an adjustable current generator that converts a reference current into {HEAD ~ a driving current} according to {TAIL ~ a current control signal} 
an adjustable current generator that converts a reference current into { HEAD ~ a driving current } according to { TAIL ~ a current control signal }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL