Electronics > Beginners

Rogol 1054Z actual bandwidth

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rhb:
Has anyone actually determined that there are 3 analog anti-alias filters?  It seems quite unlikely.  I'd expect the change to be in the FPGA.  It certainly is in the Instek GDS-2000E scopes.

I've not sat down to work out the implications of aliasing if you stay in the time domain and don't do trace interpolation.

I did verify that my LeCroy DDA-125/LC648DLX display of a <40 ps step function does not change whether I am sampling at 2 GSa/s, 4 GSa/s or using the random Interleaved Sampling mode.

Reg

rstofer:
Dave did a teardown and pointed out a Varicap to select between 100 MHz and 50 MHz - around 21:51

Fungus:

--- Quote from: rhb on November 10, 2019, 09:37:03 pm ---Has anyone actually determined that there are 3 analog anti-alias filters?

--- End quote ---

Yes. It connects/disconnect different capacitors to the the analog input circuitry depending on the bandwidth option in the firmware.


--- Quote from: rhb on November 10, 2019, 09:37:03 pm ---It seems quite unlikely.  I'd expect the change to be in the FPGA.

--- End quote ---

Nope.


--- Quote from: rstofer on November 10, 2019, 10:49:28 pm ---Dave did a teardown and pointed out a Varicap to select between 100 MHz and 50 MHz - around 21:51

--- End quote ---

He also did a reverse engineer of the input circuitry:


tooki:

--- Quote from: rhb on November 10, 2019, 09:37:03 pm ---Has anyone actually determined that there are 3 analog anti-alias filters?  It seems quite unlikely.  I'd expect the change to be in the FPGA.  It certainly is in the Instek GDS-2000E scopes.

--- End quote ---
Yep. All of us that have answered you have done so based on actual knowledge of this hardware, not speculation. The DS1xx4Z series has been dissected and discussed to death here on eevblog, such that practically none of its operating principles and design is unknown.

Also, they’re not antialiasing filters per se. They're just bandwidth limits. Since all of them are below Nyquist, they’re not just there for antialiasing. Also, it’s 4 of them: 100, 70, 50, and 20MHz. The first three are used to capture consumer surplus (i.e. enable multiple price points), while the 20MHz is the user-selectable bandwidth limit.

rstofer:

--- Quote from: Fungus on November 10, 2019, 11:51:55 pm ---
He also did a reverse engineer of the input circuitry:


--- End quote ---

To cut to the chase, look around 32:00 where Dave describes exactly how the bandwidth selection works.
This firmware selection of 50, 70, 100, 20 MHz is a settled issue.  It's shown in the schematic, it's proven by testing, it's settled!

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