Part Number: TRF372017
I am using the TRF372017 in fractional mode with a carrier around 2GHz. I have the loop filter set near the 30.72MHz fPFD example within table 30 in the datasheet. With only a carrier on the RF output the phase noise on the LO port is measuring ~1degree in my band of interest. When I input pseudo random data onto the BB input the RF spectrum appears as expected on the RF output. The modulated output also appears on the LO output, looking like an RF output with horrible carrier suppression. How much isolation should I expect between the LO output and the RF output? Are there possibly settings within the device that I could have not tuned properly that would cause this?
In reply to Keith Barkley:
I will try to reproduce your issue in the lab and will get back to you as soon as I have results.
It appears that there exists coupling between the baseband input (that gets modulated up) and the LO output port. There isn't anything that you could do via the registers to correct for this, as far as I am aware. I measured the isolation on the LO port over various frequency offsets and have attached them to this post. If this is an issue for your application, I believe that the TRF3722 may be a better fit. Its overall performance is improved over the TRF372017, and I believe that it will have better isolation as well.
In reply to Abdallah Obidat:
In reply to Brandon Sorn:
The data above was measured on the LO output port and compared the power of the LO against the power of the modulated RF output. This issue of coupling between the baseband input and LO, manifests itself as a diminished RF output on the LO port. Tuning the output impedance will probably affect the isolation to a degree. Also, the isolation does improve when the output is loaded with a 50 ohm termination. I do not believe, however, that there is a way to completely eliminate the RF output from the LO port without attenuation. You could try attenuating your input signal and you’ll notice an improvement in isolation.
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