Dynamic reconfiguration schemes for megabit BiCMOS SRAMs and performance evaluation

Abstract

In this paper two dynamic configuration schemes are discussed for megabit BiCMOS static random access memories (SRAMs). Dynamic reconfiguration schemes allows failure detection at the chip level and automatic reconfiguration to fault free memory cells within the chip. The first scheme is a standby system approach where the I/O lines of the memory can be dynamically switched to spare bit slices in the SRAM. This scheme is implemented through a switching network at the memory interface. Every memory access is controlled by a fault status table (FST) which memorizes the fault conditions of each memory block. This FST is implemented outside the memory system. A second dynamic reconfiguration scheme for BiCMOS SRAMs is addressed through a graceful degradation approach. Basic design considerations and performance evaluation of megabit BiCMOS SRAMs using dynamic reconfiguration schemes are presented. The basic properties of the proposed schemes and a prototype VLSI chip implementation details are discussed. BiCMOS SRAM access time improvement of about 35%, chip area of 25%, and chip yield of 10% are achieved, respectively, as compared to conventional methods. A comparison of reliability improvement of 1 Mb BiCMOS SRAMs using dynamic configuration schemes is presented. These two dynamic reconfiguration schemes have considerable importance in reliability improvement when compared to conventional methods. The major advantage is that the size of reconfiguration of the system can be considerably reduced.