Rigol caught with their pants down! (DS1052E Oscilloscope)

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As promised, an exposé of an issue with the Rigol DS1052E oscilloscope in my
latest video blog:
http://www.alternatezone.com/eevblog /

Dave.
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Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


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You corrected the number of PLLs in the FPGA, how do they get the
clocks' phases aligned? I'm no expert on digital scopes, but I suppose
the clock frequency changes depending on the time base?
Do they just drop some ADCs and keep the frequency, thereby permitting
the use of trace delays to get the 100ps delays or what?
Are the GS/s figures real time or equivalent time?
I think it is possible Rigol tests the ADCs and bins them in-house. Do
you think they might run the power supply a bit "hotter" to get the
parts to work at higher clocks?

Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


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Beats me.
Could be as simple as fixed tuned gate delay inside the FPGA, or could be
some more complex system that auto-calibrates perhaps.

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Only when required when the memory is full.
On short memory mode (1GS/s, 16KB) a relay clicks in at 100ns/div and it
tells you it's doing 1GS/s on 50ns/div to 5ns/div.
No such click occurs when in long memory mode (500MS/s 1Mpoints), and it
stays on 500MS/s up to 100ns/div.
The relay is thus most likley switching the input signal between either 5 or
10 ADC's depending upon the requirement.

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1GS/s real time of course, that's been the selling point of these Rigol
scopes for the last 5 years or so.

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I don't think so, likely they have just done exhaustive testing of these
parts to ensure the work. Binning each one in house would be possible, but
messy.
Perhaps AD are the ones pulling the swifty and charging a huge premium
(almost 3 times) for the exact same part?

Dave.
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Re: Rigol caught with their pants down! (DS1052E Oscilloscope)




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It could have been a purchasing error, that actually works.
Or, the parts marked as 40 don’t meet the specs over temperature for a
100/80 mhz clock.
Perhaps  NL specs are not met but Rigol can compensate for the error.
I've seen -40c to 85c parts work beyond the rated specs, with some
additional error.

Cheers
 



Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


PS: Another piece of consumer electronics that was on the shelves for
10 years was the Commodore 64. I'm sure it underwent internal changes
but it was the same machine for years.

Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


On Mon, 20 Jul 2009 07:52:09 +1000, "David L. Jones"

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<snip>

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Tuning gate delays in an FPGA doesn't work.  Routing is over half the
delay and there is no way to fix that part.  Every time you "wire" the
part it'll have a different routing and your delays will be off.
Indeed, the idea is to make sure you don't rely on placement or
routing.

<snip>


Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


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I think you can place and wire parts of it by hand to get around some
of it, but it would
still change with temperature, voltage, etc.

Some Xilinx fpgas have programmable delays in the IOs, 64taps each at
1/64th of a ~200MHz (afair)
reference clock.  a closed loop keeps the delay constant with temp
etc.

-Lasse

Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


On Tue, 21 Jul 2009 04:42:36 -0700 (PDT), " snipped-for-privacy@fonz.dk"

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You might do it once.  You'll never maintain the mess.

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Yes, there is an I/O delay, but it's certainly not that large.  There
is also delay in the DLLs on that order, but there are a lot of
restrictions on those (clocks only).

Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


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had to check, virtex5 has a programmable IOdelay, 64 taps of each
~78ps with the nominal 200MHz reference

-Lasse

Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


On Tue, 21 Jul 2009 17:20:04 -0700 (PDT), " snipped-for-privacy@fonz.dk"

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Is it fully programmable?  I surely don't remember that, though I
didn't use a Virtex-5.

Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


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when used as output delay it is programmable at compile time, when
used for input
it is programmable at compile time but can be changed at runtime.

haven't used it either think it is new for virtex5 and later

-Lasse

Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


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Why not? I'm pretty sure a 50MHz and 100MHz are exactly the same
too.... :)

Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


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I meant a 50MHz and 100MHz scope up there.

Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


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Maybe, and I've mentioned this in a previous blog comment.
There is a chance the 50MHz and 100MHz model front ends are identical except
for maybe some different value parts on the 50MHz model to limit the
bandwidth.
Would be interesting to see both circuits side-by-side.
Given that both sample at 1GS/s and everything else is indentical too,
modding the 50MHz unit might just be possible.

Dave.

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Re: Rigol caught with their pants down! (DS1052E Oscilloscope)



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Does this Rigol claim to do 1Gsps on non periodic signals? If not (like
other sampling scopes), perhaps they're just sliding the phase of the A-D's
while still clocking them within their rated specs.

Did you ever measure the clocks to the A-D chips?

Bob
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Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


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Yes, that's always been its big selling point. 1GS/s real-time.

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It also has a selectable equivalent time sampling mode (up to 10GS/s), but
you have to specifically select this through a menu.
In this mode the 1Mpoint memory comes in at 100ns/div.

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No, I haven't open my unit. But bet your bottom dollar they are 100MHz,
simply no other way to do it.

Dave.

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Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


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Obviously their engineers grew up over-clocking AMD/Intel motherboards
then :)

I was initially concerned about the temperature the ad9288-40 is
running at when it's over clocked from 40 to 100Mhz, which won't be an
issue since they have a version that runs at 100Mhz, probably using
the same die.

I'd also be concerned about whether the 40Mhz part can convert at
100Mhz, but looking at the data sheet, there doesn't seem to be any
perceivable difference in the switching/dynamic characteristics, apart
from one each having a specified maximum conversion rate.

As long as the scope perfoms to spec, I don't see anything wrong
otherwise

Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


On Sun, 19 Jul 2009 22:04:25 +1000, "David L. Jones"

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Do the scopes work?

John



Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


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Yep, they work. So Rigol are obviously getting away with it by hook or by
crook.
If AD are deliberately under-speccing their normal chips, then it's a clever
ploy by Rigol to exploit it.

Dave.
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Re: Rigol caught with their pants down! (DS1052E Oscilloscope)


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So give it a 1 Ghz signal and see if it it looks right then.

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