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