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