Products > Test Equipment
Sniffing the Rigol's internal I2C bus
<< < (438/899) > >>
tirulerbach:
Hello,

Just to make sure: Is the JTAG-port on DS2202A at 3.3 Volt?
Carrington:

--- Quote from: clifford on December 28, 2013, 12:53:51 pm ---
--- Quote from: Wim13 on December 28, 2013, 09:04:49 am ---One thing you have to add to your simulation.
The scoop entry is also a low pass filter, in this case a 300 Mhz low pass filter,

--- End quote ---

This is tricky because the 16pF / 1 MOhm scope input is already part of the 300 MHz spec. But I've created bode plots of the original circuit and with an added first order 300 MHz low pass:

http://imgur.com/a/sMYNH

This set of images also contains a transient simulation of the circuit with the added additional filter. As you can see, the rise time is slightly lower now but it does not really make any difference regarding the qualitative effect of the short transmission line between the termination resistor and the scope input.


--- Quote from: Wim13 on December 28, 2013, 09:04:49 am ---thats why signals going to the 300 Mhz always look always like a sine wave, because of the low pass filter.
All the harmonics are gone after 150 Mhz, all is left is a sine wave..

So a scoop of 300 Mhz is usefool to 20 Mhz.

--- End quote ---

I think you are confusing bandwidth and sampling frequency here. All DS2000 scopes have a sampling frequency of 2 GHz.

Also: The harmonics above the nyquist frequency (1 GHz in this case) are not gone or magically filtered by the sampling. They show up as aliasing frequencies. You have to actively filter those components out using an anti-aliasing filter. If you sample fast enough you already have significant low pass characteristics on your input path and don't need to build a filter, its just implicitly there. That's the 300 MHz in this case.

But those filters never do have an ideal sinc impulse response. So you will never see a signal just morphing into a pure sine wave when approaching the filter edge frequency. (You can build such filters in a DSP of course: Just perform an FFT, mask out the frequencies you do not want, and run an IFFT. But you will never see the equivalent of that in an analog filter.)

There is this rule of thumb that you should have at least a factor 10 between sampling frequency and bandwidth. It is a good rule of thumb, but it is not the ultimate answer. The minimum factor between sampling frequency an signal bandwidth depends on the kind of signal you are interested in, the kind of aliasing filter you are using and the interpolation method you are using. In most RF applications you can get pretty close to the nyquist frequency, because you have extremely band-limited signals, use high order filters and you effectively use a sin(x)/x interpolation (you will never actually look at the signal in the time domain, but the algorithms work with an equivalent representation).

--- End quote ---
@ clifford: I agree, and I add some additional information that is related, read also attached fille:


--- Quote from: Carrington on December 02, 2013, 06:34:00 pm ---Highly summarized:
  - For real time sampling acquisition and bandlimited signal: Fs > 2Fmax.
    Now use common sense: Everything depends on the details that you want (I'm not talking about ADC dynamic range), more details -> more frequency components -> more BW, then -> more Fs.
    i.e.: The sampling rate must also be sufficient for an acceptable reconstruction of the signal, for example a square pulse.   

  - For equivalent time sampling acquisition and only periodic bandlimited signal, then Fs can be less than signal's BW. But I think that this is not the case.

An interesting document (211 to 236) [220]:
http://w140.com/Handbook_of_Oscilloscope_Technology.pdf

--- End quote ---

--- Quote from: marmad on December 03, 2013, 10:11:07 pm ---For sin(x)/x interpolation, a sampling rate of 2.5x the highest frequency is considered good enough to faithfully reconstruct the signal from the samples. But sin(x)/x is highly susceptible to errors if the original signal contains frequencies higher than the Nyquist frequency.

That is why the Rigol DS2000 series automatically switches from sin(x)/x interpolation to linear interpolation when the sampling rate <= 500MSa/s - because the Nyquist frequency starts to drop too low for reliable reconstruction. For example, @ 200MSa/s the Nyquist frequency is 100MHz - which easily passes through the BW filter.

When you use linear interpolation, it's cruder so it requires a higher sample rate ratio for faithful reconstruction (at least 8x, but 10x is considered the rule of thumb as AndrejaKo mentioned), but it won't introduce false peaks at slower sample rates like sin(x)/x might.

I'm not sure which (or when, if switching between them) interpolation scheme the Owon uses.

--- End quote ---

--- Quote from: Carrington on December 04, 2013, 12:00:28 am ---Only as complement: pages 260-262 of the previous link.
Thanks marmad.

--- End quote ---
Carrington:

--- Quote from: tirulerbach on December 28, 2013, 02:36:41 pm ---Hello,
Just to make sure: Is the JTAG-port on DS2202A at 3.3 Volt?

--- End quote ---
Yes, I think.
dtran11:

--- Quote from: eltar on December 12, 2013, 06:18:57 pm ---
--- Quote from: eV1Te on December 12, 2013, 06:06:30 pm ---I will try it later tonight as well, just need to hack something together that generates a fast rising edges first, to test the 100 MHz with  :)

--- End quote ---

I can try it too. Is latest DS1000Z firmware 00.02.01.SP1 requested for unlocking 100MHz?
Do we have some info or change list for this firmware? Thanks :)

--- End quote ---

I just got a DS1074Z. Do the keys still work if I upgrade to 00.02.01.SP1? Also is there anyway to revert the options if I need to send in for repair?

Thanks
Avotronics:


--- Quote from: dtran11 on December 28, 2013, 04:23:30 pm ---
--- Quote from: eltar on December 12, 2013, 06:18:57 pm ---
--- Quote from: eV1Te on December 12, 2013, 06:06:30 pm ---I will try it later tonight as well, just need to hack something together that generates a fast rising edges first, to test the 100 MHz with  :)

--- End quote ---

I can try it too. Is latest DS1000Z firmware 00.02.01.SP1 requested for unlocking 100MHz?
Do we have some info or change list for this firmware? Thanks :)

--- End quote ---

I just got a DS1074Z. Do the keys still work if I upgrade to 00.02.01.SP1? Also is there anyway to revert the options if I need to send in for repair?

Thanks

--- End quote ---

Ifaik the DS1000Z isn't hackable yet.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod