| 摘要 |
PURPOSE: A CAM(Content Addressable Memory) cell sensing circuit is provided to improve the stability of a sensing operation by supplying a fixed voltage with a sensing node. CONSTITUTION: A sensing signal(CAMSEL) and a delayed sensing signal of high level are applied to the first NAND gate(21). A low level signal of the first NAND gate(21) turns on the first PMOS transistor(P21), and a source voltage(Vcc) is supplied with the first node(Q21) through the first PMOS transistor(P21). The source voltage(Vcc) is divided by the first NMOS transistor and the second NMOS transistor(N21,N22). For this reason, the potential of the first node(Q21) reaches to dropped potential as much as threshold voltage of the first NMOS transistor and the second NMOS transistor(N21,N22). The third NMOS transistor(N23) is turned on by the potential of the first node(Q21), and the source voltage(Vcc) is supplied with the second node(Q22). After this, the source voltage supplied with the second node(Q22) is dropped to a fixed voltage by the turned on fourth NMOS transistor(N24) and the fifth NMOS transistor(N25). The source voltage(Vcc) is supplied with the second node(Q22) sustaining fixed potential through the second NMOS transistor(Q22) which is turned on, and the second node(Q22) sustains higher potential than the source voltage(Vcc). A path is formed by the turned on sixth NMOS transistor(N26) and the CAM cell. At this time, the sixth NMOS transistor(N26) is turned on by the sensing signal(CAMSEL) of high level. The potential of the second node(Q22) is in a high state on the occasion of the programmed CAM cell, and is in a low state on the occasion of the removed CAM cell.
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