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Improve S-parameter example: change node names to make plot clearer, 

add port impedance parameters to subcircuit and simply string parameter.
This commit is contained in:
Giles Atkinson 2026-03-15 18:43:11 +00:00
parent 499c1d3dca
commit fe8193cdfb
1 changed files with 15 additions and 14 deletions
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29
examples/sp/file.cir
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@ -11,10 +11,10 @@ Example circuit to read a Touchstone-format parameter file.
* Original circuit for SP analysis
VP2 _net0 0 dc 0 ac 0.316228 SIN(0 0.316228 1G) portnum 2 z0 50
VP2 filter_out 0 dc 0 ac 0.316228 SIN(0 0.316228 1G) portnum 2 z0 50
VP1 _net1 0 dc 0 ac 0.316228 SIN(0 0.316228 1G) portnum 1 z0 50
C1 _net2 _net1 4.7P
C5 _net3 _net0 4.7P
C5 _net3 filter_out 4.7P
C3 _net3 _net2 1P
C4 _net3 0 15P
C2 0 _net2 15P
@ -27,9 +27,8 @@ L1 0 _net2 66N
VP3 net1 0 dc 0 ac 0.316228 ; Same as VP1 but that must not be loaded.
ri net1 sin 50
.param in_file="137MHz_BPF.s2p"
X1 sin sout 0 s2p_generic touchstone=in_file
ro sout 0 50
X1 sin sp_model_out 0 s2p_generic touchstone="137MHz_BPF.s2p"
ro sp_model_out 0 50
* Control section, run simulations.
@ -45,20 +44,22 @@ wrs2p new_137MHz_BPF.s2p
alter vp2 ac = 0
AC LIN 71 107MEG 167MEG
set xbrushwidth=2
plot group_delay(_net0) sp1.Group_Delay group_delay(sout)
plot db(_net0) cph(_net0) db(sout) cph(sout)
plot group_delay(filter_out) sp1.Group_Delay group_delay(sp_model_out)
plot db(filter_out) cph(filter_out) db(sp_model_out) cph(sp_model_out)
.endc
* Subcircuit for SP behavioral device
* The touchstone file has:
* HZ S RI R 50
* Z1 = 50 Z2 = 50
* so default impedences may be used with it.
.SUBCKT s2p_generic 1 2 3 touchstone={touchstone}
.SUBCKT s2p_generic 1 2 3 touchstone="device.sp2" z1=50 z2=50
* Pin 3 is the reference plane (usually it should be connected to GND)
* HZ S RI R 50
* Z1 = 50 Z2 = 50
R1N 1 100 -5.000000e+01
R1P 100 101 100.000000
R2N 2 200 -5.000000e+01
R2P 200 201 100.000000
R1N 1 100 {-z1}
R1P 100 101 {2*z1}
R2N 2 200 {-z2}
R2P 200 201 {2*z2}
* S11 FREQ R_I
A0101 %vd 100 3 %vd 101 102 m_a0101