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Analog IC design methodology

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kr_vinci

New Member
Hello,

I would like to know about the methodologies used by Analog IC designers. What kind of tools do they use?

I know it may be a very general question, but still like to know about these things.

Thanks,

Vinayak
 

crutschow

Well-Known Member
Most Helpful Member
Some type of SPICE simulator (P-SPICE, LTSpice, Electronic Workbench, etc.) is usually used to help verify the operation of general Analog circuits during the design. It allows you to view the circuit operation without building a breadboard. Of course it has it's limitations and may occasionally give faulty results thus you need to have a good idea what the circuit should be doing so you can spot results that are incorrect.

For high frequency RF and microwave analog design there are specialized SPICE type simulators to handle the parasitics and other parameters that particularly affect HF designs.
 

kr_vinci

New Member
Thanks for the reply, crutschow. I understand that most of the time analog designers use SPICE or related simulation engines to simulate the circuits which they have designed. But it almost means that SPICE is basically used for verification purpose.

But how about the designing itself? are there any tools available which can help? Once we know the problem, how do we approach it?

I am kind of new in this area. I know how to do the hand calculations, but how about designers in industry? do they use some sort of specialized tools?
 

Torben

Well-Known Member
Hi kr_vinci, and welcome to the forum!

What tasks exactly are you looking to find tools for? Design calculations, layout, or something else?


Torben

[Edit: I'm no expert in this area. We have lots of those here, though. :) I'm just trying to fish out information which may help you get a good answer.]
 
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crutschow

Well-Known Member
Most Helpful Member
But how about the designing itself? are there any tools available which can help? Once we know the problem, how do we approach it?

I am kind of new in this area. I know how to do the hand calculations, but how about designers in industry? do they use some sort of specialized tools?
I've done analog design for many years and I'm not aware of much available for doing the initial design approach. It really depends upon the knowledge and experience of the designer. Certainly, at a minimum you need a basic knowledge in all things electronic: electric and magnetic fields, DC and AC circuit theory (resistors, capacitors, inductors, transformers), semiconductor theory (diodes, transistors, SCRs, triacs, etc.), amplifier design (transistor, op amps, etc.). Without that basic knowledge, it would be difficult to sythesize an otimum analog design given a set of requirements.

From the basic knowledge of how various circuit elements work, you work to generate a circuit that will do what you want. In general you try to come up with more than one approach and then pick the one that is the most simple but still meets all the requirements. As part of this effort you would likely simiulate parts of the circuit with SPICE to verify that it works as desired. At the end, of course, you would want to simulate the complete circuit (or as much as possible, based upon its complexity). Finally, you breadboard the circuit to verify it's operation. Of course, if you're referring the design of the actual IC chip then it may not be possible to breadboard since the complexity of the circuit and/or the effect of parasitics will make a breadboard impractical.

For a beginner it's a great help to have a mentor with experience in the area you're working but I know that's not always possible. A good place to start is a Google search for design information about a particular problem you're trying to solve. And forums like this, of course, are a good source of information. But, in general, analog design synthesis is a creative process that, at least at the present state of computer tools, is still largely done by the human brain. There are few short cuts.
 

Mikebits

Well-Known Member
Hello,

I would like to know about the methodologies used by Analog IC designers. What kind of tools do they use?

I know it may be a very general question, but still like to know about these things.

Thanks,

Vinayak

Are you asking about how analog chips are designed or are you asking how analog designers implement IC's into a circuit?

If I remember correctly, the last company I worked at our ASIC designers used a couple tools. They were called Cadence and the other was Synopsys. They were front to back design tools with sim package as well. I think the pricetag was far beyond the reach of mere mortal hobby folks.
 

crutschow

Well-Known Member
Most Helpful Member
If I remember correctly, the last company I worked at our ASIC designers used a couple tools. They were called Cadence and the other was Synopsys. They were front to back design tools with sim package as well. I think the pricetag was far beyond the reach of mere mortal hobby folks.
Those tools are used in the circuit layout of the IC chip and simulation of the circuits. Determining the circuit design and configuration is still largely a human task.
 

Mikebits

Well-Known Member
Those tools are used in the circuit layout of the IC chip and simulation of the circuits. Determining the circuit design and configuration is still largely a human task.

Not entirely correct. I used Synopsys a few times. I wrote code in VHDL, the tool was used for sim to synthesis, it created all design files. The RF group used a language similar to VHDL but was a mixed language code. They used Cadence. The RF guys were pretty advanced in what tools they used as opposed to digit guys.
 
