This paper examines circuit design of buffered routing switches in symmetrical, island-style FPGAs. The effects of switch size, tile length, level-restoring, and slow input slew rates are examined. Two new fanin-based switch designs are used to eliminate nearly all of the increase in delay that arises from fanout with a previous switch design. Alternating between buffers and pass transistors is shown to improve connection delay without fanout by 25%. To take advantage of this, we propose schemes to replace some buffers with pass transistors to simultaneously reduce area and delay. Routing a suite of MCNC benchmark circuits shows that 14% in areadelay, or 7% in delay can be saved using the new switch schemes. Alternatively, approximately 13% in area can be saved with no degradation to delay.

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