Low Pass Filter  Butterworth/Sallen-Key

V1 1 0 DC 0 AC 1

*** first-degree(linear) 

R9 1 out1  15.9k
C3 out1 0  1000p

*** third-degree(cubic)

R5 1 2  36.9k
R6 2 0  63.1k
X1 2 3 3  OPAMP1

R1 3 4  15.9k
R2 4 5  15.9k
C1 4 out3  1000p
C2 5 0  1000p
X2 5 6 out3  OPAMP1
R3 6 out3  5.85k
R4 6 0  10k

*** fiveth-degree

R7 1 7  61k
R8 7 0  39k
X3 7 8 8  OPAMP1

R11 8 9  15.9k
R12 9 10  15.9k
R13 11 12  1.52k
R14 11 0  10k
C11 9 12  1000p
C12 10 0  1000p
X4 10 11 12  OPAMP1

R21 12 13  15.9k
R22 13 14  15.9k
R23 15 out5  12.3k
R24 15 0  10k
C21 13 out5  1000p
C22 14 0  1000p
X5 14 15 out5  OPAMP1

.SUBCKT OPAMP1  1 2 3
R1 1 2  10Meg
E1 4 0 1 2  100k
E2 5 0 6 0  1
R2 4 6  1k
C1 6 0  1.5915u
R3 5 3  50
.ENDS OPAMP1

.AC DEC 100 100 1Meg

*#set units=degrees
*#destroy all
*#run
*#plot db(V(out1)) db(V(out3)) db(V(out5))
*#plot ph(V(out1)) ph(V(out3)) ph(V(out5))

.END