An output of the operational amplifier is fed back to an input of {HEAD ~ the operational amplifier} through a current varying element that varies {TAIL ~ current levels} of the input of the operational amplifier to remove a level shift of an output signal of the differential amplifier 
An output of the operational amplifier is fed back to an input of { HEAD ~ the operational amplifier } through a current varying element that varies { TAIL ~ current levels } of the input of the operational amplifier to remove a level shift of an output signal of the differential amplifier
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH