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Printed coil design, Help

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atakan_1907

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Hi all,
Im new to rf electronics and want to design an on-pcb coil to use in a tda7000 receiver circuit. I calculated the desired inductance as 250nH.
Altought im searching and reading about it for a while, couldnt make it. I tried asitic, agilent ads etc but ... no!
How can i calculate it and draw on proteus or even ms-paint =)
Could someone guide me to understand the principle and design my own?
Please dont just give me links, explain. I dont even know the thickness of copper on a pcb =)
 

250 nH is a pretty large PCB inductor. You would be better off using an airwound coil.
 
This calculator computes the inductance of a microstrip etched on a PCB, which according to the ARRL handbook is:

L= 0.00508*b*(ln(2*b/(w+h))+.5+0.2235*(w+h)/b)

where:

w is width of the strip in inches,
b is the length in inches,
h is the distance between the strip and the ground plane, and
L is inductance in uH.
 
How big, 4 cm2 or larger?
Is that formula for just a strip? Sth like this? ========================
 

Sorry, i didnt get a good answer :(
Could someone explain how to calculate and draw an etched coil?
I saw the inductance calculator before but its not clear enough.
 

I can suggest you this link:

Stanford Microwave Integrated Circuits Laboratory -- Stanford University

Here you can find not only a quite good calculator, but also an academic article explaining how to do.
I used the article to develop a software that, in facts, given the desired inductance and the physical constraints, gives you the best match.

But please be careful with printed coils. I did some experiments and at the end replaced PCB coils with good quality, traditional inductors due to parasitic capacitances and other side effects (I was working at 500 MHz).
 
You have to find out the structure width that can be reproduced in your PCB technology, e.g. 150 um. A square spiral will be most easy to draw.

Although I'm sure, a printed inductor will work for FM radio frequencies, it will considerably larger than a wire wound SMD inductor.
 
Last edited:
Or be a little bit moe practical. By trial and error... **broken link removed**
 

That large of an inductance is going to require multiple turns. A single loop will not have the inductance. Since you will need to jumper over the coil to get to the middle (start) with a multilayer trace, it is best to simulate such a thing in an EM simulator to model the full effects. Anything else will be a crude approximation.
 

@biff44:

The equations that I linked to, and the equations used in the online calculator in post #7, are designed for multi-turn inductors.
I am working on inductor analysis with EM simulators, but use these equations as a starting point. click!
From my experience, the equations are often accurate to within 3% or so, if we compare DC inductance to EM analysis results.

I agree that for the stacked multi-layer inductors in post #9, you would better use an EM simulator because the coupling between the segments on different layers is not know exactly.
 

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