Peak-to-average pumping efficiency improvement for charge pump in Phase Change Memories

The emerging Phase Change Memory (PCM) is considered as a promising candidate to replace DRAM as the next generation main memory since it has better scalability and lower leakage power. However, the high write power consumption has become a main challenge in adopting PCM as main memory. In addition to the fact that writing to PCM cells requires high write current and voltage, current loss in the charge pumps (CPs) also contributes a large percentage of the high power consumption. The pumping efficiency of a PCM chip is a concave function of the write current. Based on the characteristics of the concave function, the overall pumping efficiency can be improved if the write current is uniform. In this paper, we propose the peak-to-average (PTA) write scheme, which smooths the write current fluctuation by regrouping write units. An off-line optimal Integer Programming (IP) formulation and an efficient online algorithm are proposed to achieve this goal. Experimental results show that PTA can improve the charge pump efficiency to similar to 40% with little overhead. Meanwhile, PTA can achieve 17.0% energy reduction on average.