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Radix 4 carry lookahead tree and redundant cell therefor

  • US 5,095,458 A
  • Filed: 04/02/1990
  • Issued: 03/10/1992
  • Est. Priority Date: 04/02/1990
  • Status: Expired due to Fees
First Claim
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1. A carry lookahead tree-type logic circuit comprisinga plurality of substantially similar subcircuits;

  • each of said subcircuits having at least four input terminals, at least two output terminals, and an internal logic circuit;

    each of said subcircuits being connected in multi-stages to form a three level tree with at least fourteen subcircuits on a first level, four subcircuits on a second level, and two subcircuits on a third level;

    each of said subcircuits on said first level operable to produce block propagate and generate terms for four inputs on its input terminals;

    three of said subcircuits on said second level connected in circuit to receive the block propagate and generate terms produced by four subcircuits on said first level and to produce block propagate and generate terms therefrom;

    the fourth of said subcircuits on said second level connected in circuit to receive the block propagate and generate terms produced by at least two subcircuits on said first level;

    one of said subcircuits on said third level connected in circuit to receive the block propagate and generate terms produced by the subcircuits on said second level and to produce block propagate and generate terms therefrom;

    the other of said subcircuits on said third level connected in circuit to receive signals relating to carries from two of said subcircuits on said second level and to further make those signals available as output therefrom;

    whereby the other of said subcircuits on said third level provides information as to intermediate carries on linear boundaries in said carry lookahead tree-type circuit.

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