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