means for comparing the extracted components with {HEAD ~ a reference voltage} to derive {TAIL ~ an error signal}, 
to derive
means for comparing the extracted components with { HEAD ~ a reference voltage } to derive { TAIL ~ an error signal } ,
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH