First of all folks, I have SPICE on my computer. I have had it there for at least a decade. Before that I used an early version of MICROCAP, which I still use sometimes, when I need AC or TRANSIENT ANALYSIS.
As this power amplifier (JC-1) is the product of evolution of a circuit that I first designed 35 years ago, I am somewhat familiar with its tradeoffs, and it just isn't worth doing a SPICE simulation of it at this point. It is not a bad idea, just that I am not on someone's payroll to make the effort required.
Just this week, I spoke to Walt Jung about computer emulation. He uses LT Spice and has recommended it to me. Unfortunately, I have a MAC, not a PC, and I have yet to make this darn computer emulate the LT Spice circuit. If I show weakness here, it is in working with the computer, and making IT bark!
Anyway, Walt was telling me that the computer gave one result and the prototype gave another. Which would you choose? I was going over the hard data just last nignt which points this out, that will be published in a future issue of 'Audio Express' as a response to an LTE.
If someone out there wants to go through the time and effort to emulate the JC-1 into LT Spice and find out interesting things about it, I would be willing to send them a schematic.
Personally, I have 2 JC-1's within 2 meters of me that are not being used at the moment, that I could take to my test bench (3 meters away) and test, if I wished. I just don't wish to, in order to see if my amp can tolerate multiple ceramic caps DIRECTLY across the terminals. I don't want to drive my Porsche over a speed bump at 100 mph, either, just to see if it can do it safely. It is the same sort of reasoning.
Spice is just fine, if you are comfortable with it, but it is not the real thing, it is just an emulation. I wouldn't get too cocky about that, sonny.
As this power amplifier (JC-1) is the product of evolution of a circuit that I first designed 35 years ago, I am somewhat familiar with its tradeoffs, and it just isn't worth doing a SPICE simulation of it at this point. It is not a bad idea, just that I am not on someone's payroll to make the effort required.
Just this week, I spoke to Walt Jung about computer emulation. He uses LT Spice and has recommended it to me. Unfortunately, I have a MAC, not a PC, and I have yet to make this darn computer emulate the LT Spice circuit. If I show weakness here, it is in working with the computer, and making IT bark!
Anyway, Walt was telling me that the computer gave one result and the prototype gave another. Which would you choose? I was going over the hard data just last nignt which points this out, that will be published in a future issue of 'Audio Express' as a response to an LTE.
If someone out there wants to go through the time and effort to emulate the JC-1 into LT Spice and find out interesting things about it, I would be willing to send them a schematic.
Personally, I have 2 JC-1's within 2 meters of me that are not being used at the moment, that I could take to my test bench (3 meters away) and test, if I wished. I just don't wish to, in order to see if my amp can tolerate multiple ceramic caps DIRECTLY across the terminals. I don't want to drive my Porsche over a speed bump at 100 mph, either, just to see if it can do it safely. It is the same sort of reasoning.
Spice is just fine, if you are comfortable with it, but it is not the real thing, it is just an emulation. I wouldn't get too cocky about that, sonny.
Yes, and things also became confused because there were two discussions going on before the split. Just for reference 
, the start of this particular one was Glen's post 1457 on this page of the thread. Strangely, if I try to link to the post directly, it goes to the wrong place - probably due to the split.
Anyway, as I mentioned earlier to Glen, I tried to connect fT to the hybrid-pi parameters, and then to the SPICE parameters that relate to it in equation 11 on this page. This was for a more complete fix of bad MJL3281A/MJL1302A models from an earlier thread that I remember you were a part of.
, the start of this particular one was Glen's post 1457 on this page of the thread. Strangely, if I try to link to the post directly, it goes to the wrong place - probably due to the split.Anyway, as I mentioned earlier to Glen, I tried to connect fT to the hybrid-pi parameters, and then to the SPICE parameters that relate to it in equation 11 on this page. This was for a more complete fix of bad MJL3281A/MJL1302A models from an earlier thread that I remember you were a part of.
john curl said:First of all folks, I have SPICE on my computer. I have had it there for at least a decade. Before that I used an early version of MICROCAP, which I still use sometimes, when I need AC or TRANSIENT ANALYSIS.
As this power amplifier (JC-1) is the product of evolution of a circuit that I first designed 35 years ago, I am somewhat familiar with its tradeoffs, and it just isn't worth doing a SPICE simulation of it at this point. It is not a bad idea, just that I am not on someone's payroll to make the effort required.
