In general, {HEAD ~ transistors} used in {TAIL ~ circuitry} are designed to have this optimum concentration 
In general , { HEAD ~ transistors } used in { TAIL ~ circuitry } are designed to have this optimum concentration
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH