first voltage source connected across {HEAD ~ each} of {TAIL ~ said photodiodes}, biasing each of said photodiodes; and 
first voltage source connected across { HEAD ~ each } of { TAIL ~ said photodiodes } , biasing each of said photodiodes ; and
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH