{HEAD ~ Transistor} 168 has its emitter coupled to {TAIL ~ low voltage source A} via resistor 170, the combination of which forms a current source 
{ HEAD ~ Transistor } 168 has its emitter coupled to { TAIL ~ low voltage source A } via resistor 170 , the combination of which forms a current source
HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH