Driver to drive?

[Jim Thompson]

On Sat, 10 Nov 2012 17:12:50 -0800, Jon Kirwan
<jonk@infinitefactors.org> wrote:

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.

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.

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

For manufacturers of discrete devices, there's no money in spending
time fully characterizing their devices for "Spice".

In the monolithic world it's entirely different. Foundries provide me
full characterization including substrate effects.

And Slowman bloviates. He can't tell an emitter from a collector
without a drawing >:-}

...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 | |
| Voice480)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.

 

[Michael A. Terrell]

Jim Thompson wrote:

And Slowman bloviates. He can't tell an emitter from a collector
without a drawing >:-}

Well based on the fact that he emitts crap and collected welfare for
a decade puts him squarely in the Bipolar camp...

 

[Jim Thompson]

On Sun, 11 Nov 2012 12:17:22 -0500, legg <legg@nospam.magma.ca> wrote:

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

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

Everyone has their own idea, see below, based on a variety of amateur
(usually a know-it-all PhD curve-fitting techniques...

..MODEL Q2N2222_XN NPN(Is=31f Xti=3 Eg=1.11 Vaf=50 Bf=256 Ne=1.34
+ Ise=14f Ikf=50m
+ Xtb=1.5 Br=3.175 Nc=2 Isc=750p Ikr=0 Rc=300m Cjc=7.3p Mjc=341.6m
+ Vjc=750m Fc=500m Cje=22p Mje=377m Vje=750m Tr=95n Tf=332p Itf=10
+ Vtf=30 Xtf=200 Re=300m Rb=30 Re=500m kf=1f

..MODEL 2N2222A_XN NPN(IS=30.611f NF=1.00124 BF=220 IKF=520m VAF=104
+ ISE=7.5f NE=1.41 NR=1.005
+ BR=4 IKR=240m VAR=28 ISC=10.6525p NC=1.3728 RB=130m RE=220m RC=120m
+ CJC=9.12p MJC=350.8m VJC=408.9m CJE=27.01p TF=325p TR=100n)

..model Q2N2222 NPN(Is=14.34f Xti=3 Eg=1.11 Vaf=74.03 Bf=100 Ne=1.307
+ Ise=14.34f Ikf=.2847 Xtb=1.5 Br=6.092 Nc=2 Isc=0 Ikr=0 Rc=1
+ Cjc=38p Mjc=.3416 Vjc=.75 Fc=.5 Cje=126p Mje=.377Vje=.75
+ Tr=200n Tf=12n Itf=.6 Vtf=1.7 Xtf=3 Rb=10)

..model Q2N2222A NPN(Is=14.34f Xti=3 Eg=1.11 Vaf=74.03 Bf=255.9
+ Ne=1.307
+ Ise=14.34f Ikf=.2847 Xtb=1.5 Br=6.092 Nc=2 Isc=0 Ikr=0 Rc=1
+ Cjc=7.306p Mjc=.3416 Vjc=.75 Fc=.5 Cje=22.01p Mje=.377 Vje=.75
+ Tr=46.91n Tf=411.1p Itf=.6 Vtf=1.7 Xtf=3 Rb=10)
* National pid=19 case=TO18
* 88-09-07 bam creation

..MODEL Q2N2222 NPN (
+ IS = 3.97589E-14
+ BF = 195.3412
+ NF = 1.0040078
+ VAF = 53.081
+ IKF = 0.976
+ ISE = 1.60241E-14
+ NE = 1.4791931
+ BR = 1.1107942
+ NR = 0.9928261
+ VAR = 11.3571702
+ IKR = 2.4993953
+ ISC = 1.88505E-12
+ NC = 1.1838278
+ RB = 56.5826472
+ IRB = 1.50459E-4
+ RBM = 5.2592283
+ RE = 0.0402974
+ RC = 0.4208
+ CJE = 2.56E-11
+ VJE = 0.682256
+ MJE = 0.3358856
+ TF = 3.3E-10
+ XTF = 6
+ VTF = 0.574
+ ITF = 0.32
+ PTF = 25.832
+ CJC = 1.40625E-11
+ VJC = 0.5417393
+ MJC = 0.4547893
+ XCJC = 1
+ TR = 3.2E-7
+ CJS = 0
+ VJS = .75
+ MJS = 0
+ XTB = 1.6486
+ EG = 1.11
+ XTI = 5.8315
+ KF = 0
+ AF = 1
+ FC = 0.83

..MODEL Q2N2222A/ZTX NPN IS =3.0611E-14 NF =1.00124 BF =220 IKF=0.52
+ VAF=104 ISE=7.5E-15 NE =1.41 NR =1.005 BR =4 IKR=0.24
+ VAR=28 ISC=1.06525E-11 NC =1.3728 RB =0.13 RE =0.22
+ RC =0.12 CJC=9.12E-12 MJC=0.3508 VJC=0.4089
+ CJE=27.01E-12 TF =0.325E-9 TR =100E-9

...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 | |
| Voice480)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.

 

[Jon Kirwan]

On Sun, 11 Nov 2012 11:00:46 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Sat, 10 Nov 2012 17:12:50 -0800, Jon Kirwan
jonk@infinitefactors.org> wrote:

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.

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.

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

For manufacturers of discrete devices, there's no money in spending
time fully characterizing their devices for "Spice".

Why is that, though? At least, if they ever sell more than
10,000 of them anyway. It takes time, yes. But once for each
time they change the process/FAB. How many times is that?
Can't be that bad considering all the other time that goes
into setting up and manufacturing a line of parts.

In the monolithic world it's entirely different. Foundries provide me
full characterization including substrate effects.
snip

Well, they have a personal interest in wanting your work to
actually be competitive and work well, too. So of course.
Discrete design engineers are mere peons -- and perhaps as a
rule not allowed to rely upon a detailed and thorough
understanding of the physics involved, so what was learned is
often soon forgotten as unused or unreliable instead of being
re-inforced every day, as it may otherwise be if a detailed
knowledge could be relied upon to make their work more
competitive.

I suppose a difference here is that in your work, you are
designing for a specific process and FAB situation, so using
ALL of the knowledge can help create highly competitive
results, whereas people doing discrete design cannot depend
on a specific process/FAB being used. So developing specific
knowledge doesn't pay off in the same ways. Plus, I suspect
that manufacturers would anticipate 100's of times as many
phone calls and pestering emails from engineers if they
provided the information and they just don't want the hassle,
especially since many of the engineers would have forgotten
so much and would need "re-education" which itself would cost
them still more time and effort. Better to just say less and
cut down on pre-sale and after-sale support calls for 5 cent
parts, perhaps.

Jon

 

[Bill Sloman]

On Nov 12, 5:00 am, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
Web-Site.com> wrote:

On Sat, 10 Nov 2012 17:12:50 -0800, Jon Kirwan









j...@infinitefactors.org> wrote:
On Sat, 10 Nov 2012 15:50:02 -0800 (PST), Bill Sloman
bill.slo...@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.

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.

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

For manufacturers of discrete devices, there's no money in spending
time fully characterizing their devices for "Spice".

In the monolithic world it's entirely different.  Foundries provide me
full characterization including substrate effects.

And Slowman bloviates.  He can't tell an emitter from a collector
without a drawing >:-}

It's not trivial, unless you are prepared to risk reverse biasing the
base-emitter junction to breakdown.

--
Bill Sloman, Sydney

 

[Bill Sloman]

On Nov 12, 5:10 am, "Michael A. Terrell" <mike.terr...@earthlink.net>
wrote:

Jim Thompson wrote:

And Slowman bloviates.  He can't tell an emitter from a collector
without a drawing >:-}

   Well based on the fact that he emitts crap and collected welfare for
a decade puts him squarely in the Bipolar camp...

Along with Michael, who has been collecting welfare for longer. He
won't admit that it's welfare, any more than I would agree that
unemployment benefit was welfare, but it's close enough for this kind
of half-baked abuse.

--
Bill Sloman, Sydney

 

[Bill Sloman]

On Nov 12, 5:31 am, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
Web-Site.com> wrote:

On Sun, 11 Nov 2012 12:17:22 -0500, legg <l...@nospam.magma.ca> wrote:
On Sat, 10 Nov 2012 22:53:08 +0100, o pere o <m...@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

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

Everyone has their own idea, see below, based on a variety of amateur
(usually a know-it-all PhD curve-fitting techniques...

.MODEL Q2N2222_XN NPN(Is=31f Xti=3 Eg=1.11 Vaf=50 Bf=256 Ne=1..34
+ Ise=14f Ikf=50m
+ Xtb=1.5 Br=3.175 Nc=2 Isc=750p Ikr=0 Rc=300m Cjc=7.3p Mjc=341.6m
+ Vjc=750m Fc=500m Cje=22p Mje=377m Vje=750m Tr=95n Tf=332p Itf=10
+ Vtf=30 Xtf=200 Re=300m Rb=30 Re=500m kf=1f

.MODEL 2N2222A_XN NPN(IS=30.611f NF=1.00124 BF=220 IKF=520m VAF=104
+ ISE=7.5f NE=1.41 NR=1.005
+ BR=4 IKR=240m VAR=28 ISC=10.6525p NC=1.3728 RB=130m RE=220m RC=120m
+ CJC=9.12p MJC=350.8m VJC=408.9m CJE=27.01p TF=325p TR=100n)

.model Q2N2222  NPN(Is=14.34f Xti=3 Eg=1.11 Vaf=74.03 Bf=100 Ne=1.307
+ Ise=14.34f Ikf=.2847 Xtb=1.5 Br=6.092 Nc=2 Isc=0 Ikr=0 Rc=1
+ Cjc=38p Mjc=.3416 Vjc=.75 Fc=.5 Cje=126p Mje=.377Vje=.75
+ Tr=200n Tf=12n Itf=.6 Vtf=1.7 Xtf=3 Rb=10)

.model Q2N2222A NPN(Is=14.34f Xti=3 Eg=1.11 Vaf=74.03 Bf=255.9
+ Ne=1.307
+ Ise=14.34f Ikf=.2847 Xtb=1.5 Br=6.092 Nc=2 Isc=0 Ikr=0 Rc=1
+ Cjc=7.306p Mjc=.3416 Vjc=.75 Fc=.5 Cje=22.01p Mje=.377 Vje=.75
+ Tr=46.91n Tf=411.1p Itf=.6 Vtf=1.7 Xtf=3 Rb=10)
* National      pid=19          case=TO18
* 88-09-07 bam  creation

.MODEL Q2N2222 NPN      (
+         IS = 3.97589E-14
+         BF = 195.3412
+         NF = 1.0040078
+        VAF = 53.081
+        IKF = 0.976
+        ISE = 1.60241E-14
+         NE = 1.4791931
+         BR = 1.1107942
+         NR = 0.9928261
+        VAR = 11.3571702
+        IKR = 2.4993953
+        ISC = 1.88505E-12
+         NC = 1.1838278
+         RB = 56.5826472
+        IRB = 1.50459E-4
+        RBM = 5.2592283
+         RE = 0.0402974
+         RC = 0.4208
+        CJE = 2.56E-11
+        VJE = 0.682256
+        MJE = 0.3358856
+         TF = 3.3E-10
+        XTF = 6
+        VTF = 0.574
+        ITF = 0.32
+        PTF = 25.832
+        CJC = 1.40625E-11
+        VJC = 0.5417393
+        MJC = 0.4547893
+       XCJC = 1
+         TR = 3.2E-7
+        CJS = 0
+        VJS = .75
+        MJS = 0
+        XTB = 1.6486
+         EG = 1.11
+        XTI = 5.8315
+         KF = 0
+         AF = 1
+         FC = 0.83

.MODEL Q2N2222A/ZTX NPN IS =3.0611E-14 NF =1.00124 BF =220 IKF=0.52
+              VAF=104 ISE=7.5E-15 NE =1.41 NR =1.005 BR =4 IKR=0.24
+              VAR=28 ISC=1.06525E-11 NC =1.3728 RB =0.13 RE =0.22
+              RC =0.12 CJC=9.12E-12 MJC=0.3508 VJC=0.4089
+              CJE=27.01E-12 TF =0.325E-9 TR =100E-9

Of course, a professional would have set up a matrix, where you could
directly compare the different values assigned to a specific parameter
in each different model

awk might even do it for you ...

--
Bill Sloman, Sydney

 

[Jim Thompson]

On Sun, 11 Nov 2012 13:25:23 -0800, Jon Kirwan
<jonk@infinitefactors.org> wrote:

On Sun, 11 Nov 2012 11:00:46 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Sat, 10 Nov 2012 17:12:50 -0800, Jon Kirwan
jonk@infinitefactors.org> wrote:

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.

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.

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

For manufacturers of discrete devices, there's no money in spending
time fully characterizing their devices for "Spice".

Why is that, though? At least, if they ever sell more than
10,000 of them anyway. It takes time, yes. But once for each
time they change the process/FAB. How many times is that?
Can't be that bad considering all the other time that goes
into setting up and manufacturing a line of parts.

In the monolithic world it's entirely different. Foundries provide me
full characterization including substrate effects.
snip

Well, they have a personal interest in wanting your work to
actually be competitive and work well, too. So of course.
Discrete design engineers are mere peons -- and perhaps as a
rule not allowed to rely upon a detailed and thorough
understanding of the physics involved, so what was learned is
often soon forgotten as unused or unreliable instead of being
re-inforced every day, as it may otherwise be if a detailed
knowledge could be relied upon to make their work more
competitive.

I suppose a difference here is that in your work, you are
designing for a specific process and FAB situation, so using
ALL of the knowledge can help create highly competitive
results, whereas people doing discrete design cannot depend
on a specific process/FAB being used. So developing specific
knowledge doesn't pay off in the same ways. Plus, I suspect
that manufacturers would anticipate 100's of times as many
phone calls and pestering emails from engineers if they
provided the information and they just don't want the hassle,
especially since many of the engineers would have forgotten
so much and would need "re-education" which itself would cost
them still more time and effort. Better to just say less and
cut down on pre-sale and after-sale support calls for 5 cent
parts, perhaps.

Jon

One might argue that designing so that "any old shit" device will work
is what real engineering is all about ;-)

In my youth, with help from my oldest son, the programmer, we wrote a
bipolar device model parameter extractor.

I suspect it can now be done with Matlab or even Excel... all you need
is good data for IC and IB versus VBE and VCE.

I suspect that the OP's problem is just C-B or B-E capacitances that
he hadn't considered in his thought processes... "clean" clips only
exist in one's imagination >:-}

...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 | |
| Voice480)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.

 

[Jon Kirwan]

On Sun, 11 Nov 2012 14:44:40 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Sun, 11 Nov 2012 13:25:23 -0800, Jon Kirwan
jonk@infinitefactors.org> wrote:

On Sun, 11 Nov 2012 11:00:46 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Sat, 10 Nov 2012 17:12:50 -0800, Jon Kirwan
jonk@infinitefactors.org> wrote:

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.

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.

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

For manufacturers of discrete devices, there's no money in spending
time fully characterizing their devices for "Spice".

Why is that, though? At least, if they ever sell more than
10,000 of them anyway. It takes time, yes. But once for each
time they change the process/FAB. How many times is that?
Can't be that bad considering all the other time that goes
into setting up and manufacturing a line of parts.

In the monolithic world it's entirely different. Foundries provide me
full characterization including substrate effects.
snip

Well, they have a personal interest in wanting your work to
actually be competitive and work well, too. So of course.
Discrete design engineers are mere peons -- and perhaps as a
rule not allowed to rely upon a detailed and thorough
understanding of the physics involved, so what was learned is
often soon forgotten as unused or unreliable instead of being
re-inforced every day, as it may otherwise be if a detailed
knowledge could be relied upon to make their work more
competitive.

I suppose a difference here is that in your work, you are
designing for a specific process and FAB situation, so using
ALL of the knowledge can help create highly competitive
results, whereas people doing discrete design cannot depend
on a specific process/FAB being used. So developing specific
knowledge doesn't pay off in the same ways. Plus, I suspect
that manufacturers would anticipate 100's of times as many
phone calls and pestering emails from engineers if they
provided the information and they just don't want the hassle,
especially since many of the engineers would have forgotten
so much and would need "re-education" which itself would cost
them still more time and effort. Better to just say less and
cut down on pre-sale and after-sale support calls for 5 cent
parts, perhaps.

Jon

One might argue that designing so that "any old shit" device will work
is what real engineering is all about ;-)

Not if you want to achieve the best possible results or
topologies that depend upon a much fuller knowledge of
parameters. It's just not possible for justify how a PUJT
arranged discrete BJT pair works, if you don't take into
account the reduction in beta as current declines. The
topology just doesn't work otherwise. I'm sure there are many
other examples. Knowing all the gears within gears, so to
speak, allows for a wider range of interesting topologies to
unfold, taking advantage of some behavior area or another.

In my youth, with help from my oldest son, the programmer, we wrote a
bipolar device model parameter extractor.

Nifty. I'd love to see it work on the Fairchild datasheet to
extract Ne and Ise.

I suspect it can now be done with Matlab or even Excel... all you need
is good data for IC and IB versus VBE and VCE.

Right. And there is the problem with datasheets. Of course,
with a tester, you can get that. But you may need to slew
down to 5nA (or less) base currents to extract the slope (Ne)
and the intercept (Ise.)

I suspect that the OP's problem is just C-B or B-E capacitances that
he hadn't considered in his thought processes... "clean" clips only
exist in one's imagination >:-}

I didn't look at the circuit so I can't add any thoughts.

Jon

 

[Jim Thompson]

On Sun, 11 Nov 2012 14:05:44 -0800, Jon Kirwan
<jonk@infinitefactors.org> wrote:

On Sun, 11 Nov 2012 14:44:40 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Sun, 11 Nov 2012 13:25:23 -0800, Jon Kirwan
jonk@infinitefactors.org> wrote:

On Sun, 11 Nov 2012 11:00:46 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Sat, 10 Nov 2012 17:12:50 -0800, Jon Kirwan
jonk@infinitefactors.org> wrote:

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.

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.

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

For manufacturers of discrete devices, there's no money in spending
time fully characterizing their devices for "Spice".

Why is that, though? At least, if they ever sell more than
10,000 of them anyway. It takes time, yes. But once for each
time they change the process/FAB. How many times is that?
Can't be that bad considering all the other time that goes
into setting up and manufacturing a line of parts.

In the monolithic world it's entirely different. Foundries provide me
full characterization including substrate effects.
snip

Well, they have a personal interest in wanting your work to
actually be competitive and work well, too. So of course.
Discrete design engineers are mere peons -- and perhaps as a
rule not allowed to rely upon a detailed and thorough
understanding of the physics involved, so what was learned is
often soon forgotten as unused or unreliable instead of being
re-inforced every day, as it may otherwise be if a detailed
knowledge could be relied upon to make their work more
competitive.

I suppose a difference here is that in your work, you are
designing for a specific process and FAB situation, so using
ALL of the knowledge can help create highly competitive
results, whereas people doing discrete design cannot depend
on a specific process/FAB being used. So developing specific
knowledge doesn't pay off in the same ways. Plus, I suspect
that manufacturers would anticipate 100's of times as many
phone calls and pestering emails from engineers if they
provided the information and they just don't want the hassle,
especially since many of the engineers would have forgotten
so much and would need "re-education" which itself would cost
them still more time and effort. Better to just say less and
cut down on pre-sale and after-sale support calls for 5 cent
parts, perhaps.

Jon

One might argue that designing so that "any old shit" device will work
is what real engineering is all about ;-)

Not if you want to achieve the best possible results or
topologies that depend upon a much fuller knowledge of
parameters. It's just not possible for justify how a PUJT
arranged discrete BJT pair works, if you don't take into
account the reduction in beta as current declines. The
topology just doesn't work otherwise. I'm sure there are many
other examples. Knowing all the gears within gears, so to
speak, allows for a wider range of interesting topologies to
unfold, taking advantage of some behavior area or another.

In my youth, with help from my oldest son, the programmer, we wrote a
bipolar device model parameter extractor.

Nifty. I'd love to see it work on the Fairchild datasheet to
extract Ne and Ise.

Our tool was called, appropriately enough, NE.exe ;-)

I suspect it can now be done with Matlab or even Excel... all you need
is good data for IC and IB versus VBE and VCE.

Datasheets are useless. When I suggested to a major OpAmp
manufacturer that the real way to make behavioral models was to have
me run the real netlist side-by-side with my behavioral implementation
until I attained a complete match... I was basically shown the door
:-(

Right. And there is the problem with datasheets. Of course,
with a tester, you can get that. But you may need to slew
down to 5nA (or less) base currents to extract the slope (Ne)
and the intercept (Ise.)

I suspect that the OP's problem is just C-B or B-E capacitances that
he hadn't considered in his thought processes... "clean" clips only
exist in one's imagination >:-}

I didn't look at the circuit so I can't add any thoughts.

Jon

I saved it to my LTspice directory, but haven't tried it yet... too
much honey-do in the roll-up to Thanksgiving.

And there's already chit-chat about the Christmas scheduling... we're
celebrating it on December 29 this year to accommodate the college
students and the granddaughter already graduated and working.

And my sensitive mind suspects something coming I didn't expect to
live to see... that _granddaughter_ announcing her engagement ;-)

Maybe I'll make it to great-grandfather

...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 | |
| Voice480)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.

 

[Jim Thompson]

On Sun, 11 Nov 2012 14:44:40 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

[snip]

I suspect that the OP's problem is just C-B or B-E capacitances that
he hadn't considered in his thought processes... "clean" clips only
exist in one's imagination >:-}

...Jim Thompson

Confirmed. Actually PSpice reports more negative than LTspice, but
LTspice takes some "liberties" for speed.

The culprit is the B-E capacitance.

The OP should use a smaller (RF) device with lower capacitances.

...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 | |
| Voice480)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.

 

[legg]

On Sun, 11 Nov 2012 12:17:22 -0500, legg <legg@nospam.magma.ca> wrote:

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

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.

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.

ISC, VJE, VJC, VJS, XCJC, FC, MJE, MJC, MJS, ITF, VTF, XTF.

RL

Everyone has their own idea, see below, based on a variety of amateur
(usually a know-it-all PhD curve-fitting techniques...
snip
...Jim Thompson

All those models have the same problem w/r to reverse emitter current
at 25MHz.

Looks like CJE is four orders of magnitude higher than BFR93a or
BFP405.

Correcting this on any of the 2n2222 models fixes it, but I'm not sure
how an emitter junction could be expected to exhibit capacitance in
the 1E-15 range.

RL

 

[o pere o]

On 11/12/2012 01:05 AM, Jim Thompson wrote:

On Sun, 11 Nov 2012 14:44:40 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

[snip]

I suspect that the OP's problem is just C-B or B-E capacitances that
he hadn't considered in his thought processes... "clean" clips only
exist in one's imagination >:-}

...Jim Thompson

Confirmed. Actually PSpice reports more negative than LTspice, but
LTspice takes some "liberties" for speed.

The culprit is the B-E capacitance.

The OP should use a smaller (RF) device with lower capacitances.

...Jim Thompson

Thanks for the input! At 27 kHz, the 2N2222a clips nicely at the bottom.
But, while I expected the 2N2222 to work bad, I would certainly not have
expected this for the BFR93a... in an emitter follower!

Otoh, could you expand on the "liberties" that LTspice takes? Sometimes
speed is not the most important thing.

Pere

 

[o pere o]

On 11/12/2012 03:34 AM, legg wrote:

On Sun, 11 Nov 2012 12:17:22 -0500, legg <legg@nospam.magma.ca> wrote:

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

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.

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.

ISC, VJE, VJC, VJS, XCJC, FC, MJE, MJC, MJS, ITF, VTF, XTF.

RL

Everyone has their own idea, see below, based on a variety of amateur
(usually a know-it-all PhD curve-fitting techniques...
snip
...Jim Thompson

All those models have the same problem w/r to reverse emitter current
at 25MHz.

Looks like CJE is four orders of magnitude higher than BFR93a or
BFP405.

Correcting this on any of the 2n2222 models fixes it, but I'm not sure
how an emitter junction could be expected to exhibit capacitance in
the 1E-15 range.

RL

Well, I have been using a 2N222s model with Cje=22 pF. The BFR93 gives
2pF, i.e. one order of magnitude less and the BFP 405 gives 3.7 fF.

Now it is about time to make some measurements...

Pere

 

[Jim Thompson]

On Mon, 12 Nov 2012 09:55:30 +0100, o pere o <me@somewhere.net> wrote:

On 11/12/2012 01:05 AM, Jim Thompson wrote:
On Sun, 11 Nov 2012 14:44:40 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

[snip]

I suspect that the OP's problem is just C-B or B-E capacitances that
he hadn't considered in his thought processes... "clean" clips only
exist in one's imagination >:-}

...Jim Thompson

Confirmed. Actually PSpice reports more negative than LTspice, but
LTspice takes some "liberties" for speed.

The culprit is the B-E capacitance.

The OP should use a smaller (RF) device with lower capacitances.

...Jim Thompson


Thanks for the input! At 27 kHz, the 2N2222a clips nicely at the bottom.

Your ASC file shows 27e6, that's 27M(ega)Hz, not 27kHz.

But, while I expected the 2N2222 to work bad, I would certainly not have
expected this for the BFR93a... in an emitter follower!

At 27MHz and 1K load, only a few pF does you in.

Otoh, could you expand on the "liberties" that LTspice takes? Sometimes
speed is not the most important thing.

Pere

A glaring example: Their diode model is just a switch. And the
convergence algorithm skips the fine details unless you specify
otherwise... read the manual for details.

...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 | |
| Voice480)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.

 

[legg]

On Mon, 12 Nov 2012 09:55:50 +0100, o pere o <me@somewhere.net> wrote:

On 11/12/2012 03:34 AM, legg wrote:
On Sun, 11 Nov 2012 12:17:22 -0500, legg <legg@nospam.magma.ca> wrote:

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

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.

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.

ISC, VJE, VJC, VJS, XCJC, FC, MJE, MJC, MJS, ITF, VTF, XTF.

RL

Everyone has their own idea, see below, based on a variety of amateur
(usually a know-it-all PhD curve-fitting techniques...
snip
...Jim Thompson

All those models have the same problem w/r to reverse emitter current
at 25MHz.

Looks like CJE is four orders of magnitude higher than BFR93a or
BFP405.

Correcting this on any of the 2n2222 models fixes it, but I'm not sure
how an emitter junction could be expected to exhibit capacitance in
the 1E-15 range.

RL


Well, I have been using a 2N222s model with Cje=22 pF. The BFR93 gives
2pF, i.e. one order of magnitude less and the BFP 405 gives 3.7 fF.

Now it is about time to make some measurements...

Pere

BFR93a in the file I have has CJE of 3.2E-15, similar to BFP405. If
this is altered to 2.2pF, an emitter excursion to -2.5V occurs.

RL

 

[legg]

On Mon, 12 Nov 2012 09:55:50 +0100, o pere o <me@somewhere.net> wrote:

On 11/12/2012 03:34 AM, legg wrote:
On Sun, 11 Nov 2012 12:17:22 -0500, legg <legg@nospam.magma.ca> wrote:

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

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.

ISC, VJE, VJC, VJS, XCJC, FC, MJE, MJC, MJS, ITF, VTF, XTF.

RL

Everyone has their own idea, see below, based on a variety of amateur
(usually a know-it-all PhD curve-fitting techniques...
snip
...Jim Thompson

All those models have the same problem w/r to reverse emitter current
at 25MHz.

Looks like CJE is four orders of magnitude higher than BFR93a or
BFP405.

Correcting this on any of the 2n2222 models fixes it, but I'm not sure
how an emitter junction could be expected to exhibit capacitance in
the 1E-15 range.

RL


Well, I have been using a 2N222s model with Cje=22 pF. The BFR93 gives
2pF, i.e. one order of magnitude less and the BFP 405 gives 3.7 fF.

Now it is about time to make some measurements...

Pere

There is also an issue with CJC, in combination with RB, that defines
the delay and speed of the falling edge of the emitter-follower
rectifier. Capacitance with the same orders of magnitude difference
show up, producing a spike, if significant.

Gummel-Poon BJT modeling is aimed at small-signal representations,
where DC-biased variables are roughly static (even if non-linear).
I've seen this combated with look-up tables, but it's slooooow.

Still can't see femtofarads in bipolar parts, considering size and
packaging.

RL

 

[Jim Thompson]

On Mon, 12 Nov 2012 14:22:48 -0500, legg <legg@nospam.magma.ca> wrote:

On Mon, 12 Nov 2012 09:55:50 +0100, o pere o <me@somewhere.net> wrote:

On 11/12/2012 03:34 AM, legg wrote:
On Sun, 11 Nov 2012 12:17:22 -0500, legg <legg@nospam.magma.ca> wrote:

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

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.

ISC, VJE, VJC, VJS, XCJC, FC, MJE, MJC, MJS, ITF, VTF, XTF.

RL

Everyone has their own idea, see below, based on a variety of amateur
(usually a know-it-all PhD curve-fitting techniques...
snip
...Jim Thompson

All those models have the same problem w/r to reverse emitter current
at 25MHz.

Looks like CJE is four orders of magnitude higher than BFR93a or
BFP405.

Correcting this on any of the 2n2222 models fixes it, but I'm not sure
how an emitter junction could be expected to exhibit capacitance in
the 1E-15 range.

RL


Well, I have been using a 2N222s model with Cje=22 pF. The BFR93 gives
2pF, i.e. one order of magnitude less and the BFP 405 gives 3.7 fF.

Now it is about time to make some measurements...

Pere

There is also an issue with CJC, in combination with RB, that defines
the delay and speed of the falling edge of the emitter-follower
rectifier. Capacitance with the same orders of magnitude difference
show up, producing a spike, if significant.

Gummel-Poon BJT modeling is aimed at small-signal representations,
where DC-biased variables are roughly static (even if non-linear).
I've seen this combated with look-up tables, but it's slooooow.

Wrong. If you properly extract all the parameters it correctly models
everything but deep saturation and injection into substrate. PSpice
adds the ability to model that region (used to be useful in TTL days
;-); and also provides an alternate model, MEXTRAM.

Still can't see femtofarads in bipolar parts, considering size and
packaging.

RL

The intrinsic device might go that low if the emitter is implanted
rather than diffused.

From an Atmel process (Atmel46K, that I've run at 5GHz ....

cje_ceb_1x_mean = 1.02114E-14 ; 0.01pF !!

...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 | |
| Voice480)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.

 

[legg]

On Mon, 12 Nov 2012 12:41:46 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Mon, 12 Nov 2012 14:22:48 -0500, legg <legg@nospam.magma.ca> wrote:

On Mon, 12 Nov 2012 09:55:50 +0100, o pere o <me@somewhere.net> wrote:

snip
The 2n2222a model may be missing (from inspection of popular models)
ISC, VJE, VJC, VJS, XCJC, FC, MJE, MJC, MJS, ITF, VTF, XTF.
snip
Everyone has their own idea, see below, based on a variety of amateur
(usually a know-it-all PhD curve-fitting techniques...
snip
...Jim Thompson

All those models have the same problem w/r to reverse emitter current
at 25MHz.

Looks like CJE is four orders of magnitude higher than BFR93a or
BFP405.

Correcting this on any of the 2n2222 models fixes it, but I'm not sure
how an emitter junction could be expected to exhibit capacitance in
the 1E-15 range.

RL


Well, I have been using a 2N222s model with Cje=22 pF. The BFR93 gives
2pF, i.e. one order of magnitude less and the BFP 405 gives 3.7 fF.

Now it is about time to make some measurements...

Pere

There is also an issue with CJC, in combination with RB, that defines
the delay and speed of the falling edge of the emitter-follower
rectifier. Capacitance with the same orders of magnitude difference
show up, producing a spike, if significant.

Gummel-Poon BJT modeling is aimed at small-signal representations,
where DC-biased variables are roughly static (even if non-linear).
I've seen this combated with look-up tables, but it's slooooow.

Wrong. If you properly extract all the parameters it correctly models
everything but deep saturation and injection into substrate. PSpice
adds the ability to model that region (used to be useful in TTL days
;-); and also provides an alternate model, MEXTRAM.

Could you identify the parameters that ensure this accuracy?
Does it include any of those presently missing?

RL

 

[Fred Abse]

On Sat, 03 Nov 2012 08:29:46 -0700, Fred Abse wrote:

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

The sample was too long to get meaningful open and shorted measurements,
but the TDR showed some unexpected results.

On a 1.2 meter length of cable. transit time was 9.5 nanoseconds, giving
a velocity of 42.11% of c. That corresponds to a dielectric permittivity
of 5.64, which is too high for any flexible dielectric I know of. That
suggests that the inner conductor is a helix. Resistance is 186.66 ohms
per meter. Inductance calculates (from rho at the sending end, and
velocity), to be 1.07 uH per meter, and capacitance 58.6 pF per meter.

The following model corresponds quite closely with measured data:


..model scopecbl ltra (
+ len=1.2
+ R=186.666
+ L=1.07E-006
+ C=5.86E-011)

The following is a good approximation to what the TDR shows. Change the
time (X) axis to "time/2" to show one-way time.


Version 4
SHEET 1 880 680
WIRE -160 128 -320 128
WIRE -16 128 -64 128
WIRE -320 272 -320 208
WIRE -160 272 -160 160
WIRE -160 272 -320 272
WIRE -64 272 -64 160
WIRE -64 272 -160 272
WIRE -16 272 -16 160
WIRE -16 272 -64 272
WIRE 32 272 -16 272
WIRE 80 272 80 160
WIRE 80 272 32 272
FLAG 32 272 0
SYMBOL ltline 32 144 R0
SYMATTR InstName O1
SYMATTR Value scopecbl
SYMBOL voltage -320 112 R0
WINDOW 3 -159 -8 Left 2
WINDOW 123 24 132 Left 2
WINDOW 39 24 28 Left 2
SYMATTR Value PULSE(0 1 0 22p 22p 1u 2u 1)
SYMATTR SpiceLine Rser=50
SYMATTR InstName V1
SYMBOL tline -112 144 R0
SYMATTR InstName T1
SYMATTR Value Td=1n Z0=50
TEXT -312 384 Left 2 !.tran 0 100n 0 1p
TEXT -312 336 Left 2 !.opt plotwinsize=0
TEXT -40 336 Left 2 !.model scopecbl ltra (\n+ len=1.2\n+ R=186.666\n+ L=1.07E-006\n+ C=5.86E-011)
TEXT -312 360 Left 2 !.plot v(n001)
TEXT -176 72 Left 2 ;TDR Simulation



--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)