The reference voltage Vref defines {HEAD ~ the DC level} of both the virtual ground and {TAIL ~ the output node} 
of
The reference voltage Vref defines { HEAD ~ the DC level } of both the virtual ground and { TAIL ~ the output node }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL