Hantek2d42 bugs report

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Hello Amy, how was the Holidays, I hope you have enjoyed it.

So I have a new handheld 2D42 and I'm enjoying it so far but I found some bugs that I would like to report, if you don't mind:
FW: 2019011101
PCB: 0000001
FPGA: V02

1- In oscilloscope mode, pressing Autoset button does not limit the memory depth
Description: Activate only one channel, let's say CH1. Change memory depth from 3k to 6k. Keep only CH1 on and apply a signal to CH1 and CH2. Press Autoset button. The memory depth won't be limited automaticaly to 3k and you will see both waveforms on the screen all crazy, as the data is broken. Setting de mem. depth manually to 3k solve it. Fixed (in FW 20190220001)
If you turn on CH2 by pressing Channel -> CH2 -> On the memory depth is automatically limited to 3k, that is fine.

2- In DMM mode, selecting the Buzzer function using the arrow keys ">" or "<" does not activate the buzzer and it is silent I need do press F3 for it to work. Fixed (in FW 20190220001)

3- This one is probably a hardware limitation/problem. In th AWG mode, the waveform is clipping on the negative side as I increase the amplitude to near the 2.5V limit or if I set a negative offset (see picture)


4- The jitter of the AFG is pretty horrendous, specially with frequencies over 1MHz. Is that normal?



5-Waveforms presents some artifacts under various settings of frequencie and amplitude (I am still trying to isolate this one)


regards,

gf1

... In th AWG mode, the waveform is clipping on the negative side as I increase the amplitude to near the 2.5V limit or if I set a negative offse...

I'm facing the same issue as well on my 2D72. I measure a supply voltage of +5V / -3.3V on the output amp (EL5166) of the AWG. According to the datasheet, the output of the EL5166 can swing to within 1V of either supply rail, so -2.5V is actually beyond this limit. Fixing this issue would IMO require a hardware change (i.e. increase the negative supply voltage of the amp).

The jitter of the AFG is pretty horrendous, specially with frequencies over 1MHz. Is that normal?

• Since the AWG's DAC is clocked at 250MSPS, the pulse width of both, the positive and negative pulse of the quare wave, can only be an integral multiples of 4ns. If the selected frequency does not grant this, then some of the pulses need to be streched or shortened in order that the generated frequency is correct  on average.
• Additional (theoretical) limitations are imposed by the way how Direct Digital Synthesis (DDS) works. One of them are phase truncation errors, but there is also the limitation that a DDS generator can only generate frequencies wich are integral multiple of DAC_clock_freqency / dds_accumulator_size, where dds_accumulator_size is a power of 2 (I don't know what's the accumulator size on the hantek series 2000).
  

For instance, a 5MZh square wave would fulfill the condition (1), but the DDS can't generate exactly 5MHz, due to condition (2). But the closest frequency which can be generated by the DDS generator does no longer fulfill condition (1) and also suffers from phase truncation errors. So you are rather limited regarding the square wave frequencies which can be generated "exactly" without stretching/shortening some of the pulses  (=> basically only power of 2 fractions of the DAC clock freqency).

If I try for instance 7.8125 MZh (= 250MZh / 32) on my 2D72, I get a nice square wave - but not for any arbitrary frequency.

Regarding DDS, see for instance https://www.analog.com/media/en/ ... utorials/MT-085.pdf, or one of the many other DDS resources which can be found in the internet.

EDIT:
Square waves and pulses with very steep edges and/or small pulse widths are of course the worst case waveforms forms for DDS, when they should be reproduced at higher frequencies. Sine waves are not a problem in this regard, since they are already band-limited to the sine wave frequency. But for other kind of waveforms, the resampling done by the DDS may eventually violate the Nyquist–Shannon sampling when generating signals with higher frequencies, and this implies that the signal cannot be reconstructed exactly from the sampled data.

A possible workaround you can do is to increase the rise time (and thus reduce the bandwidth) of the square wave manually, by approximating a square wave with a trapezia. If you generate, for instance, a trapezia on the Hantek 2000, with RiseDuty=FallDuty=0.08 and HighDuty=FallDuty=0.42 with 5MHZ, then you'll notice less jitter than with a 5MHz square wave - but at the cost of renouncing the steep rise time of a true square wave.



Regards,
gf1

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thoquz replied at 2019-4-27 17:38
Hi Amy, sometimes it does not read what the frequency is, so I have to use the cursor.
The cursor ca ...

Which FW version are you using? There was a bug with the frequency measurement that I reported some time ago but it was already fixed in the latest FW.
https://www.eediscuss.com/forum. ... 2&fromuid=26055

You can get the newest version here:
https://www.eediscuss.com/forum. ... 8&fromuid=26055

thoquz

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?

gf1

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. ]

gf1

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

amy

Sorry, the firmware bugs have not been updated yet.

OASJ2YSeeEhBQo1

Hi Amy, thanks again for the update. I will try the FPGA update tonight.

Any news about the other issues reported as well?

amy

Hi, about the waveform burr, our engineer modify the FPGA.Please use this to update.

OASJ2YSeeEhBQo1

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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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.