Want a chip to block AC contamination

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
I am a newbee in RF circuit design.

I found sometimes the small AC components from input antenna (< 1.5 GHz) can
contaminate the DC Power supply (Vcc) without a proper protection. Vcc is
used to feed the first stage amplifer. Of course I can use a traditional LC
networks to block the AC components  from Vcc. However, I hope somebody can
recommend me a small IC chip which can do the same job as the LC networks,
or even better performance, to block the AC components from Vcc.
Any products available in the market please let me know.
Thanks in advance.

Johnson



Re: Want a chip to block AC contamination
On Thu, 24 Feb 2005 22:21:52 -0700, "Johnson Liuis"

Quoted text here. Click to load it

The problem with traditional lumped LC filters at UHF frequencies is
that both the L and the C have parasitic capacitances and inductances,
so there could be quite bad self resonances at frequencies that are
hard to predict.

Some ferrites intended for RFI suppression not only increase the
inductance of the wire passing through it, but are also quite lossy at
higher frequencies, thus effectively damping any parasitic resonances.
I would not be too surprised, if some ferrite manufacturers would
offer such inductances as surface mountable components.

In addition a low inductance and low loss (at UHF) chip capacitor
should be mounted as close as possible to the inductor and the other
end directly to a solid ground plane.

Paul
 

Re: Want a chip to block AC contamination
Great, Paul,

Could you please recommend me a few manufacturers for ferrites intended for
RFI suppression, as well the manufacturers for low inductance and low loss
(at UHF) chip capacitor?

Thanks.

John

Quoted text here. Click to load it



Re: Want a chip to block AC contamination
On Fri, 25 Feb 2005 09:23:45 -0700, "Johnson Liuis"

Quoted text here. Click to load it

Unfortunately I have no idea about the current market situation, but
when I was working with 430 and 1300 MHz equipment for more than a
decade ago, I used Fair-Rite ferrites and some "high-Q" chip
capacitors from various manufacturers.

It should be noted that the PCB track layout is critical, since 1 mm
of wire or PCB track will have an inductance about 1 nH, which has an
inductive reactance about 10 ohms, making any filter quite
inefficient. Multiple chip capacitors from Vcc to a solid ground plane
will effectively put the inductances in parallel, thus reducing the
inductive reactance.

For narrow band filtering, various resonant 1/4 or 1/2 wave stubs can
also be used, however, these might be an overkill in this case.

Paul


Re: Want a chip to block AC contamination
Thank you very much, Paul,

It reminds me that a senior RF guy in our group once  adopted wave stubs to
improve the performance, now I understand why!

Johnson


Quoted text here. Click to load it
for
loss



Re: Want a chip to block AC contamination
Hello John,

Quoted text here. Click to load it

As Paul suggested, Fair-Rite is a good source. But there are dozens of
other manufacturers. Ferrites are also offered by companies like
Philips, TDK, Tokin, Kaschke, Epcos, Dongying Xinyi, Fenghua and many
others. Look for the expression "ferrite bead" when searching. If for
some reason you cannot obtain samples fast enough contact Amidon. They
carry Fair-Rite cores and it is where I usually got my EMI stuff when
running out a needed core size. And buy a bag full of cores since when
people find out how useful they are they are consumed faster than rice
cakes.

http://www.amidoncorp.com /

As for caps it's the usual sources like Panasonic, AVX etc. Best is to
check with a distributor in your area since that is probebly the only
way to obtain samples quickly. They'll probably carry several brands.
Digikey should work, too.

Regards, Joerg

http://www.analogconsultants.com

Re: Want a chip to block AC contamination

Thank you very very much for sharing the treasure with us!

Johnson

Quoted text here. Click to load it
for
loss



Re: Want a chip to block AC contamination
Quoted text here. Click to load it

I will second that.  Digikey is, to my knowledge, the only
distributor that actually carries, in stock, all the capacitors
shown in the catalog.

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer:  Electronics; Informatics; Photonics.
We've slightly trimmed the long signature. Click to see the full one.

Site Timeline