* SPICE netlist
XU1 0 N004 N007 N003 N008 0 N005 N002 AD8421 ;pnba IN-)RG1)RG2)IN+)VEE)REF)OUT)VCC
R1 N004 N007 2490
XU2 N012 N015 N013 opamp Aol=100K GBW=10Meg ;pnba invin)noninvin)out
Vref N014 0 5
R2 N015 N014 620
R3 N013 N012 620
R4 N012 N011 14k
RTrimVref N011 0 2256.4
XU3 N001 N006 Vdet opamp Aol=100K GBW=10Meg ;pnba invin)noninvin)out
R6 N006 N005 1500
Rf Vdet N001 47000
Rg N001 0 2490
R7 N006 N013 60400
C1 N006 0 100n
V2 N008 0 -14
V3 N002 0 14
Vamc1200 N003 0 AC 1
XU4 N009 N010 N009 opamp Aol=100K GBW=10Meg ;pnba invin)noninvin)out
R5 N010 N005 1500
C2 N010 0 100n
R8 Vmonitor N009 50
;dc Vamc1200 -0.025 0.025 0.01
.dc Vamc1200 -2 2 0.1
;ac dec 5 10 100k

* LTspice schematic (.asc)
Version 4
SHEET 1 1296 912
WIRE -328 -440 -328 -456
WIRE -40 -376 -120 -376
WIRE 152 -376 40 -376
WIRE 184 -376 152 -376
WIRE 296 -376 264 -376
WIRE -120 -328 -120 -376
WIRE -328 -312 -328 -360
WIRE -360 -296 -648 -296
WIRE -648 -264 -648 -296
WIRE -360 -264 -456 -264
WIRE -456 -248 -456 -264
WIRE 152 -248 152 -376
WIRE 184 -248 152 -248
WIRE 296 -232 296 -376
WIRE 296 -232 248 -232
WIRE 424 -232 296 -232
WIRE -104 -216 -184 -216
WIRE -40 -216 -104 -216
WIRE 104 -216 40 -216
WIRE 184 -216 104 -216
WIRE -360 -168 -456 -168
WIRE -648 -136 -648 -184
WIRE -360 -136 -648 -136
WIRE -648 -104 -648 -136
WIRE -328 -104 -328 -120
WIRE 392 -104 264 -104
WIRE 264 -56 264 -104
WIRE 296 -56 264 -56
WIRE 392 -40 392 -104
WIRE 392 -40 360 -40
WIRE 472 -40 392 -40
WIRE 648 -40 552 -40
WIRE -104 -24 -104 -216
WIRE 152 -24 -104 -24
WIRE 264 -24 232 -24
WIRE 296 -24 264 -24
WIRE -328 -8 -328 -24
WIRE 264 8 264 -24
WIRE 264 88 264 72
WIRE -552 184 -648 184
WIRE -424 184 -472 184
WIRE -296 184 -344 184
WIRE -264 184 -296 184
WIRE -152 184 -184 184
WIRE -56 184 -152 184
WIRE 104 184 104 -216
WIRE 104 184 24 184
WIRE -648 232 -648 184
WIRE 104 232 104 184
WIRE -296 312 -296 184
WIRE -264 312 -296 312
WIRE -152 328 -152 184
WIRE -152 328 -200 328
WIRE 104 328 104 296
WIRE -504 344 -600 344
WIRE -264 344 -424 344
WIRE -600 360 -600 344
WIRE -600 456 -600 440
FLAG -600 456 0
FLAG -648 232 0
FLAG 104 328 0
FLAG -120 -328 0
FLAG -328 -8 0
FLAG -328 -456 0
FLAG -248 -152 0
FLAG -648 -104 0
FLAG 424 -232 Vdet
FLAG 648 -40 Vmonitor
FLAG 264 88 0
SYMBOL OpAmps\\AD8421 -328 -216 R0
SYMATTR InstName U1
SYMBOL res -472 -264 R0
SYMATTR InstName R1
SYMATTR Value 2490
SYMBOL OpAmps\\opamp -232 264 R0
SYMATTR InstName U2
SYMBOL voltage -600 344 R0
SYMATTR InstName Vref
SYMATTR Value 5
SYMBOL res -408 328 R90
SYMATTR InstName R2
SYMATTR Value 620
SYMBOL res -168 168 R90
SYMATTR InstName R3
SYMATTR Value 620
SYMBOL res -328 168 R90
SYMATTR InstName R4
SYMATTR Value 14k
SYMBOL res -456 168 R90
SYMATTR InstName TrimVref
SYMATTR Value 2256.4
SYMBOL OpAmps\\opamp 216 -296 R0
SYMATTR InstName U3
SYMBOL res 56 -232 R90
SYMATTR InstName R6
SYMATTR Value 1500
SYMBOL res 280 -392 R90
SYMATTR InstName Rf
SYMATTR Value 47000
SYMBOL res 56 -392 R90
SYMATTR InstName Rg
SYMATTR Value 2490
SYMBOL res 40 168 R90
SYMATTR InstName R7
SYMATTR Value 60400
SYMBOL cap 88 232 R0
SYMATTR InstName C1
SYMATTR Value 100n
SYMBOL voltage -328 -120 R0
SYMATTR InstName V2
SYMATTR Value -14
SYMBOL voltage -328 -344 R180
SYMATTR InstName V3
SYMATTR Value 14
SYMBOL voltage -648 -280 R0
SYMATTR InstName Vamc1200
SYMATTR Value2 AC 1
SYMATTR Value ""
SYMBOL OpAmps\\opamp 328 -104 R0
SYMATTR InstName U4
SYMBOL res 248 -40 R90
SYMATTR InstName R5
SYMATTR Value 1500
SYMBOL cap 248 8 R0
SYMATTR InstName C2
SYMATTR Value 100n
SYMBOL res 568 -56 R90
SYMATTR InstName R8
SYMATTR Value 50