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Method and system for designing a circuit using RC and timing weighting of nets

  • US 5,815,406 A
  • Filed: 03/25/1996
  • Issued: 09/29/1998
  • Est. Priority Date: 03/25/1996
  • Status: Expired due to Fees
First Claim
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1. A method for designing an integrated circuit including the steps of:

  • identifying a plurality of nets having blocks of circuit components connected by conductive elements;

    assigning weights to the plurality of nets in proportion to a combination of timing and resistive-capacitive (RC) effects therein, the step of assigning weights including the steps of;

    calculating a worst case resistive-capacitive delay (Net-- RC) of a sink pin of a net under consideration,setting a minimum resistive-capacitive delay threshold (Min-- RC-- Design) associated with the pin of the net under consideration,subtracting the minimum resistive-capacitive delay threshold (Min-- RC-- Design) from the worst case resistive-capacitive delay (Net-- RC) of a sink pin of the net under consideration to acquire a first difference term (Net-- RC-Min-- RC-- Design),setting an upper limit for resistive-capacitive delay of the net (UPPER-- RC),subtracting the minimum resistive-capacitive delay threshold from the upper limit (UPPER-- RC) to acquire a second difference term (UPPER-- RC-Min-- RC-- Design),dividing the first difference term by the second difference term to acquire a first ratio (Net-- RC-Min-- RC-- Design)/(UPPER-- RC-Min-- RC-- Design),setting a relative percentage weight (FRAC-- RC) to assign to RC delay values versus SLACK values representing a difference between a measured arrival time of a logical result and an expected arrival time of the result for the net under consideration,multiplying the first ratio by the relative percentage weight (FRAC-- RC) times 100 to acquire a first sum term,determining a maximum or worst SLACK of the net under consideration (Net SLACK),setting an upper limit on SLACK (UPPER-- SLACK),subtracting the Net SLACK from the UPPER-- SLACK to acquire a third difference term,determining the minimum SLACK associated with any net within the circuit (Min-- SLACK-- Design),subtracting the minimum SLACK associated with any net from the UPPER-- SLACK to acquire a fourth difference term,dividing the third difference term by the fourth difference term to acquire a second ratio,multiplying the second ratio by (1-FRAC-- RC) times 100 to acquire a second sum term,adding the first and the second sum terms, andadding a constant to the first and the second sum terms to acquire a weight for the net; and

    selecting locations for the circuit components to reduce the length of a plurality of wires therebetween in accordance with the weights, the step of selecting locations for the circuit components including the step of running a placement program using the weight for the net.

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