technique is more stable than other techniques in any extreme condition.