Is there a something else I could use in this circuit instead of inductor?

Question

I'm making the analog interface for MCP3909 chip ,

I'm having a problem in finding any inductor where I live ..

I've two question :-

Is there a substitute of this inductors ?

What's the reason of them ..!

here's the link for the reference design manual if the image isn't clear.

Answer 1

Doesn't Digikey ship to Egypt?

They're EMI suppression coils, often referred to as "chip ferrite beads". These have low resistance at DC and low frequencies, but up to several 100s of Ohms at 100MHz or higher. The LI0805H151R-10 is 150\$\Omega\$ at 100MHz, yet only 150m\$\Omega\$ at DC.
I'm afraid there's little else you can replace it with, at least not in 0805 package. If you want to live dangerously you can replace them by a 0\$\Omega\$ jumper, but don't quote me on that! Your circuit will probably work, but most likely fail EMC tests. For a commercial design you definitely want the chip ferrite beads!

You can more or less simulate the ferrite with a wire wound resistor as Jason suggests. Assuming that a 0.15\$\Omega\$ Yageo KNP100 has about 10 turns it will be around 0.17\$\mu\$H, which theoretically gives about 100\$\Omega\$ at 100MHz. In practice the value will be higher due to the skin effect.

Note that neither the chip ferrite bead nor the wire wound resistor are ideal inductors, as the following graph of a Murata ferrite bead shows, and the simulated coil may give different results in EMC measurements. (Laird doesn't publish a graph in its datasheet).

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Chip Ferrite beads look more like resistors than inductors; there's no coil visible. That's because the coil is inside the ferrite:

This X-ray image shows an actual coil:

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Note: I now see that I've given an almost identical answer in the past, even with the same images. I had completely forgotten about that. :-)

Answer 2

I would be very surprised if you can't buy them in your country. Instead of inductor, search for ferrite bead although technically these are still inductors, they are not sold as such.

Failing that find the highest value low resistance <30R, wire wound resistor you can. It will behave pretty much the sam as an inductor at 100's of MHz.

(posted with the same caveat that using the recommended part is best for a commercial design)

Answer 3

How can you build any electronics without access to basic parts?

From your profile it appears you are an engineering student. A large part of an engineer's job is locating parts, and you need to learn how to do this.

At least four of the major electronic component distributors say they ship to Egypt or have a representative there.

Mouser

Newark

Digi-Key

Farnell

Admittedly, the shipping is going to be expensive, so you might want to combine your order with some of your fellow students'.

Answer 4

You can buy them in Egypt - or something equivalent.

You can make an adequate substitute by winding insulated wire onto a physically small leaded resistor - resistor value say above 1000 ohms. Number of turns can be discussed if needed. Probably 10 turns on a small resistor would be adequate - solder wire to resistor lead at each end so DC resistance is =~ 0 Ohms due to the wire.

If you can get small Ferrite beads or small ferrite cores you could wind wire on them BUT ferrite grade and core dimensions needs to be known.

The design will work without them but MAY add noise to the circuit being measured.
They act as interference filters.