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