If ports RF1, RF2, RF3, or RF4 on the HMC241 are not connected to any circuitry, can the
non-connected port be left floating or is a DC blocking capacitor to gnd or VCC required to be connected to the unused port?
HMC241's RF ports are DC coupled with ~Vdd. Floating the unused RF ports would change the part performance slightly. We recommend terminating unused RF ports with 50 Ohm resistors to Vdd (DC blocking capacitor is not required but Vdd should be decoupled properly) or GND (DC blocking capacitor is required).
What about the NC (No-connect pins) on the HMC241. Can I ground them as well?
Grounding usually provides better isolation between the ports. With RF parts, usually more ground is better. If they are truly no connects, then it shouldn't be a problem. Sometimes though, NCs are really connected to something that we could mess up if grounded.
The pins designated NC (Not Connected) are not internally connected to the die. It is not necessary to connect NC pins to any voltage, they can be left floating. However, the connection of NC pins to ground prevents noise injection from these pins, which may most probably distort RF and digital signals. We recommend to connect NC pins to ground.
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