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