3nd order state variable LPF (fc=754.5Hz)
* Designed by Hosoda Takayuki <lyuka@finetune.co.jp>

.WIDTH OUT=80
.OPTIONS NOPAGE RELTOL=1e-4 LIMPTS=20001
.OP
.TRAN 10u 10m 10u 10u
.AC DEC 100 10 100K

* simple ideal opamp
.SUBCKT OPAMP 1  2  3  4  5
E1  5   0   1   2   1MEG
R1      1   2   1e16
R2  3   4   30K
.ENDS
 
Vdd	1	0	15
Vss	2	0	-15
Vin	3	0	DC	0	AC	1
+PULSE	0	1	0	0	0	5e-3	10e-3

* Note. 
* R2 = R5 = R, C1 = C2 = C3 = C, 1/(RC) = w, R7 = R8
* R3 = R / c , R4 = R / b , R6 = R / a , R2 / R1 = h
* T(s)=h * w^3 / (s^3 + a * s^2 w + b * s * w^2 + c * w^3)
*
* a = 2.0, b = 2.0, c = 1.0, h = 1.0 // for Butterworth
* a = 3.0, b = 3.488, c = 1.5, h = 1
*
R1	3	4	10K
R2	9	4	10K
C1	5	4	10n
X1	0	4	1	2	5	OPAMP

R3	5	6	15K
R4	11	6	4.3K
C2	7	6	10n
X2	0	6	1	2	7	OPAMP

R5	7	8	15K
R6	9	8	5K
C3	9	8	10n
X3	0	8	1	2	9	OPAMP

R7	9	10	10K
R8	11	10	10K
X4	0	10	1	2	11	OPAMP

.PRINT TRAN V(3) V(9) (V(3)+V(9))
.PRINT AC VdB(9) VP(9)
.END