A bitline leakage compensation scheme for low-voltage SRAMs

A bitline leakage current of an SRAM, induced by leakage current of the transmission transistors in the cells that are associated with the bitline, increases as the threshold voltage (V_TH) of the transistors is reduced for high performance at low power-supply voltage (V_DD). The increased bitline leakage causes slow or incorrect read/write operation of an SRAM because the leakage current acts as noise current for a sense amplifier. In this paper, the problem has been solved from a circuitry point of view, and the scheme which detects the bitline leakage current in a precharge cycle and compensates for it during a read/write cycle is proposed. Employing this scheme, the SRAM with 360-μA bitline leakage current can perform a read/write operation at the same speed as one that has no bitline leakage current. This enables a 0.1-V reduction in V_TH, and keeps the V_TH and delay scalability of a high-performance SRAM in technology progress. An experimental 8-kb SRAM with 256 rows in fabricated in a 0.25-μm CMOS technology, which demonstrates the effectiveness of the scheme.