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Roff

Well-Known Member
Not entirely correct. I used Synopsys a few times. I wrote code in VHDL, the tool was used for sim to synthesis, it created all design files. The RF group used a language similar to VHDL but was a mixed language code. They used Cadence. The RF guys were pretty advanced in what tools they used as opposed to digit guys.
I don't think software is to the point yet where it can take the place of an experienced analog design engineer.
 

Mikebits

Well-Known Member
Well, I don't know what to tell you. From what I have seen, the RF guys build chips through software (I am talking ASIC's here, not board level). They work very close with the foundry tweaking a design until it meets a spec. They spend months on simulation and design errors cost big money. My only experience here is watercooler talk with people from the RF ASIC group. From my own experience, digital IC design is all software these days up until layout, which is a whole other group who verify timing etc.
 

crutschow

Well-Known Member
Most Helpful Member
Well, I don't know what to tell you. From what I have seen, the RF guys build chips through software (I am talking ASIC's here, not board level). They work very close with the foundry tweaking a design until it meets a spec. They spend months on simulation and design errors cost big money. My only experience here is watercooler talk with people from the RF ASIC group. From my own experience, digital IC design is all software these days up until layout, which is a whole other group who verify timing etc.
As you noted, the tools for analog are mainly to tweak and optimize the circuit design that's already configured.

The point I'm trying to make is that the synthesis of the analog circuit configuration is mainly a human task. There is no software that you can tell "I want a 5MHz BW amp with a 100MHz center frequency, 40dB gain, running on 5V, dissipating 100mW max., with a 2dB noise figure" and have it come up with a circuit design. There may be a computer sometime in the future that can do that but we are nowhere near that now.

Something like that is possibly available for certain types of digital circuit design using predesigned chunks of digital gates but that's orders of magnitude easier.
 

kr_vinci

New Member
I've done analog design for many years and I'm not aware of much available for doing the initial design approach. It really depends upon the knowledge and experience of the designer. Certainly, at a minimum you need a basic knowledge in all things electronic: electric and magnetic fields, DC and AC circuit theory (resistors, capacitors, inductors, transformers), semiconductor theory (diodes, transistors, SCRs, triacs, etc.), amplifier design (transistor, op amps, etc.). Without that basic knowledge, it would be difficult to sythesize an otimum analog design given a set of requirements.

From the basic knowledge of how various circuit elements work, you work to generate a circuit that will do what you want. In general you try to come up with more than one approach and then pick the one that is the most simple but still meets all the requirements. As part of this effort you would likely simiulate parts of the circuit with SPICE to verify that it works as desired. At the end, of course, you would want to simulate the complete circuit (or as much as possible, based upon its complexity). Finally, you breadboard the circuit to verify it's operation. Of course, if you're referring the design of the actual IC chip then it may not be possible to breadboard since the complexity of the circuit and/or the effect of parasitics will make a breadboard impractical.

For a beginner it's a great help to have a mentor with experience in the area you're working but I know that's not always possible. A good place to start is a Google search for design information about a particular problem you're trying to solve. And forums like this, of course, are a good source of information. But, in general, analog design synthesis is a creative process that, at least at the present state of computer tools, is still largely done by the human brain. There are few short cuts.

Carl, you are right. This is the general methodology which is used in the industry. well .. in case of IC design, we can use SPICE to verify our design.
 

kr_vinci

New Member
As you noted, the tools for analog are mainly to tweak and optimize the circuit design that's already configured.

The point I'm trying to make is that the synthesis of the analog circuit configuration is mainly a human task. There is no software that you can tell "I want a 5MHz BW amp with a 100MHz center frequency, 40dB gain, running on 5V, dissipating 100mW max., with a 2dB noise figure" and have it come up with a circuit design. There may be a computer sometime in the future that can do that but we are nowhere near that now.

Something like that is possibly available for certain types of digital circuit design using predesigned chunks of digital gates but that's orders of magnitude easier.

Yeah .. may be in future .. we will have such kind of software. But even today, things are become more complicated. Designers have to do all the calculations by hand. Once you decide about a topology to be used in your design, you will have to go through many iterations so that the design can be stabilized.

And because of all the secondary effects in devices, it takes more time to converge for a solution. Even after the design of one one of the module, if you will try to attach it with another module, you may have to re-iterate.

So I was just wondering if we have more support from the software side, so that we don't have to invest that much of time.
 

kr_vinci

New Member
I don't think software is to the point yet where it can take the place of an experienced analog design engineer.

Yeah .. right now even a blunt synthesis of Analog circuits can't be done with the tools I have seen. Yes, they can help, but can't be used for design purpose.
 
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