It is AC-coupled. The AD8232 implements an AC-coupled signal path through its
unique architecture.AC-coupled systems remove the DC component generated by the
contact electrodes (the half-cell potential, see Q3 above for details). Once
the highest voltage component has been removed, these systems can apply a
higher downstream gain that amplifies just the signal of interest. Thanks to
this additional signal conditioning effort, the requirements of AC-coupled
implementations are satisfied with medium-low resolution ADCs (low-cost, small
and fast), like the ones embedded in many microcontrollers.
DC-coupled solutions apply minimal signal conditioning and therefore require
high resolution ADCs to achieve the same level of dynamic range. High
resolution ADCs are bigger, more expensive and power-hungrier ADCs.
There´s no better or worse, it all depends on the system requirements but as a
general rule, AC-coupled solutions consume less power than DC-coupled