What Capacitor to Use to Filter Out 10GHz Signal - RF Cafe Forums
Post subject: What capacitor to use to filter out
10GHz signal Posted: Mon Dec 11, 2006 3:20 pm
Joined: 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 am
Feb 22, 2006 3:51 pm
You say that you
have "have a 10GHz signal riding on all my DC inputs".
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
Physical layout is increasingly critical as the frequency
Post subject: Posted: Thu Jan 18, 2007 2:57 pm
Joined: Thu Jan 11, 2007 12:59 pm
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
Check out Vishay. They
have some pretty ok mos caps. I use them up to 10GHz.