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