Bitline (BL) charge-recycling-based static random access memory (SRAM) write assist circuits (BCR-WA) are proposed to reduce the minimum operating voltage (V MIN ) of SRAM. In the proposed schemes, the charges stored on the unselected BL are utilized to raise the cell ground voltage (VSS) of the selected bit cell, and the increased cell VSS (CVSS) enhances the write ability. According to the metal routing direction of CVSS in the layout, two types of BCR-WA are proposed, BCR-WA for vertical CVSS routing (BCR-WA V ) and horizontal CVSS routing (BCR-WA H ). To evaluate the proposed circuits, HSPICE simulations are performed and the test chip is implemented using a 14-nm FinFET technology. Thanks to the charge-recycling operation, BCR-WA V and BCR-WA H can save energy by 11%-44% and 30%-66%, respectively, compared to the previous write assist circuits, with a comparable or less area overhead and an insignificant degradation in read performance (<1%) and stability (∼25-mV degradation in maximum word-lin voltage). In addition, according to simulation results, BCR-WA V and BCR-WA H can lower V MIN by 150 mV. In particular, silicon measurement result for BCR-WA H proves an 125-mV improvement in V MIN .
Bibliographical noteFunding Information:
Manuscript received July 1, 2018; revised September 26, 2018; accepted November 15, 2018. Date of publication December 24, 2018; date of current version February 21, 2019. This paper was approved by Guest Editor Jonathan Chang. This work was supported by Samsung Electronics through the High-Speed SRAM Research and Development Project. (Corresponding author: Seong-Ook Jung.) H. Jeong was with the School of Electrical and Electronic Engineering, Yonsei University, Seoul 03722, South Korea. He is now with Samsung Electronics Company, Ltd., Yongin 17113, South Korea.
© 2018 IEEE
All Science Journal Classification (ASJC) codes
- Electrical and Electronic Engineering