New advances in the routing of mixed analog and digital channels

A new channel routing algorithm for mixed analog/digital circuits is presented. This router uses two routing layers and is based on a classical vertical constraint graph (VCG) analysis. It is able to handle variable wire width, irregular top and bottom edges, and minimization of crosstalk. To make it more general and to suit the analog designers´ needs, some new features have been added: critical nets are routed in one layer if possible and pins may be present on either layer. The problem of cycles in the VCG is also addressed. It is shown that new types of cycles may appear due to analog constraints. The authors describe the proposed solution. Some results obtained on real circuits designed at CNET are reported