DS2072 HW FAIL SW BUG or What the hell? SOLVED - Page 1
Forum section: electronics / testgear

author: Carrington
author_rank: Super Contributor
timestamp: November 23, 2013, 03:29:54 pm
content: Please look carefully these images (If anyone wants try to replicate it. The sigal is a pulse of 3.3V, wide 50ns and rise time 2ns):First, all the measurements were performed under the same conditions and with the same probe (Agilent 10073D).Now let us assume that the signal integrity is maintained in both oscilloscopes, and that ~8bits can't give us more.The wave "form" is constantly changing in the SDS8102V, depending of the scale V/div, but at least it maintains the peak's amplitude within of a range, between the different scales (at least as far as ~ 8 bits reach).But please:- One volt peak that comes and goes in the DS2072 depending of the scale V/div.For 200mV/div the peak's amplitude is 1V and for 50mV/div and 100mV/div the peak's amplitude is ~ 300mV!Note 1: In both oscilloscopes the acquisition mode ispeak(for all the acquisition modes occurs exactly the same).Note 2: I've tried with all these probes:- RP3300 BW: 350MHz.- P6200 BW: 250MHz.- T5100 BW: 100MHz.And the same thing is still happening.What the hell is going on?

author: sync
author_rank: Frequent Contributor
timestamp: November 23, 2013, 06:07:05 pm
content: Quote from: Carrington on November 23, 2013, 03:29:54 pmYou are overdriving the input. Maybe the spike is a input amplifier saturation artifact.

author: Carrington
author_rank: Super Contributor
timestamp: November 23, 2013, 06:17:41 pm
content: Quote from: sync on November 23, 2013, 06:07:05 pmI doubt it.

author: RRobot
author_rank: Regular Contributor
timestamp: November 23, 2013, 06:20:35 pm
content: You've calibrated the Agilent probe and are re-triggering after each change in vertical?

author: Carrington
author_rank: Super Contributor
timestamp: November 23, 2013, 06:23:08 pm
content: Quote from: RRobot on November 23, 2013, 06:20:35 pmYes! And no matter the acquisition mode, Auto, Normal or Single. Or what probe. Is completely replicable.Even with BW limit set to 100MHz.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: November 23, 2013, 06:52:41 pm
content: I suggest looking at it in dots display to make sure that spike is actually being measured and isn't the result of interpolation. I suspect peak + vectors could exaggerate overshoot. Why are you using peak acquisition mode?

author: Carrington
author_rank: Super Contributor
timestamp: November 23, 2013, 06:57:11 pm
content: Quote from: Galaxyrise on November 23, 2013, 06:52:41 pmQuote from: Carrington on November 23, 2013, 03:29:54 pmAnd in dots display occurs exactly the same.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: November 23, 2013, 07:10:33 pm
content: Have you applied one of the bandwidth keys to the Rigol, or is it still 70MHz?

author: Carrington
author_rank: Super Contributor
timestamp: November 23, 2013, 07:13:53 pm
content: Quote from: Carrington on November 23, 2013, 06:23:08 pmAnd between 70 and 100MHz exists little or any difference.Quote from: Galaxyrise on November 23, 2013, 07:10:33 pmClearly yes.

author: marmad
author_rank: Super Contributor
timestamp: November 23, 2013, 07:31:00 pm
content: Quote from: Carrington on November 23, 2013, 06:17:41 pmAs sync suggests, it also looks like overdrive to me. On both analog and digital scopes, you can't really be certain of measurements taken if the trace is not fully contained on the display screen. And it doesn't matter if it works on one scope - it might not work on the next.I was unable to replicate your problem if I measure a pulse fully contained in the display @ 200mV, 100mV and 50mV. It works completely fine.As written by Jim Williams in hisAN74:Quote

author: Carrington
author_rank: Super Contributor
timestamp: November 23, 2013, 07:37:36 pm
content: Quote from: marmad on November 23, 2013, 07:31:00 pmThanks, I will read it.QuoteWhat do you want mean, that the internal DC offset in conjunction with the input stage distort the signal.Why this does not happen with a cheap SDS8102V?Quote from: marmad on November 23, 2013, 07:31:00 pmI don't have the equipment to do.

author: marmad
author_rank: Super Contributor
timestamp: November 23, 2013, 07:42:22 pm
content: Quote from: Carrington on November 23, 2013, 07:37:36 pmYes.QuoteAs mentioned, it can vary from scope to scope - some analog scopes I've used do it easily - while other's don't.Quote from: Carrington on November 23, 2013, 07:37:36 pmI'm not sure I understand you - I just mean can you cause the Rigol to give different measurements at those scale settings using any other signal source.

author: Carrington
author_rank: Super Contributor
timestamp: November 23, 2013, 07:43:27 pm
content: Quote from: marmad on November 23, 2013, 07:42:22 pmI need a equipment to add an external offset to the pulse, without disturbing the signal. Or a goog AWG.The previous pulse was generated with a Asix OMEGA LA.

author: Carrington
author_rank: Super Contributor
timestamp: November 23, 2013, 08:05:54 pm
content: Quote from: marmad on November 23, 2013, 07:42:22 pmSorry, but I don't understand exactly what do you want mean.Perhaps achieve that the results obtained on that scale settings does not correspond with a well known signal. With that signal completely within of this scale settings or not?

author: marmad
author_rank: Super Contributor
timestamp: November 23, 2013, 08:15:22 pm
content: Quote from: Carrington on November 23, 2013, 08:05:54 pmI don't get any cursor measurement variations when I measure a signal @ 200mV and 50mV that is contained within the graticule. Even expensive digital scopes, if displaying signals beyond the graticule limits, can overload and saturate - so unless you can show the problem with a contained signal, I can't consider it a fail or bug of the Rigol.

author: Carrington
author_rank: Super Contributor
timestamp: November 23, 2013, 08:22:07 pm
content: Quote from: marmad on November 23, 2013, 08:15:22 pmOk, now I understand.Sorry, my English is so bad that I have to edit my post constantly to correct my grammatical errors (when I detect this).

author: marmad
author_rank: Super Contributor
timestamp: November 23, 2013, 08:25:56 pm
content: Quote from: Carrington on November 23, 2013, 08:22:07 pmNo problemThe first thing I learned from the engineer who taught my how to use an analog scope was:"If the signal is not fully contained within the graticule, you can't trust that it's being displayed correctly."The same still holds true for DSOs - and the input errors can possibly affect the measurements. Some scopes handle it better than others - doesn't matter about the price of the scope.

author: Carrington
author_rank: Super Contributor
timestamp: November 23, 2013, 08:30:17 pm
content: Quote from: marmad on November 23, 2013, 08:25:56 pmWell, you have been the engineer who has taught me that.LOL... Thank you very much.

author: Carrington
author_rank: Super Contributor
timestamp: November 23, 2013, 08:40:12 pm
content: Is there any solution to inspect a signal and get a good level of detail (distorting the signal as little as possible), as a zoom?

author: marmad
author_rank: Super Contributor
timestamp: November 23, 2013, 08:56:35 pm
content: Quote from: Carrington on November 23, 2013, 08:40:12 pmVertical detail is always difficult because of the limitations of the low resolution ADC (as opposed to horizontal detail - which is only limited by the sample rate). Sometimes it helps to filter the signal with AC coupling or limiting filters to isolate a particular portion you're trying to get more vertical resolution on - sometimes it's best to export the sampled data to external software for more detailed examination.

author: Carrington
author_rank: Super Contributor
timestamp: November 23, 2013, 09:04:12 pm
content: Quote from: marmad on November 23, 2013, 08:56:35 pmSure, because probably in the sampled data there are more information than that shown on the oscilloscope screen.

author: MarkL
author_rank: Unknown
timestamp: November 23, 2013, 10:40:53 pm
content: Quote from: Carrington on November 23, 2013, 08:40:12 pmOne approach is to build a circuit to limit the vertical amplification to a narrow voltage range. Take a look at (yet another) famous Jim Williams app note, "AN47 - High Speed Amplifier Techniques":http://www.linear.com/docs/4138On pages 39-41, he describes two possible circuits for a "Differential Comparator Amplifier with Adjustable Offset" using the LT1193 and LT1194 op amps which can recover quickly from overloaded inputs.You would set up the circuit to give you amplification in the voltage range of interest, and then anything outside the range would be clamped by the op amp. The scope should be set up so that the clamped range is on-screen (or at least at levels guaranteed to be unsaturated and free of distortions).

author: Carrington
author_rank: Super Contributor
timestamp: November 23, 2013, 10:47:01 pm
content: @ MarkL.Thank you so much Markl, this forum is great.Great people make a great forum.@ syncMy apologies for questioning his answer, now I see that you was right.

author: Carrington
author_rank: Super Contributor
timestamp: November 23, 2013, 11:44:45 pm
content: What's Up is Down and What's Down is Up.

author: Carrington
author_rank: Super Contributor
timestamp: November 24, 2013, 01:36:13 am
content: Artifacts?If anyone wants try to replicate it. The sigal is a pulse of 3.3V, wide 50ns and rise time 2ns.

author: Carrington
author_rank: Super Contributor
timestamp: November 24, 2013, 01:41:43 am
content: More images:

author: Teneyes
author_rank: Frequent Contributor
timestamp: November 24, 2013, 07:26:35 am
content: Quote from: Carrington on November 23, 2013, 03:29:54 pm@CarringtonYou may wish to try using math function to zoom and have cursors operate.First it is good to adjust scale to full vertical display ( plus a bit more for max resolution.Next Use Math function to remove DC offset , and scale up the remaindersee picsAdd cursors using Math, and remember to scale down the cursor readingHiRres may Help also

author: Teneyes
author_rank: Frequent Contributor
timestamp: November 24, 2013, 07:42:52 am
content: @CarringtonBe Aware of the SinX/X displaying of sample pointshere are sample points and the resulting Rigol display1 sample off a line2 samples off a Line

author: Carrington
author_rank: Super Contributor
timestamp: November 24, 2013, 11:29:48 am
content: @ TeneyesMath function to zoom? Does not seem very convenient.With what equipment generated this samples? -> 1 sample off a line and 2 samples off a Line.Thanks.DS2072s input stage (it is not my oscilloscope):I don't think that this effect occurs in the rebranded LMH6518.So only remains the first stage.Although I'm not sure, because it is the only one who varies the gain.Damn, I would love to measure with another oscilloscope at several points of that input stage. But it violate the warranty.I tried with another 3.3V pulse (tr1.5ns) generated in a CYCLONE II and exactly the same.Schematic of a input stage (does not correspond to the DS2072):

author: Carrington
author_rank: Super Contributor
timestamp: November 24, 2013, 01:11:02 pm
content: Oscilloscope probe with spring, that's the setup that I used to measure.Probablymarmad is right,but I'm still not totally convinced.- Can someone with a DS2072, DS2102 or DS2202 try to replicate my results?

author: echen1024
author_rank: Super Contributor
timestamp: November 24, 2013, 03:13:19 pm
content: Quote from: marmad on November 23, 2013, 07:42:22 pmMy crap siglent used to rarely overdrive, but now my DS1000Z does. I know that some Tek scopes do as well.

author: Carrington
author_rank: Super Contributor
timestamp: November 24, 2013, 03:20:00 pm
content: You have increased the BW in your DS100Z?Normally, the input divider with compensation (resistors + capacitance) is factory adjusted, but:And if it is not adjusted properly on my device due to a BW increased? But this explanation is not very convincing to me.

author: Carrington
author_rank: Super Contributor
timestamp: November 24, 2013, 05:28:20 pm
content: Let us suppose that the first stage (trts) has unity gain. And that a lower internal DC offset applied to this first stage implies less distortion by saturation.Now I use the SDS8102V to measure the previous square pulse. Then I choose the AC coupling mode in the DS2072 and I measure the signal in the input stage of SD8102V (yes internally, just at the output off SDS8102V's first input stage). In this way I can shift the signal with the SDS8102V's internal DC offset. Whereupon I get this signal (see attached). To frame it properly I just had to apply a few mV of offset in the DS2072. But despite everything I get the same results. Yes, I know the signal is not entirely within of the reticle. But for all levels no matter how small it always going to saturation?

author: Carrington
author_rank: Super Contributor
timestamp: November 24, 2013, 08:32:56 pm
content: The SDS8102V's input stage is very similar to this, but is based on the BF862 and BFT93 but it work completely with +-5V.

author: Teneyes
author_rank: Frequent Contributor
timestamp: November 24, 2013, 10:28:31 pm
content: Quote from: Carrington on November 24, 2013, 11:29:48 amA Sonic Screwdriver, or a Neutrino gun on the ADCNOT !just hand patched the waveform File and re-loaded it into the DSO

author: Carrington
author_rank: Super Contributor
timestamp: November 25, 2013, 12:01:32 pm
content: Quote from: Teneyes on November 24, 2013, 10:28:31 pmOk, it seemed too good to be true...

author: marmad
author_rank: Super Contributor
timestamp: November 25, 2013, 12:23:26 pm
content: Quote from: Carrington on November 24, 2013, 05:28:20 pmI appreciate your frustration, but you're trying to do something that the instrument isn't really designed to do.And you know, it wasn't that long ago that the only way you could measure waveform voltage levels, etc, was to manually count graticule divisions. In fact that's still how I do it on my old Tektronix analog.

author: Carrington
author_rank: Super Contributor
timestamp: November 25, 2013, 12:50:52 pm
content: Quote from: marmad on November 25, 2013, 12:23:26 pmI understand your position, and I appreciate your help, but what bothers me is that if something is known then it can be avoided.

author: Carrington
author_rank: Super Contributor
timestamp: November 25, 2013, 04:45:10 pm
content: Which part cause this problem in the DS2072?I wonder if changing some part (trt or rebranded LMH6518) by other in the input stage would help to solve the problem.Although, perhaps, is due to the preamplifiers configuration.By now we know that this also happens in the DS1000Z.In the old DS1000 series. Also happens?

author: Carrington
author_rank: Super Contributor
timestamp: November 25, 2013, 05:52:07 pm
content: Signal Acquisition ConsiderationsSome signals are just more difficult to work with than others. For example, looking at the ripple or overshoot on the high-voltage switching waveform of a power supply can be a problem. If you attenuate the signal to fit within the graticule, the small details may be lost, as shown in the 8-bit simulation in the figure. A high-resolution scope with sufficiently low noise may allow you to zoom the captured waveform while retaining enough resolution to make your measurements.This kind of application is difficult to deal with because several factors can catch the unwary engineer. AC coupling isn’t going to help because the noise/ripple frequencies aren’t much different from the higher frequencies that define the switching edge.You could try turning up the sensitivity and triggering on one of the waveform edges. That may produce a stable image, but you probably would be overdriving the scope channel preamp, which means that you may be looking at the preamp recovery from saturation rather than the shape of the switching waveform. For this reason, an analog scope also would have trouble with this application.Your scope specifications may include the recovery characteristics,so this setup can still work if you only measure the waveform after allowing for the preamp’s recovery time.Adding input offset could be useful to the degree that it might allow you to minimize the amount of preamp overdrive.Sometimes, engineers build special signal-conditioning circuits to apply ahead of a scope. In this case, a fast diode clipping circuit in combination with an amount of offset could preserve the overshoot and ripple but significantly reduce the overall signal amplitude.All these problems are avoided by using a high-resolution scope andkeeping the entire switching signal within the preamp and ADC dynamic range.Source:http://www.evaluationengineering.com/special-reports/201307/instruments/Resolving-Finer-Detail.html

author: tinhead
author_rank: Super Contributor
timestamp: November 25, 2013, 08:12:08 pm
content: You overdriving the input stage, on some DSOs this might looks better, on others worse, but overdrive is an overdrive and when you overdrive the measured result might be everything but ok.Attached results of similar setup on my Tekway, made with 3 probes :- original Hantek PP150 probe- Testec HF512 (passive 500MHz) probe- Texas 250/II (passive 250MHz) probeNote, the shape of the overdrive depends as well on the probe BW and the probe itself. With proper HF probes (the ones having compensation for LF and HF, like the Texas and Testec) the shape looks better - but of course it still overdrives. It depends as well on the DSO BW, so when you do such measurments don't enable any BW filters.As you can see Hantek probe is not good enough to handle fast edges, not only due missing HF compensation (only LF) but as well due the probe BW. The Texas probe looks on 500mV/DIV and the 2.5x overdrive good, but with 5x overdrive it does overshoot too much (it can not be compensated out, so it is like it is). The best seems to be the Testec probe, it does have some ringing but the signal shape is constant (of course more overdrive = more ringing)It is hard to say if the signal shape on your Rigol looks like it looks due wrong probes, wrong probe compensation, not matching probes, broken DSO or the design itself - or combination of one or more. Maybe someone else (but please, not a Rigol fanboy) could try similar setup and report the results. For me especially the 200mV/DIV looks too bad to be pure overdrive.-----Rigol probably even know that there is an bit more overdrive than expected, but maybe decided to not do anything about. Or they expected to get more, but then recognized that it is within their expectation. Or maybe they simply copied part of DS1000CA series schematics and even routed the one diode but then recognized that "this is not necessary" - choose one or moreSeriously, hard to say what idea was behind, but when you look exactly there is not populated sot23 between the two opamps in input stage - the diode used here (on Rigol CA) does have T2H marking (actually T2 is marking, H is date code) which is HSMS-286C (Microwave detector diode). So when you really whish to "play" with overdrive, the best place is between the two opamps, i would not touch the first part of the input stage, there is nothing wrong (as it is exact the same on my Tekway and the shape looks better even with the crap Hantek probe). But still, wait first until someone else confirm the signal shape during overdrive. These diodes are not really expensive, but who knows if the firmware has been made to work with them together.

author: Carrington
author_rank: Super Contributor
timestamp: November 25, 2013, 09:04:40 pm
content: Honestly, I never had this problem before. So I asked for help in the forum. Thank to all who have contributed with their comments (especially to marmad and tinhead).And leaving aside the brand, I appreciate your sincerity. Also I must admit, that I am a little distrustful.I hope you understand. I apologize if I offended someone.

author: tinhead
author_rank: Super Contributor
timestamp: November 25, 2013, 09:39:26 pm
content: Quote from: marmad on November 25, 2013, 08:30:17 pmi would, generally said, not recommend to trust an distributor or fanboy or any other persons affected by any other kind of "affiliation" (by manufacturer or distibutor or any other revenue source). Sure, there are some trustful people even if i know they work for X or Y, best example is 'w2aew', but there are as well others (good know here in forum) who are only revenue biased.On the other side this is a simple test which can be done by every owner of X or Y brand, so only an idiot would try to fake results.There might/will be difference between same probes/DSO models, but they have to be there due compensation errors and parts tolerance. So compensate LF first, then try to change HF compensation (if available) to get best shape results and amplitude accuracy of a test signal first, and then the overdrive result will be the best you can get. The signal source must be something between 500ps and 5ns, square, and 3-4Vpp. That's all, so in principle any 5-20MHz quarz oscillator (with matching series resistor to get nice signal shape) is good enought. And yeah, same probes as used by Carrington would be the best.

author: Hydrawerk
author_rank: Super Contributor
timestamp: November 25, 2013, 10:25:28 pm
content: Have you seen thisOvercoming Overdrive Recovery on High-Speed Digital Storage Oscilloscopes?http://cp.literature.agilent.com/litweb/pdf/5989-0068EN.pdf

author: tinhead
author_rank: Super Contributor
timestamp: November 25, 2013, 10:48:37 pm
content: Quote from: Hydrawerk on November 25, 2013, 10:25:28 pmright, this is exactly what i remembered having read somewhere. One have however know that there is a small problem with "digital magnification", you will never get the full DSO resolution in the magnified signal. So it make sense, when possible, to enable high-res mode to at least increase resolution of the part of the waveform which will be magnified.

author: Carrington
author_rank: Super Contributor
timestamp: November 25, 2013, 11:36:06 pm
content: Quote from: Hydrawerk on November 25, 2013, 10:25:28 pm@ Hydrawerk, thanks.I suppose that this was what Teneyes meant in his previous post.Quote from: tinhead on November 25, 2013, 10:48:37 pmWould be very interesting make a PC application to implement the technique recommended by Agilent.I think that the following information was published by tinhead somewhere here.Code:TESTEC TT-HF512 500MHz x10 Probe1MHz 0dBm50MHz -0.1dBm100MHz -0.1dBm150MHz -0.2dBm200MHz +0.2dBm250MHz +0.2dBm300MHz +0.4dBm350MHz -0.3dBm400MHz -0.7dBm450MHz -1.7dBm500MHz -2.2dBm550MHz -2.8dBmTEXAS 250/II 250MHz x10 Probe1MHz 0dBm50MHz -0.3dBm100MHz -0.5dBm150MHz -0.1dBm200MHz -0.4dBm250MHz -0.1dBm300MHz 0.0dBm350MHz +0.3dBm400MHz 0.0dBm450MHz -0.5dBm500MHz -1.1dBm550MHz -2.4dBmHantek P6200 200MHz x1/x10 Probe1MHz 0dBm25MHz 0dBm50MHz +1.7dBm75MHz +2.9dBm100MHz +3.8dBm125MHz +4.4dBm150MHz +4.5dBm175MHz +4.7dBm200MHz +4.9dBm

author: tinhead
author_rank: Super Contributor
timestamp: November 26, 2013, 07:32:47 am
content: Quote from: marmad on November 26, 2013, 02:11:26 amhttp://en.wiktionary.org/wiki/fanboyfanboy -Someone who is utterly devoted to a single subject or hobby, often to the point where it is considered anobsessionSo yes, the definition of fanboy i know (nerd) is not a problem, but when fanboy starts to be too obsessed, and this is probably one of the reason why usage of this word increasing in online discussions, it start to be a problem. Of course there will be fanboys capable of seeing the reality, but due human nature they will be minority in the fanboy group. Another reason why the usage on fanboy increasing if the fact that today it is enought to say only few times something possitive about single "thing" to get a fanboy sticker, no matter if one was right or not. Due this, i'm using the word "fanboy" only to describe people who simply too obsessed and blind, and "nerd" for all the others (the not blind "fanboys" and all the geeks).

author: Orange
author_rank: Frequent Contributor
timestamp: November 26, 2013, 03:15:23 pm
content: Another pissing contest between marmad and thinhead

author: Orange
author_rank: Frequent Contributor
timestamp: November 26, 2013, 03:23:07 pm
content: Well thank you for this compliment !

author: Carrington
author_rank: Super Contributor
timestamp: November 26, 2013, 03:30:42 pm
content: @ tinhead, marmad, please don't follow this path. As a hippie would say, peace.

author: tinhead
author_rank: Super Contributor
timestamp: November 26, 2013, 06:02:02 pm
content: Quote from: marmad on November 26, 2013, 03:08:47 pmof course is wikipedia not an academic source, but .. wait, academic? Luckily we don't need that here. We talking about definition of obsessed people, but when you don't like wiki, what's about these "U.S. of A.- made and nude free" sources ?http://english.stackexchange.com/questions/51493/what-is-the-etymology-of-fanboihttp://technologizer.com/2010/05/17/fanboy/http://www.urbandictionary.com/define.php?term=fanboyQuote from: marmad on November 26, 2013, 03:08:47 pmOf course typical fanboy will not get a one cent back from what so ever source for posting bullshit, but definitely get satisfied when ppl reply to his statemet. The way how a fanboy think is "i xxx the whole day, my xxx is great, now everybody said that's great so i'm great", more or less like that. I can give you a small hint, people full in love are "fanboys" as well, they blind, they don't see anything what obvious, they will never say something against the person they love. To be passionated about something is great, to post about as well. But one have to be careful to not get obsessed, that's all.

author: Carrington
author_rank: Super Contributor
timestamp: November 27, 2013, 01:11:43 am
content: This goes for both:Everyone has the right to defend their ideas (within a rational limit), and I like to think that we are in a free world (although unfortunately sometimes this is not true).What can I say? I'd like that everyone will get along, but not always it can be...

author: marmad
author_rank: Super Contributor
timestamp: November 27, 2013, 01:13:35 am
content: Quote from: Carrington on November 27, 2013, 01:11:43 amTinhead and I hashed things out via PM - so I think things are fine between us

author: Carrington
author_rank: Super Contributor
timestamp: November 27, 2013, 01:22:23 am
content: Quote from: marmad on November 27, 2013, 01:13:35 amReally, I'm so glad.We are human and make mistakes, we can not avoid it, but we can learn from them.

author: tinhead
author_rank: Super Contributor
timestamp: November 27, 2013, 01:24:04 am
content: Quote from: Carrington on November 27, 2013, 01:22:23 amunfortunately, see below why

author: Carrington
author_rank: Super Contributor
timestamp: November 27, 2013, 01:34:21 am
content: Quote from: tinhead on November 27, 2013, 01:24:04 amYeah, no wonder that you don't want to be human.