Question about noise figure change after Rin lowered for an ADC

Hi,

I read noise figure calculation from Maxim AN. For ADC NF calculation, it says:


.........
3. As RIN is lowered, the full-scale power level increases, thereby increasing the effective noise figure for a constant SNR.

The link of the above statement is from here:

http://www.maximintegrated.com/en/ap...ex.mvp/id/1197

It is contrary to my first guessing. Could you explain it to me?

Thanks,