{HEAD ~ The peaks} of the forward and rear output pulses are converted into {TAIL ~ DC voltage levels}, which are then fed into a comparator circuit 
are converted into
{ HEAD ~ The peaks } of the forward and rear output pulses are converted into { TAIL ~ DC voltage levels } , which are then fed into a comparator circuit
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH