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