a gate electrode of said third N channel MOS transistor receives {HEAD ~ a reference potential} at said {TAIL ~ second potential level} 
a gate electrode of said third N channel MOS transistor receives { HEAD ~ a reference potential } at said { TAIL ~ second potential level }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL