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