In integrated circuitry having both analog and digital circuits fabricated on the same substrate, switching transients produced by the digital circuitry can propagate through the substrate and induce deleterious effects in the associated analog circuitry. Such switching transients are greatly minimized...http://www.google.es/patents/US5149992?utm_source=gb-gplus-sharePatente US5149992 - MOS folded source-coupled logic
