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In the documentation for the Keysight DSOX1204G, it has the interesting note for the sampling rate of:

2 GSa/s (half channels)
1 GSa/s (all channels)

So, if I use all 4 channels on the scope, I get GSa/s, and if I use only two channels I get 2 GSa/s. I would assume at the core of the scope there's some low resolution ADC with a convert line that is tied to a 1GHz signal. For the 2 GSa/s are they just tying two ADCs together at the inputs but putting the convert lines 180 degrees out of phase, or is it something more interesting?

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    \$\begingroup\$ Yes, current scopes work by having multiple slower rate ADCs (with fast analog bandwidth) which can cooperate to take samples at a higher rate for a given channel, or be assigned to different channels. For a given model (cost) you can operate it to maximize speed or channels, or you buy a different more expensive model with a different product of rate * channels. \$\endgroup\$ – Chris Stratton Jan 10 at 1:41
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Daniel from Keysight here - this is a very common behavior for this range of oscilloscope. Essentially, manufacturers (like us) build out acquisition boards to handle two channels at a time.

So, a four channel scope has two acquisition boards*. When you use two channels on the same board, the ADC has to cut its sampling in half. It spends 50% on one channel and 50% on the other.

If you'd like to dig in more, I highly recommend this talk given by one of our ADC designers:

https://www.youtube.com/playlist?list=PLzHyxysSubUmxGOMVpiKLxouweh2AAlG1

**Acquisition systems would be more accurate, as it's often just one PCB. However, each "path" will have chips/ASICs/ADCs/processors that handle two signals per chip.*

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  • \$\begingroup\$ That seems to be it. I was just hoping for something more interesting. \$\endgroup\$ – b degnan Jan 17 at 17:04
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    \$\begingroup\$ Nope, sorry! Time domain interleaving :) \$\endgroup\$ – Daniel Bogdanoff - Keysight Jan 17 at 17:13

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