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ADF4159 Charge Pump Polarity Issue

When the polarity is negative, the correct single frequency point can be obtained, but the signal quality is poor; when the polarity is positive, the frequency point falls at the lowest point of the VCO.But my VCO increases in frequency as the voltage increases, so I need the charge pump polarity to be positive, what should I do? 

The attached figure is the single-point spectrum and register configuration diagram when the polarity is negative