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ADF4351 strong RFout distorsion under 150MHz

Question asked by mirkedge on Nov 24, 2014
Latest reply on Nov 24, 2014 by rbrennan

I'm evaluating the ADF4351 mounted on the respectively Eval Board.
I need to carry out a wide band synthesizer between 50MHz and 3GHz
So I replaced L2 and L3 (7.5nH) inductors with two 50 ohm resistors.

All ok over frequency above 200MHz.
Conversely in both pullup cases (with inductances and with 50ohm resitances)

I can't generate a single-harmonic signal under 150-200Mhz.

The synthetization at lower frequency generates a strong distorsion (also with even order harmonics) in the RFoutput.
It seems like a sort of an amplitude saturation, although the out level in terms of Vpp voltage remains the same.
I tried anyway to reduce the RFoutput level to the presetted -4dBm level however the distosion was still present.
Somebody have any idea, WHY?