How are circuits which use complex ICs normally simulated? The 2019 Stack Overflow Developer Survey Results Are In Announcing the arrival of Valued Associate #679: Cesar Manara Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)A decent library of component simulation, schematic and PCB layout?How is abstraction used in Analogue circuit design?LTSpice Level 2 Simulation CMOS followerWhat software can I use to simulate I.B.I.S Models?SPICE Programs worth learning forHow to get a CMOS transistor SPICE model?How do I determine mosfet capacitances (Cgs, Cds, Cgd, …) in LTSPICE?How to interpret LTspice simulation outputs for improving dual channel boost converter design using LTC3788Mextram Spice Model for TransistorSignificance of timing simulation for FPGA

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How are circuits which use complex ICs normally simulated?



The 2019 Stack Overflow Developer Survey Results Are In
Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)A decent library of component simulation, schematic and PCB layout?How is abstraction used in Analogue circuit design?LTSpice Level 2 Simulation CMOS followerWhat software can I use to simulate I.B.I.S Models?SPICE Programs worth learning forHow to get a CMOS transistor SPICE model?How do I determine mosfet capacitances (Cgs, Cds, Cgd, …) in LTSPICE?How to interpret LTspice simulation outputs for improving dual channel boost converter design using LTC3788Mextram Spice Model for TransistorSignificance of timing simulation for FPGA



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22












$begingroup$


I understand that it is common practice in electronic design to simulate a circuit in some spice program before building it. Sometimes a project requires the use of complex ICs, for instance an IC which performs charge control for a Li-Po battery or an IC which acts as PWM controller. Manufacturers generally don't make spice models of these sorts of complex components available. I would like to find out from any electronics engineers/designers what they do in this situation. How do you simulate such a circuit? Or is it more a case of working with the manufacturer designs provided in the application section of the datasheet and trusting that the designs will work. Maybe you abstract these ICs and simulate other portions of your circuit with the kind of output signal they would provide?



I would appreciate any real world practical examples from your experience in electronic design to illustrate how you approach simulation of circuits which make use of off the shelf ICs which do not have spice models available.










share|improve this question









$endgroup$











  • $begingroup$
    Charge control -> PWM doesn't sound that bad IMHO. I would try to build up the IC with ideal function blocks and look-up-tables (things which are fast to simulate) and see if that would get me close enough. If not, there are ways to combine VHDL and analog in the same simulation. How accurate do you need it?
    $endgroup$
    – winny
    Apr 9 at 11:09










  • $begingroup$
    There are mixed-signal simulators.
    $endgroup$
    – analogsystemsrf
    Apr 9 at 11:31

















22












$begingroup$


I understand that it is common practice in electronic design to simulate a circuit in some spice program before building it. Sometimes a project requires the use of complex ICs, for instance an IC which performs charge control for a Li-Po battery or an IC which acts as PWM controller. Manufacturers generally don't make spice models of these sorts of complex components available. I would like to find out from any electronics engineers/designers what they do in this situation. How do you simulate such a circuit? Or is it more a case of working with the manufacturer designs provided in the application section of the datasheet and trusting that the designs will work. Maybe you abstract these ICs and simulate other portions of your circuit with the kind of output signal they would provide?



I would appreciate any real world practical examples from your experience in electronic design to illustrate how you approach simulation of circuits which make use of off the shelf ICs which do not have spice models available.










share|improve this question









$endgroup$











  • $begingroup$
    Charge control -> PWM doesn't sound that bad IMHO. I would try to build up the IC with ideal function blocks and look-up-tables (things which are fast to simulate) and see if that would get me close enough. If not, there are ways to combine VHDL and analog in the same simulation. How accurate do you need it?
    $endgroup$
    – winny
    Apr 9 at 11:09










  • $begingroup$
    There are mixed-signal simulators.
    $endgroup$
    – analogsystemsrf
    Apr 9 at 11:31













22












22








22


4



$begingroup$


I understand that it is common practice in electronic design to simulate a circuit in some spice program before building it. Sometimes a project requires the use of complex ICs, for instance an IC which performs charge control for a Li-Po battery or an IC which acts as PWM controller. Manufacturers generally don't make spice models of these sorts of complex components available. I would like to find out from any electronics engineers/designers what they do in this situation. How do you simulate such a circuit? Or is it more a case of working with the manufacturer designs provided in the application section of the datasheet and trusting that the designs will work. Maybe you abstract these ICs and simulate other portions of your circuit with the kind of output signal they would provide?



I would appreciate any real world practical examples from your experience in electronic design to illustrate how you approach simulation of circuits which make use of off the shelf ICs which do not have spice models available.










share|improve this question









$endgroup$




I understand that it is common practice in electronic design to simulate a circuit in some spice program before building it. Sometimes a project requires the use of complex ICs, for instance an IC which performs charge control for a Li-Po battery or an IC which acts as PWM controller. Manufacturers generally don't make spice models of these sorts of complex components available. I would like to find out from any electronics engineers/designers what they do in this situation. How do you simulate such a circuit? Or is it more a case of working with the manufacturer designs provided in the application section of the datasheet and trusting that the designs will work. Maybe you abstract these ICs and simulate other portions of your circuit with the kind of output signal they would provide?



I would appreciate any real world practical examples from your experience in electronic design to illustrate how you approach simulation of circuits which make use of off the shelf ICs which do not have spice models available.







design simulation






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Apr 9 at 6:36









BlargianBlargian

313211




313211











  • $begingroup$
    Charge control -> PWM doesn't sound that bad IMHO. I would try to build up the IC with ideal function blocks and look-up-tables (things which are fast to simulate) and see if that would get me close enough. If not, there are ways to combine VHDL and analog in the same simulation. How accurate do you need it?
    $endgroup$
    – winny
    Apr 9 at 11:09










  • $begingroup$
    There are mixed-signal simulators.
    $endgroup$
    – analogsystemsrf
    Apr 9 at 11:31
















  • $begingroup$
    Charge control -> PWM doesn't sound that bad IMHO. I would try to build up the IC with ideal function blocks and look-up-tables (things which are fast to simulate) and see if that would get me close enough. If not, there are ways to combine VHDL and analog in the same simulation. How accurate do you need it?
    $endgroup$
    – winny
    Apr 9 at 11:09










  • $begingroup$
    There are mixed-signal simulators.
    $endgroup$
    – analogsystemsrf
    Apr 9 at 11:31















$begingroup$
Charge control -> PWM doesn't sound that bad IMHO. I would try to build up the IC with ideal function blocks and look-up-tables (things which are fast to simulate) and see if that would get me close enough. If not, there are ways to combine VHDL and analog in the same simulation. How accurate do you need it?
$endgroup$
– winny
Apr 9 at 11:09




$begingroup$
Charge control -> PWM doesn't sound that bad IMHO. I would try to build up the IC with ideal function blocks and look-up-tables (things which are fast to simulate) and see if that would get me close enough. If not, there are ways to combine VHDL and analog in the same simulation. How accurate do you need it?
$endgroup$
– winny
Apr 9 at 11:09












$begingroup$
There are mixed-signal simulators.
$endgroup$
– analogsystemsrf
Apr 9 at 11:31




$begingroup$
There are mixed-signal simulators.
$endgroup$
– analogsystemsrf
Apr 9 at 11:31










5 Answers
5






active

oldest

votes


















30












$begingroup$

In my experience the widespread use of simulation of entire boards is mostly a myth outside of physics simulations in RF.



Simulation rules for IC design of course, because the prototyping costs are so insane, and for anything involving HDL design, but for general electronics, not so much.



Where the sim really helps is for things like filters and control loops where you really want to make sure the breakpoints and phase shifts are what you expected, but these are typically a small blob of a half dozen or so parts that you can simulate in isolation.



Attempts to simulate an entire board of reasonable complexity tend to fail either on numerical stability or just simply on run time, which explodes once you start adding reasonable parasitics.



Generally you simulate the bits you are not sure about, which is usually less then 10% of a design (The rest is 'data sheet engineering' of power supplies and IO stuff).






share|improve this answer









$endgroup$












  • $begingroup$
    Most actual real-world electronics designers prototype physical circuits on breadboards instead of simulate. I do know of a few exceptions though: Apple uses Verilog to design boards so simulation is almost built-in
    $endgroup$
    – slebetman
    2 days ago






  • 1




    $begingroup$
    Well I don't do breadboards (Nasty, unreliable, capacitive things), but yea dead bugging something over a bit of scrap copper clad as a groundplane is fairly normal around here. I have pre cut 0.4mm thick pcb traces in various widths (impedances) that I can just glue down as needed.
    $endgroup$
    – Dan Mills
    2 days ago


















14












$begingroup$

Although a lot of tools exist, the two primary forms of simulation are analog (SPICE, LTSPICE or Simetrix for example) and signal integrity (with something like Hyperlynx if you have very deep pockets).



There are power analysis tools, but I have seen some very odd results that do not apparently equate with physical reality.



There are mixed signal tools, although the digital side tends to be behavioural.



The problems we run up against are:



1 No simulation model exists for the part. If you have a complete datasheet you can make a decent stab at rolling your own or use a part that does have a model.
Rolling your own model for anything non-trivial is a very time consuming exercise.



Note that anything beyond a primitive (diode, transistor or simple passive) is a behavioural model that reflects device operation in the continuous state. See this application note for what is actually in such a model. Note that things like ferrites and chokes are very complex; although they can be modeled as a circuit (to achieve the response in the datasheet) it can be very time consuming.



2 Run time. I simulated the entire power path for an ejection seat to include the EEDs and thermal batteries as part of an independent safety review of the sequencer electronics. As the cables to the control and firing circuits were quite long, they were modeled as loosely coupled transformer windings. The circuit contained perhaps 40 elements and took (on a multi-core high end machine) over 30 hours to do a single transient run.



3 Some parts of the circuitry are not really suitable for simulation or should not need it. If I have a simple optocoupled isolation stage to toggle a control switch, it should not need simulation if the data sheets have been used properly (of course, that is a completely different subject as I have seen many designs where that was not the case).



4 In Signal Integrity simulation, most simulators do not take into account that controlled impedances are +/-10% at best, and will vary layer to layer. Such simulations are useful to see gross issues, but you can still get bitten by such details. In addition, most simulators cannot model the return path (although post layout simulations are getting better).



5 Virtually all simulation models are compromises to reflect the most common use case; I have had to modify models significantly to see corner case behaviour.



A full board (or often multi-board) system would be prohibitive in terms of time to actually run, so only the parts we are interested in checking are simulated.



Another issue is that for macro-models, start-up behaviour is undefined in many cases and no simulator in the world will help if start-up behaviour is critical (as it can be in flight safety critical equipment) - you simply have to measure it.



Simulations can certainly help designers, but they are not anywhere close to perfect and should not be relied on for actual circuit operation; they are indicative of circuit operation.






share|improve this answer









$endgroup$




















    10












    $begingroup$

    When using such ICs, I find myself often following the "cookbook" of the manufacturer. This should lead to a working circuit in most cases and often you have a circuit you can more or less integrate into your design as is.



    But in some cases, I also build a SPICE model for a part of the circuit with its external components. E.g. feedback loop frequency response in a voltage regulator, comparator inputs with internally switched current sources. In this cases I use ideal elements from the Spice library and add the specified characteristics from the datasheet to it, e.g. input leakage, capacitance, ESD diodes. For digital highspeed devices, the manufacturer provides often so called IBIS models, which model the electrical behaviour of the inputs/outputs. This allows for signal integrity analyses (which may include the PCB as a component).



    While generally it may be true that you often won't find more complex SPICE models available, I would like to mention Linear Technology/LTspice as an exception, they provide models for ICs like PWM controllers. Other manufacturers offer you web- or spreadsheet based design tools which allow you e.g. efficiency calculations.






    share|improve this answer











    $endgroup$




















      9












      $begingroup$


      I understand that it is common practice in electronic design to simulate a circuit in some spice program before building it.




      I haven't seen whole-board simulation being used except for small, simple circuits. Instead, the whole board is analyzed in parts, and most appropriate methods are used for each part. For example, a typical microcontroller based system might be analyzed like this:



      • Switching mode power supply would be simulated in SPICE

      • Battery charger based on IC would be designed based on datasheet and manual calculations

      • Microcontroller would be connected according to datasheet or manufacturer example schematic

      • Radio antenna would be simulated in specialized RF simulator, or designed according to specifications a manufacturer has already verified

      And any constraints between the parts would be verified manually, such as "microcontroller needs at least 200 mA supply" and "SMPS must handle 500 mA load".






      share|improve this answer









      $endgroup$




















        0












        $begingroup$

        In my limited experience, I have found that I do not need to simulate an entire system. Generally, there is only one small portion of the circuit that is hard to understand. And for that, the demo version of spice is usually enough. Likewise, in finite element modeling, there is only one small portion of the antenna structure that is hard to understand, so the demo version of FEMAP is sufficient.



        As for your particular simulation problem, spice has provisions for you to construct your own model of whatever device you like. Alas, this requires a somewhat deeper understanding to get good results, but it can be done. (I don't remember if the demo version of spice supports this.)






        share|improve this answer









        $endgroup$













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          5 Answers
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          5 Answers
          5






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          30












          $begingroup$

          In my experience the widespread use of simulation of entire boards is mostly a myth outside of physics simulations in RF.



          Simulation rules for IC design of course, because the prototyping costs are so insane, and for anything involving HDL design, but for general electronics, not so much.



          Where the sim really helps is for things like filters and control loops where you really want to make sure the breakpoints and phase shifts are what you expected, but these are typically a small blob of a half dozen or so parts that you can simulate in isolation.



          Attempts to simulate an entire board of reasonable complexity tend to fail either on numerical stability or just simply on run time, which explodes once you start adding reasonable parasitics.



          Generally you simulate the bits you are not sure about, which is usually less then 10% of a design (The rest is 'data sheet engineering' of power supplies and IO stuff).






          share|improve this answer









          $endgroup$












          • $begingroup$
            Most actual real-world electronics designers prototype physical circuits on breadboards instead of simulate. I do know of a few exceptions though: Apple uses Verilog to design boards so simulation is almost built-in
            $endgroup$
            – slebetman
            2 days ago






          • 1




            $begingroup$
            Well I don't do breadboards (Nasty, unreliable, capacitive things), but yea dead bugging something over a bit of scrap copper clad as a groundplane is fairly normal around here. I have pre cut 0.4mm thick pcb traces in various widths (impedances) that I can just glue down as needed.
            $endgroup$
            – Dan Mills
            2 days ago















          30












          $begingroup$

          In my experience the widespread use of simulation of entire boards is mostly a myth outside of physics simulations in RF.



          Simulation rules for IC design of course, because the prototyping costs are so insane, and for anything involving HDL design, but for general electronics, not so much.



          Where the sim really helps is for things like filters and control loops where you really want to make sure the breakpoints and phase shifts are what you expected, but these are typically a small blob of a half dozen or so parts that you can simulate in isolation.



          Attempts to simulate an entire board of reasonable complexity tend to fail either on numerical stability or just simply on run time, which explodes once you start adding reasonable parasitics.



          Generally you simulate the bits you are not sure about, which is usually less then 10% of a design (The rest is 'data sheet engineering' of power supplies and IO stuff).






          share|improve this answer









          $endgroup$












          • $begingroup$
            Most actual real-world electronics designers prototype physical circuits on breadboards instead of simulate. I do know of a few exceptions though: Apple uses Verilog to design boards so simulation is almost built-in
            $endgroup$
            – slebetman
            2 days ago






          • 1




            $begingroup$
            Well I don't do breadboards (Nasty, unreliable, capacitive things), but yea dead bugging something over a bit of scrap copper clad as a groundplane is fairly normal around here. I have pre cut 0.4mm thick pcb traces in various widths (impedances) that I can just glue down as needed.
            $endgroup$
            – Dan Mills
            2 days ago













          30












          30








          30





          $begingroup$

          In my experience the widespread use of simulation of entire boards is mostly a myth outside of physics simulations in RF.



          Simulation rules for IC design of course, because the prototyping costs are so insane, and for anything involving HDL design, but for general electronics, not so much.



          Where the sim really helps is for things like filters and control loops where you really want to make sure the breakpoints and phase shifts are what you expected, but these are typically a small blob of a half dozen or so parts that you can simulate in isolation.



          Attempts to simulate an entire board of reasonable complexity tend to fail either on numerical stability or just simply on run time, which explodes once you start adding reasonable parasitics.



          Generally you simulate the bits you are not sure about, which is usually less then 10% of a design (The rest is 'data sheet engineering' of power supplies and IO stuff).






          share|improve this answer









          $endgroup$



          In my experience the widespread use of simulation of entire boards is mostly a myth outside of physics simulations in RF.



          Simulation rules for IC design of course, because the prototyping costs are so insane, and for anything involving HDL design, but for general electronics, not so much.



          Where the sim really helps is for things like filters and control loops where you really want to make sure the breakpoints and phase shifts are what you expected, but these are typically a small blob of a half dozen or so parts that you can simulate in isolation.



          Attempts to simulate an entire board of reasonable complexity tend to fail either on numerical stability or just simply on run time, which explodes once you start adding reasonable parasitics.



          Generally you simulate the bits you are not sure about, which is usually less then 10% of a design (The rest is 'data sheet engineering' of power supplies and IO stuff).







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Apr 9 at 12:24









          Dan MillsDan Mills

          12.1k11225




          12.1k11225











          • $begingroup$
            Most actual real-world electronics designers prototype physical circuits on breadboards instead of simulate. I do know of a few exceptions though: Apple uses Verilog to design boards so simulation is almost built-in
            $endgroup$
            – slebetman
            2 days ago






          • 1




            $begingroup$
            Well I don't do breadboards (Nasty, unreliable, capacitive things), but yea dead bugging something over a bit of scrap copper clad as a groundplane is fairly normal around here. I have pre cut 0.4mm thick pcb traces in various widths (impedances) that I can just glue down as needed.
            $endgroup$
            – Dan Mills
            2 days ago
















          • $begingroup$
            Most actual real-world electronics designers prototype physical circuits on breadboards instead of simulate. I do know of a few exceptions though: Apple uses Verilog to design boards so simulation is almost built-in
            $endgroup$
            – slebetman
            2 days ago






          • 1




            $begingroup$
            Well I don't do breadboards (Nasty, unreliable, capacitive things), but yea dead bugging something over a bit of scrap copper clad as a groundplane is fairly normal around here. I have pre cut 0.4mm thick pcb traces in various widths (impedances) that I can just glue down as needed.
            $endgroup$
            – Dan Mills
            2 days ago















          $begingroup$
          Most actual real-world electronics designers prototype physical circuits on breadboards instead of simulate. I do know of a few exceptions though: Apple uses Verilog to design boards so simulation is almost built-in
          $endgroup$
          – slebetman
          2 days ago




          $begingroup$
          Most actual real-world electronics designers prototype physical circuits on breadboards instead of simulate. I do know of a few exceptions though: Apple uses Verilog to design boards so simulation is almost built-in
          $endgroup$
          – slebetman
          2 days ago




          1




          1




          $begingroup$
          Well I don't do breadboards (Nasty, unreliable, capacitive things), but yea dead bugging something over a bit of scrap copper clad as a groundplane is fairly normal around here. I have pre cut 0.4mm thick pcb traces in various widths (impedances) that I can just glue down as needed.
          $endgroup$
          – Dan Mills
          2 days ago




          $begingroup$
          Well I don't do breadboards (Nasty, unreliable, capacitive things), but yea dead bugging something over a bit of scrap copper clad as a groundplane is fairly normal around here. I have pre cut 0.4mm thick pcb traces in various widths (impedances) that I can just glue down as needed.
          $endgroup$
          – Dan Mills
          2 days ago













          14












          $begingroup$

          Although a lot of tools exist, the two primary forms of simulation are analog (SPICE, LTSPICE or Simetrix for example) and signal integrity (with something like Hyperlynx if you have very deep pockets).



          There are power analysis tools, but I have seen some very odd results that do not apparently equate with physical reality.



          There are mixed signal tools, although the digital side tends to be behavioural.



          The problems we run up against are:



          1 No simulation model exists for the part. If you have a complete datasheet you can make a decent stab at rolling your own or use a part that does have a model.
          Rolling your own model for anything non-trivial is a very time consuming exercise.



          Note that anything beyond a primitive (diode, transistor or simple passive) is a behavioural model that reflects device operation in the continuous state. See this application note for what is actually in such a model. Note that things like ferrites and chokes are very complex; although they can be modeled as a circuit (to achieve the response in the datasheet) it can be very time consuming.



          2 Run time. I simulated the entire power path for an ejection seat to include the EEDs and thermal batteries as part of an independent safety review of the sequencer electronics. As the cables to the control and firing circuits were quite long, they were modeled as loosely coupled transformer windings. The circuit contained perhaps 40 elements and took (on a multi-core high end machine) over 30 hours to do a single transient run.



          3 Some parts of the circuitry are not really suitable for simulation or should not need it. If I have a simple optocoupled isolation stage to toggle a control switch, it should not need simulation if the data sheets have been used properly (of course, that is a completely different subject as I have seen many designs where that was not the case).



          4 In Signal Integrity simulation, most simulators do not take into account that controlled impedances are +/-10% at best, and will vary layer to layer. Such simulations are useful to see gross issues, but you can still get bitten by such details. In addition, most simulators cannot model the return path (although post layout simulations are getting better).



          5 Virtually all simulation models are compromises to reflect the most common use case; I have had to modify models significantly to see corner case behaviour.



          A full board (or often multi-board) system would be prohibitive in terms of time to actually run, so only the parts we are interested in checking are simulated.



          Another issue is that for macro-models, start-up behaviour is undefined in many cases and no simulator in the world will help if start-up behaviour is critical (as it can be in flight safety critical equipment) - you simply have to measure it.



          Simulations can certainly help designers, but they are not anywhere close to perfect and should not be relied on for actual circuit operation; they are indicative of circuit operation.






          share|improve this answer









          $endgroup$

















            14












            $begingroup$

            Although a lot of tools exist, the two primary forms of simulation are analog (SPICE, LTSPICE or Simetrix for example) and signal integrity (with something like Hyperlynx if you have very deep pockets).



            There are power analysis tools, but I have seen some very odd results that do not apparently equate with physical reality.



            There are mixed signal tools, although the digital side tends to be behavioural.



            The problems we run up against are:



            1 No simulation model exists for the part. If you have a complete datasheet you can make a decent stab at rolling your own or use a part that does have a model.
            Rolling your own model for anything non-trivial is a very time consuming exercise.



            Note that anything beyond a primitive (diode, transistor or simple passive) is a behavioural model that reflects device operation in the continuous state. See this application note for what is actually in such a model. Note that things like ferrites and chokes are very complex; although they can be modeled as a circuit (to achieve the response in the datasheet) it can be very time consuming.



            2 Run time. I simulated the entire power path for an ejection seat to include the EEDs and thermal batteries as part of an independent safety review of the sequencer electronics. As the cables to the control and firing circuits were quite long, they were modeled as loosely coupled transformer windings. The circuit contained perhaps 40 elements and took (on a multi-core high end machine) over 30 hours to do a single transient run.



            3 Some parts of the circuitry are not really suitable for simulation or should not need it. If I have a simple optocoupled isolation stage to toggle a control switch, it should not need simulation if the data sheets have been used properly (of course, that is a completely different subject as I have seen many designs where that was not the case).



            4 In Signal Integrity simulation, most simulators do not take into account that controlled impedances are +/-10% at best, and will vary layer to layer. Such simulations are useful to see gross issues, but you can still get bitten by such details. In addition, most simulators cannot model the return path (although post layout simulations are getting better).



            5 Virtually all simulation models are compromises to reflect the most common use case; I have had to modify models significantly to see corner case behaviour.



            A full board (or often multi-board) system would be prohibitive in terms of time to actually run, so only the parts we are interested in checking are simulated.



            Another issue is that for macro-models, start-up behaviour is undefined in many cases and no simulator in the world will help if start-up behaviour is critical (as it can be in flight safety critical equipment) - you simply have to measure it.



            Simulations can certainly help designers, but they are not anywhere close to perfect and should not be relied on for actual circuit operation; they are indicative of circuit operation.






            share|improve this answer









            $endgroup$















              14












              14








              14





              $begingroup$

              Although a lot of tools exist, the two primary forms of simulation are analog (SPICE, LTSPICE or Simetrix for example) and signal integrity (with something like Hyperlynx if you have very deep pockets).



              There are power analysis tools, but I have seen some very odd results that do not apparently equate with physical reality.



              There are mixed signal tools, although the digital side tends to be behavioural.



              The problems we run up against are:



              1 No simulation model exists for the part. If you have a complete datasheet you can make a decent stab at rolling your own or use a part that does have a model.
              Rolling your own model for anything non-trivial is a very time consuming exercise.



              Note that anything beyond a primitive (diode, transistor or simple passive) is a behavioural model that reflects device operation in the continuous state. See this application note for what is actually in such a model. Note that things like ferrites and chokes are very complex; although they can be modeled as a circuit (to achieve the response in the datasheet) it can be very time consuming.



              2 Run time. I simulated the entire power path for an ejection seat to include the EEDs and thermal batteries as part of an independent safety review of the sequencer electronics. As the cables to the control and firing circuits were quite long, they were modeled as loosely coupled transformer windings. The circuit contained perhaps 40 elements and took (on a multi-core high end machine) over 30 hours to do a single transient run.



              3 Some parts of the circuitry are not really suitable for simulation or should not need it. If I have a simple optocoupled isolation stage to toggle a control switch, it should not need simulation if the data sheets have been used properly (of course, that is a completely different subject as I have seen many designs where that was not the case).



              4 In Signal Integrity simulation, most simulators do not take into account that controlled impedances are +/-10% at best, and will vary layer to layer. Such simulations are useful to see gross issues, but you can still get bitten by such details. In addition, most simulators cannot model the return path (although post layout simulations are getting better).



              5 Virtually all simulation models are compromises to reflect the most common use case; I have had to modify models significantly to see corner case behaviour.



              A full board (or often multi-board) system would be prohibitive in terms of time to actually run, so only the parts we are interested in checking are simulated.



              Another issue is that for macro-models, start-up behaviour is undefined in many cases and no simulator in the world will help if start-up behaviour is critical (as it can be in flight safety critical equipment) - you simply have to measure it.



              Simulations can certainly help designers, but they are not anywhere close to perfect and should not be relied on for actual circuit operation; they are indicative of circuit operation.






              share|improve this answer









              $endgroup$



              Although a lot of tools exist, the two primary forms of simulation are analog (SPICE, LTSPICE or Simetrix for example) and signal integrity (with something like Hyperlynx if you have very deep pockets).



              There are power analysis tools, but I have seen some very odd results that do not apparently equate with physical reality.



              There are mixed signal tools, although the digital side tends to be behavioural.



              The problems we run up against are:



              1 No simulation model exists for the part. If you have a complete datasheet you can make a decent stab at rolling your own or use a part that does have a model.
              Rolling your own model for anything non-trivial is a very time consuming exercise.



              Note that anything beyond a primitive (diode, transistor or simple passive) is a behavioural model that reflects device operation in the continuous state. See this application note for what is actually in such a model. Note that things like ferrites and chokes are very complex; although they can be modeled as a circuit (to achieve the response in the datasheet) it can be very time consuming.



              2 Run time. I simulated the entire power path for an ejection seat to include the EEDs and thermal batteries as part of an independent safety review of the sequencer electronics. As the cables to the control and firing circuits were quite long, they were modeled as loosely coupled transformer windings. The circuit contained perhaps 40 elements and took (on a multi-core high end machine) over 30 hours to do a single transient run.



              3 Some parts of the circuitry are not really suitable for simulation or should not need it. If I have a simple optocoupled isolation stage to toggle a control switch, it should not need simulation if the data sheets have been used properly (of course, that is a completely different subject as I have seen many designs where that was not the case).



              4 In Signal Integrity simulation, most simulators do not take into account that controlled impedances are +/-10% at best, and will vary layer to layer. Such simulations are useful to see gross issues, but you can still get bitten by such details. In addition, most simulators cannot model the return path (although post layout simulations are getting better).



              5 Virtually all simulation models are compromises to reflect the most common use case; I have had to modify models significantly to see corner case behaviour.



              A full board (or often multi-board) system would be prohibitive in terms of time to actually run, so only the parts we are interested in checking are simulated.



              Another issue is that for macro-models, start-up behaviour is undefined in many cases and no simulator in the world will help if start-up behaviour is critical (as it can be in flight safety critical equipment) - you simply have to measure it.



              Simulations can certainly help designers, but they are not anywhere close to perfect and should not be relied on for actual circuit operation; they are indicative of circuit operation.







              share|improve this answer












              share|improve this answer



              share|improve this answer










              answered Apr 9 at 15:45









              Peter SmithPeter Smith

              14.9k11240




              14.9k11240





















                  10












                  $begingroup$

                  When using such ICs, I find myself often following the "cookbook" of the manufacturer. This should lead to a working circuit in most cases and often you have a circuit you can more or less integrate into your design as is.



                  But in some cases, I also build a SPICE model for a part of the circuit with its external components. E.g. feedback loop frequency response in a voltage regulator, comparator inputs with internally switched current sources. In this cases I use ideal elements from the Spice library and add the specified characteristics from the datasheet to it, e.g. input leakage, capacitance, ESD diodes. For digital highspeed devices, the manufacturer provides often so called IBIS models, which model the electrical behaviour of the inputs/outputs. This allows for signal integrity analyses (which may include the PCB as a component).



                  While generally it may be true that you often won't find more complex SPICE models available, I would like to mention Linear Technology/LTspice as an exception, they provide models for ICs like PWM controllers. Other manufacturers offer you web- or spreadsheet based design tools which allow you e.g. efficiency calculations.






                  share|improve this answer











                  $endgroup$

















                    10












                    $begingroup$

                    When using such ICs, I find myself often following the "cookbook" of the manufacturer. This should lead to a working circuit in most cases and often you have a circuit you can more or less integrate into your design as is.



                    But in some cases, I also build a SPICE model for a part of the circuit with its external components. E.g. feedback loop frequency response in a voltage regulator, comparator inputs with internally switched current sources. In this cases I use ideal elements from the Spice library and add the specified characteristics from the datasheet to it, e.g. input leakage, capacitance, ESD diodes. For digital highspeed devices, the manufacturer provides often so called IBIS models, which model the electrical behaviour of the inputs/outputs. This allows for signal integrity analyses (which may include the PCB as a component).



                    While generally it may be true that you often won't find more complex SPICE models available, I would like to mention Linear Technology/LTspice as an exception, they provide models for ICs like PWM controllers. Other manufacturers offer you web- or spreadsheet based design tools which allow you e.g. efficiency calculations.






                    share|improve this answer











                    $endgroup$















                      10












                      10








                      10





                      $begingroup$

                      When using such ICs, I find myself often following the "cookbook" of the manufacturer. This should lead to a working circuit in most cases and often you have a circuit you can more or less integrate into your design as is.



                      But in some cases, I also build a SPICE model for a part of the circuit with its external components. E.g. feedback loop frequency response in a voltage regulator, comparator inputs with internally switched current sources. In this cases I use ideal elements from the Spice library and add the specified characteristics from the datasheet to it, e.g. input leakage, capacitance, ESD diodes. For digital highspeed devices, the manufacturer provides often so called IBIS models, which model the electrical behaviour of the inputs/outputs. This allows for signal integrity analyses (which may include the PCB as a component).



                      While generally it may be true that you often won't find more complex SPICE models available, I would like to mention Linear Technology/LTspice as an exception, they provide models for ICs like PWM controllers. Other manufacturers offer you web- or spreadsheet based design tools which allow you e.g. efficiency calculations.






                      share|improve this answer











                      $endgroup$



                      When using such ICs, I find myself often following the "cookbook" of the manufacturer. This should lead to a working circuit in most cases and often you have a circuit you can more or less integrate into your design as is.



                      But in some cases, I also build a SPICE model for a part of the circuit with its external components. E.g. feedback loop frequency response in a voltage regulator, comparator inputs with internally switched current sources. In this cases I use ideal elements from the Spice library and add the specified characteristics from the datasheet to it, e.g. input leakage, capacitance, ESD diodes. For digital highspeed devices, the manufacturer provides often so called IBIS models, which model the electrical behaviour of the inputs/outputs. This allows for signal integrity analyses (which may include the PCB as a component).



                      While generally it may be true that you often won't find more complex SPICE models available, I would like to mention Linear Technology/LTspice as an exception, they provide models for ICs like PWM controllers. Other manufacturers offer you web- or spreadsheet based design tools which allow you e.g. efficiency calculations.







                      share|improve this answer














                      share|improve this answer



                      share|improve this answer








                      edited Apr 9 at 7:35

























                      answered Apr 9 at 7:25









                      Manu3l0usManu3l0us

                      1,249920




                      1,249920





















                          9












                          $begingroup$


                          I understand that it is common practice in electronic design to simulate a circuit in some spice program before building it.




                          I haven't seen whole-board simulation being used except for small, simple circuits. Instead, the whole board is analyzed in parts, and most appropriate methods are used for each part. For example, a typical microcontroller based system might be analyzed like this:



                          • Switching mode power supply would be simulated in SPICE

                          • Battery charger based on IC would be designed based on datasheet and manual calculations

                          • Microcontroller would be connected according to datasheet or manufacturer example schematic

                          • Radio antenna would be simulated in specialized RF simulator, or designed according to specifications a manufacturer has already verified

                          And any constraints between the parts would be verified manually, such as "microcontroller needs at least 200 mA supply" and "SMPS must handle 500 mA load".






                          share|improve this answer









                          $endgroup$

















                            9












                            $begingroup$


                            I understand that it is common practice in electronic design to simulate a circuit in some spice program before building it.




                            I haven't seen whole-board simulation being used except for small, simple circuits. Instead, the whole board is analyzed in parts, and most appropriate methods are used for each part. For example, a typical microcontroller based system might be analyzed like this:



                            • Switching mode power supply would be simulated in SPICE

                            • Battery charger based on IC would be designed based on datasheet and manual calculations

                            • Microcontroller would be connected according to datasheet or manufacturer example schematic

                            • Radio antenna would be simulated in specialized RF simulator, or designed according to specifications a manufacturer has already verified

                            And any constraints between the parts would be verified manually, such as "microcontroller needs at least 200 mA supply" and "SMPS must handle 500 mA load".






                            share|improve this answer









                            $endgroup$















                              9












                              9








                              9





                              $begingroup$


                              I understand that it is common practice in electronic design to simulate a circuit in some spice program before building it.




                              I haven't seen whole-board simulation being used except for small, simple circuits. Instead, the whole board is analyzed in parts, and most appropriate methods are used for each part. For example, a typical microcontroller based system might be analyzed like this:



                              • Switching mode power supply would be simulated in SPICE

                              • Battery charger based on IC would be designed based on datasheet and manual calculations

                              • Microcontroller would be connected according to datasheet or manufacturer example schematic

                              • Radio antenna would be simulated in specialized RF simulator, or designed according to specifications a manufacturer has already verified

                              And any constraints between the parts would be verified manually, such as "microcontroller needs at least 200 mA supply" and "SMPS must handle 500 mA load".






                              share|improve this answer









                              $endgroup$




                              I understand that it is common practice in electronic design to simulate a circuit in some spice program before building it.




                              I haven't seen whole-board simulation being used except for small, simple circuits. Instead, the whole board is analyzed in parts, and most appropriate methods are used for each part. For example, a typical microcontroller based system might be analyzed like this:



                              • Switching mode power supply would be simulated in SPICE

                              • Battery charger based on IC would be designed based on datasheet and manual calculations

                              • Microcontroller would be connected according to datasheet or manufacturer example schematic

                              • Radio antenna would be simulated in specialized RF simulator, or designed according to specifications a manufacturer has already verified

                              And any constraints between the parts would be verified manually, such as "microcontroller needs at least 200 mA supply" and "SMPS must handle 500 mA load".







                              share|improve this answer












                              share|improve this answer



                              share|improve this answer










                              answered Apr 9 at 14:40









                              jpajpa

                              1,666711




                              1,666711





















                                  0












                                  $begingroup$

                                  In my limited experience, I have found that I do not need to simulate an entire system. Generally, there is only one small portion of the circuit that is hard to understand. And for that, the demo version of spice is usually enough. Likewise, in finite element modeling, there is only one small portion of the antenna structure that is hard to understand, so the demo version of FEMAP is sufficient.



                                  As for your particular simulation problem, spice has provisions for you to construct your own model of whatever device you like. Alas, this requires a somewhat deeper understanding to get good results, but it can be done. (I don't remember if the demo version of spice supports this.)






                                  share|improve this answer









                                  $endgroup$

















                                    0












                                    $begingroup$

                                    In my limited experience, I have found that I do not need to simulate an entire system. Generally, there is only one small portion of the circuit that is hard to understand. And for that, the demo version of spice is usually enough. Likewise, in finite element modeling, there is only one small portion of the antenna structure that is hard to understand, so the demo version of FEMAP is sufficient.



                                    As for your particular simulation problem, spice has provisions for you to construct your own model of whatever device you like. Alas, this requires a somewhat deeper understanding to get good results, but it can be done. (I don't remember if the demo version of spice supports this.)






                                    share|improve this answer









                                    $endgroup$















                                      0












                                      0








                                      0





                                      $begingroup$

                                      In my limited experience, I have found that I do not need to simulate an entire system. Generally, there is only one small portion of the circuit that is hard to understand. And for that, the demo version of spice is usually enough. Likewise, in finite element modeling, there is only one small portion of the antenna structure that is hard to understand, so the demo version of FEMAP is sufficient.



                                      As for your particular simulation problem, spice has provisions for you to construct your own model of whatever device you like. Alas, this requires a somewhat deeper understanding to get good results, but it can be done. (I don't remember if the demo version of spice supports this.)






                                      share|improve this answer









                                      $endgroup$



                                      In my limited experience, I have found that I do not need to simulate an entire system. Generally, there is only one small portion of the circuit that is hard to understand. And for that, the demo version of spice is usually enough. Likewise, in finite element modeling, there is only one small portion of the antenna structure that is hard to understand, so the demo version of FEMAP is sufficient.



                                      As for your particular simulation problem, spice has provisions for you to construct your own model of whatever device you like. Alas, this requires a somewhat deeper understanding to get good results, but it can be done. (I don't remember if the demo version of spice supports this.)







                                      share|improve this answer












                                      share|improve this answer



                                      share|improve this answer










                                      answered yesterday









                                      richard1941richard1941

                                      33715




                                      33715



























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