A Post Processing Method for Reducing Substrate Coupling in Mixed-Signal Integrated Circuits

摘要

Due to the heavily doped substrate material in modern MOS technologies, digital interference couples to sensitive analog nodes much more easily than in technologies with p' substrates. The guard ring method of isolating sensitive nodes is no longer as effective as before. In this contribution we investigate the isolation of analog circuits by etching a gap between analog and digital circuits from the back of the wafer. Experiments show that interference coupling 35dB above noise floor is completely removed when a gap is etched around the analog circuit.