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Author: OASJ2YSeeEhBQo1

Hantek2d42 bugs report

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Post time 2019-3-22 05:18:12 | Show all posts
Edited by gf1 at 2019-3-22 06:20
OASJ2YSeeEhBQo1 replied at 2019-3-16 13:21
Finally I had time to test the proposed modification. I've changed R61 to 1.5K as indicated, insta ...
In the first picture the AWG is off, in the second AWG is set to sine wave, 1MHz, 1V and turned on. There is nothing conected to the inputs.

That's really heavy!
I've never seen such a high amplitude on mine.

Does it make a difference in your case whether the AWG is open or driving a load?

Was USB connected to PC or power supply?

Does the noise amplitude (in div units on the display) change with V/div setting of CH2?
(particularly for <= 200 mv/div, which bypass the 50:1 attenuator directly at the input)

EDIT:

Unless the noise would happen to enter directly at the input, the ranges 500mv...10V/div are more or less equivilalent to 10mV...200mV/div - the only difference between them is the 50:1 input attenuator, which is either present or bypassed (relay-switched).

If the noise amplitude on the display is independent of V/div setting, then it is likely injected after the 2nd attenuator stage (otherwise it would be attenuted gradually as well, when switching from 10mv/div  step by step to 200mV/div).


gf1




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Post time 2019-3-22 14:47:02 | Show all posts
Sorry, our Engineer hasn't given me a conclusion yet.  I'll urge him to reply next week.

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 Author| Post time 2019-3-24 11:57:30 | Show all posts

RE: Hantek2d42 bugs report

gf1 replied at 2019-3-22 05:18
That's really heavy!
I've never seen such a high amplitude on mine.


I tought that is strange too, the noise problem on CH2 was clearly noticeable before but I don't rementer it was this bad. Maybe it got worse after the change made to the resistor or the FW update but I'm not sure, I wasn't paying much attention to this problem before. I'll try to revert the changes later to see if there is any improvement.

Does it make a difference in your case whether the AWG is open or driving a load?
None
Was USB connected to PC or power supply?
No, tested both ways. The only problem (already reported) when connecting the USB cable is the few mV offset added to the traces.


Does the noise amplitude (in div units on the display) change with V/div setting of CH2?
No, the signal looks exactly the same whatever voltage scale I use, the only configuration that reduces the displayed noise a bit is turning on the BW limit, anything else has no effect.


Sorry, our Engineer hasn't given me a conclusion yet.  I'll urge him to reply next week.
I'm looking forward to that. I hope they will consider the other suggestions as well.



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 Author| Post time 2019-3-27 12:27:05 | Show all posts
Edited by OASJ2YSeeEhBQo1 at 2019-3-27 14:48

Just to keep this thread alive while we wait for the other solutions:

12 -The Measure windows doesn't compute the frequency of the signal if at least part of it is not crossing the center line of the screen. That means, if I move the trace to the top half or the bottom half of the screen, the oscilloscope reads the frequency as 0.00. See pictures, I am using FW 2019031201.
   

Please, also note the difference between MAX and Min values caused by a small offset in the channel that I can't get rid off even after calibration (maybe it is a similar bug in the calibration rotine as reported in the other thread about the 6074?)




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Post time 2019-4-1 15:09:43 | Show all posts
Hi, about the waveform burr, our engineer modify the FPGA.Please use this to update.



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 Author| Post time 2019-4-2 07:35:42 | Show all posts
Hi Amy, thanks again for the update. I will try the FPGA update tonight.

Any news about the other issues reported as well?

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Post time 2019-4-2 11:33:52 | Show all posts
Sorry, the firmware bugs have not been updated yet.

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Post time 2019-4-3 02:32:09 | Show all posts
Edited by gf1 at 2019-4-3 13:15
amy replied at 2019-4-1 15:09
Hi, about the waveform burr, our engineer modify the FPGA.Please use this to update.

Thank you very much, Amy, and congratulations! I installed the FPGA code and it looks much better now There are still small glitches visible, but I think that's now a level we need to accept. I also compared to the AWG of my 6074BD, and I see almost no difference now.

gf1




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Post time 2019-4-10 05:26:14 | Show all posts
Edited by gf1 at 2019-4-10 07:02

I'd like to come back to this low-frequency scope noise issue when the AWG is driving a load.
When I increase the AWG frequency to about 5500 Hz, then I get this picture:



Again there is no signal connected to both scope inputs, but the scope inputs are 50 Ohm terminated (in order that the BNC connectors don't pick up EMI). The AWG is set to 5500 Hz square wave, 2.3V amplitude, and drives a 50 Ohm load. The peak-peak noise amplitude on both, CH1 and CH2 is almost 1 div , when the channels are set to either 10mv/div or 500mv/div.

Here's what I've analyzed so far:

  • If the AWG is driving a load (particularly with square wave with fast risetime), is is of course unavoidable that it creates load transients on the power supply rails.
  • The DC converter for the negative supply has obviously a rather small phase margin, so that its load transient response shows significant overshoot/ringing, with crossover frequency of about 5500 Hz. When the AWG is set to 500 Hz, the overshoot is about 40mV pp. With an AWG frequency of ~5500 Hz, we hit the resonance frequency of the DC conveter, and amplitude is even higher (-> above image).
  • Besides the dynamic transient response, there is also a small residual ohmic voltage drop on the power supply rail which follows the AWG waveform. With the AWG set to 500 Hz, this component is only about 7mV pp  (but even this is sufficient to couple about 2mV pp into the scope frontend).
  • The power supply rails of the AWG and the scope frontends are not sufficiently decoupled from each other.
  • The FET buffer amplifier in the frontends has a very low PSRR with regard to V- at low frequencies (not more than ~10dB). The weak spot are the two current sinks which are biased by a resistive devider between the (noisy) V- and GND, copuling the noise into the constant current. There is a bypass capacitor, but it is much to small to help at low frequencies. There is also the DC compensation path for the FET buffer via the opamp, but it joins in at only even lower frequencices (< 20 Hz ?) and does not help at say 500 Hz.

So far I could achieve the best mitigation by adding an additional 100uF bypass from the bias point of the current sinks in the frontends to V-, and adding 1000uF low ESR from V- to GND near the AWG's output amp (where the load transients originate). Well, 1000uF is of course pretty large. Alternatively I tried to add a  feedforward capacitor of 10nF to the V- DC converter. This does indeed improve the ringing and the amplitude of transient response, reducing the amplitude of the 5500 Hz scope noise (image above) from 1 div to 1/3-1/2 div pp, but this is still too much, and the 1000uF bypass still performes better. I'm still investigating/trying...

[ Btw, I'm talking about low-frequency noise. High-frequency noise ist yet another issue. ]




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Post time 2019-4-27 17:38:02 | Show all posts
Hi Amy, sometimes it does not read what the frequency is, so I have to use the cursor.
The cursor can easily show me the time (period) in seconds, but it does not show the frequency which is just 1/time.
This should be an very easy update, could you please ask the engineers?
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