{HEAD ~ VREF} is fed back to the bases of {TAIL ~ transistors} 106 and 108 
{ HEAD ~ VREF } is fed back to the bases of { TAIL ~ transistors } 106 and 108
HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH