Coding for sensing in Content Addressable Memories

We study binary Content Addressable Memories (CAMs) that employ a resistive element to store content. A CAM has a match line for every word stored which is sensed in order to determine a match/no match condition. We show how simple, low redundancy coding techniques can dramatically improve the ability to differentiate a match from a mismatch, effectively allowing a CAM design that stores nearly twice as many bits in the same memory as a competing design that stores each bit and its complement. The theory of coding for asymmetric errors is relevant in this problem; we rely on it to prove that ⌊n/2⌋ out of n constant weight codes are optimal for sensing.