| Products > Test Equipment |
| Siglent SDS1x04X-E BodePlot II (SFRA) features and testings |
| << < (9/21) > >> |
| Pitrsek:
The phase difference between channels should be taken care off during calibration, that's not a reason at all. Drop in the injection voltage could be compensated on the generator side. Actually I believe that they really should include a DC coupling mode, especially if this thing is coming to scopes with 50R inputs(most of the scopes that I worked with had 50R input DC coupled). And with 50R inputs, there is full new world of S parameters and impedance measurements... Yes, measuring low frequency takes time, that's give fact. I'm not asking for making it a default settings, I'm asking for a possibility to go lower, if the user wants to. Use case is rather simple, try measure open loop gain of an opamp... For a lot of slower opamps, the dominant pole is rather low. |
| Performa01:
--- Quote from: Pitrsek on January 05, 2020, 01:47:42 pm ---The phase difference between channels should be taken care off during calibration, that's not a reason at all. Drop in the injection voltage could be compensated on the generator side. --- End quote --- Calibration in a DSO takes care of the runtime differences between channels, which in turn lead to a continually increasing phase shift proportional to the input frequency. A DSO cannot compensate for the phase errors caused by slight differences in the corner frequencies of the AC coupled input path. What you’re describing, sounds much more like the user calibration of a VNA test setup. In contrast, Bode Plotters don’t do a calibration/normalization run. --- Quote from: Pitrsek on January 05, 2020, 01:47:42 pm ---Actually I believe that they really should include a DC coupling mode, especially if this thing is coming to scopes with 50R inputs(most of the scopes that I worked with had 50R input DC coupled). --- End quote --- Yes indeed, all Siglent DSOs beyond the SDS1000X-E entry level have switchable 50 ohm inputs, starting with the SDS2000X-E. And yes, these inputs are either DC or AC coupled, regardless of the selected input impedance. --- Quote from: Pitrsek on January 05, 2020, 01:47:42 pm ---And with 50R inputs, there is full new world of S parameters and impedance measurements... --- End quote --- Once again you are talking about a VNA here – and apart from that I don’t think I have ever seen s-parameters used below 10Hz ;) Seriously though, you don’t suggest that a cheap DSO should be able to replace a VNA with s-parameter test set, do you? Or – to get back to the <10Hz discussion – a Dynamic Signal Analyzer? The fact that the Bode Plot in Siglent DSOs is more than just a me-too feature, hence can be used for some serious work in certain areas, cannot hide the fact that it is just a software module in an entry level (or midrange, in case of the SDS5000X) DSO, hence it's got to have some limitations. --- Quote from: Pitrsek on January 05, 2020, 01:47:42 pm ---Yes, measuring low frequency takes time, that's give fact. I'm not asking for making it a default settings, I'm asking for a possibility to go lower, if the user wants to. --- End quote --- You need not convince me. As stated earlier, I’ve already requested this quite a while ago, because I also know use cases for this, like very slow high precision control loops. The problem is that Siglent has lots of projects and limited resources, so they need to prioritize things. Extending the range of the Bode Plot certainly isn’t high on their list. In fact I constantly need to promote and defend the Bode Plotter, especially against consultants coming from the higher end industries, because the Bode Plot is generally seen as a hobbyist feature, or for one man workshops at best. I fight for it, simply because I was once young and on a budget myself and want hobbyists to get something useful for the most common use cases without having to reach out for some half-broken ancient boat anchor. Under these preconditions, I’m glad that we still got the Bode Plot II and I’m positive it will see further improvement - just not as a high priority. --- Quote from: Pitrsek on January 05, 2020, 01:47:42 pm ---Use case is rather simple, try measure open loop gain of an opamp... For a lot of slower opamps, the dominant pole is rather low. --- End quote --- While this sounds like a use case, I don’t think many will do that. The characterization of chips in general, like operational amplifiers, is the task of the semiconductor manufacturer (who certainly won’t use an SDS1004X-E for this) and they publish the results in the data sheets. So why not just use that? The only other scenario I could think of would be the incoming components inspection in the industries using that chip, but once again I cannot imagine them using a cheap DSO for the task. And they will most likely not care for the corner frequency in the open loop response, but just measure the frequency response at the intended gain instead. In general, measuring the open loop response of an OpAmp is far from being straight forward and consequently not common at all. |
| Pitrsek:
We've started to mix two thing together, let me separate that. 10Hz - I consider the limit to be bit to high, I'm not telling it's useless. I think it could be improved. Open loop gain was an example because that's what I'm doing now. But in general any slow loop would benefit from the expanded bandwidth - sometime the dominant pole is really low. The open loop measurement is actually rather simple and straight forward. If you have inverting configuration, measure voltage at virtual ground (pre-amp is needed) and divide by opamp output voltage. If it's no-ninverting configuration, differential amplifier is needed to extract opamp input voltage. You'd be surprised how many vendors do not bother to state the details of the open loop gain... I think it's a bit of a chicken and egg problem. It's not done regularly because you do not have the needed equipment, and it kinda works most of the time(until it does not...). Yes, it's a bit of niche at this time. It's a same as loop gain measurement - look at the amount of literature and info that's available now. It's not like the theory has changed or that the issues were not there 20yr ago, it's just that tools were not as widespread as are now. Now every scope mfgr now has an appnote about loop gain measurement. In my previous jobs, before we bought impedance/loop gain analyser, there was not much general interest in impedance profile of discrete parts, or loop measurement. Then we bought analyser, and everybody saw how useful it is. The company bought another one to keep up with demand from engineers... Once you make it accessible, then everyone is like "how could i lived without it"? I'm not suggesting that you should be able to replace your VNA with a budget scope, I'm suggesting that with some extra effort, the bode plotter could be made much more useful. And most of the required stuff is already there! Personally I consider impedance profile measurements to be extremely useful - again, some manufacturers do not provide models/data, sometime the bias effect are missing, or you'd like to know output impedance of power supply, or a filter. There are a lot of good reasons why you'd like to do impedance sweeps. Yes, you have a hard limits in bandwidth and dynamic range and you'll never have the same performance as dedicated equipment, but for quite some measurements it could well be enough. Even if it's a software module, i believe it's extremely useful. And if calibration routines are added, so you can make impedance sweeps, it could be pretty awesome. I'm well aware that full calibration routines are not trivial, but it's no rocket science either(especially the normalisation). TLDR - it's great feature, I'm glad it's there, it could be improved to make it quite a bit more useful. |
| Pitrsek:
Actually since they do sell VNA, they ought to have a decent grasp about the calibration routine. Probably different team, on different floor, but the know how is there. Just saying, It could be a nice intro in the impedance measurements for users on budget. And it would be useful... You'd like to have a bigger dynamic range and higher frequency limit? Here, there's our VNA. And this would conclude my 2cents of unsolicited free advice :) |
| mrprecision:
I had contact toSiglent, they will fix the bodeplot 2 bug with the next firmware version. |
| Navigation |
| Message Index |
| Next page |
| Previous page |