While the design target was 50 ohms, device characterization for several lots has shown it to be closer to 60 ohms. That said, operating with a low IF input resistance reduces PIN_0dBFS of the AD6676. This in turn can reduce the P1dB requirements of the device driving the AD6676 thus allowing it to operate at lower supply level (i.e. 3.3 V vs 5.0 V) as well as at reduced power consumption. Alternatively, the lower PIN_0dBFS can be used to extend the IF AGC range where the P1dB of the device driving the AD6676 (i.e. mixer) often sets the upper limit.
