Nwell Structure for Substrate Noise Isolation
Original Publication Date: 1988-Dec-01
Included in the Prior Art Database: 2005-Feb-15
A semiconductor structure is shown for electrically isolating carrier, substrate and power supply noise from the analog portion of analog standard cell (ASC) products. It is necessary to protect analog circuits from carrier noise that is generated by both digital and analog circuits as well as power supply noise. An NWell structure for substrate noise isolation provides for carrier isolation, allows for a safe substrate contact and contributes to power supply decoupling capacitance. Referring to the figure, the cross-section of an NWell (NW) guard ring is shown which is used to surround an analog design area of a ASC master image semiconductor chip. The guard ring resides under a thick oxide (not shown) so that the wiring capacitance is not affected.