A Comparative Study of Single- and Dual-Threshold Voltage SRAM Cells

Abstract

In this paper, a comparison has been drawn between 5 transistor (5T), 6T and 7T SRAM cells. All the cells have been designed using both single-threshold (conventional) and dual-threshold (dual-Vt) voltage techniques. Their respective delays and power consumption have been calculated at 180 nm and 65 nm CMOS technology. With technology scaling, power consumption decreases by 80% to 90%, with some increase in write time because of the utilization of high- Vt transistors in write critical path. The results show that the read delay of 7T SRAM cell is 9% lesser than 5T SRAM cell and 29% lesser than 6T SRAM cell due to the lower resistance of the read access delay path. While read power of 5T SRAM cell is reduced by 10% and 24% as compared to 7T SRAM, 6T SRAM cell respectively. The write speed, however, is degraded by 1% to 3% with the 7T and 5T SRAM cells as compared to the 6T SRAM cells due to the utilization of single ended architecture. While write power of 5T SRAM cell is reduced by up to 40% and 67% as compared to 7T SRAM, 6T SRAM cell respectively.

Keywords

• 5T SRAM
• 65 nm CMOS technology
• 6T SRAM
• 7T SRAM
• low power SRAM
• power reduction technique