ADC Interleaving

I am considering trying to interleave two 250MS/s ADCs. Would this be a
good idea? possible? or too much trouble?

Cheers

Jon 

I mean you want to reach 500MS/s sampling?

It could be possible, you must be careful in designing PCB,

Jerzy Gbur

In general, you will find that this is a lot of trouble.

That said, it is done. See the AD12401 at www.analog.com for an example
of a module that interleaves two ADC.

If you want to interleave multiple ADCs there are three main parameters
that must be matched or corrected for on the ADCs. To the extent that
they are not matched, the quality will degrade.

1.  DC offset.  Easy to track and remove if it is not matched.
2.  Gain. Needs to be matched or equalized across your frequency range
of interest.
3.  Sampling phase offset.  This is the one that will cause you big
problems.  If the ADCs have any phase error in when they sample, it
will cause spurs in the data. The hight of the spurs depends on the
sampling phase error.  The data sheet for the AD9481 gives an error
budget of < 2 ps for interleaving two 8 bit 250 MS/s ADCs with a 100MHz
analog input.  That error budget will go down if your analog input is
higher frequency, or if you want more bits of resolution.

I think that there are some graphs of sampling phase error budgets vs
other parameters some where on the Analog web site, but I do not
remember where.



Regards,

John McCaskill

>I mean you want to reach 500MS/s sampling?
>
>It could be possible, you must be careful in designing PCB,
>
>Jerzy Gbur
>
>

Yes I would like to reach that sampling, but I guess there are a lot of
other things to take into consideration apart from the pcb like the ADC
errors etc.

Cheers

Jon

See the First Quarter XCell article "Capturing Data from Gigasample 
Analog-to-Digital Converters" for an excellent example by Ian King 
showing how to read a pair of 1.5 Gsps ADCs into directly into an LX15.

maxascent wrote:
> I am considering trying to interleave two 250MS/s ADCs. Would this be a
> good idea? possible? or too much trouble?
> 
> Cheers
> 
> Jon