Beginner simulation, Linux, qucs

[x64]

Hi.

I'm new to qucs software, and I wanna simulate a simple LC resonator. I tried to do it myself, but this software seems to be much more complicated than what I thought.

What I'm looking for is the sinusoidal graph for voltage of capacitor.

Will appreciate your helps ; :wink:

 

[keith1200rs]

I don't know qucs, but SIMetrix.co.uk has a Linux version of its Spice simulator with a free version limited only by circuit size.

Keith

 

[russ]

I have never used qucs but Ngspice is a good simulation tool for linux. On the other hand, if you are not limited by operating system; try LTspice. It only runs on windows, good tool from Linear and has no limitation.

 

[keith1200rs]

LTspice has serious problems with convergence and I wouldn't recommend it.

Keith

 

[satyanaryana]

Ok,i undrstand your problem it is verysimple .place a "dc simulation" in editor,where ur ckt design .

 

[keith1200rs]

You won't get a sinusoidal graph of any sort with a DC simulation of a capacitor. A transient analysis with a sine source would.

Keith

 

[cmos_ajay]

Hello Keith,
Which "low cost" simulator would you recommend for home / hobby use ? I have used LTSPICE before and I know its limitations. What is your opinion of B2SPICE A/D and how reliable is it for cmos analog ic design ??
Can it display operating point parameters on schematic ?

 

[keith1200rs]

I haven't used B2SPICE A/D - I just spotted it and thought it looked interesting. The best way to see what they are like is to get hold of the demo versions and try them out.

I have used LTspice, but only because it is the only way to simulate some of Linear Technology's devices. I have often had convergence problems with it but that may be their models rather than the simulator. I do find their interface very clunky.

In a way, most simulators are similar 'under the hood'. What sets some apart from others is the ease of use and user interface. Some people will disagree with this view, I am sure.

Keith

 

[rapidcoder]

I have often had convergence problems with it but that may be their models rather than the simulator.

I'll tell you: it is the simulator. It is based on a standard Newton-Raphson algorithm that doesn't guarantee global convergence. The more non-linear and complicated the circuit is, the more chances you have to get convergence failure.
The only problem is that probably all of the simulators use the same NR algorithm - they differ with some hacks that improve NR convergence in some cases. Probably LTSpice's hacks are not as good as of other commercial simulators.

In a way, most simulators are similar 'under the hood'.

Most SPICE based probably are. But actually the simulator we are working on is *totally* different.
1. It uses a globally convergent method that can find a solution regardless of model non-linearity (the solution must only exist), and doesn't require a starting point.
2. It is fully modular, written in a high-level language.
3. It uses symbolic manipulation whenever possible, instead of numeric analysis, which means that linear parts of the circuits come almost for free (for example you can freely add a resistor or capacitor here and there and it doesn't affect the simulation speed).
4. It controls the amplitude of numeric round-off errors, so they can never cause convergence failures.
5. It uses modified BDF integration scheme instead of default trapezoidal in most other simulators. Trapezoidal suffer from ringing and instabilities in fast switching circuits.
6. It allows for easily writing new models with differential equations and real code with variables / ifs / loops / procedures / high level data structures etc. You can add new model code without restarting the simulator (yet it is *compiled* on the fly, not interpreted, thus *fast*).
7. It is almost as fast as LTSpice (we haven't optimized it too much), but faster than many other SPICE simulators.