Device variability in modern processes has become a major concern in SRAM design leading to degradation of both performance and yield. Variation induced offset in the sense amplifiers requires a larger bitline differential, which slows down SRAM access times and causes increased power consumption. The effect aggravated in the sub-threshold region. In this paper, we propose a circuit that reduces the sense amp offset using an auto-zeroing scheme with automatic temperature, voltage, and aging tracking. The circuit enables flexible tuning of the offset voltage. Measurements taken from a 45 nm test chip show the circuit is able to limit the offset to 20 mV. A 16kB SRAM is designed using the auto-zeroing circuit for the sense amps. The reduction in the total read energy and delay is reported for various configurations of the memory.
References
[1]
Ryan, J.F.; Calhoun, B.H. Minimizing Offset for Latching Voltage-Mode Sense Amplifiers for Sub-Threshold Operation. In Proceedings of the 9th International Symposium on Quality Electronic Design, San Jose, California, USA, 17–19 March 2008; pp. 127–132.
[2]
Wang, A.; Chandrakasan, A.P.; Kosonocky, S.V. Optimal Supply and Threshold Scaling for Subthreshold CMOS Circuits. In Proceedings of the IEEE Computer Society Annual Symposium on VLSI, Pittsburgh, PA, USA, 25–26 April 2002; pp. 5–9.
[3]
Verma, N.; Chandrakasan, A.P. A 256 kb 65 nm 8T subthreshold SRAM employing sense-amplifier redundancy. IEEE J. Solid State Circ. 2008, 43, 141–149, doi:10.1109/JSSC.2007.908005.
[4]
Pileggi, L.; Keskin, G.; Li, X.; Mai, K.; Proesel, J. Mismatch Analysis and Statistical Design at 65 nm and Below. In Proceedings of the IEEE Custom Integrated Circuits Conference, San Jose, California, USA, 21–24 September 2008; pp. 9–12.
[5]
Bhargava, M.; McCartney, M.P.; Hoefler, A.; Mai, K. Low-overhead, Digital Offset Compensated, SRAM Sense Amplifiers. In Proceedings of the IEEE Custom Integrated Circuits Conference, San Jose, California, USA, 13–16 September 2009; pp. 705–708.
[6]
Sachdev, M.; Sharifkhani, M.; Shah, J.S.; Rennie, D. Sense-amplification with Offset Cancellation for Static Random Access Memories. U.S. Patent Application 12/757,033, 8 April 2010.
[7]
Beshay, P.; Calhoun, B.H.; Ryan, J.F. Sub-threshold Sense Amplifier Compensation Using Auto-zeroing Circuitry. In Proceedings of the 2012 IEEE Subthreshold Microelectronics Conference, Waltham, Massachusetts, USA, 9–10 October 2012; pp. 1–3.
