* SPICE netlist
C1 0 ADC_out 0.1p
C2 0 ADC_out_dsp 0.1p
XU2 N002 FDA_IN+ FDA_IN- N004 VS+ VS- FDA_OUT_N FDA_OUT_P _DIS VOCM Refin 0 0 ADA4945-HP ;pnba 1)2)3)4)5)6)7)8)9)10)11)12)13
V11 VOCM 0 1.5
V12 _DIS 0 3.3
R1 N001 N002 {RF}
R3 N005 N004 {RF}
C3 FDA_IN+ N002 {CFilt_2}
C4 FDA_IN- N004 {CFilt_2}
R9 ADC_IN+ FDA_OUT_P 25
R10 ADC_IN- FDA_OUT_N 25
R11 AUXIN+ FDA_OUT_P 100
R12 AUXIN- FDA_OUT_N 100
C7 ADC_IN+ ADC_IN- 78p
C8 AUXIN+ AUXIN- 10p
R13 N001 Vin_p {RG}
R14 N005 Vin_n {RG}
V_FS N006 0 {fs}
V_SEL N008 0 {sel}
V_DEC N007 0 {decimation}
C9 N001 0 {CFilt_1}
C10 0 N005 {CFilt_1}
R5 N001 FDA_IN+ {RMFB}
R6 N005 FDA_IN- {RMFB}
V1 VS+ 0 {FDA_Vsp}
V2 VS- 0 {FDA_Vsn}
V6 VDD33 0 {ADC_VDD33}
V14 CNV 0 PULSE(0 1.1 {ACQ_delay} 0.2n 0.2n {0.9*(1/fs)} {1/fs})
Vin_n N003 Vin_n SINE(0 {input_Vpp/4} {input_freq}) AC 0.5 0
Vin_cm N003 0 {input_cm} AC 0
Vin_p Vin_p N003 SINE(0 {input_Vpp/4} {input_freq}) AC 0.5 0
XU1 0 VDD33 Refin ADC_IN+ ADC_IN- AUXIN+ AUXIN- CNV ADC_out ADC_out_dsp N007 N008 N006 ADC_out AD4081 ;pnba GND)Vdd)REFIN)IN+)IN-)AUXIN+)AUXIN-)CNV)Vout)DSPOUT)DEC)SEL)FS)DSPIN
V3 Refin 0 3
.tran 5u
.meas NOISE output_noise_rms INTEG V(onoise) FROM 10 TO {Fmax_noise_integration}
.meas NOISE full_scale_sine_rms PARAM 2*VREF/(2*sqrt(2))
.param VREF=3
.meas NOISE dynamic_range PARAM 20*log10(full_scale_sine_rms/output_noise_rms)
.param Fmax_noise_integration = 1G
.meas NOISE ENOB PARAM (dynamic_range - 1.76)/6.02
.param FDA_VSp = 5V
.param FDA_VSn = -5V
.param fs = 40MEG
.param ACQ_delay = 10n
.param input_Vpp=2.966
.param input_freq = 500k
.param input_cm = 0
.param ADC_VDD33 = 3.3V
.param decimation 4
.param AFE_gain = 1 ;--> AFE gain = Rf/Rg
.param RF = 499
.param RMFB = 499
.param RG = {RF/AFE_gain}
.param CFilt_1=150p
.param CFilt_2=56p
.meas AC ADC_out_max MAX MAG(V(ADC_out))
.meas AC bw_3db FIND frequency WHEN mag(V(ADC_out))=(ADC_out_max/sqrt(2))
.param sel 3

* LTspice schematic (.asc)
Version 4
SHEET 1 3664 1472
WIRE -728 -736 -744 -736
WIRE -8 -736 -24 -736
WIRE 264 -736 248 -736
WIRE -744 -688 -744 -736
WIRE -24 -688 -24 -736
WIRE 248 -688 248 -736
WIRE -1640 -656 -1656 -656
WIRE -1416 -656 -1432 -656
WIRE -1208 -656 -1224 -656
WIRE -1656 -608 -1656 -656
WIRE -1432 -608 -1432 -656
WIRE -1224 -608 -1224 -656
WIRE -744 -576 -744 -608
WIRE -24 -576 -24 -608
WIRE 248 -576 248 -608
WIRE -1656 -496 -1656 -528
WIRE -1432 -496 -1432 -528
WIRE -1224 -496 -1224 -528
WIRE 1112 -400 936 -400
WIRE 1144 -400 1112 -400
WIRE 936 -368 936 -400
WIRE 936 -224 936 -288
WIRE -488 -192 -776 -192
WIRE -200 -192 -408 -192
WIRE -360 -80 -568 -80
WIRE -200 -80 -200 -192
WIRE -200 -80 -296 -80
WIRE 1496 0 1480 0
WIRE -1576 32 -1624 32
WIRE -1112 32 -1576 32
WIRE -952 32 -1032 32
WIRE -776 32 -776 -192
WIRE -776 32 -952 32
WIRE -712 32 -776 32
WIRE -568 32 -568 -80
WIRE -568 32 -632 32
WIRE -56 32 -136 32
