Can an electronic device continuously sweep the voltage?

Question

Modern power supplies can sweep the potential in a given range with a specific rate. I am curious if the electronic devices can continuously sweep the voltage (in a perfect sense) or it is just step-based changes, which seem like sweeping?

For example, consider sweeping with from 0 to 10V in 10,000s. Does the sweep has a resolution of say 1mV, and the data looks like

time/s    voltage/V
1         0.001
2         0.002
3         0.003

Or it is absolutely continuous, as the voltage is 0.0025 at 2.5s, 0.002513 at 2.513s?

Note that my question is not about the voltage resolution, but if the change from 2 and 3s is a step from 0.002 to 0.003V or it is still a gradual change.

I can think of a very simple proof concept. Have a potentiometer in a voltage divider connected to a motor. Is it an electronic device? It is if you ask me... — Eugene Sh., Aug 10 '17 at 18:56
@EugeneSh. not if it's a wirewound pot... and even if it's not.. continuous is a matter of degrees. — Trevor_G, Aug 10 '17 at 18:57
@Trevor We can argue that there is no "continuous" at all in our quantum-ruled world. — Eugene Sh., Aug 10 '17 at 18:58
@EugeneSh. That's exactly my question, is the voltage quantized at very small timescales? — Googlebot, Aug 10 '17 at 19:00
How many sides does a circle have? What if it's displayed on an HD screen? — Bort, Aug 10 '17 at 19:00
@Bort we can draw a circle by increasing the sides (the resolution) of a polygon. This is my question. Does the sweeping procedure in power supplies is like drawing a circle by a polygon? Does the voltage jump from a value to another (if looking closely)? — Googlebot, Aug 10 '17 at 19:04
it really depends on how you design it. of course you can design to be fully continuous but I guess with current technology the "arbitrarily smooth enough" digital solution be cheaper and easier to make. To get it "theoretically" absolute smooth you just go old school and use technologies from the 80s and do it full-analog. But that's just the theory. Say the digital solution produces less noise than the analog, then the digital solution still wins. — user3528438, Aug 10 '17 at 19:05
@All I am not sure about the theory, but I believe the voltage is susceptible to the Heisenberg uncertainty principle just like anything else. — Eugene Sh., Aug 10 '17 at 19:05
@EugeneSh. Heisenberg uncertainty is for semi-infinitely small scales. I used the term `quantized` as an analogy. We are talking about the time scale of milliseconds, not 10^-47s. — Googlebot, Aug 10 '17 at 19:08
@EugeneSh.: The quantum-mechanical aspects of this are discussed here: [Are voltages discrete when we zoom in enough?](https://physics.stackexchange.com/q/131674/17516) — Dave Tweed, Aug 10 '17 at 19:50
@BORT Interesting discussion, one could argue that forever. Unless you are arguing with your wife.. in which case you are wrong no matter which side you take. — Trevor_G, Aug 10 '17 at 20:04
Pondering about quantum mechanical effects does not make sense here. Long before they get practically relevant noise will get more relevant. (Yes, noise can be some kind of quantum mechanical effect; but it doesn't manifest in defined staircase steps) — Curd, Aug 10 '17 at 20:11

score 8 · Accepted Answer · answered Aug 10 '17 at 19:05

If using a digital system, then yes, you would expect a "staircase" of 1 mV steps. This occurs internally in many analog to digital converters. The input is compared with an internal binary-generated staircase waveform and when the input level is reached the binary count is read and stored.

Figure 1. Counter type ADC. Source: Daenotes.

An analog triangle-wave or sawtooth generator would give a continuous sweep.

Trevor_G · Answer 2 · 2017-08-10T19:18:32.043

4

It really depends.

If the sweep is generated digitally by a micro then no.

If it's generated using a saw-tooth curve based on charging some cap then much more so.

However, nothing is truly linear, and arguably if it is a switching power supply there are a few more variables you need to worry about.

edited Aug 10 '17 at 19:18

answered Aug 10 '17 at 19:06

Trevor_G

46,364
8
68
151

Harry Svensson · Answer 3 · 2017-08-10T19:24:54.173

It depends really much on the PSU.

If a R2/R ladder is used, then it will move in steps, but right at the step-transition it will be charging/discharging some parasitic capacitance so it won't be a true discontinued step. It will still be connected. But you can put as many stages as you want in your R2/R ladder network to improve on your resolution, but the more stages you add the more sensitive it will be to noise, because you're making the bits mean less and less and less the longer the ladder gets.

If however the sweep is made by using a Constant Current Source together with a capacitor, then you will see the voltage as a straight line. But at what resolution though? If we look at the picosecond scale then we will see the steps yet again as electrons move around. Same thing with the R2/R ladder, though it's much easier to notice.

A MOSFET can be utilized to make a Voltage Controlled Current Source, and it can be controlled in a digital manner to set the \$\frac{dV}{dT}\$. You can set the voltage of the gate with an R2/R ladder, then the straight line (Voltage across the Capacitor over Time) will have different finite angles. Or you could use an op-amp together with an R2/R ladder and make use of control theory to make the op-amp come up with the voltage for the gate that will make the capacitor charge at some specific \$\frac{dV}{dT}\$ so it takes 10 seconds for it to reach X volt. It's still digital, though the op-amp does all the magic.

Or just put a motor on a potentiometer. Again, it depends on the PSU you're talking about. An answer is ever as good as the question, a broad question gives an uncertain and broad answer.

Would you really see steps due to electron movement at picosecond scale? Or is that limit much lower? — curious_cat, Aug 11 '17 at 05:09
@curious_cat You're right, at the picoseconds scale you would maybe not see it, but at the femtoseconds scale you _should_. -- Hmm, I'm still thinking if you really would see a **step**. Because the electrons move in a continuous manner (ish?), well they are teleporting around as well with their quantum tunneling... I just read [Dave Tweeds answer over at Physics Exchange](https://physics.stackexchange.com/q/131674/17516). So Voltage is _not_ discrete... -- Either way, I don't think it really matters what answer we come up with, I doubt that whatever we say will be relevant to the question. — Harry Svensson, Aug 11 '17 at 12:15

score 1 · Answer 4 · answered Aug 11 '17 at 04:43

If the Power Supply has 4 output pins: force and sense for each polarity, you can inject a voltage between Force and Sense for either polarity, using a function generator of the Older Style with linear triangle waves.

Place 1Ohm resistor between Force and Sense, and run a 100_Ohm to output of the function generator.

Can an electronic device continuously sweep the voltage?

4 Answers4