Semiconductor integrated circuit device with reduced power consumption
A technique for reducing power consumption of a content addressable memory (CAM) system is provided. In a CAM system, an equalizer circuit is coupled to a border portion between a plurality of match line parts generated by dividing each match line corresponding to a piece of entry data, and a precharge circuit precharges each of the match line parts collectively corresponding to a piece of entry data to voltage VDD or VSS. When comparing the entry data and search data, the equalizer circuit couples, in accordance with a control signal, the match line parts after the match line parts are precharged by the precharge circuit. In an equalization period, search operation through the search line is started. A search transistor for comparing search data and entry data includes an NMOS search transistor.
1. A semiconductor integrated circuit including a content addressable memory device, comprising:
a memory cell array including:
a first memory cell containing a first part of entry data and a second memory cell containing a second part of the entry data;
a first match line and a second match line coupled to the first memory cell and the second memory cell, respectively; and
a first search line carrying a first part of search data and a second search line carrying a second part of the search data, the first search line and the second search lines being coupled to the first memory cell and the second memory cell, respectively, the search data of the first and second search lines being compared with the entry data of the first and second memory cells;
an equalizer circuit disposed between the first match line and the second match line;
a first precharge circuit coupled to the first match line; and
a second precharge circuit coupled to the second match line,
wherein the first precharge circuit precharges the first match line to a first potential and the second precharge circuit precharges the second match line to a second potential different from the first potential,
the equalizer circuit couples, in accordance with a control signal, the first match line and the second match line after the first match line and the second match line are precharged,
the first search line and the second search line are active when the first match line and the second match line are coupled by the equalizer circuit, and
where the entry data does not match the search data, both the first match line and the second match line are discharged to the second potential.
2. The semiconductor integrated circuit according to claim 1 ,
wherein the second potential is lower than the first potential, and
wherein the semiconductor integrated circuit is configured such that, when comparing the entry data and the search data, the second match line precharged to the second potential is, unless the search data changes, kept at a potential of the second search line.
3. The semiconductor integrated circuit according to claim 1 , wherein the first and second memory cells each include a comparator circuit for comparing the search data supplied through the first and second search lines and the entry data, the comparator circuit including a negative channel metal oxide semiconductor (NMOS) transistor.
4. The semiconductor integrated circuit according to claim 1 ,
wherein the first match line and the second match line are parts of one match line that corresponds to a piece of the entry data, and
wherein the first precharge circuit supplies the first match line with voltage VDD as the first potential and the second precharge circuit supplies the second match line with voltage VSS as the second potential.
5. The semiconductor integrated circuit according to claim 1 , further comprising:
a third match line; and
a third precharge circuit coupled to the third match line,
wherein the first match line, the second match line, and the third match line are serially connected, and
wherein the second precharge circuit is configured to precharge the second match line to the second potential and the first precharge circuit and the third precharge circuit are configured to precharge the first and third match line to the first potential.
6. The semiconductor integrated circuit according to claim 1 , further comprising a match amplifier coupled to at least one of the first match line or the second match line, wherein
when comparing the entry data and the search data, the match amplifier starts sensing a potential of the at least one of the first match line or the second match line after equalization by the equalizer circuit.
7. The semiconductor integrated circuit according to claim 1 , wherein the first match line and the second match line are selectably precharged to the first potential or the second potential.