I'm designing a 4 layer PCB. The two outer layers are going to be routing layers, the 2nd layer a ground layer, and the 3rd layer a split power plane layer.
I have a negative and positive power supply, split on layer 3. These two supplies power three different voltage regulators. Two of these 3, create different bias voltages (to reverse bias photodiodes), and one one is used to create a 3.3V rail for an IC RF amp. Does it make sense to make the 3.3V rail a split power plane on the third layer? It only powers one IC, and since I'm amplyfing analogue RF signals, it needs to be as low noise as possible. What about making split planes for the bias voltages?
I guess more generally, when does it make sense to have a plane, vs a trace for a net?