Version 4 SHEET 1 1792 1860 WIRE -1152 192 -1152 160 WIRE -1152 240 -1152 192 WIRE -1152 352 -1152 320 WIRE -1152 640 -1152 608 WIRE -1152 688 -1152 640 WIRE -1152 800 -1152 768 WIRE -1152 1280 -1152 1232 WIRE -1152 1680 -1152 1648 WIRE -1152 1728 -1152 1680 WIRE -1152 1840 -1152 1808 WIRE -1072 640 -1152 640 WIRE -1072 1680 -1152 1680 WIRE -1056 192 -1152 192 WIRE -1056 1232 -1152 1232 WIRE -832 192 -976 192 WIRE -832 640 -992 640 WIRE -832 1232 -976 1232 WIRE -832 1680 -992 1680 WIRE -800 384 -800 368 WIRE -800 480 -800 464 WIRE -800 1424 -800 1408 WIRE -800 1520 -800 1504 WIRE -768 640 -832 640 WIRE -768 1680 -832 1680 WIRE -752 192 -832 192 WIRE -752 1232 -832 1232 WIRE -288 192 -672 192 WIRE -288 368 -800 368 WIRE -288 368 -288 192 WIRE -288 640 -688 640 WIRE -288 640 -288 368 WIRE -272 1232 -672 1232 WIRE -272 1408 -800 1408 WIRE -272 1408 -272 1232 WIRE -256 368 -288 368 WIRE -240 1408 -272 1408 WIRE -80 1216 -80 1184 WIRE -80 1264 -80 1216 WIRE -80 1376 -80 1344 WIRE -80 1712 -80 1664 WIRE 0 1664 -80 1664 WIRE 16 1216 -80 1216 WIRE 240 1216 96 1216 WIRE 240 1664 80 1664 WIRE 272 1408 272 1392 WIRE 272 1504 272 1488 WIRE 304 1664 240 1664 WIRE 320 1216 240 1216 WIRE 816 1392 272 1392 WIRE 816 1664 384 1664 WIRE 816 1664 816 1392 WIRE 848 1392 816 1392 FLAG -1152 352 0 FLAG -832 192 in- FLAG -832 640 in+ FLAG -256 368 out IOPIN -256 368 Out FLAG -800 480 0 FLAG -1152 800 0 FLAG -1152 160 1 IOPIN -1152 160 In FLAG -1152 608 2 IOPIN -1152 608 In FLAG -832 1232 in_- FLAG -832 1680 in_+ FLAG -240 1408 out_ IOPIN -240 1408 Out FLAG -800 1520 0 FLAG -1152 1840 0 FLAG -1152 1648 2_ IOPIN -1152 1648 In FLAG -80 1376 0 FLAG 240 1216 in__- FLAG 240 1664 in__+ FLAG 848 1392 out__ IOPIN 848 1392 Out FLAG 272 1504 0 FLAG -80 1712 0 FLAG -80 1184 1__ IOPIN -80 1184 In FLAG -1152 1280 0 SYMBOL res -1072 208 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res -768 208 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R2 SYMATTR Value 10k SYMBOL res -1088 656 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R3 SYMATTR Value 10k SYMBOL res -784 656 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R4 SYMATTR Value 20k SYMBOL voltage -1152 224 R0 SYMATTR InstName V1 SYMATTR Value 0 SYMBOL voltage -1152 672 R0 SYMATTR InstName V2 SYMATTR Value 1 SYMBOL bv -800 368 R0 SYMATTR InstName B1 SYMATTR Value V=limit(-10, {GAIN}*V(in+,in-), 10) SYMBOL res -1072 1248 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R1_ SYMATTR Value 10k SYMBOL res -768 1248 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R2_ SYMATTR Value 10k SYMBOL res -1088 1696 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R3_ SYMATTR Value 10k SYMBOL voltage -1152 1712 R0 SYMATTR InstName V4 SYMATTR Value 1 SYMBOL bv -800 1408 R0 SYMATTR InstName B2 SYMATTR Value V=limit(-10, {GAIN}*V(in_+,in_-), 10) SYMBOL res 0 1232 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R1__ SYMATTR Value 10k SYMBOL res -16 1680 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R3__ SYMATTR Value 10k SYMBOL res 288 1680 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R4__ SYMATTR Value 10k SYMBOL voltage -80 1248 R0 SYMATTR InstName V5 SYMATTR Value 1 SYMBOL bv 272 1392 R0 SYMATTR InstName B3 SYMATTR Value V=limit(-10, {GAIN}*V(in__+,in__-), 10) TEXT -864 352 Left 0 ;in- TEXT -864 480 Left 0 ;in+ TEXT -744 312 Left 0 ;Amplifier\nVout=GAIN*V(in+,in-) TEXT -1160 24 Left 0 !.op TEXT -864 1408 Left 0 ;in- TEXT -864 1520 Left 0 ;in+ TEXT -744 1352 Left 0 ;Amplifier\nVout=GAIN*V(in+,in-) TEXT 208 1392 Left 0 ;in- TEXT 208 1504 Left 0 ;in+ TEXT 328 1336 Left 0 ;Amplifier\nVout=GAIN*V(in+,in-) TEXT -904 936 Left 0 ;With correctly connected feedback\nV(1)=0, R4=infinity\n \nVout = (R1+R2)/(R1+(R1+R2)/G)\n \nVout = 1.996V with GAIN=1000 TEXT 168 928 Left 0 ;With wrongly connected feedback\nV(2)=0, R2=infinity\n \nVout = (R3+R4)/(R3-(R3+R4)/G)\n \nVout = 2.004V with GAIN=1000 TEXT -1168 -16 Left 0 !.param GAIN=1000 TEXT -920 -72 Left 0 ;The general case with positive and negative feedback\n \nGAIN is the open loop gain of the amplifier.\n \nVout = ( V2*R4/(R3+R4) - V1*R2/(R1+R2) ) / ( 1/GAIN + R1/(R1+R2) - R3/(R3+R4) )\n \nVout = 3.97614V with R1, R2,R3=10k, R4=20k, G=1000 TEXT -72 192 Left 0 ;Why is the result of the .OP analysis nearly the same\nregardless on which pin the feedback is connected?\n \nThis example shows that there is a theoretical solution \nwith only feedback to the positive input of an amplifier.\nThis solution is only possible in the static calculation \nof an .OP analysis which is done in .OP, .DC, .AC and \n.NOISE analysis of SPICE, but not in a dynamic large\nsignal calculation of a .TRAN analysis. The output voltage \nwould run to the limits of the amplifier in the ladder case.\nHelmut Sennewald TEXT -464 832 VRight 0 ;C O R R E C T TEXT -248 784 Left 0 ;B TEXT -224 808 Left 0 ;A TEXT -200 832 Left 0 ;D TEXT -160 872 Left 0 ;I TEXT -136 896 Left 0 ;D TEXT -88 944 Left 0 ;A TEXT -112 920 Left 0 ;E LINE Normal -928 352 -928 192 LINE Normal -880 352 -928 352 LINE Normal -928 480 -880 480 LINE Normal -928 640 -928 480 LINE Normal -928 1408 -928 1232 LINE Normal -880 1408 -928 1408 LINE Normal -928 1520 -880 1520 LINE Normal -928 1680 -928 1520 LINE Normal 144 1392 144 1216 LINE Normal 192 1392 144 1392 LINE Normal 144 1504 192 1504 LINE Normal 144 1664 144 1504 LINE Normal -496 1072 -496 736 LINE Normal -432 1072 -432 736 LINE Normal -464 1104 -528 1040 LINE Normal -400 1040 -464 1104 LINE Normal -24 1040 -317 750 LINE Normal 16 990 -271 705 LINE Normal 16 1040 -64 1040 LINE Normal 16 944 16 1040 RECTANGLE Normal -336 544 -880 288 RECTANGLE Normal -304 1584 -880 1328 RECTANGLE Normal 784 1568 192 1312