Substrate-Aware Mixed-Signal Macrocell Placement in WRIGHT

We describe a set of placement algorithms for handling substrate-coupled switching noise. A typical mixed-signal IC has both sensitive analog and noisy digital circuits, and the common substrate parasitically couples digital switching transients into the sensitive analog regions of the chip. To preserve the integrity of sensitive analog signals, it is thus necessary to electrically isolate the analog and digital. We argue that optimal area utilization requires such isolation be designed into the system during first-cut chip-level placement. We present algorithms that incorporate commonly used isolation techniques within an automatic placement framework. Our substrate-noise evaluation mechanism uses a simplified substrate model and simple electrical representations for the noisy digital macrocells. The digital/analog interactions determined through these models are incorporated into a simulated annealing macrocell placement framework. Automatic placement results indicate these substrate-aware algorithms allow efficient mixed-signal placement optimization.