Editing Content-addressable memory (section)

==Ternary CAMs==
[[File:Ternary CAM cell schematic.jpg|thumb|CMOS Ternary CAM cell consisting of two 6T SRAM cells plus 4 comparison transistors. Normally opposite logic levels, either '0' and '1' or '1' and '0' will be stored in the two cells. For a don't care condition '0' will be stored in both cells so that the match line ML will not be pulled low for any combination of search line (SL) data.]]
'''Binary CAM''' is the simplest type of CAM and uses data search words consisting entirely of [[boolean logic|1s and 0s]].  '''Ternary CAM''' ('''TCAM''')<ref>{{Cite book | url=https://books.google.com/books?id=-rnt_ik0mSYC&q=TCAM&pg=PA71 | title=CCNP BCMSN Exam Certification Guide: CCNP Self-study| isbn=9781587200779| last1=Hucaby| first1=David| year=2004| publisher=Cisco Press}}</ref> allows a [[ternary logic|third matching state]] of ''X'' or ''don't care'' for one or more bits in the stored word, thus adding flexibility to the search. For example, a stored word of ''10XX0'' in a ternary CAM will match any of the four search words ''10000'', ''10010'', ''10100'', or ''10110''.  The added search flexibility comes at an additional cost over binary CAM as the internal memory cell must now encode three possible states instead of the two for the binary CAM.  This additional state is typically implemented by adding a mask bit (''care'' or ''don't care'' bit) to every memory cell.
In 2013, [[IBM]]  fabricated a nonvolatile TCAM using 2-transistor/2-resistive-storage (2T-2R) cells.<ref>Jing Li, R. Montoye, M. Ishii, K. Stawiasz, T. Nishida, K. Maloney, G. Ditlow, S. Lewis, T. Maffitt, R. Jordan, Leland Chang, P. Song, "1Mb 0.41 μm2 2T-2R cell nonvolatile TCAM with two-bit encoding and clocked self-referenced sensing", [[IEEE]] Symposium on VLSI Technology, 2013.</ref> A design of TCAM using hybrid Ferroelectric [[FeFET]] was recently published by a group of International scientists.<ref>Xunzhao Yin, Yu Qian, M. Imani, K. Ni, Chao Li, Grace Li Zhang, Bing Li, Ulf Schlichtmann, Cheng Zhuo, "Ferroelectric Ternary Content Addressable Memories for Energy-Efficient Associative Search", [[IEEE]] Transactions on Computer-Aided Design of Integrated Circuits and Systems, April 2023.</ref>