Electronic – Modular Analog Circuit formula solver

analogsimulationtransistors

I've been thinking of making a database / program to make building analog circuits easier. I wanted to make sure there isn't anything else like this that I can contribute to instead of going through the effort of creating something from scratch. Lets see if I can describe what I am thinking about in my head in words:

With this program or database you would be able to select a type of circuit block and enter the desired specifications of the circuit. The solver would then automatically determine the resistor values, capacitor values and components necessary to meet the specifications set.

How about an example? Let's say that I want to design a BJT common emitter amplifier like the one:

enter image description here

When designing an amplifier like this I really only care about a few things and don't always want to go through and calculate everything every-time. I would input the maximum AC voltage in, the output impedance of the previous stage, the positive and negative rail voltages, and the desired voltage gain / current gain. In turn, it would be able to solve for the resistors & capacitor values needed and if it was REALLY cool, suggest a few transistors that would work for it.

Disclaimer – I'm sure I missed something…

Now with a simple circuit like this you may think, "Is this really necessary?" My answer to this is, not really. But imagine if you could now select these blocks, connect them together and design entire circuits. I have been thinking about using Falstad circuit simulator or circuit lab and some html scripting for this. There are many other things in my head right now about this, but I will keep them to myself to keep this post simple.

So, my overall questions are:
Is there anything else out there like this that I can contribute to? Is this completely impractical? Would anyone else be interested in having a tool like this?

Best Answer

I think you have good idea, however it already exists in some variations. I found one example for BJT cascode stage: http://www.daycounter.com/Calculators/Cascode/BJT-Cascode-Calculator.phtml

But also, I'm encouraging you to make it on your own way for few elementary different topologies, having in mind this few points: 1. it should be online; 2. it should be in pure javascript (not Java or Flash) 3. dialogs should be in schematic 4. SVG for that matter should be the markup language of choice

That's only my opinion. Good luck with this nice idea.

Related Solutions

Electronic – LTSpice Automation

Running a simulation multiple times and changing multiple component values is a bit more involved than just changing one (which is not so bad)

Here is the concept for changing one value:

Add a .param statement using the SPICE directive icon on the far right, e.g. for a resistance value .param X=R
To use it you would enter {x} into the resistor value, then include e.g. .step param X 100 500 50 to step the value between 100 and 500 in increments of 50.

Example:

Step Example

Result:

Graph

For multiple values, the only way I found to work was using a list of values for X, and using the table statement. This is probably best explained with an example (reading the help for the commands used will probably be helpful here). But note that the table command syntax is in the form table(index, x1, y1, x2, y2, .... xn, yn), takes index as input and returns an interpolated value for x=index based on the supplied x,y pairs.

In one of my simulations I needed to perform 12 simulations whilst changing 3 different component values, here are the commands:

.step param X list 1 2 3 4 5 6 7 8 9 10 11 12
.param Rin1 = table(X, 1, 1,1p, 2, 1p, 3, 1p, 4, 4478, 5, 4080, 6, 3400, 7, 2200, 8, 1p, 9, 1p, 10, 1p, 11, 1p, 12, 1p)
.param Rin2 = table(X, 1, 4997, 2, 4997, 3, 4997, 4, 499, 5, 897, 6, 1577, 7, 2777,  8, 4997, 9, 4997, 10, 4997, 11, 4997, 12, 4997)
.param Tval = table(X, 1, 56, 2, 56, 3, 27, 4, 1G, 5, 1G, 6, 1G, 7, 1G, 8, 1G, 9, 330, 10, 330, 11, 120, 12, 120)
.param Kval = table(X, 1, 316, 2, 147, 3, 147, 4, 6340, 5, 6340, 6, 6340, 7, 6340, 8, 6340, 9, 6340, 10, 825, 11, 825, 12, 316)

Result:

Gain Example

Hopefully you get the idea, you could maybe produce a script that would produce the necessary SPICE commands when you fill in your desired values. Or just create a template (e.g. I just copied and pasted the above into a few different simulations and changed the values)

If the above doesn't do what you want, then maybe look at something like NI's multisim (I think it has some batch simulation options, although I'm not sure how useful they are) It may also be helpful to ask on the LTSPice forum and see if someone knows of a better way of doing things.

Electronic – Amplifier analog design – how to effectively do it when gain varies so much

One option not mentioned is to use packaged difference amplifiers or instrumentation amplifiers, where all the internal resistors are very effectively trimmed to high accuracy. This effectively minimized the risk of mismatched resistors, which can really kill common mode rejection (which is often a bigger problem than non-exact gains).

If high precision gain is a real must, an instrumentation amplifier sets the gain using only one resistor, and that can be as high precision as you're willing to pay for. Alternatively, a lower resistor and a trimmer pot can be used for adjustment

Best Answer

Related Solutions

Electronic – LTSpice Automation

Electronic – Amplifier analog design – how to effectively do it when gain varies so much

Related Topic