ADC for digital oscilloscope

[ronshm]

Hi

For my digital oscilloscope project i'm looking for a suitable ADC.

The minimum sample rate should be >=20Msps.
The max input voltage should be +/- 10v.

I'm thinking of 10bit ADC with two's complement output formt, seems to me that it should be easier to converte the negative half of the signal this way.
I also need a circuit to scale down the signal.

Can you advice me about a suitable ADC and scale down circuit ?

I would be thankful for any help.

 

[dick_freebird]

You're not going to get that kind of range and rate in the
same device, expect. At least, back when I was working
in 30V technologies you couldn't.

More likely you will have a switched attenuation network
at the front end (your vertical/div) and work with whatever
ADC provides you the sampling speed / accuracy you want.

You would have to frequency-flatten that attenuator. Perhaps
look into digital step attenuator chips that have already done
this internally. However many of these are not DC-friendly.

Looking at some of the "USB oscilloscope" products out there,
in the details you can see they use fairly low accuracy ADCs
(base resolution 8 bits, 1-5GSPS with some weasel wording
about interleaving).

If the data is post-processed then the encoding scheme will
not matter much.

I bet you have way more fun trying to make a good trigger,
than the waveform capture itself.

 

[karesz]

Hi ronshm,
You should check for ADCs of max frequencies with designed (i.e.) 10 Bits...
You will find only types with input ranges of maybe 2.5V or eventually only +/-0.5V at the Uref...
But its not a problem because you need so & so an input amp & attenuator(s) too.
With their combinations are oscilloscopes over tenth of years realised at typical input ranges of i.e. 1mV/div up to 10V/div...
Onchip attenuators (suggested by dick_freebird too) arent in my opinion very good for oscilloscopes...
More problematics will give your triger electronics, dick_freebird suggested too; these is the most "bad part of DIY" oscopes :-(.
K.

 

[ronshm]

Thanks for your answers.
As a student i have limited resources, so i'm checking the options in order to make the best system i can.

 

[karesz]

Hi,
_OK!
I think; your solution is from TI or NI to take, in all cases only "frequently consumed" types....
Google will present for you surly enough types?
K.

Added after 31 minutes:

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After some (pre)selection check for possible prices & deliverer: http://octopart.com/
K.

 

[ronshm]

Hi karesz,

Thank you very mush for the information

 

[karesz]

Your welcome!
For some system/circuit ideas I would read/study manuals-circuits from good industrial scopes
Some collecting web sides:
http://bama.edebris.com/manuals/
http://www.ko4bb.com/Test_Equipment/
http://www.eserviceinfo.com/
http://www.bitsavers.org/pdf
K.