Tsuyoshi Nakamura | December 26, 2012
Sandisk Corp. v. Kingston Tech. Co., Inc.
October 9, 2012
Panel: Prost, Reyna and Wallach. Opinion by Prost. Dissent by Reyna.
The claim construction of the term “relative time” caused the issue whether one of two different embodiments of the specification should be excluded from the scope of literal infringement. The district court excluded the second embodiment, focusing on the claim term “time.” CAFC disagrees, emphasizing the significance of the claim term “relative.” Judge Reyna dissents.
The patent at issue relates to a flash memory technology such as used in USB thumb drives. Unlike typical computer memory, the old data on the flash memory cell must be erased every time new data is written to the cell. The memory cells are erased an entire block at a time, while data is written to the cell one page at a time; the erasure of data, therefore, occurs in larger segments than the writing of data. These erase/write cycles wear down the memory cell until the cell eventually no longer reliably stores information.
Sandisk’s 6,763,424 patent (“424 patent”) covers a method for performing “partial block” updates in flash memory devices. When the flash memory system makes minor updates to already stored data, such as by changing a few words in a document, it performs a “partial block” update; in other words, only part of the data block is updated. The controller writes only the pages with the updated data into the new block as opposed to rewriting the entire block of data. The new data shares a logical address with the superseded data. The controller reads the data from the blocks, identifying those pages that have been superseded by a more recently updated page sharing the logical address. When the controller reports the data to the host system, it substitutes the superseded pages with this updated data.
The issue is the claim construction of the claim term, “relative time.”
Claim 1 of ‘424 patent recites:
…recording a relative time of programming the at least one page of new data and the at least one page of superseded data…
The specification discloses two embodiments corresponding to this claim limitation. The district court construed this claim limitation as requiring the recording of an actual time of programming and excluded the second embodiment. CAFC disagrees and construes it to cover both embodiments. Judge Reyna dissents, in favor of the district court.
The first embodiment of the specification discloses writing a time stamp onto each individual page that “provides an indication of its time of programming, at least relative to the time that other pages with the same logical address are programmed.”
The second embodiment of the specification does not store the time stamp as part of each page, but rather, a single time stamp can be recorded for each block, and is updated each time a page of data is written into the block. Within the block, the new data is physically stored after the old data such that the most recent page with a particular logical address is determined by the relative physical order of those pages within the block. Data is then read from pages in an order of descending physical address, starting from the last page of the most recently updated block containing data pages having the same LBN [Logical Block Number].
CAFC holds that the claims only require “recording a relative time of programming,” not “a time of programming.” The use of “relative” is significant: whereas “recording the time of programming” would suggest that a time of programming must be recorded for each page, “recording a relative time of programming” merely requires recording some indication of the order of programming for those pages sharing a logical address. The claims place no limitation on how the claimed “recording” occurs.
According to Judge Reyna, the first embodiment is faithful to the claim language, recording a time stamp in each individual page. The second is not. In the second embodiment, pages are written in order within the block, and the most current data for a logical page within a block will always be the last physical page in the block containing data for that logical page. However, since the physical pages do not contain any timestamp data, relative or otherwise, all that can be said is that the pages were written at the same time or after the time stamp in the physical block. In other words, although the relative order can be inferred from the physical number of the page, nothing is known about the relative times.
The majority avoids the distinction between “order” and “relative time” by focusing on the “relative” limitation in the claim and ignoring the limitations that the time must be recorded and that it must be a time. According to the dissent, this construction improperly ignores express limitations of the claims and uses the specification to broaden the patent.
The claim term “relative time” consists of “relative” and “time,” the former comes from the second embodiment and the latter comes from the first embodiment. If the specification includes a clear indication that the claimed “relative time” at least covers both of the first and second embodiments, this kind of uncertainty in the claim construction could have been avoided in advance. Kingston could have argued that an ordinary and customary meaning of “relative time” refers to a scientific term in physics (developed by Albert Einstein). In that case, Sandisk would have borne higher burden to make judges understand that the present invention is different from the “relativity.”