Two operational amplifiers 68 and 70 form part of circuit 50 with inverting terminal 72 of {TAIL ~ op amp} 68 common with anode 54 of {HEAD ~ photodiode} 52 
Two operational amplifiers 68 and 70 form part of circuit 50 with inverting terminal 72 of { TAIL ~ op amp } 68 common with anode 54 of { HEAD ~ photodiode } 52
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH