Substrate noise in mixed signal circuits: two case studies [CMOS]

There are many noise sources in integrated circuits that can affect sensitive analog nodes. The role of substrate noise is often glossed over since the designer 'knows' that guard rings and separation of the analog section from digital circuits should take care of the noise. However, with smaller geometries now being the norm, it is increasingly difficult to isolate analog nodes from noise induced on the substrate. Also, package economics have introduced other factors that weigh heavily against the analog designer. This paper explores two cases of noise induced on the substrate affecting operation of analog circuits.