Lookup Table Buffer Tree Synthesis for Delay Optimization
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Solution Overview
Problem
Existing circuit synthesis approaches often produce non-optimal buffer trees due to ad hoc methods, leading to poor quality results in high fan-out nets and inadequate delay optimization.
Innovation Solution
The use of a lookup table to determine optimal buffer or inverter sizes and spacings based on capacitive loads, by grouping sink nodes into clusters, calculating cost metrics, and placing buffers or inverters at optimal locations within the buffer tree while avoiding routing and placement blockages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ad hoc buffer tree synthesis is used, then the synthesis process is simple, but the quality of buffer trees is poor and delay optimization is inadequate
Solution Approach 1:
The patent pre-calculates and stores optimal buffer sizes and spacings for various capacitive loads in lookup tables before the actual buffer tree synthesis. This preliminary preparation enables the synthesis process to quickly retrieve pre-determined optimal values without performing complex real-time calculations, thus maintaining simplicity while achieving high-quality buffer trees with optimized delay performance
Solution Approach 2:
The patent transforms the complex optimization problem into a parameter lookup process by pre-computing optimal buffer parameters (size, spacing) for different capacitive load conditions. During synthesis, the system only needs to determine the capacitive load and perform a table lookup to obtain the optimal parameters, converting a complex optimization task into a simple parameter retrieval operation that maintains both simplicity and quality
2Reliability
If lookup table method is used to determine optimal buffer sizes and spacings, then delay optimization is improved, but the complexity of the synthesis process increases
Solution Approach 1:
The patent performs the complex optimization calculations in advance and stores the results in lookup tables. The optimal buffer sizes and spacings for various capacitive loads are pre-determined using detailed delay models and optimization algorithms. During actual buffer tree synthesis, the system simply queries the pre-computed tables based on the calculated capacitive load, achieving excellent delay optimization without the complexity of real-time optimization computations
Solution Approach 2:
The lookup table serves as an intermediary between the complex delay optimization problem and the simple buffer tree synthesis process. The table encapsulates the results of complex optimization calculations and provides a straightforward mapping from capacitive load to optimal buffer parameters, acting as a mediator that translates complex optimization requirements into simple lookup operations
3Manufacturing precision
If buffers are placed at optimal locations avoiding routing blockages, then placement quality is improved, but the time required for placement increases
Solution Approach 1:
The patent determines optimal buffer locations by considering local routing conditions and blockages. For each potential buffer placement location, the system evaluates the local routing environment and selects positions that avoid blockages while maintaining optimal spacing. This local optimization approach ensures high placement quality by adapting to specific local constraints without requiring a complete re-evaluation of the entire buffer tree
Solution Approach 2:
The patent pre-determines optimal buffer spacings for various capacitive loads and uses these pre-computed values to quickly identify suitable placement locations. By having the optimal spacing values ready in advance, the system can rapidly scan through potential locations and select appropriate positions that avoid routing blockages, significantly reducing the time required for placement while maintaining high placement quality
Data Source
AI summary
Systems and techniques are described for performing buffer tree synthesis. Some embodiments create a lookup table based on information contained in a cell library. The lookup table is then used during buffer tree synthesis.