US 2014/0192579 A1Published application

Two phase search content addressable memory with power-gated main-search

AssigneeInternational Business Machines Corporation

InventorsIgor Arsovski, Michael T. Fragano, Travis R. Hebig

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Abstract

Low leakage CAMs and method of searching low leakage CAMs. The method includes performing a pre-search and compare on a small number of pre-search bits with pre-search CAM cells powered to normal voltage levels at all times while the main-search CAM cells are powered to a lower voltage level. Only if a match is detected on the pre-search bits are the main-search CAM cells powered-up to normal voltage levels and the search of the main-search bits activated. The main-search CAM cells are powered to normal voltage levels during read and write operations.

Claims21

Dependent claims

A content addressable memory, comprising:

an array of content addressable memory cells arranged in rows and columns and partitioned into a pre-search section and a main-search section;
and
each row of content addressable memory cells including:
a row of content addressable memory cells of said pre-search section connected between a first positive voltage rail and ground and connected to a pre-matchline of said content addressable memory;
a corresponding row of content addressable memory cells of said main-search section connected to a light-sleep circuit, to ground and to a main-matchline of said content addressable memory, said light-sleep circuit configured to connect content addressable memory cells of said main-search section to a second positive voltage rail in a light-sleep state and to connect content addressable memory cells of said corresponding row of content addressable memory cells of said main-search section to said first positive voltage rail in an awake state;
a pre-search circuit connected to a pre-search matchline and (i) configured to perform a pre-search of said row of content addressable memory cells of said pre-search section and (ii) configured, only if a match is found, place said light-sleep circuit in said awake state;
and
a main-search circuit connected to a main matchline and configured to activate a main-search of said row of content addressable memory cells of said main-search section only if a match is found by said corresponding pre-search circuit.

5 more elements

A method of searching a content addressable memory, comprising:

providing an array of content addressable memory cells arranged in rows and columns and partitioned into a pre-search section and a main-search section;
applying a first positive voltage to content addressable memory cells of said pre-search section;
applying a second positive voltage to content addressable memory cells of said main-search section, said second voltage lower than said first voltage;
applying a search word comprising a set of pre-search bits and main-search bits to said content addressable memory;
performing a pre-search of each row of content addressable memory cells of said pre-search section using said set of pre-search bits;
only for each row of content addressable memory cells where a match was found as a result of performing said pre-search, de-applying said second voltage and applying said first voltage to said content addressable memory cells of said main-search section and then performing a main-search of those rows of content addressable memory cells of said main-search section using said set of main-search bits;
for each row of content addressable memory cells where no match was found as a result of performing said pre-search or as a result of performing said main-search, generating a no-match signal;
and
for each row of content addressable memory cells where a match was found as a result of performing said pre-search and as a result of performing said main-search, generating a match signal.

6 more elements

Dependencies are inferred from the claim text.