the first circuit, filter and oscillator constitute {HEAD ~ a phase locked loop} to synchronize {TAIL ~ the internal clock signal} to the externally provided clock signal 
to synchronize
the first circuit , filter and oscillator constitute { HEAD ~ a phase locked loop } to synchronize { TAIL ~ the internal clock signal } to the externally provided clock signal
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH