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