Diode-Connected Transistors
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From: Stephan Goldstein on 21 Jul 2010 20:01 On Tue, 20 Jul 2010 18:02:54 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >Got an E-mail from Grant advising that I promised a comparison of the >various ways of doing Diode-Connected Transistors. So here it is... > >www.analog-innovations.com/SED/DiodeConnectedTransistors.pdf > > ...Jim Thompson This is interesting as far as it goes, but I have some questions... What type of model is this - Gummel-Poon, G-P with extensions (e.g. Kull-Nagel modeling of quasisaturation, this is common), Mextram, or ?? I think it's not likely to be HiCUM or VBIC95, which never found widespread use, most likely it's GP It's not as accurate as Mextram, especially at high collector currents, but is pretty much the lingua franca of publicly available simulators. Where did the model come from, and how accurate is it, especially at high current? Generating accurate models, especially for high collector currents, is rather tricky. The model guys I work with have spent a long time learning how to do it well. How well do you trust the reverse parameters in the model? These are often sloppily done, or simply left as model defaults. Does the model include self-heating effects? These have a very strong influence on the high-current behavior. Standard TO-92 can be in the hundreds of degrees per Watt, this effect can't become important! Some of the smaller transistors I've worked with in dielectrically-isolated monolithic processes have thermal resistances of several *thousand* degrees per Watt! I recall a paper from many years ago that did this sort of comparison, including (possibly) reverse-recovery time. The conclusion was that the shorted base-collector gave the best diode overall. I spent half an hour rifling through all my files this morning but couldn't find it, and I had no luck on the IEEE web site. It's frustrating as I can clearly visualize the pages; it might have been IEEE or IRE, I don't believe it was IEE. If I can find it I'll post the reference. It was probably done in the 1960s or early 1970s. steve
From: Jim Thompson on 21 Jul 2010 20:19 On Wed, 21 Jul 2010 20:01:51 -0400, Stephan Goldstein <sgoldHAM(a)alum.mit.edu> wrote: >On Tue, 20 Jul 2010 18:02:54 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: > >>Got an E-mail from Grant advising that I promised a comparison of the >>various ways of doing Diode-Connected Transistors. So here it is... >> >>www.analog-innovations.com/SED/DiodeConnectedTransistors.pdf >> >> ...Jim Thompson > >This is interesting as far as it goes, but I have some questions... > >What type of model is this - Gummel-Poon, G-P with extensions >(e.g. Kull-Nagel modeling of quasisaturation, this is common), >Mextram, or ?? ************************************** * Model Generated by MODPEX * *Copyright(c) Symmetry Design Systems* * All Rights Reserved * * UNPUBLISHED LICENSED SOFTWARE * * Contains Proprietary Information * * Which is The Property of * * SYMMETRY OR ITS LICENSORS * *Commercial Use or Resale Restricted * * by Symmetry License Agreement * ************************************** * Model generated on Aug 7, 01 * MODEL FORMAT: PSpice *$ ..MODEL Q2n3904 npn +IS=1.26532e-10 BF=206.302 NF=1.5 VAF=1000 ; Look at IS and VAF :-) +IKF=0.0272221 ISE=2.30771e-09 NE=3.31052 BR=20.6302 +NR=2.89609 VAR=9.39809 IKR=0.272221 ISC=2.30771e-09 +NC=1.9876 RB=5.8376 IRB=50.3624 RBM=0.634251 +RE=0.0001 RC=2.65711 XTB=0.1 XTI=1 +EG=1.05 CJE=4.64214e-12 VJE=0.4 MJE=0.256227 +TF=4.19578e-10 XTF=0.906167 VTF=8.75418 ITF=0.0105823 +CJC=3.76961e-12 VJC=0.4 MJC=0.238109 XCJC=0.8 +FC=0.512134 CJS=0 VJS=0.75 MJS=0.5 +TR=6.82023e-08 PTF=0 KF=0 AF=1 This is an ON-Semiconductor-supplied library No quasi-saturation.... only I/C houses seem to supply that information. >I think it's not likely to be HiCUM or VBIC95, >which never found widespread use, most likely it's GP It's not as >accurate as Mextram, especially at high collector currents, but is >pretty much the lingua franca of publicly available simulators. > >Where did the model come from, and how accurate is it, especially >at high current? Who knows? I didn't do the modeling myself. >Generating accurate models, especially for high >collector currents, is rather tricky. The model guys I work with >have spent a long time learning how to do it well. Overnight I had a request. I simply spit it thru the mechanism. I only believe (in my I/C world) in BE_CB_Short > >How well do you trust the reverse parameters in the model? These >are often sloppily done, or simply left as model defaults. Not much! I spent much of my early years writing software to extract NE, ISE, etc., kind of data > >Does the model include self-heating effects? Of course not. Though one could create a subcircuit, IF you were so inclined. Personally I rarely EVER use on-chip diodes for other than signal and level-shifting activities. >These have a very >strong influence on the high-current behavior. Standard TO-92 >can be in the hundreds of degrees per Watt, this effect can't >become important! Some of the smaller transistors I've worked >with in dielectrically-isolated monolithic processes have thermal >resistances of several *thousand* degrees per Watt! > >I recall a paper from many years ago that did this sort of comparison, >including (possibly) reverse-recovery time. The conclusion was that >the shorted base-collector gave the best diode overall. I spent half >an hour rifling through all my files this morning but couldn't find >it, and I had no luck on the IEEE web site. It's frustrating as I can >clearly visualize the pages; it might have been IEEE or IRE, I don't >believe it was IEE. If I can find it I'll post the reference. It was >probably done in the 1960s or early 1970s. > >steve Having just been thru a painful episode with IBIS models I would gleefully donate the powder necessary to blow all IEEE committees to hell ;-) ...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 | Spice is like a sports car... Only as good as the person behind the wheel.
From: Stephan Goldstein on 21 Jul 2010 21:08 On Wed, 21 Jul 2010 17:19:32 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: <Lots of snippage> > >Having just been thru a painful episode with IBIS models I would >gleefully donate the powder necessary to blow all IEEE committees to >hell ;-) > > ...Jim Thompson Indeed. We fought the same (IBIS) battle a few years ago, with inconclusive results after a lot of effort expended. It was kind of funny/sad really, the customer requesting this was worried about all the wrong things, and somehow believe that having a model they could simulate would make up for a rather large case of cluelessness. They were all wrapped up in the high-speed digital interconnect between their chip and ours, and not nearly concerned enough about the very high-quality signal path required between our chip's output and the real world...
From: Stephan Goldstein on 21 Jul 2010 21:19 On Wed, 21 Jul 2010 17:19:32 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Wed, 21 Jul 2010 20:01:51 -0400, Stephan Goldstein ><sgoldHAM(a)alum.mit.edu> wrote: > >>On Tue, 20 Jul 2010 18:02:54 -0700, Jim Thompson >><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >> >>>Got an E-mail from Grant advising that I promised a comparison of the >>>various ways of doing Diode-Connected Transistors. So here it is... >>> >>>www.analog-innovations.com/SED/DiodeConnectedTransistors.pdf >>> >>> ...Jim Thompson >> >>This is interesting as far as it goes, but I have some questions... >> >>What type of model is this - Gummel-Poon, G-P with extensions >>(e.g. Kull-Nagel modeling of quasisaturation, this is common), >>Mextram, or ?? > >************************************** >* Model Generated by MODPEX * >*Copyright(c) Symmetry Design Systems* >* All Rights Reserved * >* UNPUBLISHED LICENSED SOFTWARE * >* Contains Proprietary Information * >* Which is The Property of * >* SYMMETRY OR ITS LICENSORS * >*Commercial Use or Resale Restricted * >* by Symmetry License Agreement * >************************************** >* Model generated on Aug 7, 01 >* MODEL FORMAT: PSpice >*$ >.MODEL Q2n3904 npn >+IS=1.26532e-10 BF=206.302 NF=1.5 VAF=1000 ; Look at IS and VAF :-) >+IKF=0.0272221 ISE=2.30771e-09 NE=3.31052 BR=20.6302 >+NR=2.89609 VAR=9.39809 IKR=0.272221 ISC=2.30771e-09 >+NC=1.9876 RB=5.8376 IRB=50.3624 RBM=0.634251 >+RE=0.0001 RC=2.65711 XTB=0.1 XTI=1 >+EG=1.05 CJE=4.64214e-12 VJE=0.4 MJE=0.256227 >+TF=4.19578e-10 XTF=0.906167 VTF=8.75418 ITF=0.0105823 >+CJC=3.76961e-12 VJC=0.4 MJC=0.238109 XCJC=0.8 >+FC=0.512134 CJS=0 VJS=0.75 MJS=0.5 >+TR=6.82023e-08 PTF=0 KF=0 AF=1 > >This is an ON-Semiconductor-supplied library > It has the _look_ of being extracted, but with that IS and VAF I'd be mighty suspicious. RE looks pretty unrealistic at 100 micro-ohms. >No quasi-saturation.... only I/C houses seem to supply that >information. Yes, it's difficult to extract, and I don't think any publicly available simulators support those kinds of models. > >>I think it's not likely to be HiCUM or VBIC95, >>which never found widespread use, most likely it's GP It's not as >>accurate as Mextram, especially at high collector currents, but is >>pretty much the lingua franca of publicly available simulators. >> >>Where did the model come from, and how accurate is it, especially >>at high current? > >Who knows? I didn't do the modeling myself. > >>Generating accurate models, especially for high >>collector currents, is rather tricky. The model guys I work with >>have spent a long time learning how to do it well. > >Overnight I had a request. I simply spit it thru the mechanism. I >only believe (in my I/C world) in BE_CB_Short > Ditto, I wouldn't trust anything else. >> >>How well do you trust the reverse parameters in the model? These >>are often sloppily done, or simply left as model defaults. > >Not much! I spent much of my early years writing software to extract >NE, ISE, etc., kind of data > >> >>Does the model include self-heating effects? > >Of course not. Though one could create a subcircuit, IF you were so >inclined. > That's an interesting area, actually. The standard subcircuit (used in the Mextram model) is a parallel RC and current source. The current is based on Ic*Vce, R gives the static self-heating, and C makes the time-constant, which can be low microseconds for small dielectrically-isolated transistors. The transistor has an additional node that represents the device temperature in Kelvin as a voltage relative to ground. The "logical" thing to do would be to connect together the thermal nodes of two closely-spaced critical transistors like an input pair to model thermal crosstalk, but this gives a VERY wrong, non-physical result. It turns out that modeling anything more than individual device self-heating with any degree of accuracy is a *very* hard problem. >Personally I rarely EVER use on-chip diodes for other than signal and >level-shifting activities. > >>These have a very >>strong influence on the high-current behavior. Standard TO-92 >>can be in the hundreds of degrees per Watt, this effect can't >>become important! Some of the smaller transistors I've worked >>with in dielectrically-isolated monolithic processes have thermal >>resistances of several *thousand* degrees per Watt! >> >>I recall a paper from many years ago that did this sort of comparison, >>including (possibly) reverse-recovery time. The conclusion was that >>the shorted base-collector gave the best diode overall. I spent half >>an hour rifling through all my files this morning but couldn't find >>it, and I had no luck on the IEEE web site. It's frustrating as I can >>clearly visualize the pages; it might have been IEEE or IRE, I don't >>believe it was IEE. If I can find it I'll post the reference. It was >>probably done in the 1960s or early 1970s. >> >>steve > >Having just been thru a painful episode with IBIS models I would >gleefully donate the powder necessary to blow all IEEE committees to >hell ;-) > > ...Jim Thompson
From: Jim Thompson on 21 Jul 2010 21:22 On Wed, 21 Jul 2010 21:08:36 -0400, Stephan Goldstein <sgoldHAM(a)alum.mit.edu> wrote: >On Wed, 21 Jul 2010 17:19:32 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: > ><Lots of snippage> >> >>Having just been thru a painful episode with IBIS models I would >>gleefully donate the powder necessary to blow all IEEE committees to >>hell ;-) >> >> ...Jim Thompson > >Indeed. We fought the same (IBIS) battle a few years ago, with >inconclusive results after a lot of effort expended. It was kind of >funny/sad really, the customer requesting this was worried about all >the wrong things, and somehow believe that having a model they could >simulate would make up for a rather large case of cluelessness. They >were all wrapped up in the high-speed digital interconnect between >their chip and ours, and not nearly concerned enough about the very >high-quality signal path required between our chip's output and the >real world... What I don't understand... why not just a behavioral model that runs under Spice? Why all this dumbness of tabulating V-I and T-V data? More Cadence self-aggrandizement ?:-) ...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 | Spice is like a sports car... Only as good as the person behind the wheel.
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