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Why do we separate analog and digital grounds?
On the other hand, analog circuitry is quite vulnerable to noise—on both power supply rails and grounds—so it is sensible to separate analog and digital circuitry to prevent digital noise from corrupting analog performance. Many ADCs and DACs have separate analog ground (AGND) and digital ground (DGND) pins.
What is analog ground?
The analog ground is intended as reference voltage for the ADCs and DACs or Analog Compare interfaces whereas all other logic is considered to be digital. You will also often see that analog and digital ground are connected to each other directly or via a ferrite.
How are analog and digital ground planes connected?
The analog and digital grounds should both be connected to the analog ground plane. The power supply should be connected to the board at the digital partition and power the noisy digital circuitry directly.
How are analog and digital supplies used in mixed signal applications?
For example, separate analog and digital supplies with separate analog and digital grounds, joined at the star point, are common in mixed-signal applications. It is a fact of life that digital circuitry is noisy.
Where are the analog and digital ground pins on an ADC?
The labels, “analog ground” and “digital ground,” on these pins refer to the internal parts of the converter to which the pins are connected and not to the system grounds to which they must go. For an ADC, these two pins should generally be joined together and to the analog ground of the system.
What’s the grounding philosophy for a mixed signal device?
Digital and analog design engineers tend to view mixed-signal devices from different perspectives, so the purpose of this article is to describe a general grounding philosophy that will work for most mixed-signal devices, without the need to know the specific details of their internal circuits.