ADF4107 PLL Frequency Synthesizer

I have a frequency Synthesizer circuit (4-5 GHz) which I am debugging and testing.It uses ADF4107 IC.

The IC on just power-up and applying input reference source gives some 4.236GHz frequency , but the instant we program it for 4 GHz it gives 3.99 (and an unstable )frequency output. But this happens for programming for any output frequency .i.e it gives the same output (3.99 GHz irrespective of input register values.)

MUXOUT gives correct values of DVdd and Dgnd at pinout (when programmed accordingly=>Ic is responding to programming).

When we try to program MUXOUT output for displaying R-counter Output it gives very weak(almost 2mv pk-pk) voltage signal with the same frequency as of the RF source without dividing,but unexpectedly when we program MUXOUT for N-divider output, N divider gives the correct expected value.(the same as channel Spacing).

This situation occurs for output frequency of 4 GHz.

When we try to program the IC for 4.5 GHz, N-divider output is not as expected ( gives 177kHz instead of expected 200kHz). R-divider output is again very weak voltage signal (2mv pk-pk and frequency same as of RF-source).

Any suggestions for reason of this unusual behavior of IC? Does the low Voltage level of 0.3 V pk-pk of reference source anything to do with this?

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