Reference Calibration of Body-voltage Sensing Circuit for High-speed STT-RAMs

With the continuing scaling of MTJ, the high-speed reading of STT-RAM becomes increasingly difficult. Recently, a body-voltage sensing circuit (BVSC) has been proposed for boosting the sensing speed. This paper analyzes the effectiveness of using the reference calibration technique to compensate for the device mismatches and improve the read margin of BVSC. HSPICE simulation results show that a 2-bit reference calibration can improve the worst-case read margin in a 1-Mb memory by over 3 times. This leads to up to 30% higher yield across all process corners. In order to maintain the yield improvement even in the worst-case corner, independent calibration circuitry has to be deployed for each memory array.