Structured design method for generating a mesh power bus structure in high density layout of VLSI chips
First Claim
1. A method for layout of a power bus distribution structure for the target surface of a large scale integrated circuit which includes macrocells and domains of standard logic cells arranged in rows, comprising the steps of:
- predetermining minimum values of source factor for all standard cell domains and macrocells to produce predetermined minimum values;
generating a complete power bus distribution structure including routing channels associated with elements of said complete power bus distribution structure, said routing channels being adjacent the sides of macrocells and standard cell domains, said routing channels being adapted for carrying signal wires and wires of said power bus distribution structure;
determining those routing channels which are critical to the size of said target area to identify critical routing channels;
selecting one of said critical routing channels to identify a selected critical routing channel;
creating, if not already created, a profile of signal wire routing density for at least said selected critical routing channel;
subdividing into segments at least that portion of said power bus distribution structure routed through said selected critical routing channel, said segments having ends intersecting orthogonal portions of said power bus distribution structure;
identifying as a highest density segment, from among said segments of said power bus distribution system routed through said selected critical routing channel, that one segment not yet processed which is associated with the largest of said signal wire routing densities;
temporarily deleting said highest density segment of said power bus distribution structure from said power bus distribution structure to form a temporarily segment pruned power bus distribution structure;
calculating the present source factors for the macrocells and standard cell domains of said temporarily segment pruned power bus distribution structure;
comparing said present source factors of said macrocells and standard cell domains of said temporarily segment pruned power bus distribution structure with said predetermined minimum values, and if any one of the present source factors is less than the corresponding predetermined minimum value, restoring said temporarily deleted highest density segment, and if said present source factors of said macrocells and standard cell domains are all greater than their corresponding predetermined minimum values, permanently deleting said highest density segment to produce a segment pruned power bus distribution structure;
repeating said step of (a) identifying as a highest density segment, (b) temporarily deleting, (c) calculating and (d) comparing, until all power bus segments within said selected critical routing channel have been processed to form a routing channel pruned bus distribution structure; and
repeating said steps of (a) determining those routing channels which are critical, (b) selecting one of said critical routing channels, (c) creating a profile, (d) subdividing into segments, (e) identifying as a highest density segment, (f) temporarily deleting, (g) calculating, (h) comparing, and (i) repeating, until no further pruning is possible.
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Abstract
An automated LSI chip layout arrangement includes automated layout of the power bus distribution network. A complete interlocking mesh of buses is run in routing channels lying between groups of circuits to be powered. Each segment of the mesh powering net which affects the chip size is tested to see if it can be removed without adversely affecting the power distribution. If it can be removed, the segment is deleted. The next segment which is critical to the size of the chip is then tested, and the process is continued. Those segments of the power bus distribution network which do not affect the size of the chip are not eliminated. Thus, a low-resistance power distribution bus network is guaranteed, and chip size is minimized.
177 Citations
16 Claims
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1. A method for layout of a power bus distribution structure for the target surface of a large scale integrated circuit which includes macrocells and domains of standard logic cells arranged in rows, comprising the steps of:
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predetermining minimum values of source factor for all standard cell domains and macrocells to produce predetermined minimum values; generating a complete power bus distribution structure including routing channels associated with elements of said complete power bus distribution structure, said routing channels being adjacent the sides of macrocells and standard cell domains, said routing channels being adapted for carrying signal wires and wires of said power bus distribution structure; determining those routing channels which are critical to the size of said target area to identify critical routing channels; selecting one of said critical routing channels to identify a selected critical routing channel; creating, if not already created, a profile of signal wire routing density for at least said selected critical routing channel; subdividing into segments at least that portion of said power bus distribution structure routed through said selected critical routing channel, said segments having ends intersecting orthogonal portions of said power bus distribution structure; identifying as a highest density segment, from among said segments of said power bus distribution system routed through said selected critical routing channel, that one segment not yet processed which is associated with the largest of said signal wire routing densities; temporarily deleting said highest density segment of said power bus distribution structure from said power bus distribution structure to form a temporarily segment pruned power bus distribution structure; calculating the present source factors for the macrocells and standard cell domains of said temporarily segment pruned power bus distribution structure; comparing said present source factors of said macrocells and standard cell domains of said temporarily segment pruned power bus distribution structure with said predetermined minimum values, and if any one of the present source factors is less than the corresponding predetermined minimum value, restoring said temporarily deleted highest density segment, and if said present source factors of said macrocells and standard cell domains are all greater than their corresponding predetermined minimum values, permanently deleting said highest density segment to produce a segment pruned power bus distribution structure; repeating said step of (a) identifying as a highest density segment, (b) temporarily deleting, (c) calculating and (d) comparing, until all power bus segments within said selected critical routing channel have been processed to form a routing channel pruned bus distribution structure; and repeating said steps of (a) determining those routing channels which are critical, (b) selecting one of said critical routing channels, (c) creating a profile, (d) subdividing into segments, (e) identifying as a highest density segment, (f) temporarily deleting, (g) calculating, (h) comparing, and (i) repeating, until no further pruning is possible. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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Specification