{Sallen-Key active filters.
see IRE Transactions on Circuit Theory,
CT-2, pp 74-85 (March 1955).
These are numbered according to the charts
in the paper. Most of these use a non-
inverting controlled source, which is easy
to implement. A few, numbers 5, 7, 12, and
15 require an inverting high input impedance
amplifier, which generally requires more
circuitry.}

{circuit 1.
Vo/Vi = k/(s^2 + d*s +1)
lowpass}
r1 1 4
r2 4 5
c1 2 4
c2 5 3
U 2 3 5 3
f 1 3 2 3
p g21
end

{circuit 3.
Vo/Vi = k*s^2/(s^2 + d*s +1)
highpass}
c1 1 4
c2 4 5
r1 4 2
r2 5 3
U 2 3 5 3
f 1 3 2 3
p g21
end

{circuit 5.
Vo/Vi = k*s/(s^2 + d*s +1)
bandpass}
r1 1 4
r2 5 3
c1 4 2
c2 4 5
U 2 3 3 5
f 1 3 2 3
p g21
end

{circuit 7.
Vo/Vi = k*s/(s^2 + d*s +1)
bandpass}
c1 1 4
c2 5 3
r1 4 2
r2 4 5
U 2 3 3 5
f 1 3 2 3
p g21
end

{circuit 10.
Vo/Vi = k*(s + b)/(s^2 + d*s +1)
asymmetric bandpass}
r1 2 4
r2 1 5
c1 4 3
c2 5 4
U 2 3 5 3
f 1 3 2 3
p g21
end

{circuit 11.
Vo/Vi = k*(s + b)/(s^2 + d*s +1)
asymmetric bandpass}
r1 1 5
r2 2 4
c1 5 3
c2 4 5
U 2 3 5 3
f 1 3 2 3
p g21
end

{circuit 12.
Vo/Vi = k*(s + b)/(s^2 + d*s +1)
asymmetric bandpass}
r1 1 4
r2 1 5
c1 2 4
c2 4 5
U 2 3 3 5
f 1 3 2 3
p g21
end

{circuit 13.
Vo/Vi = k*s*(s + b)/(s^2 + d*s +1)
asymmetric bandpass}
r1 3 4
r2 4 5
c1 2 4
c2 1 5
U 2 3 5 3
f 1 3 2 3
p g21
end

{circuit 14.
Vo/Vi = k*s*(s + b)/(s^2 + d*s +1)
asymmetric bandpass}
r1 5 3
r2 2 4
c1 1 5
c2 4 5
U 2 3 5 3
f 1 3 2 3
p g21
end

{circuit 15.
Vo/Vi = k*s*(s + b)/(s^2 + d*s +1)
asymmetric bandpass}
r1 2 4
r2 4 5
c1 1 4
c2 1 5
U 2 3 3 5
f 1 3 2 3
p g21
end

{circuit 16.
Vo/Vi = k*(s^2 + b*s +1)/(s^2 + d*s +1)
biquad}
r1 2 4
r2 1 5
c1 1 4
c2 4 5
U 2 3 5 3
f 1 3 2 3
p g21
end

{circuit 17.
Vo/Vi = k*(s^2 + b*s +1)/(s^2 + d*s +1)
biquad}
r1 1 4
r2 4 5
c1 2 4
c2 1 5
U 2 3 5 3
f 1 3 2 3
p g21
end

{circuit 18.
Vo/Vi = k*(s^2 +1)/(s^2 + d*s +1)
biquad}
{note twin tee has fixed proportions
produced by repeated symbolic values.
the result here has a common uncancelled factor in the numerator
and the denominator}
r1 1 4
r1 4 5
r1 6 2
r1 6 2
c1 1 6
c1 6 5
c1 4 2
c1 4 2
U 2 3 5 3
f 1 3 2 3
p g21
end


{examples to show parameter equivalences:}
z11 1 3
z22 2 4
rm12 3 5 6 7
rm21 4 6 5 7
f 1 7 2 7
end

y11 1 3
y22 2 4
gm21 2 4 1 3
gm12 1 3 2 4
gx 3 4
f 1 3 2 4
end

y11 1 3
y22 2 3
gm21 2 3 1 3
gm12 1 3 2 3
f 1 3 2 3
end

{deboo gyrator examples}
r1 4 7
r1 3 4
r1 5 6
r1 3 6
g1 1 3
g1 1 2
g1 5 2
o 3 7 1 4
o 5 7 2 6
f 1 7 2 7
p z11 p  z12 p z21 p z22
p y11
p y12
p y21
p y22
end

c1 1 7
c2 2 7
r1 4 7
r1 3 4
r1 5 6
r1 3 6
g1 1 3
g1 1 2
g1 5 2
o 3 7 1 4
o 5 7 2 6
f 1 7 2 7
p z11
p  z22
end

{compare to native gyrator}
gy 1 7 2 7
f 1 7 2 7
p z11 p z12 p z21 p z22
p y11
p y12
p y21
p y22
end


c1 1 7
c2 2 7
gy 1 7 2 7
f 1 7 2 7
p z11 p z22
end

{examples to show ambiguity due to the nullor model of opamps}
{ideal opamp, positive feedback}
opamp 2 0 3 0
rin 1 3
rf 2 3
f 1 0 2 0
p g21
end

{ideal opamp, negative feedback}
opamp 2 0 0 3
rin 1 3
rf 2 3
f 1 0 2 0
p g21
end

{vcvs, positive feedback}
uvcvs 2 0 3 0
rin 1 3
rf 2 3
f 1 0 2 0
p g21
end

{vcvs, negative feedback}
uvcvs 2 0 0 3
rin 1 3
rf 2 3
f 1 0 2 0
p g21
end

{vcis, negative feedback}
gmvcis 2 0 3 0
rin 1 3
rf 2 3
f 1 0 2 0
p g21
end

{vcis, positive feedback}
gmvcis 2 0 0 3
rin 1 3
rf 2 3
f 1 0 2 0
p g21
end


{example demonstrating numeric value substitution}
{from tuttle, v.1,1958, pp343-344}
f 1 2 3 4
p z11
c1 1 3 v 78.56
c2 3 4 v 11.42
c3 4 2 v 1.111
r1 3 4 v 0.0268
r2 4 2 v 0.03446
end

f 1 2 3 4
p z11
c1 1 3 v 78.56
c2 3 4 {v 11.42}
c3 4 2 v 1.111
r1 3 4 v 0.0268
r2 4 2 v 0.03446
end

f 1 2 3 4
p z11
c1 1 3 {v 78.56}
c2 3 4 {v 11.42}
c3 4 2 {v 1.111}
r1 3 4 {v 0.0268}
r2 4 2 {v 0.03446}
end
