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eggman2

Are you an electrical engineer?

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If you are, I got some questions for you?

I will start off by asking what kind of laws/principles/theorems do you deal with in real life circuit analysis?

What kind of software do you use?

Does the computer do most of the work?

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I am.

Circuit analysis tends to be very simple. Usually I need no "theorem" nor "law" at all. just currents, voltages, impedances. Exceptions are rare. Or maybe I've forgotten that the computations I make bear a name.

But you shouldn't imagine that electrical engineering is only circuit analysis.

Software: forget about that.

Computer: no.

And: if you imagine that a software or computer replaces the designer's understanding and ability to compute, you will fail. Beware: your question suggests that you imagine that software replaces knowledge, but a designer that understands his stuffs doesn't need any software. Electronic circuits are easy to compute by hand, and just a pocket calculator is faster and safer than any computer simulation.

In fact, at least a friend and me often cable electronic circuits without drawing them in advance, and compute the components mentally. That's very far from needing software.

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On 9/11/2018 at 7:13 PM, eggman2 said:

If you are, I got some questions for you?

I will start off by asking what kind of laws/principles/theorems do you deal with in real life circuit analysis?

What kind of software do you use?

Does the computer do most of the work?

Your questions seem to address the work of circuit designers. If not, please provide more details. If so, here are some answers:

Analog circuit design:

  1. Experienced circuit designers are familiar with the general characteristics of the components and elementary building blocks being used and (first) analyse circuits on a qualitative/functional basis. This kind of analysis is also but only indirectly based on fundamental laws as e.g. Ohm's law, Kirchoff's law, etc.
  2. Variations of SPICE are often used to design circuits. For the design of integrated circuits also SPECTRE and SABER are used.
  3. The engineer develops and adjusts the circuit topology. The computer does the time-consuming quantitative computations in order to help the designer to size the circuit components to meet the given specifications. Due to the complexity of analog designs, there are still no automated expert systems which allow general analog circuits to be synthesized completely by computer software.

However, in digital circuit design, the circuit designer programs the logical functions and limiting constraints to be synthesized by computer software. As a result, the work done by the computer is siginificantly larger in digital designs than in analog designs.

Mixed-mode circuits use both analog and digital circuits. Hence, their design methodology ranges between those of analog and digital circuits.

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For high speed digital I often analyzed worst case component propagation times as well as propagation down the circuit board traces.

For medical designs "Failure Effects and Modes Analysis" was employed.  In other words, what happens on any single component failure?  The first medical company I worked at went a step further and analyzed two point failures when one of the failures was undetectable.  Later in servers a similar analysis was performed to address malign hacks and their mitigation.

One of my favorites from college was modeling op-amp circuits as a virtual short in computing the output.

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On 1/13/2019 at 11:07 AM, Will9135 said:

The engineer develops and adjusts the circuit topology. The computer does the time-consuming quantitative computations in order to help the designer to size the circuit components to meet the given specifications. Due to the complexity of analog designs, there are still no automated expert systems which allow general analog circuits to be synthesized completely by computer software.

I strongly disagree with the use of software to design an analog circuit. I used software to design analog chips, hand computation for macroscopic circuits, so I know both.

Computing an analog circuit is generally trivial. I often do it without writing anything nor even drawing a diagram, cabling the breadboard directly while computing in my head, sometimes with a pocket calculator. My opinion is that anyone who needs software for that isn't able to design a circuit. The result would be bad, with or without software.

What makes an analog design work isn't generally the diagram - unless the designer fails even there - but the good cabling, shielding, board design, for the electromagnetic compatibility. It's also a matter of proper component selection, knowing the detailed behaviour of each component technology. A simulation software helps zilch for that, which is the core difficulty of the job and takes most time. If a designer uses Spice to cope with the diagram, that suggests that he isn't even aware of all the other difficulties. Problems ahead.

Engineering schools and universities replaced workbench time with simulation because it costs less, and because many teachers aren't even aware of what analog design is. Such a very incomplete curriculum is a direct path to circuits that don't work.

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I retired about 12 years ago but I still take an interest in engineering.  As an analogue engineer, I had to do a fully toleranced design analysis on one project to prove in theory that our design should work. To do this manually would have been tedious, and very time consuming, so I used spice modelling.  For anything non trivial I dont see any alternative to using a computer. 

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2 minutes ago, Chris S said:

I retired about 12 years ago but I still take an interest in engineering.  As an analogue engineer, I had to do a fully toleranced design analysis on one project to prove in theory that our design should work. To do this manually would have been tedious, and very time consuming, so I used spice modelling.  For anything non trivial I dont see any alternative to using a computer. 

And doing this for a design containing several million transistors would be impossible without simulation.

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