ABCs of ADCs - Analog-to-Digital Converter Basics (PDF)
ABCs of ADCs - Analog-to-Digital Converter Basics (PDF)
ABCs of ADCs - Analog-to-Digital Converter Basics (PDF)
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Resis<strong>to</strong>r Pack Danger500*V REF +V REF -AV DD0V DCR P**500*500*0.1uFV CC0.1-+500*R SV INAADCV REFR SV INB* OPTIONAL RESISTOR NETWORK** OPTIONAL PULL-UP RESISTOR WHEN USING INTERNAL REFERENCE45This innocuous-looking circuit has a hidden danger. The “optional resis<strong>to</strong>r network” has somerather large capacitances that creates problems for even very slow op-amps. For example, thecapacitance between the output side <strong>of</strong> the feedback resis<strong>to</strong>r and the op-amp “+” input side <strong>of</strong>the two resis<strong>to</strong>rs connected there may cause oscillation. Sometimes the frequency <strong>of</strong>oscillation is so high it is difficult <strong>to</strong> find and we only see the results <strong>of</strong> a rectification within theamplifier or the ADC. The result is the production <strong>of</strong> an <strong>of</strong>fset. If the <strong>of</strong>fset is large enough, thedevice could be forced in<strong>to</strong> a non-linear mode <strong>of</strong> operation.Resis<strong>to</strong>r packs are fine in digital applications, but be careful with them in linear circuits.<strong>ABCs</strong> <strong>of</strong> <strong>ADCs</strong> - Rev 3, June 2006Authored by: Nicholas “Nick” Gray45Copyright © 2003, 2004, 2006 National Semiconduc<strong>to</strong>rCorporationAll rights reserved
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