# What Does Simulator Do to Solve a Circuit? - RF Cafe Forums

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rfseek
Post subject: What does simulator do to solve a circuit?
Unread postPosted: Sun Apr 24, 2005 12:42 am
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Joined: Sun Apr 24, 2005 12:21 am
Posts: 1
I would like to have a knowhow of behind the scene working principle of simulators for the various types of solutions?

1. What does a simulator say, ADS, do for S parameter simulation or in other words how does it solve the circuit when u use lumped elements and when u use the transmission lines?

2. What is the analysis procedure of the simulator while performing an ac analysis and Harmonic balance?

3. In time domain solution what kind of equations are solved by the simulator?

I would appreciate if somebody can explain me these?

Thanks

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Qacer
Post subject:
Unread postPosted: Tue Apr 26, 2005 9:29 pm
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Captain

Joined: Sat Apr 23, 2005 2:09 pm
Posts: 17
Location: Tampa, FL
I don't have a clue, either.

I actually took a matrix computations class once and the professor said that circuit simulators such as spice use it to solve problems. It actually makes sense especially if you're dealing with the DC stuff and z-parameters. You can kinda see how the computer would solve such a problem by using matrix analysis. I'm assuming that other simulators do the same thing. Also, it was mentioned that there are different numerical techniques for matrix computations that one can use to speed up the calculation.

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AP
Post subject:
Unread postPosted: Mon May 16, 2005 1:00 pm

Qacer wrote:
I don't have a clue, either.

I actually took a matrix computations class once and the professor said that circuit simulators such as spice use it to solve problems. It actually makes sense especially if you're dealing with the DC stuff and z-parameters. You can kinda see how the computer would solve such a problem by using matrix analysis. I'm assuming that other simulators do the same thing. Also, it was mentioned that there are different numerical techniques for matrix computations that one can use to speed up the calculation.

I"m pretty sure ADS uses ABCD matrices for each element that it just multiplies together - then converts to S-Paramters at the end.

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Guest
Post subject: Circuit Simulators - How They Work
Unread postPosted: Tue May 17, 2005 11:53 am

An excellent book on this topic is Applied Circuit Theory by P.R. Adby. There is a reprint of this formerly out-of-print book available from Oscar Books (you can also search for it on www.bookfinder.com)

He covers both passive circuits ("ABCD" or "Chain Matrix" approach, for example) and active circuits.

Good Luck!

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Guest
Post subject:
Unread postPosted: Wed May 18, 2005 11:47 am

I think that time domain simulation and Frequency domain have quite different approach.

ABCD matrix are for frequency domain steady state solutions.

Time domain simulation as I remember use discretised differential equations networks and very small step sizes to make time incremental simultation.

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guest
Post subject: circuit sim
Unread postPosted: Sun May 22, 2005 4:16 am

this might help!

http://web.engr.oregonstate.edu/~karti/ece521.html

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Guest
Post subject:
Unread postPosted: Sun May 29, 2005 12:40 pm

Anonymous wrote:
I think that time domain simulation and Frequency domain have quite different approach.

ABCD matrix are for frequency domain steady state solutions.

Time domain simulation as I remember use discretised differential equations networks and very small step sizes to make time incremental simultation.

I think this is somehow a right answer

LLY

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Guest
Post subject:
Unread postPosted: Tue May 31, 2005 3:09 pm

I agree with the time domain differential equation solver and then conversion to s-parameters for programs like ADS.

I remember the Runge Kutta method taught in my ODE class and always wodnered at the time who the heck would use such a thing!

Im sure it's this or another more efficient numerical method to solve the DFQs..... Processor power, throughput time and pipelining, is key with these huge models!!!! :shock:

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