QPL9547 for UHF

RF Solutions RF Low Noise Amplifiers
1

Hi, I would like to use the QPL9547 for UHF antenna amplification and also power the amp over the coax cable. The antenna’s impedance is 300Ω so a balun is used to match it to 50Ω. C2 and L2 form a “Tee” to split the DC and RF. The rest is mostly like QPL9547 eval board but with the values adjusted for UHF. I’m not sure about these values and I am curious what others think.

  • Xc for C1 / C2 @ 300Mhz is 0.5Ω
  • Xc for C1 / C2 @ 600Mhz is 0.25Ω
  • Xl for L1 / L2 @ 300Mhz is 283Ω
  • Xl for L1 / L2 @ 600Mhz is 565Ω

Do those values make sense for the QPL9547? I tried to find an inductor in that area with a self resonant frequency as high as possible. This inductor has a 1.9Ghz self resonant frequency.

QPL9547_uhf_schematic
QPL9547_uhf_schematic1334×532 162 KB

2

Looks OK. May be worth adding some higher frequency decoupling like 100pF.

3

ok thank you. Better to replace C3 and C6 with 100pF or add in addition to? I assume the 100pF should be the closest to L1 and R1, then larger caps?

QPL9547_uhf_pcb
QPL9547_uhf_pcb1492×553 225 KB

4

I would just add a 100pF on supply close to L1. You my not actually need two 10uF capacitors as they are so close together.
On layout please make sure each capacitor has at least 1 dedicated ground via. Don’t share ground vias between decoupling capacitors. You also want to add ground vias under the LNA package.