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