Author Topic: which one's better? Rigol DS1202CA or Instek GDS-2202  (Read 7044 times)

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Offline blueboyTopic starter

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which one's better? Rigol DS1202CA or Instek GDS-2202
« on: June 17, 2011, 12:09:50 am »
Hi guys
can help me again..?
which one's better for my home lab?

1- Rigol DS1202CA [ 200Mhz , 2 GSs/s , 1450 $  , Made in China]
Code: [Select]
http://www.tequipment.net/RigolDS1202CA.html
or

2- GwInstek DSO 2202 [ 200Mhz , 1 GSa/s , 1450 $ , Made in Tiwan ]
Code: [Select]
http://www.tequipment.net/InstekGDS-2202.html
plz share ur own review
thanks..
 

Offline Mechatrommer

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Re: which one's better? Rigol DS1202CA or Instek GDS-2202
« Reply #1 on: June 17, 2011, 04:49:46 am »
well, 2GS/s vs 1GS/s tells me something!
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline Bored@Work

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Re: which one's better? Rigol DS1202CA or Instek GDS-2202
« Reply #2 on: June 17, 2011, 05:47:17 am »
plz share ur own review

Why don't you get your lazy arse up and read the specs?
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Offline blueboyTopic starter

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Re: which one's better? Rigol DS1202CA or Instek GDS-2202
« Reply #3 on: June 17, 2011, 10:17:50 pm »
Hey Guys..

I know the 2Gs/s sample rate is better 1Gs/s ...

i just find report about INSTEK GDS-220X
Code: [Select]
https://www.youtube.com/watch?v=BdPkQHO4A68&feature=related
and a rate compare between Rigol DS1000CD & GW Instek GDS2000
Code: [Select]
https://www.youtube.com/watch?v=zuE-jkpyN4Q&feature=related
and report a problem in Rigol DS1102
Code: [Select]
https://www.youtube.com/watch?v=W7Opur1Xbvs&feature=related
but i cant find nothing about Rigol DS1202CA.. its mean it had not any bugs?
Can i trust to this China Scope "Rigol 1202CA?

thanks
 

Offline Mechatrommer

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Re: which one's better? Rigol DS1202CA or Instek GDS-2202
« Reply #4 on: June 17, 2011, 10:23:44 pm »
link pleaseeeeeee... :)
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline tinhead

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Re: which one's better? Rigol DS1202CA or Instek GDS-2202
« Reply #5 on: June 18, 2011, 12:00:27 am »
the answer is very simple:

Instek GDS-2202 have 100Mhz single shot bw which is indication for 100MHz clocked interleaved ADCs.
Rigol DS1202CA have one two channel 1GSs ADC.

On Rigol CA, if you sample with 2GSs then they are interleaved too, so the double sample rate is not necessarily better than 10 x 100MHz clocked ADCs (or 8 x 125MHz) on other models (Instek, Rigol D/E, Hantek and so on).
Sure, you will have maybe a bit less aliasing issues due higher (single) sampling freq, but the diff will be small.

This means Rigol CA series is better (at least on paper), but only if you enable both channels (to prevent interleaving).
And btw, 1GSs is anyway enough for 200MHz bw.


« Last Edit: June 18, 2011, 12:02:12 am by tinhead »
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Offline Mechatrommer

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Re: which one's better? Rigol DS1202CA or Instek GDS-2202
« Reply #6 on: June 18, 2011, 12:33:56 am »
so meaning with both channel on, rigol is not in interleaved mode, so assuming the adc chip and brand is near perfect, and with "proper" sincx, rigol can reconstruct 400MHz signal perfectly?
ok we know rigol sincx is sux, so we just turn off the sincx in scope, and hack it in pc software later for proper sincx? ??? :P
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

alm

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Re: which one's better? Rigol DS1202CA or Instek GDS-2202
« Reply #7 on: June 18, 2011, 04:00:25 pm »
According to the Nyquist-Shannon sampling theorem, you can reconstruct a signal if you sample faster than two times the bandwidth of the signal. So if you sample at 1GS/s, signals with a bandwidth less than 500MHz can be completely reconstructed. The major issue with applying this theorem to a DSO is that it's about the signal bandwidth, i.e. the fastest frequency component in the signal. In real life, the front-end doesn't have an infinite roll-off, so higher frequency components will be present. The limited sampling time (<< infinite) also adds extra high-frequency components. This screws up your ideal interpolation. This is why scopes with a Gaussian response need a sampling rate about 10x higher than the bandwidth, but scopes with a so-called brick-wall response need only a 2-4x higher sampling rate. Agilent has a nice appnote about this.

Another issue is that you need ideal sinc interpolation of infinite length.

Of course the DS1052E has nowhere near 500MHz analog bandwidth, so the whole discussion is mostly academic.
 

Offline tinhead

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Re: which one's better? Rigol DS1202CA or Instek GDS-2202
« Reply #8 on: June 20, 2011, 12:48:30 pm »
so meaning with both channel on, rigol is not in interleaved mode, so assuming the adc chip and brand is near perfect, and with "proper" sincx, rigol can reconstruct 400MHz signal perfectly?

a perfectly synchronous interleaved ADCs will do the job exact the same as non-interleaved one,
but in the reality you will never get them to work perfect, so additional waveform distortion
is coming from interleaving, see Agilent app note 5989-5732EN.pdf

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Offline Mechatrommer

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Re: which one's better? Rigol DS1202CA or Instek GDS-2202
« Reply #9 on: June 20, 2011, 03:25:27 pm »
thats what i tried to demo. in non interleaved mode, signal reconstruction should be better, or what? and alm's answer, if there's higher order harmonics then of course aliasing will occur, no matter how perfect sincx is. and i think, we should also consider noise, where in reality zero noise adc is nonexistence. so even a perfect 400MHz sine is injected, the internal of dso will create harmonics from noise which will corrupt sincx. and the point is, as you said, a perfect interleaving mode is impossible, making reconstruction even worst.
« Last Edit: June 20, 2011, 03:34:52 pm by Mechatrommer »
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline tinhead

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Re: which one's better? Rigol DS1202CA or Instek GDS-2202
« Reply #10 on: June 20, 2011, 07:40:19 pm »
in non interleaved mode, signal reconstruction should be better, or what?

the reconstruction itself is always as good as the sampled data, no matter if interleaved or not.
With interleaved ADCs the clock path need to be very exact, which can be of course tuned because as EE
you can calculate potential clock delay. However the random jitter will be already enough to
create waveform distortion during sinx reconstruction. On Rigol E/Hantek/UNI-T etc. class of DSOs we have already
up to 650ps total jitter which is large number and you can see distortion already on signals above samplerate/10.

The jitter (and resulting error) is not because of interleaved ADCs but because of bad clock, which is of course
typical because in all these designs FPGA is responsible for clock generation.
You can take any DSO (with int. ADCs), connect all the ADCs to low jitter clock domain (let say total jitter 50ps, for UNI-T you will need 4 clocks on same die, for Rigol 10 clocks ... ugly thing, and of course the phase shift need to be controlled by sw in let say 50-150ps steps) calibrate DSO and you will see almost perfectly reconstructed 200MHz sine wave on 1GSs range DSO.
However if you look what's available on market you will see that such low jitter clocks are expensive, they actually
costs more than complette DSO in china.

So for sure this tech. works almost perfect, but only if you don't care about costs. As Rigol started with CA
series there was no Agilent DSOX series, and the price for CA series was really high. Today you can
buy 60MHz CA model for 500EUR, which is cheap (PLL clock and ADC costs already 250EUR).
You can imagine now why there is only small sample memory - because nobody would buy 100MHz chinese
DSO for 2k EUR (it is not only extra memory chip necessary, the FPGA need to be faster and have additional i/o pins,
the additional dev. work costs money too).


... so even a perfect 400MHz sine is injected, the internal of dso will create harmonics from noise which will corrupt sincx. and the point is, as you said, a perfect interleaving mode is impossible, making reconstruction even worst.

the noise didn't really matter that much, for good reconstruction on interleaved ADCs you need to have low jitter clocks,
good signal path, good calibration/compensation for potential parts tolerance and of course exact the same vertical  ADC gain/response. For 8bit ADCs the vertical gain/tolerance are not that critical as long you not push them to the limits.

So again, common problem for all low ranage DSOs is the clock jitter, and of course all manufacuturers know it (that's probably they even don't care about not sufficient filtered ADC supply, or overclocked ADCs .. because it didn't really matter, the jitter is destroying everything anyway ).

Now back to topic, for sure Rigol CA with non interleaved ADC is a good value for money however there are other design aspects which i personaly don't like, especially the odd display, definitely too small sample memory and yeah the firmware.
I don't want to be human! I want to see gamma rays, I want to hear X-rays, and I want to smell dark matter ...
I want to reach out with something other than these prehensile paws and feel the solar wind of a supernova flowing over me.
 


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