[SOLVED] Basic question about groundplane underneath the inductor.

[palmeiras]

Hi guys,
How does the ground plane underneath the inductor in integrated circuit work? What is its function?

In the design manual, it is said that it does not need to be grounded. This is my doubt. Because, if it is not grounded, how does it will conduct the induced current to the ground, and therefore, to mitigatte induced currents on substrate.
(At least, I guess that this is the main function of the ground plane: mitigating induced currents on the substrate).

Thank you very much in advance,

Regards.

 

[andre_luis]

hi palmeiras,

I never noticed some orientation regarding aviodance to shield the area downside the inductor.
Maybe it is some requirement proper to the component you are using.

Could provide more details ?

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[enjunear]

Hi guys,
How does the ground plane underneath the inductor in integrated circuit work? What is its function?

In the design manual, it is said that it does not need to be grounded. This is my doubt. Because, if it is not grounded, how does it will conduct the induced current to the ground, and therefore, to mitigatte induced currents on substrate.
(At least, I guess that this is the main function of the ground plane: mitigating induced currents on the substrate).

Thank you very much in advance,

Regards.

Inductors do not require a groundplane, in fact, the typically operate best with no additional metals nearby. An inductor works by generating a magnetic field, which forms a closed loop of magnetic fields around the inductor. By inserting a metal plane nearby, all you do it interrupt those nice magnetic fields. On a PCB, the only thing that requires a ground plane to operate correctly are the traces. Most lines need a return conductor directly below them in order to maintain a correct line impedance (microstrip, stripline, etc). Capacitors and inductors are only degraded by installing them on a PCB, since you add additional parasitic losses by introducing solder pads (added shunt capacitance to ground), and having a lossy dielectric between the signal and it's return (shunt inductance and resistance).

If you are talking about using a SMT inductor that solders to a PCB (like ), then the magnetic field lines exit from the opening at one end of the coil, and wrap around to the opposite end. If you recall your electromagnetic field theory, E-field lines terminate orthogonally to electric conductors (metal surfaces), and H-field lines (magnetic fields) run parallel to electric conductors, so they do not terminate at metal boundaries like electric fields. However, having an electric conductor in the vicinity of an inductor will constrain the H-fields, causing an effective loss in the part... additional resistance at AC (not DC).

In most RF board designs, we clear out the metal below the inductors, because it will de-Q the inductor, adding effective parasitic resistance, which negatively impacts circuit (filter) performance.

 

[andre_luis]

...Inductors do not require a groundplane, in fact, the typically operate best with no additional metals nearby. An inductor works by generating a magnetic field, which forms a closed loop of magnetic fields around the inductor. By inserting a metal plane nearby, all you do it interrupt those nice magnetic fields...

I don´t agree totally to this concept.

If inductor main purpose is to irradiate or dissipate the wave energy ( i.e. : Antenna, Beads, etc... ), in fact you are correct.
However, inductors at most elactronic circuits, are designed to perform some energy storage ( SMPS ), and the magnectic field is desirable to flow inside the core.
Some magnectic field crossig over the core, is not welcome, and must be shielded in order to don´t induce current over neighboard tracks.

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[enjunear]

I don´t agree totally to this concept.

If inductor main purpose is to irradiate or dissipate the wave energy ( i.e. : Antenna, Beads, etc... ), in fact you are correct.
However, inductors at most elactronic circuits, are designed to perform some energy storage ( SMPS ), and the magnectic field is desirable to flow inside the core.
Some magnectic field crossig over the core, is not welcome, and must be shielded in order to don´t induce current over neighboard tracks.

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A magnetic core is not a ground plane. You don't use the dielectric in a PCB to support/improve the magnetic fields generated by a coil.

 

[andre_luis]

A magnetic core is not a ground plane...

It was not stated.
Sorry, but I do not understood how this expanation fits to above assertion.

I guess we are talking about different subjects.

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[palmeiras]

Hi Andre and enjunear,
Thanks for your replies. I misunderstood the information provided in the design manual. It is mandatory to connect the groundplanes of inductors and bondpads.
Thanks again.