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Circuit Design Techniques for a Floating-Point Processor

Hu, Timothy
Technical Report Identifier: CSD-87-372
September 23, 1987

Abstract: This report presents some novel circuit design techniques used in the datapath of the SPUR floating-point unit. Three most interesting circuit blocks are discussed which include a fast adder, a leading one detector and a shifter. Mixed logic with static and dynamic circuits are used. The chip is implemented in a 1.6 micron, N-well, double-metal CMOS process (HP CMOS40).

The timing and area of the above three modules are as follows:
66 bit adder
* Delay - Crystal 36 ns, SPICE 33 ns
* Size - 4757 x 553 lambda, which is 3806 x 442 um.
67 bit Leading one detector
* Delay - Crystal 20.5 ns, SPICE 18 ns
* Size - 4901 x 463 lambda, which is 3920 x 320 um.
67 bit shifter with Sticky Logic
* Delay - Shifting 15 ns, Sticky bit (latched into output latch) 25 ns
* Size - The whole module with decoder is 5359 x 1414 lambda, which is 4287 x 1131 um.