The L2 cache used a unique row-redundancy scheme. It is implemented
at the 32 kB level and is illustrated in Fig. 9. Spare
rows for one array are located in the adjacent array as opposed to
the same array. In other words, spare rows for the top array are
located in the bottom array and vice versa. When redundancy is
enabled, the incoming address is compared with the address of
the defective row and if it matches, the adjacent array (which is
normally not enabled) is enabled to read from or write into the
spare row. Using this kind of scheme enables a large ( 30%)
reduction in X-decoder area. The area reduction is achieved because
the multiplexing required in the X-decoder to bypass the
defective row/rows in the traditional row redundancy scheme is
no longer needed in this scheme.
N-well power for the Primary and L2 cache memory cells
is separated out as a test hook. This allows weakening of the
pMOS loads of the SRAM bit cells by raising their threshold
voltage, thus enabling screening cells with marginal static noise
margin. This significantly reduces defective parts per million
(DPPM) and improves reliability.