Noise: *Megavolts* in for picovolts out??

"Robert Baer" schrieb im Newsbeitrag news:erX4e.1846$ snipped-for-privacy@newsread2.news.pas.earthlink.net...

Hello Robert,

You shouldn't cry "wolf" if there is no wolf.

Your circuit has wrong DC-operating points for many of your amplifiers. They have saturated outputs. So it's no wonder that the results look strange. Before one tries .AC or .NOISE, it's mandatory to run a .OP or .DC to see that no output is limited.

After I have fixed your design, the results are as expected.

Best Regards, Helmut

Version 4 SHEET 1 1220 708 WIRE -256 128 -256 96 WIRE -256 240 -256 208 WIRE -160 -32 -160 -64 WIRE -128 96 -256 96 WIRE -128 96 -128 48 WIRE -96 16 -96 -208 WIRE -96 48 -128 48 WIRE -96 240 -96 208 WIRE -96 256 -96 240 WIRE -96 448 -96 336 WIRE -80 16 -96 16 WIRE -64 240 -96 240 WIRE -64 320 -64 240 WIRE -32 208 -32 128 WIRE -16 208 -32 208 WIRE -16 240 -64 240 WIRE 0 -64 -160 -64 WIRE 0 16 0 -64 WIRE 0 464 0 416 WIRE 16 -208 -96 -208 WIRE 16 160 16 -208 WIRE 16 192 16 160 WIRE 32 16 0 16 WIRE 96 128 -32 128 WIRE 96 224 48 224 WIRE 96 224 96 128 WIRE 96 336 96 224 WIRE 96 416 80 416 WIRE 128 16 112 16 WIRE 128 32 128 16 WIRE 128 128 96 128 WIRE 128 128 128 112 WIRE 144 160 16 160 WIRE 144 240 144 160 WIRE 256 -208 16 -208 WIRE 256 -144 256 -208 WIRE 256 -32 256 -64 WIRE 256 112 256 -32 WIRE 304 -64 304 -144 WIRE 304 0 304 -64 WIRE 304 192 304 160 WIRE 304 288 304 192 WIRE 320 -144 304 -144 WIRE 320 192 304 192 WIRE 336 -64 304 -64 WIRE 336 -32 256 -32 WIRE 336 288 304 288 WIRE 336 320 -64 320 WIRE 368 -80 368 -112 WIRE 368 240 144 240 WIRE 368 272 368 240 WIRE 448 -144 400 -144 WIRE 448 -48 400 -48 WIRE 448 -48 448 -144 WIRE 448 192 400 192 WIRE 448 304 400 304 WIRE 448 304 448 192 WIRE 480 -208 256 -208 WIRE 480 -112 368 -112 WIRE 480 -112 480 -208 WIRE 480 304 448 304 WIRE 480 304 480 144 WIRE 496 -96 496 -128 WIRE 512 -128 496 -128 WIRE 512 -48 448 -48 WIRE 512 144 480 144 WIRE 608 -128 592 -128 WIRE 608 -48 592 -48 WIRE 608 -48 608 -128 WIRE 608 48 608 -48 WIRE 608 144 592 144 WIRE 608 144 608 80 WIRE 608 176 608 144 WIRE 608 288 608 176 WIRE 624 48 608 48 WIRE 624 80 608 80 WIRE 656 -208 480 -208 WIRE 656 32 656 -208 WIRE 688 -48 608 -48 WIRE 688 176 608 176 WIRE 688 288 608 288 WIRE 784 -48 768 -48 WIRE 784 64 688 64 WIRE 784 64 784 -48 WIRE 800 288 768 288 WIRE 800 320 800 288 WIRE 816 -208 656 -208 WIRE 816 176 768 176 WIRE 816 176 816 -208 WIRE 832 -48 784 -48 WIRE 832 64 784 64 WIRE 928 -48 912 -48 WIRE 928 -32 928 -48 WIRE 928 64 912 64 WIRE 928 64 928 32 WIRE 928 176 928 64 WIRE 1008 -208 816 -208 WIRE 1008 96 1008 -208 FLAG -96 448 0 FLAG 16 256 0 FLAG 256 192 0 FLAG 1008 176 0 FLAG 0 544 0 FLAG -160 48 0 FLAG 368 -16 0 FLAG 368 336 0 FLAG 656 96 0 FLAG 800 320 0 FLAG 928 336 0 FLAG 496 -96 0 FLAG -256 240 0 SYMBOL res -112 32 R0 WINDOW 0 36 54 Left 0 WINDOW 3 30 79 Left 0 SYMATTR InstName TR1 SYMATTR Value 18.2K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res -112 112 R0 WINDOW 0 -34 45 Left 0 WINDOW 3 -44 74 Left 0 SYMATTR InstName R1 SYMATTR Value 549 SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res -112 240 R0 WINDOW 0 -41 37 Left 0 WINDOW 3 -55 70 Left 0 SYMATTR InstName PC SYMATTR Value {PC} SYMBOL Opamps\\\\opamp2 16 160 R0 WINDOW 3 -31 131 Left 0 SYMATTR Value AD8605 SYMATTR InstName U1 SYMBOL res 240 -160 R0 WINDOW 0 -64 62 Left 0 WINDOW 3 -99 24 Left 0 SYMATTR InstName RTAA SYMATTR Value {20K-TA} SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 240 96 R0 WINDOW 0 -67 68 Left 0 WINDOW 3 -56 29 Left 0 SYMATTR InstName RTAB SYMATTR Value {TA} SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL Misc\\\\battery 1008 80 R0 WINDOW 0 9 6 Left 0 WINDOW 3 11 -32 Left 0 SYMATTR InstName VBAT SYMATTR Value 5.0V SYMBOL res -16 448 R0 WINDOW 0 1 32 Right 0 WINDOW 3 -10 68 Right 0 SYMATTR InstName RM1 SYMATTR Value 1K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 80 320 R0 WINDOW 0 39 39 Left 0 WINDOW 3 34 70 Left 0 SYMATTR InstName TR2A SYMATTR Value 45.3K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res -16 432 R270 WINDOW 0 -20 88 VLeft 0 WINDOW 3 -46 94 VLeft 0 SYMATTR InstName TR2B SYMATTR Value {TR2} SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 128 0 R90 WINDOW 0 -20 39 VRight 0 WINDOW 3 46 38 VRight 0 SYMATTR InstName R92 SYMATTR Value 976K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 16 0 R90 WINDOW 0 -19 36 VRight 0 WINDOW 3 50 26 VRight 0 SYMATTR InstName R91 SYMATTR Value 5Meg SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res -144 64 R180 WINDOW 0 78 69 Right 0 WINDOW 3 93 33 Right 0 SYMATTR InstName R93 SYMATTR Value 0.001 SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 112 16 R0 SYMATTR InstName R90 SYMATTR Value 7.5K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL Opamps\\\\opamp2 368 -112 R0 WINDOW 3 13 115 Left 0 SYMATTR Value AD8605 SYMATTR InstName U2 SYMBOL Opamps\\\\opamp2 368 240 R0 WINDOW 3 28 95 Left 0 SYMATTR Value AD8605 SYMATTR InstName U3 SYMBOL res 416 -160 R90 WINDOW 0 -20 39 VRight 0 WINDOW 3 -21 -27 VRight 0 SYMATTR InstName R2 SYMATTR Value 100K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 416 176 R90 WINDOW 0 -11 10 VRight 0 WINDOW 3 -12 -49 VRight 0 SYMATTR InstName R3 SYMATTR Value 100K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 288 64 R0 WINDOW 0 36 51 Left 0 WINDOW 3 70 50 Left 0 SYMATTR InstName R4 SYMATTR Value 10K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 288 -16 R0 WINDOW 0 40 62 Left 0 WINDOW 3 77 63 Left 0 SYMATTR InstName R5 SYMATTR Value {250K-SENS} SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL Opamps\\\\opamp2 656 0 R0 WINDOW 3 20 104 Left 0 SYMATTR Value AD8605 SYMATTR InstName U4 SYMBOL res 608 128 R90 WINDOW 0 50 48 VRight 0 WINDOW 3 77 31 VRight 0 SYMATTR InstName R6 SYMATTR Value 20.0K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 608 -64 R90 WINDOW 0 50 48 VRight 0 WINDOW 3 77 31 VRight 0 SYMATTR InstName R7 SYMATTR Value 20.0K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 784 -64 R90 WINDOW 0 50 48 VRight 0 WINDOW 3 77 31 VRight 0 SYMATTR InstName R8 SYMATTR Value 100K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 784 160 R90 WINDOW 0 50 48 VRight 0 WINDOW 3 77 31 VRight 0 SYMATTR InstName R9 SYMATTR Value 200K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 784 272 R90 WINDOW 0 50 48 VRight 0 WINDOW 3 77 31 VRight 0 SYMATTR InstName R10 SYMATTR Value 100K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 928 48 R90 WINDOW 0 50 48 VRight 0 WINDOW 3 77 31 VRight 0 SYMATTR InstName R11 SYMATTR Value 47.0K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 928 -64 R90 WINDOW 0 50 48 VRight 0 WINDOW 3 77 47 VRight 0 SYMATTR InstName R12 SYMATTR Value 4.73K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL polcap 912 -32 R0 SYMATTR InstName C1 SYMATTR Value 10µF SYMBOL res 912 160 R0 SYMATTR InstName R13 SYMATTR Value 2.20k SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 912 240 R0 WINDOW 0 1 32 Right 0 WINDOW 3 -10 68 Right 0 SYMATTR InstName RM2 SYMATTR Value 1K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 608 -144 R90 WINDOW 0 -21 74 VRight 0 WINDOW 3 -20 7 VRight 0 SYMATTR InstName R14 SYMATTR Value 200K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL voltage -256 112 R0 WINDOW 123 24 132 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMATTR Value 2.5 TEXT -200 -264 Left 0 ;.INCLUDE D:\\\\SPICE\\\\AD8605.LIB TEXT 72 -400 Left 0 !.PARAM TA=10.00K TR2=1.25K PC=1G SENS=249K ; new TEXT -200 -296 Left 0 ;.OPTIONS OPTS NUMDGT=4 RELTOL=0.0001 ITL1=850 TEXT -200 -200 Left 0 !.op TEXT 80 464 Left 0 ;*5K pot TEXT 720 48 Left 0 ;N016 TEXT -192 -472 Left 0 !.noise V(n016) V1 oct 8 1E-1 1E6 TEXT -192 -360 Left 0 !.include ad8605.cir TEXT -192 -400 Left 0 ;.ac dec 100 1 100k TEXT -192 -432 Left 0 ;.dc V1 2.49 2.51 1m TEXT 72 -360 Left 0 ;.PARAM TA=8.00K TR2=1.25K PC=12.5K SENS=249K TEXT 168 -472 Left 0 ;V1 changed to 2.5V, PC set to 1G, TA changed to 10k

SPICE model file ad605.cir:

• AD605.cir

*

• AD8605 SPICE Macro-model
• Typical Values
• 05/02, Ver. 1.0
• SB, ADSiV apps

*

• Copyright 2002 by Analog Devices

*

• Refer to "README.DOC" file for License Statement. Use of this
• model indicates your acceptance of the terms and provisions in
• the License Statement.

*

• Node Assignments
• noninverting input
• | inverting input
• | | positive supply
• | | | negative supply
• | | | | output
• | | | | |
• | | | | | ..SUBCKT AD8605 1 2 99 50 45

*

• INPUT STAGE
• M1 14 7 8 8 PIX L=1E-6 W=1600E-6 M2 16 2 8 8 PIX L=1E-6 W=1600E-6 M3 17 7 10 10 NIX L=1E-6 W=1600E-6 M4 18 2 10 10 NIX L=1E-6 W=1600E-6 RC5 14 50 4E+3 RC6 16 50 4E+3 RC7 99 17 4E+3 RC8 99 18 4E+3 C1 14 16 0.6E-12 C2 17 18 0.6E-12 I1 99 8 100E-6 I2 10 50 100E-6 V1 99 9 0.3 V2 13 50 0.3 D1 8 9 DX D2 13 10 DX EOS 7 1 POLY(3) (22,98) (73,98) (81,98) 10E-6 1 1 1 IOS 1 2 0.05E-12

*

• CMRR 100dB, POLE AT 4.5KHz
• ECM1 21 98 POLY(2) (1,98) (2,98) 0 0.5 0.5 CCM1 21 22 3.54E-10 RCM1 21 22 100E3 RCM2 22 98 1

*

• PSRR=95dB, ZERO AT 534Hz
• EPSY 98 72 POLY(1) (99,50) 0 1 CPS3 72 73 5.30E-9 RPS3 72 73 56234 RPS4 73 98 1

* *

• VOLTAGE NOISE REFERENCE OF 8nV/rt(Hz)
• VN1 80 98 0 RN1 80 98 16.45E-3 HN 81 98 VN1 7 RN2 81 98 1

*

• INTERNAL VOLTAGE REFERENCE
• EREF 98 0 POLY(2) (99,0) (50,0) 0 .5 .5 GSY 99 50 (99,50) 48E-6 EVP 97 98 POLY(1) (99,50) -0.6 0.5 EVN 51 98 POLY(1) (50,99) 0.6 0.5

*

• GAIN STAGE
• G1 98 30 POLY(2) (14,16) (17,18) 0 56.3E-6 56.3E-6 R1 30 98 5.43E8 CF 45 30 9E-12 D3 30 97 DX D4 51 30 DX

*

• OUTPUT STAGE
• M5 45 46 99 99 POX L=1E-6 W=1.08E-3 M6 45 47 50 50 NOX L=1E-6 W=1.61E-3 EG1 99 46 POLY(1) (98,30) 0.4644 1 EG2 47 50 POLY(1) (30,98) 0.4394 1

*

• MODELS
• ..MODEL POX PMOS (LEVEL=2,KP=10E-6,VTO=-0.328,LAMBDA=0.01,RD=0) ..MODEL NOX NMOS (LEVEL=2,KP=10E-6,VTO=+0.328,LAMBDA=0.01,RD=0) ..MODEL PIX PMOS (LEVEL=2,KP=10E-6,VTO=-0.328,LAMBDA=0.01,KF=2.5E-31,AF=1,TOX=100E-3) ..MODEL NIX NMOS (LEVEL=2,KP=10E-6,VTO=+0.328,LAMBDA=0.01,KF=2.5E-31,AF=1,TOX=100E-3) ..MODEL DX D(IS=1E-14,RS=5) ..ENDS AD8605

* *$

Helmut Sennewald wrote:

------------ SNIPped for brevity --------- Sorry about that; the bridge was connected incorrectly. I fixed that and get about 230mV in for 300uV out; a lot better but still rather puzzling. Here is the fix: Version 4 SHEET 1 1220 708 WIRE -256 128 -256 96 WIRE -256 240 -256 208 WIRE -160 -32 -160 -64 WIRE -128 48 -128 -176 WIRE -128 96 -256 96 WIRE -128 96 -128 48 WIRE -96 16 -96 -208 WIRE -96 48 -128 48 WIRE -96 240 -96 208 WIRE -96 256 -96 240 WIRE -96 448 -96 336 WIRE -80 16 -96 16 WIRE -64 240 -96 240 WIRE -64 320 -64 240 WIRE -32 208 -32 128 WIRE -16 208 -32 208 WIRE -16 240 -64 240 WIRE 0 -64 -160 -64 WIRE 0 16 0 -64 WIRE 0 464 0 416 WIRE 16 -208 -96 -208 WIRE 16 160 16 -208 WIRE 16 192 16 160 WIRE 32 16 0 16 WIRE 96 128 -32 128 WIRE 96 224 48 224 WIRE 96 224 96 128 WIRE 96 336 96 224 WIRE 96 416 80 416 WIRE 128 16 112 16 WIRE 128 32 128 16 WIRE 128 128 96 128 WIRE 128 128 128 112 WIRE 144 160 16 160 WIRE 144 240 144 160 WIRE 256 -176 -128 -176 WIRE 256 -144 256 -176 WIRE 256 -32 256 -64 WIRE 256 112 256 -32 WIRE 304 -64 304 -144 WIRE 304 0 304 -64 WIRE 304 192 304 160 WIRE 304 288 304 192 WIRE 320 -144 304 -144 WIRE 320 192 304 192 WIRE 336 -64 304 -64 WIRE 336 -32 256 -32 WIRE 336 288 304 288 WIRE 336 320 -64 320 WIRE 368 -80 368 -112 WIRE 368 240 144 240 WIRE 368 272 368 240 WIRE 448 -144 400 -144 WIRE 448 -48 400 -48 WIRE 448 -48 448 -144 WIRE 448 192 400 192 WIRE 448 304 400 304 WIRE 448 304 448 192 WIRE 480 -208 16 -208 WIRE 480 -112 368 -112 WIRE 480 -112 480 -208 WIRE 480 304 448 304 WIRE 480 304 480 144 WIRE 496 -96 496 -128 WIRE 512 -128 496 -128 WIRE 512 -48 448 -48 WIRE 512 144 480 144 WIRE 608 -128 592 -128 WIRE 608 -48 592 -48 WIRE 608 -48 608 -128 WIRE 608 48 608 -48 WIRE 608 144 592 144 WIRE 608 144 608 80 WIRE 608 176 608 144 WIRE 608 288 608 176 WIRE 624 48 608 48 WIRE 624 80 608 80 WIRE 656 -208 480 -208 WIRE 656 32 656 -208 WIRE 688 -48 608 -48 WIRE 688 176 608 176 WIRE 688 288 608 288 WIRE 784 -48 768 -48 WIRE 784 64 688 64 WIRE 784 64 784 -48 WIRE 800 288 768 288 WIRE 800 320 800 288 WIRE 816 -208 656 -208 WIRE 816 176 768 176 WIRE 816 176 816 -208 WIRE 832 -48 784 -48 WIRE 832 64 784 64 WIRE 928 -48 912 -48 WIRE 928 -32 928 -48 WIRE 928 64 912 64 WIRE 928 64 928 32 WIRE 928 176 928 64 WIRE 1008 -208 816 -208 WIRE 1008 96 1008 -208 FLAG -96 448 0 FLAG 16 256 0 FLAG 256 192 0 FLAG 1008 176 0 FLAG 0 544 0 FLAG -160 48 0 FLAG 368 -16 0 FLAG 368 336 0 FLAG 656 96 0 FLAG 800 320 0 FLAG 928 336 0 FLAG 496 -96 0 FLAG -256 240 0 SYMBOL res -112 32 R0 WINDOW 0 36 54 Left 0 WINDOW 3 30 79 Left 0 SYMATTR InstName TR1 SYMATTR Value 18.2K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res -112 112 R0 WINDOW 0 -34 45 Left 0 WINDOW 3 -44 74 Left 0 SYMATTR InstName R1 SYMATTR Value 549 SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res -112 240 R0 WINDOW 0 -41 37 Left 0 WINDOW 3 -55 70 Left 0 SYMATTR InstName PC SYMATTR Value {PC} SYMBOL Opamps\\\\opamp2 16 160 R0 WINDOW 3 -31 131 Left 0 SYMATTR Value AD8605 SYMATTR InstName U1 SYMBOL res 240 -160 R0 WINDOW 0 -64 62 Left 0 WINDOW 3 -99 24 Left 0 SYMATTR InstName RTAA SYMATTR Value {20K-TA} SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 240 96 R0 WINDOW 0 -67 68 Left 0 WINDOW 3 -56 29 Left 0 SYMATTR InstName RTAB SYMATTR Value {TA} SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL Misc\\\\battery 1008 80 R0 WINDOW 0 9 6 Left 0 WINDOW 3 11 -32 Left 0 SYMATTR InstName VBAT SYMATTR Value 5.0V SYMBOL res -16 448 R0 WINDOW 0 1 32 Right 0 WINDOW 3 -10 68 Right 0 SYMATTR InstName RM1 SYMATTR Value 1K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 80 320 R0 WINDOW 0 39 39 Left 0 WINDOW 3 34 70 Left 0 SYMATTR InstName TR2A SYMATTR Value 45.3K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res -16 432 R270 WINDOW 0 -20 88 VLeft 0 WINDOW 3 -46 94 VLeft 0 SYMATTR InstName TR2B SYMATTR Value {TR2} SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 128 0 R90 WINDOW 0 -20 39 VRight 0 WINDOW 3 46 38 VRight 0 SYMATTR InstName R92 SYMATTR Value 976K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 16 0 R90 WINDOW 0 -19 36 VRight 0 WINDOW 3 50 26 VRight 0 SYMATTR InstName R91 SYMATTR Value 5Meg SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res -144 64 R180 WINDOW 0 78 69 Right 0 WINDOW 3 93 33 Right 0 SYMATTR InstName R93 SYMATTR Value 0.001 SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 112 16 R0 SYMATTR InstName R90 SYMATTR Value 7.5K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL Opamps\\\\opamp2 368 -112 R0 WINDOW 3 13 115 Left 0 SYMATTR Value AD8605 SYMATTR InstName U2 SYMBOL Opamps\\\\opamp2 368 240 R0 WINDOW 3 28 95 Left 0 SYMATTR Value AD8605 SYMATTR InstName U3 SYMBOL res 416 -160 R90 WINDOW 0 -20 39 VRight 0 WINDOW 3 -21 -27 VRight 0 SYMATTR InstName R2 SYMATTR Value 100K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 416 176 R90 WINDOW 0 -11 10 VRight 0 WINDOW 3 -12 -49 VRight 0 SYMATTR InstName R3 SYMATTR Value 100K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 288 64 R0 WINDOW 0 36 51 Left 0 WINDOW 3 70 50 Left 0 SYMATTR InstName R4 SYMATTR Value 10K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 288 -16 R0 WINDOW 0 40 62 Left 0 WINDOW 3 77 63 Left 0 SYMATTR InstName R5 SYMATTR Value {250K-SENS} SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL Opamps\\\\opamp2 656 0 R0 WINDOW 3 20 104 Left 0 SYMATTR Value AD8605 SYMATTR InstName U4 SYMBOL res 608 128 R90 WINDOW 0 50 48 VRight 0 WINDOW 3 77 31 VRight 0 SYMATTR InstName R6 SYMATTR Value 20.0K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 608 -64 R90 WINDOW 0 50 48 VRight 0 WINDOW 3 77 31 VRight 0 SYMATTR InstName R7 SYMATTR Value 20.0K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 784 -64 R90 WINDOW 0 50 48 VRight 0 WINDOW 3 77 31 VRight 0 SYMATTR InstName R8 SYMATTR Value 100K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 784 160 R90 WINDOW 0 50 48 VRight 0 WINDOW 3 77 31 VRight 0 SYMATTR InstName R9 SYMATTR Value 200K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 784 272 R90 WINDOW 0 50 48 VRight 0 WINDOW 3 77 31 VRight 0 SYMATTR InstName R10 SYMATTR Value 100K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 928 48 R90 WINDOW 0 50 48 VRight 0 WINDOW 3 77 31 VRight 0 SYMATTR InstName R11 SYMATTR Value 47.0K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 928 -64 R90 WINDOW 0 50 48 VRight 0 WINDOW 3 77 47 VRight 0 SYMATTR InstName R12 SYMATTR Value 4.73K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL polcap 912 -32 R0 SYMATTR InstName C1 SYMATTR Value 10µF SYMBOL res 912 160 R0 SYMATTR InstName R13 SYMATTR Value 2.20k SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 912 240 R0 WINDOW 0 1 32 Right 0 WINDOW 3 -10 68 Right 0 SYMATTR InstName RM2 SYMATTR Value 1K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 608 -144 R90 WINDOW 0 -21 74 VRight 0 WINDOW 3 -20 7 VRight 0 SYMATTR InstName R14 SYMATTR Value 200K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL voltage -256 112 R0 SYMATTR InstName V1 SYMATTR Value 1.91V TEXT -200 -264 Left 0 !.INCLUDE D:\\\\SPICE\\\\AD8605.LIB TEXT -200 -232 Left 0 !.PARAM TA=8.00K TR2=1.25K PC=12.5K SENS=249K TEXT 200 -264 Left 0 !;.PRINT V(N005) V(N012) V(N013) V(N016) I(RM1) I(RM2) V(N004) V(N009) TEXT -200 -296 Left 0 !.OPTIONS OPTS NUMDGT=4 RELTOL=0.0001 ITL1=850 ITL6=850 NOPAGE NOMOD TEXT 80 464 Left 0 ;*5K pot TEXT 720 48 Left 0 ;N016 TEXT 416 -232 Left 0 !;op TEXT 104 272 Left 0 ;N005 TEXT 488 312 Left 0 ;N013 TEXT 456 -24 Left 0 ;N012 TEXT 488 -232 Left 0 !.noise V(N016) V1 dec 8 1E-1 1E3

Hello Robert,

Why is there no analysis command in your file?

What are the 230mV? Did you want type 230uV?

By the way, the noise density at the ouput V(N016) is about

230uV at 1/(2pi)Hz.

Your circuit looks really useless after your latest change. I talk about the connection of resistor RTAA to the input source. Now the circuit amplifies only a very small fraction of the input.

Still LTspice simulates it correctly. I never believe that you simulate with LTspice. You would get correct results with LTspice as I have got.

What simulator do you use?

Best Regards, Helmut

1) The file is from LTspice, and Simulate/Run gives a list of points in a window. Selecting inoise and/or onoise then results in a graph covering the frequency range specified in the .noise card. 2) Hope you got the whole file; i see only a few lines above. 3) 40 percent of the bridge drive is not a "very small fraction". 4) If you look carefully, you will note that the bridge is rather close to balance; a large input signal would thus be attenuated by the bridge. However, the SENSitivity is at max, near a gain of 21 and the last stage has a gain of about 5 for an approximate total gain of 105. I presume that you have guessed that TA (RtaA & RtaB) is a pot with an adjustable wiper. I did not find any way to put in a Bourns pot of a given description (one would like a PCB layout to conform to parts). ** In simulations for DC op points, i have been able to run the bridge balanced from ground to the 1.91V max and get satisfying results. Granted that at (or near) ground, the opamps act a little fussy, but that is to be expected.

"Robert Baer" schrieb im Newsbeitrag news:SU66e.3553$ snipped-for-privacy@newsread2.news.pas.earthlink.net...

Hello Robert, now it is clear for me what the misunderstanding between us and the simulation is.

I hadn't realized that the difference signal of your bridge circuit should be the input for your amplifier, because your first circuit was different. Now it's clear why we get the totally misleading high values for V(inoise). The source supplying the bridge resistors were specified as the input source. This bridge has a very high common mode supression and thus SPICE will calculate a very high V(inoise) to achieve the calculated V(onoise). The correction has been very simple. We have to add a dummy voltage source V2(0V) into one side of the bridge. After that change, V(inoise) is nearly 1/100 of V(onoise) as we ever had expected. Nevertheless, the values calculated by LTspice have been always mathematically correct.

Best Regards, Helmut

PS: I have beautyfied your schematic to give it a more professional look. Ok, I still left these many test resistors on the left side. Btw, there are examples for potentiometers in the LTspice user group on Yahoo. A potentiometer basically is a subcircuit with two resistors and one parameter(wiper position). The parameter is passed from the schematic to the subcircuit.

The LTspice schematic test.asc . Warning, maybe there are splitted lines which have to be manually corrected. News server often fold lines longer than e.g. 70 characters. Please keep both files in the same directory.

Version 4 SHEET 1 1392 708 WIRE -512 -144 -512 -208 WIRE -512 -32 -512 -64 WIRE -384 -208 -512 -208 WIRE -384 -80 -384 -208 WIRE -384 32 -384 0 WIRE -384 240 -384 112 WIRE -384 336 -384 240 WIRE -384 448 -384 416 WIRE -256 240 -384 240 WIRE -176 -112 -208 -112 WIRE -96 240 -176 240 WIRE -96 368 -96 240 WIRE -80 208 -80 112 WIRE -80 528 -80 496 WIRE -80 624 -80 608 WIRE -64 -112 -96 -112 WIRE -64 -64 -64 -112 WIRE -64 48 -64 16 WIRE -64 208 -80 208 WIRE -64 240 -96 240 WIRE -48 496 -80 496 WIRE -32 -112 -64 -112 WIRE -32 192 -32 160 WIRE -32 272 -32 256 WIRE -16 160 -32 160 WIRE 48 224 0 224 WIRE 80 -112 48 -112 WIRE 80 -64 80 -112 WIRE 80 112 -80 112 WIRE 80 112 80 16 WIRE 80 224 48 224 WIRE 80 224 80 112 WIRE 80 400 80 224 WIRE 80 496 32 496 WIRE 80 496 80 480 WIRE 224 -208 -384 -208 WIRE 224 -160 224 -208 WIRE 224 -48 224 -80 WIRE 224 -16 224 -48 WIRE 224 96 224 64 WIRE 384 -80 384 -208 WIRE 384 -16 384 -80 WIRE 384 96 384 64 WIRE 384 208 384 176 WIRE 384 336 384 208 WIRE 432 -208 384 -208 WIRE 432 -80 384 -80 WIRE 432 -48 224 -48 WIRE 432 208 384 208 WIRE 432 336 384 336 WIRE 432 368 -96 368 WIRE 464 -96 464 -128 WIRE 464 -16 464 -32 WIRE 464 320 464 288 WIRE 464 400 464 384 WIRE 480 -128 464 -128 WIRE 480 288 464 288 WIRE 576 -208 512 -208 WIRE 576 -64 496 -64 WIRE 576 -64 576 -208 WIRE 576 208 512 208 WIRE 576 352 496 352 WIRE 576 352 576 208 WIRE 608 -64 576 -64 WIRE 608 208 576 208 WIRE 624 -176 624 -208 WIRE 656 -208 624 -208 WIRE 656 -64 608 -64 WIRE 656 208 608 208 WIRE 768 -208 736 -208 WIRE 768 -64 736 -64 WIRE 768 -64 768 -208 WIRE 768 64 768 -64 WIRE 768 208 736 208 WIRE 768 208 768 96 WIRE 768 320 768 208 WIRE 784 64 768 64 WIRE 784 96 768 96 WIRE 816 48 816 16 WIRE 816 128 816 112 WIRE 816 208 768 208 WIRE 816 320 768 320 WIRE 848 -64 768 -64 WIRE 848 16 816 16 WIRE 928 208 896 208 WIRE 928 320 896 320 WIRE 928 368 928 320 WIRE 960 -64 928 -64 WIRE 960 80 848 80 WIRE 960 80 960 -64 WIRE 1008 -64 960 -64 WIRE 1088 80 960 80 WIRE 1088 80 1088 -32 WIRE 1120 -32 1088 -32 WIRE 1120 80 1088 80 WIRE 1232 -240 1168 -240 WIRE 1232 -224 1232 -240 WIRE 1232 -128 1232 -144 WIRE 1232 -32 1200 -32 WIRE 1232 -16 1232 -32 WIRE 1232 80 1200 80 WIRE 1232 80 1232 48 WIRE 1232 144 1232 80 WIRE 1232 256 1232 224 WIRE 1232 368 1232 336 WIRE 1296 80 1232 80 FLAG -384 448 0 FLAG -32 272 0 FLAG 224 96 0 FLAG 1232 -128 0 FLAG -80 624 0 FLAG -64 48 0 FLAG 464 -16 0 FLAG 464 400 0 FLAG 816 128 0 FLAG 928 368 0 FLAG 1232 368 0 FLAG 624 -176 0 FLAG -512 -32 0 FLAG 1008 -64 o4 IOPIN 1008 -64 Out FLAG 608 208 o3 FLAG 608 -64 o2 FLAG 48 224 o1 FLAG 1296 80 out IOPIN 1296 80 Out FLAG 1168 -240 vcc IOPIN 1168 -240 Out FLAG 928 208 vcc IOPIN 928 208 In FLAG -16 160 vcc IOPIN -16 160 In FLAG 480 288 vcc IOPIN 480 288 In FLAG 480 -128 vcc IOPIN 480 -128 In FLAG -208 -112 vcc IOPIN -208 -112 In FLAG 848 16 vcc IOPIN 848 16 In SYMBOL res -400 -96 R0 WINDOW 0 36 54 Left 0 WINDOW 3 30 79 Left 0 SYMATTR InstName TR1 SYMATTR Value 18.2K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res -400 16 R0 WINDOW 0 38 41 Left 0 WINDOW 3 38 76 Left 0 SYMATTR InstName R1 SYMATTR Value 549 SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res -400 320 R0 WINDOW 0 47 48 Left 0 WINDOW 3 37 79 Left 0 SYMATTR InstName PC SYMATTR Value {PC} SYMBOL Opamps\\\\opamp2 -32 160 R0 WINDOW 3 23 92 Left 0 SYMATTR Value AD8605 SYMATTR InstName U1 SYMBOL res 208 -176 R0 WINDOW 0 45 43 Left 0 WINDOW 3 37 92 Left 0 SYMATTR InstName RTAA SYMATTR Value {20K-TA} SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 208 -32 R0 WINDOW 0 42 74 Left 0 WINDOW 3 45 40 Left 0 SYMATTR InstName RTAB SYMATTR Value {TA} SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL Misc\\\\battery 1232 -240 R0 WINDOW 0 9 6 Left 0 WINDOW 3 33 84 Left 0 SYMATTR InstName VBAT SYMATTR Value 5.0V SYMBOL res -96 512 R0 WINDOW 0 1 32 Right 0 WINDOW 3 -10 68 Right 0 SYMATTR InstName RM1 SYMATTR Value 1K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 64 384 R0 WINDOW 0 39 39 Left 0 WINDOW 3 34 70 Left 0 SYMATTR InstName TR2A SYMATTR Value 45.3K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res -64 512 R270 WINDOW 0 55 80 VLeft 0 WINDOW 3 -19 80 VLeft 0 SYMATTR InstName TR2B SYMATTR Value {TR2} SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 64 -128 R90 WINDOW 0 -20 39 VRight 0 WINDOW 3 46 38 VRight 0 SYMATTR InstName R92 SYMATTR Value 976K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res -80 -128 R90 WINDOW 0 -19 36 VRight 0 WINDOW 3 50 26 VRight 0 SYMATTR InstName R91 SYMATTR Value 5Meg SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res -48 32 R180 WINDOW 0 -12 70 Right 0 WINDOW 3 -12 35 Right 0 SYMATTR InstName R93 SYMATTR Value 0.001 SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 64 -80 R0 SYMATTR InstName R90 SYMATTR Value 7.5K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL Opamps\\\\opamp2 464 -128 R0 WINDOW 3 17 95 Left 0 SYMATTR Value AD8605 SYMATTR InstName U2 SYMBOL Opamps\\\\opamp2 464 288 R0 WINDOW 3 26 95 Left 0 SYMATTR Value AD8605 SYMATTR InstName U3 SYMBOL res 528 -224 R90 WINDOW 0 -16 39 VRight 0 WINDOW 3 48 28 VRight 0 SYMATTR InstName R2 SYMATTR Value 100K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 528 192 R90 WINDOW 0 -17 30 VRight 0 WINDOW 3 48 16 VRight 0 SYMATTR InstName R3 SYMATTR Value 100K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 368 80 R0 WINDOW 0 33 46 Left 0 WINDOW 3 36 74 Left 0 SYMATTR InstName R4 SYMATTR Value 10K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 368 -32 R0 WINDOW 0 40 62 Left 0 WINDOW 3 41 90 Left 0 SYMATTR InstName R5 SYMATTR Value {250K-SENS} SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL Opamps\\\\opamp2 816 16 R0 WINDOW 3 26 94 Left 0 SYMATTR Value AD8605 SYMATTR InstName U4 SYMBOL res 752 192 R90 WINDOW 0 -23 46 VRight 0 WINDOW 3 53 31 VRight 0 SYMATTR InstName R6 SYMATTR Value 20.0K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 752 -80 R90 WINDOW 0 -17 46 VRight 0 WINDOW 3 53 31 VRight 0 SYMATTR InstName R7 SYMATTR Value 20.0K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 944 -80 R90 WINDOW 0 -24 44 VRight 0 WINDOW 3 49 34 VRight 0 SYMATTR InstName R8 SYMATTR Value 100K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 912 192 R90 WINDOW 0 -16 46 VRight 0 WINDOW 3 51 35 VRight 0 SYMATTR InstName R9 SYMATTR Value 200K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 912 304 R90 WINDOW 0 -18 40 VRight 0 WINDOW 3 51 31 VRight 0 SYMATTR InstName R10 SYMATTR Value 100K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 1216 64 R90 WINDOW 0 -20 44 VRight 0 WINDOW 3 51 33 VRight 0 SYMATTR InstName R11 SYMATTR Value 47.0K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 1216 -48 R90 WINDOW 0 -18 37 VRight 0 WINDOW 3 53 32 VRight 0 SYMATTR InstName R12 SYMATTR Value 4.73K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL polcap 1216 -16 R0 SYMATTR InstName C1 SYMATTR Value 10µF SYMBOL res 1216 128 R0 SYMATTR InstName R13 SYMATTR Value 2.20k SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 1216 240 R0 WINDOW 0 86 33 Right 0 WINDOW 3 70 70 Right 0 SYMATTR InstName RM2 SYMATTR Value 1K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL res 752 -224 R90 WINDOW 0 -19 36 VRight 0 WINDOW 3 44 32 VRight 0 SYMATTR InstName R14 SYMATTR Value 200K SYMATTR SpiceLine tol=1 pwr=0.1 SYMBOL voltage -512 -160 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 1.91V SYMBOL voltage -160 240 R90 WINDOW 0 -32 56 VBottom 0 WINDOW 3 35 85 VTop 0 WINDOW 123 35 38 VTop 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value 0 SYMATTR Value2 AC 1 TEXT -392 -392 Left 0 ;.INCLUDE D:\\\\SPICE\\\\AD8605.LIB TEXT -392 -360 Left 0 !.PARAM TA=8.00K TR2=1.25K PC=12.5K SENS=249K TEXT 96 488 Left 0 ;*5K pot TEXT -392 -328 Left 0 !;op TEXT -392 -544 Left 0 !.noise V(o4) V2 oct 50 1E-1 1E6 TEXT -392 -432 Left 0 !.include ad8605.cir TEXT -392 -472 Left 0 ;.ac dec 100 1 100k TEXT -392 -504 Left 0 ;.dc V1 1.9 1.92 1m TEXT -248 160 Left 0 ;INoise TEXT 992 -104 Left 0 ;ONoise TEXT -24 -544 Left 0 ;V2 is required for the analysis. TEXT -504 -232 Left 0 ;Bridge Circuit LINE Normal 336 160 160 160 LINE Normal 336 -256 336 160 LINE Normal -576 -256 336 -256 LINE Normal -576 16 -576 -256 LINE Normal -448 16 -576 16 LINE Normal -448 512 -448 16 LINE Normal -304 512 -448 512 LINE Normal -304 -176 -304 512 LINE Normal 160 -176 -304 -176 LINE Normal 160 160 160 -176 RECTANGLE Normal -160 304 -272 144 RECTANGLE Normal 1072 -16 976 -128

The model file AD8605.cir.

• AD8605 SPICE Macro-model
• Typical Values
• 05/02, Ver. 1.0
• SB, ADSiV apps

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• Copyright 2002 by Analog Devices

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• Refer to "README.DOC" file for License Statement. Use of this
• model indicates your acceptance of the terms and provisions in
• the License Statement.

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• Node Assignments
• noninverting input
• | inverting input
• | | positive supply
• | | | negative supply
• | | | | output
• | | | | |
• | | | | | ..SUBCKT AD8605 1 2 99 50 45

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• INPUT STAGE
• M1 14 7 8 8 PIX L=1E-6 W=1600E-6 M2 16 2 8 8 PIX L=1E-6 W=1600E-6 M3 17 7 10 10 NIX L=1E-6 W=1600E-6 M4 18 2 10 10 NIX L=1E-6 W=1600E-6 RC5 14 50 4E+3 RC6 16 50 4E+3 RC7 99 17 4E+3 RC8 99 18 4E+3 C1 14 16 0.6E-12 C2 17 18 0.6E-12 I1 99 8 100E-6 I2 10 50 100E-6 V1 99 9 0.3 V2 13 50 0.3 D1 8 9 DX D2 13 10 DX EOS 7 1 POLY(3) (22,98) (73,98) (81,98) 10E-6 1 1 1 IOS 1 2 0.05E-12

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• CMRR 100dB, POLE AT 4.5KHz
• ECM1 21 98 POLY(2) (1,98) (2,98) 0 0.5 0.5 CCM1 21 22 3.54E-10 RCM1 21 22 100E3 RCM2 22 98 1

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• PSRR=95dB, ZERO AT 534Hz
• EPSY 98 72 POLY(1) (99,50) 0 1 CPS3 72 73 5.30E-9 RPS3 72 73 56234 RPS4 73 98 1

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• VOLTAGE NOISE REFERENCE OF 8nV/rt(Hz)
• VN1 80 98 0 RN1 80 98 16.45E-3 HN 81 98 VN1 7 RN2 81 98 1

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• INTERNAL VOLTAGE REFERENCE
• EREF 98 0 POLY(2) (99,0) (50,0) 0 .5 .5 GSY 99 50 (99,50) 48E-6 EVP 97 98 POLY(1) (99,50) -0.6 0.5 EVN 51 98 POLY(1) (50,99) 0.6 0.5

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• GAIN STAGE
• G1 98 30 POLY(2) (14,16) (17,18) 0 56.3E-6 56.3E-6 R1 30 98 5.43E8 CF 45 30 9E-12 D3 30 97 DX D4 51 30 DX

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• OUTPUT STAGE
• M5 45 46 99 99 POX L=1E-6 W=1.08E-3 M6 45 47 50 50 NOX L=1E-6 W=1.61E-3 EG1 99 46 POLY(1) (98,30) 0.4644 1 EG2 47 50 POLY(1) (30,98) 0.4394 1

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• MODELS
• ..MODEL POX PMOS (LEVEL=2,KP=10E-6,VTO=-0.328,LAMBDA=0.01,RD=0) ..MODEL NOX NMOS (LEVEL=2,KP=10E-6,VTO=+0.328,LAMBDA=0.01,RD=0) ..MODEL PIX PMOS (LEVEL=2,KP=10E-6,VTO=-0.328,LAMBDA=0.01,KF=2.5E-31,AF=1,TOX=100E-3) ..MODEL NIX NMOS (LEVEL=2,KP=10E-6,VTO=+0.328,LAMBDA=0.01,KF=2.5E-31,AF=1,TOX=100E-3) ..MODEL DX D(IS=1E-14,RS=5) ..ENDS AD8605

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