# Qucs - what is DC sweep?

But I have no idea what is DC sweep, AC sweep, parameter sweep, Vsweep, ... and so why to even use them.

Could anyone please help explain what are these "sweep" terms?

P.S. I'm not an electrical engineer, just that basic electronics is a first year subject so highly technical terms will mean almost nothing.

• Thanks for accepting my answer, but you could have waited a little longer to see if a better answer comes along (which it probably will). – Majenko Jul 14 '11 at 17:09
• @MattJenkins, a few people have been pushing this, but the only way someone could answer better is if they answered more of the kind of sweeps. You did answer enough to get the users started and able to start using the system, now that they understand it is choosing what the X-axis is they can probably ascertain with logic what the others are. It is just that first cliff in the learning curve that can break backs. While I think there may have been a better answer, I think the acceptance was reasonable. One day wait is good, but if the problem is solved and the user is moving on, so be it – Kortuk Jul 14 '11 at 22:48
• @Kortuk, @MattJenkins : in fact i saw other sweep like AC sweep, transient sweep but the beauty of Matt Jenkins answer is that as Korkut points it out, by putting the answer in a general, understandable and simple context i think with a fair understanding of the type of simulation and the nature of the graph to plot ( and google for extra help ) one should be able to understand other kinds of sweeps. That justifies my acceptance of MattJenkins' elegant answer. – Toussaint Jul 15 '11 at 1:29
• @MattJenkins, you could also edit your answer to explain what all of the sweeps correlate to. – Kortuk Jul 15 '11 at 3:28

SMIIW...

The term 'sweep' in this context refers to a change from one value to another.

So a $$\V_{SWEEP}\$$ of 3-8V would be a change from 3V to 8V over a predefined time.

A DC Sweep would therefore be a change in voltage of a DC source. An AC sweep could be a change in an AC voltage over time, or more commonly, a change in AC frequency over time.

Any adjustable parameter can be the subject of a sweep - for instance turning a 100KΩ potentiometer from one extreme to the other would be a sweep of 0Ω-100KΩ

If you look at this picture:

(source: infn.it)

You can see that $$\V_{SWEEP}\$$ goes from 0V to 1.5V, and the output (V2.1) is calculated for each point along that sweep as the output from the circuit if the input were what $$\V_{SWEEP}\$$ was at that time.

• Thanks a lot!!!! it's a start to know at least the meaning of terms used. So the let's say in case of a semiconductor diode, one wanted to plot its V-I characteristics curve ( Voltage for x-axis and Current for y-axis) , the "parameter sweep" will depend upon the voltage as it is the changing parameter here! I hope i right, am i? Thanks – Toussaint Jul 14 '11 at 17:14
• Yep - you got it spot on. – Majenko Jul 14 '11 at 19:30
• Every time I've seen it, "AC sweep" means a change of frequency, not voltage. – endolith Jul 14 '11 at 20:56
• @endolith That's useful to know. Answer edited to reflect. – Majenko Jul 14 '11 at 21:01
• Thanks for the information, it saves me future trouble with AC simulation!! – Toussaint Jul 15 '11 at 1:17

If you didn't have a simulator and were sitting in front of lab equipment, and you wanted to characterize something, you might change a knob over some range and write down the resulting behavior of the circuit, perhaps plotting the data on a graph as you went. The knob could be controlling amplitude, frequency, whatever else you have a knob for on your equipment. You'd be taking measurements with a scope or meter of some kind.

A "sweep" usually means you're only turning one knob, because it's a lot easier to sit there turning one knob a little at a time, pausing for each measurement, than it is to randomly hopscotch over a grid of measurements. If you wanted a wider range of measurements you might do one sweep, change some other settings, and sweep the first one again.

The software is basically doing the same thing for you, to a simulated circuit. Some lab equipment can be programmed to do the same thing to a real circuit. With software, it may be a lot easier to change more than one variable at a time (say both amplitude and frequency), but it can also be more confusing what is affecting what. Holding a system down to where only one variable is changing at a time is a standard way of making it easier to learn what's going on.

• Okay, well we have labs so this bring the question to a real world case and thus it helps for a deeper understanding of the concept, thanks! – Toussaint Jul 15 '11 at 1:21