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

摘要

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.

主权项

1. 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; anda 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.