What S/W will simulate a transmission line type pulse transformer?

[[email protected]]

I tried simulating a transmission line transformer (one end connected
in parallel, the other end in series) using "CircuitMaker 2000" and
"MultiSim 8", but apparently the models these programs use (even the
lossy line model) are not appropriate for this type of simulation.

I'm wondering, does anyone know of software that will realistically
simulate such transmission line based circuits in the time domain?
Thank you.

 

[John Popelish]

I tried simulating a transmission line transformer (one end connected
in parallel, the other end in series) using "CircuitMaker 2000" and
"MultiSim 8", but apparently the models these programs use (even the
lossy line model) are not appropriate for this type of simulation.

I'm wondering, does anyone know of software that will realistically
simulate such transmission line based circuits in the time domain?
Thank you.

I have been working up a spice model of a transmission line
transformer that approximates it with 16 inductances and 17
capacitances. It was meant to model a transformer wound through two
flat cable cores, so that the winding pair runs straight down the
slots, with the ends as far as possible from each other. It includes
the 120 mutual inductance coupling factors that model the reduction of
coupling efficiency as turns get further apart and both the normal
transmission line capacitance per length and the capacitance between 1
turn and the next of the pair. The responses have not been tested
against actual measurements, but they look quite reasonable, as long
as the phase shift per inductance segment is a small part of a cycle.

I selected the inductance and capacitance values to fit test data on a
particular example, but you can change them.

I built it for LTspice, free download at:
http://www.linear.com/company/software.jsp

If you would like to have a copy of this component model and its
symbol file, email me.

 

[John Larkin]

I have been working up a spice model of a transmission line
transformer that approximates it with 16 inductances and 17
capacitances. It was meant to model a transformer wound through two
flat cable cores, so that the winding pair runs straight down the
slots, with the ends as far as possible from each other. It includes
the 120 mutual inductance coupling factors that model the reduction of
coupling efficiency as turns get further apart and both the normal
transmission line capacitance per length and the capacitance between 1
turn and the next of the pair. The responses have not been tested
against actual measurements, but they look quite reasonable, as long
as the phase shift per inductance segment is a small part of a cycle.

I selected the inductance and capacitance values to fit test data on a
particular example, but you can change them.

I built it for LTspice, free download at:
http://www.linear.com/company/software.jsp

If you would like to have a copy of this component model and its
symbol file, email me.

A long string of L's and C's makes a good transmission line model, but
the number of sections explodes as a power of the delay/risetime
ratio. I've done lines with hundreds of sections.

Most Spice transmission line models contain a hidden isolation
transformer (you can apply DC between the 'shields' of opposite ends)
and aren't very realistic for things like transmission-line
transformers.

John

 

[Mike Engelhardt]

John,

Most Spice transmission line models contain a hidden
isolation transformer (you can apply DC between the
'shields' of opposite ends) and aren't very realistic
for things like transmission-line transformers.

In SPICE-speak, the transmission line device of SPICE
handles a single node. A length of coax has two nodes,
normal mode and common mode. To invert, you need to
model both modes. The classic example is in Larry
Nagel's PhD thesis(Berkeley 1975), but here's a
deck that will show how to do a transmission line
inverter in LTspice on the netlist level:

* transmission line inverter
T2 0 0 OUT 0 Td=50n Z0=75 ; center conductor
T1 IN 0 0 OUT Td=70n Z0=50 ; shield higher Z but faster
V1 IN 0 PULSE(0 1 0 1n 1n 10n) Rser=50
..tran 0 500n 0 1n
..end

The general case is that a cable has as many modes
as conductors including the shield. That the SPICE
transmission line device supplies only a single node
is an odd concept to be sure -- a cable with but a
single wire but controlled impedance. Just the same,
it's supper useful if you ground each end of one of
the sides. Then you can simulate the normal mode and
skip the common mode if it doesn't interest you.

--Mike

 

[John Larkin]

John,


In SPICE-speak, the transmission line device of SPICE
handles a single node. A length of coax has two nodes,
normal mode and common mode. To invert, you need to
model both modes.

This is a super-wideband inverter, in both Spice and real life:

(----------------)
in+ ----( coax )----(---------------)
in- ----(----------------)----( coax )------ out+
(---------------)------ out-

The Spice version is perfect. The real version has problems if IN- and
OUT- are both grounded (the whole thing becomes a short) and that
limits low-frequency response. Slipping a ferrite over it somewhere
helps the lf end a lot. The center crossover should be zero-length.
Done with a couple of hunks of hardline, it's very impressive.

John

 

[Mike Engelhardt]

John,

This is a super-wideband inverter, in both Spice and real
life:

(----------------)
in+ ----( coax )----(---------------)
in- ----(----------------)----( coax )------ out+
(---------------)------ out-

The Spice version is perfect. The real version has problems
if IN- and OUT- are both grounded (the whole thing becomes a
short) and that limits low-frequency response. Slipping a
ferrite over it somewhere helps the lf end a lot. The center
crossover should be zero-length. Done with a couple of hunks
of hardline, it's very impressive.

Interesting example. Thanks.

But it doesn't work very in SPICE if you dutifully model both
modes of each cable. Your circuit above requires four SPICE
transmission line elements. Yes, if you ignore two
propagation modes, it's perfect in SPICE but that is an
error in the application of SPICE. Below is an LTspice
schematic that illustrates perfect behavior from incorrect
analysis and the results from using 4 ideal propagation modes.

Regards,

--Mike

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