{TAIL ~ The reference voltage Vref} is chosen equal to half the supply voltage to maximize {HEAD ~ the AC voltage swing} of the output node 
{ TAIL ~ The reference voltage Vref } is chosen equal to half the supply voltage to maximize { HEAD ~ the AC voltage swing } of the output node
TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH