>He said "-a connection to +15V seems to have been edited out at some point-" - >looks like a NO CONNECTION to me, and on a power supply pin, seems straightforwardWell, it depends. LTspice will complain about floating nodes, but that doesn't cover all the possibilities by a lot. I gave a few examples that would meet Bill's description but would make such an automatic check very hard to implement. Cheers Phil Hobbs
Defect in Analog Devices Spice model for the AD734
Started by ●July 4, 2015
Reply by ●July 5, 20152015-07-05
Reply by ●July 5, 20152015-07-05
On Sunday, July 5, 2015 at 2:05:11 PM UTC-4, Phil Hobbs wrote:> >He said "-a connection to +15V seems to have been edited out at some point-" - > >looks like a NO CONNECTION to me, and on a power supply pin, seems straightforward > > Well, it depends. LTspice will complain about floating nodes, but that doesn't cover all the possibilities by a lot. I gave a few examples that would meet Bill's description but would make such an automatic check very hard to implement. > > Cheers > > Phil HobbsMy first completely mindless thought on that one would be to message the user on a potential problem and let him/her either abort the sim to fix it or ignore and proceed. This is not rocket science.
Reply by ●July 5, 20152015-07-05
On 07/05/2015 02:53 PM, bloggs.fredbloggs.fred@gmail.com wrote:> On Sunday, July 5, 2015 at 2:05:11 PM UTC-4, Phil Hobbs wrote: >>> He said "-a connection to +15V seems to have been edited out at >>> some point-" - looks like a NO CONNECTION to me, and on a power >>> supply pin, seems straightforward >> >> Well, it depends. LTspice will complain about floating nodes, but >> that doesn't cover all the possibilities by a lot. I gave a few >> examples that would meet Bill's description but would make such an >> automatic check very hard to implement. >> >> Cheers >> >> Phil Hobbs > > My first completely mindless thought on that one would be to message > the user on a potential problem and let him/her either abort the sim > to fix it or ignore and proceed. This is not rocket science. >I'm not so sure it's that easy. Annoying pop-up messages about non-errors would get old pretty fast. Something written to the log file might be okay, like a compiler warning. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 5, 20152015-07-05
On Sun, 5 Jul 2015 07:50:03 -0700 (PDT), bloggs.fredbloggs.fred@gmail.com wrote:>On Sunday, July 5, 2015 at 7:58:07 AM UTC-4, Bill Sloman wrote: >> On Saturday, July 4, 2015 at 12:23:27 PM UTC+2, Bill Sloman wrote: >> > I've been using the Analog Devices Spice model in LTSpice to model the AD734 running with a current output - see Figure 25 on page 13 of the Rev E AD734 data sheet >> > >> > http://www.analog.com/media/en/technical-documentation/data-sheets/AD734.pdf >> > >> > When running a roughly 15kHz sine wave through the device, the positive current output limits at something between +200uA and +280uA. >> > >> > The voltage at the W and Z1 outputs of the AD734 is well below the rail. >> > >> > I've tried 2.2k, 6.8k and 15k current setting resistors. Only with 15k did the voltage at the W and Z1 outputs get high enough to be interesting. >> > >> > The current clipped at +200uA with 2.2k, +282.77uA at 6.8k and +267.94uA at 15k. >> > >> > The negative-going excursions looked perfectly sinusoidal, and went down to -350uA. >> > >> > Working in another region of operation, with more head-room, the currents clamped a lot higher, at about +800uA, when the negative currents were getting down to -2.4mA. >> > >> > It looks very much as if there's some kind of silly mistake in the AD734 Spice model (which would interest Jim Thompson, who wants to sell Analog Devices better Spice models). >> > >> > If the actual device acted like the model, the data sheet wouldn't talk about +/-10mA output current limits (as it does on page 13). >> > >> > It's easy enough to hand-edit .cir files, if you kno0w what you are doing. Any advice will be gratefully received. I probably should have raised this with Analog Devices directly, but the price they charge for the AD734 means that they can't be selling many of them, which doesn't suggest that I'd get a prompt response. >> >> Oops. It looks as if the defect wasn't in the Analog Devices model, but in my circuit diagram - a connection to +15V seems to have been edited out at some point and the circuit was getting it's positive power supply from its inputs, making the model inconveniently realistic - I've had that happen on real circuits, and it can take a while to work out what's going wrong. >> >> My apologies to one and all. >> >> -- >> Bill Sloman, Sydney > >LTSpice is an example of why engineers should NOT design CAD. I've never seen such absolute crap anywhere. The program should have flagged the schematic entry error.If the disconnected power supply connection was simulated accurately, then Spice did good. Spice should simulate what you draw, not question it. It does check for a few physically appropriate things, like floating nodes, singularities, and such. I sometimes connect opamp power pins to things that are not supply rails. I wouldn't want or expect Spice to prevent that.
Reply by ●July 5, 20152015-07-05
On Sunday, July 5, 2015 at 3:02:16 PM UTC-4, Phil Hobbs wrote:> On 07/05/2015 02:53 PM, bloggs.fredbloggs.fred@gmail.com wrote: > > On Sunday, July 5, 2015 at 2:05:11 PM UTC-4, Phil Hobbs wrote: > >>> He said "-a connection to +15V seems to have been edited out at > >>> some point-" - looks like a NO CONNECTION to me, and on a power > >>> supply pin, seems straightforward > >> > >> Well, it depends. LTspice will complain about floating nodes, but > >> that doesn't cover all the possibilities by a lot. I gave a few > >> examples that would meet Bill's description but would make such an > >> automatic check very hard to implement. > >> > >> Cheers > >> > >> Phil Hobbs > > > > My first completely mindless thought on that one would be to message > > the user on a potential problem and let him/her either abort the sim > > to fix it or ignore and proceed. This is not rocket science. > > > > I'm not so sure it's that easy. Annoying pop-up messages about > non-errors would get old pretty fast. Something written to the log file > might be okay, like a compiler warning.I don't think there are so many power supply pins that it would become an annoyance. Then there are all those friggin floating ground errors the pos (any SPICE) doesn't tell you about, except by displaying screwy results or locking up in some infinite loop.> > Cheers > > Phil Hobbs > > > -- > Dr Philip C D Hobbs > Principal Consultant > ElectroOptical Innovations LLC > Optics, Electro-optics, Photonics, Analog Electronics > > 160 North State Road #203 > Briarcliff Manor NY 10510 > > hobbs at electrooptical dot net > http://electrooptical.net
Reply by ●July 5, 20152015-07-05
On Sunday, July 5, 2015 at 3:55:57 PM UTC-4, John Larkin wrote:> On Sun, 5 Jul 2015 07:50:03 -0700 (PDT), > bloggs.fredbloggs.fred@gmail.com wrote: > > >On Sunday, July 5, 2015 at 7:58:07 AM UTC-4, Bill Sloman wrote: > >> On Saturday, July 4, 2015 at 12:23:27 PM UTC+2, Bill Sloman wrote: > >> > I've been using the Analog Devices Spice model in LTSpice to model the AD734 running with a current output - see Figure 25 on page 13 of the Rev E AD734 data sheet > >> > > >> > http://www.analog.com/media/en/technical-documentation/data-sheets/AD734.pdf > >> > > >> > When running a roughly 15kHz sine wave through the device, the positive current output limits at something between +200uA and +280uA. > >> > > >> > The voltage at the W and Z1 outputs of the AD734 is well below the rail. > >> > > >> > I've tried 2.2k, 6.8k and 15k current setting resistors. Only with 15k did the voltage at the W and Z1 outputs get high enough to be interesting. > >> > > >> > The current clipped at +200uA with 2.2k, +282.77uA at 6.8k and +267.94uA at 15k. > >> > > >> > The negative-going excursions looked perfectly sinusoidal, and went down to -350uA. > >> > > >> > Working in another region of operation, with more head-room, the currents clamped a lot higher, at about +800uA, when the negative currents were getting down to -2.4mA. > >> > > >> > It looks very much as if there's some kind of silly mistake in the AD734 Spice model (which would interest Jim Thompson, who wants to sell Analog Devices better Spice models). > >> > > >> > If the actual device acted like the model, the data sheet wouldn't talk about +/-10mA output current limits (as it does on page 13). > >> > > >> > It's easy enough to hand-edit .cir files, if you kno0w what you are doing. Any advice will be gratefully received. I probably should have raised this with Analog Devices directly, but the price they charge for the AD734 means that they can't be selling many of them, which doesn't suggest that I'd get a prompt response. > >> > >> Oops. It looks as if the defect wasn't in the Analog Devices model, but in my circuit diagram - a connection to +15V seems to have been edited out at some point and the circuit was getting it's positive power supply from its inputs, making the model inconveniently realistic - I've had that happen on real circuits, and it can take a while to work out what's going wrong. > >> > >> My apologies to one and all. > >> > >> -- > >> Bill Sloman, Sydney > > > >LTSpice is an example of why engineers should NOT design CAD. I've never seen such absolute crap anywhere. The program should have flagged the schematic entry error. > > If the disconnected power supply connection was simulated accurately, > then Spice did good. Spice should simulate what you draw, not question > it. It does check for a few physically appropriate things, like > floating nodes, singularities, and such.That would be some other program but not SPICE, SPICE is simple.> > I sometimes connect opamp power pins to things that are not supply > rails. I wouldn't want or expect Spice to prevent that.
Reply by ●July 5, 20152015-07-05
On Sun, 5 Jul 2015 13:24:22 -0700 (PDT), bloggs.fredbloggs.fred@gmail.com wrote:>On Sunday, July 5, 2015 at 3:55:57 PM UTC-4, John Larkin wrote: >> On Sun, 5 Jul 2015 07:50:03 -0700 (PDT), >> bloggs.fredbloggs.fred@gmail.com wrote: >> >> >On Sunday, July 5, 2015 at 7:58:07 AM UTC-4, Bill Sloman wrote: >> >> On Saturday, July 4, 2015 at 12:23:27 PM UTC+2, Bill Sloman wrote: >> >> > I've been using the Analog Devices Spice model in LTSpice to model the AD734 running with a current output - see Figure 25 on page 13 of the Rev E AD734 data sheet >> >> > >> >> > http://www.analog.com/media/en/technical-documentation/data-sheets/AD734.pdf >> >> > >> >> > When running a roughly 15kHz sine wave through the device, the positive current output limits at something between +200uA and +280uA. >> >> > >> >> > The voltage at the W and Z1 outputs of the AD734 is well below the rail. >> >> > >> >> > I've tried 2.2k, 6.8k and 15k current setting resistors. Only with 15k did the voltage at the W and Z1 outputs get high enough to be interesting. >> >> > >> >> > The current clipped at +200uA with 2.2k, +282.77uA at 6.8k and +267.94uA at 15k. >> >> > >> >> > The negative-going excursions looked perfectly sinusoidal, and went down to -350uA. >> >> > >> >> > Working in another region of operation, with more head-room, the currents clamped a lot higher, at about +800uA, when the negative currents were getting down to -2.4mA. >> >> > >> >> > It looks very much as if there's some kind of silly mistake in the AD734 Spice model (which would interest Jim Thompson, who wants to sell Analog Devices better Spice models). >> >> > >> >> > If the actual device acted like the model, the data sheet wouldn't talk about +/-10mA output current limits (as it does on page 13). >> >> > >> >> > It's easy enough to hand-edit .cir files, if you kno0w what you are doing. Any advice will be gratefully received. I probably should have raised this with Analog Devices directly, but the price they charge for the AD734 means that they can't be selling many of them, which doesn't suggest that I'd get a prompt response. >> >> >> >> Oops. It looks as if the defect wasn't in the Analog Devices model, but in my circuit diagram - a connection to +15V seems to have been edited out at some point and the circuit was getting it's positive power supply from its inputs, making the model inconveniently realistic - I've had that happen on real circuits, and it can take a while to work out what's going wrong. >> >> >> >> My apologies to one and all. >> >> >> >> -- >> >> Bill Sloman, Sydney >> > >> >LTSpice is an example of why engineers should NOT design CAD. I've never seen such absolute crap anywhere. The program should have flagged the schematic entry error. >> >> If the disconnected power supply connection was simulated accurately, >> then Spice did good. Spice should simulate what you draw, not question >> it. It does check for a few physically appropriate things, like >> floating nodes, singularities, and such. > >That would be some other program but not SPICE, SPICE is simple.In LT Spice, connect two voltage sources. Or leave a current source unloaded. Or make a double assignment in a .PARAM expression. You'll get warnings. It doesn't seem to mind one end of a cap floating, but that's physically OK. It sensibly complains about a totally floating component or circuit. Overall, it behaves pretty well.
Reply by ●July 5, 20152015-07-05
On Sunday, July 5, 2015 at 4:55:53 PM UTC-4, John Larkin wrote:> On Sun, 5 Jul 2015 13:24:22 -0700 (PDT), > bloggs.fredbloggs.fred@gmail.com wrote: > > >On Sunday, July 5, 2015 at 3:55:57 PM UTC-4, John Larkin wrote: > >> On Sun, 5 Jul 2015 07:50:03 -0700 (PDT), > >> bloggs.fredbloggs.fred@gmail.com wrote: > >> > >> >On Sunday, July 5, 2015 at 7:58:07 AM UTC-4, Bill Sloman wrote: > >> >> On Saturday, July 4, 2015 at 12:23:27 PM UTC+2, Bill Sloman wrote: > >> >> > I've been using the Analog Devices Spice model in LTSpice to model the AD734 running with a current output - see Figure 25 on page 13 of the Rev E AD734 data sheet > >> >> > > >> >> > http://www.analog.com/media/en/technical-documentation/data-sheets/AD734.pdf > >> >> > > >> >> > When running a roughly 15kHz sine wave through the device, the positive current output limits at something between +200uA and +280uA. > >> >> > > >> >> > The voltage at the W and Z1 outputs of the AD734 is well below the rail. > >> >> > > >> >> > I've tried 2.2k, 6.8k and 15k current setting resistors. Only with 15k did the voltage at the W and Z1 outputs get high enough to be interesting. > >> >> > > >> >> > The current clipped at +200uA with 2.2k, +282.77uA at 6.8k and +267.94uA at 15k. > >> >> > > >> >> > The negative-going excursions looked perfectly sinusoidal, and went down to -350uA. > >> >> > > >> >> > Working in another region of operation, with more head-room, the currents clamped a lot higher, at about +800uA, when the negative currents were getting down to -2.4mA. > >> >> > > >> >> > It looks very much as if there's some kind of silly mistake in the AD734 Spice model (which would interest Jim Thompson, who wants to sell Analog Devices better Spice models). > >> >> > > >> >> > If the actual device acted like the model, the data sheet wouldn't talk about +/-10mA output current limits (as it does on page 13). > >> >> > > >> >> > It's easy enough to hand-edit .cir files, if you kno0w what you are doing. Any advice will be gratefully received. I probably should have raised this with Analog Devices directly, but the price they charge for the AD734 means that they can't be selling many of them, which doesn't suggest that I'd get a prompt response. > >> >> > >> >> Oops. It looks as if the defect wasn't in the Analog Devices model, but in my circuit diagram - a connection to +15V seems to have been edited out at some point and the circuit was getting it's positive power supply from its inputs, making the model inconveniently realistic - I've had that happen on real circuits, and it can take a while to work out what's going wrong. > >> >> > >> >> My apologies to one and all. > >> >> > >> >> -- > >> >> Bill Sloman, Sydney > >> > > >> >LTSpice is an example of why engineers should NOT design CAD. I've never seen such absolute crap anywhere. The program should have flagged the schematic entry error. > >> > >> If the disconnected power supply connection was simulated accurately, > >> then Spice did good. Spice should simulate what you draw, not question > >> it. It does check for a few physically appropriate things, like > >> floating nodes, singularities, and such. > > > >That would be some other program but not SPICE, SPICE is simple. > > In LT Spice, connect two voltage sources. Or leave a current source > unloaded. Or make a double assignment in a .PARAM expression. You'll > get warnings. > > It doesn't seem to mind one end of a cap floating, but that's > physically OK. It sensibly complains about a totally floating > component or circuit. > > Overall, it behaves pretty well.Maybe, but that has nothing to do with simulating an IC with power pin open.
Reply by ●July 5, 20152015-07-05
On Sun, 5 Jul 2015 15:17:07 -0700 (PDT), bloggs.fredbloggs.fred@gmail.com wrote:>On Sunday, July 5, 2015 at 4:55:53 PM UTC-4, John Larkin wrote: >> On Sun, 5 Jul 2015 13:24:22 -0700 (PDT), >> bloggs.fredbloggs.fred@gmail.com wrote: >> >> >On Sunday, July 5, 2015 at 3:55:57 PM UTC-4, John Larkin wrote: >> >> On Sun, 5 Jul 2015 07:50:03 -0700 (PDT), >> >> bloggs.fredbloggs.fred@gmail.com wrote: >> >> >> >> >On Sunday, July 5, 2015 at 7:58:07 AM UTC-4, Bill Sloman wrote: >> >> >> On Saturday, July 4, 2015 at 12:23:27 PM UTC+2, Bill Sloman wrote: >> >> >> > I've been using the Analog Devices Spice model in LTSpice to model the AD734 running with a current output - see Figure 25 on page 13 of the Rev E AD734 data sheet >> >> >> > >> >> >> > http://www.analog.com/media/en/technical-documentation/data-sheets/AD734.pdf >> >> >> > >> >> >> > When running a roughly 15kHz sine wave through the device, the positive current output limits at something between +200uA and +280uA. >> >> >> > >> >> >> > The voltage at the W and Z1 outputs of the AD734 is well below the rail. >> >> >> > >> >> >> > I've tried 2.2k, 6.8k and 15k current setting resistors. Only with 15k did the voltage at the W and Z1 outputs get high enough to be interesting. >> >> >> > >> >> >> > The current clipped at +200uA with 2.2k, +282.77uA at 6.8k and +267.94uA at 15k. >> >> >> > >> >> >> > The negative-going excursions looked perfectly sinusoidal, and went down to -350uA. >> >> >> > >> >> >> > Working in another region of operation, with more head-room, the currents clamped a lot higher, at about +800uA, when the negative currents were getting down to -2.4mA. >> >> >> > >> >> >> > It looks very much as if there's some kind of silly mistake in the AD734 Spice model (which would interest Jim Thompson, who wants to sell Analog Devices better Spice models). >> >> >> > >> >> >> > If the actual device acted like the model, the data sheet wouldn't talk about +/-10mA output current limits (as it does on page 13). >> >> >> > >> >> >> > It's easy enough to hand-edit .cir files, if you kno0w what you are doing. Any advice will be gratefully received. I probably should have raised this with Analog Devices directly, but the price they charge for the AD734 means that they can't be selling many of them, which doesn't suggest that I'd get a prompt response. >> >> >> >> >> >> Oops. It looks as if the defect wasn't in the Analog Devices model, but in my circuit diagram - a connection to +15V seems to have been edited out at some point and the circuit was getting it's positive power supply from its inputs, making the model inconveniently realistic - I've had that happen on real circuits, and it can take a while to work out what's going wrong. >> >> >> >> >> >> My apologies to one and all. >> >> >> >> >> >> -- >> >> >> Bill Sloman, Sydney >> >> > >> >> >LTSpice is an example of why engineers should NOT design CAD. I've never seen such absolute crap anywhere. The program should have flagged the schematic entry error. >> >> >> >> If the disconnected power supply connection was simulated accurately, >> >> then Spice did good. Spice should simulate what you draw, not question >> >> it. It does check for a few physically appropriate things, like >> >> floating nodes, singularities, and such. >> > >> >That would be some other program but not SPICE, SPICE is simple. >> >> In LT Spice, connect two voltage sources. Or leave a current source >> unloaded. Or make a double assignment in a .PARAM expression. You'll >> get warnings. >> >> It doesn't seem to mind one end of a cap floating, but that's >> physically OK. It sensibly complains about a totally floating >> component or circuit. >> >> Overall, it behaves pretty well. > >Maybe, but that has nothing to do with simulating an IC with power pin open.It works just like real life!
Reply by ●July 6, 20152015-07-06
On Sunday, July 5, 2015 at 7:26:02 PM UTC+2, Phil Hobbs wrote:> On 07/05/2015 01:14 PM, Jim Thompson wrote: > > On Sun, 05 Jul 2015 12:55:52 -0400, Phil Hobbs > > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > > > [snip] > >>> > >>> LTSpice is an example of why engineers should NOT design CAD. I've > >>> never seen such absolute crap anywhere. The program should have > >>> flagged the schematic entry error. > >> > >> Dunno. Seems as though it wouldn't be that easy in general to > >> distinguish a missing flag from a decoupling network such as a cap > >> multiplier, or an externally boosted amp (common-emitter BJT > >> wraparounds, with their bases driven by resistors in the op amp supply > >> lead). It would be crazy-making to have to design around the quirks of > >> a buggy warning system. > >> > >> What algorithm would you suggest? > >> > >> Something like an assertion in C might be possible, but it's just as > >> easy to treat a misbehaving sim like a misbehaving proto--the first > >> thing you check is the power supplies, the second thing is the enable > >> lines, the third thing is the CM limits, which can lead to startup > >> problems, etc., etc. > > > Spice simulators can't detect faults in circuit schematics. All they > > can do is detect floating nodes. Apparently LTspice doesn't concern > > itself with "VP" of a symbol, since there's probably some path to > > ground within the model. Generally PSpice would call that a float, > > and balk. > > LTspice does detect floating nodes, but it doesn't know that a net that > goes to the VCC pins of two op amps is actually floating. Danglers are > easy to spot.That was my problem - the circuit contains two AD734s and the +15V pins on both were connected - to each other - but not to anywhere else. -- Bill Sloman, Sydney
