ADC for digital oscilloscope

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.

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.

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.

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.

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:

Hali,
You can search (i.e.) on these collection (if your antivirus SW is actualized! :-() for a good selection: **broken link removed**
After some (pre)selection check for possible prices & deliverer: http://octopart.com/
K.

Hi karesz,

Thank you very mush for the information

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.