Just this week, I spoke to Walt Jung about computer emulation. He uses LT Spice and has recommended it to me. Unfortunately, I have a MAC, not a PC, and I have yet to make this darn computer emulate the LT Spice circuit. If I show weakness here, it is in working with the computer, and making IT bark!
Anyway, Walt was telling me that the computer gave one result and the prototype gave another. Which would you choose? I was going over the hard data just last nignt which points this out, that will be published in a future issue of 'Audio Express' as a response to an LTE.
If someone out there wants to go through the time and effort to emulate the JC-1 into LT Spice and find out interesting things about it, I would be willing to send them a schematic.
Personally, I have 2 JC-1's within 2 meters of me that are not being used at the moment, that I could take to my test bench (3 meters away) and test, if I wished. I just don't wish to, in order to see if my amp can tolerate multiple ceramic caps DIRECTLY across the terminals. I don't want to drive my Porsche over a speed bump at 100 mph, either, just to see if it can do it safely. It is the same sort of reasoning.
Spice is just fine, if you are comfortable with it, but it is not the real thing, it is just an emulation. I wouldn't get too cocky about that, sonny.
Nobody's disagreeing with you, John, except where you tend to put SPICE down because you have made a reasonable choice not to use it for yourself.
You're preaching to the choir; most of "you folks" here are intelligent enough not to believe every single thing they get from a SPICE simulation. Even apart from the limitations of what is only an approximation of the real world, we still have the garbage-in, garbage out problem.
SPICE is only one of many tools, but don't put down those who use it to advantage as being too lazy or inept to protoype their design. By the same token, we will not put you down for choosing not to use it in light of your experience over the years.
Based on some of the very reasonable points you have brought up about output coils, some good SPICE experiments might show that output coils are needed less than many of us think.
Bob
I've been using spice in different forms for many years too, from textfile dos version at school and amispice on amiga and then multisim on windows , but only as a hobby..
My experiences with spice is, sure it does'nt react exactly as in real life but often you can develop some kind of feeling that the circuit is wrong when the simulator behaves badly. And also the later multisim's are ridiculously fast to work with.
MY point was: If you've been playing with it for this long it's impossible to take it seriously, you will know how it works by feel.. and what spice's weird errors and stuff ACtually means..
My work I do to make money in this world is circuitboard repars, most often for trains, sometimes digital and sometimes analog circuits.
Sometimes I stumble upon a design that I feel is just -wrong- , I say to myself, SURE this works in therory but what a fool to acually DO it..
I visited my friend that's in some kind of high school (whatever it's called there) anyhow they were making a robot that played soccer with very advanced camera image recognition and shitloads of stuff i didn't understand, BUT then i looked at their stepper motor driver and just said, you've been having problems with the stepper driver right?? without hesitation. He was a bit surprised and said , yeah a bit , how the hell did you see that..I said naeeh I just a feeling I got when looking at thoose circuits.. hmm my point again is you got to have a sense for feeling..
My experiences with spice is, sure it does'nt react exactly as in real life but often you can develop some kind of feeling that the circuit is wrong when the simulator behaves badly. And also the later multisim's are ridiculously fast to work with.
MY point was: If you've been playing with it for this long it's impossible to take it seriously, you will know how it works by feel.. and what spice's weird errors and stuff ACtually means..
My work I do to make money in this world is circuitboard repars, most often for trains, sometimes digital and sometimes analog circuits.
Sometimes I stumble upon a design that I feel is just -wrong- , I say to myself, SURE this works in therory but what a fool to acually DO it..
I visited my friend that's in some kind of high school (whatever it's called there) anyhow they were making a robot that played soccer with very advanced camera image recognition and shitloads of stuff i didn't understand, BUT then i looked at their stepper motor driver and just said, you've been having problems with the stepper driver right?? without hesitation. He was a bit surprised and said , yeah a bit , how the hell did you see that..I said naeeh I just a feeling I got when looking at thoose circuits.. hmm my point again is you got to have a sense for feeling..
john curl said:
John,
I have done both, worked for small companies where we did a design and just built it, and large companies where major simulation efforts were done.
I'm curious, you say Parasound just builds it, which is fine many companies do this, however I'm wondering do they run the prototypes in an environmental chamber to verify/test over the intended temperature range, or beyond for life testing? Also, do they do this over the allowable line voltage range?
This is a required verification step for many military designs.
Pete B.
You know, in EE school we had a class called "Numerical analysis" which covers computer simulation of pretty much anything.
The first thing that they teach you is that you should know HOW your simulator works, so that you know WHAT you are simulating, and how much you can trust the results.
Simulations are just a way to solve equations which represent an arbitrarily chosen part of reality. And reality is always right.
Drawing a circuit in Spice and then pressing a button to get a nice curve, means nothing.
If the effects you are interested in are well represented by the models your simulator uses, and are not swamped in reality by stuff that the simulator doesn't model, then you'll get something usable. When you know what you're doing, that tends to be the case.
However, when the things you try to study are not in your models, "knowing what you're doing" can mean many things, like not running the simulation at all since you know it will be useless, or hacking subcircuits from measurements to get a better model, or running it anyway, and comparing with real measurements, and studying the interesting differences.
But don't spit on simulations. Without them, you wouldn't be sitting in front of your computer, because it could never have been designed.
Stuff that SPICE lacks :
- thermal effects (self-heating, thermal inertia, thermal runaway, influence of temperature on transistor hFE isn't well modelled)
- Gummel-Poon is full of holes, like Cbc variation with Vce, etc
- Some transistor models are really suspicious
- Doesn't model layout, ground loops, etc (Protel does signal integrity and crosstalk modelling though)
- MOSFETs and JFETs aren't very realistic
- all transistors are perfectly matched (in real life, you'll get offsets)
- etc
The first thing that they teach you is that you should know HOW your simulator works, so that you know WHAT you are simulating, and how much you can trust the results.
Simulations are just a way to solve equations which represent an arbitrarily chosen part of reality. And reality is always right.
Drawing a circuit in Spice and then pressing a button to get a nice curve, means nothing.
If the effects you are interested in are well represented by the models your simulator uses, and are not swamped in reality by stuff that the simulator doesn't model, then you'll get something usable. When you know what you're doing, that tends to be the case.
However, when the things you try to study are not in your models, "knowing what you're doing" can mean many things, like not running the simulation at all since you know it will be useless, or hacking subcircuits from measurements to get a better model, or running it anyway, and comparing with real measurements, and studying the interesting differences.
But don't spit on simulations. Without them, you wouldn't be sitting in front of your computer, because it could never have been designed.
Stuff that SPICE lacks :
- thermal effects (self-heating, thermal inertia, thermal runaway, influence of temperature on transistor hFE isn't well modelled)
- Gummel-Poon is full of holes, like Cbc variation with Vce, etc
- Some transistor models are really suspicious
- Doesn't model layout, ground loops, etc (Protel does signal integrity and crosstalk modelling though)
- MOSFETs and JFETs aren't very realistic
- all transistors are perfectly matched (in real life, you'll get offsets)
- etc
MAN!!! I hate it when I cant find something... I saw this article about a computer/or software that does thousands of evolutions on a base concept, compareing it etc... it was pretty new...
The jist of it basicaly was, if you have enough of those babies, humans only have to ask... and supply some parameters...
The jist of it basicaly was, if you have enough of those babies, humans only have to ask... and supply some parameters...
peufeu said:
I agree completely. SPICE is tremendously useful as long as you respect its limitations.
Often, the insight that it provides is not seriously compromized by its limitations, and I have to admit that I have uncovered many of my own mistakes and misconceptions in SPICE simulations. The ability to probe node voltages and currents at will (without "disturbing" the circuit) allows for a lot of useful (and quick) poking around. It also doesn't take much time to get a simulation up and running to the point where it begins to deliver useful results, and is certainly not something that is limited to big companies.
Although it doesn't do a very good job of modeling board layout, I have often found it useful and insightful to add some parasitic inductances here and there to see their effect.
But there is no substitute for building the thing and measuring it diligently. I tend to reject papers where the claimed results are based solely on SPICE simulations. Candidly, I must also admit that there have been times when I have designed and built a circuit without SPICE, and when it did not do what I expected, I resorted to SPICEing it. In those cases I probably would have saved myself hours if I had done it the other way around.
Bob
Recently, on another topic :
- hey check this circuit
- it will go into thermal runaway
- but no, it works well in spice
- it will burn all the same
Does someone know of some simulation software with the new transistor models like VBIC / Mextram, and that doesn't cost $20K ? I'd really like to try those.
- hey check this circuit
- it will go into thermal runaway
- but no, it works well in spice
- it will burn all the same
Does someone know of some simulation software with the new transistor models like VBIC / Mextram, and that doesn't cost $20K ? I'd really like to try those.
peufeu said:
Your example above really falls into the category of don't expect it to do what it is not coded or set up to do automatically. I believe that such a thermal analysis could be done, given that there are electrical analogies to thermal "circuits", however I don't plan on doing this any time soon. Obviously, you could have a voltage that represents temperature in the real physical design. It's all just more work and more CPU cycles.
Pete B.
Yes, that's what my above example was meant to show : blind trust in tools is, well, blind.
The purpose is not to simulate thermal runaway (for this, a subcircuit is OK), but to simulate self-heating effects in a complete amplifier, which influence both Vbe and hFE, and hence, open loop gain, phase margins, output bias, input stage balance, offset, etc, etc.
I've done the temperature-voltage thing with capacitors to represent thermal capacitance of transistor die. But the SPICE models don't have a temperature node, so you have to play with dependent sources, and modelling hFE variations is a pain.
Also, Mextram is better for other stuff like non-constant capacitances in BJT...
The purpose is not to simulate thermal runaway (for this, a subcircuit is OK), but to simulate self-heating effects in a complete amplifier, which influence both Vbe and hFE, and hence, open loop gain, phase margins, output bias, input stage balance, offset, etc, etc.
I've done the temperature-voltage thing with capacitors to represent thermal capacitance of transistor die. But the SPICE models don't have a temperature node, so you have to play with dependent sources, and modelling hFE variations is a pain.
Also, Mextram is better for other stuff like non-constant capacitances in BJT...
GRollins said:
You should understand that your statements are based on how you think real world engineering is done.
The fact is that many people can hack together a design on a bench and make it work, but most professionals know that a production design has to work over process, voltage, and temperature (PVT). Why is this so important in industry? Money and reliability ... If you do a design that makes it to production, ships, and a large percentage of the units are returned due to marginal failures, then that product might cause the company losses rather than profits. Big problem.
Small designs, and reprogrammable designs such as FPGAs can be built and tested in the lab, but this is not practical for large designs or chips being custom or semi-custom fabricated.
Simulation of complete systems, or even often subsystems was not practical years ago due to time constraints, however today in the last 10 to 15 years it is.
I worked in the semiconductor industry where we guaranteed chips (complex often more than 100,000 transistors) to behave the same as in simulation for both functional and (analog) timing behavior over process, voltage, and temperature. We used a variety of simulators, probably many that you never heard of, some for functional verification, and others for timing verification. Cells in libraries are characterized with SPICE, but SPICE is just part of the solution.
Designs were not accepted from a customer that had not been simulated since the simulation was part of the contract to fab (expensive) the part. If the part performed as simulated but did not work in the system then it was a customer's error, if the part did not behave as simulated then it was our issue. Test vectors were captured from a simulation run, and run against the real part on a tester.
We made mistakes from time to time, and it was usually an error in the model, or a bug in the simulator but most often the better tools did work well. Obvioulsy, one had to choose a quality tool set since bugs could mean failure/delays for a project. I did designs also as a customer and saw poor quality tools that nearly sunk several projects.
My point here is that people who claim that SPICE and simulation are useless as a blanket statement would be proven wrong by major segments of the engineering industry.
I have used SPICE for probably more than 20 years, and obviously if you do not have a validated set of models for your semis you cannot blame the simulator. You should also become familiar with the limitations of the models.
You are right, you don't know the temperature in the room, but the fact is that you should be testing over the full intended operating conditions to verify that your design is robust.
Pete B.
peufeu said:
You mention layout, we had a group dedicated to simulating package, board, and backplane effects at one large company where I worked. There are advanced simulation tools for modelling interconnects.
I did crude interconnect/layout simulations in SPICE, years ago, where to get reasonably accurate results showing ringing and ground bounce I had to include bonding wire, lead frame inductance and a transmission line model for the board trace. The model is only as good as what you give the simulator.
It is a lot of work and the advanced tools are expensive.
Pete B.