Patent ID: 7345897
Filing Date: 2008-03-18
Classification: G11C

Abstract:
1. An apparatus configured to identify matching values differing in less than a predetermined number of ternary content-addressable memory (TCAM) cells, the apparatus comprising: a TCAM entry including t TCAM entry cells, each particular TCAM entry cell of said TCAM entry cells being configured to identify whether or not a bit value of a lookup word in a bit position in the lookup word corresponding to said particular TCAM cell matches the particular TCAM entry cell's predetermined value of a set of values including: one, zero and don't care; a match line, coupled to each of said TCAM entry cells, configured to provide a match reference voltage after the match line is precharged during a precharge phase prior to a matching phase of a lookup operation on the lookup word; wherein the match line is responsive to said identifications of not matching by said TCAM cells, wherein said match reference voltage falls at rate corresponding to the number of active discharge paths in said TCAM entry cells said identifying not matching for the lookup word; and a comparator, coupled to the match line, configured to identify whether or not the match reference voltage is above or below a predetermined voltage level selected to reflect a matching of the lookup word by at least t-u said TCAM cells at a predetermined time of the lookup operation, wherein the predetermined voltage level is selected such that said match reference voltage will be above the predetermined voltage level at the predetermined time if u or less of said TCAM cells said identified as not matching and the match reference voltage will be below the predetermined voltage level at the predetermined time if at least u+1 said TCAM cells said identified as not matching; wherein t>u>0.