Driver to drive?

Fred Abse wrote:
On Wed, 31 Oct 2012 17:46:03 -0400, tm wrote:

1/10 th the circuit loading.

There's a problem with that. The proposed 1:1000 single-stage probe
requires a parallel compensating capacitance 1/1000 of the total
scope-plus-cable capacitance, which is likely to be in the order of 50pF,
which implies a compensating capacitor of 50 fF, or 0.05 pF. across the
probe series resistor. This is probably impossible to realize.

The Tektronix 1:100 HV probe used a special "leaf-and-collar" capacitor of
a few pF, across the 100M probe resistor, which is taking things about as
far as they can go, and still withstand the voltage gradient across the
resistor. The capacitor dielectric was Freon, rather than air, giving a
higher dielectric strength. Freons have a permittivity of around 2, which
helps as well. The probe actually had a load of 100K at the scope end of
the cable, not just the 1meg/22pF scope input, giving 1:1000 ratio.
Compensation adjustment was done at the scope end of the cable, as is
ubiquitous in higher-end probes today.


Correct, except it is 1000:1; all else is OK.
Click to expand...

I am purposely using a larger capacitance as i am not mechanically
inclined; easy to put plastic tube around resistors, centered with thin
sheet, and wrap adhesive copper foil on outside cut for same length as
resistor.
Easy to calculate capacitance of the resulting coax (resistor / air /
inner tube surface / acrylic / outer tube surface = = floating shield.
 
Fred Abse wrote:
On Tue, 30 Oct 2012 20:33:39 -0800, Robert Baer wrote:

Sorry...mistype... cable is about 50 ohms per foot.

Says so on the schematic in the probe manual.

Probe cables, at least modern ones, use foam dielectric, hence lower
capacitance per foot.

I've got some probes with removable cables, I'll TDR one when I get the
time. I'll have a go at open and shorted measurements, too, and calculate
the complex Zo. With a resistive center, Zo will be significantly complex
at higher frequencies than "regular" coax.

Thought of a way to (perhaps) make resistive coax with element in the
Click to expand...
50 ohm per foot region.
Find some Nichrome or other resistive (heater) wire,and use Teflon
sleeving in successive layers or use shrink tubing in successive layers.
Slip braid around that.
 
josephkk wrote:
On Sat, 03 Nov 2012 12:55:56 -0400, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:


Fred Abse wrote:

On Tue, 30 Oct 2012 21:31:19 -0400, Michael A. Terrell wrote:

Are you fir real?

He's just taking the pith.


That's just nuts!

How squirrely is this going to get?
Click to expand...

Acorn't tell you!
 
On Sat, 03 Nov 2012 22:29:36 -0400, the renowned "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

josephkk wrote:

On Sat, 03 Nov 2012 12:55:56 -0400, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:


Fred Abse wrote:

On Tue, 30 Oct 2012 21:31:19 -0400, Michael A. Terrell wrote:

Are you fir real?

He's just taking the pith.


That's just nuts!

How squirrely is this going to get?


Acorn't tell you!
Click to expand...
Yew guys are knot getting board with these jokes?


("My Tree Puns"... Fred MacMurray?)


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
Spehro Pefhany wrote:
On Sat, 03 Nov 2012 22:29:36 -0400, the renowned "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:


josephkk wrote:

On Sat, 03 Nov 2012 12:55:56 -0400, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:


Fred Abse wrote:

On Tue, 30 Oct 2012 21:31:19 -0400, Michael A. Terrell wrote:

Are you fir real?

He's just taking the pith.


That's just nuts!

How squirrely is this going to get?


Acorn't tell you!

Yew guys are knot getting board with these jokes?

("My Tree Puns"... Fred MacMurray?)
Click to expand...

Ash me no questions, I'll trellis you no lies!
 
On Sat, 03 Nov 2012 12:37:23 -0400, tm wrote:

Certainly not disagreeing with you Fred. In fact I don't know of any
1000:1 probes that are good at high frequency measurements. But for DC
measurements, you would want a 1Gohm probe for best accuracy measurements.
Click to expand...
The discussion is about oscilloscope probes. Thousand meg. DC HV probes
are a dime a dozen. Most for use with 10M DMMs, so there's a 1M load
resistor in those. I have one. Don't use it much.

Also, I think I read somewhere that the Freon 114 used in the 6015 probe
had a permittivity near to 1. There was some discussion of using F-11 as
a replacement but its permittivity is up there and the probe does not
work well with it.
Click to expand...
Could be. I just looked up the CFC dielectric properties table in Kaye and
Laby. All there are around 2. It doesn't specifically mention 1.1.4.

There is some good information on the yahoo tekscopes group archives
concerning this probe.
Click to expand...
I don't do Yahoo groups.

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)
 
On Sat, 03 Nov 2012 18:21:07 -0800, Robert Baer wrote:

Correct, except it is 1000:1; all else is OK.
Click to expand...
Whassadifference?

My usual convention for transfer functions is Vout/Vin.

Equal to 1/1000.
Or 1:1000

BTW, I would never use a high-voltage probe that didn't have an internal
load .

Consider the situation where there is HV applied, and the scope amplifier
is inadvertently switched to GND (which means the input socket will be
open circuit).
Practically the full HV will appear at the amplifier input socket.
The insulation won't stand that.

Even worse, a 7A13, switched to "near infinite impedance".

Relying on the scope's input resistance is dangerous. We all make mistakes.

I'm sure that UL, CSA, VDE, TüV, et al. would agree.

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)
 
On 11/03/2012 10:12 PM, josephkk wrote:
On Sat, 03 Nov 2012 18:25:19 -0800, Robert Baer<robertbaer@localnet.com
wrote:

Fred Abse wrote:
On Tue, 30 Oct 2012 20:33:39 -0800, Robert Baer wrote:

Sorry...mistype... cable is about 50 ohms per foot.

Says so on the schematic in the probe manual.

Probe cables, at least modern ones, use foam dielectric, hence lower
capacitance per foot.

I've got some probes with removable cables, I'll TDR one when I get the
time. I'll have a go at open and shorted measurements, too, and calculate
the complex Zo. With a resistive center, Zo will be significantly complex
at higher frequencies than "regular" coax.

Thought of a way to (perhaps) make resistive coax with element in the
50 ohm per foot region.
Find some Nichrome or other resistive (heater) wire,and use Teflon
sleeving in successive layers or use shrink tubing in successive layers.
Slip braid around that.

Nicrhome is ok for heater uses, but i prefer constantan for electronic
purposes. Check out the properties differences, it will be worth it.
Click to expand...
You can solder to constantan, for a start!

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
josephkk wrote:
On Sat, 03 Nov 2012 18:25:19 -0800, Robert Baer<robertbaer@localnet.com
wrote:

Fred Abse wrote:
On Tue, 30 Oct 2012 20:33:39 -0800, Robert Baer wrote:

Sorry...mistype... cable is about 50 ohms per foot.

Says so on the schematic in the probe manual.

Probe cables, at least modern ones, use foam dielectric, hence lower
capacitance per foot.

I've got some probes with removable cables, I'll TDR one when I get the
time. I'll have a go at open and shorted measurements, too, and calculate
the complex Zo. With a resistive center, Zo will be significantly complex
at higher frequencies than "regular" coax.

Thought of a way to (perhaps) make resistive coax with element in the
50 ohm per foot region.
Find some Nichrome or other resistive (heater) wire,and use Teflon
sleeving in successive layers or use shrink tubing in successive layers.
Slip braid around that.

Nicrhome is ok for heater uses, but i prefer constantan for electronic
purposes. Check out the properties differences, it will be worth it.

?-)
I vaguely one of them can be soldered; which one?
Click to expand...
 
josephkk wrote:
On Sat, 03 Nov 2012 18:25:19 -0800, Robert Baer<robertbaer@localnet.com
wrote:

Fred Abse wrote:
On Tue, 30 Oct 2012 20:33:39 -0800, Robert Baer wrote:

Sorry...mistype... cable is about 50 ohms per foot.

Says so on the schematic in the probe manual.

Probe cables, at least modern ones, use foam dielectric, hence lower
capacitance per foot.

I've got some probes with removable cables, I'll TDR one when I get the
time. I'll have a go at open and shorted measurements, too, and calculate
the complex Zo. With a resistive center, Zo will be significantly complex
at higher frequencies than "regular" coax.

Thought of a way to (perhaps) make resistive coax with element in the
50 ohm per foot region.
Find some Nichrome or other resistive (heater) wire,and use Teflon
sleeving in successive layers or use shrink tubing in successive layers.
Slip braid around that.

Nicrhome is ok for heater uses, but i prefer constantan for electronic
purposes. Check out the properties differences, it will be worth it.

?-)
I vaguely remember that one can be soldered; which one is that?
Click to expand...
 
josephkk wrote:
On Sat, 03 Nov 2012 18:21:07 -0800, Robert Baer<robertbaer@localnet.com
wrote:

Fred Abse wrote:
On Wed, 31 Oct 2012 17:46:03 -0400, tm wrote:

1/10 th the circuit loading.

There's a problem with that. The proposed 1:1000 single-stage probe
requires a parallel compensating capacitance 1/1000 of the total
scope-plus-cable capacitance, which is likely to be in the order of 50pF,
which implies a compensating capacitor of 50 fF, or 0.05 pF. across the
probe series resistor. This is probably impossible to realize.

The Tektronix 1:100 HV probe used a special "leaf-and-collar" capacitor of
a few pF, across the 100M probe resistor, which is taking things about as
far as they can go, and still withstand the voltage gradient across the
resistor. The capacitor dielectric was Freon, rather than air, giving a
higher dielectric strength. Freons have a permittivity of around 2, which
helps as well. The probe actually had a load of 100K at the scope end of
the cable, not just the 1meg/22pF scope input, giving 1:1000 ratio.
Compensation adjustment was done at the scope end of the cable, as is
ubiquitous in higher-end probes today.


Correct, except it is 1000:1; all else is OK.

I am purposely using a larger capacitance as i am not mechanically
inclined; easy to put plastic tube around resistors, centered with thin
sheet, and wrap adhesive copper foil on outside cut for same length as
resistor.
Easy to calculate capacitance of the resulting coax (resistor / air /
inner tube surface / acrylic / outer tube surface = = floating shield.


Whoosh

?-/
Look at it this way; two coax capacitors in parallel one inside the
Click to expand...
other.
First one from resistor as center conductor and inner surface of
plastic tube for "outer" coax and air being the dielectric.
Second one has its center conductor as the inner surface of the
plastic tube, and the outer coax is the outside that has the conductive
foil; the plastic being the dielectric.

In physics, that inner surface would be called a Gaussian surface.
 
On Tue, 06 Nov 2012 17:23:12 -0800, the renowned Robert Baer
<robertbaer@localnet.com> wrote:

josephkk wrote:
On Sat, 03 Nov 2012 18:25:19 -0800, Robert Baer<robertbaer@localnet.com
wrote:

Fred Abse wrote:
On Tue, 30 Oct 2012 20:33:39 -0800, Robert Baer wrote:

Sorry...mistype... cable is about 50 ohms per foot.

Says so on the schematic in the probe manual.

Probe cables, at least modern ones, use foam dielectric, hence lower
capacitance per foot.

I've got some probes with removable cables, I'll TDR one when I get the
time. I'll have a go at open and shorted measurements, too, and calculate
the complex Zo. With a resistive center, Zo will be significantly complex
at higher frequencies than "regular" coax.

Thought of a way to (perhaps) make resistive coax with element in the
50 ohm per foot region.
Find some Nichrome or other resistive (heater) wire,and use Teflon
sleeving in successive layers or use shrink tubing in successive layers.
Slip braid around that.

Nicrhome is ok for heater uses, but i prefer constantan for electronic
purposes. Check out the properties differences, it will be worth it.

?-)
I vaguely remember that one can be soldered; which one is that?
Click to expand...
Constantan. Type T (Cu-Constantan) can have junctions soft-soldered
without any kind of special flux. Some J (Fe-Constantan) wire has the
iron copper-clad so the same is true.

--sp


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
Phil Hobbs wrote:
On 11/03/2012 10:12 PM, josephkk wrote:
On Sat, 03 Nov 2012 18:25:19 -0800, Robert Baer<robertbaer@localnet.com
wrote:

Fred Abse wrote:
On Tue, 30 Oct 2012 20:33:39 -0800, Robert Baer wrote:

Sorry...mistype... cable is about 50 ohms per foot.

Says so on the schematic in the probe manual.

Probe cables, at least modern ones, use foam dielectric, hence lower
capacitance per foot.

I've got some probes with removable cables, I'll TDR one when I get the
time. I'll have a go at open and shorted measurements, too, and
calculate
the complex Zo. With a resistive center, Zo will be significantly
complex
at higher frequencies than "regular" coax.

Thought of a way to (perhaps) make resistive coax with element in the
50 ohm per foot region.
Find some Nichrome or other resistive (heater) wire,and use Teflon
sleeving in successive layers or use shrink tubing in successive layers.
Slip braid around that.

Nicrhome is ok for heater uses, but i prefer constantan for electronic
purposes. Check out the properties differences, it will be worth it.


You can solder to constantan, for a start!

Cheers

Phil Hobbs

Thanks!
Click to expand...
I knew one of them could be soldered..so that is the wire to use if
the right resistivity can be has with a "reasonable" wire gauge (for the
sleeving and outer braid shield).
 
On Tue, 06 Nov 2012 17:28:39 -0800, Robert Baer wrote:

?-/
Look at it this way; two coax capacitors in parallel one inside the
other.
First one from resistor as center conductor and inner surface of
plastic tube for "outer" coax and air being the dielectric.
Second one has its center conductor as the inner surface of the
plastic tube, and the outer coax is the outside that has the conductive
foil; the plastic being the dielectric.
Click to expand...
Have you forgotten the stated end-to-end capacitance per Ohmite data?

In the case of MOX-2-13XXXX it's 0.6pF. I suspect that this will be the
dominant parameter.

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)
 
Spehro Pefhany wrote:
On Tue, 06 Nov 2012 17:23:12 -0800, the renowned Robert Baer
robertbaer@localnet.com> wrote:

josephkk wrote:
On Sat, 03 Nov 2012 18:25:19 -0800, Robert Baer<robertbaer@localnet.com
wrote:

Fred Abse wrote:
On Tue, 30 Oct 2012 20:33:39 -0800, Robert Baer wrote:

Sorry...mistype... cable is about 50 ohms per foot.

Says so on the schematic in the probe manual.

Probe cables, at least modern ones, use foam dielectric, hence lower
capacitance per foot.

I've got some probes with removable cables, I'll TDR one when I get the
time. I'll have a go at open and shorted measurements, too, and calculate
the complex Zo. With a resistive center, Zo will be significantly complex
at higher frequencies than "regular" coax.

Thought of a way to (perhaps) make resistive coax with element in the
50 ohm per foot region.
Find some Nichrome or other resistive (heater) wire,and use Teflon
sleeving in successive layers or use shrink tubing in successive layers.
Slip braid around that.

Nicrhome is ok for heater uses, but i prefer constantan for electronic
purposes. Check out the properties differences, it will be worth it.

?-)
I vaguely remember that one can be soldered; which one is that?

Constantan. Type T (Cu-Constantan) can have junctions soft-soldered
without any kind of special flux. Some J (Fe-Constantan) wire has the
iron copper-clad so the same is true.

--sp


Best regards,
Spehro Pefhany
Tried the BabyBird (GooGull); most hits were Chinese sellers, many do
Click to expand...
not say how to buy, those that do say how much do not give resistivity
of the wire (ohms per unit length).
So still have zero idea if any of the wire that might be available is
in the right resistance range.
Nobody seems to have a range of wire sizes.
 
BJT SPICE models are not specifically small or large signal models, they
are general representations for transient or AC mode simulations.

What waveforms are you getting?

Qucs uses a SPICE backend? Have you tried manipulating the simulation
parameters to see if it's producing an accurate, stable result?

Can you generate a SPICE netlist and post it here?

Tim

--
Deep Friar: a very philosophical monk.
Website: http://seventransistorlabs.com

"o pere o" <me@somewhere.net> wrote in message
news:k7mic6$amu$1@dont-email.me...
To make a long story short, I ended up simulating an emitter follower
with Qucs. This simulator has some transistor models embedded, but you
are able to insert PSpice models and subcircuits if you need more.

When you increase input signal level up to the point where the output
should clip at zero, one transistor model clips correctly (BFP405, from
Qucs) but others not (BFR93a, 2N2222A). The BFR93a model is a PSpice
model from the NXP site and I have tried several 2N2222a models (one
from Qucs itself, one PSpice model from Zetex and another PSpice model
from somewhere): none of these clips at zero although it does at
VCC=3.3.

Tried the same circuit in LTSpice with the same result. Am I the only
one experiencing this? Has anyone got better large-signal models
-especially for the BFR93a?

Pere
Click to expand...
 
On Sat, 10 Nov 2012 22:53:08 +0100, o pere o <me@somewhere.net> wrote:

To make a long story short, I ended up simulating an emitter follower
with Qucs. This simulator has some transistor models embedded, but you
are able to insert PSpice models and subcircuits if you need more.

When you increase input signal level up to the point where the output
should clip at zero, one transistor model clips correctly (BFP405, from
Qucs) but others not (BFR93a, 2N2222A). The BFR93a model is a PSpice
model from the NXP site and I have tried several 2N2222a models (one
from Qucs itself, one PSpice model from Zetex and another PSpice model
from somewhere): none of these clips at zero although it does at VCC=3.3.

Tried the same circuit in LTSpice with the same result. Am I the only
one experiencing this? Has anyone got better large-signal models
-especially for the BFR93a?

Pere
Click to expand...
Sounds more like definitional problems than a model issue.

(1) I presume you output is the emitter (VE) ??
(2) What do you mean by "clip at zero"?
(3) Are V2 and V3 fixed values?

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
On Nov 11, 9:06 am, "Tim Williams" <tmoran...@charter.net> wrote:
BJT SPICE models are not specifically small or large signal models, they
are general representations for transient or AC mode simulations.

What waveforms are you getting?

Qucs uses a SPICE backend?  Have you tried manipulating the simulation
parameters to see if it's producing an accurate, stable result?

Can you generate a SPICE netlist and post it here?

Deep Friar: a very philosophical monk.
Website:http://seventransistorlabs.com

"o pere o" <m...@somewhere.net> wrote in messagenews:k7mic6$amu$1@dont-email.me...

To make a long story short, I ended up simulating an emitter follower
with Qucs. This simulator has some transistor models embedded, but you
are able to insert PSpice models and subcircuits if you need more.

When you increase input signal level up to the point where the output
should clip at zero, one transistor model clips correctly (BFP405, from
Qucs) but others not (BFR93a, 2N2222A). The BFR93a model is a PSpice
model from the NXP site and I have tried several 2N2222a models (one
from Qucs itself, one PSpice model from Zetex and another PSpice model
from somewhere): none of these clips at zero although it does at
VCC=3.3.

Tried the same circuit in LTSpice with the same result. Am I the only
one experiencing this? Has anyone got better large-signal models
-especially for the BFR93a?
Click to expand...
The transistor models you can get from NXP are Gummel-Poon models, as
are the models that come with LTSpice.

LTspice also supports the superior VBIC - Vertical Bipolar Inter
Company - model but manufactures treat the parameters for VBIC models
as "commercial in confidence" and don't publish them.

Gummel-Poon doesn't model inverted transistors very accurately, and
some time ago I wanted to get hold of a VBIC model to see it it would
do better, as it has been claimed that it would, but nobody around
here had any non-proprietary data that they were prepared to share
with me.

In principle it isn't too difficult to make up a set of VBIC
parameters from Gummel-Poon data and a few extra measurements, but
nobody seems to have bothered to do it.

--
Bill Sloman, Sydney
 
On Sat, 10 Nov 2012 15:50:02 -0800 (PST), Bill Sloman
<bill.sloman@ieee.org> wrote:

On Nov 11, 9:06 am, "Tim Williams" <tmoran...@charter.net> wrote:
BJT SPICE models are not specifically small or large signal models, they
are general representations for transient or AC mode simulations.

What waveforms are you getting?

Qucs uses a SPICE backend?  Have you tried manipulating the simulation
parameters to see if it's producing an accurate, stable result?

Can you generate a SPICE netlist and post it here?

Deep Friar: a very philosophical monk.
Website:http://seventransistorlabs.com

"o pere o" <m...@somewhere.net> wrote in messagenews:k7mic6$amu$1@dont-email.me...

To make a long story short, I ended up simulating an emitter follower
with Qucs. This simulator has some transistor models embedded, but you
are able to insert PSpice models and subcircuits if you need more.

When you increase input signal level up to the point where the output
should clip at zero, one transistor model clips correctly (BFP405, from
Qucs) but others not (BFR93a, 2N2222A). The BFR93a model is a PSpice
model from the NXP site and I have tried several 2N2222a models (one
from Qucs itself, one PSpice model from Zetex and another PSpice model
from somewhere): none of these clips at zero although it does at
VCC=3.3.

Tried the same circuit in LTSpice with the same result. Am I the only
one experiencing this? Has anyone got better large-signal models
-especially for the BFR93a?

The transistor models you can get from NXP are Gummel-Poon models, as
are the models that come with LTSpice.

LTspice also supports the superior VBIC - Vertical Bipolar Inter
Company - model but manufactures treat the parameters for VBIC models
as "commercial in confidence" and don't publish them.

Gummel-Poon doesn't model inverted transistors very accurately, and
some time ago I wanted to get hold of a VBIC model to see it it would
do better, as it has been claimed that it would, but nobody around
here had any non-proprietary data that they were prepared to share
with me.
Click to expand...
Support for GP and VBIC is one thing. You point out how hard
it is to get the VBIC model parameters. But even the GP
parameters are rarely even close to fully provided.

For example, the models I've seen for BJTs are pretty weak in
low current beta. They usually don't include figures for Ise
(which defaults to 0) or Ne (defaulted to 1.5, which matters
not at all if Ise=0.) [Or in the older literature where these
parameters are called C_2=Ise/Is and n_EL.] The models I've
seen just assume that a log plot of Ic and Ib versus Vbe is a
nice line all the way back towards Vbe=0V, instead of the
dramatic knee that actually takes place because actual BJTs
have extra effects from recombinations of surface carriers
and carriers in the emitter-base space-charge layer, and also
due to the formation of emitter-base surface channels. Almost
never do I find these low current parameters modeled, nor is
there usually enough information in the data sheet to develop
them (they start their charts typically with base currents
near a microamp, with any serious beta drop-off not shown.)
Modelling a discrete equivalent to a PUJT, for example, isn't
possible without them because the beta drop at low currents
is what makes the difference between a simulation that models
real behavior of the discrete pair and one that completely
fails and instead finds a stable quiescent point.

In principle it isn't too difficult to make up a set of VBIC
parameters from Gummel-Poon data and a few extra measurements, but
nobody seems to have bothered to do it.
Click to expand...
I'd just like to see GP parameters, even. Rarely do I see
much more than EM2 model parameters, with a few strays from
GP added to the mix.

It would be interesting to sweep low base currents from say
5nA to 500nA in order to actually get Ise and Ne to use in
simulation. But it's not been a priority of any kind, yet. I
just remain aware of the problem. The BJT models that are
readily available rarely make use of anything close to all
the GP model parameters. And Ise and Ne are merely EM3 model
parameters (pre-GP.)

So while it may be not too difficult to add what's needed to
get VBIC, assuming you have all the GP parameters, the
problem is that you rarely have all the GP parameters. So the
difficulty now rises rapidly because of all the holes in the
missing modelling parameters for GP or even EM3 in the models
that us unwashed mortals can get.

Jon
 
On Sat, 10 Nov 2012 22:53:08 +0100, o pere o <me@somewhere.net> wrote:

To make a long story short, I ended up simulating an emitter follower
with Qucs. This simulator has some transistor models embedded, but you
are able to insert PSpice models and subcircuits if you need more.

When you increase input signal level up to the point where the output
should clip at zero, one transistor model clips correctly (BFP405, from
Qucs) but others not (BFR93a, 2N2222A). The BFR93a model is a PSpice
model from the NXP site and I have tried several 2N2222a models (one
from Qucs itself, one PSpice model from Zetex and another PSpice model
from somewhere): none of these clips at zero although it does at VCC=3.3.

Tried the same circuit in LTSpice with the same result. Am I the only
one experiencing this? Has anyone got better large-signal models
-especially for the BFR93a?

Pere
Click to expand...
At 25MHz, your input signal is using the bipolar transistor as
rectifier, clamped by the CB junction.

You'd need a lot of accurate reverse and dynamic parameters in your
model, to get anything close to reality.

The 2n2222a model may be missing (from inspection of popular models)
ISC, VJE, VJC, VJS, XCJC, FC, MJE, MJC, MJS, ITF, VTF, XTF.

RL
 
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