Method of and apparatus for providing look ahead column redundancy access within a memory

Abstract

A look ahead column redundancy circuit provides high speed memory access to both regular memory arrays and redundant memory arrays. In the preferred embodiment of the present invention, the information on both the address bus and the information on the next address bus are decoded by redundant column decoders in parallel. The decoded information from the redundant column decoders is then provided to a redundancy column pathway as the addressing information from the address bus and the next address bus is provided to a main column pathway. The information on the address bus is latched when beginning at a new column address. The information on the next address bus is latched for the next column address when operating in a burst cycle mode. The main column pathway preferably includes a latch, a main column decoder and a main column select circuit. A disable signal is also activated by the redundant column decoders if the addressing information for a current memory access operation corresponds to an address within the redundant memory array. When activated, the disable signal disables the main column select circuit within the main column pathway. If the addressing information for a current memory access operation does not correspond to an address within the redundant memory array, then the memory access operation is performed within the main memory array without any delays. Since the decoding is performed before the information is latched onto the column address bus, the proper pathway is selected without the need for any additional delay.