Version 4
SHEET 1 880 776
WIRE 208 -96 208 -128
WIRE -80 16 -112 16
WIRE 48 16 0 16
WIRE 80 16 48 16
WIRE 192 16 160 16
WIRE 208 16 208 -16
WIRE 208 16 192 16
WIRE 272 16 208 16
WIRE 320 16 272 16
WIRE 416 16 400 16
WIRE -112 64 -112 16
WIRE 48 128 48 16
WIRE 192 128 48 128
WIRE 416 144 416 16
WIRE 416 144 256 144
WIRE 480 144 416 144
WIRE 528 144 480 144
WIRE 192 160 160 160
WIRE -112 192 -112 144
WIRE 160 192 160 160
FLAG 160 192 0
FLAG 208 -128 0
FLAG -112 192 0
FLAG 528 144 out
FLAG 192 16 M
DATAFLAG 480 144 "round($*1k)/1k"
DATAFLAG 272 16 "round($*2k)/1k"
SYMBOL Opamps\\opamp 224 80 R0
SYMATTR InstName U1
SYMATTR SpiceLine Aol=1000K
SYMBOL Misc\\EuropeanResistor 304 32 R270
WINDOW 0 27 56 VTop 2
WINDOW 3 5 56 VBottom 2
SYMATTR InstName R2
SYMATTR Value 4k
SYMBOL Misc\\EuropeanResistor 64 32 R270
WINDOW 0 27 56 VTop 2
WINDOW 3 5 56 VBottom 2
SYMATTR InstName R1
SYMATTR Value 2k
SYMBOL Misc\\EuropeanResistor 192 -112 R0
SYMATTR InstName R3
SYMATTR Value 1k
SYMBOL voltage -112 48 R0
SYMATTR InstName V1
SYMATTR Value 1
SYMBOL Misc\\EuropeanResistor -96 32 R270
WINDOW 0 27 56 VTop 2
WINDOW 3 5 56 VBottom 2
SYMATTR InstName R4
SYMATTR Value 1k
TEXT -128 272 Left 2 !.op
TEXT -128 312 Left 2 !.lib opamp.sub
TEXT -128 368 Left 2 ;Herleitung über Stromsumme am mittleren Knoten M.\n \nUm = -I1*R1\n \nI1 + I2 + I3 = 0\n \nI1 +(Ua-Um)/R2 +(0-Um)/R3= 0\n \nI1 +I1*R1/R2 +I1*R1/R3 = -Ua/R2\n \nUa = -I1*(R2 +R1 +R1*R2/R3)\n \nUa = -I1*(R1 +R2 +R1*R2/R3)\n \n\nRf = R1 +R2 +R1*R2/R3