WIRE 1144 32 1144 -400
WIRE 632 48 216 48
WIRE 744 48 712 48
WIRE 872 48 744 48
WIRE 920 48 872 48
WIRE -1624 64 -1624 32
WIRE -56 64 -104 64
WIRE 1736 64 1640 64
WIRE 1832 64 1736 64
WIRE -952 80 -952 32
WIRE 1480 80 1480 0
WIRE 1480 80 1448 80
WIRE -56 96 -72 96
WIRE 1736 96 1736 64
WIRE -136 112 -136 32
WIRE -104 112 -104 64
WIRE -72 112 -72 96
WIRE 920 128 920 48
WIRE 1496 128 1448 128
WIRE -568 144 -568 32
WIRE -440 144 -568 144
WIRE -184 144 -440 144
WIRE 72 144 -8 144
WIRE 136 144 72 144
WIRE 216 144 216 48
WIRE 216 144 184 144
WIRE 264 144 216 144
WIRE 392 144 344 144
WIRE 584 144 392 144
WIRE 872 144 584 144
WIRE 872 160 872 144
WIRE 888 160 872 160
WIRE -200 176 -200 -80
WIRE -184 176 -200 176
WIRE -8 176 -8 144
WIRE 392 176 392 144
WIRE -1624 192 -1624 144
WIRE -1624 192 -1832 192
WIRE -952 192 -952 144
WIRE -952 192 -1000 192
WIRE 744 192 744 48
WIRE 888 192 872 192
WIRE 1736 192 1736 160
WIRE -1000 208 -1000 192
WIRE -440 208 -568 208
WIRE -184 208 -440 208
WIRE -1832 224 -1832 192
WIRE -1624 224 -1624 192
WIRE 1480 224 1448 224
WIRE 1640 224 1640 64
WIRE 1640 224 1480 224
WIRE -952 240 -952 192
WIRE -184 240 -200 240
WIRE -184 272 -232 272
WIRE -8 272 -8 240
WIRE 72 272 -8 272
WIRE 136 272 184 144
WIRE 136 272 72 272
WIRE 184 272 136 144
WIRE 216 272 184 272
WIRE 264 272 216 272
WIRE 392 272 392 240
WIRE 392 272 344 272
WIRE 584 272 392 272
WIRE 872 272 872 192
WIRE 872 272 584 272
WIRE 1480 272 1480 224
WIRE 1480 272 1448 272
WIRE 1736 304 1448 304
WIRE 1816 304 1736 304
WIRE -232 320 -232 272
WIRE -72 320 -72 304
WIRE 1736 336 1736 304
WIRE -1832 352 -1832 304
WIRE -1624 352 -1624 304
WIRE -1576 352 -1624 352
WIRE -1112 352 -1576 352
WIRE -952 352 -952 304
WIRE -952 352 -1032 352
WIRE -776 352 -952 352
WIRE -712 352 -776 352
WIRE -568 352 -568 208
WIRE -568 352 -632 352
WIRE 1048 352 1048 320
WIRE -104 368 -104 304
WIRE -88 368 -104 368
WIRE 216 368 216 272
WIRE 632 368 216 368
WIRE 744 368 744 256
WIRE 744 368 712 368
WIRE 872 368 744 368
WIRE 920 368 920 224
WIRE 920 368 872 368
WIRE -136 400 -136 304
WIRE -88 400 -136 400
WIRE 1736 432 1736 400
WIRE -568 464 -568 352
WIRE -360 464 -568 464
WIRE -200 464 -200 240
WIRE -200 464 -296 464
WIRE -776 560 -776 352
WIRE -472 560 -776 560
WIRE -200 560 -200 464
WIRE -200 560 -392 560
WIRE 1144 592 1144 320
WIRE 1144 592 1048 592
WIRE 1272 592 1272 320
WIRE 1368 592 1272 592
WIRE 1048 640 1048 592
WIRE 1208 640 1208 320
WIRE 1368 640 1368 592
WIRE 1048 736 1048 720
WIRE 1208 736 1208 720
WIRE 1368 736 1368 720
FLAG 1048 352 0
FLAG 1736 192 0
FLAG 1736 432 0
FLAG 1832 64 ADC_out
FLAG 1816 304 ADC_out_dsp
FLAG -56 64 VOCM
FLAG -56 32 VS+
FLAG -88 400 VS-
FLAG -232 320 0
FLAG -24 -576 0
FLAG -8 -736 VOCM
FLAG 248 -576 0
FLAG 264 -736 _DIS
FLAG -88 368 _DIS
FLAG -440 144 FDA_IN+
FLAG -440 208 FDA_IN-
FLAG -72 320 0
FLAG 872 48 AUXIN+
