How to convert amplifier's input referred voltage noise to noise figure

In RF system design, noise figure is parameter to calculate receiver's sensitivity. But analog base-band specify noise with input or output referred voltage noise. How to convert it to noise figure? See the article "Calculating noise figure in op amps" below:

http://focus.ti.com/lit/an/slyt094/slyt094.pdf
Another article tells "Matching the noise performance of the operational amplifier to the ADC"
http://focus.ti.com/lit/an/slyt237/slyt237.pdf