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