Content addressable memory (CAM) cell having column-wise conditional data pre-write
View Patent ↗A content addressable memory (CAM) device can include a plurality of CAM cells arranged in rows and columns to form multi-byte words. Each CAM cell can include a comparator circuit and one or more data storing circuits. Each comparator circuit can have one or more charge transfer paths arranged between a match line and a first voltage source node. Each data storing circuit can include a write circuit that provides a controllable impedance path between one or more charge transfer paths and a data storage node of the data storing circuit.
1. A content addressable memory (CAM) device, comprising:
a plurality of CAM cells arranged in rows and columns to form multi-byte words, each CAM cell comprising
a stack section having a plurality of transistors forming at least one charge transfer path between a match line and a voltage supply node, and
at least one memory cell having a first storing node and a second storing node, the first storing node being connected to a bit line by a first access transistor, the second storing node being connected to allow charge to flow between the at least one charge transfer path and the second storing node; wherein
the at least one charge transfer path of each CAM cell of the same column is commonly coupled to a data line and enabled in response to the data line carrying a predetermined signal value.
2. The CAM device of claim 1 , wherein:
each CAM cell includes
a first write circuit that includes the first access transistor and provides a first data value to the first storing node of a first memory cell in response to a first pre-write signal, and
a second write circuit that provides the first data value to a third storing node of a second memory cell in response to a second pre-write signal.
3. The CAM device of claim 2 , wherein:
the first write circuit is coupled to receive a pre-write voltage from the stack section during a pre-write operation.
4. The CAM device of claim 3 , wherein:
the second pre-write circuit is coupled to receive the pre-write voltage from the stack section during a pre-write operation.
5. The CAM device of claim 1 , wherein:
the stack section compares data stored at the first storing node of a first memory cell with a first compare data value and compares the data stored at a third data node of a second memory cell with a complementary compare data value, and provides a low impedance path between the match line and the voltage supply node according to a first compare result and a high impedance path between the match line and the first voltage level according to a second compare result.
6. The CAM device of claim 1 , wherein:
the first data storing circuit and the second data storing circuit comprise static random access memory cells.
7. The CAM circuit of 1 , further including:
the CAM cells include
a first CAM cell with a first data storing circuit and second data storing circuit, and
a second CAM cell, physically adjacent to the first CAM cell, having an adjacent first data storing circuit and an adjacent second data storing circuit, wherein
the first data storing circuit and adjacent first data storing circuit each comprise X-cells and the second data storing circuit and second adjacent data storing circuit each comprise Y-cells and the first data storing circuit and second data storing circuit are interleaved with the first adjacent data storing circuit and second adjacent data storing circuit within a same row of CAM cells.