51 ohm matching resistor at PLL IC input... required

Hi all,

i was wondering if it is really needed to place a 51 ohm resistor in parallel to the RF input of a 3GHz Frequency Synthesizer? wouldn't this just decrease the power by 3 dB? assuming the copper trace feeding the input is a controlled 50 ohm impedance.

Maybe that is the design looking for. To decrease the power with 3dB.

uhm..... they already used a PAT-3 3dB attenuator along the line. wouldn't the 3dB attenuator sufficient to provide the impedance match between the source and the RF input of the PLL IC? thanks a lot!

Placing a 50Ohm resistor parallel to the input pin mean that the input pin should be high impedance. But what kind of an input has high impedance at 3GHz? If your circuit is narrow banded, you could try to LC match the input to 50Ohm. I think they know their input is far off 50 Ohm, so they just placed a 50Ohm resistor and inserted a 3dB pad and live with the result...