Question on biasing circuitry - RF Cafe Forums
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Post subject: Question on biasing circuitry Posted: Tue Apr 25, 2006 2:14 am
Joined: Tue Apr 25, 2006 2:01 am
I am noticing a difference in the overall gain (of an LNA) depending on where the off-chip decoupling capacitors are placed (close to or away from the chip). Any ideas on why this might be happening?
Post subject: LNA bypassingPosted: Tue Apr 25, 2006 5:36 pm
Joined: Wed Feb 22, 2006 3:51 pm
Even a short trace on a PCB looks like a non-negligible inductor at a high-enough frequency. So a bypass capacitor away from the chip might even look inductive, depending on the length of pcb trace and the operating frequency. That would give unintended feedback via the power supply pin of the IC, which would affect the gain.