Auto-Scaling Overdrive Method Using Adaptive Charge Amplification for PRAM Write Performance Enhancement

A PRAM write driver with an auto-scaling overdrive method is presented. The proposed overdrive method significantly reduces the rise time of the cell-current pulse for bit-line parasitic components of 3 pF and 6 k $\Omega$ , and it lowers the complexity of the overdrive control using an adaptive charge amplification technique. A rise time of less than 15 ns is achieved and shortened up to 4.7 times, and the total write-throughput is increased. The rise time is reduced consistently for all levels of the target-current by the auto-scaling effect. Therefore, cell heating control becomes more linear in program-and-verify (PNV) operation. Due to its simple adding-on structure, it is easily compatible with a conventional write driver. A prototype chip was implemented using a 0.18- $\mu$ m CMOS process. It is also applicable to smaller-scale technology.