* SPICE netlist
R1 N010 N009 50
R2 0 N010 2k
R3 N010 N011 1k
R4 N011 0 1k
R5 N011 0 1Meg
V1 N009 0 12
I1 0 N011 10m
V2 N007 0 500mV
XU2 N004 N008 NC_01 0 N012 LT1720 ;pnba In+)In-)V+)V-)OUT
XU3 N004 N014 NC_02 0 N013 LT1720 ;pnba In+)In-)V+)V-)OUT
R6 N003 0 1k
R7 N004 N003 9k
R8 N002 N008 4k
R9 N008 N014 2k
R10 N014 0 4k
R11 N002 N012 10k
R12 N005 N012 680
R13 N002 N013 10k
R14 N006 N013 680
D1 N002 N005 QTLP690C
D2 N002 N006 QTLP690C
V3 N001 0 10
XU1 N007 N003 NC_03 0 N004 LT1001 ;pnba In+)In-)V+)V-)OUT
.op

* LTspice schematic (.asc)
Version 4
SHEET 1 2288 752
WIRE 536 -376 408 -376
WIRE 824 -376 616 -376
WIRE 408 -360 408 -376
WIRE 792 -232 520 -232
WIRE 904 -232 792 -232
WIRE 1032 -232 904 -232
WIRE 1144 -232 1032 -232
WIRE 904 -200 904 -232
WIRE 1144 -200 1144 -232
WIRE 248 -168 200 -168
WIRE 296 -168 248 -168
WIRE 472 -168 376 -168
WIRE 520 -168 520 -232
WIRE 120 -136 120 -168
WIRE 792 -120 792 -232
WIRE 904 -120 904 -136
WIRE 1032 -120 1032 -232
WIRE 1144 -120 1144 -136
WIRE 248 -72 248 -168
WIRE 264 -72 248 -72
WIRE 472 -56 472 -168
WIRE 472 -56 328 -56
WIRE 584 -56 472 -56
WIRE 264 -40 120 -40
WIRE 520 -40 520 -88
WIRE 632 -40 520 -40
WIRE -1048 -24 -1144 -24
WIRE -920 -24 -968 -24
WIRE -840 -24 -920 -24
WIRE -664 -24 -760 -24
WIRE -552 -24 -664 -24
WIRE -424 -24 -552 -24
WIRE 792 -24 792 -40
WIRE 792 -24 696 -24
WIRE 904 -24 904 -40
WIRE 904 -24 792 -24
WIRE 584 -8 584 -56
WIRE 632 -8 584 -8
WIRE 1032 -8 1032 -40
WIRE 1144 -8 1144 -40
WIRE 1144 -8 1032 -8
WIRE 296 8 296 -24
WIRE -1144 24 -1144 -24
WIRE -552 24 -552 -24
WIRE -424 24 -424 -24
WIRE 120 24 120 -40
WIRE 520 24 520 -40
WIRE -664 40 -664 -24
WIRE -920 56 -920 -24
WIRE 664 56 664 8
WIRE 520 136 520 104
WIRE 632 136 520 136
WIRE 1032 152 1032 -8
WIRE 1032 152 696 152
WIRE -1144 168 -1144 104
WIRE -920 168 -920 136
WIRE -920 168 -1144 168
WIRE -792 168 -920 168
WIRE -664 168 -664 120
WIRE -664 168 -792 168
WIRE -552 168 -552 104
WIRE -552 168 -664 168
WIRE -424 168 -424 104
WIRE -424 168 -552 168
WIRE 120 168 120 104
WIRE 472 168 472 -56
WIRE 632 168 472 168
WIRE -792 200 -792 168
WIRE 664 216 664 184
WIRE 520 264 520 136
WIRE 520 376 520 344
FLAG -792 200 0
FLAG 120 168 0
FLAG 120 -136 0
FLAG 664 56 0
FLAG 664 216 0
FLAG 520 376 0
FLAG 296 8 0
FLAG 408 -360 0
DATAFLAG 240 288 ""
DATAFLAG 240 160 ""
DATAFLAG 304 480 "I(R2)"
DATAFLAG 16 160 "I(V1)"
DATAFLAG 16 288 ""
DATAFLAG 496 176 ""
DATAFLAG 496 288 ""
SYMBOL res -952 -40 R90
SYMATTR InstName R1
SYMATTR Value 50
SYMBOL res -904 152 R180
SYMATTR InstName R2
SYMATTR Value 2k
SYMBOL res -856 -8 R270
SYMATTR InstName R3
SYMATTR Value 1k
SYMBOL res -568 8 R0
SYMATTR InstName R4
SYMATTR Value 1k
SYMBOL res -440 8 R0
SYMATTR InstName R5
SYMATTR Value 1Meg
SYMBOL voltage -1144 8 R0
SYMATTR InstName V1
SYMATTR Value 12
SYMBOL current -664 120 R180
SYMATTR InstName I1
SYMATTR Value 10m
SYMBOL voltage 120 8 R0
SYMATTR InstName V2
SYMATTR Value 500mV
SYMBOL Comparators\\LT1720 664 -88 R0
SYMATTR InstName U2
SYMBOL Comparators\\LT1720 664 88 R0
SYMATTR InstName U3
SYMBOL res 216 -184 R90
SYMATTR InstName R6
SYMATTR Value 1k
SYMBOL res 392 -184 R90
SYMATTR InstName R7
SYMATTR Value 9k
SYMBOL res 504 -184 R0
SYMATTR InstName R8
SYMATTR Value 4k
SYMBOL res 504 8 R0
SYMATTR InstName R9
SYMATTR Value 2k
SYMBOL res 504 248 R0
SYMATTR InstName R10
SYMATTR Value 4k
SYMBOL res 776 -136 R0
SYMATTR InstName R11
SYMATTR Value 10k
SYMBOL res 888 -136 R0
SYMATTR InstName R12
SYMATTR Value 680
SYMBOL res 1016 -136 R0
SYMATTR InstName R13
SYMATTR Value 10k
SYMBOL res 1128 -136 R0
SYMATTR InstName R14
SYMATTR Value 680
SYMBOL LED 888 -200 R0
SYMATTR InstName D1
SYMATTR Value QTLP690C
SYMBOL LED 1128 -200 R0
SYMATTR InstName D2
SYMATTR Value QTLP690C
SYMBOL voltage 632 -376 R90
SYMATTR InstName V3
SYMATTR Value 10
SYMBOL OpAmps\\LT1001 296 -120 R0
SYMATTR InstName U1