a second constant current source that is connected to the first bit line, {HEAD ~ the second constant current source} generating {TAIL ~ a reference current} for the second memory cell column; and 
generating
a second constant current source that is connected to the first bit line , { HEAD ~ the second constant current source } generating { TAIL ~ a reference current } for the second memory cell column ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH