In absence of {HEAD ~ a clock signal} received at the first node, the second circuit uses {TAIL ~ the frequency reference input} received at the second input node to control the frequency of the oscillator 
In absence of { HEAD ~ a clock signal } received at the first node , the second circuit uses { TAIL ~ the frequency reference input } received at the second input node to control the frequency of the oscillator
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH