In another circuit one of either the anodes or {TAIL ~ cathodes} of each diode is common and the other is input into the inverting terminal of {HEAD ~ a separate operational amplifier} 
In another circuit one of either the anodes or { TAIL ~ cathodes } of each diode is common and the other is input into the inverting terminal of { HEAD ~ a separate operational amplifier }
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD