No abstract

In this paper, we apply the concept of over-thecell routing to the global routing problem in leaf cell synthesis. A cell layout is divided into 5 routing regions in our model. The global routing problem can be formulated as to route those critical net segments over the diffusions or the middle channel such that the overall cell height is minimum. In addition, the routing of transmission gates has been a problem because it produces a cyclic constraint in the middle channel. We propose a new routing pattem which is cyclic free for trysmission gate connections. In this proposed approach, we first generate tree patterns for each net. Then we model and solve the global routing as an integer linear programming problem. Finally. we complete the detailed routing of the cell layout. For all the cell benchmarks (less than 50 transistors), we are able to solve them in very short time. In comparison with previous results, our approach produces denser layouts.