Error catch RAM for memory tester has SDRAM memory sets configurable for size and speed

摘要

DRAM speed of operation in an Error Catch RAM can be increased by a combination of interleaving signals for different Banks of memory in a Group thereof and multiplexing between those Groups of Banks. A three-way multiplexing between three Groups of four Banks each, combined with a flexible four-fold interleaving scheme for signals to a Group produces an increase in speed approaching a factor of twelve, while requiring only three memory busses. Each of the twelve Banks represents the entire available address space, and any individual write cycle might access any one of the twelve Banks. A utility mechanism composes results for all twelve Banks during a read cycle at an address into a unified result. There is a mechanism to track of the integrity of the composed results, as further write operations can produce the need for another composing step. There are four Memory Sets, two are "internal" SRAM's and two are "external" DRAM's. The SRAM's are integral parts of VLSI circuits, while the DRAM's are individual packaged parts adjacent that VLSI. The amount of DRAM is optional. For DRAM memory sets the multiplexing and interleaving mode allows full random access at speeds of up to 100 MHz. For speeds will not exceed 33 MHz, the DRAM's can be configured to provide three times the depth in return for the lower speed by removing the multiplexing between Groups in favor of just interleaving upon one larger Group; Bank enable bits that were used as part of the multiplexing can now be used as regular address bits to increase the size of the address space of the one Group that remains. If the testing to the DUT fits the "linear" mode of access, a twelve-fold increase in memory depth is available, even when the DUT is tested at the highest speed the tester can operate at. This eliminates the interleaving scheme in favor of addressing within a single Bank at a time. Another reconfiguration is to combine the external memory sets into one memory set that has twice the depth of either uncombined set, regardless of other (i.e., the speed related) modes of operation.