Reference signal requirements for RFFC5071

RF Solutions RF All Other (switches, controls, attenuators, ..)
1

Hi, I have a few questions about the reference signal requirements:

  1. Can the synthesizer accept logic type (CMOS/LVPECL/LVDS, etc…) square waveform reference signal or does it have to be clipped sine wave as the datasheet suggests?
  2. I am using multiple RFFC507x ICs on the same PCB. What is the best distribution strategy to provide the reference signal to each IC (power divider or fanout buffer or something else) if I have a single input to the board?
  3. What is the input impedance at the reference input pin (REF_IN)? Is it high impedance or 50 ohms?

Thanks and best regards,
Noman

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  1. A clipped sine wave is recommended as it has the best trade off of fast edges for phase noise with lower harmonics than a square wave. The level is important, as going above the max of 1500mVp-p in the datasheet will create higher clock and clock harmonic leakage at the mixer output. So yes you could use a square waveform, as long as the level is within the range specified in the datasheet, and taking out harmonics may help.
  2. No particular recommendation for distribution network. It would depend on the clock frequency and level available. A resistive splitting network may be OK, or you could use some active buffers. Good to have isolation between the RFFC507x devices to prevent any unwanted interactions. Active buffers would be the lower risk approach.
  3. The REF_IN pin is high impedance. It was designed to be used with TCXOs that can drive load of 10KOhm//10pF. It is more like several 100KOhms//1-2pF.

Note that if you have multiple RFFC507x devices on one PCB it is important to keep them isolated. As well as isolating clock, digital, and supply lines, this includes use of shielding to prevent any radiated coupling. This is especially important if any of the devices are tuned to the same LO frequency (or multiples of) to prevent injection pulling effects.