I'm laying out a PCB for a passive speaker crossover utilizing air-core conductors. As I'm going about my usual PCB layout process, it just dawned on me that the copper pour/ground plane I typically apply to boards may interfere with the inductance of the air core inductors.
Is this something I need to worry about?
Is this something I need to worry about?
It is possible to have interaction with the ground plane, but you can remove the copper under the inductors.
These effects do happen even in the audio band, and are well known to pcb layout engineers. The interaction
of the ground plane with other pcb layers is used to lower parasitic inductance and reduce noise.
These effects do happen even in the audio band, and are well known to pcb layout engineers. The interaction
of the ground plane with other pcb layers is used to lower parasitic inductance and reduce noise.
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You don't need a groundplane anyway for a passive crossover as the signal levels are high and impedance low, noise-pickup is not an issue, and as there is no gain unwanted feedback is not an issue. The things you need to worry about are magnetic coupling between the inductors and between an inductor and nearby transformers. Inductors are commonly placed at right-angles to minimize magnetic coupling.
However air-core inductors have significant external fields that will interact with conducting surfaces - this is something you can test with a suitable meter. Toroidal wound coils are the least sensitive.
However air-core inductors have significant external fields that will interact with conducting surfaces - this is something you can test with a suitable meter. Toroidal wound coils are the least sensitive.
Thanks for your input.
As lazy as it sounds, I use ground planes to simplify routing. Instead of routing traces for a ground, I simply drop a big fat ground plane which neatens up the layout.
Good call on the testing, don't know why I didn't think of it earlier. Just tested my inductors on a piece of blank copper clad board and it turns out, the inductance drops just a touch (~0.05mH) when placed on the copper. This actually works out in my favor since the inductors (in air) were measuring a touch higher than their nominal value.
As lazy as it sounds, I use ground planes to simplify routing. Instead of routing traces for a ground, I simply drop a big fat ground plane which neatens up the layout.
Good call on the testing, don't know why I didn't think of it earlier. Just tested my inductors on a piece of blank copper clad board and it turns out, the inductance drops just a touch (~0.05mH) when placed on the copper. This actually works out in my favor since the inductors (in air) were measuring a touch higher than their nominal value.