Carry Selecting system type adder
AssigneeMitsubishi Denki Kabushiki Kaisha System LSI Kaihatsu Kenkyusho
InventorHiroyuki Morinaka
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Abstract
An adder including a first exclusive OR device, a second exclusive OR device for receiving an output of the first exclusive OR device and a generating signal G(i-1), exclusive ORing the output result of the first exclusive OR device and the generating signal G(i-1), and outputting the calculated result as a sum Si0, and a third exclusive OR device for receiving an output of the second exclusive OR device and a propagating signal P(i-1), exclusive ORing the output result of the second exclusive OR device and the propagating signal P(i-1), and outputting the calculated result as a sum Si1, whereby the amount of hardware and power consumption of the adder used in a carry selecting system is reduced.
Claims6
A carry selecting system type adder comprising:
- a first exclusive OR device for receiving an augend Ai and an addend Bi and performing an exclusive OR operation on said augend and said addend, i being an integer and ranging from 1 to N;
- a second exclusive OR device for receiving an output of said first exclusive OR device;
- a carry signal generating circuit for generating a carry generate signal G(i-1), wherein said second exclusive OR device performs an exclusive OR operation on said output of said first exclusive OR device and said carry generate signal to calculate a sum Si0 in a case that a carry input value for each bit of said augend and said addend is "0", and outputting the sum Si0;
- a third exclusive OR device for receiving an output of said second exclusive OR device;
- and
- a carry propagate signal circuit for generating a carry propagate signal P(i-1), wherein said third exclusive OR device performs an exclusive OR operation on said output of said second exclusive OR device and said carry propagate signal to calculate a sum Si1 in the case that the carry input value for each bit of said augend and said addend is "1", and outputting the sum Si1.
Dependencies are inferred from the claim text.