Design of a Schmitt-Trigger-Based 7T SRAM cell for variation resilient Low-Energy consumption and reliable internet of things applications

Abstract

The internet of things (IoTs)-based systems require battery-enabled energy-efficient memory circuits to operate at low voltage domain, especially below the transistor’s threshold. This study presents a single-ended 7T SRAM cell for IoTs applications. Cell core of the proposed 7T SRAM cell is composed of a novel Schmitt-trigger circuit in which a dynamic body bias technique is applied to a standard CMOS inverter through a feedback mechanism, whereby the threshold voltages of two MOSFETs can be changed, thus changing the switching voltage. The proposed 7T SRAM cell employs only one bitline to perform both read and write operations to reduce active power consumption. Read operation of the proposed 7T SRAM cell is conducted using only a single n-type MOSFET transistor driven by QB node. This transistor isolates bitline from storage nodes during read operation, improving read stability (RSNM) and read delay (TRA). A p-type MOSFET controlled by write wordline is placed inside the cell core to cut its feedback path off during write operation. This mechanism eliminate writing ‘1′ issue in single-ended SRAM cell and facilitate write ‘1′ operation, resulting in write-ability (WSNM) enhancement. To prove superiority of the proposed 7T SRAM cell in the various design metrics, it is compared with six state-of-the-art SRAM cells at subthreshold supply of VDD = 0.3 V. The proposed 7T SRAM cell is the second/first/third best cell in terms of RSNM/WSNM/write access time (TWA). Furthermore, an improvement of at least 2.55X in TRA and 12.58X (2.02X) in read (write) energy consumption is achieved by the proposed 7T SRAM cell. Although, the proposed 7T SRAM cell offers some disadvantages, nevertheless it offers the best proposed figure of merit.