Electronics and Communications in Japan, Part II: Electronics (English translation of Denshi Tsushin Gakkai Ronbunshi)

Area reduction and improvements in speed and compression ratio for a Lempel-Ziv data compression circuit using a content addressable memory

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LZ77 code obtains high compression ratios by searching for and eliminating repeated data. The parallel search capability of content addressable memory (CAM) allows very high-speed hardware implementation. This article describes smaller and faster CAM and improvements of a priority encoder to get a higher compression ratio. By modifying the critical path, which is the feedback to the search logic, circuit size can be reduced and speed can be doubled. A conventional priority encoder outputs an absolute address according to the search result. The encoders shown here output the relative address, or output the difference in length between the longest and the second-longest matching data. Compression formats that cannot be handled by the conventional encoder, and a coding scheme for higher compression ratio, can be adopted by using the new encoders.