# US 10,372,836 B2 · Integrated circuit buffering solutions considering sink delays

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- Number: US 10,372,836 B2
- Document ID: US10372836B2
- Status: Granted
- Kind: B2
- Application number: 15/848,053
- Filed: 2017-12-20
- Published: 2018-12-27
- Granted: 2019-08-06
- Earliest claimed: 2017-06-22
- Assignees: International Business Machines Corporation
- Applicants: International Business Machines Corporation
- Inventors: Ying Zhou; Stephen T. Quay; Lakshmi N. Reddy; Gustavo E. Tellez; Gi-Joon Nam; Jiang Hu
- Web page: https://patentgrep.com/patent/US10372836B2

## CPC

- G06F 30/3312: Timing analysis
- G06F 30/00: Computer-aided design [CAD]
- G06F 30/327: Logic synthesis; Behaviour synthesis, e.g. mapping logic, HDL to netlist, high-level language to RTL or netlist
- G06F 30/39: Circuit design at the physical level (physical level design for reconfigurable circuits G06F30/347)
- G06F 30/394: Routing (G06F30/396 takes precedence)
- G06F 30/398: Design verification or optimisation, e.g. using design rule check [DRC], layout versus schematics [LVS] or finite element methods [FEM] (optical proximity correction [OPC] design processes G03F1/36)
- G06F 2119/12: Timing analysis or timing optimisation
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)

## Abstract

Optimizing timing in a VLSI circuit by generating a set of buffer solutions and determining a most critical delay and a sum of critical delays for each solution in the set of solutions. Quantifying a relationship between the most critical delay and the sum of critical delays for each solution. Comparing each solution's quantified relationship to the quantified relationship of each other solution in the set of solutions. Identifying, based on the comparing of each solution's relationship to the relationship of each other solution in the set of solutions, at least one solution in the set of solutions to have a worse relationship between the most critical delay and the sum of critical delays than the other solutions in the set of solutions. Pruning the at least one solution from the set of solutions.

## Claims

### Claim 1

A method for optimizing timing in a VLSI circuit comprising:
generating a set of buffer solutions;
determining a most critical delay and a sum of critical delays for each solution in the set of solutions;
quantifying, for each solution, a relationship between the most critical delay and the sum of critical delays;
comparing each solution's relationship to the relationship of each other solution in the set of solutions;
identifying, based on the comparing of each solution's relationship to the relationship of each other solution in the set of solutions, at least one solution in the set of solutions to have a worse relationship between the most critical delay and the sum of critical delays than the other solutions in the set of solutions; and
pruning the at least one solution from the set of solutions.

### Claim 2 (depends on 1)

The method of claim 1, further comprising continuing to prune solutions from the set of solutions until a target number of solutions remains.

### Claim 3 (depends on 1)

The method of claim 1, further comprising submitting at least one remaining solution to an integrated circuit design process.

### Claim 4 (depends on 1)

The method of claim 1, further comprising displaying at least one solution remaining in the set of the solutions on a user interface.

### Claim 5 (depends on 1)

The method of claim 1, wherein quantifying a relationship between the most critical delay and the sum of critical delays comprises calculating a p-norm of the sum of delays.

### Claim 6 (depends on 5)

The method of claim 5, wherein a solution has a worse relationship between the most critical delay and the sum of critical delays when the solution's p-norm of the sum of delays comprises a higher value than a p-norm of the sum of delays of at least one other solution of the set of solutions.

### Claim 7 (depends on 5)

The method of claim 5, wherein the set of solutions is created according to a set of design parameters; and
wherein a solution has a worse relationship between the most critical delay and the sum of delays when the solution's relationship is associated with a value which deviates from the design parameters by a greater margin than a value associated with the relationship between the most critical delay and the sum of critical delays of at least one other solution of the set of solutions.

### Claim 8 (depends on 1)

The method of claim 1, further comprising determining a load cap and a buffer cost for each solution of the set of solutions.

### Claim 9 (depends on 8)

The method of claim 8, further comprising comparing each solution's load cap and buffer cost with the load cap and buffer cost of each other solution in the set of solutions, wherein each solution has a characterization and the characterization comprises the solution's load cap, buffer cost, and relationship between the most critical delay and the sum of critical delays; and
wherein the identifying, based on the comparing of each solution's relationship to the relationship of each other solution in the set of solutions, at least one solution of the set of solutions to have a worse relationship than the other solutions in the set of solutions further comprises identifying, based on the comparing of each solution's load cap and buffer cost with the load cap and buffer cost of each other solution in the set of solutions, at least one solution of the set of solutions to have a worse characterization than the other solutions in the set of solutions.

### Claim 10 (depends on 9)

The method of claim 9, wherein a solution has a worse characterization if the solution's load cap has a lower value and the solution's buffer cost has a higher value than a load cap and a buffer cost of at least one other solution of the set of solutions.

### Claim 11 (depends on 1)

The method of claim 1, wherein the circuit comprises one or more nodes and the most critical delay for each solution is found by calculating the delay at each node and identifying the node with the largest delay.

### Claim 12 (depends on 1)

The method of claim 1, wherein the circuit comprises a source and one or more sinks, and wherein the sum of critical delays for a solution is calculated using a measurement of each critical delay in the solution taken from the sink to the source.

### Claim 13

A method for optimizing timing in a VLSI circuit comprising:
generating a set of buffer solutions;
determining a most critical delay, a sum of critical delays, and a buffer cost for each solution of the set of solutions;
quantifying, for each solution, a relationship between the most critical delay and the sum of critical delays;
creating a first list containing each solution with a highest most critical delay for a given buffer cost, the first list having a first knee point, the first knee point having an associated critical delay cap;
determining a threshold based on the critical delay cap associated with the first knee point;
creating a second list containing each solution with a best relationship between the most critical delay and the sum of critical delays for a given buffer cost, the second list having a second knee point;
pruning the second list based on the threshold;
adjusting, in response to pruning the second list based on the threshold, the second knee point; and
selecting at least one solution from the adjusted second knee point.

### Claim 14 (depends on 13)

The method of claim 13, wherein selecting at least one solution from the second knee point comprises selecting a set of final solutions in proximity to the knee point.

### Claim 15 (depends on 14)

The method of claim 14, wherein the set of final solutions is sized according to a set of design parameters.

### Claim 16 (depends on 13)

The method of claim 13, further comprising communicating the at least one selected solution for circuit fabrication.

### Claim 17 (depends on 13)

The method of claim 13, wherein each solution is further characterized with a load cap.

### Claim 18 (depends on 17)

The method of claim 17, wherein a solution has a worse relationship if the solution's relationship between the most critical delay and the sum of delays comprises a higher value than a relationship between the most critical delay and the sum of delays of at least one other solution of the set of solutions.

### Claim 19 (depends on 18)

The method of claim 18, wherein the set of solutions is created according to a set of design parameters; and
wherein a solution has a worse relationship if the solution's relationship between the most critical delay and the sum of delays is associated with a value which deviates from the design parameters by a greater margin than a value associated with the relationship between the most critical delay and the sum of delays of at least one other solution of the set of solutions.