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ADF4002 differential RF drive with transformer?

Question asked by deltapapat65d on Jun 10, 2015
Latest reply on Jun 15, 2015 by Brigid.Duggan

I would like to use a transformer to drive the ADF4002 RF inputs ports differentially, while using the transformer for the needed DC isolation. I am using the ADF4002 at lower frequencies, and suitable coupling caps very much slow down the turn-on time when coming out of power down using the CE pin due to the internal impedance of the RF input port bias network. The transformer allows the deletion of the caps, and has only ~1 pF primary to secondary capacitance allowing for quite fast settling of the input bias voltage, about 2-3 uS. Is there any reason not to use a transformer to supply the RF drive to the RF+ and RF- inputs? I realize that the RF ports ports present a fairly large load impedance at lower frequencies. The needed 50 ohm termination for this application is provided by a resistor across the transformer. I have attached a sketch of the possible implementation.