When using AC excitation, is it possible to use only one Micrel FET MIC4427
Yes you only need a single MIC4427.
The AD7730 has 2 channels and you need to use both the OUTA and OUTB channels
The upper and lower sections of the bridge are driven via AC and are anti-phase
with each other
(180 degrees different). That is why each end requires an inverter on 1 of the
transistors or FETs so that it is biased to turn on at the correct time.
Two of the FETs are p-channel and the other pair are n-channel.