![]() It’s the IC designer’s job to make the chip work in spite of this. The rapidly changing digital currents produce a voltage at point B which will inevitably couple into point A of the analog circuits through the stray capacitance. There is really nothing the IC designer can do about the wirebond inductance and resistance associated with connecting the pads on the chip to the package pins. ![]() The diagram shows a simple model of an ADC. Inside an IC that has both analog and digital circuits, such as an ADC, the grounds are usually kept separate to avoid coupling digital signals into the analog circuits. The pin names, AGND and DGND, refer to what’s going on inside the component itself and do not necessarily imply what you should do with them externally. So are lots of folks! Much of the confusion comes from the labeling of the ADC ground pins in the first place. First of all, don’t feel bad that you are confused about what to do with your analog and digital grounds. Your data sheets usually say to tie the analog and digital grounds together at the device, but I don’t want the ADC to become my system’s star ground point. I’ve read your data sheets and application notes and also attended your seminars, but I’m still confused about how to deal with analog (AGND) and digital (DGND) ground pins on an ADC. Ask the Applications Engineer-12: Grounding (Again)
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