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how to make a PCB coil?

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ranco980

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Hi,

i am making a board with a video chip and in the recomended circuit there is a coil components that is suppose to between 0.1 to 0.4n. this component has a note that says:

* Formed by the printed circuit pattern (L = 0.5 to 1.0mm/W = 0.5 to 1.0mm)

i was wondering how exactly i do that, i never made a coil using the PCB traces before!

Thx and BR
Ran.
 

It's not particularly a coil, rather than a short straight PCB trace. You'll have higher parasitic inductances a many places in your circuit. Unless you're targetting to a mutiple GHz microwave circuit, the note sounds rather ignorant. Strictly spoken, the inductance of a PCB trace can't be calculated without knowing the substrate height and the return path (e.g. existence of a ground plane).
 
Thank you FvM for your reply!

the circuit is for an HD video transmiter, besides the basic worry for pcb traces does that note means i should have extra care for how i build my circuit?

Thx again & BR
Ran.
 

besides the basic worry for pcb traces does that note means i should have extra care for how i build my circuit?
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I assume, that the PCB wiring of the device may be critical somehow. But I don't see yet, for which place of the circuit it can be reasonable to mention a 0.5 to 1.0 mm long trace specifically. But I don't want to say it's impossible. Can you tell the device type?
 

its an high defenition transmitter, the specific part to which the note reffers is an analog voltage input. the drawing shows one pin connected to 3.3V via this 'PCB-coil" and the other pin to GND via this 'pcb coil'. this 'coil' seems very logic to me, deviding the voltage comming in to digital pins from the ones comming in to analog pins is done all the times, especially when high rate digital IO is invloved (which is the case here) but i have never done such a board before, maby i should just place an actual coil?, would it matter if i place something not in at these values?

Thx again and BR
 

You din't show the original suggestion, but it sounds far off from reasonable digital or mixed design methods. However, if the chip vendor means to suggest it, he should clearly tell where to place the said coil, otherwise it's just a kind of twaddle.

For decoupling of digital supply pins, there are some profound standard methods: Placing low inductance chip capacitors directly at the supply pins, if necessary, adding ferrite beads. Parasitic inductances are everywehere, even the pin to chip bond wire inductance will be in a several nH order of magnitude. An artificial 0.4 nH inductance is "less than nothing" in this relation.
 

I think i know what to do know

BR
Ran
 

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