means for supplying two kinds of clock signals having the same frequency and {HEAD ~ a phase difference} of {TAIL ~ 180 degrees}; and 
of
means for supplying two kinds of clock signals having the same frequency and { HEAD ~ a phase difference } of { TAIL ~ 180 degrees } ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH