Assistive Circuit for Lowering Minimum Operating Voltage and Balancing Read/Write Margins in an SRAM Array

There is a trade-off between read stability and writability under a full-/half-select condition in static random access memory (SRAM). Another trade-off in the minimum operating voltage between the read and write operation also exists. A new peripheral circuit for SRAM arrays, called a variation sensor, is demonstrated here to balance the read/write margins (i.e., to optimize the read/write trade-off) as well as to lower the minimum operation voltage for both read and write operations. A test chip is fabricated using an industrial 45-nm bulk complementary metal oxide semiconductor (CMOS) process to demonstrate the operation of the variation sensor. With the variation sensor, the word-line voltage is optimized to minimize the trade-off between read stability and writability (V-WL,V-OPT = 1.055 V) as well as to lower the minimum operating voltage for the read and write operations simultaneously (V-MIN,V-READ = 0.58 V, V-MIN,V-WRITE = 0.82 V for supply voltage ((VDD)) = 1.1 V).