Fast evaluation of symmetric-feasible sequence-pairs for analog topological placement

Using nonslicing topological representations in device-level analog placement has recently gained interest since only feasible placements are analyzed, and since the number of devices in analog blocks is typically no more than 100 and, therefore, no scalability problem may occur. In this context, Balasa and Lampaert introduced the concept of symmetric-feasible sequence-pair in order to take into account during the exploration of the sequence-pair solution space the typical presence of symmetry groups of devices in analog designs. This paper presents a fast evaluation algorithm-of O(n log log n) complexity-for symmetric-feasible sequence-pairs, superior to the algorithm in having a quadratic complexity. Similar to Tang and Wong´s sequence-pair evaluation, this algorithm is based on the longest common subsequence computation, using an efficient priority queue data structure introduced by Johnson . A prototype analog placement tool based on this algorithm has been implemented. The novel approach exhibits significantly better computation times than other traditional analog placement techniques.