Algorithm and Architecture for a Low Power Content Addressable Memory Based on Sparse Clustered Networks

Existing system:

             A CONTENT-addressable memory (CAM) is a type of memory that can be accessed using its contents rather than an explicit address. In order to access a particular entry in such memories, a search data word is compared against previously stored entries in parallel to find a match. Each stored entry is associated with a tag that is used in the comparison process. Once a search data word is applied to the input of a CAM, the matching data word is retrieved within a single clock cycle if it exists. This prominent feature makes CAM a promising candidate for applications where frequent and fast look-up operations are required, such as in translation look-aside buffers (TLBs), network routers database accelerators, image processing, parametric curve extraction, Hough transformation, Huffman coding/decoding, virus detection Lempel–Ziv compression, and image coding.

A new family of associative memories based on sparse clustered networks (SCNs) has been recently introduced, and implemented using field-programmable gate arrays (FPGAs). Such memories make it possible to store many short messages instead of few long ones as in the conventional Hopfield with significantly lower level of computational complexity. Furthermore, a significant improvement is achieved in terms of the number of information bits stored per memory bit (efficiency). In this paper, a variation of this approach and a corresponding architecture are introduced to construct a classifier that can be trained with the association between a small portion of the input tags and the corresponding addresses of the output data. The term CAM refers to binary CAM (BCAM) throughout this paper. Originally included in preliminary results were introduced for architecture with particular parameters conditioned on uniform distribution of the input patterns. In this paper, an extended version is presented that elaborates the effect of the design’s degrees of freedom, and the effect of non-uniformity of the input patterns on energy consumption and the performance.

            The architecture (SCN-CAM) of this paper consists of an SCN-based classifier coupled to a CAM-array. The CAM-array is divided into several equally sized sub-blocks, which can be activated independently. For a previously trained network and given an input tag, the classifier only uses a small portion of the tag and predicts very few sub-blocks of the CAM to be activated. Once the sub-blocks are activated, the tag is compared against the few entries in them while keeping the rest deactivated and thus lowers the dynamic energy dissipation.

Disadvantage:

• They cost is high
• They occupy a relatively large footprint on a card.
• They consume excessive power.

Proposed system:
            In proposed architecture is addressable the 512bit input data in the memory by using SCN- DDR Based Dual CAM methodology.

Content Addressable Memories:

            We now take a more detailed look at CAM architecture. A small model is shown in Fig. 3. The figure shows a CAM consisting of 4 words, with each word containing 3 bits arranged horizontally (corresponding to 3 CAM cells). There is a matchline corresponding to each word (ML_0, ML_1, etc.) feeding into matchline sense amplifiers (MLSAs), and there is a differential searchline pair corresponding to each bit of the search word ( SL_0, SL_1, SL₀’_, SL1’ etc.). A CAM search operation begins with loading the search-data word into the search-data registers followed by precharging all matchlines high, putting them all temporarily in the match state. Next, the searchline drivers broadcast the search word onto the differential searchlines, and each CAM core cell compares its stored bit against the bit on its corresponding searchlines. Matchlines on which all bits match remain in the precharged-high state. Matchlines that have at least one bit that misses, discharge to ground. The MLSA then detects whether its matchline has a matching condition or miss condition. Finally, the encoder maps the matchline of the matching location to its encoded address.

Advantages:

• They cost is low
• High Speed interface to storage data
• High Speed to Check the Content addressable data

Software Implementation:

• Modelsim
• Xilinx