The voltage at {HEAD ~ the function} of {TAIL ~ D1} and Q1 is a square wave 
of
The voltage at { HEAD ~ the function } of { TAIL ~ D1 } and Q1 is a square wave
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH