Diode-Connected Transistors
in [Design]
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From: Jim Thompson on 21 Jul 2010 21:25 On Wed, 21 Jul 2010 21:19:45 -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: > >>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* UNPUBLISHED LICENSED SOFTWARE * 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. PSpice does. As far back as when I put TTL outputs on PLL chips :-) > >> >>>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. There's actually a chapter in one of my PSpice tomes addressing thermal modeling. > >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 ...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: John Larkin on 21 Jul 2010 22:10 On Wed, 21 Jul 2010 15:18:13 +1000, Grant <omg(a)grrr.id.au> 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 > >John L. was going to check BJT diode performance back on the thread: > >>Subject: Re: Types of diode-connected BJTs >>Date: Fri, 09 Jul 2010 08:04:56 -0700 >>Message-ID: <1hee36hr0l0mm2dri4eml98is3mntfidld(a)4ax.com> >>... >>I'll try the BFT25 with the emitter open and shorted to the base, when >>I get a chance. I'd be interested in comparing both leakage and >>capacitance. As I mentioned, fA leakage testing is tedious. > >Hope you find time for this one John? > >I though Jim T. was going to do something with these too, now he has. He ran Spice. I measured actual transistors. > >Might've been a different thread that I can't find? > > >Time flies differently when one is having all their teeth ripped >out :) > >Grant. OK, I gave it a try. My measurement resolution is 1 fA, but things get dicey down there and things take minutes to settle. My best guess is that, at 5 volts reverse, the c-b junction of a BFT25A leaks about 4 fA at room temp. If I repeat with b-e shorted, it increases to about 7 or maybe 8 fA, close to twice the leakage. I did parallel the transistor with a 1T resistor (which leaks 5 whopping picoamperes at 5 volts) and got close to the expected current, so my measurement rig isn't being too obviously silly. Even if I'm off some, the BFT25 c-b junction is the lowest leakage diode I've ever encountered. John
From: Grant on 21 Jul 2010 22:44 On Wed, 21 Jul 2010 19:10:04 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Wed, 21 Jul 2010 15:18:13 +1000, Grant <omg(a)grrr.id.au> 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 >> >>John L. was going to check BJT diode performance back on the thread: >> >>>Subject: Re: Types of diode-connected BJTs >>>Date: Fri, 09 Jul 2010 08:04:56 -0700 >>>Message-ID: <1hee36hr0l0mm2dri4eml98is3mntfidld(a)4ax.com> >>>... >>>I'll try the BFT25 with the emitter open and shorted to the base, when >>>I get a chance. I'd be interested in comparing both leakage and >>>capacitance. As I mentioned, fA leakage testing is tedious. >> >>Hope you find time for this one John? >> >>I though Jim T. was going to do something with these too, now he has. > >He ran Spice. I measured actual transistors. > >> >>Might've been a different thread that I can't find? >> >> >>Time flies differently when one is having all their teeth ripped >>out :) >> >>Grant. > >OK, I gave it a try. My measurement resolution is 1 fA, but things get >dicey down there and things take minutes to settle. My best guess is >that, at 5 volts reverse, the c-b junction of a BFT25A leaks about 4 >fA at room temp. If I repeat with b-e shorted, it increases to about 7 >or maybe 8 fA, close to twice the leakage. > >I did parallel the transistor with a 1T resistor (which leaks 5 >whopping picoamperes at 5 volts) and got close to the expected >current, so my measurement rig isn't being too obviously silly. > >Even if I'm off some, the BFT25 c-b junction is the lowest leakage >diode I've ever encountered. Thanks, John. I was unsure whether you had connected the emitter back when you mentioned how low the c-b junction leakage was. Someone wrote that connecting the emitter (can't find the thread, though) changed things -- can't remember if it was good or bad, I thought it was good, possibly in a totally different context. So now we now about the very sensitive end of low leakage diodes :) Complete with sanity check! I settled for a 1N3595 recently as it leaks a lot less (1nA) than the 'HC4053 analog mux chip (100nA, both datasheet 25'C numbers) it is protecting from signal over-voltage. For the curious, I have two signals, out of OP07s running from +12V and -5V, via 1k6 resistor, a 1N3595 diode to 4V stops the signal exceeding 5V as it goes into a 'hc4053 mux switch. There's a cap to analog ground as well. The 4V is a TL431 with scaling resistors (could use 3.9V zener) sinking several mA so it has low impedance. I'm using +12/-5 because the OP07 output doesn't go anywhere near supply rails, and the negative signal on one channel may go about a volt or so -ve. Both signals can go to ~3V +ve. Grant.
From: John Larkin on 21 Jul 2010 22:59 On Thu, 22 Jul 2010 12:44:18 +1000, Grant <omg(a)grrr.id.au> wrote: >On Wed, 21 Jul 2010 19:10:04 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Wed, 21 Jul 2010 15:18:13 +1000, Grant <omg(a)grrr.id.au> 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 >>> >>>John L. was going to check BJT diode performance back on the thread: >>> >>>>Subject: Re: Types of diode-connected BJTs >>>>Date: Fri, 09 Jul 2010 08:04:56 -0700 >>>>Message-ID: <1hee36hr0l0mm2dri4eml98is3mntfidld(a)4ax.com> >>>>... >>>>I'll try the BFT25 with the emitter open and shorted to the base, when >>>>I get a chance. I'd be interested in comparing both leakage and >>>>capacitance. As I mentioned, fA leakage testing is tedious. >>> >>>Hope you find time for this one John? >>> >>>I though Jim T. was going to do something with these too, now he has. >> >>He ran Spice. I measured actual transistors. >> >>> >>>Might've been a different thread that I can't find? >>> >>> >>>Time flies differently when one is having all their teeth ripped >>>out :) >>> >>>Grant. >> >>OK, I gave it a try. My measurement resolution is 1 fA, but things get >>dicey down there and things take minutes to settle. My best guess is >>that, at 5 volts reverse, the c-b junction of a BFT25A leaks about 4 >>fA at room temp. If I repeat with b-e shorted, it increases to about 7 >>or maybe 8 fA, close to twice the leakage. >> >>I did parallel the transistor with a 1T resistor (which leaks 5 >>whopping picoamperes at 5 volts) and got close to the expected >>current, so my measurement rig isn't being too obviously silly. >> >>Even if I'm off some, the BFT25 c-b junction is the lowest leakage >>diode I've ever encountered. > >Thanks, John. > >I was unsure whether you had connected the emitter back when you >mentioned how low the c-b junction leakage was. Someone wrote that >connecting the emitter (can't find the thread, though) changed >things -- can't remember if it was good or bad, I thought it was >good, possibly in a totally different context. > > >So now we now about the very sensitive end of low leakage diodes :) >Complete with sanity check! > > >I settled for a 1N3595 recently as it leaks a lot less (1nA) than the >'HC4053 analog mux chip (100nA, both datasheet 25'C numbers) it is >protecting from signal over-voltage. > >For the curious, I have two signals, out of OP07s running from +12V >and -5V, via 1k6 resistor, a 1N3595 diode to 4V stops the signal >exceeding 5V as it goes into a 'hc4053 mux switch. There's a cap >to analog ground as well. The 4V is a TL431 with scaling resistors >(could use 3.9V zener) sinking several mA so it has low impedance. Good. Don't count on the HC40xx mux ESD diodes to clamp signals, even if the source resistance is high. Once you get a little beyond the rails, the internal series switch fets can be turned on, and all hell breaks loose, many nanoamps of it. Central Semi makes some nice dual super-low-leakage surface-mount diodes, 10s of fA. John
From: krw on 21 Jul 2010 23:30 On Wed, 21 Jul 2010 18:22:53 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >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 ?:-) Semi manufacturers treat their models like the family jewels they are. You signed NDAs for all the models you have, didn't you? IBIS models aren't (at least none that I know of) released under NDA because they really are behavioral.
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