Electronic – Why is there a 0R resistor linking GND and AGND in analog voltage reference circuit


This is related to another question I've just posted (What's the purpose of a ferrite bead inductor on this circuit?), regarding the battery charger described in the AVR450 Application Note – Battery Charger for SLA, NiCd, NiMH and Li-Ion Batteries, which one day I hope to build.

On page 40, there's a schematic showing the MCU connections (picture below). Marked in red is a 0Ω resistor that is puzzling me. I suspect that it is just a wire jumper linking AGND and GND. But I don't understand why there's a jumper there.


My questions:

  1. What does the jumper represent?
  2. Why are AGND and GND separated like that?

Best Answer

Digital circuits are noisy, but they can (mostly) handle their own noise without noticing. Analog circuits notice noise a lot; in fact, they have to pass noise just like a signal because they really can't tell the difference.

The best way to keep digital noise out of analog circuits is to keep them separate, both physically and electrically. But they have to be connected somehow in order to convert from one to the other, hence the jumper in exactly one spot, which is probably next to the converter on the physical board.