Re: [Discuss-gnuradio] ADC Specs

[Brian Padalino]

On Mon, Dec 15, 2008 at 4:41 PM, Aadil Volkwin <address@hidden> wrote:
>
> Hi, I have read this information regarding the USRP ADC
>
> "The full range on the ADCs is 2V peak to peak, and the input is 50 ohms
> differential. This is equates to 40mW, or 16dBm."
>
> Please may someone enlighten me, how the 40mW and 16dBm values were
> calculated?

I am not sure where those numbers came from directly, but the 50 Ohms
differential might be wrong.  From the datasheet here:

    http://www.analog.com/static/imported-files/data_sheets/AD9860_9862.pdf

Page 2 shows the differential input resistance to be 200 Ohms with the
maximum differential input being 2Vp-p.

Regardless (and assuming the 50 Ohms), the equations are only Ohms Law
and conversion into dBm.

  P = V^2 / R
  P = 1.0V^2 / 50 Ohms
  P = 20mW

Since there are two inputs, we double that to be 40mW of power used up.

  10*log10( P / 1mW )
  10*log10( 40mW / 1 mW )
  16.02 dBm

Hope this helped.

Brian