Spurious-free dynamic range (SFDR) is two-thirds the difference between the 2-tone, third-order intercept
) and the minimum discernible signal (MDS). Referring back to Figure
1, it can be seen that the 3rd-order product line has a 3:1 slope while the fundamental output line has a 1:1
slope. Therefore, the 3rd-order products are always three times as far from the IP3 as the fundamental output. If
you use the SFDR as the power of the output tones (dBm) and plug it into the equation for IP3 calculation from the
Intercept Points (IP3 & IP2) section of the RF Cafe web site, the power of the 3rd-order products will be right at
the MDS power level.