ABCs of ADCs - Analog-to-Digital Converter Basics (PDF)

High Capacitance onADC OutputsV D / V DRSupplyBounceL BONDChargeDischargeGroundBounceADCL BONDC BUSC INDriven Device32Charging bus and device input capacitances causes noise on the supply line, as we havediscussed. Discharging these capacitances adds noise to the ADC substrate (die ground) andsupply bus, which can appear at the input as noise. The task, then, is to minimize thesecurrents.Minimizing the load capacitance at the output will minimize the currents needed to charge anddischarge them, lowering the noise produced by the converter itself. This implies that oneoutput pin should drive only one input device pin (use a fan-out of one) and the length of theADC output lines should be as short as possible.ABCs of ADCs - Rev 3, June 2006Authored by: Nicholas “Nick” Gray32Copyright © 2003, 2004, 2006 National SemiconductorCorporationAll rights reserved