The circuit includes {TAIL ~ a first tracking bit line}, {HEAD ~ a second tracking bit line}, a tracking cell, and a control logic circuit 
The circuit includes { TAIL ~ a first tracking bit line } , { HEAD ~ a second tracking bit line } , a tracking cell , and a control logic circuit
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH