Driver to drive?

[Lostgallifreyan]

Joerg <invalid@invalid.invalid> wrote in
news:7dbmdvF2bkgdrU1@mid.individual.net:

Lostgallifreyan wrote:
Joerg <invalid@invalid.invalid> wrote in
news:7dbdd3F2b0r74U2@mid.individual.net:

Lostgallifreyan wrote:
If anyone is following this and wants to try modelling their own
stuff, I found what might be a way.
Intusoft make a tool called SpiceMod which is part of a package they
call ICAP4 though it seems the demo setup doesn't have that tool,
just some very good noted on it, and modelling in general:
The file WkwModels.pdf from the demo install answers a lot fo the
questions I had about modelling diodes, which parameters to tweak,
and extraction from data sheets.

I don't know if the lack of response to me is because of a thousand
experts silently screming RTFM at me, or because it's actually
asomething they DON'T KNOW. Given that Intusoft explain that this is
a serious challenge for experts too, I'm assuming maybe they really
don't know, so they might benefit from that file as much as I will.

Most of us just use a regular diode to simulate because all one
(usually) wants to know is that there definitely won't be any ever so
slight spike in diode current because LDs can go poof in microseconds.
Simulating the optics part would be a major challenge, I think.


Thought that might provoke an expert. I agree, same here, that's all
I usually need too, though like that EDN manual says, a more detailed
model that allows models to give warning of imminent demise is useful.
Modelling for ESD is likely daft, better that we just take care and put
in TVS's and such, but when it comes to fast modulation, a model
definitely helps. Surely you'd have a use for that, no?


I have designed LD circuitry but I am not an expert. Senor Hobbs would
be one. TVS don't work well. Their cutoff isn't terribly well defined
and they have too much capacitance for this. Just handle the things with
care. I've never killed one with ESD, knock on wood ;-)


While I found that a string of four 1N4148's produced a modelled
overshoot almost exactly like what I saw on an oscilloscope months
before I considered looking at spice, I got a very different result
when trying four 1N4001's so it really does need something better than
reaching for a standard diode, in a model OR as a dummy diode in a real
circuit (where a optically dead laser diode is best anyway). So it
really comes down to trying to get something usefully close! EDN's
model seems ideal, aimed at solving this problem for general use, as
opposed to the elaborate models in private university publications.
EDN's is probably tested too, proofread and verified before publishing.

http://www.e-insite.net/ednmag/archives/1998/071698/pdf/15di.pdf
(Halfway through file).


"File not found" :-(

Sorry, right file, wrong location. Try this:
http://www.edn.com/archives/1998/071698/pdf/15di.pdf

Some of the 4000 series behave more like PIN diodes.


If anyone can help by making that into asy and sub files for LTspice it
will help me a lot, and probably a lot of other people too. Four days
of searching have found lots of other people askign questions, and very
few answers, and NONE complete and verified. Someone could get well
known for solving this so other people can have an easier time of it.


It's going to be lots of work. You'll need to get into behavioral models
and while people have modeled large chunks of jet engines with that it
was a ton of work.

I've been finding (and been sent) spice models that are in various stages of
completion and complexity. Ignoring the rest for now, I'm focussing on that
EDN one because it looks like it's meant to be complete. But it's NOT in a
single subcircuit file that can be adapted to LTspice, or anything else. I
don't think it needs modelling, just translation.

For modelling, I'll look into that too, as equations are given in that PDF
file I mentioned earlier, from Intusoft. In their descriptions of how to use
SpiceMod (which I learned costs 600 bucks(!) and is therefore the most
expensive few tens of kilobytes I've ever heard of) they show a screen that
neatly prioritises the data sheet specs for pluging into the equations. While
the details for transisotrs (bar a MOSFET) are not similarly revealed, there
ought to be enough there in their diode explanations to model a laser diode,
electrically. But again, all I'm asking for here right now is for someone who
knows how, to translate that EDN article to a subcircuit ready to plug into
LTspice. (I can make my own symbol file).

 

[Lostgallifreyan]

Joerg <invalid@invalid.invalid> wrote in
news:7dbmdvF2bkgdrU1@mid.individual.net:

I have designed LD circuitry but I am not an expert. Senor Hobbs would
be one. TVS don't work well. Their cutoff isn't terribly well defined
and they have too much capacitance for this. Just handle the things with
care. I've never killed one with ESD, knock on wood ;-)

Interesting. Robin Bowden didn't make strong recommendations for them either.
Just a resistor/capacitor network, and a zener. I concur, though at the time
I was all for varistors too as I'd found a LOT fo them cheaply on eBay at the
time.. But they apparently change characteristics rapidly over time fi they
see anything like the conditions they have to limit, so I'm not too keen now.

Some of the 4000 series behave more like PIN diodes.

Trying not to get away from the focus of the thread because I really do want
direct help with model translation as it's unlikely I can do it alone, but
this IS interesting to me.. PIN are those fast photodiodes, right? Often used
for detecting very short laser pulses and such? When I modelled my driver
using the 1N4005 model I found, I got a lot of ringing. I also saw a
correlation with the changing of Vf with hard changes between zero and full
drive. I analogised it with the hitting of a hard object as opposed to a
softer one that inherently damps the impact. If a PIN diode is to respond
fast it seems reasonable to think that it is capable of hard brittle
responses, otherwise it could not hope to react in time to register a very
short laser pulse. Is this a reasonable way to view it? And if so, why so
with rectifiers and not signal diodes? Or LED's which I imagine are similar
to laser diodes, being usually GaAs based.

 

[Lostgallifreyan]

Lostgallifreyan <no-one@nowhere.net> wrote in
news:Xns9C57D85EDFFE4zoodlewurdle@216.196.109.145:

I also saw a
correlation with the changing of Vf with hard changes between zero and
full drive.

Meaning: Diode models with little change in Vf with current at 500 KHz square
wave drive were also those which rang the most.

 

[Joerg]

Lostgallifreyan wrote:

Joerg <invalid@invalid.invalid> wrote in
news:7dbmdvF2bkgdrU1@mid.individual.net:

Lostgallifreyan wrote:

[...]

While I found that a string of four 1N4148's produced a modelled
overshoot almost exactly like what I saw on an oscilloscope months
before I considered looking at spice, I got a very different result
when trying four 1N4001's so it really does need something better than
reaching for a standard diode, in a model OR as a dummy diode in a real
circuit (where a optically dead laser diode is best anyway). So it
really comes down to trying to get something usefully close! EDN's
model seems ideal, aimed at solving this problem for general use, as
opposed to the elaborate models in private university publications.
EDN's is probably tested too, proofread and verified before publishing.

http://www.e-insite.net/ednmag/archives/1998/071698/pdf/15di.pdf
(Halfway through file).

"File not found" :-(


Sorry, right file, wrong location. Try this:
http://www.edn.com/archives/1998/071698/pdf/15di.pdf

Well, laser diodes are a lot more complicated that this simple model.
Onset of lasing which happens sort of digital at xx percent of max
current, non-linear relationship between output and input power,
overload behavior, wavelength drift with heat and so on.

Some of the 4000 series behave more like PIN diodes.


If anyone can help by making that into asy and sub files for LTspice it
will help me a lot, and probably a lot of other people too. Four days
of searching have found lots of other people askign questions, and very
few answers, and NONE complete and verified. Someone could get well
known for solving this so other people can have an easier time of it.

It's going to be lots of work. You'll need to get into behavioral models
and while people have modeled large chunks of jet engines with that it
was a ton of work.


I've been finding (and been sent) spice models that are in various stages of
completion and complexity. Ignoring the rest for now, I'm focussing on that
EDN one because it looks like it's meant to be complete. But it's NOT in a
single subcircuit file that can be adapted to LTspice, or anything else. I
don't think it needs modelling, just translation.

For modelling, I'll look into that too, as equations are given in that PDF
file I mentioned earlier, from Intusoft. In their descriptions of how to use
SpiceMod (which I learned costs 600 bucks(!) and is therefore the most
expensive few tens of kilobytes I've ever heard of) they show a screen that
neatly prioritises the data sheet specs for pluging into the equations. While
the details for transisotrs (bar a MOSFET) are not similarly revealed, there
ought to be enough there in their diode explanations to model a laser diode,
electrically. But again, all I'm asking for here right now is for someone who
knows how, to translate that EDN article to a subcircuit ready to plug into
LTspice. (I can make my own symbol file).

Seriously, it's a lot more intricate than that. Just to give you an
example from the non-LD world: One of the transistor models of an
amplifier I recently ran is about two dozen lines of SPICE entries.
Those are the sims where the fans come on hard and the office temp
creeps up another 3F or so.

I don't think you'll get around behavioral models here.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Joerg]

Lostgallifreyan wrote:

Joerg <invalid@invalid.invalid> wrote in
news:7dbmdvF2bkgdrU1@mid.individual.net:

I have designed LD circuitry but I am not an expert. Senor Hobbs would
be one. TVS don't work well. Their cutoff isn't terribly well defined
and they have too much capacitance for this. Just handle the things with
care. I've never killed one with ESD, knock on wood ;-)


Interesting. Robin Bowden didn't make strong recommendations for them either.
Just a resistor/capacitor network, and a zener. I concur, though at the time
I was all for varistors too as I'd found a LOT fo them cheaply on eBay at the
time.. But they apparently change characteristics rapidly over time fi they
see anything like the conditions they have to limit, so I'm not too keen now.

How do you want to protect a laser diode with any of these?

Some of the 4000 series behave more like PIN diodes.


Trying not to get away from the focus of the thread because I really do want
direct help with model translation as it's unlikely I can do it alone, but
this IS interesting to me.. PIN are those fast photodiodes, right? Often used
for detecting very short laser pulses and such? When I modelled my driver
using the 1N4005 model I found, I got a lot of ringing. I also saw a
correlation with the changing of Vf with hard changes between zero and full
drive. I analogised it with the hitting of a hard object as opposed to a
softer one that inherently damps the impact. If a PIN diode is to respond
fast it seems reasonable to think that it is capable of hard brittle
responses, otherwise it could not hope to react in time to register a very
short laser pulse. Is this a reasonable way to view it? And if so, why so
with rectifiers and not signal diodes? Or LED's which I imagine are similar
to laser diodes, being usually GaAs based.

Photodiodes are reverse biased if you need speed while PIN diodes used
as controlled RF resistors are forward biased and the current sets the
resistance. But that works only if the carrier lifetime is sufficient
for the frequencies it has to work at.

For more data regarding LD models I'd get in contact with a few
university research labs. It is not a trivial task at all.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Phil Hobbs]

Joerg wrote:

Lostgallifreyan wrote:

<snip>

Thought that might provoke an expert. I agree, same here, that's
all I usually need too, though like that EDN manual says, a more
detailed model that allows models to give warning of imminent demise
is useful. Modelling for ESD is likely daft, better that we just take
care and put in TVS's and such, but when it comes to fast modulation,
a model definitely helps. Surely you'd have a use for that, no?


I have designed LD circuitry but I am not an expert. Senor Hobbs would
be one. TVS don't work well. Their cutoff isn't terribly well defined
and they have too much capacitance for this. Just handle the things with
care. I've never killed one with ESD, knock on wood ;-)


While I found that a string of four 1N4148's produced a modelled
overshoot almost exactly like what I saw on an oscilloscope months
before I considered looking at spice, I got a very different result
when trying four 1N4001's so it really does need something better than
reaching for a standard diode, in a model OR as a dummy diode in a
real circuit (where a optically dead laser diode is best anyway). So
it really comes down to trying to get something usefully close! EDN's
model seems ideal, aimed at solving this problem for general use, as
opposed to the elaborate models in private university publications.
EDN's is probably tested too, proofread and verified before publishing.

http://www.e-insite.net/ednmag/archives/1998/071698/pdf/15di.pdf
(Halfway through file).


"File not found" :-(

Try:
http://preview.tinyurl.com/mfg8g8

Some of the 4000 series behave more like PIN diodes.


Yeah, they can take _forever_ to turn on. Not much use for protection

diodes in most cases.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

 

[Joerg]

Phil Hobbs wrote:

Joerg wrote:
Lostgallifreyan wrote:

snip
Thought that might provoke an expert. I agree, same here, that's
all I usually need too, though like that EDN manual says, a more
detailed model that allows models to give warning of imminent demise
is useful. Modelling for ESD is likely daft, better that we just take
care and put in TVS's and such, but when it comes to fast modulation,
a model definitely helps. Surely you'd have a use for that, no?


I have designed LD circuitry but I am not an expert. Senor Hobbs would
be one. TVS don't work well. Their cutoff isn't terribly well defined
and they have too much capacitance for this. Just handle the things
with care. I've never killed one with ESD, knock on wood ;-)


While I found that a string of four 1N4148's produced a modelled
overshoot almost exactly like what I saw on an oscilloscope months
before I considered looking at spice, I got a very different result
when trying four 1N4001's so it really does need something better
than reaching for a standard diode, in a model OR as a dummy diode in
a real circuit (where a optically dead laser diode is best anyway).
So it really comes down to trying to get something usefully close!
EDN's model seems ideal, aimed at solving this problem for general
use, as opposed to the elaborate models in private university
publications. EDN's is probably tested too, proofread and verified
before publishing.

http://www.e-insite.net/ednmag/archives/1998/071698/pdf/15di.pdf
(Halfway through file).


"File not found" :-(

Try:
http://preview.tinyurl.com/mfg8g8

Thanks, by now I've seen it. But the model presented ain't much to write
home about, IMHO.

Some of the 4000 series behave more like PIN diodes.


Yeah, they can take _forever_ to turn on. Not much use for protection
diodes in most cases.

OTOH, for the RF guy their are very close to the definition of a free
lunch

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Lostgallifreyan]

Joerg <invalid@invalid.invalid> wrote in
news:7dbqhaF2bk1miU1@mid.individual.net:

For more data regarding LD models I'd get in contact with a few
university research labs. It is not a trivial task at all.

EDN (who I trust quite deeply on matters of useful working ideas) seem to
think that a moderately simple diode model can be enough when making basic
driver models. All I'm asking for is translation of that model to a
subcircuit file I can use in LTspice. I'm new to spice but it's already clear
to me that it is UNWISE to model more detail than is strictly needed. So I
think EDN have the right idea. I'm after something that other people can
also easily use and benefit from, I'm not after a perfect detailed model I
can win prizes with.

 

[Lostgallifreyan]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote in
news:xq6dneoJYJOZK-3XnZ2dnUVZ_vKdnZ2d@supernews.com:

Yeah, they can take _forever_ to turn on. Not much use for protection
diodes in most cases.

I'm not after protection diodes. I knew I should NOT have digressed into that
point. All I'm asking for is a translation to LTspice, for that EDN idea. I
typed out the net list to help, but that's all I know how to do right now.

 

[Lostgallifreyan]

Joerg <invalid@invalid.invalid> wrote in
news:7dbrk7F2bch8pU1@mid.individual.net:

Thanks, by now I've seen it. But the model presented ain't much to write
home about, IMHO.

I read somewhere that it was a better version of an earlier one in a Pspice
library. How good does it have to be? No point in modelling more detail than
needed as a starting point. We don't even HAVE that much, any of us hobbyists
and small scale designers. If experts raise their hands in horror saying
there's no point in simple modelling rather than too much detail (with which
Intusoft, who really know this stuff, would solidly disagree), then we'll all
continue to have nothing to go on except dead laser diodes! Surely someone
who knows how might change this?

 

[Phil Hobbs]

Joerg wrote:

Phil Hobbs wrote:
Joerg wrote:
Lostgallifreyan wrote:

snip
Thought that might provoke an expert. I agree, same here, that's
all I usually need too, though like that EDN manual says, a more
detailed model that allows models to give warning of imminent demise
is useful. Modelling for ESD is likely daft, better that we just
take care and put in TVS's and such, but when it comes to fast
modulation, a model definitely helps. Surely you'd have a use for
that, no?


I have designed LD circuitry but I am not an expert. Senor Hobbs
would be one. TVS don't work well. Their cutoff isn't terribly well
defined and they have too much capacitance for this. Just handle the
things with care. I've never killed one with ESD, knock on wood ;-)


While I found that a string of four 1N4148's produced a modelled
overshoot almost exactly like what I saw on an oscilloscope months
before I considered looking at spice, I got a very different result
when trying four 1N4001's so it really does need something better
than reaching for a standard diode, in a model OR as a dummy diode
in a real circuit (where a optically dead laser diode is best
anyway). So it really comes down to trying to get something usefully
close! EDN's model seems ideal, aimed at solving this problem for
general use, as opposed to the elaborate models in private
university publications. EDN's is probably tested too, proofread and
verified before publishing.

http://www.e-insite.net/ednmag/archives/1998/071698/pdf/15di.pdf
(Halfway through file).


"File not found" :-(

Try:
http://preview.tinyurl.com/mfg8g8


Thanks, by now I've seen it. But the model presented ain't much to write
home about, IMHO.


Some of the 4000 series behave more like PIN diodes.


Yeah, they can take _forever_ to turn on. Not much use for protection
diodes in most cases.


OTOH, for the RF guy their are very close to the definition of a free
lunch

Wow, for you a free lunch must be _really_ free!

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

 

[Joerg]

Lostgallifreyan wrote:

Joerg <invalid@invalid.invalid> wrote in
news:7dbqhaF2bk1miU1@mid.individual.net:

For more data regarding LD models I'd get in contact with a few
university research labs. It is not a trivial task at all.


EDN (who I trust quite deeply on matters of useful working ideas) seem to
think that a moderately simple diode model can be enough when making basic
driver models. All I'm asking for is translation of that model to a
subcircuit file I can use in LTspice. I'm new to spice but it's already clear
to me that it is UNWISE to model more detail than is strictly needed. So I
think EDN have the right idea. I'm after something that other people can
also easily use and benefit from, I'm not after a perfect detailed model I
can win prizes with.

You'll have to do that piece by piece. LTSpice's preferred method is
graphics entry. For example, instead of writing out the netlist line for
G you place a voltage dependent current source via point and click and
connect it up in the schematic editor.

If you are new to SPICE I strongly suggest not to start with a project
like this but first use some of the supplied "jigs" or example circuits
and play around with those. Unless you really understand the program it
is very easy to reach wrong sim results.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Phil Hobbs]

Lostgallifreyan wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote in
news:xq6dneoJYJOZK-3XnZ2dnUVZ_vKdnZ2d@supernews.com:

Yeah, they can take _forever_ to turn on. Not much use for protection
diodes in most cases.


I'm not after protection diodes. I knew I should NOT have digressed into that
point. All I'm asking for is a translation to LTspice, for that EDN idea. I
typed out the net list to help, but that's all I know how to do right now.

I know, it's just an interesting point.

<Obligatory on-topic content>

I rather suspect you're barking up the wrong tree with a SPICE model of
a diode laser...it isn't the terminal voltage you care about, it's the
light output, and that depends on a whole lot of optical and thermal
things that SPICE is never, ever going to get right. They have widely
differing timescales, for one thing, which SPICE is horrible at, and for
another thing, small amounts of optical feedback have a _huge_ effect on
DL performance, including feeding back to the terminal voltage.

</Obligatory on-topic content>

Cheers

Phil Hobbs



--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

 

[Joerg]

Lostgallifreyan wrote:

Joerg <invalid@invalid.invalid> wrote in
news:7dbrk7F2bch8pU1@mid.individual.net:

Thanks, by now I've seen it. But the model presented ain't much to write
home about, IMHO.



I read somewhere that it was a better version of an earlier one in a Pspice
library. How good does it have to be? ...

That depends on you. If you want the sims to model all the way to
failure modes I'd really be surprised if PSPICE had something in a
library that would even come close. My PSPICE license is too old so I
wouldn't know. But that would be one tough job.

Again, a laser diode is not a linear device when you look at lasing
output. Not at all.

... No point in modelling more detail than
needed as a starting point. We don't even HAVE that much, any of us hobbyists
and small scale designers. If experts raise their hands in horror saying
there's no point in simple modelling rather than too much detail (with which
Intusoft, who really know this stuff, would solidly disagree), ...

Let them disagree. Will they pay for your dead laser diodes?

... then we'll all
continue to have nothing to go on except dead laser diodes! Surely someone
who knows how might change this?

All I am saying is that I believe it is impossible to correctly model a
laser diode by trying to find electrical equivalents for all its
behaviors. You need a behavioral model in addition. All it takes for a
LD to die is optical overload inside the cavity. A brief wiggle of a
fiber connector, a spike of a few usec ... poof. The EDN model isn't
helping you with that.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Lostgallifreyan]

Joerg <invalid@invalid.invalid> wrote in
news:7dbt02F2b7dkrU1@mid.individual.net:

You'll have to do that piece by piece. LTSpice's preferred method is
graphics entry. For example, instead of writing out the netlist line for
G you place a voltage dependent current source via point and click and
connect it up in the schematic editor.

I suspected as much. Actually my guess is that their equivalent circuit
needs to be constructed then turned into a subcircuit. There's no doubt it
CAN ultimately be written as a single subcircuit file, I don't know why EDN's
contributor didn't go all the way.

If you are new to SPICE I strongly suggest not to start with a project
like this but first use some of the supplied "jigs" or example circuits
and play around with those. Unless you really understand the program it
is very easy to reach wrong sim results.

I always reality-check things. I only intend to use LTspice the way I do my
case designs and other physical models in SketchUp. Sure, a posh CAD tool can
design me a proper screw thread while SketchUp hasn't a chance of this (at
least, not the version 4 I choose to stay with), but the idea is to quickly
aid visualisation, not to substitute for reality.

 

[Lostgallifreyan]

Joerg <invalid@invalid.invalid> wrote in
news:7dbtfqF2aoitdU1@mid.individual.net:

Lostgallifreyan wrote:
Joerg <invalid@invalid.invalid> wrote in
news:7dbrk7F2bch8pU1@mid.individual.net:

Thanks, by now I've seen it. But the model presented ain't much to
write home about, IMHO.



I read somewhere that it was a better version of an earlier one in a
Pspice library. How good does it have to be? ...


That depends on you. If you want the sims to model all the way to
failure modes I'd really be surprised if PSPICE had something in a
library that would even come close. My PSPICE license is too old so I
wouldn't know. But that would be one tough job.

Again, a laser diode is not a linear device when you look at lasing
output. Not at all.

No, but I'm looking at electrical INput..

... No point in modelling more detail than
needed as a starting point. We don't even HAVE that much, any of us
hobbyists and small scale designers. If experts raise their hands in
horror saying there's no point in simple modelling rather than too much
detail (with which Intusoft, who really know this stuff, would solidly
disagree), ...


Let them disagree. Will they pay for your dead laser diodes?

No, but they DO take my point when I tell them that SpiceMod shouldn't cost a
personal user more than a very few of them.

... then we'll all
continue to have nothing to go on except dead laser diodes! Surely
someone who knows how might change this?


All I am saying is that I believe it is impossible to correctly model a
laser diode by trying to find electrical equivalents for all its
behaviors. You need a behavioral model in addition. All it takes for a
LD to die is optical overload inside the cavity. A brief wiggle of a
fiber connector, a spike of a few usec ... poof. The EDN model isn't
helping you with that.

Well, Tim G at Intusoft kindly said if I sent him some model numbers, he'd
see what he can do. I sent him 5 data sheets. Got to try my luck, no?
Besides, they might give a workable average for the kinds of high power red
single mode diodes hobbyists are using.

From what I've seen of my dead diodes, they are still electrically very
similar to live ones so I'm not concerned with advanced optical modelling.

 

[Lostgallifreyan]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote in news:FcadnUCm-
5ZRI-3XnZ2dnUVZ_vKdnZ2d@supernews.com:

I rather suspect you're barking up the wrong tree with a SPICE model of
a diode laser...it isn't the terminal voltage you care about, it's the
light output, and that depends on a whole lot of optical and thermal
things that SPICE is never, ever going to get right. They have widely
differing timescales, for one thing, which SPICE is horrible at, and for
another thing, small amounts of optical feedback have a _huge_ effect on
DL performance, including feeding back to the terminal voltage.

During the transitions, perhaps, but in steady state operation there seems to
be a remarkable electrical similarity between a dead diode and a live one.
What matters is the way the diode responds to hard electrical changes on the
input, as that's what makes the ringing and damaging overshoots. This is true
with NO consideration of optical nature, and just modelling that alone,
realistically for real laser diodes, is a lot more than we currently have.
And likely not that big an ask, it's just not been done much, it seems.

 

[Joerg]

Lostgallifreyan wrote:

Joerg <invalid@invalid.invalid> wrote in
news:7dbt02F2b7dkrU1@mid.individual.net:

You'll have to do that piece by piece. LTSpice's preferred method is
graphics entry. For example, instead of writing out the netlist line for
G you place a voltage dependent current source via point and click and
connect it up in the schematic editor.


I suspected as much. Actually my guess is that their equivalent circuit
needs to be constructed then turned into a subcircuit. There's no doubt it
CAN ultimately be written as a single subcircuit file, I don't know why EDN's
contributor didn't go all the way.

Yes, it should be feasible to place it in a subcircuit. However, since
you said you just started out with LTSpice I suggest not to do that (yet).

If you are new to SPICE I strongly suggest not to start with a project
like this but first use some of the supplied "jigs" or example circuits
and play around with those. Unless you really understand the program it
is very easy to reach wrong sim results.


I always reality-check things. I only intend to use LTspice the way I do my
case designs and other physical models in SketchUp. Sure, a posh CAD tool can
design me a proper screw thread while SketchUp hasn't a chance of this (at
least, not the version 4 I choose to stay with), but the idea is to quickly
aid visualisation, not to substitute for reality.

I use DesignCAD 3D for that. Ten bucks at a liquidator. Mostly because
it can read in AutoCAD files.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Lostgallifreyan]

Joerg <invalid@invalid.invalid> wrote in
news:7dbvjkF2bdsc0U3@mid.individual.net:

I use DesignCAD 3D for that. Ten bucks at a liquidator. Mostly because
it can read in AutoCAD files.

Ah, but Ghost lets me retain a known working OS config, recalled at will, and
an INTENSELY useful side effect of this is infinitely renewable demo periods.

 

[Joerg]

Lostgallifreyan wrote:

Joerg <invalid@invalid.invalid> wrote in
news:7dbtfqF2aoitdU1@mid.individual.net:

Lostgallifreyan wrote:
Joerg <invalid@invalid.invalid> wrote in
news:7dbrk7F2bch8pU1@mid.individual.net:

Thanks, by now I've seen it. But the model presented ain't much to
write home about, IMHO.


I read somewhere that it was a better version of an earlier one in a
Pspice library. How good does it have to be? ...

That depends on you. If you want the sims to model all the way to
failure modes I'd really be surprised if PSPICE had something in a
library that would even come close. My PSPICE license is too old so I
wouldn't know. But that would be one tough job.

Again, a laser diode is not a linear device when you look at lasing
output. Not at all.

No, but I'm looking at electrical INput..

That's the easy part

BTW, I do not understand why EDN placed the SPICE list as a graphic.
Somehow that doesn't leave a very professional taste.

... No point in modelling more detail than
needed as a starting point. We don't even HAVE that much, any of us
hobbyists and small scale designers. If experts raise their hands in
horror saying there's no point in simple modelling rather than too much
detail (with which Intusoft, who really know this stuff, would solidly
disagree), ...

Let them disagree. Will they pay for your dead laser diodes?


No, but they DO take my point when I tell them that SpiceMod shouldn't cost a
personal user more than a very few of them.

The ones I dealt with last were about $1200 a pop. Lots of them. The
client would have been very p....d if I had blown some.

... then we'll all
continue to have nothing to go on except dead laser diodes! Surely
someone who knows how might change this?

All I am saying is that I believe it is impossible to correctly model a
laser diode by trying to find electrical equivalents for all its
behaviors. You need a behavioral model in addition. All it takes for a
LD to die is optical overload inside the cavity. A brief wiggle of a
fiber connector, a spike of a few usec ... poof. The EDN model isn't
helping you with that.


Well, Tim G at Intusoft kindly said if I sent him some model numbers, he'd
see what he can do. I sent him 5 data sheets. Got to try my luck, no?
Besides, they might give a workable average for the kinds of high power red
single mode diodes hobbyists are using.

From what I've seen of my dead diodes, they are still electrically very
similar to live ones so I'm not concerned with advanced optical modelling.

Often you can still use them as LEDs

What killed them?

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.