I guess one can talk about AC and DC ground in several contexts, but one context would be:
In a circuit there is an area which is confined between to common or differential mode inductors. The DC ground will be the same on either side, but the AC ground may not necessarily be the same.
1. DC ground is the local DC power supplies ground or common return, it is used to power the local analog and digital ckts of the device or unit in question.
AC ground is the AC powerline SAFETY GROUND or green wire.
These two points can be connected directly for a hard grounded DC system. They can be connected via a 100 ohm to 33K ohm resistor to create a soft ground system. (once past about 330 ohms a cap in parallel is also used).
2. In transistor & opamp ckts and in RF work, DC ground is the power & bias path, while AC ground is the signal path for signal ground via a cap.... or an AC ground (ie one that is DC blocked but a short ckt to HF AC signals).
Suggestions:
Reference:
1. IEEE Std 142-1991 "IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems," (Green Book)
1. There are various AC grounds, e.g.:
1a. Equipment ground that may contain a lot of noise (noisy ground). This ground is usual ground in power distribution systems, e.g. receptacles (120VAC, 15A, one phase)
1b. Computer or Instrument Ground, which is often called "quiet" since it contains a minimum or no noise. It is run over separated ground conductors from the noisy ground.
1c. Special or dedicated grounds, e.g. for substations, substation mats, etc.
2. Also, there are various DC grounds, e.g.
2a. DC ground tied to chassis that may contain noise, i.e. noisy ground
2b. DC ground that is quiet, i.e. with the minimum noise or no noise. It may be local leading to a local dc power supply and behind shielding.
2c. DC ground bus system of computers, Reference 1
2d. DC ground for mobile equipment, Reference 1
