Re: [Discuss-gnuradio] Resolution of USRP N210 and N200

[Isdren Gineer]

To add to what Ben has wrote, if decimation is involved in the processing stages it is possible to get a higher resolution than that of the initial samples. For example, a decimation by a factor of two can increase the bit precision by one. So in this case, it could depend on where the interface is being defined. Perhaps the ADC chips being used are indeed 14 bits, as per the spec sheet, but the implementations of the different LFRX versions may have different post-ADC processing stages. If this is the case, while the precision of the ADC chips is 14 bits, the output of the LFRX could have a higher resolution.

For those wanting to learn more, this is the principle behind sigma-delta ADCs.

On Tue, Nov 5, 2013 at 4:12 PM, Ben Hilburn <address@hidden> wrote:

Hi Ting -

Sorry, there really wasn't a good reason for me to not answer your question, regardless =)

So the ADCs are indeed 14 bits, but those samples go through a lot of processing on a number of different platforms, and get sent over a few different buses. At any of these stages, depending on your system parameters, there might be conversions and scaling factors applied to the data, which changes the representation. Remember that since the ADC is a 14-bit ADC, you are never really getting more precision than those 14-bits; they are just different ways of representing that data.

Does that help, at all?

Cheers,

Ben

On Tue, Nov 5, 2013 at 11:34 AM, Ben Hilburn <address@hidden> wrote:

Ting -

This question really isn't GNURadio related. If you resend it over the USRP-Users list, though, we will help explain things quickly!

http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com

Cheers,

Ben

On Sat, Nov 2, 2013 at 12:22 AM, Ting Wu <address@hidden> wrote:

Hi,

 

Both of USRP N210 and N200 have 14 bit ADC, which means a range of +/-2e13=+/-8129.

However, as I tested a N210 with LFRX, I got values from -32704 ~ 30073, close to +/-2e15=32768.

Last year, I also tested a N200 with LFRX, I got values from -16357 ~ 16241, close to +/-2e14=16384.

The sampling rate was set to 4 MHz.

 

So why does the ADC has a real resolution higher than 14 bit, and are N210 and N200 the same?

I’m really new to the world of ADC, so some basics would be very helpful.

 

Thanks!

 

Wu

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