AoE x-Chapters, 4x.26, MOSFET current source, nodal analysis

[Winfield Hill]

Chris Jones wrote...

I guess I might have a rather unusual idea of what a schematic is, and
this might be what causes me to take issue with what you said. To me,
a schematic ought to be something that, when simulated (by some ideal
simulator!), applying Kirchoff's laws, Ohm's law, i=C.dv/dt and so on,
would sufficiently accurately predict the behavior of the real system.

To me, if the predictions are wrong, then I blame the schematic as
being an inaccurate representation of the system, rather than blaming
the equations used to simulate the behaviour of the schematic.

Yes, I agree in that, for example, if the build documentation
schematic showed e.g., a resistor and a MOSFET, the simulation
schematic should show the resistor's inductance or capacitance,
as needed, and the MOSFET's Ciss, gm, and other aspects. But
things get more painful when the part is say a high-performance
op-amp, and you don't know what's in the manufacturer's model.


--
Thanks,
- Win

 

On Wed, 14 Aug 2019 22:00:44 +1000, Chris Jones
<lugnut808@spam.yahoo.com> wrote:

On 13/08/2019 00:02, Phil Hobbs wrote:
On 8/12/19 9:11 AM, Chris Jones wrote:
On 10/08/2019 17:05, Phil Hobbs wrote:
On 8/9/19 4:50 PM, Winfield Hill wrote:
Here's a new section I'm hoping to complete, so it can be added to
the x-Chapter book before it goes to the printer in a few weeks.
Please look it over, but don't be too harsh, about its lack of
mathematical vigor.  It's closer to our usual back-of-the envelope
approach to calculations. Fixes for errors, suggestions for
clarification, improved accuracy, and comments welcome.

https://www.dropbox.com/s/7zl3yi789idg3s8/4x.26_Loop%20%26%20Nodal%20Analysis.pdf?dl=1



Nice.  I like your making a virtue out of a necessity (hand-drawn
figures).

One point that might be worth a footnote is that Kirchhoff's laws are a
low-frequency approximation, applicable only when radiation and
self-capacitance are negligible.

If your schematic is really complete, then I think that the laws apply
usefully, at least until the point where radiation is efficient. I am
assuming here that current through parasitic capacitances is counted
just as much as if it were a current flowing through a terminal of an
intentional capacitor. If, in your schematic and arithmetic, you leave
out things like the inductance and self-capacitance of wires, (and in
difficult cases, even the distributed capacitance at different points
along the inductance of wires), then of course the result of applying
Kirchoff's laws to the (incomplete) schematic won't predict the
behaviour of the actual construction. I suspect that radiation could
also be modelled in a way that allows Kirchoff's laws to be applied but
that the resulting schematic would be too complicated.

Nope. Transmission lines at the schematic level are non-local, i.e. you
can't write a system of ODEs to describe a circuit with transmission
lines or significant radiation. Kirchhoff's laws are derived from
Maxwell's equations in the limit of low frequency (or alternatively, of
small size for a fixed frequency).
I would say that that a wire on a schematic is not a valid
representation of a transmission line, and if necessary I would
approximate a transmission line as a ladder of (ideally infinitely) many
series inductors and shunt capacitors. Of course very many components
are required for this to be reasonably accurate.

The number of LCs goes as the square of Td/Tr. Gets ugly quick. And
the step response rings.

LT Spice has two transmission line models that seem to work well. I
use them all the time.

 

[Kevin Aylward]

"Phil Hobbs" wrote in message
news:eae0dac9-c6fe-5300-719c-63f69bfc347f@electrooptical.net...

Hmm Phil, to put this in my own words... and please correct me if I'm
wrong..
or I'm only part right. I think a limitation of K's laws is that they
treat V and I as instantaneously the same everywhere.

George H.
(every theory is an approximation at some level)

Everywhere on a given circuit node or loop, right. Anything with
transmission-line behaviour can't be modelled as an ODE--the fields

Not really.... An ODE (Ordinary Differential Equation) is pretty much any
differential equation of one variable, in contrast to a Partial Differential
Equation. Once the length of a line is fixed its usual partial differential
equations become ODE.

What you probably mean is that an ideal transmission line is a pure delay.
This means an exp(-tau.S) transfer function, which is not a rational
function of S.

Spice has to do extra stuff, as in convolution, to handle TLines. It slows
it down a tad...

inside the T-line can be modelled with PDEs (Maxwell), but circuits are
all ODEs. The T-line has invisible internal state, so its circuit
behaviour is nonlocal.

Not really....

"Non local" pretty much universally means FTL (faster than the speed of
light). A transmission line is most certainly local.

What you probably mean is that a transmission line requires spice to do some
special stuff, as above.

-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

 

[whit3rd]

On Monday, August 12, 2019 at 12:25:12 PM UTC-7, Phil Hobbs wrote:

transmission-line behaviour can't be modelled as an ODE--the fields
inside the T-line can be modelled with PDEs (Maxwell), but circuits are
all ODEs. The T-line has invisible internal state, so its circuit
behaviour is nonlocal.

If Spice converged much faster, the transmission line could be a few
hundred series inductors and a few hundred parallel capacitors...
the practical hardware (a spool of good coax cable) is just 'way cheaper
to operate than an accurate model is.

 

[Phil Hobbs]

On 8/14/19 4:42 PM, Kevin Aylward wrote:

"Phil Hobbs"  wrote in message
news:eae0dac9-c6fe-5300-719c-63f69bfc347f@electrooptical.net...


Hmm Phil, to put this in my own words... and please correct me if I'm
wrong..
or I'm only part right.  I think a limitation of K's laws is that they
treat V and I as instantaneously the same everywhere.

George H.
(every theory is an approximation at some level)

Everywhere on a given circuit node or loop, right.  Anything with
transmission-line behaviour can't be modelled as an ODE--the fields

Not really.... An ODE (Ordinary Differential Equation) is pretty much
any differential equation of one variable, in contrast to a Partial
Differential Equation. Once the length of a line is fixed its usual
partial differential equations become ODE.

Nope. ODEs don't have memory, T-lines do. (At least from a circuits POV.)

What you probably mean is that an ideal transmission line is a pure
delay. This means an exp(-tau.S) transfer function, which is not a
rational function of S.

Kirchoff's laws do not apply to transmission lines. Current disappears
into one end and emerges from the other end sometime later. The
currents into the circuit nodes don't sum to zero, and neither do the
voltages around loops.

Spice has to do extra stuff, as in convolution, to handle TLines. It
slows it down a tad...

As I said, the approximation can often be patched up by hand like that.

inside the T-line can be modelled with PDEs (Maxwell), but circuits are
all ODEs.  The T-line has invisible internal state, so its circuit
behaviour is nonlocal.

Not really....

"Non local" pretty much universally means FTL (faster than the speed of
light).

Nope. It means that the governing equations require information from
more than one space-time point. All differential equations are local.
Nonlocal systems need integral equations.

A transmission line is most certainly local.

Nope, not from a circuits point of view. To find out what's going to
come out at time t, you have to know the what went in at time t-tau.

What you probably mean is that a transmission line requires spice to do
some special stuff, as above.

Nope. I wasn't talking about SPICE at all.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

On Thu, 15 Aug 2019 11:17:35 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 8/14/19 4:42 PM, Kevin Aylward wrote:
"Phil Hobbs"  wrote in message
news:eae0dac9-c6fe-5300-719c-63f69bfc347f@electrooptical.net...


Hmm Phil, to put this in my own words... and please correct me if I'm
wrong..
or I'm only part right.  I think a limitation of K's laws is that they
treat V and I as instantaneously the same everywhere.

George H.
(every theory is an approximation at some level)

Everywhere on a given circuit node or loop, right.  Anything with
transmission-line behaviour can't be modelled as an ODE--the fields

Not really.... An ODE (Ordinary Differential Equation) is pretty much
any differential equation of one variable, in contrast to a Partial
Differential Equation. Once the length of a line is fixed its usual
partial differential equations become ODE.

Nope. ODEs don't have memory, T-lines do. (At least from a circuits POV.)


What you probably mean is that an ideal transmission line is a pure
delay. This means an exp(-tau.S) transfer function, which is not a
rational function of S.

Kirchoff's laws do not apply to transmission lines. Current disappears
into one end and emerges from the other end sometime later. The
currents into the circuit nodes don't sum to zero, and neither do the
voltages around loops.

The LT Spice tline part acts as if it has an ideal DC-true 1:1
transformer inside. The ends can be at radically different common-mode
voltages and it works fine.

That avoids dealing with the em effects of the "shield". Modeling a
twisted pair takes three tlines.

Spice has to do extra stuff, as in convolution, to handle TLines. It
slows it down a tad...

I've wondered how the tline is implemented inside, and how it relates
to the current time step size.

 

[Phil Hobbs]

On 8/14/19 8:00 AM, Chris Jones wrote:

On 13/08/2019 00:02, Phil Hobbs wrote:
On 8/12/19 9:11 AM, Chris Jones wrote:
On 10/08/2019 17:05, Phil Hobbs wrote:
On 8/9/19 4:50 PM, Winfield Hill wrote:
Here's a new section I'm hoping to complete, so it can be
added to the x-Chapter book before it goes to the printer in
a few weeks. Please look it over, but don't be too harsh,
about its lack of mathematical vigor. It's closer to our
usual back-of-the envelope approach to calculations. Fixes
for errors, suggestions for clarification, improved accuracy,
and comments welcome.

https://www.dropbox.com/s/7zl3yi789idg3s8/4x.26_Loop%20%26%20Nodal%20Analysis.pdf?dl=1





Nice. I like your making a virtue out of a necessity
(hand-drawn figures).

One point that might be worth a footnote is that Kirchhoff's
laws are a low-frequency approximation, applicable only when
radiation and self-capacitance are negligible.

If your schematic is really complete, then I think that the laws
apply usefully, at least until the point where radiation is
efficient. I am assuming here that current through parasitic
capacitances is counted just as much as if it were a current
flowing through a terminal of an intentional capacitor. If, in
your schematic and arithmetic, you leave out things like the
inductance and self-capacitance of wires, (and in difficult
cases, even the distributed capacitance at different points along
the inductance of wires), then of course the result of applying
Kirchoff's laws to the (incomplete) schematic won't predict the
behaviour of the actual construction. I suspect that radiation
could also be modelled in a way that allows Kirchoff's laws to be
applied but that the resulting schematic would be too
complicated.

Nope. Transmission lines at the schematic level are non-local,
i.e. you can't write a system of ODEs to describe a circuit with
transmission lines or significant radiation. Kirchhoff's laws are
derived from Maxwell's equations in the limit of low frequency (or
alternatively, of small size for a fixed frequency).
I would say that that a wire on a schematic is not a valid
representation of a transmission line, and if necessary I would
approximate a transmission line as a ladder of (ideally infinitely)
many series inductors and shunt capacitors. Of course very many
components are required for this to be reasonably accurate.

At frequencies where the number of required components is excessive,
I would then say that a schematic is not a good way to describe the
physical system.
And if you have to model the circuit "in a way that allows
Kirchhoff's laws to be applied", you've implicitly admitted that
they don't apply to the actual circuit.
If by actual circuit we mean the physical object, then really I only
expect Maxwell's equations to describe it, and I'm not very good at
solving those. In a completely general sense I'm not even sure how
one would try to apply Kirchoff's laws to an arbitrary three
dimensional piece of electronics.

Don't get me wrong--K's equations are useful and all, but they
have limits. Being a physicist, I fully recognize the usefulness
of sleazy approximations, but you have to remember that that's what
they are, or you'll get snookered.
Agreed.

I guess I might have a rather unusual idea of what a schematic is,
and this might be what causes me to take issue with what you said. To
me, a schematic ought to be something that, when simulated (by some
ideal simulator!), applying Kirchoff's laws, Ohm's law, i=C.dv/dt and
so on, would sufficiently accurately predict the behavoiur of the
real system.

To me, if the predictions are wrong, then I blame the schematic as
being an inaccurate representation of the system, rather than blaming
the equations used to simulate the behaviour of the schematic.
Perhaps my philosophy on this topic comes from having had the job of
making a schematic (sometimes pulling in netlists from field solvers)
in order to simulate my design as implemented in a physical product.
There was an expectation that I would use a circuit simulator
provided to me, that did try to apply Kirchoff's laws (though not
perfectly in the case of KCL). I did at least have the luxury that
the physical dimensions of the system were a tiny fraction of a
wavelength.

Well, you're kind of using a private language there, as you say.


Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Tim Williams]

"Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message
news:qj3t2i$941$1@dont-email.me...

Nope. ODEs don't have memory, T-lines do. (At least from a circuits POV.)

Great. Now I have to go buy 20GB of SRAM!

Kirchoff's laws do not apply to transmission lines. Current disappears
into one end and emerges from the other end sometime later. The currents
into the circuit nodes don't sum to zero, and neither do the voltages
around loops.

So ports.....don't exist?

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[Steve Wilson]

Winfield Hill <winfieldhill@yahoo.com> wrote:

tabbypurr@gmail.com wrote...

Really it's the sim that's wrong, but you can tackle
its shortcomings by adding in parts to the sim's input so it sims more
features of the real circuit.

LTSpice lets you add parasitic aspects to basic parts,
like resistors, but these are hidden on the schematic,
so you have no idea whether the modeller made additions,
or whether he made the right ones. I prefer seeing a
SPICE schematic, with the parasitic parts explicitly
showing, so you know what was taken care of, and how.
To my mind, these aspects are up to the engineering
doing the SPICE schematic drafting, and not up to the
SPICE program. The LTSpice approach is bad, not good.
So I disagree, it's not the sim that's wrong.

Where it is important, I add the parasitics externally.

 

[Winfield Hill]

tabbypurr@gmail.com wrote...

Really it's the sim that's wrong, but you can tackle
its shortcomings by adding in parts to the sim's input
so it sims more features of the real circuit.

LTSpice lets you add parasitic aspects to basic parts,
like resistors, but these are hidden on the schematic,
so you have no idea whether the modeller made additions,
or whether he made the right ones. I prefer seeing a
SPICE schematic, with the parasitic parts explicitly
showing, so you know what was taken care of, and how.
To my mind, these aspects are up to the engineering
doing the SPICE schematic drafting, and not up to the
SPICE program. The LTSpice approach is bad, not good.
So I disagree, it's not the sim that's wrong.


--
Thanks,
- Win

 

[Phil Hobbs]

On 8/15/19 2:56 PM, Kevin Aylward wrote:

"Phil Hobbs"  wrote in message news:qj3t2i$941$1@dont-email.me...



What you probably mean is that an ideal transmission line is a pure
delay. This means an exp(-tau.S) transfer function, which is not a
rational function of S.

Kirchoff's laws do not apply to transmission lines.  Current
disappears into one end and emerges from the other end sometime
later.  The currents into the circuit nodes don't sum to zero, and
neither do the voltages around loops.

Which is what you expect as transmission lines correctly account for the
fact the FTL is impossible, that is, it shows that signals take a finite
time to propagate from A to B, thus transmissions lines behave
*locally*. Period.

In your dreams. Nonlocality doesn't imply FTL, whatever your Sunday
supplement version of quantum field theory might tell you. The
Boltzmann transport equation is also nonlocal, and that applies to your
coffee cup. YCLIU.

In contrast to Kirchoff's Laws. Those laws assume that all voltages and
currents are instantaneously connected. They ignore propagation delay
effects, thus Kirchoff's Laws are non-local. Period.

You're inventing a private language to avoid being wrong in public.
G'wan, Kevin, you're just hitting your stride, man!

Thus... you have the definitions backwards.

Spice has to do extra stuff, as in convolution, to handle TLines. It
slows it down a tad...

As I said, the approximation can often be patched up by hand like that.


inside the T-line can be modelled with PDEs (Maxwell), but circuits are
all ODEs.  The T-line has invisible internal state, so its circuit
behaviour is nonlocal.

Not really....

"Non local" pretty much universally means FTL (faster than the speed
of light).

Nope.  It means that the governing equations require information from
more than one space-time point.  All differential equations are local.
Nonlocal systems need integral equations.

We, apparently, have different definitions of locality.

https://en.wikipedia.org/wiki/Principle_of_locality

https://en.wikipedia.org/wiki/Faster-than-light_neutrino_anomaly

Thus, to date the only accepted apparent FTL, i.e. non-local behaviour
that I am aware of, is the statistical correlations between entangled
particles, which cannot be used to transfer information at FTL

It is inherent in transmission lines that there is delay for transfer of
information, which is *the* fundamental property of the definition of
locality in physics, so it is indeed interesting that there are those
that claim the opposite.

No, that's a particular definition in relativistic quantum field theory.
We're talking classical E&M here.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Phil Hobbs]

On 8/15/19 2:39 PM, Tim Williams wrote:

"Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message
news:qj3t2i$941$1@dont-email.me...

Nope. ODEs don't have memory, T-lines do.  (At least from a circuits
POV.)


Great.  Now I have to go buy 20GB of SRAM!


Kirchoff's laws do not apply to transmission lines.  Current
disappears into one end and emerges from the other end sometime
later.  The currents into the circuit nodes don't sum to zero, and
neither do the voltages around loops.

So ports.....don't exist?

Tim

A port is not a node. KCL talks about _nodes_.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Kevin Aylward]

"Phil Hobbs" wrote in message news:qj3t2i$941$1@dont-email.me...

What you probably mean is that an ideal transmission line is a pure delay.
This means an exp(-tau.S) transfer function, which is not a rational
function of S.

Kirchoff's laws do not apply to transmission lines. Current disappears
into one end and emerges from the other end sometime later. The currents
into the circuit nodes don't sum to zero, and neither do the voltages
around loops.

Which is what you expect as transmission lines correctly account for the
fact the FTL is impossible, that is, it shows that signals take a finite
time to propagate from A to B, thus transmissions lines behave *locally*.
Period.

In contrast to Kirchoff's Laws. Those laws assume that all voltages and
currents are instantaneously connected. They ignore propagation delay
effects, thus Kirchoff's Laws are non-local. Period.

Thus... you have the definitions backwards.

Spice has to do extra stuff, as in convolution, to handle TLines. It
slows it down a tad...

As I said, the approximation can often be patched up by hand like that.


inside the T-line can be modelled with PDEs (Maxwell), but circuits are
all ODEs. The T-line has invisible internal state, so its circuit
behaviour is nonlocal.

Not really....

"Non local" pretty much universally means FTL (faster than the speed of
light).

Nope. It means that the governing equations require information from more
than one space-time point. All differential equations are local. Nonlocal
systems need integral equations.

We, apparently, have different definitions of locality.

https://en.wikipedia.org/wiki/Principle_of_locality

https://en.wikipedia.org/wiki/Faster-than-light_neutrino_anomaly

Thus, to date the only accepted apparent FTL, i.e. non-local behaviour that
I am aware of, is the statistical correlations between entangled particles,
which cannot be used to transfer information at FTL

It is inherent in transmission lines that there is delay for transfer of
information, which is *the* fundamental property of the definition of
locality in physics, so it is indeed interesting that there are those that
claim the opposite.

-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

 

[George Herold]

On Thursday, August 15, 2019 at 3:32:02 PM UTC-4, Phil Hobbs wrote:

On 8/15/19 2:56 PM, Kevin Aylward wrote:
"Phil Hobbs"  wrote in message news:qj3t2i$941$1@dont-email.me...



What you probably mean is that an ideal transmission line is a pure
delay. This means an exp(-tau.S) transfer function, which is not a
rational function of S.

Kirchoff's laws do not apply to transmission lines.  Current
disappears into one end and emerges from the other end sometime
later.  The currents into the circuit nodes don't sum to zero, and
neither do the voltages around loops.

Which is what you expect as transmission lines correctly account for the
fact the FTL is impossible, that is, it shows that signals take a finite
time to propagate from A to B, thus transmissions lines behave
*locally*. Period.

In your dreams. Nonlocality doesn't imply FTL, whatever your Sunday
supplement version of quantum field theory might tell you. The
Boltzmann transport equation is also nonlocal, and that applies to your
coffee cup. YCLIU.


In contrast to Kirchoff's Laws. Those laws assume that all voltages and
currents are instantaneously connected. They ignore propagation delay
effects, thus Kirchoff's Laws are non-local. Period.

You're inventing a private language to avoid being wrong in public.
G'wan, Kevin, you're just hitting your stride, man!

Hmm, I gotta agree with Kevin, Kirchoff's laws are non-local.
Just like Newtons law of gravity is non-local. At least that's how I understand
how 'local' is used in physics. Non local implies action at a distance.. (again my understanding.)

But then again I thought I agreed with everything you said... ?
(Did you use the 'local' word?)

George H.

Thus... you have the definitions backwards.

Spice has to do extra stuff, as in convolution, to handle TLines. It
slows it down a tad...

As I said, the approximation can often be patched up by hand like that..


inside the T-line can be modelled with PDEs (Maxwell), but circuits are
all ODEs.  The T-line has invisible internal state, so its circuit
behaviour is nonlocal.

Not really....

"Non local" pretty much universally means FTL (faster than the speed
of light).

Nope.  It means that the governing equations require information from
more than one space-time point.  All differential equations are local.
Nonlocal systems need integral equations.

We, apparently, have different definitions of locality.

https://en.wikipedia.org/wiki/Principle_of_locality

https://en.wikipedia.org/wiki/Faster-than-light_neutrino_anomaly

Thus, to date the only accepted apparent FTL, i.e. non-local behaviour
that I am aware of, is the statistical correlations between entangled
particles, which cannot be used to transfer information at FTL

It is inherent in transmission lines that there is delay for transfer of
information, which is *the* fundamental property of the definition of
locality in physics, so it is indeed interesting that there are those
that claim the opposite.

No, that's a particular definition in relativistic quantum field theory.
We're talking classical E&M here.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[boB]

On Thu, 15 Aug 2019 18:01:13 GMT, Steve Wilson <no@spam.com> wrote:

Winfield Hill <winfieldhill@yahoo.com> wrote:

tabbypurr@gmail.com wrote...

Really it's the sim that's wrong, but you can tackle
its shortcomings by adding in parts to the sim's input so it sims more
features of the real circuit.

LTSpice lets you add parasitic aspects to basic parts,
like resistors, but these are hidden on the schematic,
so you have no idea whether the modeller made additions,
or whether he made the right ones. I prefer seeing a
SPICE schematic, with the parasitic parts explicitly
showing, so you know what was taken care of, and how.
To my mind, these aspects are up to the engineering
doing the SPICE schematic drafting, and not up to the
SPICE program. The LTSpice approach is bad, not good.
So I disagree, it's not the sim that's wrong.

Where it is important, I add the parasitics externally.

LTspice does have some parasitics like ESR for instance that helps
keep the matrix from being ill conditioned as I understand it.

Also, there are places to add parasitics sometimes that do not take
extra compute time as it would if you added them externally.
That is why you should probably use them when available.

 

[Phil Hobbs]

On 8/15/19 4:22 PM, George Herold wrote:

On Thursday, August 15, 2019 at 3:32:02 PM UTC-4, Phil Hobbs wrote:
On 8/15/19 2:56 PM, Kevin Aylward wrote:
"Phil Hobbs"  wrote in message news:qj3t2i$941$1@dont-email.me...



What you probably mean is that an ideal transmission line is a pure
delay. This means an exp(-tau.S) transfer function, which is not a
rational function of S.

Kirchoff's laws do not apply to transmission lines.  Current
disappears into one end and emerges from the other end sometime
later.  The currents into the circuit nodes don't sum to zero, and
neither do the voltages around loops.

Which is what you expect as transmission lines correctly account for the
fact the FTL is impossible, that is, it shows that signals take a finite
time to propagate from A to B, thus transmissions lines behave
*locally*. Period.

In your dreams. Nonlocality doesn't imply FTL, whatever your Sunday
supplement version of quantum field theory might tell you. The
Boltzmann transport equation is also nonlocal, and that applies to your
coffee cup. YCLIU.


In contrast to Kirchoff's Laws. Those laws assume that all voltages and
currents are instantaneously connected. They ignore propagation delay
effects, thus Kirchoff's Laws are non-local. Period.

You're inventing a private language to avoid being wrong in public.
G'wan, Kevin, you're just hitting your stride, man!

Hmm, I gotta agree with Kevin, Kirchoff's laws are non-local.
Just like Newtons law of gravity is non-local. At least that's how I understand
how 'local' is used in physics. Non local implies action at a distance.. (again my understanding.)

But then again I thought I agreed with everything you said... ?
(Did you use the 'local' word?)

Seems like there's a sort of double vision there--you're not applying
the Kirchhoff approximation consistently.

Kirchhoff's voltage law: the sum of all voltages around any loop is
zero. (Equivalently, curl E = 0)

Kirchhoff's current law: the sum of all currents entering a node is zero.

Being consistent about the low-frequency approximation, nodes and loops
have negligible size. Otherwise you couldn't write a system of ODEs to
describe the circuit. So Kirchhoff's laws are local in the physical sense.

I invite anyone here to write a system of ODEs for a circuit containing
a transmission line.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Chris Jones]

On 16/08/2019 03:02, Phil Hobbs wrote:

On 8/14/19 8:00 AM, Chris Jones wrote:
On 13/08/2019 00:02, Phil Hobbs wrote:
On 8/12/19 9:11 AM, Chris Jones wrote:
On 10/08/2019 17:05, Phil Hobbs wrote:
On 8/9/19 4:50 PM, Winfield Hill wrote:
Here's a new section I'm hoping to complete, so it can be
added to the x-Chapter book before it goes to the printer in
a few weeks. Please look it over, but don't be too harsh,
about its lack of mathematical vigor.  It's closer to our
usual back-of-the envelope approach to calculations. Fixes
for errors, suggestions for clarification, improved accuracy,
and comments welcome.

https://www.dropbox.com/s/7zl3yi789idg3s8/4x.26_Loop%20%26%20Nodal%20Analysis.pdf?dl=1






Nice.  I like your making a virtue out of a necessity
(hand-drawn figures).

One point that might be worth a footnote is that Kirchhoff's
laws are a low-frequency approximation, applicable only when
radiation and self-capacitance are negligible.

If your schematic is really complete, then I think that the laws
apply usefully, at least until the point where radiation is
efficient. I am assuming here that current through parasitic
capacitances is counted just as much as if it were a current
flowing through a terminal of an intentional capacitor. If, in
your schematic and arithmetic, you leave out things like the
inductance and self-capacitance of wires, (and in difficult
cases, even the distributed capacitance at different points along
the inductance of wires), then of course the result of applying
Kirchoff's laws to the (incomplete) schematic won't predict the
behaviour of the actual construction. I suspect that radiation
could also be modelled in a way that allows Kirchoff's laws to be
applied but that the resulting schematic would be too
complicated.

Nope.  Transmission lines at the schematic level are non-local,
i.e. you can't write a system of ODEs to describe a circuit with
transmission lines or significant radiation.  Kirchhoff's laws are
derived from Maxwell's equations in the limit of low frequency (or
alternatively, of small size for a fixed frequency).
I would say that that a wire on a schematic is not a valid
representation of a transmission line, and if necessary I would
approximate a transmission line as a ladder of (ideally infinitely)
many series inductors and shunt capacitors. Of course very many
components are required for this to be reasonably accurate.

At frequencies where the number of required components is excessive,
I would then say that a schematic is not a good way to describe the
physical system.
And if you have to model the circuit "in a way that allows
Kirchhoff's laws to be applied", you've implicitly admitted that
they don't apply to the actual circuit.
If by actual circuit we mean the physical object, then really I only
 expect Maxwell's equations to describe it, and I'm not very good at
 solving those. In a completely general sense I'm not even sure how
one would try to apply Kirchoff's laws to an arbitrary three
dimensional piece of electronics.



Don't get me wrong--K's equations are useful and all, but they
have limits.  Being a physicist, I fully recognize the usefulness
of sleazy approximations, but you have to remember that that's what
they are, or you'll get snookered.
Agreed.

I guess I might have a rather unusual idea of what a schematic is,
and this might be what causes me to take issue with what you said. To
me, a schematic ought to be something that, when simulated (by some
ideal simulator!), applying Kirchoff's laws, Ohm's law, i=C.dv/dt and
so on, would sufficiently accurately predict the behavoiur of the
real system.

To me, if the predictions are wrong, then I blame the schematic as
being an inaccurate representation of the system, rather than blaming
the equations used to simulate the behaviour of the schematic.
Perhaps my philosophy on this topic comes from having had the job of
making a schematic (sometimes pulling in netlists from field solvers)
in order to simulate my design as implemented in a physical product.
There was an expectation that I would use a circuit simulator
provided to me, that did try to apply Kirchoff's laws (though not
perfectly in the case of KCL). I did at least have the luxury that
the physical dimensions of the system were a tiny fraction of a
wavelength.

Well, you're kind of using a private language there, as you say.

Perhaps yes, and it has the useful property that for my "schematics", as
far as I can tell, Kirchoff's laws do hold. Obviously I would like to
find out any situations where that isn't true, as I don't want wrong
predictions of the behaviour of a real system, but at that point I would
probably declare the drawing to be no longer a valid "schematic" of the
real system, again by my weird definition, and then I might try to fix
it. Perhaps I am alone in holding these attitudes, but they have served
me well so far.

 

[Kevin Aylward]

"Phil Hobbs" wrote in message news:qj4bve$uv1$1@dont-email.me...

On 8/15/19 2:56 PM, Kevin Aylward wrote:

"Phil Hobbs" wrote in message news:qj3t2i$941$1@dont-email.me...



What you probably mean is that an ideal transmission line is a pure
delay. This means an exp(-tau.S) transfer function, which is not a
rational function of S.

Kirchoff's laws do not apply to transmission lines. Current disappears
into one end and emerges from the other end sometime later. The
currents into the circuit nodes don't sum to zero, and neither do the
voltages around loops.

Which is what you expect as transmission lines correctly account for the
fact the FTL is impossible, that is, it shows that signals take a finite
time to propagate from A to B, thus transmissions lines behave *locally*.
Period.

In your dreams. Nonlocality doesn't imply FTL, whatever your Sunday
supplement version of quantum field theory might tell you. The Boltzmann
transport equation is also nonlocal, and that applies to your coffee cup.
YCLIU.

Twaddle.

Your are seriously confused. The *definition* of non-locality is FTL Period.
No iffs or buts.

We, apparently, have different definitions of locality.

https://en.wikipedia.org/wiki/Principle_of_locality

https://en.wikipedia.org/wiki/Faster-than-light_neutrino_anomaly

Thus, to date the only accepted apparent FTL, i.e. non-local behaviour
that I am aware of, is the statistical correlations between entangled
particles, which cannot be used to transfer information at FTL

It is inherent in transmission lines that there is delay for transfer of
information, which is *the* fundamental property of the definition of
locality in physics, so it is indeed interesting that there are those that
claim the opposite.

No, that's a particular definition in relativistic quantum field theory.
We're talking classical E&M here.

Twaddle.

Again, your are seriously confused. The *definition* of non-locality is FTL
Period. No iffs or buts.

It has zero to do with Quantum Mechanics. You are really stepping out of
your depth here.

Locality and non-locality are terms intimately connected with the
construction of Special Relativity. Its not debatable.

I suggest you actually read the link:

https://en.wikipedia.org/wiki/Principle_of_locality


"In physics, the principle of locality states that an object is directly
influenced only by its immediate surroundings. A theory which includes the
principle of locality is said to be a "local theory". This is an alternative
to the older concept of instantaneous "action at a distance". Locality
evolved out of the field theories of classical physics. The concept is that
for an action at one point to have an influence at another point, something
in the space between those points such as a field must mediate the action.
To exert an influence, something, such as a wave or particle, must travel
through the space between the two points, carrying the influence."

Don't even try to contradict it, it would only makes you come across as an
"Einstein was wrong crank"

Classical E&M theory is a local theory, it is thus simply impossible for
transmission lines to behave non-locally. End off.

Thus Kirchhoff's Laws are nonlocal. Kirchhoff's Laws require voltages and
current information to be propagated instantaneously.

I suggest some refresher courses in physics, because you are only
embarrassing yourself.

-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

 

[Kevin Aylward]

"Phil Hobbs" wrote in message news:qj5rve$hkc$1@dont-email.me...

I invite anyone here to write a system of ODEs for a circuit containing a
transmission line.

Totally irrelevant.

Locality is defined by whether or not there is action at a distance faster
that the speed of light, not by properties of any equation. Its a physical
observational definition, not mathematical. If information is propagated
FTL, its non-local. Period.

Whatever custom definition you are using for "locality" is not one that ever
occurs in any Physics context, especially with regard to Maxwell's
Equations.

-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

 

[Tim Williams]

"Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message
news:qj4bmo$s1v$2@dont-email.me...

A port is not a node. KCL talks about _nodes_.

Well yeah, a port is a branch that connects nodes.

So the port currents don't go anywhere?

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/