What capacitor to use to filter out 10GHz signal - RF Cafe Forums
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Post subject: What capacitor to use to filter out 10GHz
signal Posted: Mon Dec 11, 2006 3:20 pm
Mon Dec 11, 2006 3:17 pm
I have a 10GHz signal riding
on all my DC inputs. I am thinking of using a low pass RC filter. But
what kind of capacitor to use? Ceramic MLCC?
Post subject: 10 GHz bypassPosted: Wed Dec 13, 2006 12:44
Joined: Wed Feb 22, 2006 3:51 pm
You say that you have "have a 10GHz signal riding
on all my DC inputs".
A classic approach is to bypass the DC
inputs, and use a resistor, inductor, or lossy ferrite to isolate the
DC from the RF.
However, I'd like to caution you that one possible
problem with an RC lowpass is the quality of the ground. At 10 GHz (wavelength
about 3 cm), it doesn't take much distance to be an appreciable fraction
of a wavelength. So, while a small MLC SMT capacitor would probably
work, proper functioning would really almost more depend on the available
ground path. As a rule of thumb, you should reach a ground plane within
1/10 of a wavelength, or 3mm. (And preferably less!)
layout is increasingly critical as the frequency goes up.
Post subject: Posted:
Thu Jan 18, 2007 2:57 pm
Joined: Thu Jan
11, 2007 12:59 pm
Just wanted to mention that 10GHz
easily can get outside an ordinary T-filter often used in digital circuits,
as mentioned earlier the dimensions of the filters are often larger
than 3mm. In a project some years ago I found feedthrough capacitors
specified to 10GHz, think it was Murata but there are probably plenty
of them out there - just be sure that they really are specified at least
to the frequency you use or have problems with!
Post subject: Posted: Thu Jan 18, 2007
Joined: Thu Sep 25, 2003 1:19 am
Check out Vishay. They have some
pretty ok mos caps. I use them up to 10GHz.