Why are there no 24-bit dso's?

[colorado.rob]

Maybe you can look about a new open source project i started to design,
a 2 channels analyzer based on LTC2380-24 high performance 24bits 1.6MSPS SAR ADC.

You get full dynamic range at 30sps.  Great for those bass notes.

[radiolistener]

You get full dynamic range at 30sps.  Great for those bass notes.

it can be used to analyze low frequency harmonics of drum sound with 145 dB dynamic range 

[tinhead]

colorado.rob, well... but everything changes and progress does not stand still 

So, let's say 8 bit is not reachable for 10-20 GHz sampling rate 

AD9213

[ogden]

colorado.rob, well... but everything changes and progress does not stand still 

So, let's say 8 bit is not reachable for 10-20 GHz sampling rate 

AD9213

fIN = 4000 MHz ENOB=7.8 Bits. Does not qualify as "reach 8 bits".

[tinhead]

colorado.rob, well... but everything changes and progress does not stand still 

So, let's say 8 bit is not reachable for 10-20 GHz sampling rate 

AD9213

fIN = 4000 MHz ENOB=7.8 Bits. Does not qualify as "reach 8 bits".

sure, taking 10.25GSPS/2.56 and ENOB at that freq you definitely right, 7.8 is not 8, even if it close to it.

But one can make it equal, assuming that ENOB will increase with lower sampling rate:
 
10.25GSPS > 10GSPS, so 10.25 - 10 / 10 = 2.5%
8 - 7.8 / 8 = 2.5%

[ogden]

colorado.rob, well... but everything changes and progress does not stand still 

So, let's say 8 bit is not reachable for 10-20 GHz sampling rate 

AD9213

fIN = 4000 MHz ENOB=7.8 Bits. Does not qualify as "reach 8 bits".

sure, taking 10.25GSPS/2.56 and ENOB at that freq you definitely right, 7.8 is not 8, even if it close to it.

But one can make it equal, assuming that ENOB will increase with lower sampling rate:
 
10.25GSPS > 10GSPS, so 10.25 - 10 / 10 = 2.5%
8 - 7.8 / 8 = 2.5%

I am not sure your math is applicable to ENOB of ADC, but in general I agree - on lower sample rates that ADC will reach 8 bits ENOB sooner or later. This is to answer original question for 10x time - there are compromises. You can get either precision or speed, but not both at the same time. There is progress obviously, but "law" will remain forever.