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