A 256 Mb SDRAM using a register-controlled digital DLL

Abstract

This 256 Mb synchronous DRAM with 1 ns clock access is stable against temperature, voltage, and process variation by use of an innovative register-controlled delay locked loop (RDLL). Unlike most conventional high-density DRAMs, the bit-lines are placed above the storage capacitors in this DRAM to relax design rules of the core area. The noise issues are analyzed and resolved to help implement the technology in mass production of 0.28 to 0.24 /spl mu/m 200 MHz DRAMs.