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Unconnected part LTSpice seems to need (weird ...)

Started by Joerg August 14, 2011
On Wed, 17 Aug 2011 11:02:07 -0700, Joerg <invalid@invalid.invalid> wrote:

>John Larkin wrote: >> On Wed, 17 Aug 2011 09:32:26 -0700, Joerg <invalid@invalid.invalid> >> wrote: >> >>> Phil Hobbs wrote: >>>> On 08/16/2011 05:56 AM, Fred_Bartoli wrote: > >[...] > >>> >>>>> And ill conditionned systems can give you pretty chaotic results (change >>>>> some starting conditions just a little bit and you have 'unpredictable' >>>>> widely different result). No surprise there. >>>>> >>>>> It's not spice fault, it's you that don't see the implication of what >>>>> you're doing, as I already said. >>>> It's a reasonable question why it should work at all, though, and why it >>>> silently generates wrong answers without complaining. >>>> >>>> ISTM it's a minor bug in the heuristics. >>>> >>> Forrest Gump would have said "It's like a box of chocolates, you never >>> know what you gonna get" :-) >> >> Some sims will go from running in seconds to running in hours, with >> minor changes. >> >> I used to run a DOS sim, called ECA, that didn't use the Spice core. >> It was cool, ran very fast on a 486. It would announce, but cruise >> right through, warnings of singularities, divide by zero, all that >> stuff. It just kept going. >> > >Interesting, I also grew up with good old ECA224 but that was when the >286 was the latest and greatest. It was quite a useful simulator. >Someone told me it merged into EWB but when I tried that at a client I >did not like it anymore. For my consulting office I bought MicroSim >PSpice. It came with those nice cloth covered IBM-style binders. > >I find this sim behavior odd. It seems only naturaly that, in a >"what-if" scenario, an engineer disconnects just one leg of a part. >After all, that's how we also do it in real life. SPICE is not supposed >to "partially smoosh that" and then not tell anyone.
Mikey is fond of hanging "gmin" on unconnected nodes. I would suspect there's a setting to turn that off, then you get "floating node" errors until you find them all ;-) ...Jim Thompson [On the Road, in New York] -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Jim Thompson wrote:
> On Wed, 17 Aug 2011 11:02:07 -0700, Joerg <invalid@invalid.invalid> wrote: > >> John Larkin wrote: >>> On Wed, 17 Aug 2011 09:32:26 -0700, Joerg <invalid@invalid.invalid> >>> wrote: >>> >>>> Phil Hobbs wrote: >>>>> On 08/16/2011 05:56 AM, Fred_Bartoli wrote: >> [...] >> >>>>>> And ill conditionned systems can give you pretty chaotic results (change >>>>>> some starting conditions just a little bit and you have 'unpredictable' >>>>>> widely different result). No surprise there. >>>>>> >>>>>> It's not spice fault, it's you that don't see the implication of what >>>>>> you're doing, as I already said. >>>>> It's a reasonable question why it should work at all, though, and why it >>>>> silently generates wrong answers without complaining. >>>>> >>>>> ISTM it's a minor bug in the heuristics. >>>>> >>>> Forrest Gump would have said "It's like a box of chocolates, you never >>>> know what you gonna get" :-) >>> Some sims will go from running in seconds to running in hours, with >>> minor changes. >>> >>> I used to run a DOS sim, called ECA, that didn't use the Spice core. >>> It was cool, ran very fast on a 486. It would announce, but cruise >>> right through, warnings of singularities, divide by zero, all that >>> stuff. It just kept going. >>> >> Interesting, I also grew up with good old ECA224 but that was when the >> 286 was the latest and greatest. It was quite a useful simulator. >> Someone told me it merged into EWB but when I tried that at a client I >> did not like it anymore. For my consulting office I bought MicroSim >> PSpice. It came with those nice cloth covered IBM-style binders. >> >> I find this sim behavior odd. It seems only naturaly that, in a >> "what-if" scenario, an engineer disconnects just one leg of a part. >> After all, that's how we also do it in real life. SPICE is not supposed >> to "partially smoosh that" and then not tell anyone. > > Mikey is fond of hanging "gmin" on unconnected nodes. I would suspect there's > a setting to turn that off, then you get "floating node" errors until you find > them all ;-) >
I'd certainly prefer floating node error messages over guestimating what LTSpice might hang onto a node that is unconnected in the schematic. -- Regards, Joerg http://www.analogconsultants.com/
"Joerg" <invalid@invalid.invalid> a &#2013265929;crit dans le message de 
news:9avccjFfkgU1@mid.individual.net...
> Martin Brown wrote: >> On 14/08/2011 23:33, Joerg wrote: >>> Folks, >>> >>> This is close to voodoo but repeatable. Unfortunately I can't disclose >>> the schematic since it is for a client. Just wondering , anyone had this >>> before? >>> >>> At the far end of a TX line I used to have a diode connected across >>> because a previous version of a chip would have such a substrat path. >>> Nice waveforms, fast sims. Everything as expected and peachy. Now the >>> new iteration of the chip design won't have this diode path so I chopped >>> off its cathode connection. Sims fine. So I deleted the diode -> >>> ka-crunch ... sim slows down and the ouput is junk. >>> >>> If I put the diode back in and connect only its anode -> fine. If I >>> leave the anode open and only connect the cathode it still sims but the >>> results are different. >>> >>> <scratching head> >> >> I am always amazed how well spice works these days. Best I can suggest >> is start deleting other nodes and components to try and get a minimum >> size network that shows the problem and can be disclosed publicly. >> > > I did that a couple of days ago, it's attached again. > > >> If you only connect the anode but to the wrong side of where the diode >> goes do you get the "anode connected" behaviour or the other one? >> > > Then the sim completely bombed on me. Like Fred said, it is possible > that SPICE incudes this diode in the matrix and chokes on it. But then > it's supposed to issue an error message and not just fly straight into > terrain. >
Looking a bit further (I don't use LTspice as my current production tool) it happens that: * a default 10^-12 gmin option is permanently set. No way to defeat it, apprat from, maybe, setting it to zero. * look at the log file. The unconnected node is detected. -- Thanks, Fred.
Fred_Bartoli wrote:
> > "Joerg" <invalid@invalid.invalid> a &#2013265929;crit dans le message de > news:9avccjFfkgU1@mid.individual.net... >> Martin Brown wrote: >>> On 14/08/2011 23:33, Joerg wrote: >>>> Folks, >>>> >>>> This is close to voodoo but repeatable. Unfortunately I can't disclose >>>> the schematic since it is for a client. Just wondering , anyone had >>>> this >>>> before? >>>> >>>> At the far end of a TX line I used to have a diode connected across >>>> because a previous version of a chip would have such a substrat path. >>>> Nice waveforms, fast sims. Everything as expected and peachy. Now the >>>> new iteration of the chip design won't have this diode path so I >>>> chopped >>>> off its cathode connection. Sims fine. So I deleted the diode -> >>>> ka-crunch ... sim slows down and the ouput is junk. >>>> >>>> If I put the diode back in and connect only its anode -> fine. If I >>>> leave the anode open and only connect the cathode it still sims but the >>>> results are different. >>>> >>>> <scratching head> >>> >>> I am always amazed how well spice works these days. Best I can suggest >>> is start deleting other nodes and components to try and get a minimum >>> size network that shows the problem and can be disclosed publicly. >>> >> >> I did that a couple of days ago, it's attached again. >> >> >>> If you only connect the anode but to the wrong side of where the diode >>> goes do you get the "anode connected" behaviour or the other one? >>> >> >> Then the sim completely bombed on me. Like Fred said, it is possible >> that SPICE incudes this diode in the matrix and chokes on it. But then >> it's supposed to issue an error message and not just fly straight into >> terrain. >> > > Looking a bit further (I don't use LTspice as my current production > tool) it happens that: > * a default 10^-12 gmin option is permanently set. No way to defeat it, > apprat from, maybe, setting it to zero. > * look at the log file. The unconnected node is detected. >
Thanks, this would explain a lot. That's what Jim suspected, he beat you by 14 minutes :-) Well, if it can't be turned off I guess I'll have to learn to live with that stuff. No complaints because LTSpice is free and generally doesn't crash. Other SPICEs cost an arm amnd a leg and crash a lot. -- Regards, Joerg http://www.analogconsultants.com/
On Wed, 17 Aug 2011 15:40:55 -0700, Joerg <invalid@invalid.invalid> wrote:

>Fred_Bartoli wrote: >> >> "Joerg" <invalid@invalid.invalid> a &#2013265929;crit dans le message de >> news:9avccjFfkgU1@mid.individual.net... >>> Martin Brown wrote: >>>> On 14/08/2011 23:33, Joerg wrote: >>>>> Folks, >>>>> >>>>> This is close to voodoo but repeatable. Unfortunately I can't disclose >>>>> the schematic since it is for a client. Just wondering , anyone had >>>>> this >>>>> before? >>>>> >>>>> At the far end of a TX line I used to have a diode connected across >>>>> because a previous version of a chip would have such a substrat path. >>>>> Nice waveforms, fast sims. Everything as expected and peachy. Now the >>>>> new iteration of the chip design won't have this diode path so I >>>>> chopped >>>>> off its cathode connection. Sims fine. So I deleted the diode -> >>>>> ka-crunch ... sim slows down and the ouput is junk. >>>>> >>>>> If I put the diode back in and connect only its anode -> fine. If I >>>>> leave the anode open and only connect the cathode it still sims but the >>>>> results are different. >>>>> >>>>> <scratching head> >>>> >>>> I am always amazed how well spice works these days. Best I can suggest >>>> is start deleting other nodes and components to try and get a minimum >>>> size network that shows the problem and can be disclosed publicly. >>>> >>> >>> I did that a couple of days ago, it's attached again. >>> >>> >>>> If you only connect the anode but to the wrong side of where the diode >>>> goes do you get the "anode connected" behaviour or the other one? >>>> >>> >>> Then the sim completely bombed on me. Like Fred said, it is possible >>> that SPICE incudes this diode in the matrix and chokes on it. But then >>> it's supposed to issue an error message and not just fly straight into >>> terrain. >>> >> >> Looking a bit further (I don't use LTspice as my current production >> tool) it happens that: >> * a default 10^-12 gmin option is permanently set. No way to defeat it, >> apprat from, maybe, setting it to zero. >> * look at the log file. The unconnected node is detected. >> > >Thanks, this would explain a lot. That's what Jim suspected, he beat you >by 14 minutes :-) > >Well, if it can't be turned off I guess I'll have to learn to live with >that stuff. No complaints because LTSpice is free and generally doesn't >crash. Other SPICEs cost an arm amnd a leg and crash a lot.
In PSpice each component's pins can be defined as connect with gmin or report error. So maybe it's a component issue? ...Jim Thompson [On the Road, in New York] -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On 8/17/2011 5:40 PM, Joerg wrote:
> Fred_Bartoli wrote: >> >> "Joerg"<invalid@invalid.invalid> a &#2013265929;crit dans le message de >> news:9avccjFfkgU1@mid.individual.net... >>> Martin Brown wrote: >>>> On 14/08/2011 23:33, Joerg wrote: >>>>> Folks, >>>>> >>>>> This is close to voodoo but repeatable. Unfortunately I can't disclose >>>>> the schematic since it is for a client. Just wondering , anyone had >>>>> this >>>>> before? >>>>> >>>>> At the far end of a TX line I used to have a diode connected across >>>>> because a previous version of a chip would have such a substrat path. >>>>> Nice waveforms, fast sims. Everything as expected and peachy. Now the >>>>> new iteration of the chip design won't have this diode path so I >>>>> chopped >>>>> off its cathode connection. Sims fine. So I deleted the diode -> >>>>> ka-crunch ... sim slows down and the ouput is junk. >>>>> >>>>> If I put the diode back in and connect only its anode -> fine. If I >>>>> leave the anode open and only connect the cathode it still sims but the >>>>> results are different. >>>>> >>>>> <scratching head> >>>> >>>> I am always amazed how well spice works these days. Best I can suggest >>>> is start deleting other nodes and components to try and get a minimum >>>> size network that shows the problem and can be disclosed publicly. >>>> >>> >>> I did that a couple of days ago, it's attached again. >>> >>> >>>> If you only connect the anode but to the wrong side of where the diode >>>> goes do you get the "anode connected" behaviour or the other one? >>>> >>> >>> Then the sim completely bombed on me. Like Fred said, it is possible >>> that SPICE incudes this diode in the matrix and chokes on it. But then >>> it's supposed to issue an error message and not just fly straight into >>> terrain. >>> >> >> Looking a bit further (I don't use LTspice as my current production >> tool) it happens that: >> * a default 10^-12 gmin option is permanently set. No way to defeat it, >> apprat from, maybe, setting it to zero. >> * look at the log file. The unconnected node is detected. >> > > Thanks, this would explain a lot. That's what Jim suspected, he beat you > by 14 minutes :-) > > Well, if it can't be turned off I guess I'll have to learn to live with > that stuff. No complaints because LTSpice is free and generally doesn't > crash. Other SPICEs cost an arm amnd a leg and crash a lot. >
In LTSpice click Tools/Control Panel. Click the Spice tab. Change Gmin as you wish in the upper right box. John S
John S wrote:
> On 8/17/2011 5:40 PM, Joerg wrote: >> Fred_Bartoli wrote: >>> >>> "Joerg"<invalid@invalid.invalid> a &#2013265929;crit dans le message de >>> news:9avccjFfkgU1@mid.individual.net... >>>> Martin Brown wrote: >>>>> On 14/08/2011 23:33, Joerg wrote: >>>>>> Folks, >>>>>> >>>>>> This is close to voodoo but repeatable. Unfortunately I can't >>>>>> disclose >>>>>> the schematic since it is for a client. Just wondering , anyone had >>>>>> this >>>>>> before? >>>>>> >>>>>> At the far end of a TX line I used to have a diode connected across >>>>>> because a previous version of a chip would have such a substrat path. >>>>>> Nice waveforms, fast sims. Everything as expected and peachy. Now the >>>>>> new iteration of the chip design won't have this diode path so I >>>>>> chopped >>>>>> off its cathode connection. Sims fine. So I deleted the diode -> >>>>>> ka-crunch ... sim slows down and the ouput is junk. >>>>>> >>>>>> If I put the diode back in and connect only its anode -> fine. If I >>>>>> leave the anode open and only connect the cathode it still sims >>>>>> but the >>>>>> results are different. >>>>>> >>>>>> <scratching head> >>>>> >>>>> I am always amazed how well spice works these days. Best I can suggest >>>>> is start deleting other nodes and components to try and get a minimum >>>>> size network that shows the problem and can be disclosed publicly. >>>>> >>>> >>>> I did that a couple of days ago, it's attached again. >>>> >>>> >>>>> If you only connect the anode but to the wrong side of where the diode >>>>> goes do you get the "anode connected" behaviour or the other one? >>>>> >>>> >>>> Then the sim completely bombed on me. Like Fred said, it is possible >>>> that SPICE incudes this diode in the matrix and chokes on it. But then >>>> it's supposed to issue an error message and not just fly straight into >>>> terrain. >>>> >>> >>> Looking a bit further (I don't use LTspice as my current production >>> tool) it happens that: >>> * a default 10^-12 gmin option is permanently set. No way to defeat it, >>> apprat from, maybe, setting it to zero. >>> * look at the log file. The unconnected node is detected. >>> >> >> Thanks, this would explain a lot. That's what Jim suspected, he beat you >> by 14 minutes :-) >> >> Well, if it can't be turned off I guess I'll have to learn to live with >> that stuff. No complaints because LTSpice is free and generally doesn't >> crash. Other SPICEs cost an arm amnd a leg and crash a lot. >> > > In LTSpice click Tools/Control Panel. > Click the Spice tab. > Change Gmin as you wish in the upper right box. >
Could be dicey. If I set it to zero other things my go kablouie because it's then universal. -- Regards, Joerg http://www.analogconsultants.com/
On Wed, 17 Aug 2011 16:44:36 -0700, Joerg <invalid@invalid.invalid> wrote:

>John S wrote: >> On 8/17/2011 5:40 PM, Joerg wrote: >>> Fred_Bartoli wrote: >>>> >>>> "Joerg"<invalid@invalid.invalid> a &#2013265929;crit dans le message de >>>> news:9avccjFfkgU1@mid.individual.net... >>>>> Martin Brown wrote: >>>>>> On 14/08/2011 23:33, Joerg wrote: >>>>>>> Folks, >>>>>>> >>>>>>> This is close to voodoo but repeatable. Unfortunately I can't >>>>>>> disclose >>>>>>> the schematic since it is for a client. Just wondering , anyone had >>>>>>> this >>>>>>> before? >>>>>>> >>>>>>> At the far end of a TX line I used to have a diode connected across >>>>>>> because a previous version of a chip would have such a substrat path. >>>>>>> Nice waveforms, fast sims. Everything as expected and peachy. Now the >>>>>>> new iteration of the chip design won't have this diode path so I >>>>>>> chopped >>>>>>> off its cathode connection. Sims fine. So I deleted the diode -> >>>>>>> ka-crunch ... sim slows down and the ouput is junk. >>>>>>> >>>>>>> If I put the diode back in and connect only its anode -> fine. If I >>>>>>> leave the anode open and only connect the cathode it still sims >>>>>>> but the >>>>>>> results are different. >>>>>>> >>>>>>> <scratching head> >>>>>> >>>>>> I am always amazed how well spice works these days. Best I can suggest >>>>>> is start deleting other nodes and components to try and get a minimum >>>>>> size network that shows the problem and can be disclosed publicly. >>>>>> >>>>> >>>>> I did that a couple of days ago, it's attached again. >>>>> >>>>> >>>>>> If you only connect the anode but to the wrong side of where the diode >>>>>> goes do you get the "anode connected" behaviour or the other one? >>>>>> >>>>> >>>>> Then the sim completely bombed on me. Like Fred said, it is possible >>>>> that SPICE incudes this diode in the matrix and chokes on it. But then >>>>> it's supposed to issue an error message and not just fly straight into >>>>> terrain. >>>>> >>>> >>>> Looking a bit further (I don't use LTspice as my current production >>>> tool) it happens that: >>>> * a default 10^-12 gmin option is permanently set. No way to defeat it, >>>> apprat from, maybe, setting it to zero. >>>> * look at the log file. The unconnected node is detected. >>>> >>> >>> Thanks, this would explain a lot. That's what Jim suspected, he beat you >>> by 14 minutes :-) >>> >>> Well, if it can't be turned off I guess I'll have to learn to live with >>> that stuff. No complaints because LTSpice is free and generally doesn't >>> crash. Other SPICEs cost an arm amnd a leg and crash a lot. >>> >> >> In LTSpice click Tools/Control Panel. >> Click the Spice tab. >> Change Gmin as you wish in the upper right box. >> > >Could be dicey. If I set it to zero other things my go kablouie because >it's then universal.
The VALUE of gmin isn't the problem, it's that unconnected pins are being connected to ground (most likely) via gmin. I basically only use LTspice as a viwer and to run netlists, so I don't know the ins-and-outs of configuring pins. Make sure your symbols don't default to connecting thru gmin, rather than balking. ...Jim Thompson [On the Road, in New York] -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Wed, 17 Aug 2011 19:59:44 -0400, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

>On Wed, 17 Aug 2011 16:44:36 -0700, Joerg <invalid@invalid.invalid> wrote: > >>John S wrote: >>> On 8/17/2011 5:40 PM, Joerg wrote: >>>> Fred_Bartoli wrote: >>>>> >>>>> "Joerg"<invalid@invalid.invalid> a &#2013265929;crit dans le message de >>>>> news:9avccjFfkgU1@mid.individual.net... >>>>>> Martin Brown wrote: >>>>>>> On 14/08/2011 23:33, Joerg wrote: >>>>>>>> Folks, >>>>>>>> >>>>>>>> This is close to voodoo but repeatable. Unfortunately I can't >>>>>>>> disclose >>>>>>>> the schematic since it is for a client. Just wondering , anyone had >>>>>>>> this >>>>>>>> before? >>>>>>>> >>>>>>>> At the far end of a TX line I used to have a diode connected across >>>>>>>> because a previous version of a chip would have such a substrat path. >>>>>>>> Nice waveforms, fast sims. Everything as expected and peachy. Now the >>>>>>>> new iteration of the chip design won't have this diode path so I >>>>>>>> chopped >>>>>>>> off its cathode connection. Sims fine. So I deleted the diode -> >>>>>>>> ka-crunch ... sim slows down and the ouput is junk. >>>>>>>> >>>>>>>> If I put the diode back in and connect only its anode -> fine. If I >>>>>>>> leave the anode open and only connect the cathode it still sims >>>>>>>> but the >>>>>>>> results are different. >>>>>>>> >>>>>>>> <scratching head> >>>>>>> >>>>>>> I am always amazed how well spice works these days. Best I can suggest >>>>>>> is start deleting other nodes and components to try and get a minimum >>>>>>> size network that shows the problem and can be disclosed publicly. >>>>>>> >>>>>> >>>>>> I did that a couple of days ago, it's attached again. >>>>>> >>>>>> >>>>>>> If you only connect the anode but to the wrong side of where the diode >>>>>>> goes do you get the "anode connected" behaviour or the other one? >>>>>>> >>>>>> >>>>>> Then the sim completely bombed on me. Like Fred said, it is possible >>>>>> that SPICE incudes this diode in the matrix and chokes on it. But then >>>>>> it's supposed to issue an error message and not just fly straight into >>>>>> terrain. >>>>>> >>>>> >>>>> Looking a bit further (I don't use LTspice as my current production >>>>> tool) it happens that: >>>>> * a default 10^-12 gmin option is permanently set. No way to defeat it, >>>>> apprat from, maybe, setting it to zero. >>>>> * look at the log file. The unconnected node is detected. >>>>> >>>> >>>> Thanks, this would explain a lot. That's what Jim suspected, he beat you >>>> by 14 minutes :-) >>>> >>>> Well, if it can't be turned off I guess I'll have to learn to live with >>>> that stuff. No complaints because LTSpice is free and generally doesn't >>>> crash. Other SPICEs cost an arm amnd a leg and crash a lot. >>>> >>> >>> In LTSpice click Tools/Control Panel. >>> Click the Spice tab. >>> Change Gmin as you wish in the upper right box. >>> >> >>Could be dicey. If I set it to zero other things my go kablouie because >>it's then universal. > >The VALUE of gmin isn't the problem, it's that unconnected pins are being >connected to ground (most likely) via gmin. I basically only use LTspice as a >viwer and to run netlists, so I don't know the ins-and-outs of configuring >pins. Make sure your symbols don't default to connecting thru gmin, rather >than balking. > > ...Jim Thompson > > [On the Road, in New York]
topologycheck Num. 1 Set to zero to skip check for floating nodes, loops of voltage sources, and non-physical transformer winding topology Make sure it's set to "1" ...Jim Thompson [On the Road, in New York] -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Wed, 17 Aug 2011 20:08:11 -0400, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

>On Wed, 17 Aug 2011 19:59:44 -0400, Jim Thompson ><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: > >>On Wed, 17 Aug 2011 16:44:36 -0700, Joerg <invalid@invalid.invalid> wrote: >> >>>John S wrote: >>>> On 8/17/2011 5:40 PM, Joerg wrote: >>>>> Fred_Bartoli wrote: >>>>>> >>>>>> "Joerg"<invalid@invalid.invalid> a &#2013265929;crit dans le message de >>>>>> news:9avccjFfkgU1@mid.individual.net... >>>>>>> Martin Brown wrote: >>>>>>>> On 14/08/2011 23:33, Joerg wrote: >>>>>>>>> Folks, >>>>>>>>> >>>>>>>>> This is close to voodoo but repeatable. Unfortunately I can't >>>>>>>>> disclose >>>>>>>>> the schematic since it is for a client. Just wondering , anyone had >>>>>>>>> this >>>>>>>>> before? >>>>>>>>> >>>>>>>>> At the far end of a TX line I used to have a diode connected across >>>>>>>>> because a previous version of a chip would have such a substrat path. >>>>>>>>> Nice waveforms, fast sims. Everything as expected and peachy. Now the >>>>>>>>> new iteration of the chip design won't have this diode path so I >>>>>>>>> chopped >>>>>>>>> off its cathode connection. Sims fine. So I deleted the diode -> >>>>>>>>> ka-crunch ... sim slows down and the ouput is junk. >>>>>>>>> >>>>>>>>> If I put the diode back in and connect only its anode -> fine. If I >>>>>>>>> leave the anode open and only connect the cathode it still sims >>>>>>>>> but the >>>>>>>>> results are different. >>>>>>>>> >>>>>>>>> <scratching head> >>>>>>>> >>>>>>>> I am always amazed how well spice works these days. Best I can suggest >>>>>>>> is start deleting other nodes and components to try and get a minimum >>>>>>>> size network that shows the problem and can be disclosed publicly. >>>>>>>> >>>>>>> >>>>>>> I did that a couple of days ago, it's attached again. >>>>>>> >>>>>>> >>>>>>>> If you only connect the anode but to the wrong side of where the diode >>>>>>>> goes do you get the "anode connected" behaviour or the other one? >>>>>>>> >>>>>>> >>>>>>> Then the sim completely bombed on me. Like Fred said, it is possible >>>>>>> that SPICE incudes this diode in the matrix and chokes on it. But then >>>>>>> it's supposed to issue an error message and not just fly straight into >>>>>>> terrain. >>>>>>> >>>>>> >>>>>> Looking a bit further (I don't use LTspice as my current production >>>>>> tool) it happens that: >>>>>> * a default 10^-12 gmin option is permanently set. No way to defeat it, >>>>>> apprat from, maybe, setting it to zero. >>>>>> * look at the log file. The unconnected node is detected. >>>>>> >>>>> >>>>> Thanks, this would explain a lot. That's what Jim suspected, he beat you >>>>> by 14 minutes :-) >>>>> >>>>> Well, if it can't be turned off I guess I'll have to learn to live with >>>>> that stuff. No complaints because LTSpice is free and generally doesn't >>>>> crash. Other SPICEs cost an arm amnd a leg and crash a lot. >>>>> >>>> >>>> In LTSpice click Tools/Control Panel. >>>> Click the Spice tab. >>>> Change Gmin as you wish in the upper right box. >>>> >>> >>>Could be dicey. If I set it to zero other things my go kablouie because >>>it's then universal. >> >>The VALUE of gmin isn't the problem, it's that unconnected pins are being >>connected to ground (most likely) via gmin. I basically only use LTspice as a >>viwer and to run netlists, so I don't know the ins-and-outs of configuring >>pins. Make sure your symbols don't default to connecting thru gmin, rather >>than balking. >> >> ...Jim Thompson >> >> [On the Road, in New York] > >topologycheck > Num. > 1 > Set to zero to skip check for floating nodes, loops of voltage sources, and >non-physical transformer winding topology > >Make sure it's set to "1" > > ...Jim Thompson > > [On the Road, in New York]
Also... "Mark unconnected pins: Draw a small square at each unconnected pin to flag it as unconnected." ...Jim Thompson [On the Road, in New York] -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.