FLAG 584 144 ADC_IN+
FLAG 584 272 ADC_IN-
FLAG 872 368 AUXIN-
FLAG 72 144 FDA_OUT_N
FLAG 72 272 FDA_OUT_P
FLAG 1048 736 0
FLAG 1208 736 0
FLAG 1368 736 0
FLAG -1656 -496 0
FLAG -1432 -496 0
FLAG -1640 -656 VS+
FLAG -1416 -656 VS-
FLAG -1224 -496 0
FLAG -1208 -656 VDD33
FLAG -744 -576 0
FLAG -728 -736 CNV
FLAG -1832 352 0
FLAG -1576 32 Vin_p
FLAG -1576 352 Vin_n
FLAG 1496 0 VDD33
FLAG 1496 128 CNV
FLAG 936 -224 0
FLAG 1112 -400 Refin
FLAG -1000 208 0
FLAG -56 96 Refin
SYMBOL cap 1720 160 M180
SYMATTR InstName C1
SYMATTR Value 0.1p
SYMBOL cap 1720 400 M180
SYMATTR InstName C2
SYMATTR Value 0.1p
SYMBOL OpAmps\\ADA4945-HP -136 208 R0
SYMATTR InstName U2
SYMBOL voltage -24 -704 R0
SYMATTR InstName V11
SYMATTR Value 1.5
SYMBOL voltage 248 -704 R0
SYMATTR InstName V12
SYMATTR Value 3.3
SYMBOL res -504 -176 R270
SYMATTR InstName R1
SYMATTR Value {RF}
SYMBOL res -488 576 R270
SYMATTR InstName R3
SYMATTR Value {RF}
SYMBOL cap -360 -64 R270
SYMATTR Value {CFilt_2}
SYMATTR InstName C3
SYMBOL cap -360 480 R270
SYMATTR Value {CFilt_2}
SYMATTR InstName C4
SYMBOL res 360 128 R90
SYMATTR InstName R9
SYMATTR Value 25
SYMBOL res 360 256 R90
SYMATTR InstName R10
SYMATTR Value 25
SYMBOL res 728 32 R90
SYMATTR InstName R11
SYMATTR Value 100
SYMBOL res 728 352 R90
SYMATTR InstName R12
SYMATTR Value 100
SYMBOL cap 376 176 R0
SYMATTR InstName C7
SYMATTR Value 78p
SYMBOL cap 728 192 R0
SYMATTR InstName C8
SYMATTR Value 10p
SYMBOL res -1016 16 R90
SYMATTR InstName R13
SYMATTR Value {RG}
SYMBOL res -1016 336 R90
SYMATTR InstName R14
SYMATTR Value {RG}
SYMBOL voltage 1048 624 M0
SYMATTR InstName V_FS
SYMATTR Value {fs}
SYMBOL voltage 1208 624 M0
SYMATTR InstName V_SEL
SYMATTR Value {sel}
SYMBOL voltage 1368 624 M0
SYMATTR InstName V_DEC
SYMATTR Value {decimation}
SYMBOL cap -968 80 R0
SYMATTR Value {CFilt_1}
SYMATTR InstName C9
SYMBOL cap -968 240 R0
SYMATTR Value {CFilt_1}
SYMATTR InstName C10
SYMBOL res -728 48 R270
SYMATTR InstName R5
SYMATTR Value {RMFB}
SYMBOL res -728 368 R270
SYMATTR InstName R6
SYMATTR Value {RMFB}
SYMBOL voltage -1656 -624 R0
SYMATTR InstName V1
SYMATTR Value {FDA_Vsp}
SYMBOL voltage -1432 -624 R0
SYMATTR InstName V2
SYMATTR Value {FDA_Vsn}
SYMBOL voltage -1224 -624 R0
SYMATTR InstName V6
SYMATTR Value {ADC_VDD33}
SYMBOL voltage -744 -704 R0
SYMATTR Value PULSE(0 1.1 {ACQ_delay} 0.2n 0.2n {0.9*(1/fs)} {1/fs})
SYMATTR InstName V14
SYMBOL voltage -1624 208 R0
SYMATTR Value2 AC 0.5 0
SYMATTR Value SINE(0 {input_Vpp/4} {input_freq})
SYMATTR InstName Vin_n
SYMBOL voltage -1832 208 R0
SYMATTR Value2 AC 0
SYMATTR InstName Vin_cm
SYMATTR Value {input_cm}
SYMBOL voltage -1624 48 R0
SYMATTR Value2 AC 0.5 0
SYMATTR Value SINE(0 {input_Vpp/4} {input_freq})
SYMATTR InstName Vin_p
SYMBOL AD4081 1144 176 R0
SYMATTR InstName U1
SYMBOL voltage 936 -384 R0
SYMATTR InstName V3
SYMATTR Value 3